Feasibility of intensity-modulated radiation therapy (IMRT) with PET-defined simultaneous integrated boost (SIB) for distal rectal adenocarcinoma (DRA).

Abstract

550 Background: PET/CT guided preoperative IMRT is being used with increasing frequency in standard practice but reports of methods, efficacy, and toxicity are limited. We report the AGH experience from 2007-2010 of IMRT with SIB for DRA. Methods: 22 pts with stage IB–IV DRA (8 with anal canal involvement) were treated with preoperative concurrent IMRT with SIB, 5FU-based chemotherapy. 15 received weekly oxaliplatin. All had PET/CT simulation. The planned target volume included PET-avid primary tumor and LNs with median margins of 3mm (range, 0–13), in a median of 24 fx (range, 20–28), a median dose of 2.25 Gy/fx (range, 1.9–2.4 Gy) to a median total dose of 53.3 Gy (range, 50.6–57.2 Gy). Clinical target volume included non PET-avid 1st echelon LNs with a median dose of 2.0 Gy/fx (range, 1.6–2.3 Gy) to a total median dose of 47 Gy (range, 40.7–54.04 Gy). Median follow-up was 18 mos (range, 4–35). Late toxicities were scored using CTCAE v. 3.0. Results: 17 of 22 patients (TNM stages IB (3), IIA (3), IIB (1), IIIA (2), IIIB (7), IV (1)) were treated curatively. The remaining 5 pts were treated palliatively. The median length of time from completion of radiation to surgery was 81 days (range, 48–398). 5 pts did not have surgery due to advanced metastatic disease (3), death (1) or biopsy proven complete response (CR) (1). R0 resection was accomplished in 15 of 17 surgical pts including 13/14 curative and 2/3 palliative cases. R1 resection occurred in 2 pts; 1 with stage IIIB and 1 with stage IV. No pts had R2 resection. 6 pts (5 with T2 lesions and 1 with a T4 lesion) had a pathologic CR. 2 of 3 non-surgical pts with metastatic disease had LRF at 5 and 11 mos. 9/22 pts had no late toxicity, 9/22 ≤ grade 2 and 4/22 had grade 3 late toxicity. No patients with T2 tumors had grade 3 late toxicity, and this appeared to be related to lower GTV. Kaplan-Meier freedom from grade 3late toxicity was 85% at 18 mos. Conclusions: IMRT with SIB is an accurate targeting technique in pts with DRA that showed a pathologic CR in 100% of T2 lesions. Advanced T stage and larger GTV were possible risk factors for grade 3 late toxicity. [Table: see text] No significant financial relationships to disclose.