EP-1260: Risk factors for acute toxicity in prostate cancer patients receiving hypofractionated IMRT

Abstract

Purpose/Objective: To evaluate the impact of clinical and dosimetric risk factors on acute gastrointestinal (GI) and genitourinary (GU) toxicity during hypofractionated intensitymodulated radiotherapy (IMRT) in patients with prostate cancer. Materials and Methods: Between May 2009 and August 2014, 195 patients with prostate cancer and negative lymph nodes underwent IMRT. Median age was 74 years (range 57-85). Disease stage: T1a in 3 patients (1.54%), T1b in 2 (1.03%), T1c in 28 (14.36%), T2a in 21 (10.77%), T2b in 36 (18.46%), T2c in 83 (42.56%), T3a in 9 (4.62%), T3b in 13 (6.67%); Gleason scores were 2- 6 in 114 patients (58.47 %),7 in 55 (28.21 %) and 8-10 in 26 (13.34%). Median basal PSA was 8.1 ng/ml (range 1.6-42.59 ng/ml). 107/195 patients (54.87%) received hormonal therapy (LHRH analogue and/or antiandrogen). IMRT was delivered with 15 MV photons. Planning target volume (PTV) consisted of CTV plus 1 cm in all directions except at the prostate-rectal interface where the margin was 0.5 cm. A hypofractionated regimen delivered a prescribed dose of 74.25 Gy in 33 fractions (2.25 Gy/fraction) to the prostate and, if involved, to the seminal vescicles (SV). When the risk of SV involvement was >15% according Roach's formula SV received 62 Gy in 33 fractions (1.879 Gy/fraction) using a simultaneous integrated boost (SIB-IMRT) . Median prostate volume was 43.93 cm3 (range 16.72-161.60 cm3). Acute toxicity was scored using Common Terminology Criteria for Adverse Events (CTCAE) version 3.0. Results: At median follow-up of 26 months (range 3-60) acute genitourinary (GU) toxicity was observed in 140 (71.80%) patients: G1 in 81 (41.54%), G2 in 49 (25.13%), G3 in 10 (5.13%). Acute gastrointestinal (GI) toxicity, consisting mainly of proctitis, was observed in 79 (40.51%) patients: G1 in 44 (22.56%), G2 in 33 patients (16.92 %), G3 in 2 patients (1.03%). There was no G4 acute GU or GI toxicity. Administration of 3-OH-Methylglutaryl CoA reductase inhibitors (statins) significantly reduced the GI toxicity rate and grade (p =0.028 and p =0.029 respectively; Chi-Square test). Large prostate volume was associated with a higher rate and grade of acute GU toxicity (p = 0.02 Mann-Whitney test and p = 0.003 Spearman's correlation). Bladder V50 correlated with a higher grade of acute GU toxicity (p =0.038 Spearman's correlation) . GU and GI toxicities rate and grade were strongly interrelated (p =0.000; Chi-Square test). Conclusions: Hypofractionated IMRT for prostate cancer is safe and is associated with low acute toxicities. A large pretreatment prostate volume was associated with increased GU toxicity. We hypothesized that statins use might lower the incidence of GI toxicity. During treatment planning bladder V50 should be reduced in order to avoid GU toxicity.