Commissioning and quality assurance of a commercial stereotactic treatment planning ssytem for extracranial IMRT

Abstract

Abstract:

A 3D treatment-planning system (TPS) for stereotactic intensity-modulated radiotherapy (SIMRT) using a micro multi-leaf collimator has been made available by Radionics. In this work, we report our comprehensive quality assurance (QA) procedure for commissioning this TPS. First, the accuracy of stereotaxy established with a body frame was checked to ensure accurate determination of a target position within the planning system. Secondly, the CT-to-electron density conversion curve used in the TPS was fitted to our site-specific measurement data to ensure the accuracy of dose calculation and measurement verification in a quality assurance (QA) phantom. Using the QA phantom, the radiological pathlengths against known geometrical depths were verified to ensure the accuracy of the ray-tracing algorithm. We also checked inter- and intra-leaf leakage/transmission. Measurements for dose verification were performed in various head/neck and prostate IMRT treatment plans using the patient-specific optimized fluence maps. Both ion chamber and film were used for point dose and isodose distribution verifications. To ensure that adjacent organs-at-risk (OARs) receive the expected dose, we used the Monte Carlo method to calculate dose distributions and dose-volume histograms for these OARs.
The dosimetric accuracy satisfied the published acceptability criteria. The Monte Carlo calculations confirmed the measured dose distributions for target volumes. For organs located on the beam boundary or outside the beam, some differences in DVH were noticed. However, the plans calculated by both methods met our clinical criteria. It is concluded that the accuracy of the XKnifeTM RT2 treatment planning system is sufficient for the clinical implementation of stereotactic intensity modulated radiotherapy.