Author: Mark W. Geurts, Bridget Ann Melke 👨🔬
Affiliation: Aspirus Health 🌍
Purpose:
To develop a tool that streamlines and standardizes the process of positioning the SRS MapCHECK detector for intersecting multiple metastases during SRS QA of Single-Isocenter, Multiple Target (SIMT) SRS patient plans.
Methods:
SIMT SRS RT plans were exported from the Aria database as RT Structure Set, Plan, and Dose DICOM files. A Python script was created to extract data, such as treatment isocenter and PTV location. The script calculates each PTV’s center and radius, then evaluates potential detector intersections by comparing each PTV (origin) against all others. For each origin PTV, 72 starting search points are defined along the periphery of a circle centered on and ¾ the size of the origin PTV, and sample coordinates spanning the detector’s length are recorded for each angle in 5-degree increments from 0-180 degrees around each starting search point. Sample point intersections with the remaining PTVs are tallied, with points near the center given greater weight. The script ensures measurements do not cause gantry or couch collisions and outputs the optimal PTVs, required couch displacements, and angle rotations for phantom setup.
Results:
Ten SIMT SRS patient plans (2-8 targets each) were analyzed. The script output was manually verified using Eclipse’s External Beam Planning tools and the Sun Nuclear QA setup tool. Verification ensured the detector passed through all listed target volumes and remained within the detector’s dimensions. All plans passed verification, with 2 to 4 targets visible per measurement plane output. No couch-gantry collisions occurred, confirming the accuracy of calculated couch shifts and detector angles.
Conclusion:
An automated script was developed to optimize the positioning of the SRS MapCHECK in SIMT SRS QA, maximizing PTV intersections. This method simplifies the workflow, enhances consistency and efficiency in the QA process, and allows more time for other critical tasks, resulting in improved overall productivity.