Purpose: To implement recommendations of TG 329 for dose-to-tissue corrections
Methods: Traditionally, our department reported dose as dose-to-water. We have undertaken the task of changing the reporting to dose-to-tissue, following the guidance of TG 329. Our department is using Varian Eclipse treatment planning system for external beam therapy plans, with AAA algorithm for photon beams and eMC for electron beams. For both algorithms, TG 329 recommends applying 0.99 correction factor to reference calibration dose in water. We have applied this correction factor and then recalculated the models. Verification of this change was then performed. This included both phantom plans as well as selected patient plans. We have compared Monitor Units, isodose distributions, dose profiles, and dose-volume histograms of plans done before the change and after the dose-to-tissue corrections were applied.
Results: For photon beams, plan recalculation after adjusting reference calibration dose leads to different Monitor Units but the same isodose distribution when static MLC is used. In case of VMAT plans (that have not been re-optimized) MUs stay the same, but there is a change of isodose distribution. For both such scenarios, we verified that the 0.99 factor is correctly reflected in the isodose distribution and MUs. For electron beams, due to the stochastic nature of Monte Carlo algorithm, in order to verify the expected 1% change, we had to reduce statistical uncertainty below the level used clinically.
Conclusion: A change to dose-to-tissue reporting was successfully implemented in our clinic.