Proton Therapy Center, Hospital of Trento, Azienda Provinciale per I Servizi Sanitari (APSS), Italy.
Proton Therapy Center, Hospital of Trento, Azienda Provinciale per I Servizi Sanitari (APSS), Italy.
Radiother Oncol. 2017 Apr;123(1):112-118. doi: 10.1016/j.radonc.2017.02.008. Epub 2017 Mar 7.
Proton therapy is the emerging treatment modality for craniospinal irradiation (CSI) in pediatric patients. Herein, special methods adopted for CSI at proton Therapy Center of Trento by pencil beam scanning (PBS) are comprehensively described.
Twelve pediatric patients were treated by proton PBS using two/three isocenters. Special methods refer to: (i) patient positioning in supine position on immobilization devices crossed by the beams; (ii) planning field-junctions via the ancillary-beam technique; (iii) achieving lens-sparing by three-beams whole-brain-irradiation; (iv) applying a movable-snout and beam-splitting technique to reduce the lateral penumbra. Patient-specific quality assurance (QA) program was performed using two-dimensional ion chamber array and γ-analysis. Daily kilovoltage alignment was performed.
PBS allowed to obtain optimal target coverage (mean D98%>98%) with reduced dose to organs-at-risk. Lens sparing was obtained (mean D1∼730cGyE). Reducing lateral penumbra decreased the dose to the kidneys (mean Dmean<600cGyE). After kilovoltage alignment, potential dose deviations in the upper and lower junctions were small (average 0.8% and 1.2% respectively). Due to imperfect modeling of range shifter, QA showed better agreements between measurements and calculations at depths >4cm (mean γ>95%) than at depths<4cm.
The reported methods allowed to effectively perform proton PBS CSI.
质子治疗是儿童颅脊髓照射（CSI）的新兴治疗方式。在此，我们全面描述了特伦托质子治疗中心采用笔形束扫描（PBS）进行 CSI 的特殊方法。
12 名儿童患者采用质子 PBS 治疗，使用两个/三个等中心点。特殊方法包括：（i）患者仰卧在固定设备上，使射线穿过患者身体；（ii）通过辅助射线技术规划射野衔接；（iii）采用三束全脑照射实现晶状体豁免；（iv）采用可移动的探头和束分裂技术减少侧向半影。采用二维离子室阵列和γ分析进行了针对患者的质量保证（QA）程序。每日进行千伏级对准。
PBS 可实现最佳靶区覆盖（平均 D98%＞98%），同时降低了危及器官的剂量。实现了晶状体豁免（平均 D1∼730cGyE）。减少侧向半影降低了肾脏的剂量（平均 Dmean＜600cGyE）。进行千伏级对准后，上下交界处的潜在剂量偏差较小（平均分别为 0.8%和 1.2%）。由于对射程位移器的建模不完善，QA 显示在深度＞4cm 处（平均γ＞95%）的测量值与计算值之间的一致性更好，而在深度＜4cm 处则稍差。
报告的方法可有效实施质子 PBS CSI。
