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Sci—Thurs AM: YIS—07: Dosimetric Consequences of Surgical Cavity Contour Variability in Accelerated Partial Breast Irradiation
Author(s) -
Kosztyla R,
Olson R,
Carolan H,
Balkwill S,
Moiseenko V,
Kwan W
Publication year - 2009
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 - 10.1118/1.3244167
Subject(s) - contouring , medicine , nuclear medicine , radiation treatment planning , dosimetry , radiation therapy , radiology , computer science , computer graphics (images)
Contouring variability of the surgical cavity (SC) can have important implications in the planning and delivery of accelerated partial breast irradiation (APBI). This study aims to quantify the dosimetric consequences of these variations. Methods: Twelve patients with breast lesions suitable for APBI underwent four CT scans: one planning CT and three CTs during treatment. Three radiation oncologists contoured the SC on each CT. In addition, for three patients, oncologists repeated SC contouring twice to assess intraobserver variations. SC contour variability was quantified by constructing a representative SC (RSC) and calculating the standard deviation (SD) at each RSC contour point. Treatment fields from the original plan were applied to repeat CTs. The dosimetric impact of contour variations was assessed using the equivalent uniform dose (EUD) formalism. Dose‐volume constraints for normal tissues were also examined during treatment. Results: The maximum interobserver RSC SD was larger than the maximum intraobserver SD (1.50 versus 0.90 cm; p = 0.025 ). Despite these differences, there was adequate dose coverage of the SC. The SC EUD was less than 38.0 Gy in only 9.3% of CT studies. Dose‐volume constraints for the thyroid and ipsilateral lung were satisfied for all CT studies. While heart constraints were met for right‐sided lesions, they were not met for two CT studies for a left‐breast patient. Conclusions: Planning margins used for APBI provide adequate dose coverage despite contour variability. The planning dose constraint for the heart is not always met during treatment for left‐breast patients.