Hit 'em where it hurts.

Top Line: Prostate cancer is pathologically multifocal in the vast majority of cases.
The Study: This, coupled with historic limitations in radiographically visualizing discrete tumors, led to most treatment strategies targeting the entire prostate. It turns out, analogous to bulky lymphoma, dominant prostatic lesions are the sites most likely to harbor resistant disease after conventional treatment. With the advent of sophisticated prostate MRIs, selective radiation dose-escalation to dominant lesions via either brachytherapy or highly-targeted SBRT techniques has become a reality. This phase 2 trial enrolled 80 patients of all risk levels with MRI-visible prostate tumors and <30% risk of nodal involvement. All patients received 2 Gy x 38 = 76 Gy via VMAT to the entire prostate plus margin with additional dose to the MRI-dominant lesion via either a simultaneous integrated boost (SIB) of 2.5 Gy x 38 = 95 Gy (n=40) or a HDR brachy boost of 10 Gy x 1 in the week preceding VMAT (n=40) in a non-randomized fashion. Plans called for 50% of the rectum and bladder to receive <53 Gy and 30% <70 Gy. Both mean and max dominant tumor doses were higher with brachy, but grade 1-2 toxicities were pretty similar. There were two acute grade 3 GU toxicities (one in each arm) and one acute grade 3 GI toxicity in the SIB arm. One late grade 3 GU and one late grade 3 GI toxicities occurred, both with SIB. In both arms, urinary and bowel quality of life declined at 6 weeks and recovered at 6 months.
TBL: Dose-escalation to MRI-dominant prostate tumors is feasible and safe with either external beam or brachy techniques—TBD is their impacts on long-term disease control. | Sanmamed, Radiother Oncol 2020

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