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TH‐D‐ValA‐09: An Objective Approach to Establishing Tolerances On Photon Beam Modeling Using the Equivalent Uniform Dose
Author(s) -
RangelBaltazar A,
Ploquin N,
Kay I,
Doll C,
Dunscombe P,
Baker Tom
Publication year - 2006
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 - 10.1118/1.2241931
Subject(s) - dosimetry , pinnacle , beam (structure) , radiation treatment planning , equivalent dose , nuclear medicine , prostate , photon , physics , optics , medical physics , radiation therapy , medicine , radiology , cancer
Purpose: To perturb a photon beam model in a controlled manner and to examine the consequences for the Equivalent Uniform Doses (EUD) of the target and organs at risk in external beam radiation therapy of the prostate. Method and Materials: We have developed seven similar but different therapy beam models in the Pinnacle® Treatment Planning System. One model generates beam data close to the golden data provided by Varian® and serves as the reference model for this study. The six other models are modifications of the reference model designed to result in controlled deviations of a particular region of the dose profiles (descending depth dose, build‐up, horns, tail, penumbra and field width). We have analyzed the consequences of planning with these perturbed models on the quality of 4 prostate treatment plans in terms of the EUDs of the PTV, rectum and bladder in comparison with the reference model. Monitor units were kept constant for all plans. Results: to maintain a change in the EUD to the prostate, bladder or rectum of less than 2%, tolerances on the various regions of the dose profiles are as follows: descending depth dose 2%; horns 3%; field width ±1mm. Deviations in the build‐up region and tail of ±10% and ±5% respectively did not change the EUDs of any structure by more than 2%. Conclusion: Currently accepted tolerances on photon beam modeling are broadly internally consistent in so far as they result in similar effects on plan dosimetry, at least for 4 field conformal prostate treatments.