Assessment of the dosimetric impact of intra-fraction motion during frameless treatment delivery on GammaKnife® Icon™.

Unlabelled: This study investigated the impact of patient motion on the dosimetric quality of treatment plans for metastatic patients undergoing frameless GammaKnife Icon™ treatments. By quantifying dosimetric robustness at increasing high definition motion management (HDMM) gating tolerances, this study investigated the possibility of increasing the HDMM threshold for patients treated at our centre from our current standard of 1 mm.

Methods: Motion was retrospectively simulated by shifting the stereotactic co-ordinates of shots in treatment plans using three motion models.

A standardised method for use of the Leksell GammaPlan Inverse Planning module for metastases.

Aim: The aim of this investigation was to develop a standardised method for using the inverse planning module in Leksell GammaPlan.

Methods: Leksell GammaPlan version 10 and higher contains an inverse planning module, consisting of functions to automatically fill a target volume with shots and subsequently optimise their resulting dosimetry. A standardised method for using the inverse planning module was developed for metastases, using the following optimisation parameter weightings: {coverage 0.

A high-precision, geometric and registration accuracy full-system test method for adaptive SRS, demonstrated on Gamma Knife® Icon™.

A novel full-system test (FST) phantom and method have been developed to demonstrate and quality assure the geometric accuracy of image co-registration and overall shot delivery in the context of SRS using Gamma Knife® Icon™. The method uses Vernier scale bars to achieve sub-voxel precision co-registration measurements and pin-located radiochromic films to determine overall shot delivery precision. Validation tests demonstrated that artificially applied registration errors of < 0.

A comparison of the convolution and TMR10 treatment planning algorithms for Gamma Knife radiosurgery.

Aims: To compare the accuracies of the convolution and TMR10 Gamma Knife treatment planning algorithms, and assess the impact upon clinical practice of implementing convolution-based treatment planning.

Methods: Doses calculated by both algorithms were compared against ionisation chamber measurements in homogeneous and heterogeneous phantoms. Relative dose distributions calculated by both algorithms were compared against film-derived 2D isodose plots in a heterogeneous phantom, with distance-to-agreement (DTA) measured at the 80%, 50% and 20% isodose levels.