Purpose: Stereotactic radiosurgery (SRS) utilizes intensity-modulated radiation therapy (IMRT) to deliver a highly conformal radiation dose to areas of intracranial disease, as small as 5mm in diameter. Many clinics perform quality assurance (QA) of SRS plans using a diode array, such as Sun Nuclear MapCheck2. MapCheck2 offers great clinical metrics for large fields, however; it lacks in providing adequate data for small targets. The lack of data is due to the spacing of the diodes (7.07mm) in the array relative to the size of the treatment field. In this work, MapCheck2 in high-density (HD) mode was evaluated and compared to the myQA SRS system with a spatial resolution of 0.4mm.
Methods: Five previously treated SRS plans were delivered to MapCheck2 positioned at the isocenter of a Varian TrueBeam STx with HDMLC. In a second measurement, MapCheck2 was shifted 5mm in the x-axis and the plan was delivered to the shifted position. SNC Patient software allows both measured dose files to be merged, therefore enabling this HD mode. This effectively doubles the data collected for the QA plan and inherently the resolution. The gamma passing rates from the HD mode were compared to the passing rates from both MapCheck2 with standard mode and the myQA SRS system for the same plan.
Results: The number of collected data points acquired in HD mode effectively doubled relative to standard mode. In all cases measured, the gamma passing rates at 2%/2mm were improved in HD mode, up to 8.4%. Compared to the myQA SRS system, the gamma passing rates were within 1.3% on average.
Conclusion: MapCheck2 in HD mode allows for a more accurate QA assessment and could be of great use in the clinic for small targets.
Funding Support, Disclosures, and Conflict of Interest: This project was supported by IBA