Ablative re-irradiation of inoperable pancreatic cancer: A case study of gastrointestinal sparing through MR-guided online adaptive radiotherapy

摘要

Historically, re-irradiation has been performed with CT-based nonadaptive modalities. MR-guided online adaptive radiotherapy (MRgoART) has the potential to improve the therapeutic ratio by delivering higher tumor dose and/or minimizing dose to proximal organs at 2 risk (OARs). In this case study, we report on our initial experience with MRgoART for the management of gastrointestinal OAR sparing in re-irradiation setting. We describe the treatment of a 68-year-old male who was diagnosed with locally advanced, unresectable, pancreatic adenocarcinoma. Initial course included FOLFIRINOX followed by 45 Gy/25 fractions (fx) on Radixact unit with concurrent capecitabine, followed by planned sequential 14.4 Gy/8 fx on an MR Linac. A year later, the patient received a re-irradiation dose of 50 Gy in 5 fractions due to local progression of the body/tail of the pancreas. For the re-irradiation and initial plan, cumulative dose calculation was performed using 2 methods: deformable dose (Ddeform) and organ-by-organ point dose summation (Drigid). All summations were scaled in EQD2. The respective gastrointestinal (GI) lumen 0.03 cc maximum dose for Ddeform/Drigid was 108.5 Gy/121.5 Gy (small bowel), 111.5 Gy/56.6 Gy (large bowel), 112.3 Gy/105.2 Gy (duodenum), and 104.9 Gy/114.6 Gy (stomach), respectively. For on-table adaptive radiotherapy (ART), OAR contours were deformed and edited within 3 cm of the planning target volume (PTV) on daily MR. Initial plan was recalculated on daily MR and followed by plan re-optimization. Plan quality was compared between initial and ART plan. Due to superior plan quality for GI OAR sparing and/or target coverage, the ART plan was used for delivery on all fractions. The patient tolerated treatment well with minimal fatigue. On-table ART combined with daily MR imaging enabled ablative dose delivery, without undue GI toxicity. Although challenges of cumulative dose computation still remain, our initial experience of MRgoART shows promise in the re-irradiation setting when considering ablative doses. (C) 2020 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.