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SU‐E‐T‐271: A Variable Target Comparison of Whole Breast and Partial Breast Irradiation Fractionation Regimens. Do the Current Margins Make Sense?
Author(s) -
Al Sulaimani E,
Arthur D,
Todor D
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 - 10.1118/1.3612222
Subject(s) - equivalence (formal languages) , breast cancer , margin (machine learning) , nuclear medicine , medicine , fractionation , radiation treatment planning , radiology , radiation therapy , computer science , mathematics , cancer , chemistry , pure mathematics , chromatography , machine learning
Purpose: A novel, variable target approach is used in this study to establish equivalence, in a radiobiological sense, between whole breast and partial breast irradiation schemes. We are questioning the meaning of margins, as they are currently used to create planning target volumes. Ultra‐short fractionation regimens have been recently proposed for APBI, reducing the number of fractions from 10 to as few as two. This work addresses the concept of ˈequivalenceˈ between the currently accepted regimens (both WBI and APBI) and the newly proposed ones. Methods: Four early stage breast cancer patients were included. Two patients were treated with interstitial BT and two patients with balloon BT. Three regimens for WBI were simulated by creating uniform doses for all targets. EUBED and gBEUD were computed and the parameter ‘a’ identified based on equivalence of standard WBI with interstitial APBI. The equivalence of new proposed ultra‐short regimens in balloon BT namely (7Gy × 4fx), (8.25Gy × 3fx) and (10.25Gy × 2 fx) was then compared with the ˈtraditionalˈ APBI. Results: a=‐1 was identified from WBI and APBI equivalence. At GTV+1.0 cm margin, we find gBEUDˈs for ultra‐short regimens to be 20% or higher than current standard fractionation scheme. Conclusions: Somehow unexpected is that despite a larger margin (15mm), the interstitial implants seem to be equivalent, within the validity of the radiobiological model considered, for significantly smaller targets than the one the treatment was planned for. For the balloon BT, the planned margin of 1cm around the balloon, seemed a lot more consistent with the ‘true’ target for which the WBI and APBI would be equivalent. When the new, ultra‐short regimens were compared with the traditional (3.4Gy × 10fx), we find that their equivalent targets are larger than the 1cm planning margin, even when compared with the standard WBI regimen.