Abstract
PurposeHow modern cardiac sparing techniques and beam delivery systems using advanced x-ray and proton beam therapy (PBT) can reduce incidental radiation exposure doses to cardiac and pulmonary organs individually or in any combination is poorly investigated.MethodsAmong 15 patients with left-sided breast cancer, partial wide tangential 3D-conformal radiotherapy (3DCRT) delivered in conventional fractionation (CF) or hypofractionated (HF) schedules; PBT delivered in a CF schedule; and volumetric modulated arc therapy (VMAT) delivered in an HF schedule, each under continuous positive airway pressure (CPAP) and free-breathing (FB) conditions, were examined. Target volume coverage and doses to organs-at-risk (OARs) were calculated for each technique. Outcomes were compared with one-way analysis of variance and the Bonferroni test, with p-values <0.05 considered significant.ResultsTarget volume coverage was within acceptable levels in all interventions, except for the internal mammary lymph node D95 (99% in PBT, 90% in VMAT-CPAP, 84% in VMAT-FB, and 74% in 3DCRT). The mean heart dose (MHD) was the lowest in PBT (<1 Gy) and VMAT-CPAP (2.2 Gy) and the highest in 3DCRT with CF/FB (7.8 Gy), respectively. The mean lung dose (MLD) was the highest in 3DCRT-CF-FB (20 Gy) and the lowest in both VMAT-HF-CPAP and PBT (approximately 5–6 Gy). VMAT-HF-CPAP and PBT delivered a comparable maximum dose to the left ascending artery (7.2 and 6.13 Gy, respectively).ConclusionsBoth proton and VMAT in combination with CPAP can minimize the radiation exposure to heart and lung with optimal target coverage in regional RT for left-sided breast cancer. The clinical relevance of these differences is yet to be elucidated. Continued efforts are needed to minimize radiation exposures during RT treatment to maximize its therapeutic index.
Highlights
Modern multi-disciplinary treatment for breast cancer, including radiation therapy (RT), has improved patients’ long-term survival rates [1]
Among 15 patients with left-sided breast cancer, partial wide tangential 3Dconformal radiotherapy (3DCRT) delivered in conventional fractionation (CF) or hypofractionated (HF) schedules; proton beam therapy (PBT) delivered in a CF schedule; and volumetric modulated arc therapy (VMAT) delivered in an HF schedule, each under continuous positive airway pressure (CPAP) and free-breathing (FB) conditions, were examined
Target volume coverage was within acceptable levels in all interventions, except for the internal mammary lymph node D95 (99% in PBT, 90% in VMAT-CPAP, 84% in VMAT-FB, and 74% in 3DCRT)
Summary
Modern multi-disciplinary treatment for breast cancer, including radiation therapy (RT), has improved patients’ long-term survival rates [1]. Delayed side effects associated with RT are gaining more importance [2,3,4]. Recent studies have reported that the risk of secondary lung cancer and cardiovascular toxicity is associated with the mean radiation dose delivered to the heart and lung [5]. According to Darby et al, the risk of major coronary events increases linearly by 7.4% per 1-Gy increase in the mean heart dose (MHD) [6]. The use of comprehensive regional nodal irradiation (RNI) in RT has increased after evidence from landmark trials became available [7, 8]. Extended RT increases the MHD, increasing the risk of major coronary events [9]
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