Abstract
The Gamma Knife Check software is an FDA approved second check system for dose calculations in Gamma Knife radiosurgery. The purpose of this study was to evaluate the accuracy and the stability of the commercial software package as a tool for independent dose verification. The Gamma Knife Check software version 8.4 was commissioned for a Leksell Gamma Knife Perfexion and a 4C unit at the University of Pittsburgh Medical Center in May 2012. Independent dose verifications were performed using this software for 319 radiosurgery cases on the Perfexion and 283 radiosurgery cases on the 4C units. The cases on each machine were divided into groups according to their diagnoses, and an averaged absolute percent dose difference for each group was calculated. The percentage dose difference for each treatment target was obtained as the relative difference between the Gamma Knife Check dose and the dose from the tissue maximum ratio algorithm (TMR 10) from the GammaPlan software version 10 at the reference point. For treatment plans with imaging skull definition, results obtained from the Gamma Knife Check software using the measurement‐based skull definition method are used for comparison. The collected dose difference data were also analyzed in terms of the distance from the treatment target to the skull, the number of treatment shots used for the target, and the gamma angles of the treatment shots. The averaged percent dose differences between the Gamma Knife Check software and the GammaPlan treatment planning system are 0.3%, 0.89%, 1.24%, 1.09%, 0.83%, 0.55%, 0.33%, and 1.49% for the trigeminal neuralgia, acoustic neuroma, arteriovenous malformation (AVM), meningioma, pituitary adenoma, glioma, functional disorders, and metastasis cases on the Perfexion unit. The corresponding averaged percent dose differences for the 4C unit are 0.33%, 1.2%, 2.78% 1.99%, 1.4%, 1.92%, 0.62%, and 1.51%, respectively. The dose difference is, in general, larger for treatment targets in the peripheral regions of the skull owing to the difference in the numerical methods used for skull shape simulation in the GammaPlan and the Gamma Knife Check software. Larger than 5% dose differences were observed on both machines for certain targets close to patient skull surface and for certain targets in the lower half of the brain on the Perfexion, especially when shots with 70 and/or 110 gamma angles are used. Out of the 1065 treatment targets studied, a 5% cutoff criterion cannot always be met for the dose differences between the studied versions of the Gamma Knife Check software and the planning system for 40 treatment targets.PACS number(s): 87.55.Qr, 87.56.Fc
Highlights
An independent check of a treatment planning dose calculation process is a mandated component of the quality assurance in radiation therapy.[1,2,3] The goal of an independent second check of dose calculation is not to correct the primary calculation, but to ensure that the primary calculation has been done accurately for the safe and effective treatment of the patient
The number of treatment targets with more than 5% dose difference is 36 for the Perfexion and 5 for the 4C units
The five treatment targets with more than 5% dose difference on the 4C unit were identified as targets close to patient skull surface
Summary
An independent check of a treatment planning dose calculation process is a mandated component of the quality assurance in radiation therapy.[1,2,3] The goal of an independent second check of dose calculation is not to correct the primary calculation, but to ensure that the primary calculation has been done accurately for the safe and effective treatment of the patient. The second physics check of the dose calculation in Gamma Knife radiosurgery has been done in many different ways in the past. Some institutions have developed in-house computer programs to verify the treatment shot times from the planning system for a prescribed dose.[4,5,6,7,8,9,10,11] These programs usually perform a point-dose calculation based on tissue–air ratio (TAR) lookup table for narrow 60Co beams[12] and an algorithm for patient skull geometry reconstruction.[13,14,15] At other institutions, this independent check has been done by comparing the reported dose rate from the planning system with that obtained from a precalculated decay table, under the assumption that the dose calculation in the planning system should always be accurate provided a correct dose rate of the Gamma Knife unit is used. The application of the in-house second physics check programs for Gamma Knife radiosurgery is usually limited by the resources available for the continuous development of the software packages to keep up with the changes in treatment units and treatment techniques. The dose rate comparison method is a straight forward approach, but cannot identify potential problems in the planning system that are related to the corruption of the output factor and beam profile data
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
