Early Experiences of Image Guided Prostate and Pelvic Nodal Irradiation With Intensity Modulated Radiation Treatment in Localized Prostate Cancer

Background To present the early findings of a phase I clinical trial studying the use of intensity modulated radiation treatment (IMRT) to treat at risk pelvic and lower para-aortic lymph nodes in patients with high risk prostate cancer while escalating dose. Dose escalation was performed with a technique particularly aiming to limit the dose to surrounding critical structures. Methods A total of 12 patients were treated with an IMRT plan that delivered 45 Gy to the pelvic lymph nodes, prostate and proximal seminal vesicles. This was followed by an image guided IMRT plan that delivered 9 Gy to the prostate and seminal vesicles and then an additional 21.6 Gy delivered to the prostate for a total dose of 75.6 Gy to the prostate. Gastrointestinal (GI) and genitourinary (GU) toxicity were recorded weekly throughout treatment and in follow up (range: 20 - 49 months). Results At diagnosis, median age was 64, median PSA 15.5 (range: 5 - 103) and Gleason score ranged 7 - 9. The median dose to the bladder was 52 Gy, the median dose to the rectum was 53 Gy and the median dose to the small bowel was 26 Gy. During treatment, Grade 2 GU toxicity was noted in 3/12 (25%) patients and Grade 2 GI toxicity was noted in 2/12 patients (16%). At a median follow-up of 28 months, Grade 2 late GI toxicity was seen in 1/12 (8%) and late GU in 3/12 (25%) of patients. There were no acute or late grade 3 and 4 GU or GI toxicities. Conclusions Our study shows the feasibility of using IMRT for pelvic and lower para-aortic nodal irradiation as the toxicities are low for the total dose that was delivered. This shows promise for reducing normal tissue doses, improving target control, and potentially allowing for additional dose escalation to the pelvic/lower para-aortic lymph nodes in our successive cohorts.