A Dosimetric evaluation of Plastic Water-Diagnostic-Therapy (PWDT)

Abstract

High precision radiotherapy planning and quality assurance requires accurate dosimetric and geometric phantom measurements.  The phantom design requires materials with both mechanical strength and resilience as well dosimetric properties close to water over the diagnostic and therapy range. Plastic Water Diagnostic Therapy (PWDT)ä is a phantom material manufactured by CIRS Inc. designed for water equivalence in photon beams from 0.04MeV to 100MeV which also has good mechanical properties. This presentation reports the results of CT imaging and dosimetric studies of PWDTä to determine the material’s suitability in both  CT and therapy energy ranges.The water equivalence of PWDTä was characterised in a series of experiments in which basic dosimetric properties were determined over for photon energies of 80kV_p, 100kV_p, 250kV_p, 4MV, 6MV, 10MV and 18MV.  Properties measured included the build-up and percentage depth dose curves for several field sizes and relative dose factors as a function of field size.  In addition, the PWDTä phantom was CT scanned at beam qualities ranging from 80 to 140kV_p to determine the water equivalence of the phantom in the diagnostic energy range. The dosimetric quantities measured with PWDTä agreed within 1.5% with those determined in water and Solid Waterä.  CT scans of the phantom where found to generate Hounsfeld numbers within 0.8% of water.  These results suggest that Plastic Water Diagnostic Therapy material is suitable for both regular radiotherapy quality assurance measurements and IMRT verification work. Sample IMRT verification results are presented.