Room: Stars at Night Ballroom 4
Purpose: For stereotactic radiosurgery using Leksell Gamma Knife (GK), it is important to perform an independent dose calculation as part of a routine quality assurance procedure to ensure patient safety and prevent the chance of treatment errors. This project is to develop a GK Perfexion/Icon second dose calculation system for clinical use.
Methods: Tissue Maximum Ratio (TMR10) dose calculation algorithm was implemented in our system. The needed physics data, such as source locations, virtual source distance, output factor and dose profiles for each specific collimator size and each ring, were collected from Elekta. 2D dose profiles were used for 8mm and 16mm collimators due to the lack of rotational symmetric of the titled sources compared to collimator axis. Fast Siddonâ€™s raytracing algorithm was employed to find skull entry point for each beam to correct the attenuation, using skull geometry exported from Leksell GammaPlan TPS system.
Results: We have preliminarily tested our system on five patients treated with GK for brain metastase, trigeminal neuralgia, vestibular schwannoma, and meningioma. For the reference points reported in GammaPlan, the deviation of our calculation is within 0.8%. We also recalculated ~1600 dose points randomly chosen from the 3D dose volume and compared with their corresponding values obtained by GammaPlan. The average absolute dose difference between our system and GammaPlan on these points is 3.01% with a standard deviation of 2.27%. This relatively large deviation on the points extracted from 3D dose volume may be contributed by the interpolation used in GammaPlan to generate 3D dose and also the high dose gradient of GK beams.
Conclusion: We have developed a GK second dose calculation system for our clinical use. Further validation and refinement of our system is needed through collaboration with Elekta. This dose engine will also facilitate our research in GK auto-planning.