A REPORT ON CANCER

Background

Cancer is a class of diseases characterized by out-of-control cell growth. There are over 100 different types of cancer, and each is classified by the type of cell that is initially affected.Cancer harms the body when damaged cells divide uncontrollably to form lumps or masses of tissue called tumors. Early detection of cancer can greatly improve the odds of successful treatment and survival. [1]

There are three ways to treat cancer such as radiotherapy, chemotherapy and surgery. Radiation treatment, also known as radiotherapy, destroys cancer by focusing high-energy rays on the cancer cells. This causes damage to the molecules that make up the cancer cells and leads them to commit suicide. Radiotherapy utilizes high-energy gamma-rays that are emitted from metals such as radium or high-energy x-rays that are created in special machines like Cobalt-60 or (LINAC) Linear Accelerators. [1] Radiotherapy is a multidisciplinary specialty which uses complex equipment and radiation source for delivery of treatment for cancer patients.

In Bangladesh about 200,000 people diagnose cancer annually among which 150,000 people die. Among the three major treatment modalities for cancer, radiotherapy is the cheapest modality in comparison to chemotherapy and surgery.

Cobalt 60 and Linear Accelerator are used in radiotherapy now-a-days all over the world. Although proton therapy has already started its journey in the state of the art technologies for the treatment of cancer, it still remains applied in the developed countries only. For developing country like our Bangladesh we still depend on the Cobalt 60 machines and the Linacs. We are now able to serve the patients with IMRT and in the near future with IGRT.

After the Linac is installed Acceptance tests and Commissioning is a compulsory job. Acceptance tests and Commissioning are the steps that need to be performed in order to prepare or optimize the radiotherapy machine for the treatment. Acceptance tests and Commissioning posse a major part of quality assurance for radiotherapy.

In Delta Hospital Ltd. the machine I worked with is the Varian Clinac 2100C DMX Linear accelerator. The Clinac DMX is a streamlined, high-performance and reliable platform that incorporates a broad range of imaging and treatment options, including dynamic motion management. The linear accelerator is built on the new, high-performance iX platform, and the system can be custom configured. That means every facility always starts with the best and builds forward. Some of its standard features are as follows:[2]

It has two photon energies: 6MV and 10MV and four electron energies: 6 MeV, 9 MeV, 12 MeV, 15 MeV. It has tight isocenter alignment of the gantry, couch, collimator, and imagers; exact couch, remote control of patient position, improved positional accuracy and compact stand. It has 40 pair MLC. The machine is provided with wedges of 15°, 30°, 45° and 60°.

Acceptance tests assure that the specifications contained in the purchase order are fulfilled and that the environment is free of radiation and electrical hazards to staff and patients. The tests are performed in the presence of a manufacturer’s representative. Upon satisfactory

completion of the acceptance tests, the physicist signs a document certifying that these conditions are met. [1]

Commissioning is the process to optimize and calibrate the machine to deliver the treatment to the patients. Radiation treatment outcome is directly related to the accuracy in the delivered dose to the patient that is dependent on the accuracy of beam data used in the treatment planning process. These data are obtained during the initial commissioning of the linear accelerator and are treated as the standard data for clinical use and should be verified periodically. [1]

Main Objectives of the study

The main objective of the study is to observe the acceptance testing and determine the commissioning for photon beams of a linear accelerator.Acceptance tests of the Clinical Linear Accelerator (CLINAC) 2100C DMX needs to be done to check if the vendor provided all the equipments and facilities as required by the hospital.

For the mechanical checks the followings have to be observed and checked:The CLINAC is provided with modulator, couch, collimator, proper wedges and applicators, chilling system, collimator rotation, gantry rotation, couch rotation, crosshair alignment, independent jaw position readouts, gantry rotation readout calibration, couch mechanical motions, collimator rotation readout calibration and all other necessary equipments to carry out proper patient treatment.

For the radiative checks:The machine has the proper field size alignment; optical distance indicator (ODI), dose linearity with MU settings, coincidence of light field and X-ray field, static MLC, photon and electron depth of ionization, photon and electron field flatness and symmetry, short term dose reproducibility, gantry rotation spoke shot.

For commissioning the objectives are: To determine the central axis percentage depth dose curves, To determine beam profiles, To determine output factors, To determine tissue maximum ratio (TMR), To carry out absolute dosimetry, To calculate monitor unit.

Present Condition and Scope of Acceptance Tests and CommissioningCurrently there are six hospitals which are equipped with modern Linear Accelerators (LINACs).

National Institute of Cancer Research and Hospital – 3 Linacs Dhaka Medical College and Hospital – 1 Linac Bogra Ziaur Rahman Medical College and Hospital – 1 Linac Delta Hospital Limited – 1 Linac Khaja Younus Ali Medical College and Hospital – 1 Linac Square Hospital – 1 Linac

We have done my research work at the Delta Hospital Limited. This hospital is well equipped with two Cobalt-60 teletherapy machines and a new Varian Linear Accelerator for radiotherapy and a Varian Acuity Simulator. The hospital provides 3D CRT (Conformal Radiotherapy) for the cancer patients. The hospital has well trained medical physicist and

staff. They have been trained in foreign countries like India, Germany, USA and several other countries.

Materials and Methods

Instruments RequiredTo perform the acceptance tests and commissioning of a linear accelerator some instruments and procedures are required:

1.1.1 Radiation Survey Equipments:

Radiation survey equipments such as a Geiger counter and a large volume ionization chamber are required to carry out radiation survey for all treatment rooms. For facilities with a treatment unit operated above 10 MeV, neutron survey equipment such as Bonner spheres, long counters and BF3 counters are necessary.[1]

Table: 01. Survey Meter Unit – 1

Gamma Beta Survey meter Unit 01Model 290Serial 91532Manufacturer VICTOREEN, USACalibration date 10.20.2000

(previously checked by checked source)Dose scale Sv/h, mR/h 2.10 mSv/h

Table: 02. Survey Meter Unit - 2Gamma Beta Survey meter Unit 02Model 451B-RYRSerial 0000001612Manufacturer Fluke BiomedicalCalibration date 29-06-2009Dose scale Sv/h, mR/h mR/hTable: 03. Survey Meter Unit - 3Gamma Beta Survey meter Unit 03Model 451B-DE-SIRYRSerial 0000001150Manufacturer Fluke BiomedicalCalibration date 01-07-2010Dose scale Sv/h, mR/h Sv/h

