Large and in charge.
Top Line: Large prostate volumes are a relative contraindication for prostate brachytherapy, but should it affect your decision to hypofractionate external beam treatment?
The Study: Let’s back up for a moment. Brachytherapy is not contraindicated for large prostate glands due to diminished effectiveness but rather due to a concern about feasibility and increased toxicity, which may be avoided with equally effective alternative treatments. However, it’s also been clearly established that larger prostates portend worse GU toxicity with conventionally-fractionated external beam radiation, as well. Perhaps hypofractionation will be the savior? Here is a look back at 472 men receiving moderate hypofractionation (almost exclusively 2.5 Gy x 28 = 70 Gy) for prostate cancer at Duke from 2008-2018. The primary variable of interest was size of the prostate planning target volume (PTV), which was deemed “large” if falling in the highest quartile, >138 cc (median prostate volume in this cohort was 76 cc). As expected, there were no differences in biochemical recurrence nor survival based on prostate PTV size. However, also unsurprisingly, those with a large prostate PTV had significantly higher rates of late grade 2+ GU toxicity (59% v 48%) occurring on a significantly shorter timescale. Importantly, this remained true on multivariate analysis even when controlling for baseline AUA score, suggesting size is not simply a surrogate for worse baseline function. Conversely, there was no association between large prostate PTV and GI toxicity.
TBL: Larger prostate volumes increase the risk of GU toxicity across all radiation modalities, highlighting the need to investigate adjunctive strategies (e.g., longer neoadjuvant ADT for downsizing?) to mitigate risk for this population. | Nateson, Adv Radiat Oncol 2022