Premium
SU‐FF‐T‐265: Comparison of Absorbed Dose‐To‐Medium and Absorbed‐Dose‐To‐Water for (head and Neck and Prostate) IMRT Treatment Plans
Author(s) -
Dogan N,
Siebers J,
Keall P
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1997994
Subject(s) - nuclear medicine , absorbed dose , prostate cancer , dosimetry , medicine , prostate , percentage depth dose curve , dose volume histogram , effective dose (radiation) , radiation treatment planning , radiation therapy , radiology , physics , ionization chamber , cancer , ion , quantum mechanics , ionization
Purpose: Conventional photon dose calculation algorithms typically report the absorbed dose‐to‐water(D water ). Monte Carlo(MC) dose calculation algorithms, however, by default reports the absorbed dose‐to‐medium(D medium ). It has been suggested that for clinical comparisons, MC‐D medium results should be converted into D water to ensure valid comparisons. The goal of this study is to assess if the difference between D water and D medium is clinically significant for MC calculated IMRT plans. Method and Materials: Ten patients with H&N and ten patients with prostate cancer were selected for this study. Existing IMRT plans were re‐calculated using an EGS4‐based MC dose calculation system. D medium was converted to D water by multiplying D medium results by average water‐to‐medium stopping power ratio. D water and D medium results for target and critical structures were evaluated using the DVH‐based indices: D 2 (dose to 2% of the structure volume), D 50 (dose to 50% of the structure volume), D 98 (dose to 98% of the target volume), and D mean (mean dose). Results: For H&N, although the changes in average dose‐volume indices were less than 1.5%, up to 6.2% differences in PTV CTV D 2 were observed for individual patients. The cord and brainstem D 2 indices changed up to 2.5% and 2.7% respectively. For prostate, the differences in the indices for targets were less than 1%. The changes in critical structure indices were less than 1%, except for two patients in which changes up to 2.7% in rectum D 50 index were observed. The increases in the range of 4.5– 11.5% in the femur dose‐volume indices were observed in converting from D medium to D water due to the high calcium content of the hard bones. Conclusion: This study showed that converting dose‐to‐medium to dose‐to‐water in MC‐based IMRT plans may significantly change the structure doses for some cases, especially when hard bone containing structures such as the femurs are present.