Effect of Large Prostate Volume on Efficacy and Toxicity of Moderately Hypofractionated Radiation Therapy in Patients With Prostate Cancer.

PURPOSE

To evaluate the effect of prostate volume on outcomes after moderately hypofractionated radiation therapy (mHFRT) for prostate cancer.

METHODS AND MATERIALS

Prostate cancer patients treated with mHFRT at a Veteran's Affairs Medical Center from August 20, 2008, to January 31, 2018, were identified. Patients were placed into a large prostate planning target volume (LPTV) cohort if their prostate PTV was in the highest quartile. Acute/late genitourinary (GU) and gastrointestinal toxicity events among patients with and without LPTV were compared. Multivariable analyses estimated the effect of factors on toxicity. Overall survival, biochemical recurrence-free survival, and freedom from late GU/gastrointestinal toxicity of patients with and without LPTV were estimated via Kaplan-Meier.

RESULTS

Four hundred and seventy-two patients were included. Ninety-three percent received 70 Gy in 2.5 Gy fractions; 75% received androgen deprivation therapy. Median follow-up was 69 months. Patients with LPTV (PTV >138.4 cm) had a higher late 2 + GU toxicity compared with those without (59% vs 48%,  = .03). Earlier time to late 2 + GU toxicity was associated with LPTV (hazard ratio 1.36; 95% confidence interval [CI], 1.00-1.86;  = .047), androgen deprivation therapy use (hazard ratio 1.60; 95% CI, 1.13-2.27;  = .01), and higher baseline American Urologic Association symptom score (odds ratio 1.03; 95% CI, 1.02-1.05; < .001). At 2 years, freedom from late 2 + GU toxicity was 46% (95% CI, 47%-54%) for those with LPTV versus 61% (95% CI, 55%-65%) for those without ( = .04). Late grade 3 GU toxicity was 7% for those with LPTV and 4% for those without. No differences in overall survival or biochemical recurrence-free survival were observed between patients with or without LPTV.

CONCLUSIONS

LPTV did not affect efficacy of mHFRT for prostate cancer; however, it was associated with increased risk and earlier onset of late grade 2 + GU toxicity.