A PIRADS life.

Top Line: The FLAME trial showed that escalating dose to MRI-defined intraprostatic lesions while respecting OAR constraints improved biochemical control without increasing toxicity. 

The Study: DELINEATE is another trial that investigated simultaneous integrated boost (SIB) to intra-prostatic disease. DELINEATE was a single-institution, multi-cohort, non-randomized phase 2 trial from the UK of 256 men with intermediate or high risk prostate cancer treated with definitive radiation. Here we have 5-year toxicity outcomes. There were three different dose cohorts: A) 74 Gy in 37 fractions to the prostate and seminal vesicles, B) 60 Gy in 20 fractions to the prostate and seminal vesicles, and, to make things harder to interpret, C) 74 Gy in 37 fractions to the prostate and seminal vesicles with simultaneous 60 Gy in 37 fractions to the pelvic lymph nodes. Suitable boost lesions were PIRADS 3 or higher with corresponding biopsy findings. Boost lesions were delineated on T2 and diffusion-weighted sequences. The boost target was the lesion plus a 2mm prostate-confined margin minus the urethra. The urethra was contoured with specific constraints during treatment planning. Important to note is that the SIB target was prescribed to the median dose (D50%) so max doses were ~111-112% of prescription dose (82 Gy in 37 fractions and 67 Gy in 20 fractions). In the conventional cohort, the maximum urethra D2% was 77Gy (ideal) and 83Gy (mandatory). The maximum rectum D2% was 76Gy (mandatory). In the hypofractionated cohort, the maximum urethra D2% was 62.4 (ideal) and 67.3 (mandatory). The maximum rectum D2% was 61.6Gy (mandatory). At 5 years, the cumulative rates of RTOG grade 2+ toxicity were 3.6% (A), 7.2% (B), and 8.4% (C). Cumulative grade 2+ GU toxicity was 12.9% (A), 18.2% (B), and 18.2% (C). The CTCAE toxicity outcomes reported in DELINEATE are comparable to those reported in FLAME. Biochemical control was >95% in all cohorts. 

TBL: Late toxicity outcomes from DELINEATE support the safety of focal dose-escalation of MRI-defined lesions with both conventional fractionation and hypofractionation. | Tree, Int J Radiat Oncol Biol Phys 2022