Print Email Facebook Twitter Derivation of mean dose tolerances for new fractionation schemes and treatment modalities Title Derivation of mean dose tolerances for new fractionation schemes and treatment modalities Author Perko, Z. (TU Delft RST/Reactor Physics and Nuclear Materials; Massachusetts General Hospital) Bortfeld, Thomas (Massachusetts General Hospital) Hong, Theodore (Massachusetts General Hospital) Wolfgang, John (Massachusetts General Hospital) Unkelbach, Jan (Massachusetts General Hospital; University Hospital Zürich) Date 2018-02-01 Abstract Avoiding toxicities in radiotherapy requires the knowledge of tolerable organ doses. For new, experimental fractionation schemes (e.g. hypofractionation) these are typically derived from traditional schedules using the biologically effective dose (BED) model. In this report we investigate the difficulties of establishing mean dose tolerances that arise since the mean BED depends on the entire spatial dose distribution, rather than on the dose level alone. A formula has been derived to establish mean physical dose constraints such that they are mean BED equivalent to a reference treatment scheme. This formula constitutes a modified BED equation where the influence of the spatial dose distribution is summarized in a single parameter, the dose shape factor. To quantify effects we analyzed 24 liver cancer patients for whom both proton and photon IMRT treatment plans were available. The results show that the standard BED equation - neglecting the spatial dose distribution - can overestimate mean dose tolerances for hypofractionated treatments by up to 20%. The shape difference between photon and proton dose distributions can cause 30-40% differences in mean physical dose for plans having identical mean BEDs. Converting hypofractionated, 5/15-fraction proton doses to mean BED equivalent photon doses in traditional 35-fraction regimens resulted in up to 10 Gy higher doses than applying the standard BED formula. The dose shape effect should be accounted for to avoid overestimation of mean dose tolerances, particularly when estimating constraints for hypofractionated regimens. Additionally, tolerances established for one treatment modality cannot necessarily be applied to other modalities with drastically different dose distributions, such as proton therapy. Last, protons may only allow marginal (5-10%) dose escalation if a fraction-size adjusted organ mean dose is constraining instead of a physical dose. Subject biologically effective doseIMRTmean dose constraintsnormal tissue toleranceproton therapy To reference this document use: http://resolver.tudelft.nl/uuid:a5fb6b31-7beb-42e1-9780-b03900aa7e8c DOI https://doi.org/10.1088/1361-6560/aa9836 Embargo date 2018-08-05 ISSN 0031-9155 Source Physics in Medicine and Biology, 63 (3) Bibliographical note Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public. Part of collection Institutional Repository Document type journal article Rights © 2018 Z. Perko, Thomas Bortfeld, Theodore Hong, John Wolfgang, Jan Unkelbach Files PDF Perk_2018_Phys._Med._Biol ... averne.pdf 2.31 MB Close viewer /islandora/object/uuid:a5fb6b31-7beb-42e1-9780-b03900aa7e8c/datastream/OBJ/view