Ionometric dosimetry equipments refer to equipments such as several ionization chambers (thimble or plane-parallel type), a versatile electrometer cable and connectors fitting to the electrometer and all chambers, thermometer, barometer (for absolute dose measurements). Ionization chambers are required to compile the radiation beam properties measured during the acceptance testing and commissioning of a radiation treatment unit. There are two types of ionization chambers such as Thimble type and Plane Parallel type. A thimble ionization chamber is mainly used for photon beam while the plane parallel ionization chamber is

mainly used for electron beam. They measure a number of relative quantities and factors, which include central axis percentage depth doses (PDDs), output factors and penumbra.[1]

Phantoms:

There are two types of phantom such as Radiation Field Analyzer (RFA) or Water Phantom and Plastic Phantom.

Radiation Field Analyzer or Water Phantoms:

A water phantom that field is required for acceptance testing and commissioning. This type of water phantom is frequently referred to as a radiation field analyzer (RFA) or an isodose plotter. Although a 2-D RFA is adequate, a 3-D RFA is preferable, as it allows the scanning of the radiation field in orthogonal directions without changing the phantom set-up. The traversing mechanism have an accuracy of movement of 1 mm and a precision of 0.5 mm. A 3-D scanner of an RFA can able to scan 50 cm in both horizontal dimensions and 40 cm in the vertical dimension. The water tank can at least 10 cm larger than the scan in each dimension. The RFA can be filled with water and then positioned with the radiation detector centered on the central axis of the radiation beam. The traversing mechanism can move the radiation detector along the principal axes of the radiation beam. After the gantry has been leveled with the beam directed vertically downwards, leveling of the traversing mechanism is accomplished by scanning the radiation detector along the central axis of the radiation beam, indicated by the image of the cross-hair. Any deviation of the radiation detector from the central axis, as the detector is moved away from the water surface, indicates that the traversing mechanism is not leveled.[1]

Plastic Phantoms:

Fig: 05. Plastic Phantom

For ionometric measurements in the buildup region a polystyrene or water equivalent plastic phantom is convenient. A useful configuration for this phantom consists of ten blocks of 25 × 25 × 5 cm3. One block was drilled to accommodate a Farmer type ionization chamber with the centre of the hole 1 cm from one surface. A second block was machined to place the entrance window of a parallel-plate chamber at the level of one surface of the block. This arrangement allows measurements with the parallel-plate chamber with no material between the window and the radiation beam. An additional seven blocks of the same material as the rest of the phantom should be 25 × 25 cm2. These blocks should be 0.5, 1, 2, 4, 8, 16 and 32

mm thick. These seven blocks combined with the 5 cm thick blocks allow measurement of depth ionization curves in 0.5 mm increments to any depth from the surface to 40 cm with the parallel-plate chamber and from 1 to 40 cm with the Farmer chamber. The depth of 40 cm is the limit, because 10 cm of backscatter should be maintained downstream from the measurement point. A plastic phantom for film dosimetry is also required. It is convenient to design one section of the phantom to serve as a film cassette. Other phantom sections can be placed adjacent to the cassette holder to provide full scattering conditions.Use of ready pack film irradiated parallel to the central axis of the beam requires that the edge of the film be placed at the surface of the phantom and that the excess paper be folded down and secured to the entrance surface of the phantom. Pinholes should be placed in a corner of the downstream edge of the paper package so that air can be squeezed out before placing the ready pack in the phantom, otherwise air bubbles will be trapped between the film and the paper. Radiation will be transmitted no attenuated through these air bubbles, producing incorrect data. Plastic phantoms are also commonly used for routine quality control measurements. The design of these phantoms will depend on the requirements of the quality control program. [1]

Acceptance Tests for Photon Beams

The acceptance tests have been performed by the Varian supplied Bio-medical Engineer Mr. Armin Von Desuhwanden along with other local engineers supplied by Tradevision Ltd. The duration of the acceptance tests was about 3 weeks. Medical Physicists of Delta Medical Center were present there. I was there as an observer while the acceptance tests took place.

Safety ChecksInterlocks

The initial safety check was verified that all interlocks were working properly and reliably. There are four types of interlocks such as:

Door Interlocks

Door interlocks prevented the irradiation when the door of the treatment room was open. Keeping the treatment door open it was tried to switch on the beam, but the beam was not on.

Radiation Beam-off Interlocks

The radiation beam-off interlocks stopped irradiation but they did not stop the motion of the treatment unit or patient treatment couch.

Motion Disable Interlocks

The motion-disable interlocks stopped motion of the treatment unit and patient treatment couch but they did not stop machine irradiation.

Emergency Off Interlocks

Emergency-off interlocks disabled power to the motors that drive treatment unit and treatment couch motions and power to some of the radiation producing elements of the treatment unit. The idea was to prevent both collisions between the treatment unit and personnel, patients and other equipments and to halt undesirable irradiation.

Warning Lights

After verifying that all interlocks and emergency off switches were operational, all warning lights were checked.

Patient Monitoring Equipments

To monitor and communicate with the patient inside the Linac room the proper functioning of the patient monitoring audio-video equipment has been verified. The audio-video equipment is often useful for monitoring equipments or gauges during the acceptance testing and commissioning involving radiation measurements.

Radiation Survey

A radiation survey was performed in all areas outside the treatment room. A survey for neutrons in addition to photons has been done since the linear accelerator can operate above 10MeV. The survey has been conducted using the highest energy photon beam because it has the highest penetration power.

Collimator and Head Leakage

The target on a linear accelerator is surrounded by a shielding. Most regulations require this shielding to limit the leakage radiation to a 0.1% of the useful beam at one meter from the source. The adequacy of this shielding was verified during acceptance testing. The leakage test was accomplished by closing the collimator jaws and covering the head of the treatment unit with films. The films were marked to permit the determination of their position on the machine after they are exposed and processed.

