MO-FG-CAMPUS-TeP1-04: Pseudo-In-Vivo Dose Verification of a New Mono-Isocentric Technique for the Treatment of Multiple Brain Metastases

Abstract

Purpose: To validate dose calculation and delivery accuracy of a recently introduced mono‐isocentric technique for the treatment of multiple brain metastases in a realistic clinical case. Methods: Anonymized CT scans of a patient were used to model a hollow phantom that duplicates anatomy of the skull. A 3D printer was used to construct the phantom of a radiologically bone‐equivalent material. The hollow phantom was subsequently filled with a polymer gel 3D dosimeter which also acted as a water‐equivalent material. Irradiation plan consisted of 5 targets and was identical to the one delivered to the specific patient except for the prescription dose which was optimized to match the gel dose‐response characteristics. Dose delivery was performed using a single setup isocenter dynamic conformal arcs technique. Gel dose read‐out was carried out by a 1.5 T MRI scanner. All steps of the corresponding patient's treatment protocol were strictly followed providing an end‐to‐end quality assurance test. Pseudo‐in‐vivo measured 3D dose distribution and calculated one were compared in terms of spatial agreement, dose profiles, 3D gamma indices (5%/2mm, 20% dose threshold), DVHs and DVH metrics. Results: MR‐identified polymerized areas and calculated high dose regions were found to agree within 1.5 mm for all targets, taking into account all sources of spatial uncertainties involved (i.e., set‐up errors, MR‐related geometric distortions and registration inaccuracies). Good dosimetric agreement was observed in the vast majority of the examined profiles. 3D gamma index passing rate reached 91%. DVH and corresponding metrics comparison resulted in a satisfying agreement between measured and calculated datasets within targets and selected organs‐at‐risk. Conclusion: A novel, pseudo‐in‐vivo QA test was implemented to validate spatial and dosimetric accuracy in treatment of multiple metastases. End‐to‐end testing demonstrated that our gel dosimetry phantom is suited for such QA procedures, allowing for 3D analysis of both targeting placement and dose.