brachytherapy and gyn malignancy. brachytherapy brachytherapy (brachy, from the greek for “short...

Brachytherapy and GYN malignancy

Brachytherapy

bull Brachytherapy (brachy from the Greek for ldquoshort distancerdquo) consists of placing sealed radioactive sources close to or contact with the target tissue

bull Interstitial intracavity or transluminal approach

bull Temporary or permanent implant

bull Low or high dose rate

Introduction

bull Discovery in 1898

bull Short distance (cm)

bull High radiation dose can be delivered locally to the tumor with rapid dose fall-off in the surrounding normal tissue

Radioactive sources

Radioactive sourcesRadium-226

bull Average energy 083Mev (05mm of platinum)bull A filtration of at least 05mm platinum is sufficient

to absorb all the α particles and most of the β particles emitted by the radium and its daughter products

bull Half life ~1600 yearsbull It was loaded into cells about 1cm long and 1mm

in diameter bull Radium sources are manufactured as needles or

tubes in a variety of lengths and activities

Radioactive sourcesCesium-137

bull Substitute for radium in both interstitial and intracavitary brachytherapy

bull Energy 0662Mev nearly the same penetrating power as radium

bull Half life 30 years (clinically used 7 years without replacement) It was doubly encapsulated in stainless-steel needles and tubes

Radioactive sourcesCobalt-60

bull High specific activitybull Small sources required for some special a

pplicators

bull More expensive than 137

Cs and short half life (526 years)

bull The sources can be used to replace 226Ra in intracavitary application

Radioactive sourcesIridium-192

bull It has a complicated γ ray spectrum with an average energy of 038 MeV rarr It required less shielding for personnel protection

bull It has the disadvantage of a short half-life (738 days)

bull It is fabricated in the form of thin flexible wires which can be cut to desired lengths

Radioactive sourcesIodine-125

bull Widely used for permanent implants

bull Longer half-life 594 days (convenient for storage)

bull Low photon energy (0028MeV) rarr less shielding

bull Disadvantages dosimetry of 125I is much more complex

BrachytherapyPermanently Implanted

Source Energy

T12 Dose Rate

222Rn 12MeV

383 075Gh

198Au 412keV

270 107Gh

125I 28keV 596 007Gh

13Pd 22keV 17 019Gh

Radioactive sourcesbull ICRU38 LDR sources 04-2 Gyhr (137Cs) HDR sources ge 12 Gyhr (60Co 192Ir)bull 226Ra leakage Radon gasbull 137Cs better than 226Ra less shielding and microsphe

re form with leakage gas bull 137Cs better than 60Co less shielding and cheapbull 192Ir better than 137Cs lower energy require less shiel

ding for personnal protection and higher specific activity

bull 103Pd better than 198Au and 125I less shielding and biologic advantage

Low Dose Rate (LDR) High Dose Rate (HDR)

Patient bullLong history of use bullAbility to predict rate of late complications

bullNo long term confinement to bedbullNo indwelling bladder cathetersbullNot labeled ldquoradiation risk zonerdquo to relative visitors and staffbullAvoid several anesthesias

Clinical bullImproves chances of atching tumors in sensitive phase of cell cycle

bullMaintain position of the sources during the brief treatmentbullPatient preparationbullNo specialized nursingbullAbility to treat great patient loads

Physical

bullLonger treatment times allow for leisurely review of and potential modifications to the treatment bullPlan prior to the delivery of a significant portion of treatmentbullFavorable dose-rate effect on repair of normal tissuesbullInfrequent replacement and calibration of sources because of long isotope half-life

bullShort treatment times and minimal radiation protection problemsbullPossibility of optimizing dose distribution by altering the dwell times of the source at different

Radioactive sourcesRadioactive sources

Brachytherapy and GYN Malignancy

Reference point from which lymph node position were measured on lymphoangiograms and the rang

e of locationInt J Radiat Oncol Biol Phys 34167-172 1996

Distribution of pelvic node metastases in patients with Ib-IIa cervical cancer

Gynecol Oncol 6219-24 1996

Tumor size lt=4 cm Local advanced tumor

External beam radiotherapy for GYN Malignancy

Pelvic irradiation portal in cervical cancer4-field box technique

Pelvic irradiation portal in cervical cancer4-field box technique

Combination of external beam pelvic irradiation an

d intracavitary brachytherapy (ICRT)

Brachytherapy in definitive radiotherapy of Brachytherapy in definitive radiotherapy of cervical cancercervical cancer

(Intracavity radiotherapy ICRT)(Intracavity radiotherapy ICRT)

Intracavitary Radiotherapy (ICRT)

Applicator of ICRT

Intracavitary insertion (ICRT)

Postoperative brachytherapy(Intravaginal radiotherapy)

Intravaginal radiotherapy (IVRT)

Female urethral cancer

Endometrial cancer