Mechanical ChecksCollimator Rotation

At first the gantry was leveled at 0° then the level was rotated end-over-end to check the accuracy. A calibrated 100 cm front pointer was installed. The tip of another front pointer was extended over the front edge of the couch and the Gantry was rotated between 90° to 270° to accurately set the distance of the Collimator front pointer to precisely 100 cm TSD. Then the couch top front pointer was removed. A piece 1 mm ruled graph paper was taped on the top of the couch. Then the couch top was positioned until the graph paper was just below the front pointer but not touching. Then with the graph paper aligned under the front pointer tip the collimator was rotated from 90° to 270° while observing the pointer run-out.Gantry Rotation

The front pointer, gantry and couch were set-up like the previous step with the collimator at 0°. The short front pointer was attached to the end of the couch so that the 2 mm tip was extended over the end of the couch top. With the couch at 0°, the couch vertical axis was positioned so that the tip of the collimator front pointer was aligned to the center of the short front pointer tip. Then the couch longitudinal axis was positioned so that the tip of the short front pointer was approximately 1mm away from the collimator front pointer. Then the couch lateral axis was positioned so the tip of the short front pointer was centered on but not touching the tip of the Collimator front pointer. The gantry was rotated through the full 360° while visually checking the front pointer run-out. It was verified that the front pointer tip was ≤ 1.0 mm radius throughout the entire 360° of rotation of counterweight systems.

Couch Rotation

The front pointer, gantry and couch were setup as the previous section with the collimator at 0°. The couch was slowly rotated from 90° to 270° while observing the front pointer run-out every 45°.

Crosshair Alignment

The couch top was set to 100 cm TSD and a mm ruled graph paper was stuck on to the couch top. With the crosshairs aligned on the graph paper the collimator was rotated from 90° to 270° and it was verified that the crosshair run-out was ≤1.0 mm at isocenter. It was verified that each crosshair was parallel to the upper and lower jaws. The collimator was positioned to the center position and the crosshairs were aligned to the graph paper. The upper jaws were set to 35 cm and each of the lower jaws was driven independently until both jaws were 1cm away from one end of the projected crosshair line. The distance from the crosshair to each jaw at the other end of the crosshair line was measured and verified that the worst-case error for the radial crosshair line was within specification. This line should be as accurate as possible for MLC leaf calibration.

Independent Jaw Position Readouts

The gantry was leveled at 0°. Then by using a calibration front pointer the Couch top was set to 100cm TSD. A piece of accurately ruled mm graph paper was attached to the couch top. The field light was turned on and the graph paper was aligned to the Linac crosshairs. Each jaw was independently driven so that 50% isodensity point of the projected jaw shadow corresponds to the jaw positions.

Gantry Rotation Readout Calibration

Using a precision level placed on a true surface of the interface mount, the gantry was leveled at each position.

Collimator Rotation Readout Calibration

The gantry was positioned to 90° or 270° and the collimator to approximately 0°. The top of the couch was placed near the isocenter and both sets of jaws were opened. A level on the

couch top was placed so that the light field projected a shadow of the level on the treatment room wall. Shims were used to level the level. Then the light field was turned on. While observing the shadows cast by the lower jaw edge and upper edge of the level, the lower jaws were closed and the Collimator position was adjusted until both shadows were parallel. This was the reference for the 0°. Rotate and level the gantry to 0°.

Couch Mechanical MotionsCouch Rotation

The gantry was rotated to 90° or 270°. The collimator was positioned to 0°. Then the couch was rotated to 0° and raised close to the isocenter, and moved laterally to the furthest position from the Gantry. The light field was turned on and projected the crosshair onto the edge of the Couch. A mark was placed on the edge of the couch showing the location of the vertical cross-hair. The pendant was used to move the couch laterally until it was as close as possible to the Gantry. The couch was rotated until the crosshair lines up with it again. The couch was run laterally to the furthest position again. The crosshair and couch mark were aligned. A piece of graph paper was aligned to the couch.

Couch Longitudinal Readouts

The wooden service panel was replaced with the carbon fiber panel and the Varian provided tape measure was installed into the alignment tool. Then the longitudinal alignment tool was installed onto the couch carbon fiber top at the 0 position index. The end of the tape measure was extended toward the gantry display. The couch was positioned to 0° and 100 cm TSD. A measuring tape was gently supported to keep its level and float the couch top until the crosshair aligned with the 20 cm mark. It was verified that the digital display met the specification. The couch top was floated until it aligned with the 150 cm mark on the tape.

Couch Lateral Readouts

Using the same alignment tool setup from the previous test the couch top was centered laterally by aligning the cross-hair to the scribe mark on the alignment tool. The table top was moved 23 cm to the right by measuring the distance between the crosshair and the tool scribe mark. The test was repeated with the tabletop moved 23 cm to the left of center.

Couch Vertical Readouts

The gantry was positioned to 0° using a calibration front pointer. With the couch in the test setup position, it was verified that the digital display met the specification for the 0 cm position. The gantry was rotated 50° in either direction to allow full couch extension. Sequentially the couch was driven 35 cm above the reference and it was verified that the digital display met the specification at both positions.

Optical Distance Indicator (ODI)

The field light was turned on and the crosshair and ODI rangefinder display was projected on a piece of white paper. It was verified that the ODI meets specification for the 100 cm

position in the following table. Using the same tape measuring technique in the previous test, sequentially the couch was driven 20 cm above then 30 cm below the 100 cm reference position, it was verified that the ODI display met the specification at both positions.

Gantry Rotation Spoke Shot

The collimator was set to 0° angle and the upper jaw was full opened. Using the independent jaw mode both the lower jaws were closed to 0.5 cm so that a symmetric 1.0 cm field was projected relative to the crosshair. An X-ray film was positioned using support blocks in such a way that it was standing vertically on the couch top and perpendicular to the lower jaws. Then the couch was positioned at a height so that the center of the film was near 100 cm TSD. The couch lateral was positioned so that the approximate center of the film was aligned to the Linac crosshair. The gantry was rotated successively from 90°, 0°, 275° and 185° while exposing the film at each position, then the film was developed. The 1.0 cm exposures in the center were bisected with a sharp line. At the intersection of lines the longest line of the trapezoid was measured. This represents the diameter error.

