Kinz Marvin, Alfassi Adi, Gebert Ella, Alezra Dror, Hesser Jürgen, Zygmanski Piotr
Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts, USA.
Mannheim Institute for Intelligent Systems in Medicine (MIISM), Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
Med Phys. 2025 Aug;52(8):e18007. doi: 10.1002/mp.18007.
Converging lens radiotherapy (CLRT) is a novel radiotherapy modality employing a lens which produces a nearly monoenergetic x-ray beam at 60 keV to focus radiation on deep-seated tumors, enabling highly precise dose delivery.
This study represents the first comparison of CLRT treatment plan quality to conventional intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). The goal is to provide a proof-of-concept of CLRT treatment planning and to evaluate whether CLRT could potentially offer improved organ-at-risk (OAR) sparing and target coverage.
The physical CLRT prototype system was developed by Convergent Radiotherapy and Radiosurgery Ltd. (CRnR) in Haifa, Israel, under the product name AngelCure. We initially characterized the CLRT beam model using Monte Carlo simulations, validating it with film dosimetry of the physical beam. Subsequently, we developed a 3D dose computation algorithm and novel inverse, non-coplanar treatment planning for CLRT inside the open-source radiation treatment planning platform matRad. Two prototype lenses with different focal spot sizes (A mm and B mm) were employed. Using these tools, we performed CLRT treatment plan optimization for selected treatment sites and compared our results retrospectively to conventional IMRT/VMAT patient plans from the Dana-Farber Brigham Cancer Center clinical database, which were generated in Eclipse (Varian Medical Systems, Palo Alto, CA, USA). Here, we present three cases from the central nervous system (CNS), thoracic, and genitourinary (GU) sites. We utilized conformity index (CI), target coverage index (TCI), conformal number (CN), and gradient index (GI) as plan quality metrics, together with dose-volume histogram points to compare OAR sparing.
CLRT demonstrated variable OAR dose sparing. In the CNS case, both lenses showed better hypothalamus sparing, with 0% of the volume receiving 400 cGy or more compared to 91% for Linac. For the Thoracic case, Lens A achieved 0% of esophagus volume receiving more than 1000 cGy, versus 11% for Linac. In the GU case, Lens A delivered at least 400 cGy to 0% of rectum volume, compared to 17% with Linac. CLRT demonstrated potentially better or comparable plan quality metrics, with Lens A showing perfect conformity (CI = 1.00) in the CNS case and Lens B demonstrating the steepest dose gradient (GI = 240%/cm).
This study serves as a first proof-of-concept of the treatment capabilities of a novel CLRT x-ray system. The system demonstrated, in this limited set of plans, better OAR dose sparing compared to conventional Linac-based plans across 3 different anatomical sites, accompanied by similar, and possibly better, plan quality metrics (CI, TCI, CN, GI), while maintaining comparable target coverage.
会聚透镜放射疗法（CLRT）是一种新型放射治疗方式，它使用一个透镜产生能量近60keV的近乎单能的X射线束，将辐射聚焦于深部肿瘤，从而实现高精度的剂量递送。
本研究首次比较了CLRT治疗计划质量与传统调强放射治疗（IMRT）和容积调强弧形治疗（VMAT）。目标是提供CLRT治疗计划的概念验证，并评估CLRT是否有可能改善危及器官（OAR）的保护以及靶区覆盖情况。
物理CLRT原型系统由以色列海法的会聚放射治疗与放射外科有限公司（CRnR）开发，商品名为AngelCure。我们最初使用蒙特卡罗模拟对CLRT束流模型进行了表征，并通过物理束流的薄膜剂量测定法对其进行了验证。随后，我们在开源放射治疗计划平台matRad内开发了一种三维剂量计算算法以及用于CLRT的新型逆向非共面治疗计划。使用了两个具有不同焦点尺寸（A毫米和B毫米）的原型透镜。利用这些工具，我们对选定的治疗部位进行了CLRT治疗计划优化，并将结果与来自达纳 - 法伯布列根癌症中心临床数据库中在Eclipse（美国加利福尼亚州帕洛阿尔托的瓦里安医疗系统公司）生成的传统IMRT/VMAT患者计划进行了回顾性比较。在此，我们展示了来自中枢神经系统（CNS）、胸部和泌尿生殖系统（GU）部位的三个病例。我们使用适形指数（CI）、靶区覆盖指数（TCI）、共形数（CN）和梯度指数（GI）作为计划质量指标，以及剂量 - 体积直方图点来比较OAR保护情况。
CLRT显示出不同程度的OAR剂量保护。在中枢神经系统病例中，两个透镜均显示出对下丘脑更好的保护，接受400cGy或更高剂量的体积为0%，而直线加速器为91%。对于胸部病例，透镜A使食管体积接受超过1000cGy的比例为0%，而直线加速器为11%。在泌尿生殖系统病例中，透镜A使直肠体积接受至少400cGy的比例为0%，而直线加速器为17%。CLRT显示出潜在更好或相当的计划质量指标，透镜A在中枢神经系统病例中显示出完美的适形性（CI = 1.00），透镜B显示出最陡的剂量梯度（GI = 240%/cm）。
本研究首次证明了新型CLRT X射线系统的治疗能力。在这组有限的计划中，该系统与基于传统直线加速器的计划相比显示出在3个不同解剖部位对OAR剂量更好的保护，同时伴有相似且可能更好的计划质量指标（CI、TCI、CN、GI），同时保持了相当的靶区覆盖。
