Shiba S, Trauernicht C, Robar J L
Department of Medical Physics, Stellenbosch University, Stellenbosch, South Africa; Yenzakahle Medical Physics Inc, Hilton, South Africa.
Department of Medical Physics, Stellenbosch University, Stellenbosch, South Africa.
Med Dosim. 2025;50(1):47-56. doi: 10.1016/j.meddos.2024.07.008. Epub 2024 Sep 3.
C-arm linacs have been used widely to treat multiple cranial metastases using stereotactic radiosurgery (SRS). A new generation of O-ring linacs offer several workflow advantages when compared to C-arm platforms. However, O-ring linacs are not able to employ couch rotations for noncoplanar beams used in SRS treatments. This study was conducted in order to simulate further possible developments of O-ring treatment units by assessing their geometrical efficiency. In this work we compare the plan quality for C-arm versus an O-ring platform including metrics that are relevant to SRS for multiple metastases. The comparison is conducted by incorporating tilted arcs on the O-ring platform therefore introducing noncoplanarity. Total 40 patients previously treated for SRS with 20 Gy single fraction were replanned for C-arm with a standard noncoplanar 5-arc arrangement and O-ring with both coplanar and noncoplanar beams. For the O-ring plans, we considered a default 3-arc coplanar arrangement, as well as 3- and 5-arc arrangements with arcs tipped up to 10 degrees from the axial plane. Target coverage, organ-at-risk (OAR) doses, monitor unit (MU) efficiency, conformity and gradient indices were assessed for all plans. For most metrics the O-ring geometries, even the coplanar arrangement, produced statistically comparable results to the C-arm. Small but significant differences were found for the 3 arc O-ring for PTV: D90%, D2% and MU/Gy and for the 5 arc O-ring at D2% when both were compared to the C-arm. Cumulative dose volume histograms (DVHs) for normal brain showed a cross-over between the C-arm and coplanar O-ring geometry at a low dose (2.3 ± 1.8 Gy), with O-ring associated with higher volumes above this cross-over dose. However, no statistical difference was seen in the brainstem, optic pathway and volumes of normal brain receiving 12 Gy or 20 Gy. This study has found that O-ring geometry linacs can produce SRS plans of comparable quality to those from a C-arm for multiple cranial metastases.
C型臂直线加速器已被广泛用于使用立体定向放射外科（SRS）治疗多发性脑转移瘤。与C型臂平台相比，新一代O型环直线加速器在工作流程方面具有多个优势。然而，O型环直线加速器无法采用治疗床旋转来实现SRS治疗中使用的非共面射束。本研究旨在通过评估O型环治疗单元的几何效率来模拟其进一步可能的发展。在这项工作中，我们比较了C型臂与O型环平台的计划质量，包括与多发性转移瘤的SRS相关的指标。通过在O型环平台上纳入倾斜弧来引入非共面性，从而进行比较。总共40例先前接受过单次20 Gy SRS治疗的患者，分别采用标准非共面5弧排列为C型臂重新计划，以及采用共面和非共面射束为O型环重新计划。对于O型环计划，我们考虑了默认的3弧共面排列，以及与轴向平面倾斜高达10度的3弧和5弧排列。评估了所有计划的靶区覆盖、危及器官（OAR）剂量、监测单位（MU）效率、适形度和梯度指数。对于大多数指标，O型环几何结构，即使是共面排列，与C型臂产生的统计结果相当。当将3弧O型环的PTV：D90%、D2%和MU/Gy以及5弧O型环的D2%与C型臂进行比较时，发现了微小但显著的差异。正常脑组织的累积剂量体积直方图（DVH）显示，在低剂量（2.3±1.8 Gy）时，C型臂和共面O型环几何结构之间存在交叉，高于此交叉剂量时，O型环相关的体积更高。然而，在脑干、视路以及接受12 Gy或20 Gy剂量的正常脑组织体积方面，未观察到统计学差异。本研究发现，O型环几何结构的直线加速器可以产生与C型臂相当质量的SRS计划，用于治疗多发性脑转移瘤。
