SU‐E‐T‐399: Evaluation of Selection Criteria for Computational Human Phantoms for Use in Out‐Of‐Field Organ Dosimetry for Radiotherapy Patients

Abstract

Purpose:To quantify the dosimetric uncertainty due to organ position errors when using height and weight as phantom selection criteria in the UF/NCI Hybrid Phantom Library for the purpose of out‐of‐field organ dose reconstruction.Methods:Four diagnostic patient CT images were used to create 7‐field IMRT plans. For each patient, dose to the liver, right lung, and left lung were calculated using the XVMC Monte Carlo code. These doses were taken to be the ground truth. For each patient, the phantom with the most closely matching height and weight was selected from the body size dependent phantom library. The patient plans were then transferred to the computational phantoms and organ doses were recalculated. Each plan was also run on 4 additional phantoms with reference heights and or weights. Maximum and mean doses for the three organs were computed, and the DVHs were extracted and compared. One sample t‐tests were performed to compare the accuracy of the height and weight matched phantoms against the additional phantoms in regards to both maximum and mean dose.Results:For one of the patients, the height and weight matched phantom yielded the most accurate results across all three organs for both maximum and mean doses. For two additional patients, the matched phantom yielded the best match for one organ only. In 13 of the 24 cases, the matched phantom yielded better results than the average of the other four phantoms, though the results were only statistically significant at the .05 level for three cases.Conclusion:Using height and weight matched phantoms does yield better results in regards to out‐of‐field dosimetry than using average phantoms. Height and weight appear to be moderately good selection criteria, though this selection criteria failed to yield any better results for one patient.