Room: AAPM ePoster Library
Purpose: To evaluate the feasibility of high dose rate brachytherapy (HDR-BT) inverse optimization in computing optimal treatment plans for patients with dominant intraprostatic lesions (DIL) partially covered by pubic arch interference (PAI).
Methods: Twelve lesions were identified on multi-parametric MRI by a genitourinary radiologist, then contoured by a radiation oncologist, and transferred to trans-rectal ultrasound image-sets of a separate cohort of 7 patients, with significant PAI. A study set of 105 treatment plans were optimized using inverse optimization in Oncentra(TM) Prostate such that the size and location of DIL was varied throughout the cohort. Impact of interplay between DIL size and level of prostate and DIL obstruction were analyzed by varying DIL location through the antero-lateral section of PAI obstructed prostate gland near the reference plane. A Hybrid Inverse Planning and Optimization algorithm (HIPO) was used to inverse optimize catheter positioning and dwell times to boost dose to the DIL to D90>125% while maintaining dosimetric constraints to organs-at-risk according to GEC-ESTRO guidelines for 15 Gy in 1 fraction. The number of optimization trials was limited to 600 trials. 15 catheters were used in the treatment plans.
Results: Mean DIL volume was 5.31 cc (0.71-12.41 cc), mean prostate volume was 57.5 cc (37.5-83.6 cc). All 105 focal HDR-BT plans created met the key dosimetric criteria for whole gland GEC-ESTRO recommendations. A decrease in D90 and V150 for lesion dose coverage was observed with increasing lesion volume obstructed by PAI and lesion proximity to the urethra.
Conclusion: HIPO inverse optimization is a feasible tool for optimal dose coverage towards HDRBT in patients with PAI. High dose to DIL may be delivered in cases with significant partial obstruction while sparing nearby organs-at-risk.