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TH‐E‐AUD‐05: Evaluation of Inter‐Fractional Dosimetric Variations in MammoSite Partial Breast HDR Irradiation
Author(s) -
Kim Y,
Johnson M,
Trombetta M,
Parda D,
Miften M
Publication year - 2007
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 - 10.1118/1.2761769
Subject(s) - nuclear medicine , dosimetry , medicine , fraction (chemistry) , radiation treatment planning , radiation therapy , radiology , chemistry , organic chemistry
Purpose: To evaluate the inter‐fractional dose variations due to changes in balloon shape and location in MammoSite partial breast HDR irradiation. Method and Materials: Eleven MammoSite HDR patients were treated with a dose of 34 Gy delivered in 10 fractions twice a day at our institution. For each of these patients, a plan was generated for the first fraction based on the CT scan acquired before treatment. The plan was then used for the remaining 9 fractions without any modification unless a significant change in balloon shape and/or location was observed on the CT scan acquired prior to each treatment fraction. To assess the inter‐fractional dose variations, we retrospectively contoured the target (including PTV_EVAL for planning evaluation) as well as critical structures and positioned the catheter on the CT datasets of fraction 2 – 10. Then, we generated two plans utilizing a multiple and single dwell position approaches while using the same dwell time distribution as for the clinical plan of the first fraction. A total of 220 plans generated on 110 CT datasets were evaluated using the following dosimetric metrics: PTV_EVAL coverage, target dose homogeneity index (DHI), target dose conformal index (COIN) as well as maximum dose to ipsilateral lung and skin. Results: For the multiple dwell position approach, the average (maximum) percent inter‐fractional variation relative to the first fraction was 1.5% (6.2%) for PTV_EVAL coverage, 1.1% (12.5%) for DHI, 3.4% (11.8%) for COIN, 10.2% (42.6%) for maximum ipsilateral dose, and 6.9% (29.4%) for maximum skin dose. No difference in the dosimetric values was observed using either a multiple or single dwell position approach. Conclusion: The inter‐fractional dose variation was patient‐specific and dependent upon the balloon deformity and location. While the average variation may not significantly impact the treatment, the maximum variation may be clinically significant.