Department of Radiation Oncology, Renmin Hospital, Wuhan University, Wuhan, 430060, Hubei Province, China.
Department of Radiation Oncology, Beaumont Health System, Royal Oak, MI, 48074, USA.
Radiat Oncol. 2020 Oct 7;15(1):232. doi: 10.1186/s13014-020-01676-3.
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).
Eight 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.
The 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 = NTCP/NTCP) 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.
SPArc technique can further reduce dose delivered to OARs and the probability of normal tissue complications in patients treated for left-sided WBRT.
本研究旨在探讨一种新的质子治疗技术的可行性和潜在临床获益，即利用点扫描质子弧形治疗（Spot-scanning proton arc，SPArc）技术进行左侧全乳放疗（Whole breast radiotherapy，WBRT），以进一步降低健康组织的放射剂量，并降低与传统强度调制质子治疗（Intensity modulated proton therapy，IMPT）相比正常组织并发症的发生概率。
回顾性纳入 8 例接受保乳手术后、未行区域淋巴结放疗的左侧乳腺癌患者。为每位患者生成两种质子治疗计划：用于临床治疗的垂直调强质子治疗（Vertical intensity-modulated proton therapy，vIMPT，机架角度 10°-30°）和 SPArc 治疗计划。SPArc 和 vIMPT 计划均使用±3.5%范围和 5mm 摆位误差的鲁棒性优化进行优化。采用均方根偏差剂量（Root-mean-square deviation dose，RMSD）体积直方图评估计划的鲁棒性。所有剂量学结果均基于剂量体积直方图（Dose-volume histogram，DVH）进行评估，根据 CT50 上单次 4D 动态剂量的累积评估相互作用效应。根据能量层切换时间（Energy-layer-switching-time，ELST）从 0.2 到 5s 的机架旋转模拟治疗束的输送时间。
与 vIMPT 组的 110.38cGy（p=0.001）和 170.38cGy（p=0.001）相比，心脏和左前降支（Left anterior descending，LAD）的 D1 剂量分别降低至 53.63cGy 和 82.25cGy。与 vIMPT 组相比，同侧肺的 V5Gy 和 V20Gy 分别降低至 16.77%和 3.07%（p=0.001）和 4.68%（p=0.003）。皮肤 3mm 平均剂量和最大剂量分别降低至 3999.38cGy 和 4395.63cGy，与 vIMPT 组的 4104.25cGy（p=0.039）和 4411.63cGy（p=0.043）相比。与 vIMPT 组相比，SPArc 组的风险器官（Organ at risk，OAR）的相对危险度降低（Reliable normal tissue complication probability，RNTCP）为 0.61 至 0.86，具体取决于临床终点。RMSD 体积直方图（RMSD volume histogram，RVH）分析表明，SPArc 技术在保护心脏、LAD、同侧肺和皮肤等 OAR 方面提供了更好的计划鲁棒性。当 ELST 约为 0.5s 时，平均估计的治疗束输送时间与 vIMPT 计划相当。
SPArc 技术可进一步降低左侧 WBRT 患者 OAR 接受的剂量，并降低正常组织并发症的发生概率。
