Background/Objectives: Stereotactic body radiation therapy (SBRT) for skull base reirradiation is particularly challenging, as patients have already received substantial radiation doses to the region, and nearby normal organs may have approached their tolerance limit from prior treatments. In this study, we reviewed the characteristics and capabilities of four advanced external beam radiation delivery systems and four modern treatment planning systems and evaluated the treatment plan quality of each technique using skull base reirradiation patient cases. Methods: SBRT plans were generated for sixteen skull base reirradiation patients using four modalities: the GK plan for the Elekta Leksell Gamma Knife Perfexion/ICON, the CyberKnife (CK) plan for the Accuray CyberKnife, the intensity-modulated proton therapy (IMPT) plan for the Hitachi ProBeat-FR proton therapy machine, and the volumetric-modulated arc therapy (VMAT) plan for the Varian TrueBeam STx. These plans were evaluated and compared using two novel gradient indices in addition to traditional dosimetry metrics for targets and organs at risk (OARs). The steepest border gradient quantified the percent prescription dose fall-off per millimeter at the boundary between the target and adjacent critical structures. This gradient index highlighted the system’s ability to spare nearby critical OARs. The volume gradient assessed the extent of dose spread outside the target toward the patient’s body. Results: All plans achieved comparable target coverage and conformity, while IMPT and VMAT demonstrated significantly better uniformity. The GK plans exhibited the highest border gradient, up to 20.9%/mm, followed by small-spot-size IMPT plans and CK plans. Additionally, IMPT plans showed the benefit of reduced dose spread in low-dose regions and the lowest maximum and mean doses to the brainstem and carotid artery. Conclusions: The advanced external beam radiotherapy modalities evaluated in this study are well-suited for SBRT in skull base reirradiation, which demands precise targeting of tumors with highly conformal doses and steep dose gradients to protect nearby normal structures.
背景/目的：颅底再程放疗的立体定向放射治疗（SBRT）尤其具有挑战性，因为患者该区域已接受过大量辐射剂量，且邻近正常器官可能因先前治疗已达到耐受极限。本研究回顾了四种先进外照射放射治疗系统和四种现代治疗计划系统的特性与性能，并通过颅底再程放疗病例评估了各技术的治疗计划质量。方法：针对16例颅底再程放疗患者，采用四种技术制定SBRT计划：Elekta Leksell伽玛刀Perfexion/ICON的伽玛刀计划、Accuray射波刀的射波刀计划、日立ProBeat-FR质子治疗系统的调强质子治疗计划，以及瓦里安TrueBeam STx的容积旋转调强放疗计划。除采用传统靶区和危及器官剂量学指标外，还通过两种新型梯度指数对这些计划进行评估比较。最陡边界梯度量化了靶区与邻近关键结构边界处每毫米处方剂量下降百分比，该梯度指数凸显了系统保护邻近关键危及器官的能力；体积梯度评估了靶区外向患者体内剂量扩散的范围。结果：所有计划均实现了相当的靶区覆盖度和适形度，而调强质子治疗和容积旋转调强放疗计划显示出显著更优的均匀性。伽玛刀计划展现出最高的边界梯度（达20.9%/毫米），其次是小光斑调强质子治疗计划和射波刀计划。此外，调强质子治疗计划在低剂量区具有减少剂量扩散的优势，对脑干和颈动脉的最大剂量与平均剂量均为最低。结论：本研究评估的先进外照射放疗技术非常适用于颅底再程放疗的立体定向放射治疗，该治疗需要以高度适形的剂量和陡峭的剂量梯度精准靶向肿瘤，同时保护邻近正常结构。
Advanced External Beam Stereotactic Radiotherapy for Skull Base Reirradiation
肿瘤(癌症)患者之家