Ahamed Shabbir, Padma Suvarna R, Singh Navin
Department of Radiation Physics, MNJIO and RCC, Hyderabad, Telangana, India.
Department of Physics, Jawaharlal Nehru Technological University Anantapur, Andhra Pradesh, India.
J Cancer Res Ther. 2025 Apr 1;21(3):693-699. doi: 10.4103/jcrt.jcrt_2205_24. Epub 2025 Jul 5.
To demonstrate the cause and effects of dose gradients in normal brain and resulting plan metrics using varied objective functions for generating efficient volumetric modulated arc radiosurgery plans for solitary brain metastasis.
Normal tissue and dose volume objective function (NTO and DVO) variations were applied to the virtual phantom and 23 solitary brain metastasis (SBM) cases to plan 20 Gray (Gy) doses. Initial testing on the phantom used eight variations manipulating NTO priority (50, 100, 150, 200), end-dose (25% and 10%), and DVO target dose maximum (25 and 27 Gy). Two strategies were then tested on SBM cases. First strategy (S1) used NTO priority = 100, end-dose = 25%, target maximum dose < 25 Gy. The second strategy (S2) tightened NTO and relaxed DVO by changing the corresponding parameters to 200 and 10%, and 27 Gy. Plans were analyzed comparing and correlating relevant metrics.
For the phantom case, the mean multi-leaf collimator aperture area (AA) variation between the highest NTO priority S2 plan and lowest priority S1 plan was about 46%, which brought substantial changes to 12 Gy spill outside tumor (V12), efficiency index, and prescription isodose level (PIDL). SBM cases showed about 14% lower PIDL and associated V12 reduction of about 0.7 cm3 for S2 than S1. V12 reduction was explained by AA reduction (r ≥ 0.966). For the studied PTVs, monitor units per Gy (MU/Gy) and AA product were lower for S2 indicating one or either factor was lower.
Stringent NTO and relaxed DVO functions cause aperture shrinkage to create dose gradients for overall plan efficacy.
通过使用不同的目标函数来生成针对孤立性脑转移瘤的高效容积调强弧形放射外科治疗计划，以展示正常脑组织中剂量梯度的成因及影响以及由此产生的计划指标。
将正常组织和剂量体积目标函数（NTO和DVO）的变化应用于虚拟体模和23例孤立性脑转移瘤（SBM）病例，以规划20格雷（Gy）的剂量。在体模上的初始测试使用了八种变化，分别操纵NTO优先级（50、100、150、200）、终剂量（25%和10%）以及DVO目标剂量最大值（25和27 Gy）。然后在SBM病例上测试了两种策略。第一种策略（S1）使用NTO优先级 = 100，终剂量 = 25%，目标最大剂量 < 25 Gy。第二种策略（S2）通过将相应参数更改为200和10%以及27 Gy来收紧NTO并放宽DVO。对计划进行分析，比较并关联相关指标。
对于体模病例，最高NTO优先级的S2计划与最低优先级的S1计划之间的平均多叶准直器孔径面积（AA）变化约为46%，这给肿瘤外12 Gy溢出体积（V12）、效率指数和处方等剂量水平（PIDL）带来了显著变化。SBM病例显示，S2的PIDL比S1低约14%，且相关的V12减少约0.7 cm³。V12的减少可通过AA的减少来解释（r≥0.966）。对于所研究的计划靶体积（PTV），S2的每格雷监测单位（MU/Gy）和AA乘积较低，表明其中一个或两个因素较低。
严格的NTO和宽松的DVO函数会导致孔径缩小，从而为整体计划疗效产生剂量梯度。