Coincidence of Light Field and X-ray Field

The gantry was positioned to 0°, the collimator was positioned to 0°, the field size was set to 30x30 cm2 and the couch vertical was 100 cm TSD. Then an X-ray film was taped on the couch top and field light was turned on. The edges of the field on the film package at the 50% density region were marked with a small pin. Then the film was exposed in low X-ray and another film was exposed in high X-ray. Then the films were developed and the 50% isodensity lines of the X-ray field edges were compared to the field light edges.

Static MLCLeaf Positioning Accuracy

Using a calibrated front pointer the couch top was set to 100 cm SSD. A piece of graph paper was attached to the couch top and the gantry was set to 0°. The jaws were opened to 40x40 cm2. The collimator was rotated to accurately align the crosshairs to the graph paper keeping the MLC in the park mode. One at a time all four leaf position patterns were set. Then the leaves were verified that they were at the plan position within ±1 mm.

Leaf Position Repeatability

The repeatability file pattern was set and the actual leaf positions were marked on the graph paper by drawing a line across each row of the leaves. Then the autocycle application was opened and the MLC was gone through 10 different patterns. The repeatability pattern test was again set and the leaf positions were compared to the previous measurements.

Collimator Spoke Shot

At first the film developer was turned on to warm up. Entering the Linac Service Mode the MLC interlock was override. The MLC leaves were retracted so it was possible to view the crosshair. The jaws were reopened to 25x25cm2 and the couch was set to 100 cm SSD. A

piece of X-ray film was taped on the couch top at the center to the crosshairs. The MLC was then shaped to the spoke shot pattern. The collimator was then rotated to 90°, 135°, 180° and 225°. On the developed film, each spoke shot was bisected with very thin lines, then it was verified that the lines intersect within a circle of ≤1.0 mm radius.

Coincidence of Light Field and X-ray Field

Both the gantry and the collimator were set to 180° and the couch was set to height 100cm SSD. For each exposure, the jaws were set to the MLC field size +0.5cm. Then 10x10cm 2

MLC pattern was selected. A piece of film was set up on the couch with the light field visible on one half of the film. By using a pin the edges of the light field were marked. The film was then exposed to low X-ray. The film was then shifted to expose the other half of the film with high X-ray using the same setup. The film was then developed and compared to the 50% intensity regions of X-ray edges to the marks representing the light field edges. The difference between the light field marks and the X-ray edges was verified that they are within ±2.0 mm.

Dosimetry MeasurementsPhoton Depth of Ionization

All photon depth of ionization tests were specified using a water phantom at 100 cm TSD and 10x10 cm2 field size. Then the Water phantom was set for depth dose scanning and the jaws were set to 10x10 cm2. At first the central axis depth of ionization was scanned with low X-ray then it was repeated with high X-ray.

Photon Field Flatness and Symmetry

The gantry was leveled at 0°. The Water phantom scanning system was set for crossplane scanning then the tank was leveled in both planes, using the front pointer the top surface was set at 100 cm TSD and the jaws were opened to 40x40 cm2. The probe was set to zero position and a 1 cm depth was allowed to visual probe alignment to the crosshairs. The reference probe was positioned as far as possible away from the scanning path so that it did not cause scatter and affect the scan result.

Short Term Dose Reproducibility

Short-term dose reproducibility for each energy was found ±1% or 1 Monitor Unit at a fixed dose rate. The test results were recorded and calculated using the following equation:Equation 1 = {[Reading #1- Reading #2] ÷ Reading #2} x 100

Dose Linearity with MU settings

The test results were recorded and calculated using the following equations:50 MU ERROR = {[2x50 MUAVG – 100 MUAVG] ÷ 100 MUAVG}x 100300 MU ERROR = {[(300 MUAVG ÷3) – 100 MUAVG] ÷ 100 MUAVG}x 100Dose Linearity with Dose RateThe test results were recorded and calculated using the following equations:

RR1 ERROR = {[RR1AVG – RRmid (AVG)] ÷ RRmid (AVG)} x 100RRmax ERROR = {[(RRmax)(AVG) – RRmid (AVG)] ÷ RRmid (AVG)} x 100Dose Reproducibility with Gantry AngleThe test results were recorded and calculated using the following equations:90° ERROR = {[90° AVG – 180° AVG] ÷ 180° AVG} x 100270° ERROR = {[270° AVG – 180° AVG] ÷ 180° AVG} x 100

Commissioning for Photon Beams

1.1.2 Anisotropic Analytical Algorithm (AAA)

The Anisotropic Analytical Algorithm (AAA) is a three dimensional pencil beam convolution or superposition algorithm that uses separate Monte Carlo derived modeling for primary and scattered extra-focal photons. The functional shapes of the fundamental physical expressions in the AAA enable analytical convolution, which significantly reduces the computational time. The AAA was originally conceived by Dr. Waldmar Ulmar and Dr. Wolfgang Kaissl. The development of the algorithm culminated in the publication of the triple-Gaussian photon kernel model in 1995. Important improvements have been made to the AAA dose calculation algorithm in the areas of treatment unit and tissue heterogeneity modeling, and increasing the accuracy of the scattered dose calculation. The AAA accounts for tissue heterogeneity anisotropically in the entire three-dimensional neighborhood of an interaction site, by using photon scatter kernels in multiple lateral directions. The final dose distribution is obtained by the superstition of the dose calculated with photon and electron convolutions.

Fig: 08. Treatment Unit Components, Broad Beam Division

Central Axis Percentage Depth Dose Curves

The first commissioning measurements are of the central axis Percentage Depth Dose (PDD). Central axis dose distributions inside the patient or phantom are usually normalized to Dmax = 100% at the depth of dose maximum Zmax and then referred to as the PDD distributions. The PDD is thus defined as follows:PDD(z, A, f , hµ ) = 100DQ/DP =100DQ /DP

Where DQ and DQ are the dose and dose rate, respectively, at point Q at depth Z on the central axis of the phantom and DP and DP are the dose and dose rate, respectively, at point P at Zmax

on the central axis of the phantom.

