Original Articles
Proton Reirradiation of Recurrent Rectal Cancer: Dosimetric Comparison, Toxicities, and Preliminary Outcomes

https://doi.org/10.14338/IJPT.13-00002.1Get rights and content
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Abstract

Purpose

Locally advanced rectal adenocarcinoma is effectively treated with chemoradiation and surgery; however, 10 to 25% of patients locally recur within or near a previously irradiated field. Proton radiation therapy (PRT) is ideally suited to the problem of reirradiation for locally recurrent rectal cancer (LRRC).

Patients and Methods

Seven patients with LRRC in or near prior radiation fields were enrolled on this prospective study from March 2010 to February 2011. All patients underwent positron emission tomography (PET)/computed tomography (CT) simulation and were stratified by low volume (clinical target volume<250 cm3, n=4) or high volume (>250 cm3, n=3). Primary endpoints were feasibility and acute toxicity (within 90 days from PRT initiation). Dosimetry was compared using the Wilcoxon signed-rank test. Tumor response was defined according to PERCIST criteria.

Results

Median follow-up was 14 months (4.9–22.6). Median dose of prior RT was 5040 cGy. Mean PRT dose was 6120 cGy (RBE) (range, 4500–6480 cGy). The total dose sum of prior radiation therapy treatment and PRT was 109.8 Gy (RBE) (range, 95.4–151.2). One patient had surgery prior to and 1 after PRT. Six patients received concurrent 5-fluorouracil-based chemotherapy. Bowel volume receiving 10 and 20 Gy, and the dose to 200 and 150 cm3 of bowel were significantly reduced. There were 3 acute grade 3 and 3 late grade 4 toxicities. Four patients were alive at time of follow-up. Six had a metabolic complete response, of whom 2 subsequently locally recurred. One had initial progressive disease. Of 6 symptomatic patients, 3 had complete pain resolution and 3 partial.

Conclusions

This preliminary report indicates that PRT for LRRC provides dosimetric improvements over intensity-modulated radiation therapy, particularly to the bowel. The modest rates of acute and late toxicity as well as the preliminary outcomes of high tumor and symptom control rates are promising.

Keywords

proton
intensity-modulated radiation therapy
reirradiation
pelvis
rectal
dosimetry

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