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Variations in Treatment Plan Quality for External-Beam Accelerated Partial Breast Irradiation

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W Swanson

W Swanson1,2*, L Vanbenthuysen2 , H.M. Lu2,3 , A.G. Taghian2,3 , D.P. Gierga2,3 , (1) University Massachusetts Lowell, Lowell, Massachusetts, (2) Massachusetts General Hospital, Boston, Massachusetts, (3) Harvard Medical School, Boston, MA,


SU-I-GPD-T-233 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This study investigated variations in dose distributions for patients receiving external beam accelerated partial breast irradiation (APBI). APBI plans were manually optimized using standard 3D techniques and there may be the potential to further improve plan quality utilizing knowledge from prior treatment plans.

Methods: This study examined 18 patients with left-sided cancers from the high dose cohort of a dose escalation protocol and were treated with external beam to 40 Gy using 4 Gy fractions given twice daily on 5 consecutive days. Variations in resection site (GTV), planning target volume (PTV), breast minus PTV, heart, and ipsilateral lung dose-volume-histograms (DVHs) were examined. Variations were calculated for the full range of DVH curves as well as at various clinically relevant dose-volume points. Plans outside one standard deviation were considered outliers even if they met clinical planning goals, and outliers were classified as either over- or under-dosed depending if they were greater or less than the mean dose, respectively.

Results: The mean DVH, with bands encompassing one and two standard deviations from the mean, was calculated for each region of interest (ROI). For the GTV and PTV, 6% (V95%) or 11% (V99%) of the plans were outliers; all were under-dosed. For breast-PTV (V50%), 39% of the plans were outliers, with roughly half of these over-dosed. For the lung, 6-33% of plans were outliers, and 6-22% of all plans were over-dosed, depending on the dose metric (V5Gy, V10Gy, V20Gy). Thirty percent of heart doses were outliers, but absolute doses were small (0.2 Gy mean dose). All plans met the clinical planning goals.

Conclusion: Variations in dose-volume data were noted and may indicate the potential for further improvements in plan quality despite plans meeting clinical goals. Further work will explore if variations are correlated with patient geometry or outcome.

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