Fig: 09. The Geometry of PDD Definition

The geometry for PDD definition is shown in above Fig. 08. Point Q is an arbitrary point at depth Z on the beam central axis; point P represents the specific dose reference point at Z = Zmax on the beam central axis. The PDD depends on four parameters: depth in a phantom Z, field size A, SSD f and photon beam energy hµ. The PDD ranges in value from 0 at Z ∞ to 100 at Z = Zmax.cTo measure the PDD, the surface of the water phantom was placed at the nominal SSD or at the isocenter. The vertical depth of the ionization chamber in the water phantom was determined by measuring from the bottom of the meniscus of the water to the centre of the chamber. Central axis PDD values were measured over the range of field sizes from 4×4 cm2

to 40×40 cm2. Increments between field sizes was no greater than 5 cm, but are typically 2 cm. Measurements were made to a depth of 35 or 40 cm. Chambers of 0.1 cm3 typically had diameters of 3 to 4 mm, the length of the order of 1.5 cm are used. A 0.1 cm3 chamber orientated with its central electrode parallel to the central axis of the beam was used in a water phantom.

Beam Profiles

The transverse photon beam profiles were measured to determine the off-axis dose distribution of photon beams. These profiles were measured in a water phantom with a small volume ionization chamber. The surface of the phantom was placed at 100cm SSD and the ionization chamber was scanned perpendicularly to the central axis.

Quality Index

We have measured the quality of the beam by using the 3D water phantom and OmniPro software. The central axis depth dose profile of 10x10 cm2 field size at each 2 mm increment of up to 30 cm depth. The depth dose ratio of PDD20/10 represents the beam energy of the photon radiation.

Tissue Maximum Ratio

Fig: 10. Geometry for measurement of TPR (d, AQ, hv).

(a) The geometry for the measurement of DQ at depth Z in a phantom; (b) The geometry for the measurement of DQref at depth Zref in a phantom.

The distance between the source and the point of measurement, as well as the field size at the point of measurement, is the same for (a) and (b).

TMR (Z, AQ, hv) = DQ/DQmax = DQ/DQmax

Where DQ and DQ are the dose and dose rate, respectively, at point Q at a depth Z in a phantom and DQmax and DQmax are the dose and dose rate, respectively, at point Q at Zmax.TPR (z, AQ, hv) = DQ/DQref = DQ/DQref

Where DQ and DQ are the dose and dose rate, respectively, in a phantom at arbitrary point Q on the beam central axis and DQref and DQref are the dose and dose rate, respectively, in a phantom at a reference depth Zref on the beam central axis.

Output Factors

The radiation output at Zmax, in cGy/MU for a linac, increases with an increase in collimator opening or field size. This increase in output was measured at Zmax of each field size. Alternatively, the increase in output was measured at a fixed depth for each field size and the output at Zmax determined by using the appropriate central axis PDD values. Tray Factors

Shielding blocks are mostly made of lead. The thickness of lead required to provide adequate protection of the shielded areas depends on the beam quality and the allowed transmission through the block. For that purpose a block holding device called shielding tray was used for

the radiotherapy treatment of cancer patient. The thickness of the shielding tray ????less than depth of Dmax of the respected photon beam radiation.

Wedge Factors

Wedges are used to shape the dose distribution of radiation treatment fields. The central axis wedge transmission factor is the ratio of the dose at a specified depth on the central axis of a specified field size with the wedge in the beam to the dose for the same conditions without the wedge in the beam. Central axis wedge transmission factors determined for one field size at one depth are frequently used to calculate beam-on times or MU settings for all wedged fields and depths.To measure the central axis wedge transmission factor for a given field size at one depth the ionization chamber was placed on the central axis of the beam with its axis aligned parallel to a constant thickness of the wedge. Measurements were performed with the wedge in its original position and with the wedge rotated through 180º. This set of measurements verified that the wedge and the ionization chamber were correctly positioned. The wedge position may be rotated through 180º by rotating the collimator or by rotating the wedge itself. ResultsAcceptance Tests DataRadiation Survey

Table: 04. Radiation Survey DataGantry Position Survey Point Survey ValueGantry=900 Consol Control 1.7µSv/h

Door 0.3µSv/hSimulator 0.5µSv/hStairs 1.5µSv/hX-ray Room 3.5µSv/h

Gantry=1800 Store 1.6µSv/h

Mechanical ChecksCollimator Rotation

Table: 05. Collimator RotationCollimator Angle Digital Readouts

Collimator Angle Digital Specification Result

90° ±0.5° Pass

180° ±0.5° Pass

270° ±0.5° Pass

Gantry Rotation

Table: 06. Gantry RotationGantry Angle Digital & Mechanical ReadoutsGantry Angle Digital

SpecificationResult Mechanical

SpecificationResult

0° ±0.5° Pass ±1.0° Pass

90° ±0.5° Pass ±1.0° Pass

180° ±0.5° Pass ±1.0° Pass

270° ±0.5° Pass ±1.0° Pass

360° ±0.5° Pass ±1.0° Pass

Couch RotationMechanical Isocenter MeasurementsAxis Specification Actual ResultCollimator rotation ≤1.0 mm radius PassGantry rotation w/Counterweight ≤1.0 mm radius PassCouch rotation w/Counterweight ≤1.0 mm radius Pass

Table: 07. Couch Rotation

Field Light and Crosshair Alignment

Table: 08. Field Light & Crosshair AlignmentField Light & Crosshair AlignmentOptical Test Specification @ 100cm TSD ResultField light run-out ≤1.0mm PassCrosshair run-out ≤1.0mm PassRadial crosshair parallelism(MLC leaf calibration reference line)

≤2.5mm Pass

Transverse crosshair parallelism(m3 leaf calibration reference line)

≤2.5mm Pass

Table: 09. Asymmetric ModeIndependent Jaw Digital ReadoutsJaw Position Specification ResultY1 -8cm ±2mm PassY1 20cm ±2mm Pass

Y2 20cm ±2mm PassY2 -8cm ±2mm Pass

X1 -1cm ±2mm PassX1 20cm ±2mm PassX2 20cm ±2mm PassX2 -1cm ±2mm Pass

Table: 10. Symmetric ModeSymmetric Jaw Digital Readouts

Field Size SpecificationResult

X Jaws Y Jaws6×6cm ±2mm Pass Pass30×30cm ±2mm Pass Pass

Couch Mechanical MotionsTable: 11. Couch Mechanical MotionsCouch Angle Digital & Mechanical Readouts

