High dose prostate cancer radiotherapy: Late toxicity outcomes

Abstract

Purpose: To report late radiation toxicity in a contemporary cohort of patients treated exclusively with high dose radiotherapy, daily image guidance and Intensity Modulated Radiation Therapy (IMRT) or Intensity Modulated Arc Therapy (IMAT). Methods and Materials: Patients were followed prospectively using a real time database which included toxicity reported using the modified RTOG scale. The current study included all patients treated between April 2007 and April 2012 with a minimum 12 months follow up. Patients were planned with either 7-9 field IMRT or IMAT. Rectal and bladder planning goals remained unchanged (rectal V65 < 17%, V40 < 35%; bladder V65 < 25% and V40 < 50%). Daily image guidance was used for all patients. Baseline urinary function was assessed with the international prostatic symptom score (IPSS). Late toxicity was estimated using Kaplan Meier statistics. Results: There were a total of 239 patients eligible for analysis with a median age of 72 yrs (46 yrs to 84 yrs). There were 26 diabetic patients (11%). The median IPSS prior to treatment was 6 (0-31). The majority of the patients were either intermediate risk (40%) or high risk (52%). There were 8 patients (3.3%) who had known lymph node metastases. Androgen deprivation was used in 66% of patients (19% short term and 37% long term) and 34% of the patients had pelvic lymph node irradiation with a synchronous boost (56 Gy-60 Gy in 38-40#). Mean delivered dose to the PTV was 79 Gy/38# (n= 102); 81 Gy/39# (n=16) and 83 Gy/40# (n=121). The 3 yr late gastrointestinal and genitourinary cumulative Grade 2+ toxicities were 3.2% and 13.9% respectively. A comparison of the high and low dose cohorts respectively for rectal toxicity (1.8% vs. 4.3%) and bladder toxicity (16.5% vs. 12%) was similar. Conclusion: Doses above 80 Gy can be delivered safely for prostate cancer using daily IGRT combined with IMRT/IMAT.