PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): To report physical changes in the thorax with continuous positive airway pressure (CPAP) compared to free-breathing (FB) and how it effects on the radiation dose to the heart and lung during breast cancer radiotherapy (RT) for patients with different cardiac-thoracic anatomy (CTA).
Materials/Methods: Three breast cancer patients with favorable, unfavorable, and challenging-CTA (F-CTA, UF-CTA, CH-CTA, respectively) who underwent CT-simulations with both FB and CPAP (10~12 cmH20) for planning RT were selected for this study. For each patient, both left-sided and right-sided breast cancer RT plans (Lt-RT and Rt-RT, respectively) were created using supine tangent-RT for comparison.
Results: Compared to FB, CPAP inflated the thorax, increased total lung volume by 34.3±12.1% (CPAP:4064.3±579.0 vs. FB:3040.9±496.0 cm3) in all patients, and decreased heart volume within left-sided tangent-RT field by 99.5% (0.01 vs. 2.2 cm3), 92.1% (2.8 vs. 35.5 cm3), and 93.7% (1.2 vs. 19.0 cm3) among F-CTA, UH-CTA, and CH-CTA, respectively. PTV coverage was acceptable in all RT plans. In Lt-RT, mean dose (Dmean) to the heart were decreased with CPAP than FB: 23.1% reduction (2.0 vs. 2.6 Gy) in F-CTA without internal mammary node (IMN) RT; 74.3% reduction (2.9 vs. 11.3 Gy) and 81.2% reduction (0.9 vs. 4.8 Gy) in UF-and CH-CTA, both including IMN RT. In Lt-RT, Dmean to ipsilateral lung (ipsi-Lung) were substantially decreased by 24.7% with CPAP versus FB in CH-CTA (18.0 vs. 23.9 Gy) and by 5.9~6.2% in others (F-CTA:9.1 vs. 9.7 Gy; UF-CTA:17.7 vs. 18.8 Gy). With CPAP, volume receiving ≥ 20 Gy (V20) to ipsi-Lung in Lt-RT was decreased by 25.7% (35.5% vs. 47.8%) in CH-CTA, 8.7% (15.8% vs. 17.3%) in F-CTA, and 8.4% (36.1% vs. 39.4%) in UF-CTA compared to FB. In Rt-RT, Dmean to ipsi-Lung was lower with CPAP (8.9±0.7 Gy) than FB (10.3±0.9 Gy):13.3±4.8% reduction in all patients. Compared to FB, CPAP increased distance from the sternal notch to the liver at least 2.0 cm in all patients, and decreased liver volume within right tangent-RT field by 83.6% (3.3 vs. 20.1 cm3), 35.1% (136.1 vs. 209.8 cm3), and 10.1% (54.4 vs. 60.5 cm3) in F-CTA, UH-CTA, and CH-CTA, respectively.
Conclusion: Regardless of patients' cardiac-thoracic anatomy, CPAP decreased radiation dose to the heart and lung during breast cancer RT by inflating thorax and displacing the heart inferiorly in comparison to FB. This suggests that CPAP with traditional supine tangent-RT can be an alternative method to spare the heart and lung when patients can’t access advanced RT techniques.
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