Department of Proton Therapy Center, Zibo Wanjie Cancer Hospital, Zibo, Shandong, China.
J Xray Sci Technol. 2010;18(4):443-50. doi: 10.3233/XST-2010-0265.
A comparative treatment planning study was undertaken between proton beam therapy (PBT) and intensity-modulated x-ray therapy (IMXT) for patients with recurrent nasopharyngeal carcinoma (NPC), to assess the potential benefits and limitations of the two treatment modalities.
We retrospectively analyzed seven patients with recurrent NPC treated at our proton center with PBT from 2004 to 2007. Eclipse proton treatment planning system and Eclipse inverse treatment planning system for IMXT were employed. For each patient, the IMXT plan was optimized with nine evenly spaced coplanar fields. Three coplanar beams and passive scattering mode were used for PBT. The dose prescription in cobalt Gray equivalent (CGE) for gross tumor volume (GTV) was 66CGE and for planning target volume (PTV), 62.7CGE. Dose-volume histograms (DVH) were used to evaluate the difference in dosimetric distributions for the target volume and the organs at risk (OARs).
Optimal target volume coverage and similar target conformation were achieved in both PBT and IMXT. Median conformity index was 0.72 and 0.75 (p=0.15) and median inhomogeneity coefficient was 0.14 and 0.10 (p=0.08) for PBT and IMXT, respectively. Dose to OARs was significantly lower in PBT plans than IMXT. Median maximal dose to the brainstem was 27.89CGE(cobalt Gray equivalent) and 42.45Gy (p< 0.01), and the dose to 5% of the brainstem(D5) was 12.83CGE and 19.47Gy (p< 0.001 ), for PBT and IMXT, respectively. Median maximal dose to the spinal cord was 8.38CGE and 22.91Gy (p< 0.004), and the dose to 5% of the spinal cord was 2.18CGE and 13.62Gy (p< 0.001), for PBT and IMXT, respectively.
The use of PBT, when compared with IMXT, resulted in similar levels of tumor conformation. PBT, however, exposed the OARs to a significantly lower dose, effectively sparing the brainstem, spinal cord, optic nerve and chiasm, temporal lobes and parotid glands. The superior dose distributions possible with PBT should translate into reduced morbidity and improved quality of life.
本研究对质子治疗（PBT）和调强放疗（IMXT）治疗复发性鼻咽癌（NPC）的疗效进行了比较，以评估这两种治疗方式的潜在优势和局限性。
回顾性分析了 2004 年至 2007 年在我院质子中心接受 PBT 治疗的 7 例复发性 NPC 患者的资料。采用 Eclipse 质子治疗计划系统和 Eclipse 逆向调强放疗计划系统分别对患者进行 PBT 和 IMXT 治疗计划设计。对每位患者，采用 9 个等中心共面照射野进行 IMXT 计划设计。PBT 采用 3 个共面照射野和被动散射模式，GTV 和 PTV 的处方剂量均为 66CGE。采用剂量体积直方图（DVH）评估靶区和危及器官（OARs）的剂量分布差异。
PBT 和 IMXT 均能实现靶区的最佳适形性和相似的靶区形状。PBT 和 IMXT 的中值适形度指数分别为 0.72 和 0.75（p=0.15），中值不均匀性指数分别为 0.14 和 0.10（p=0.08）。PBT 计划的 OAR 受照剂量显著低于 IMXT 计划。PBT 和 IMXT 计划中脑干的最大剂量 Dmax 分别为 27.89CGE 和 42.45Gy（p<0.01），脑干的 5%受照剂量 D5 分别为 12.83CGE 和 19.47Gy（p<0.001）；脊髓的最大剂量 Dmax 分别为 8.38CGE 和 22.91Gy（p<0.004），脊髓的 5%受照剂量 D5 分别为 2.18CGE 和 13.62Gy（p<0.001）。
与 IMXT 相比，PBT 治疗能达到相似的肿瘤适形度，但可显著降低 OAR 受照剂量，从而有效保护脑干、脊髓、视神经和视交叉、颞叶和腮腺。PBT 可能具有更好的剂量分布，这有望降低不良反应发生率，提高患者生活质量。