Couch Angle Digital Specification

Result Mechanical Specification

Result

90° ±0.5° Pass ±1.0° Pass

180° ±0.5° Pass ±1.0° Pass

270° ±0.5° Pass ±1.0° Pass

Table: 12. Couch Longitudinal ReadoutsCouch Longitudinal Digital Readouts

Longitudinal position Specification Result

20cm ±1mm Pass

150cm ±1mm Pass

Table: 13. Couch Lateral ReadoutsCouch Lateral Digital Readouts

Lateral Position Specification Result

77cm ±1mm Pass

100cm ±1mm Pass

123cm ±1mm Pass

Table: 14. Couch Vertical ReadoutsCouch Vertical Digital Readouts

Lateral Position Specification Result

65cm ±1mm Pass

100cm ±1mm Pass

100cm ±1mm Pass

Optical Distance IndicatorTable: 15. Optical Distance Indicator

ODI Optical DisplayTSD Specification Result80cm ±5mm Pass100cm ±1mm Pass130cm ±5mm Pass

Radiation Isocenter TestTable: 16. Radiation Isocenter Test

Gantry Radiation Spoke ShotTest Condition Specification ResultGantry Spoke w/Counterweight ≤1.0mm radius PassGantry Spoke w/Beam stopper Retracted

≤2.0mm radius Pass

Gantry Spoke w/Beam stopper Extended

≤2.0mm radius Pass

Coincidence of Light Field and X-ray CoincidenceTable: 17. Coincidence of Light Field and X-ray Field

Light Field and X-ray Field Coincidence

Energy Field SizeSpecification

ResultC/CD/SC/EXd EX

Lo-X 30x30 ±2.0mm ±1.5mm Pass

Hi-X 30x30 ±2.0mm ±1.5mm Pass

Static MLCTable: 18. Leaf Positioning AccuracyLeaf Positioning Accuracy

Leaf Plan Position Specification (per leaf) Result

5.0 cm ±0.1 cm Pass

-10.0 cm (A side) ±0.1 cm Pass

-10.0 cm (B side) ±0.1 cm Pass

15.0 cm ±0.1 cm Pass

Table: 19. Leaf Positioning Repeatability TestLeaf Positioning Repeatability Test Result

Leaf Positioning is repeatable within ±1 mm ±0.1 mm

Table: 20. Collimator Spoke ShotMechaniccal Check Specification ReultCollimator Spoke Shot ≤1.0 mm Pass

Table: 21. Coincidence of light Field and X-Ray FieldLight Field vs. X-Ray Field Coincidence

Energy Field Size Specification

Result

Low X 10x10 cm(8x8 cm for HD120) (3x3 cm for the BrainLAB m3)

±2.0 mm Pass

High X 10x10 cm(8x8 cm for HD120) (3x3 cm for the BrainLAB m3)

±2.0 mm Pass

Low X 24x24 cm(16x16 cm for HD120) (9x9 cm for the BrainLAB m3)

±2.0 mm Pass

High X 24x24 cm(16x16 cm for HD120) (9x9 cm for the BrainLAB m3)

±2.0 mm Pass

Dosimetry MeasurementsPhoton Depth of IonizationTable: 22. Photon Depth of IonizationPhoton Depth of Ionization

Energy BJR11

Energy BJR17

Dmax Specification Actual Dmax

10 cm Specification

Actual 10 cm %

6 MV 6 MV 1.6 cm ±0.15 cm 16 mm 67.0% ±1% 67%

10 MV 10 MV 2.4 cm ±0.15 cm 24 mm 74.0% ±1% 73.6%

Photon Field Flatness and SymmetryTable: 23. Radial PlanePhoton Beam Flatness and Symmetry – Radial (within 80% FWHM)Energy Jaw Size Flatness

SpecificationActual Flatness

Symmetry Specification

Actual Symmetry

Hi-X 10x10 Radial ±3% 2.3% ≤2% 0.6%

Lo-X 10x10 Radial ±3% 0.8% ≤2% 0.6%

Hi-X 30x30 Radial ±2.5%(±3% for 20 MV)

3.3% ≤2% 1.7%

Lo-X 30x30 Radial ±2.5% 2.4% ≤2% 1.3%

Table: 24. Transverse PlanePhoton Beam Flatness and Symmetry – Transverse (within 80% FWHM)Energy Jaw Size Flatness

SpecificationActual Flatness

Symmetry Specification

Actual Symmetry

Hi-X 10x10 Trans ±3% 2.3% ≤2% 0.3%

Lo-X 10x10 Trans ±3% 0.9% ≤2% 0.6%

Hi-X 30x30 Trans ±2.5%(±3% for 20 MV)

1.8% ≤2% 0.7%

Lo-X 30x30 Trans ±2.5% 2.0% ≤2% 0.5%

Symmetry InterlocksTable: 25. Symmetry InterlocksSymmetry Interlocks

Energy Field Size SpecificationResult

R Sym T Sym

Lo-X 40x40 cm ≤2.0% Pass Pass

Short Term Dose ReproducibilityTable: 26. Short Term Dose ReproducibilityShort Term Dose Reproducibility

Energy

50 MU(100 MU for HDTSe)

100 MU(500 MU for HDTSe)

300 MU(1000 MU for HDTSe) Specification

Hi-X 0.16 0.08 0.03 ±1%

Lo-X 0.0 0.0 0.0 ±1%

E4 0.54 0.02 0.0 ±1%

HDTSe- -0.08 0.05 0.0 ±1%

Dose Linearity SettingsTable: 27. Dose Linearity with MU SettingsDose Linearity with MU Settings

Energy Specification 50 MU Error 300 MU Error

Hi-X ±1% 0.04 -0.11

Lo-X ±1% 0.0 -0.13

E4 ±1% 0.30 -0.19

Table: 28. Dose Linearity with Dose RateDose Linearity with Dose RateEnergy Specification RR1 RRmaxHi-X ±1% 0.28 -0.16

Lo-X ±1% 0.43 -0.33E4 ±1% 0.21 -0.23

Table: 29. Dose Reproducibility with Gantry AngleDose Reproducibility with Gantry Angle

