2277: Acute Toxicity Assessment of a Single Institution Series of Prostate Cancer Patients Treated With Pelvic Intensity Modulated Radiation Therapy With Synchronous Integrated Boost to the Prostate or Prostate Bed

Abstract

We investigated the feasibility of delivering elective pelvic nodal RT combined with a hypofractionated RT regimen to the primary site by employing IMRT with a synchronous integrated boost (SIB) for patients with intermediate to high-risk prostate cancer. We analyzed acute toxicity of SIB IMRT in patients treated either primarily for prostate cancer or with post-operative or salvage RT following prostatectomy. For primary treatment, the prostate planning target volume (PTVprostate) was the prostate plus a 5 mm posterior margin and 1 cm margin in other directions; the nodal PTV (PTVnodes) included the internal, external, and lower common iliac vessels plus a 1 cm circumferential margin. SIB IMRT plans were designed to deliver 70 Gy to the PTVprostate in 28 fractions (2.5 Gy/fraction) while simultaneously delivering 50.4 Gy to the PTVnodes. Post-operative or salvage SIB IMRT included a dose of 64 Gy in 32 fractions to the PTVpost-op, here defined as the prostate bed plus a 1 cm margin, while simultaneously delivering 54.4 Gy to the PTVnodes. The NCIC CTCAE v3.0 was employed to score toxicity. Twenty-seven patients (18 definitive, 5 adjuvant, 4 salvage) were treated between early 2004 and late 2005. The median age at the beginning of treatment was 63 years (range 53–77). Twenty-two out of 27 patients received androgen suppression as a component of treatment, including all patients in the primary RT cohort. Twenty-six out of 27 patients received treatment as prescribed, with 1 patient discontinuing radiation one fraction prior to completion due to a medical problem unrelated to his treatment. Median follow-up of all patients was 9 months (3–19 months). The incidence of any acute grade 1 or 2 event was 96%. The most common acute event was urinary frequency/urgency, which occurred in 81% of patients (67% grade 1, 14% grade 2). Acute diarrhea occurred in 56% of patients (37% grade 1, 15% grade 2, 4% grade 3). The incidence of any grade 3 or higher acute toxicity was 4% (1/27); that patient experienced severe diarrhea while on treatment, but was found to have clostridium difficile colitis, and his symptoms improved rapidly on antibiotics. Pelvic IMRT with synchronous integrated boost to the prostate/prostate bed for high-risk prostate cancer, either given in the primary or post-operative/salvage setting, was acutely well tolerated in our series of patients. Additional follow-up is necessary to ensure that no unexpected late toxicity occurs. SIB IMRT to the pelvis combines elective nodal RT and hypofractionation to the primary and warrants further study in a clinical trial setting.