The Application Study Of3D Dose Verification For Volume-modulated Arc Therapies

With the rapid progress of the radiotherapy technology, such asintensity-modulated radiation therapy(IMRT) and rotational therapy, and the widespreadin clinical of these technologies, a newly developing IMRT technology:Volume-modulated arc therapy(VMAT) has been introduced which can offer variousdegrees of freedom in delivering high doses to the target in a highly conformal fashionwhile simultaneously sparing the organs at risk(OAR), for several indicationspotentially with a further shortening of treatment times. However, compared with IMRT,continuously and dynamically controling various parameters are involved in VMATplan during designing and delivering, which increasing the complexity and uncertainty.So it stimulates higher necessity to ensure the accuracy of dose delivery for VMAT.COMPASS system (IBA, Belgium) is a novel3D dose verification system whichallows reconstructing dose distribution on to the CT data of the patient based onmeasured fluence at specific gantry angle, considering the tissue heterogeneity, so itcould reflect the actual radiation dose on patient’s interest region. COMPASS systemalso has the independent calculation function, so it can be used to evaluate thecalculation accuracy of treatment planning system (TPS). Therefore, taking advantageof its technoloy, this study will evaluate the feasibility of COMPASS system using fordose verification.Several contents have been inculded in the study:1. The data model of COMPASSsoftware was assessed in Percentage depth dose (PDD), Output factor (OUF), Off-axiscurves (Profile) and the absolute dose, by comparing with3D water tank;2. The dosecalculation function and reconstruction accuracy of COMPASS system software hasbeen evaluated in homogeneous and anthropomorphic phantoms by7cases;3In orderto minimize the measurement error, the effect to the linac isocenter caused byCOMAPASS hardware was detected by BallBearing phantom;4. To evaluate the doseverification pass rate and independent calculation accuracy of COMPASS,15clinicalVMAT plans represented different cases have been verified, and the resultingassessment was evaluated using MatriXX combined with Multicube phantom.The study result demonstrated the PDDs, OUF, Profiles measured by the COMPASS system matched well with the data measured by3D water tank, and thedeviation of absolute dose were below2.5%; the accuracy of independent calculationand reconstruction of COMPASS system were closed to TPS, the deviation of absolutedose was below3%, so it could be used as the third party for dose calculation. Thegamma(3%,3mm) of15VMAT plans verified by COMPASS was91%-100%,thedeviation of dose-volume parameters was almost within3%, when compared with themeasurements of MatriXX combined with Multicube phantom, the gamma(3%,3mm)were larger than96%.Consequently, the function of independent calculation and dose reconstructionprovided by COMPASS system has the same accuracy with TPS. The3D doseverification of COMPASS system could offer more abundance and more directlyinformation for dose distribution, and ensure the development for VMAT technology.