Abstract
Detailed Monte Carlo (MC) modeling of the Leksell Gamma Knife (GK) Perfexion (PFX) collimator system is the only accurate ab initio approach appearing in the literature. As a different approach, in this work, we present a MC model based on film measurement. By adjusting the model parameters and fine‐tuning the derived fluence map for each individual source to match the manufacturer's ring output factors, we created a reasonable virtual source model for MC simulations to verify treatment planning dose for the GK PFX radiosurgery system. The MC simulation model was commissioned by simple single shots. Dose profiles and both ring and collimator output factors were compared with the treatment planning system (TPS). Good agreement was achieved for dose profiles especially for the region of plateau (<2%), while larger difference (<5%) came from the penumbra region. The maximum difference of the calculated output factor was within 0.7%. The model was further validated by a clinical test case. Good agreement was obtained. The DVHs for brainstem and the skull were almost identical and, for the target, the volume covered by the prescription (12.5 Gy to 50% isodose line) was 95.6% from MC calculation versus 100% from the TPS.PACS number(s): 87.55.dk
Highlights
The Leksell Gamma Knife (LGK) has been used extensively in the standard of care for the treatment of patients with brain tumors, arteriovenous malformations, and functional disorders.[1]
As the main purpose of our work is to develop a patient-specific dose verification tool, similar to the study by Mamalui-Hunter et al,(18) for LGK PFX, we postulate that the ab initio source model is not critical as long as the calculated dose profile for each collimator from the virtual source model agrees with the Leksell GammaPlan (LGP)-calculated dose profile
Conventional and intensity-modulated radiation therapy (IMRT).(19) It is interesting to investigate if this technique can be applied to LGK PFX Monte Carlo simulations for the purpose of developing a dose verification tool
Summary
The Leksell Gamma Knife (LGK) has been used extensively in the standard of care for the treatment of patients with brain tumors, arteriovenous malformations, and functional disorders.[1] It provides a noninvasive alternative for patients when traditional brain surgery is not an option. The new model Perfexion (PFX) of the LGK system, introduced in 2006, has a completely different collimator system with respect to its predecessors. In order to change the field size, each sector can be moved to the corresponding collimator set by servo-controlled motors located at the rear of the radiation unit. It eliminates the need for labor-extensive manual installation of the collimator helmets as in the older models. With an expanded treatment area and enhanced accuracy, the new system allows clinicians to treat tumors that were unreachable with previous technology
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