Can total psoas area predict toxicity after stereotactic body radiation therapy in borderline resectable and locally advanced pancreatic cancers?

Abstract

455 Background: Total Psoas Area (TPA), a marker of sarcopenia, found clinical utility as an independent predictor of clinical outcomes in gastrointestinal cancers as a proxy for nutritional status. Our study evaluated the relationship of TPA and other proxies of nutrition like Body Mass Index (BMI) and Body Surface Area (BSA) with outcomes in Borderline Resectable Pancreatic Cancer (BRPC) and Locally Advanced Pancreatic Cancer (LAPC) patients receiving Stereotactic Body Radiation Therapy (SBRT). Methods: In retrospective analysis of an IRB approved database, 183 BRPC and LAPC patients treated with SBRT from 2009-2016 met our selection criteria. Patients underwent gemcitabine based or FOLFIRINOX chemotherapy for 3 months prior to SBRT. Eligible patients were those with pre-SBRT planning CT imaging on Pinnacle, a treatment planning system, and an identifiable L4 vertebra. Bilateral psoas muscles were manually contoured at the L4 vertebral level. This area was normalized by patient height (median = 876.505 mm2/m). ROC curves were created for TPA, BMI and BSA. Toxicities were evaluated by binomial logistic regression; survival functions were evaluated by Kaplan-Meier. Significance was set at p < 0.05. Results: Low TPA (OR = 1.903, p = 0.036) and BSA (OR = 1.836 p = 0.048) were predictive of acute toxicities but only TPA was predictive of Grade 3+ acute toxicities (OR = 10.24, p = 0.040). Both findings were independent of tumor resectability. No association was found between TPA/BMI/BSA and late toxicities, overall survival, local progression or local recurrence. However, BRPC patients survived longer (median = 21.98 months) than their LAPC (median = 16.2 months) counterparts (p = 0.002), independent of nutritional status. Conclusions: Pre-SBRT TPA measurement is readily available and more specific than BMI or BSA as a predictor of serious acute radiotoxic complications following SBRT in BRPC/LAPC patients. However, tumor resectability remains as the only predictor of overall survival in this cohort. Whether initial pre-chemo TPA may predict acute toxicity related to chemotherapy and guide individualization of systemic regimen warrants further investigation.