Purpose: The purpose of this work is to develop an automated inverse planning approach to generate singe‐fraction and fractionated stereotactic radiosurgery (SRS) treatment plans for Gamma Knife Perfexion. Methods: Our automated approach consists of two steps: 1) a grassfire‐based algorithm to carefully determine the isocentre locations; 2) a penalty‐based optimization to find the optimal shot shapes and their intensities to minimize the deviation of the delivered dose from the objective dose in all structures. For single‐fraction SRS, a margin‐less approach was taken: conformity of dose to the gross tumor volume (GTV) with a steep dose fall‐off was prioritized. For fractionated radiosurgery, dose homogeneity was given a higher priority since planning target volumes (PTV) were applied to account for daily setup variation, and these PTVs could overlap with organs‐at‐risk (OARs). The two‐step approach was tested on seven clinical cases with PTV sizes of 0.5cm̂3–56.5cm̂3. In the tested cases, the PTV had 0%–38% overlap with OARs. Results: For single‐fraction SRS, the dose to 1mm̂3 brainstem was on average 0.24Gy (range: −2.4Gy to +2.0Gy) lower compared to manually‐generated plans. Beam‐on time varied with the number of isocentres, but on average was 33min longer than manually‐ generated plans. The optimization algorithm took 215min on average, while isocentre selection performed in <10s.For fractionated SRS, the average PTV coverage was V95=94.9% (range: 92.7%–97.6%) and the mean dose to 1 mm̂3 brainstem was 87.8% of the prescription dose (range: 35.4%‐ 108.8%). The mean beam‐on time per fraction per dose‐per‐fraction was 4.8min/Gy (range: 0.9min/Gy‐10.3min/Gy). We observed a tradeoff between conformity and OARs‐sparing in both plans, and added sensitivity to isocentre locations in fractionated plans. In all the cases, GTV received the full prescription dose. Conclusions: The results indicated that automated inverse planning yields improved conformity and OAR‐sparing for single‐ fraction SRS and is capable of generating homogeneous fractionated SRS. This work is partially funded by Elekta Instrument, AB, Stockholm, Sweden.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging