Abstract:
Background: Accurate three dimensional dosimetry is essential in modern radiotherapy techniques such as volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT). In this research work, the PRESAGE® dosimeter was used as quality assurance tool for VMAT planning for head and neck cancer. Material and Method: Computer tomography (CT) scans of an Image Radiation Oncology Core (IROC) Head and Neck anthropomorphic phantom with both IROC standard insert and PRESAGE® insert were acquired separately. Both CT scans were imported into the Pinnacle (9.4 version) TPS for treatment planning, where the structures (PTV, OARs) and TLDs were manually contoured and used to optimize a VMAT plan. Treatment planning was done using VMAT (dual arc: 182o -178o , 178o -182o ). Beam profile comparisons and gamma analysis were used to quantify agreement with film, PRESAGE® measurement and TPS calculated dose distribution.
Results: The average ratio of TLD measured to calculated doses at the four PTV locations in the H&N phantom were between 0.95 to 0.99for all three VMAT deliveries. Dose profiles were taken along the left-right, the anterior-posterior and superior-inferior axes and good agreement was found between the PRESAGE® and Pinnacle profile. The mean value of gamma results for three VMAT deliveries in axial and sagittal planes were found to be 94.24% and 93.16% when compared to film and Pinnacle respectively. The average values comparing the PRESAGE® results and dose values calculated on Pinnacle were observed to be 95.29% and 94.38% in the said planes respectively using a 5%/3mm gamma criteria.
Conclusion: The PRESAGE® dose measurements and calculated dose of pinnacle show reasonable agreement in both axial and sagittal planes for complex dual arc VMAT treatment plans. In general, the PRESAGE® dosimeter is found to be a feasible quality assurance (QA) tool of VMAT plan for HN cancer treatment.
