No abstract

Gamma Knife is a well-established radiotherapy treatment system specifically designed to treat intracranial brain lesions. One of the main advantages of Gamma Knife stereotactic radiosurgery (SRS) is its precision, enabling the clinicians to deliver very high doses in a single fraction. The first Gamma Knife device using cobalt-60 ( 60 Co) radioisotope was introduced by Lars Leksell in 1967 [1][2][3][4][5]. Since then, several models such as U, B, C, and Perfexion have been developed for stereotactic radiosurgery [4,[6][7][8]]. The latest system, Leksell Gamma Knife (LGK) Icon (Elekta Instruments AB, Stockholm, Purpose: The aim of this study was to assess the suitability of using cone-beam computed tomography images (CBCTs) produced in a Leksell Gamma Knife (LGK) Icon system to generate electron density information for the convolution algorithm in Leksell GammaPlan (LGP) Treatment Planning System (TPS). Materials and Methods: A retrospective set of 30 LGK treatment plans generated for patients with multiple metastases was selected in this study. Both CBCTs and fan-beam CTs were used to provide electron density data for the convolution algorithm. Plan quality metrics such as coverage, selectivity, gradient index, and beam-on time were used to assess the changes introduced by convolution using CBCT (convCBCT) and planning CT (convCT) data compared to the homogeneous TMR10 algorithm. Results: The mean beam-on time for TMR10 and convCBCT was found to be 18.9 ± 5.8 minutes and 21.7 ± 6.6 minutes, respectively. The absolute mean difference between TMR10 and convCBCT for coverage, selectivity, and gradient index were 0.001, 0.02, and 0.0002, respectively. The calculated beam-on times for convCBCT were higher than the time calculated for convCT treatment plans. This is attributed to the considerable variation in Hounsfield values (HU) dependent on the position within the field of view. Conclusion:The artifacts from the CBCT's limited field-of-view and considerable HU variation need to be taken into account before considering the use of convolution algorithm for dose calculation on CBCT image datasets, and electron data derived from the onboard CBCT should be used with caution.