Gastrointestinal Cancer

PV QA 1 - Poster Viewing Q&A 1

SU_3_2027 - Effect of Radiation Therapy Duration on Overall Survival in Anal Squamous Cell Carcinoma: A National Analysis

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Effect of Radiation Therapy Duration on Overall Survival in Anal Squamous Cell Carcinoma: A National Analysis
S. Mehta1, S. J. Ramey2, D. Kwon3, B. J. Rich1, A. H. Wolfson4, R. Yechieli4, L. Portelance5, and E. A. Mellon4; 1University of Miami, School of Medicine, Miami, FL, 2University of Miami; Jackson Health System, Miami, FL, 3Department of Statistics, University of Miami Sylvester Comprehensive Cancer Center, Miami, FL, 4Radiation Oncology Department, University of Miami/Sylvester Comprehensive Cancer Center, Miami, FL, 5Department of Radiation Oncology, University of Miami, Sylvester Comprehensive Cancer Center, Miami, FL

Purpose/Objective(s): Prolonged duration of radiation therapy (RT) has been associated with a decrease in overall survival (OS) in squamous cell carcinomas (SCC) of the cervix and head and neck. However, limited and varied data exist to correlate RT duration with OS in SCC of the anus (SCC-A). Therefore, we examined the impact of RT duration on OS in SCC–A and evaluated demographic disparities in RT duration using the National Cancer Database (NCDB).

Materials/Methods: Patients with SCC-A diagnosed from 2004-2014 and treated with definitive concurrent chemoradiation, defined as a start of chemotherapy and radiation within 7 days of each other, were identified in the NCDB. Additional inclusion criteria were: Stage I-III, no surgery as part of initial treatment, 25-33 fractions of RT, total RT dose (regional dose plus boost) of 45-60 Gy, and RT duration of 30-100 days. For the OS analysis, patients without available follow up for survival and those with a prior malignancy were excluded. A ratio of RT duration to number of fractions (RT-days/fractions) was used in OS analysis as a covariate in order to better normalize RT duration, given variations in fractionation used. Cox proportional hazards regression model was used for OS analysis. Negative binomial regression was used to assess the effect of demographic disparities on prolonged RT duration in the multivariable analysis (MVA). All p-values were two-sided and statistical significance was defined as p<0.05.

Results: For the OS analysis, 6,381 patients met inclusion criteria. Mean duration of RT was 48.4 days, mean total RT dose was 53.5 Gy, and the mean of RT-days/fractions was 1.64 days/fx (median: 1.55 days/fx). Mean duration of RT for patients treated with 25 fractions was 42.6 days while it was 54.8 days for patients treated with 33 fractions. Mean OS was 97.4 months and 5-year OS was 74.6%. On MVA, increasing RT-days/fractions correlated with decreasing OS (Hazard ratio 1.52; 95% confidence interval 1.30-1.78; p=0.001). Factors associated with increasing RT duration on MVA were treatment at a community or integrated network center (vs. academic center), treatment at a low volume center, treatment in the northeast region (vs. west), female gender, Medicaid insurance (vs. private insurance), living within 10 miles of reporting center (vs. > 50 miles), advanced T- or N-stage, non-IMRT/proton treatment (vs. IMRT or proton use), and multi-agent chemotherapy use (vs. single agent chemotherapy use) (p<0.05 for each). RT duration decreased from 2004 to 2014.

Conclusion: This analysis suggests that the ratio of increased RT-days/fractions is associated with decreased OS. This result suggests that decreasing treatment breaks during RT for SCC-A may improve OS. Further analysis is ongoing to identify thresholds after which OS begins to fall or drop more rapidly. Such a threshold could be used as a quality metric for definitive chemoradiation for SCC-A.

Author Disclosure: S. Mehta: None. S.J. Ramey: Travel Expenses; Intellisphere. D. Kwon: None. B.J. Rich: None. A.H. Wolfson: None. R. Yechieli: None. L. Portelance: Cervix Committee; NRG.

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