Commissioning of Proteus®PLUS: Process Considerations

Zuofeng Li, DSc, FAAPM

Dec 03

ContractSigned

Feb 04 May 04 Sep 04

Start install March 05

Gantry install

May 05

Building Complete Jan

06

1st Patient Tx

Aug 14, 2006

(1 month ahead of schedule)

UFHPTI

UFHPTI Proteus®PLUS & Proteus®ONE

Proteus®ONE – In construction

Dedicated PBS Nozzle –Upgrade to Start 2019

PBS in Universal Nozzle

Elements of Proton System Commissioning

• All radiation, electrical, magnetic, and motion related safety aspects

• Additional mechanical, imaging, proton beam system performance and reproducibility tests (beyond acceptance testing)

• CT scanner commissioning for HU number to Relative Linear Stopping Power (RLSP) calibration

• Treatment planning system beam modeling and validation

• Beam perturbation effects of immobilization devices

• Development of simulation, planning and delivery clinical flows and procedures

• Development of system and patient-specific QA procedures

• Personnel training

How Do These Differ From A Proteus®ONE?

• All radiation, electrical, magnetic, and motion related safety aspects

• Additional mechanical, imaging, proton beam system performance and reproducibility tests (beyond acceptance testing)

• CT scanner commissioning for HU number to Relative Linear Stopping Power (RLSP) calibration

• Treatment planning system beam modeling and validation

• Beam perturbation effects of immobilization devices

• Development of simulation, planning and delivery clinical flows and procedures

• Development of system and patient-specific QA procedures

• Personnel training

Proteus®PLUS vs. Proteus®ONE

• Multiple treatment rooms (vs. single room)– Potentially with both passive scattering and active

scanning techniques– Matched beams (of same technique) between rooms– 360 deg rotation gantries

• Rooms available for commissioning sequentially• Differences in beam production, transport, and

gantry systems= differences in beam quality and characteristics

Room Scheduling of Commissioning

• Availability of rooms for commissioning per schedule of purchase agreement– 1 room at a time, or– 2 rooms at a time, or– All rooms together?

• Delivery techniques– Dedicated PBS nozzles only, or– Universal nozzles with PBS + passive scattering, or– Mix of both?

Matched Beams

• Allows use of same TPS beam model for treatment planning• Allows performing a subset of beam measurements during

commissioning– Comparison of integrated depth doses

• Depth dose shapes and range accuracy

– Comparison of spot size, symmetry, position for selected gantry angles and distances to isocenter

– Absolute dose calibration– Use beam data of 1st room for reference in selection of

measurements

Development of Commissioning Plan

• Defining content of commissioning– What mechanical, imaging, and proton beam parameters to validate beyond

acceptance testing?– What measurement instruments are required?

• How to qualify these instruments for commissioning?

– What measurements are mandatory for TPS modeling?– What measurements are mandatory for validation of TPS calculation

accuracy?

• Possibility to collaborate with vendor installation team for data collection during installation?

• How much time for commissioning?• Need of partial commissioning?

– Commissioning of system with restrictions in commissioned range of beam energy or gantry rotation angles

Equipment for Commissioning• Scintillation Dosimetry System（Lynx or similar）

– High resolution with acceptable accuracy

– For spot profile, position, symmetry measurements

– Available with gantry mount for measurements at any gantry angle

– Should be validated against comparable dosimeters (such as film)

• Multi-Layer Ion Chamber System（ZEBRA or similar）– Highly efficient depth dose/range measurement with acceptable

accuracy

– Should be validated against parallel plate chamber measurements

• 2D ion chamber arrays（DigiPhant or similar)– Highly efficient lateral profile measurements in water

• Larger diameter parallel plate ion chamber

– Required for measurement of integrated depth dose curves for TPS beam modeling

PTW Bragg Peak Chamber

IBA Stingray

CT Scanner Commissioning• CT commissioning – a major source of range uncertainty:

– Scan phantom with heterogeneity materials with known relative linear stopping power (RLSP) or mass density

– Establish CT number to RLSP curve in TPS

• Implementation is TPS specific:

– User to create CT number to relative stopping

power ratio table (Eclipse)

• Need to use stoichiometric method (U Schneider, et al, PMB

1996, 41(1): 111-124) – requires user to implement fitting

program

• Need ICRU-46 heterogeneity plugs with established material compositions

– User to create CT number to mass density table followed by TPS (built-in) conversion to stopping power ratios using chemical composition values of reference materials (RayStation)

• Need calibrated reference material samples for CT scans

• May combine with stoichiomatric method for improved accuracy

• Need to evaluate effect of phantom size, reconstruction algorithm or other scan parameter variations

Mechanical Systems

• Gantry, Patient Positioning System (PPS), and snout (if applicable) motion accuracy, in particular:– Gantry isocenter accuracy:

• With or without gantry angle-specific corrections by moving PPS (or moving pencil beam)?

• Is imaging system alignment corrected the same way?

• Is beam isocenter/colinearity aligned the same way for all delivery techniques?

– PPS translation and rotation

• Corrected for patient weight/sag?

• Isocenter translation with rotational corrections?

– If snout used for mounting accessories (apertures, range compensators, etc)

• Is snout alignment dependent on snout position

and gantry angle (for maximum expected loading) ?

– Motion accuracy reproducibility (over the

course of commissioning?)

