Gamma Knife radiosurgery with CT image‐based dose calculation

Abstract

The Leksell GammaPlan software version 10 introduces a CT image‐based segmentation tool for automatic skull definition and a convolution dose calculation algorithm for tissue inhomogeneity correction. The purpose of this work was to evaluate the impact of these new approaches on routine clinical Gamma Knife treatment planning. Sixty‐five patients who underwent CT image‐guided Gamma Knife radiosurgeries at the University of Pittsburgh Medical Center in recent years were retrospectively investigated. The diagnoses for these cases include trigeminal neuralgia, meningioma, acoustic neuroma, AVM, glioma, and benign and metastatic brain tumors. Dose calculations were performed for each patient with the same dose prescriptions and the same shot arrangements using three different approaches: 1) TMR 10 dose calculation with imaging skull definition; 2) convolution dose calculation with imaging skull definition; 3) TMR 10 dose calculation with conventional measurement‐based skull definition. For each treatment matrix, the total treatment time, the target coverage index, the selectivity index, the gradient index, and a set of dose statistics parameters were compared between the three calculations. The dose statistics parameters investigated include the prescription isodose volume, the 12 Gy isodose volume, the minimum, maximum and mean doses on the treatment targets, and the critical structures under consideration. The difference between the convolution and the TMR 10 dose calculations for the 104 treatment matrices were found to vary with the patient anatomy, location of the treatment shots, and the tissue inhomogeneities around the treatment target. An average difference of 8.4% was observed for the total treatment times between the convolution and the TMR algorithms. The maximum differences in the treatment times, the prescription isodose volumes, the 12 Gy isodose volumes, the target coverage indices, the selectivity indices, and the gradient indices from the convolution and the TMR 10 calculations are 14.9%, 16.4%, 11.1%, 16.8, 6.9%, and 11.4%, respectively. The maximum differences in the minimum and the mean target doses between the two calculation algorithms are 8.1% and 4.2% of the corresponding prescription doses. The maximum differences in the maximum and the mean doses for the critical structures between the two calculation algorithms are 1.3 Gy and 0.7 Gy. The results from the two skull definition methods with the TMR 10 algorithm agree either within ± 2.5% or 0.3 Gy for the dose values, except for a 4.9% difference in the treatment times for a lower cerebellar lesion. The imaging skull definition method does not affect Gamma Knife dose calculation considerably when compared to the conventional measurement‐based skull definition method, except in some extreme cases. Large differences were observed between the TMR 10 and the convolution calculation method for the same dose prescription and the same shot arrangements, indicating that the implementation of the convolution algorithm in routine clinical use might be ...

Dosimetric effects of Onyx embolization on Gamma Knife arteriovenous malformation dose distributions

“…These were compared with the dose distributions obtained by setting all structures to the physical constants for water (MC-water), which are similar to the assumptions used by the TMR 10-based treatment algorithm in LGP. 55 The dose distributions MC-Onyx and MC-water were compared via a variety of dose metrics, including minimum/mean/maximum dose to the nidus, prescription isodose volume, selectivity index (TV PIV /PIV), coverage index (TV PIV /TV), and gradient index (PIV half /PIV), where PIV is the prescription isodose volume, TV PIV is the volume of nidus covered by the prescription isodose volume, and PIV half is the volume of the isodose surface that is onehalf of the prescription isodose. 31,32 All dose metrics were calculated in terms of percentage isodoses (i.e., percentage of maximum dose).…”

Impact of the skull contour definition on Leksell Gamma Knife® Icon™ radiosurgery treatment planning

“…The difference between the two techniques will be larger in cases where the scalp is thick and non-existent in, e.g., an elderly patient with thinned scalp particularly if they are bald. Former studies using LGK Perfexion™ and 4C™ devices, such as Xu et al study, reported the same range of discrepancy (2.5%) between the two skull contour definition techniques [14], as did the team of Kobayashi et al (2%) [6]. Rojas-Villabona et al also reported an increase of BOT of 1.45% with head contours derived from the CT scan [8].…”

Dosimetric comparison of TMR10 and convolution dose calculation algorithms in GammaPlan treatment planning system

“…These algorithms have been compared in previous studies. [4][5][6][7][8] It was found that the convolution algorithm provided greater accuracy to films within a RANDO phantom to dose distributions than that with TMR10. 4 This conclusion was supported by Nakazawa et al, 5 who advocated the use of convolution algorithm to reduce dosimetric uncertainty.…”

“…7 Treatment times were studied in one paper revealing an 8•4% larger average treatment times for identical prescriptions and shot arrangements when the convolution dose calculation was used compared to the TMR10 algorithm. 8 When implementing new dose calculation algorithms, special considerations must be given to the dose prescription. The traditional doses prescribed by radiation oncologists have been based on protocols using dose calculations where the entire scalp is treated as water.…”