Program Information
Direction Modulated Brachytherapy for HDR Treatment of Cervical Cancer
D Han1*, M Webster1 , D Scanderbeg1 , C Yashar1 , D Choi1 , B Song1 , S Devic2 , A Ravi3 , W Song1 , (1) University of California, San Diego, La Jolla, CA, (2) McGill University, Montreal, QC, (3) Sunnybrook Odette Cancer Centre, Toronto, ON
Presentations
SU-C-16A-3 Sunday 1:00PM - 1:55PM Room: 16APurpose:
To investigate a new Directional Modulated Brachytherapy (DMBT) intra-uterine tandem using various 192-Ir after-loaders.
Methods:
Dose distributions from the 192-Ir sources were modulated using a 6.3mm diameter tungsten shield (18.0g/cm3). The source moved along 6 longitudinal grooves, each 1.3mm in diameter, evenly spaced along periphery of the shield, The tungsten rod was enclosqed by 0.5mm thick Delrin (1.41g/cc). Monte Carlo N particle (MCNPX) was used to calculate dose distributions. 51million particles were calculated on 504 cores of a supercomputer. Fifteen different patients originally treated with a traditional tandem-and-ovoid applicator, with 5 fractions each, (15 patients X 5 fxs = 75 plans) were re-planned with the DMBT applicator combined with traditional ovoids, on an in-house developed HDR brachytherapy planning platform, which used intensity modulated planning capabilities using a constrained gradient optimization algorithm. For all plans the prescription dose was 6 Gy and they were normalized to match the clinical treated V100.
Results:
Generally, the DMBT plan quality was a remarkable improvement from conventional T&O plans because of the anisotropic dose distribution of DMBT. The largest difference was to the bladder which had a 0.59±0.87 Gy (8.5±28.7%) reduction in dose. This was because of the the horseshoe shape (U-shape) of the bladder. The dose reduction to rectum and sigmoid were 0.48±0.55 Gy (21.1±27.2%) and 0.10±0.38 Gy (40.6±214.9%), respectively. The D90 to the HRCTV was 6.55±0.96 Gy (conventional T&O) and 6.59±1.06 Gy (DMBT).
Conclusion:
For image guided adaptive brachytherapy, greater flexibility of radiation intensity is essential and DMBT can be the solution.
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