Insights From Image Guided Radiation Therapy Credentialing for the NRG Oncology RTOG 1112 Liver Stereotactic Body Radiation Therapy Trial.

PURPOSE: NRG Oncology trial RTOG 1112 is a randomized phase 3 study of sorafenib with or without stereotactic body radiation therapy for locally advanced hepatocellular carcinoma. Image guided radiation therapy (IGRT) credentialing is essential for this study because of the high doses, respiratory motion, and variety of delivery technologies. This analysis presents the IGRT credentialing experience. METHODS AND MATERIALS: Credentialing of volumetric IGRT requires submission of planning and localization images, planning structures, and resulting IGRT shifts for a patient treated according to the study requirements. A study reviewer uses these data to repeat the registrations and compare to the actual clinical registrations. Agreement within 5 mm was considered acceptable for credentialing. RESULTS: Volumetric images of 130 fractions from 42 institutions between June 2013 and January 2018 were reviewed. The median agreement between clinical registrations and study reviewer was 3 mm, with 95% of all fractions within 5 mm. A subanalysis identified a statistically significant difference between the use of low-contrast soft tissue and high-contrast surrogates (eg, implanted fiducial markers, surgical clips, metallic stents) for registration. Soft tissue and high-contrast surrogate registrations both agreed within 3 mm in 50% of fractions. However, soft tissue registrations exceeded 10 mm in 3% of fractions, while no high-contrast surrogate registrations exceeded 5 mm. CONCLUSIONS: The RTOG 1112 credentialing experience suggests that most institutions perform liver IGRT with sufficient accuracy to deliver stereotactic body radiation therapy safely, as assessed by expert reviewers. Both soft tissue and high-contrast surrogates appear adequate for consistent registration in most instances; however, some disagreements were observed when using soft-tissue registration targets. The use of high-contrast surrogates appears to reduce the small risk of substantial geographic miss owing to mis-registration in liver IGRT.