Energy Specification 90° 270°

Lo-X ±1.5% 0.48 0.14

Hi-X ±1.5% 0.16 0.36

Commissioning Data1.1.3 Central Axis Percentage Depth Dose Curves

Fig: 11. PDD Curves for 6 MV for Five Fields

Fig: 12. PDD Curves for 10MV for Five Fields

1.1.1 Beam Profile

Fig: 13. Beam Profiles for 6MV and 10MV Photon Energy for 10x10 Field Size

Quality IndexTable: 30. QIPhoton Energy of CLINAC DMX QI

TPR(20,10)

6 MV 0.67

10 MV 0.74

Output FactorsTable: 31. Output Factor in SSD= 100 cm TechniquesField Size in cm×cm 6 MV

Output Factor = 110 MVOutput Factor = 1

5 × 5 0.9414 0.940010 × 10 1.00 1.0015× 15 1.0349 1.034020 × 20 1.057 1.056525 × 25 1.0737 1.072530 × 30 1.0886 1.086

Table: 32. Output Factor in SAD TechniquesField Size in cm×cm 6 MV

Output factor = 110 MVOutput factor = 1

5 × 5 0.9756 0.9730210 × 10 1.00 1.0015× 15 1.109 1.12120 × 20 1.1213 1.130525 × 25 1.2613 1.274330 × 30 1.2671 1.2863

Tray FactorsTable: 33. Tray FactorsBlock Tray Thickness Photon Energy of CLINAC DMX

1. 6.5 mm6 MV 10 MV0.97 0.765

Wedge FactorsTable: 34. Wedge FactorsWedges Energy Energy

6MV wedge transmission factor 10MV wedge transmission factor150 0.7635 0.8044300 0.6138 0.6726450 0.4848 0.52771600 0.40013 0.44138

Multileaf Collimator Transmission FactorsTable: 35. MLC Transmission Factors Photon Energy of CLINAC DMX MLC transmission factor6 MV 0.9710 MV 0.675

Absolute DosimetryTable: 36. Varian 2100C DMX Absolute Dosimetry

Voltage C/100MU Average Gy100/MU

3001.820

1.820

0.8640

1.820

 150 1.812

1.8115 1.811

-3001.822

1.82551.823

300 1.8201.8201.820

Measurement of Absolute output of linear accelerator

SSD: 100 cmFxS 10x10 cm2

Phantom material: waterReference Depth: 5 cmIonization Chamber: Cylindrical (Farmer chamber)

Sl.No.1787Volume: 0.3cc

V1 = 300, V2=150Kion = ao + a1 (M1/M2) + a2 (M1/M2)2

= 2.337 – 3.636(1.820/1.8115) + 2.299(1.820/1.8115)2

= 1.004 ≈ 1Kpol = (M1+M2)/2M1

=(1.820 + 1.8225)/2(1.820) =1.0007 ≈ 1Temperature, T= 22.80 C, T0 = 200 CPressure P0= 1013.25pa, P = 1015.2paKTP = (273.2+T)/ (273.2+T0) *P0/P = 0.998Kelec = 1.000PDD20,10 = M20/M10 = 0.575TPR20, 10 = 1.2661PDD20,10 - 0.0595 = 0.668ND,W,Q = 4.773x 107 Gy/cM = 1.820x10-8CMQ = M* Kelec*Kpol* KTP* Kion =1.8249x10-8CKQ, = 0.992D, W,Q = MQ ND,W KQ,Q0 = 0.8640 ( Unit is missing)

MU= ?? for 1 Gy for 6 and 10 MV for 10x10 cm2 fieldYou need absolute MU for the calculation of MU- tablesMonitor Unit Calculations using the Formula

MU = (Ref MU) / {(SAD/SSD+Dmax)2 x OF x TMR

Table: 37. Monitor Unit Calculation for 6MV Photon EnergyEnergy 6MVFS 5 6 7 8 9 10 12 15 20 25 30Depth1.5 103.521 102.261 100.9891 99.749 98.538 97.454 96.109 94.168 92.199 90.765 89.5232 103.937 102.568 101.2929 100.049 98.736 97.65 96.302 94.451 92.569 91.13 89.7923 106.393 104.99 103.3665 101.992 100.652 99.545 98.07 96.09 93.985 92.523 91.1644 109.778 108.098 106.4163 104.888 103.398 102.154 100.532 98.296 96.041 94.35 92.8665 113.759 111.76 109.8902 108.187 106.413 105.016 103.232 100.714 234.603 96.354 94.7336 118.174 115.942 113.7264 111.826 109.853 108.283 106.198 103.481 100.654 98.658 96.7817 122.8 120.307 117.8402 115.584 113.654 111.888 109.588 106.525 103.246 100.962 99.038 127.803 125.013 122.2628 119.89 117.588 115.604 112.936 109.498 106.098 103.613 101.59 133.231 130.103 127.0303 124.53 121.953 119.723 116.779 113.047 109.241 106.407 104.09610 138.954 135.445 132.0118 129.208 126.493 123.988 120.74 116.545 112.438 109.355 106.95711 144.987 141.049 137.4001 134.432 131.384 128.568 125.142 120.574 115.974 112.472 109.84412 151.346 147.138 143.044 139.704 136.48 133.682 129.702 124.726 119.429 115.772 112.89113 157.806 153.314 149.1714 145.406 141.578 138.627 134.418 128.997 123.261 119.271 116.11214 164.58 159.782 155.1291 151.364 147.513 144.163 139.49 133.572 127.523 123.155 119.84315 171.676 166.548 161.8414 157.581 153.487 149.93 144.742 138.279 131.525 126.944 123.3116 179.724 174.209 168.878 164.331 159.965 156.177 150.641 143.549 136.188 131.163 127.16317 187.878 181.959 175.9391 171.095 166.45 162.154 156.529 149 141.193 135.47 131.26518 196.434 189.723 183.6165 178.441 173.483 168.899 162.896 154.882 146.348 140.07 135.43519 204.992 198.18 191.6301 186.098 180.804 175.911 169.206 160.696 151.643 144.761 139.87920 213.886 207.005 199.9783 194.064 188.41 183.185 176.024 166.669 157.068 149.777 144.39121 223.587 215.74 208.6551 202.33 196.292 191.087 183.065 173.103 162.609 154.889 149.20522 233.681 225.244 218.1189 211.332 204.861 199.293 190.692 180.053 168.554 160.079 154.3523 244.153 235.624 227.4528 220.196 213.286 205.167 198.572 187.213 174.951 166.236 159.57724 254.351 245.229 236.5083 229.307 221.933 215.607 206.242 194.562 181.494 171.904 164.86725 266.12 256.292 247.5222 239.205 231.855 225.068 215.009 202.077 188.161 177.971 170.51926 277.536 267.698 258.284 249.372 241.516 234.265 224.03 210.196 195.337 184.482 176.92227 290.789 279.401 269.3042 260.44 252.016 244.247 233.274 218.995 203.082 191.487 183.07328 302.692 291.341 330.0296 271.795 262.769 254.45 242.699 226.911 210.021 198.177 189.26629 316.577 303.444 292.7219 283.377 274.48 265.543 252.918 236.603 217.965 205.351 195.89230 330.737 317.58 306.0274 295.114 285.618 276.859 263.312 246.513 225.978 213.565 202.99935 410.797 393.31 378.2362 365.38 351.923 340.75 322.513 299.898 273.588 254.958 241.30140 512.479 491.638 471.9115 453.403 436.01 421.881 397.144 366.412 331.651 308.725 289.718

