Sharma Shamurailatpam Dayananda, Chadha Pranav, Talapatra Kaustav, Mahtre Vaibhav, Kumar Abhaya P, Balasubramaniam Anandh
Department of Radiation Oncology, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute, Andheri, Mumbai, India.
J Cancer Res Ther. 2014 Jan-Mar;10(1):29-37. doi: 10.4103/0973-1482.131353.
To investigate potential sparing of critical neurological structures (CNSs) during radiosurgery of vestibular schwannoma (VS) employing different techniques and dose prescription methods.
Fused CT and MRI datasets of eight patients with unilateral VS representing a wide range of target volume (0.48 to 12.08 cc; mean = 3.56 cc), shape and proximity to CNSs such as cochlea, trigeminal nerve and brainstem were re-planned employing static conformal field (SCF), dynamic conformal arc (DCA) and intensity modulated radiosurgery (IMRS) techniques. For every patient, five plans were created for a fixed margin dose of 12 Gy prescribed at 80% in three plans (SCF_80%, DCA_80%, and IMRS_80%) and 50% in another two plans (SCF_50% and DCA_50%). All plans were compared using standard dosimetric indices.
Primary goal of every plan to cover ≥99% of target volume with 12 Gy was fulfilled for all patients with minimum significant dose to target (D₉₉) ≥11.99 Gy. Best conformity index (CI Paddick = 0.62 ± 0.12) was observed in SCF_80% and DCA_80% plans whereas; sharpest dose gradient index of 3.40 ± 0.40 was resulted from DCA_50%. All five plans resulted similar maximum dose to brainstem (11.04 ± 2.23 to 11.53 ± 1.10 Gy), cochlea (9.02 ± 1.79 to 10.15 ± 1.26 Gy) and trigeminal nerve (11.55 ± 1.38 to 12.19 ± 2.12 Gy). Among 80% prescription plans, IMRS_80% reduces mean and D₅ (P < 0.05) to all CNSs. Prescription of dose at 50% isodose sharpened the dose gradient and significantly (P < 0.05) reduced mean dose and D₅ to all CNSs at the cost of target conformity (P = 0.01). Mean dose to cochlea and trigeminal nerve were least at 4.53 ± 0.86 and 6.95 ± 2.02 Gy from SCF_50% and highest at 6.65 ± 0.70 and 8.40 ± 2.11 Gy from DCA_80% plans respectively.
This dosimetric data provides a guideline for choosing optimum treatment option and scope of inter institutional dosimetric comparison for further improvement in radiosurgery of Vestibular Schwannoma (VS).
研究在前庭神经鞘瘤（VS）放射外科治疗中，采用不同技术和剂量处方方法时关键神经结构（CNSs）的潜在保留情况。
对8例单侧VS患者的融合CT和MRI数据集进行重新规划，这些数据集代表了广泛的靶体积（0.48至12.08立方厘米；平均 = 3.56立方厘米）、形状以及与CNSs（如耳蜗、三叉神经和脑干）的接近程度，采用静态适形野（SCF）、动态适形弧（DCA）和调强放射外科（IMRS）技术。对于每位患者，在三个计划（SCF_80%、DCA_80%和IMRS_80%）中以80%的处方剂量创建五个计划，处方固定边缘剂量为12 Gy，在另外两个计划（SCF_50%和DCA_50%）中以50%的处方剂量创建。使用标准剂量学指标对所有计划进行比较。
所有患者均实现了每个计划的主要目标，即以12 Gy覆盖≥99%的靶体积，靶区最小有效剂量（D₉₉）≥11.99 Gy。在SCF_80%和DCA_80%计划中观察到最佳适形指数（CI Paddick = 0.62 ± 0.12）；而DCA_50%产生了最陡的剂量梯度指数，为3.40 ± 0.40。所有五个计划导致脑干、耳蜗和三叉神经的最大剂量相似（分别为11.04 ± 2.23至11.53 ± 1.10 Gy、9.02 ± 1.79至10.15 ± 1.26 Gy和11.55 ± 1.38至12.19 ± 2.12 Gy）。在80%处方计划中，IMRS_80%降低了所有CNSs的平均剂量和D₅（P < 0.05）。在50%等剂量线处处方剂量锐化了剂量梯度，并显著（P < 0.05）降低了所有CNSs的平均剂量和D₅，但以靶区适形性为代价（P = 0.01）。SCF_50%计划中，耳蜗和三叉神经的平均剂量最低，分别为4.53 ± 0.86和6.95 ± 2.02 Gy；DCA_80%计划中最高，分别为6.65 ± 0.70和8.40 ± 2.11 Gy。
该剂量学数据为选择最佳治疗方案和机构间剂量学比较范围提供了指导，以进一步改善前庭神经鞘瘤（VS）的放射外科治疗。
