Departments of Radiology, Dentistry and Pharmaceutical Science, Okayama University Graduate School of Medicine, 2-5-1 Shikata-cho, Kita-ku, Okayama, 700-8558, Japan.
Department of Radiology, Tsuyama Chuo Hospital, Tusyama, Okayama, 708-0841, Japan.
Radiat Oncol. 2019 Nov 21;14(1):209. doi: 10.1186/s13014-019-1405-y.
Severe complications, such as eye damage and dysfunciton of salivary glands, have been reported after radiotherapy among patients with head and neck cancer. Complications such as visual impairment have also been reported after proton therapy with pencil beam scanning (PBS). In the case of PBS, collimation can sharpen the penumbra towards surrounding normal tissue in the low energy region of the proton beam. In the current study, we examined how much the dose to the normal tissue was reduced by when intensity-modulated proton therapy (IMPT) was performed using a multi-leaf collimator (MLC) for patients with maxillary sinus cancer.
Computed tomography findings of 26 consecutive patients who received photon therapy at Okayama University Hospital were used in this study. We compared D2% of the region of interest (ROI; ROI-) and the mean dose of ROI (ROI-) with and without the use of an MLC. The organs at risk (OARs) were the posterior retina, lacrimal gland, eyeball, and parotid gland. IMPT was performed for all patients. The spot size was approximately 5-6 mm at the isocenter. The collimator margin was calculated by enlarging the maximum outline of the target from the beam's eye view and setting the margin to 6 mm. All plans were optimized with the same parameters.
The mean of ROI- for the ipsilateral optic nerve was significantly reduced by 0.48 Gy, and the mean of ROI- for the ipsilateral optic nerve was significantly reduced by 1.04 Gy. The mean of ROI- to the optic chiasm was significantly reduced by 0.70 Gy. The dose to most OARs and the planning at risk volumes were also reduced.
Compared with the plan involving IMPT without an MLC, in the dose plan involving IMPT using an MLC for maxillary sinus cancer, the dose to the optic nerve and optic chiasm were significantly reduced, as measured by the ROI- and the ROI-. These findings demonstrate that the use of an MLC during IMPT for maxillary sinus cancer may be useful for preserving vision and preventing complications.
头颈部癌症患者在接受放射治疗后，会出现眼部损伤和唾液腺功能障碍等严重并发症。使用笔形束扫描（PBS）质子治疗后，也会出现视力损害等并发症。在 PBS 的情况下，准直可以使质子束的低能区中的周围正常组织的半影变尖锐。在本研究中，我们研究了在使用多叶准直器（MLC）对上颌窦癌患者进行强度调制质子治疗（IMPT）时，通过降低正常组织的剂量来减少多少剂量。
本研究使用了在冈山大学医院接受光子治疗的 26 例连续患者的计算机断层扫描结果。我们比较了有无 MLC 情况下感兴趣区域（ROI；ROI-）的 D2%和 ROI 的平均剂量（ROI-）。危险器官（OAR）为视网 膜后、泪腺、眼球和腮腺。所有患者均进行了 IMPT。等中心处的光斑大小约为 5-6mm。从束眼视图放大目标的最大轮廓，并将边缘设置为 6mm，计算出准直器边缘。所有计划均使用相同的参数进行优化。
同侧视神经的 ROI-平均值降低了 0.48Gy，同侧视神经的 ROI-平均值降低了 1.04Gy。视交叉的 ROI-平均值降低了 0.70Gy。大多数 OAR 和计划危险体积的剂量也降低了。
与不使用 MLC 的 IMPT 计划相比，在使用 MLC 的 IMPT 计划中，上颌窦癌的视神经和视交叉的剂量明显降低，通过 ROI-和 ROI-来测量。这些发现表明，在进行上颌窦癌的 IMPT 时使用 MLC 可能有助于保护视力和预防并发症。
