Department of Radiation Oncology, Royal Adelaide Hospital, Port Road, Adelaide, SA, 5000, Australia.
School of Medicine, University of Adelaide, Adelaide, SA, Australia.
Radiat Oncol. 2023 Jan 4;18(1):2. doi: 10.1186/s13014-022-02188-y.
Stereotactic radiosurgery (SRS) is the preferred treatment for vestibular schwannoma (VS) in patients with preserved hearing and tumour diameter < 3 cm. Emerging evidence suggests restricting cochlear dose could preserve hearing. This retrospective replanning study aims to compare dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans for superiority of cochlear dose sparing without compromising tumour coverage.
Eligibility criteria included sporadic VS, serviceable hearing and availability of CT and MRI for planning. The original gross tumour volume and brainstem OAR volume were retained; the cochlea was newly contoured on the planning CT scan (bone window). Each case was replanned using the three above techniques, prescribing 12 Gy to the 80% isodose line. No dose constraint was applied to the cochlea.
Eighteen patients were replanned. Mean tumour volume was 2.25 cc. Tumour coverage and tumour mean dose (DCAT: 14.2, IMRT: 14.6, VMAT: 14.5 Gy) were comparable. Paddick and RTOG conformity indices were better for DCAT (0.66 and 1.6) and VMAT (0.69 and 1.5) compared to IMRT (0.56 and 1.9). DCAT had superior gradient index (3.0) compared to VMAT (3.4) and IMRT (3.4). VMAT delivered the lowest mean brainstem maximum dose (8.3 Gy) and decreased the mean cochlear dose (3.4 Gy) by 2.3 and 2.1 Gy, and the mean cochlear maximum dose (3.6 Gy) by 2.4 and 2.5 Gy relative to DCAT and IMRT, respectively.
LINAC-based SRS treatment using VMAT can achieve better cochlear dose sparing than DCAT or IMRT while maintaining tumour coverage.
对于保留听力且肿瘤直径<3cm 的前庭神经鞘瘤（VS）患者，立体定向放射外科（SRS）是首选治疗方法。新出现的证据表明，限制耳蜗剂量可以保留听力。本回顾性重计划研究旨在比较动态适形弧形治疗（DCAT）、调强放射治疗（IMRT）和容积调强弧形治疗（VMAT）在不影响肿瘤覆盖的情况下，更好地保护耳蜗剂量。
入选标准包括散发性 VS、可利用听力以及 CT 和 MRI 用于计划。保留原始肿瘤靶区（GTV）和脑干 OAR 体积；在计划 CT 扫描（骨窗）上重新勾画耳蜗。每位患者均使用上述三种技术进行重计划，规定 12Gy 达到 80%等剂量线。耳蜗不施加剂量限制。
18 例患者接受了重计划。平均肿瘤体积为 2.25cc。肿瘤覆盖和肿瘤平均剂量（DCAT：14.2、IMRT：14.6、VMAT：14.5Gy）相当。Paddick 和 RTOG 适形指数在 DCAT（0.66 和 1.6）和 VMAT（0.69 和 1.5）中优于 IMRT（0.56 和 1.9）。DCAT 的梯度指数（3.0）优于 VMAT（3.4）和 IMRT（3.4）。VMAT 可降低平均脑干最大剂量（8.3Gy），与 DCAT 和 IMRT 相比，分别降低平均耳蜗剂量（3.4Gy）2.3 和 2.1Gy，平均耳蜗最大剂量（3.6Gy）2.4 和 2.5Gy。
基于 LINAC 的 SRS 治疗使用 VMAT 可以在保持肿瘤覆盖的同时，比 DCAT 或 IMRT 更好地保护耳蜗剂量。
