Abstract
Introduction Modern irradiation techniques such as IMRT and Volumetric Modulated Arctherapy require a quality assurance plan for the systematic control of treatment plans. In 2010, IMRT began in our radiotherapy department, two controls was set up, one with the Delta4 (Scandidos©) and the other with the PDIP module (VarianMedicalSystem©). This study compares the results of the quality tests carried out by means of two detectors. The objective is to lighten the quality assurance procedure implemented in order to reduce the delivery time in charge of patients as well as the duration of immobilization of accelerators dedicated to quality controls. Methods The Delta4 is a 3D detector measuring the dose according to two perpendicular planes. The PDIP, an algorithm developed by Varian, measures a dose image with the portal imager. These two detectors use a Gamma-index comparison between the calculated dose and the measured dose. The analysis carried out on 245 patients and 719 beams. 186 patients were treated by VMAT: 51% for head and neck cancer, 24% for pelvic cancer, 19% for prostate cancer, and 6% for other sites. IMRT was studied for 53 patients treated for a brain tumor. Gamma index criteria of 3% 3 mm with a passing threshold of 97% was used for PDIP and Delta4 analysis The implementation time (preparation, measurement, analysis) of these two controls was evaluated in a second stage. Results The beams analyzed for Gamma-Index met the criterion 3% 3 mm in 89% of the cases for the Delta4 and in 95% of the cases for the PDIP. The boxplot (Fig. 1) shows that there are no significant differences between the two detectors. Dispersion of the results is similar. The duration of the Delta4 control is estimated to 24 min versus 8 min for PDIP. Download : Download high-res image (92KB) Download : Download full-size image Conclusions In this work, there is no difference between the two detectors. As a result, it was decided to conserve double-checking to locations without sufficient experience and for doses per fraction greater than routine practice. Only PDIP is maintained for IMRT and VMAT conventional treatments. This modification reduces the times of control and optimizes the patient treatment workflow.
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