Room: Karl Dean Ballroom A1
Purpose: To compare radiotherapy treatment plans for prostate cancer, biologically-optimised using patient-specific tumour cell distributions obtained from multi-parametric MRI, generated for conventional and hypofractionated schedules.
Methods: Five prostate cancer patients that underwent radical prostatectomy were selected as part of a program to develop bio-focussed prostate radiotherapy (BiRT). The proposed biological optimisation involves using tumour control probability (TCP) to guide inverse-planned intensity-modulated radiotherapy (IMRT) and to determine a patient-specific prescription dose. Patient-specific clonogen distribution maps were derived from multiparametric MRI using machine learning methods based on ground-truth histology and used to inform the TCP model. Biologically-optimised plans with equal TCP, generated for a conventional schedule (78 Gy/39 fractions) and hypofractionated schedules (60 Gy/20 fractions, 36.25 Gy/5 fractions), were compared for each patient using dose-volume and dose distribution metrics for specific normal tissues. A single-fraction schedule was also examined using linear-quadratic and linear-quadratic-linear survival models.
Results: Biologically-optimised hypofractionated plans demonstrated a statistically significant reduction in rectal and bladder dose in comparison with conventionally-fractionated plans. The tissue sparing effect was more pronounced with extreme hypofractionation. Single-fraction prostate IMRT was feasible for both survival models in the single case investigated, though the two models predicted widely-differing estimates for optimal dose prescription.
Conclusion: This study indicates potential for significant reduction in dose to the rectum and bladder for hypofractionated treatment of prostate cancer, with the benefit enhanced if a biologically-driven dose painting approach is utilised, based on patient-level information of the clonogenic cell distribution. Results of this study supports further clinical investigations into the use of extreme hypofractionation.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Australian National Health and Medical Research Council (APP1126955).