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Normal tissue dose conformality measures to guide radiotherapy fractionation decisions
Author(s) -
Myerson Robert J.
Publication year - 2011
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 - 10.1118/1.3560417
Subject(s) - fractionation , context (archaeology) , nuclear medicine , radiation therapy , therapeutic index , dosimetry , dose fractionation , constraint (computer aided design) , mathematics , medicine , radiology , chemistry , biology , paleontology , geometry , drug , organic chemistry , psychiatry
Purpose: To determine conditions under which hypofractionation could be favorable for a normal tissue—even if tumor[ α / β ]exceeds the normal tissue's[ α / β ] .Methods: The hypofractionation sufficiency condition (HSC) for an organ is defined as a dose conformality constraint such that, if satisfied, a family of tumor control probability isoeffective fractionation schemes will show decreasing normal tissue complication probability with decreasing number of fractions.Results: In the extended equivalent uniform dose (EUD) model [obtained by replacing dose with linear quadratic (LQ) 2 Gy equivalent dose], the HSC for a normal organ is proven to be satisfied if a suitably weighted average of the relative dose [hypofractionation sufficiency index (HSI)] is less than the ratio of normal tissue to tumor[ α / β ] . The HSI is determined solely by dose distribution and the normal tissue volume factor, “ a .” If the HSC is satisfied for every normal tissue of concern, then there is a therapeutic gain with hypofractionation. The corresponding multifractionation sufficiency condition (therapeutic gain with increasing number of fractions) and multifractionation sufficiency index (MSI) are also derived. A sample clinical case is presented.Conclusions: Within the context of the LQ/EUD models, conformality measures (HSI and MSI) can be used to inform fractionation decisions.