Determining the Threshold of Radiotherapy Delivery Error Detection Using Delta4

Abstract

Intensity Modulated Radiation Therapy and Volume Modulated Arc Therapy are now widely used in cancer treatment, but due to their complex nature each clinical plan is verified before applying on patient. Many different verification systems are available for this purpose, but because there is no regulation that would make it an obligatory, manufacturers usually don’t give such information as devices error detection threshold, repeatability etc. Therefore clinics must carry out tests before using these devices. This article is dedicated to the determining of IMRT/VMAT plan verification systems Delta4 (Scandidos, Uppsala, Sweden) error detection threshold. 10 Head & Neck IMRT and 5 esophagus VMAT clinical plans were modified with intentionally introduced errors and then verified on Delta4. Positioning errors for various moving parts (MLC, Jaws, Collimator and Gantry) together with dose related errors (MU, missing control points) were tested. The resulting gamma index was compared to the one from unmodified plan. A clear detection threshold for IMRT was detected for shift, MU, Jaws, collimator and gantry errors and for VMAT for MU and Jaws errors. No clear error detection threshold within tested error size range was found for the rest of the introduced errors.