Table: 38. Monitor Unit Calculation for 10MV Photon EnergyEnergy 10MV

FS 5 6 7 8 9 10 12 15 20 25 30Depth2.3 101.662 100.38 99.131 97.912 96.723 95.562 94.243 92.42 90.452 89.102 87.9953 101.764 100.481 99.23 98.01 96.917 95.754 94.526 92.698 90.815 89.46 88.3484 103.525 102.116 100.743 99.504 98.196 97.116 95.873 94.018 92.204 90.828 89.6995 106.341 104.672 103.154 101.886 100.543 99.337 97.965 96.071 95.012 92.526 91.2816 109.549 107.82 106.136 104.607 103.116 101.77 100.258 98.215 96.021 94.388 93.1167 112.958 111.04 109.175 107.478 105.94 104.44 102.773 100.566 98.21 96.431 94.9248 116.853 114.59 112.521 110.76 109.045 107.494 105.653 103.262 100.502 98.564 97.0179 120.739 118.373 116.214 114.25 112.338 110.604 108.575 105.865 103.02 100.909 99.20510 124.739 122.117 119.723 117.683 115.697 113.9 111.53 108.602 105.422 103.128 101.2611 129.013 126.265 123.759 121.479 109.788 117.254 114.79 111.484 108.196 105.571 103.64512 133.59 130.704 127.911 125.528 123.057 120.965 118.247 114.807 111.12 108.265 106.01813 138.128 134.92 132.175 129.513 126.933 124.592 121.604 117.883 113.919 110.962 108.7714 143.186 139.806 136.544 133.76 131.061 128.444 125.323 121.286 117.014 113.941 111.38615 148.195 144.64 141.212 138.489 135.466 132.725 129.1 124.892 120.281 116.932 113.98316 153.336 149.598 145.995 142.937 139.975 137.105 133.3 128.539 123.737 119.922 117.1717 158.599 154.669 150.884 147.458 144.362 141.364 137.38 132.217 126.861 123.069 120.21118 164.501 160.096 156.112 152.749 149.264 146.12 141.932 136.514 130.71 126.566 123.41519 170.288 165.644 161.451 157.668 154.263 150.729 146.34 140.67 134.401 129.887 126.61120 176.19 171.59 166.887 163.187 159.346 155.893 151.03 145.086 138.517 133.587 129.97721 182.845 177.664 173.003 169.105 165.056 161.15 156.29 149.789 142.668 137.503 133.52822 189.314 183.847 179.26 174.843 170.287 166.195 161.099 154.548 147.076 141.432 137.27723 196.258 190.475 185.291 180.65 176.18 171.874 166.507 159.345 151.257 145.592 141.24324 202.918 197.211 191.743 186.855 182.152 177.625 171.663 164.156 155.951 149.752 145.20625 210.045 204.025 198.262 193.12 188.544 183.773 177.482 169.578 160.66 154.156 149.39726 217.691 211.327 205.24 199.821 194.613 189.984 183.352 174.707 165.36 158.545 153.30127 225.414 218.694 212.272 207.002 201.506 196.63 189.623 180.508 170.342 163.191 158.26428 233.169 226.082 219.316 213.782 208.454 203.324 195.931 186.33 175.634 168.435 162.65229 240.905 233.987 227.364 221.02 215.899 210.027 202.238 192.141 181.266 173.351 167.2930 249.783 242.465 234.907 228.766 222.864 217.187 208.964 198.752 187.27 178.562 172.53835 299.006 289.281 279.242 271.225 263.55 256.199 246.065 232.796 216.91 207.215 198.63340 356.708 344.95 332.654 322.079 312.009 303.372 290.873 273.432 254.078 240.168 229.751

CONCLUSIONS:

Acceptance Tests have been performed by the Engineer where we was present and we recorded all the data for our work. Acceptance testing was stuck because of the chiller room problem. After solving the problem we went for the commissioning and in the commissioning we could not take all the data like beam profiles for all field sizes for both photon energy. We have done the absolute dosimetry for the 6MV and 10MV Photon energy. We have also calculated the Monitor Unit tables.We have used BJR supplement 25 for the comparison of my PDD data which was very close to the data in the supplement, i.e. my data acquisition was very accurate. All the data was in the acceptable tolerance limit.

References

[1] Review of Radiation Oncology Physics: A Handbook for Teachers and Students, 2005 [2] Varian Mediacal Systems Protocol [3] http://en.wikipedia.org/wiki/Cancer[4] http://en.wikipedia.org/wiki/Radiation_therapy[5] British Journal of Radiology supplement (BJR) 25 1996[7] OmnoPro software version 7.0 (IBA)[8] Accelerator beam data commissioning equipment and procedures: Report of the TG-106 of the Therapy Physics Committee of the AAPM[9] AAPM code of practice for radiotherapy accelerators: Report of AAPM: Radiation Therapy Task Group No. 45