Imaging Systems

• Image system isocenter agreement to gantry isocenter for representative gantry angle, snout position, and PPS translation/rotation combinations

• Agreement of mechanical, imaging, and proton beam (for each delivery technique if multiple) isocenters and co-linearity

• Imaging system operability (connectivity, auto/manual registration accuracy and speed)

• Image quality (kV, mA, mAs, contrast, resolution, patient doses etc)

Mechanical and Imaging Systems

• Equipment: – Mechanical and imaging alignment test tools (may need to design and fabricate with

consideration for future periodic QA applications)

– Image quality analysis phantoms (resolution, contrast etc)

– X-ray exposure meter / CT dose phantom

and chamber for patient dose

measurements

– 3D phantom with embedded fiducial

markers to verify calculated translational

and rotational corrections of orthogonal

X-ray and CBCT imaging

– Anthropomorphic phantoms for grey-level-

based auto-registration

TPS Commissioning

• Data collection for beam modeling : Pencil beam scanning

– Integrated Depth Doses (IDDs) (measured with a large diameter parallel plate chamber) of an adequate selection of beam energies for unscanned single-spot beams (Schaffner et al, PMB 1999, 44(1):27-41)• Compare to PDD measured using a small ion chamber

– In-air spot profiles at several distances from isocenter (for spot size changes and effective SAD) and at off-axis positions (for virtual SAD) of an adequate selection of beam energies

– Absolute dose calibration in a reference field using IAEA TRS 398 protocol

– Absolute dose measurements of TPS-required fields for MU calculation

TPS Commissioning

• Data collection equipment for pencil beam scanning

– Integrated Depth Doses (IDDs): A large

diameter parallel plate chamber

Monte Carlo calculations to be used to

calculate doses NOT collected by the chamber

for modeling accuracy

– In-air spot profiles: A large area scintillation detector

system

– Absolute calibration in a reference field: NIST traceable

(ADCL calibrated) ion chamber and electrometer

system

TPS Validation

• Basic beam parameters in water (homogeneous)

– Output factors in comparison to TPS calculated MU values

• For pencil beam scanning SOBPs of various field size and range/modulation combinations to evaluate “halo” effect modeling accuracy of TPS

– SOBP depth doses of various range and modulation combinations

• Ranges, modulations, distal falloff values, entrance/plateau doses…

– SOBP lateral profiles of unmodulated pencil beam plans of various energy and field sizes

– Air gap effects on SOBP depth and lateral profiles

– Repeat for each range shifter or other accessories

TPS Validation

• Beam parameters of modulated fields in water (homogeneous) for gamma test passing rates

– Lateral profiles for MODULATED pencil beam plans with well-defined dose gradients

– Lateral profiles for MODULATED

pencil beam plans reflecting

typical clinical scenarios (brain,

H&N, prostate, breast, lung, etc)

• Film or 2D ion chamber array at

multiple depths throughout treated volume

TPS Validation

• Inhomogeneity corrections

– Accuracy of treatment plans in phantoms containing bone and/or lung slabs/blocks sandwiched/interlaced with soft tissue slabs• Each piece of phantom slabs MUST be measured for RLSP values and assigned in TPS

using CT HU to RLSP calibration table values

– SOBP and lateral profiles of beam in such heterogeneous phantoms to be measured• Films or 2D detector arrays

– Absolute doses using ion chambers

• Moving targets

– 4DCT scans used to create ICTV; ion chamber and films for absolute and relative doses in motion phantom

Commissioning of Immobilization Devices• All immobilization devices that may be traversed by the treatment beam shall be

commissioned for their range pull-back values; homogeneity; and sensitivity to setup errors– CT scans of potentially entire device to be acquired and imported into TPS

• Use TPS to calculate range pullback of devices WITHOUT override HU values

• Compare to measured range pullbacks for residue error: if unacceptable, need to override HU of device for range/dose calculation

– CT scans to be reviewed for homogeneous distribution of HU values

• Clusters of high or low density volumes may indicate poor manufacturing quality control and should be brought to vendor’s attention

– Presence of sharp density gradients should be evaluated for need to apply additional compensator smearing beyond inherent proton-in-patient scattering

– Mechanical tests of sagging with weight – typically should present NO ADDITIONAL sagging between completion of imaging localization and beam-on time

Base-of-Skull Frame Commissioning

Meas pt meas R90Measured

Pullback

Pullback

based on

CT

Diff

cm cm cm cm

1 14.72 0.40 0.57 -0.17

2 14.78 0.34 0.50 -0.16

3 14.68 0.44 0.63 -0.19

Frame displacement as function of time

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time [min]

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t - D

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Current frame (4.5kg head + 9.1kg shoulder) New revision 1 (5.1kg head + 13kg shoulder) 11/13

End-to-End Tests

• For a given test phantom (with ion chamber, TLD/OSLD, and film holders)

– Acquire CT scan of phantom

– Override HU values of phantom components as appropriate

– Calculate treatment plan

– Export to OIS

– Align phantom under image guidance

– Deliver treatment plan to phantom

– Analyze dosimeter readings for doses and gamma test pass rates

• Should perform for both static and moving phantoms

IROC TLD/OSLD and Proton Phantoms• Irradiating IROC proton TLD/OSLD and phantoms is an excellent method of third-party independent

review of commissioning results

Prostate Phantom

Other proton compatible phantoms include thorax,

spine, and head

Liver Phantom

Last But Not The Least things

• System and patient-specific QA programs• Operating procedures and protocols

– Simulation – Treatment planning– Treatment delivery– Safety and emergency (including radiation and clinical aspects)

• Education and training– Vendor provided training for therapists– In-house didactic training– In-house hands-on training/mock treatment– Competency and certification