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Comparison of Heart and Lung Dose for Prone and Supine Setups for Breast Radiotherapy

M Mille

M Mille1*, P Vadnais2, C Lee1 , S Lee2 , (1) National Cancer Institute, Rockville, MD, (2) University of Maryland School of Medicine, Columbia, MD


SU-I-GPD-T-94 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To compare heart and ipsilateral lung dose in patients receiving breast radiotherapy in prone and supine positions.

Methods: Radiotherapy records were obtained for 9 female patients who received adjuvant treatment for left breast cancer and who had both supine and prone CT images. Prone and supine tangential photon treatment plans were developed using the field-in-field technique with a prescribed dose of ~42.5 Gy delivered in 16 fractions. Each plan consisted of 2 to 4 photon beams of energy 6 MV and/or 18 MV. The heart and ipsilateral lung were contoured for performing organ dosimetry using a treatment planning system.

Results: On average, the maximum, mean, and median dose received by the heart and lung were smaller for patients treated in the prone position compared to the supine position. The mean (maximum) heart and lung dose were smaller by 0.30 Gy (12.8 Gy) and 2.83 Gy (19.13 Gy), respectively. Student’s t-testing indicated these dose differences were statistically significant at the 5% confidence level. Previous studies have implicated dose to normal heart and lung as being important contributors to late toxicities (e.g. cardiovascular disease and second lung cancers). Hence, this study suggests that patients treated in prone position will tend to have fewer radiation related adverse health outcomes. However, the choice of treatment position is also influence by the location/volume of target and size of breasts. Furthermore, for 2 patients in this study, the mean heart dose was slightly larger for the prone plan. This suggests that planning in both the prone and supine positions is useful for treatment optimization.

Conclusion: Careful choice of patient position can reduce normal heart and lung dose, thereby helping to mitigate secondary complications from left breast radiation treatment. In the future we plan to extend this work to include more patients and additional normal tissues.

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