Evaluation of a new 3D in vivo dosimetry software using portal imaging for VMAT treatments of prostate: Preliminary results

Abstract

Introduction/Objectives The control of VMAT treatments is a key issue in the Quality Assurance process. Current solutions are often cumbersome to implement and unsuitable for routine use. An innovative solution is proposed by the Dosimetry Check software (Math- Resolutions) allowing both to control pre-treatment as well as socalled transit dosimetry using the portal imager. Here we present the implementation and the evaluation of the software to control VMAT treatments of prostate. Material and methods Acquisition where made on a Clinac 2100C equipped with an IaS500. Images, acquired in continuous mode (@60 frames/rotation), CT scanner and associated structures and 3D dose matrix are imported in Dosimetry Check. Fluence matrix in air is obtained by filtered backprojection. The dose volume in the patient is calculated with Pencil Beam algorithm. Analysis is based on the comparison of point dose, dose profiles, and dose distributions in 2D and 3D. The calculation of Dose Volume Histogram and Gamma Index is also available. Results and conclusion The study focuses on 10 cases of prostate cancer treated in VMAT according to simultaneous integrated boost. The deviation of measured dose at the isocenter in pre-treatment and in transit mode is of the order of −4.0%(±1.3%) and 4.9%(±4.1%) respectively. These results improve significantly when corrected by the acquisition of an integrated image: +1.4%(±0.7%) in pre-treatment and −1.1%(±0.7%) in transit mode. Dosimetry Check software is a suitable tool to do pre-treatment control and in vivo dosimetry. The first results are satisfactory and we wish to test it on other sites, but weaknesses of Pencil Beam algorithm have to be taken into account.