Peripheral doses in patients undergoing Cyberknife treatment for intracranial lesions. A single centre experience

Abstract

BackgroundStereotactic radiosurgery/radiotherapy procedures are known to deliver a very high dose per fraction, and thus, the corresponding peripheral dose could be a limiting factor for the long term surviving patients. The aim of this clinical study was to measure the peripheral dose delivered to patients undergoing intracranial Cyberknife treatment, using the MOSFET dosimeters. The influence of the supplemental shielding, the number of monitor units and the collimator size to the peripheral dose were investigated.MethodsMOSFET dosimeters were placed in preselected anatomical regions of the patient undergoing Cyberknife treatment, namely the thyroid gland, the nipple, the umbilicus and the pubic symphysis.ResultsThe mean peripheral doses before the supplemental shielding was added to the Cyberknife unit were 51.79 cGy, 13.31 cGy and 10.07 cGy while after the shielding upgrade they were 38.40 cGy, 10.94 cGy, and 8.69 cGy, in the thyroid gland, the umbilicus and the pubic symphysis, respectively. The increase of the collimator size corresponds to an increase of the PD and becomes less significant at larger distances, indicating that at these distances the PD is predominate due to the head leakage and collimator scatter.ConclusionWeighting the effect of the number of monitor units and the collimator size can be effectively used during the optimization procedure in order to choose the most suitable treatment plan that will deliver the maximum dose to the tumor, while being compatible with the dose constraints for the surrounding organs at risk. Attention is required in defining the thyroid gland as a structure of avoidance in the treatment plan especially in patients with benign diseases.

A Dose–Volume Response Model for Brain Metastases Treated With Frameless Single-Fraction Robotic Radiosurgery: Seeking to Better Predict Response to Treatment

“…Studies examining outcomes in this technology are a minority in comparison with those investigating SRS delivered by non-CK linear accelerators and Gamma Knife (GK; Elekta, Stockholm, Sweden). 24 – 27 Tamari et al analyzed a sample of 109 lesions treated with CK and demonstrated both lesion control at 1 and 2 years (83.3% and 78.5%, respectively) and rates of radionecrosis (7%) comparable to studies using GK and non-CK linear accelerator–based SRS. 27 Tumor volume ( P = .020) and prescription dose ( P = .023) were associated with LC.…”

Frameless linac-based stereotactic radiosurgery (SRS) for brain metastases: analysis of patient repositioning using a mask fixation system and clinical outcomes

“…In addition, a mouth bite positioned against the upper dentition attached to the stereotactic frame was applied to prevent any head tilt movement. The characteristics of the system have been previously described [ 16 ]. Before the CT localization a localizer box was mounted to the BrainLAB mask system in order to provide a three-dimensional (3D) stereotactic coordinate array for target localization.…”

“…Immediately before treatment, all patients underwent CT verification to check the accuracy of isocenter position [ 16 ]. Firstly, the CT verification set was imported in the planning system and localized automatically by the planning software through identification of the stereotactic fiducials in the same way as for planning CT.…”

Extracranial dose and the risk of radiation-induced malignancy after intracranial stereotactic radiosurgery: is it time to establish a therapeutic reference level?

“…This is likely because all platforms typically treat similar volume targets. Furthermore, Vlachopoulou noted that the effect of collimator size on extracranial dose is limited to areas less than 29 cm from the target, which suggests that target volume (which increases inpatient scatter) may only affect the dose to the head, neck and upper thorax [29]. Although our data does not establish a functional dependence between prescription dose and extracranial dose, the prescription dose is a convenient descriptor facilitating comparison between different SRS treatment platforms, though we acknowledge that this can vary significantly depending on the target volume, shape, isocentre configuration and beam-on time.…”