Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, IN, USA.
Radiat Oncol. 2013 Jan 12;8:14. doi: 10.1186/1748-717X-8-14.
Cranial reirradiation is clinically appropriate in some cases but cumulative radiation dose to critical normal structures remains a practical concern. The authors developed a simple technique in 3D conformal proton craniospinal irradiation (CSI) to block organs at risk (OAR) while minimizing underdosing of adjacent target brain tissue.
Two clinical cases illustrate the use of proton therapy to provide salvage CSI when a previously irradiated OAR required sparing from additional radiation dose. The prior radiation plan was coregistered to the treatment planning CT to create a planning organ at risk volume (PRV) around the OAR. Right and left lateral cranial whole brain proton apertures were created with a small block over the PRV. Then right and left lateral "inverse apertures" were generated, creating an aperture opening in the shape of the area previously blocked and blocking the area previously open. The inverse aperture opening was made one millimeter smaller than the original block to minimize the risk of dose overlap. The inverse apertures were used to irradiate the target volume lateral to the PRV, selecting a proton beam range to abut the 50% isodose line against either lateral edge of the PRV. Together, the 4 cranial proton fields created a region of complete dose avoidance around the OAR. Comparative photon treatment plans were generated with opposed lateral X-ray fields with custom blocks and coplanar intensity modulated radiation therapy optimized to avoid the PRV. Cumulative dose volume histograms were evaluated.
Treatment plans were developed and successfully implemented to provide sparing of previously irradiated critical normal structures while treating target brain lateral to these structures. The absence of dose overlapping during irradiation through the inverse apertures was confirmed by film. Compared to the lateral X-ray and IMRT treatment plans, the proton CSI technique improved coverage of target brain tissue while providing the least additional radiation dose to the previously irradiated OAR.
Proton craniospinal irradiation can be adapted to provide complete sparing of previously irradiated OARs. This technique may extend the option of reirradiation to patients otherwise deemed ineligible for further radiotherapy due to prior dose to critical normal structures.
颅部再放疗在某些情况下是临床适用的，但关键正常结构的累积辐射剂量仍然是一个实际问题。作者在 3D 适形质子颅脊髓照射（CSI）中开发了一种简单的技术，在最小化相邻靶脑组织剂量不足的同时，对危及器官（OAR）进行屏蔽。
两个临床病例说明了使用质子治疗在先前照射的 OAR 需要避免额外辐射剂量时提供挽救性 CSI 的情况。将先前的放射治疗计划与治疗计划 CT 配准，以创建 OAR 周围的计划器官风险体积（PRV）。在 PRV 上方创建右侧和左侧颅全脑质子孔径，并创建右侧和左侧“逆孔径”，在先前被屏蔽的区域形成孔径开口，并阻塞先前开放的区域。使逆孔径开口比原始块小一毫米，以最大程度地降低剂量重叠的风险。使用逆孔径照射 PRV 侧的靶体积，选择质子束范围，使其与 PRV 的任一侧边缘相接，达到 50%等剂量线。4 个颅部质子场共同创建了 OAR 周围完全避免剂量的区域。生成了具有相反侧 X 射线的光子治疗计划，带有定制块，并使用共面调强放射治疗进行优化，以避免 PRV。评估了累积剂量体积直方图。
制定并成功实施了治疗计划，以避免先前照射的关键正常结构，同时治疗这些结构外侧的靶脑。通过胶片确认在通过逆孔径照射时不存在剂量重叠。与侧 X 射线和调强放射治疗计划相比，质子 CSI 技术提高了靶脑组织的覆盖范围，同时对先前照射的 OAR 提供了最小的额外辐射剂量。
质子颅脊髓照射可以进行调整，以完全避免先前照射的 OAR。这项技术可能会为因先前关键正常结构的剂量而被认为不适合进一步放射治疗的患者提供再放疗的选择。
