Two‐year experience with the commercial Gamma Knife Check software

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

Evaluation of a new secondary dose calculation software for Gamma Knife radiosurgery

“…The commercially available software falls short in several instances where a gamma angle of 70 or 110° is used. In fact, the Mann‐Whitney test shows a significant difference in the deviations from the TPS between standard and nonstandard gamma angles for the commercially available secondary dose calculation software, confirming dependency on the patient orientation that has been previously shown in literature . However, the same comparison is not significant for the new secondary dose calculation software, indicating that the method of beamlet rotation matrices eliminates this dependence.…”

“…The same user inputs were utilized for the second check software as the TPS. Our experience is similar to Xu et al, especially where the commercially available software performs poorly in the presence of a nonstandard gamma angle, in some cases deviating from the TPS by more than 10%. This known issue presents a clinical difficulty in that treatment cannot proceed unless the TPS and secondary dose calculation agree to within 5%, as is the recommendation taken from AAPM Task Group 40 and our clinical policy .…”

“…Different skull rendering techniques have been proposed, including modeling the skull as a sphere or using measured skull data from the use of a skull scalar instrument . These methods work well for standard patient and target geometries, but significant discrepancies from the treatment planning system (TPS) are still evident when the target is at a shallow depth or when the patient setup uses a non 90° gamma angle . It has been suggested that using an image thresholding technique may be the best method to accurately construct the patients skull for dose calculation .…”

Development and validation of a comprehensive patient‐specific quality assurance program for a novel stereotactic radiation delivery system for breast lesions

“…Several studies have previously reported on the development and use independent calculations, as such we considered it prudent to develop a method of our own. Our SEIPDC software when compared to the TPS had an average agreement −0.1 ± 1.1% for the PMMA phantom and 0.2 ± 1.3% for the water phantom.…”

Characterization and commissioning of a Leksell Gamma Knife ICON system for framed and frameless stereotactic radiosurgery

“…Past studies on the previous PU model have assessed the stability of the definition of stereotactic coordinates using a stereotactic head frame, 5 commissioning and QA of the automatic positioning system, 6 QA of the PU beam accuracy, 7 , 8 and evaluation of the dose calculation software 9 and a secondary dose calculation system. 10 Prior studies have disclosed early clinical experiences regarding frameless workflows 11 , 12 as well as predictors of treatment interruption 13 using frameless processes. However, to date, no studies have outlined commissioning experience for frameless treatment deliveries.…”