RELIABILITY EVALUATION OF SNC 3DVH® SOFTWARE FOR QUALITY ASSURANCE OF IMRT TECHNIQUES

Introduction: Treatments using Intensity-Modulation techniques (IMRT) will become the common form of Radiotherapy planning soon. Thus, a patient-specific quality assurance (QA) routine is going to be necessary given the complexity of the plans. The usual QA methods are the Gamma index passing rate (using either a matrix of detectors or film) and punctual measurements with the ionization chamber. Despite those methods assure the planned dose accuracy in the treatment planning system (TPS), they fail to convey any form of volumetric information about the dose distribution. The SNC 3DVH® system gives the possibility of comparing the dose-volume histogram (DVH) calculated by the TPS and the one irradiated by the Linear Accelerator. Objective: The purpose of this work is to study the reliability of SNC 3DVH® system by checking the possible limitations in a way to validate the software for an IMRT QA routine. Methodology: We irradiated the detector SNC ArcCheck® diode array in an Elekta Synergy® linear accelerator. The plans were created in the Elekta Monaco® TPS to guarantee a maximum Homogeneity Index (HI) of 1,02 around the studied areas. We acquired punctual measurements with a PTW TN30013 ionization chamber. Three studies were made to verify the volumetric aspect of the analysis made by the 3DVH system: (i) plans with similar DVHs, but distinct fluence maps; (ii) alterations in the dose calculation grid and (iii) linear alterations on the Monitor Units (MU) of the plan. Each plan was based in the SNC ArcCheck® phantom tomography. Results: The different fluence maps study (i) identified the differences between plans, allowing the user to locate the error in the irradiated plan. In the study with the alteration in the dose calculation grid (ii), the SNC 3DVH® showed an average deviation of 0,5% about the ionization chamber, the deviation between the 3DVH and the TPS was close to 0,0%. The linear MU study (iii) was made to verify the linear response of the system. The linear correlation presented by the 3DVH was 1,0 for every group of measures.