Abstract
To design and evaluate an anthropomorphic spine phantom for use in credentialing proton therapy facilities for clinical trial participation by the Imaging and Radiation Oncology Core Houston QA Center. A phantom was designed to perform an end-to-end audit of the proton spine treatment process, including simulation, dose calculation, and proton treatment delivery. Because plastics that simulate bone in proton beams are unknown, 11 potential materials were tested to identify suitable phantom materials. Once built, preliminary testing using passive scattering and spot scanning treatment plans (including a field junction) were created in-house and delivered 3 times to test reproducibility. The following measured attributes were compared with the calculated values: absolute dose agreement using thermoluminescent dosimeters, planar gamma agreement, distal range, junction match, and right and left profile alignment using radiochromic film. Finally, credentialing results from 10 institutions were also assessed. A suitable bone substitute was identified (Techtron HPV Bearing Grade), which had a measured relative stopping power that agreed within 1.1% of its value calculated by Eclipse. In-house passive scatter testing of the phantom demonstrated that the phantom was suitable for assessing craniospinal irradiation dose delivery. However, the in-house scanning beam results were more mixed, highlighting challenges in treatment delivery. Seven of ten institutions passed the proposed criteria for this phantom, a pass rate consistent with other Imaging and Radiation Oncology phantoms. An anthropomorphic proton spine phantom was developed to evaluate proton therapy delivery. This phantom provides a realistic challenge for centers wishing to participate in proton clinical trials and highlights the need for caution in applying advanced treatments.
Highlights
Proton therapy is gaining acceptance as a cancer treatment modality, for conducting craniospinal irradiation (CSI), for which it produces far superior dose distributions [1].The Imaging and Radiation Oncology Core Quality Assurance Center at Houston (IROC Houston), formerly known as the Radiological Physics Center, is funded by the National Cancer Institute to audit radiotherapy institutions for clinical trial participation
As with other IROC phantoms, each of these institutions was provided with the plan objectives but were otherwise instructed to treat the phantom as they would a patient
Horizontal error bars are included for each material based on the standard deviation of the Hounsfield unit (HU), while vertical error bars were determined based on the relative stopping power (RSP) uncertainty [4]
Summary
The Imaging and Radiation Oncology Core Quality Assurance Center at Houston (IROC Houston), formerly known as the Radiological Physics Center, is funded by the National Cancer Institute to audit radiotherapy institutions for clinical trial participation. This responsibility includes assessment of institutional radiation therapy programs to ensure that dose uncertainty is minimized so results from clinical trials can be reliably interpreted. Before patient enrollment in clinical trials, institutions must complete the National Cancer Institute –mandated IROC Houston proton approval process [2], which includes using anthropomorphic phantoms that verify dose delivery for special treatment techniques. The purpose of this study was to design, evaluate, and test a new anthropomorphic spine phantom for use by IROC Houston in credentialing proton therapy facilities for clinical trial participation
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