Abstract
BackgroundThis study investigated the feasibility and potential clinical benefit of utilizing a new proton treatment technique: Spot-scanning proton arc (SPArc) therapy for left-sided whole breast radiotherapy (WBRT) to further reduce radiation dose to healthy tissue and mitigate the probability of normal tissue complications compared to conventional intensity modulated proton therapy (IMPT).MethodsEight patients diagnosed with left-sided breast cancer and treated with breast-preserving surgery followed by whole breast irradiation without regional nodal irradiation were included in this retrospective planning. Two proton treatment plans were generated for each patient: vertical intensity-modulated proton therapy used for clinical treatment (vIMPT, gantry angle 10°–30°) and SPArc for comparison purpose. Both SPArc and vIMPT plans were optimized using the robust optimization of ± 3.5% range and 5 mm setup uncertainties. Root-mean-square deviation dose (RMSD) volume histograms were used for plan robustness evaluation. All dosimetric results were evaluated based on dose-volume histograms (DVH), and the interplay effect was evaluated based on the accumulation of single-fraction 4D dynamic dose on CT50. The treatment beam delivery time was simulated based on a gantry rotation with energy-layer-switching-time (ELST) from 0.2 to 5 s.ResultsThe average D1 to the heart and LAD were reduced to 53.63 cGy and 82.25 cGy compared with vIMPT 110.38 cGy (p = 0.001) and 170.38 cGy (p = 0.001), respectively. The average V5Gy and V20Gy of ipsilateral lung was reduced to 16.77% and 3.07% compared to vIMPT 25.56% (p = 0.001) and 4.68% (p = 0.003). Skin3mm mean and maximum dose were reduced to 3999.38 cGy and 4395.63 cGy compared to vIMPT 4104.25 cGy (p = 0.039) and 4411.63 cGy (p = 0.043), respectively. A significant relative risk reduction (RNTCP = NTCPSPArc/NTCPvIMPT) for organs at risk (OARs) was obtained with SPArc ranging from 0.61 to 0.86 depending on the clinical endpoint. The RMSD volume histogram (RVH) analysis shows SPArc provided better plan robustness in OARs sparing, including the heart, LAD, ipsilateral lung, and skin. The average estimated treatment beam delivery times were comparable to vIMPT plans when the ELST is about 0.5 s.ConclusionSPArc technique can further reduce dose delivered to OARs and the probability of normal tissue complications in patients treated for left-sided WBRT.
Highlights
Breast cancer is one of the most common cancers among women globally [1]
scanning proton arc (SPArc) plans showed a significant reduction in heart dose (D1) of 51.42% compared to Vertical intensity-modulated proton therapy (vIMPT) (53.63 cGy vs 110.38 cGy, p = 0.001), as well as a substantial decrease in the maximum dose to left anterior descending artery (LAD) of 51.72% (82.25 cGy vs 170.38 cGy, p = 0.001)
The study found that the mean dose of the contralateral breast was increased to 18.5 cGy in the SPArc plans compared to the vIMPT plans (12.13 cGy, p = 0.011)
Summary
Breast cancer is one of the most common cancers among women globally [1]. Breast-conserving surgery with adjuvant whole breast irradiation has become an increasingly popular treatment option for early-stage breast cancer [2,3,4,5,6]. Conventional photon treatment methods such as tangential intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) have offered increased feasibility for normal tissue sparing in left-sided breast irradiation [7,8,9]. Similar studies have shown that breast cancer patients are at a higher risk of long-term cardiac morbidity after radiation therapy treatment, which is directly related to the volume of the irradiated heart [5, 6]. This study investigated the feasibility and potential clinical benefit of utilizing a new proton treatment technique: Spot-scanning proton arc (SPArc) therapy for left-sided whole breast radiotherapy (WBRT) to further reduce radiation dose to healthy tissue and mitigate the probability of normal tissue complications compared to conventional intensity modulated proton therapy (IMPT)
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