Feasibility of Vascular Matching for Image Guided Pancreatic Stereotactic Body Radiation Therapy

Abstract

Implanted fiducial markers (IFM) and biliary stents are established as targets for image-guidance during high dose stereotactic body RT (SBRT) in the treatment of pancreatic adenocarcinoma (PDAC). IFM are often well tolerated, but may delay treatment. Furthermore, the potential for IFM/stent migration may cause insufficient target volume coverage and normal tissue toxicity. This study evaluated the use of vascular matching (VM), IFM and stent matching for image-guidance in delivery of SBRT for patients with PDAC. We hypothesize that there is no difference in shifts or efficacy between IFM, stents, and VM. Between April 2011- November 2015, 39 patients received SBRT for treatment of PDAC at our institution. Cone beam CT (CBCT) was performed for setup verification. We retrospectively analyzed 221 CBCT images for setup shifts based on either IFM, stent or celiac and SMA vasculature contoured using electronic patient information management system, version 2.60 (IMPAC Medical Systems, Inc. Sunnyvale, CA). Average shift magnitudes in each axis and average vector magnitudes were calculated. RTOG acute gastrointestinal (GI) radiation morbidity scoring criteria were used to assess toxicity. Statistical analyses were performed using JMP 12.1.0 (SAS Institute Inc., Cary, NC). Kaplan-Meier calculations as well as analysis of variance, likelihood ratio, and Wilcoxon tests were used to evaluate local control and survival and compare groups. Fifteen patients (38.5%) were treated with IFM, 9 (23%) with stents, and 15 (38.5%) with VM. Waiting times from initial consult to radiation treatment in the IFM, stent, and VM groups were 24 days (range 2-91 days), 14 days (range 9-56 days), and 19 days (range 5-39 days), respectively. The average magnitude for superior/inferior shifts was 0.45 ± 0.42 mm (IFM), 0.48 ± 0.46 mm (stent), and 0.37 ± 0.33 mm (VM) (P = 0.24), lateral shifts 0.42 ± 0.99 mm, 0.29 ± 0.35 mm, and 0.26 ± 0.22 (P = 0.26), and anterior/posterior shifts were 0.33 ± 0.40 mm, 0.34 ± 0.28 mm, and 0.37 ± 0.28 mm (P = 0.70). Vector magnitudes were 0.85 ± 1.04 mm, 0.74 ± 0.53 mm, and 0.67 ± 0.36 mm, respectively (P = 0.24). There were no documented complications from IFM or stent placement. There were no significant differences in GI toxicities between groups (P = 0.25), with a single instance of Grade 3 toxicity in the stent group. There were no significant differences in tumor resectability (P = 0.70), margin status (P = 0.43), local control (P = 0.31), or overall survival (P = 0.88). Vascular matching is a feasible, less invasive image-guidance technique that allows for reproducible and convenient SBRT delivery to PDAC and shorter treatment delays. There was no difference in positional shifts, toxicity, or outcomes for patients planned with IFM, stents, or VM. VM may be preferable over more invasive methods of target localization.