Room: AAPM ePoster Library
Purpose: To develop a standardized set of representative clinical treatment cases that pose a range of optimization problems for evaluating the plan quality and dosimetric accuracy within the commissioning process for linac-based SRS.
Methods: Five test cases with increasing complexity were created to validate delivery accuracy in SRS commissioning similar to the TG-119 test suite for IMRT commissioning. Standardized structure sets, planning goals, and delivery requirements were specified for each case including a small sphere target, irregular target, irregular target placed off-axis, multi-target, and abutting targets. All cases were calculated on an anthropomorphic head phantom. Various VMAT field arrangements including a single arc, two non-coplanar arcs, and four non-coplanar arcs were tested to generate clinically appropriate treatment plans.
Results: All plans consisted of a single-isocenter placed at the target center or geometric center of multiple targets. Planning goals for all cases included constraints for the target and brain minus PTV, along with brainstem and optic nerve for the most challenging case. The small sphere was 1.0cm in diameter. The irregular target was a clinical cavity (2.3x2.2x1.4cm³) and was shifted 4.5cm for the irregular target off-axis case. The multi-target case used the irregular target and four spheres representing metastases ranging 0.9 to 1.6cm in diameter, placed up to 7.5cm off-axis. All spherical targets received 24Gy and the cavity received 18Gy. The abutting cases included a 3.74cc lesion adjacent to the brainstem receiving 13Gy and a 1.11cc lesion adjacent to the optic nerve receiving 12Gy to further planning and delivery requirements.
Conclusion: These cases provide a novel benchmark for institutions to evaluate linac-based SRS commissioning and delivery accuracy. The rapid widespread implementation of this technique, complexity associated with dosimetry and delivery, and high profile treatment deviations that have already resulted from its use, highlight the importance of such a benchmark test suite.