Toxicity analysis of lymph node irradiation for prostate cancer patients treated with IMRT.

Abstract

41 Background: The radiation target for intensity modulated radiation therapy (IMRT) in high-risk prostate cancer (HRPC) includes both the prostate and seminal vesicles (SV). Inclusion of the regional lymph nodes (LN) has considerable variation in daily practice. Currently used prescriptions are 80 Gy to prostate and proximal SV, with 56Gy to the distal SV with (P/SV+LN) or without the pelvic LN (P/SV). The same P/SV prescription is used for intermediate risk prostate cancer (IRPC). We report the association between inclusion of the LN and toxicity for men treated from 2001 to 2009. Methods: 1,160 men treated for HRPC and IRPC with IMRT were identified in our clinical database. All patients had simulation with both CT and MRI, and utilized daily image guidance. Toxicity data were obtained from chart review. Statistical analysis was performed utilizing log rank test. Results: 408 patients were in the P/SV+LN group. There was no difference between the groups in regard to age, race, RT duration, or smoking. Median prescription dose was 78 Gy in both groups. Median follow-up was 44 months. A higher rate of late GI toxicity was seen in the group of patients treated to P/SV+LN (p<0.01), see Table. No difference was seen in toxicity >grade 2 for acute GU (33.1% vs. 30.2%, p=0.31), acute GI (5.9% vs. 3.5%, p=0.05), or late GU toxicity (13.7% vs. 13.0%, p=0.74) for P/SV+LN vs. P/SV alone at 5 years. MVA was performed for late GI toxicity controlling for radiation dose, length of radiation course, and use of androgen deprivation. Inclusion of LN RT remained a significant predictor of late GI toxicity (HR=2.0, p=0.02). For those with late GI toxicity, the most common symptoms were bleeding (69.5%), increased frequency of bowel movements (26.6%), fecal incontinence (15.7%), and proctitis (14.9%). Conclusions: Delivery of 56 Gy to the pelvic LN results in a significant increase in grade 2 or higher late GI toxicity with a HR of 2.0 in the setting of treatment with IMRT. A decision to treat the pelvic LN in HRPC should be weighed against the increase in late GI toxicity. [Table: see text]