Reporting Physics Requirements and Independent Quality Assurance Results for Credentialing Single- or Multi-Institutional Sfrt Clinical Trials for Large and Unresectable Bulky Tumors
Abstract
Purpose
We present the results of anthropomorphic phantoms (IROC Houston) irradiations at 2-academic institutions for independent verification of highly heterogenous dose distributions via 3D MLC-based SFRT plans for credentialling multi-institutional site-specific clinical trials for debulking large (≥8 cm) unresectable tumors.
Methods
After completing comprehensive in-house testing, validation and technology/facility questionnaire, a total of 6 IROC standard photon phantoms (head and neck, lung, liver, pelvis, 2 SRS head phantoms) were irradiated by 2-academic institutions for benchmarking and participating in site-specific SFRT clinical trials. For a single-dose of 15 Gy, highly heterogenous 3D static MLC-based SFRT plans were generated with 6-crossfire 6MV beams, AcurosXB dose-engine and delivered same-day via IGRT clinical workflow on TrueBeam similar to SBRT. Phantoms were sent back to the IROC for blind review, audits and independent dose verification.
Results
The measured vs calculated dose to center of the target for head and neck phantom with 6 TLDs inserts in target were 0.96–1.04. More than 98% of points met IROC gamma-index criteria of 5%/3mm in both coronal and sagittal planes. The organ-at-risk TLD readings were within ±2%. For lung, liver, pelvis phantoms, each of them had 2 TLDs inserts, measured vs calculated dose agreed within ±5%, ±4%, ±2%, respectively and films with greater than 98% agreements for all SFRT benchmarking plans in both sagittal and coronal planes. The SRS head phantoms irradiated in both institutions had absolute doses pass rates of within ±1% and greater than 98% agreements in the coronal & sagittal films.
Conclusion
Utilizing the standard IROC photon phantoms, we achieved successful pass rates of independent dose verification of highly heterogenous SFRT plans with steep dose gradient for site-specific prospective trial validation, testing & benchmarking. These results support starting site-specific single- or multi-institutional prospective SFRT clinical trials for treating site-specific large tumors with combination radiotherapy and/or immunotherapy.