Abstract PO-091: Does volumetric-modulated arc therapy improve anal cancer treatment outcome and reduce toxicity: A single institution experience

Abstract Introduction: Anal cancer (AC) is a relatively rare malignancy that can have poor prognosis if not treated at an early stage. It is difficult to conduct phase 3 clinical trials due to the low incidence rate. Standard treatment of locally advanced AC has been almost always concurrent chemotherapy and radiation therapy for several decades. In recent years, volumetric-modulated arc therapy (VMAT) has emerged as a new technology designed to reduce toxicities. The purpose of this retrospective study is to share our experience in eighteen years to see if this innovative treatment has translated into a better outcome for AC patients. Methods: This study was approved by our institution’s Research Ethics Board (REB). All electronic medical records (EMR) of patients with anal canal, anal or peri-anal malignancies who were seen between January 2002 and December 2019 were reviewed. We were using conventional radiation therapy (CRT) until 2012 when we adopted VMAT as standard radiation modality for definitive treatment of patients with locally advanced AC. We excluded melanoma, lymphoma, and adenocarcinoma of the rectum involving anal canal. Squamous cell carcinoma of the anal canal involving rectum or colon was included in the study. A total of 182 consecutive patients meet the selection criteria for analysis. Patient demographics, treatment modalities, survival and toxicity data were recorded. Kaplan-Meier survival curves and life tables using SPSS software were generated to compare outcome of patients that received VMAT versus CRT starting from the end of radiation therapy, i.e. not from date of diagnosis as some other studies in the literature. Results: Median age of our cohort was 61 years (33-98), 116 (64%) were female, majority (72%) were locally advanced stage 2 or 3 (AJCC-7), 4% were HIV positive, 62% were squamous cell carcinoma, 86% received radiotherapy, including 45% VMAT and 40% CRT, 74% received 45 Gy or higher dose, 49% had surgery, and 72% had chemotherapy. Median follow up was 29 months. The 3/5 year overall survival (OS) are 60%/47%, and the 3/5 year local control (LC) are 73%/67%, respectively. Within the sub-groups that received radiation treatment, VMAT had a higher 3/5 year OS of 68%/49%, versus CRT at 54%/45%, p<0.05 and p=0.34, respectively. The 3/5 year LC was not significantly different, 69%/60% versus 74%/71% (p=0.28 and p=0.15, respectively). There was no treatment related death and 20% had Grade 3-4 acute toxicity. Late toxicity analysis was not reliable because of the nature of this retrospective study with no consistent long-term follow up toxicity data available in EMR. The rate of diverting colostomy is high (29.7%), but mostly done prior to treatment due to obstruction. Conclusions: AC treatment outcome in our institution is comparable to published historical data. Our findings support the use of VMAT for localized AC with better OS and similar LC. Large prospective randomized controlled trials are needed to evaluate the benefit of reducing late toxicities from VMAT comparing to CRT. Citation Format: Ming Pan, Nitin Rai. Does volumetric-modulated arc therapy improve anal cancer treatment outcome and reduce toxicity: A single institution experience [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-091.

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