Heterogeneity correction for intensity-modulated frameless SRS in pituitary and cavernous sinus tumors: a retrospective study.
Heterogeneity correction for intensity-modulated frameless SRS in pituitary and cavernous sinus tumors: a retrospective study.
复制标题
DOI：
10.1186/s13014-015-0500-y
复制
发表时间：
2015-09-17
期刊：
影响因子：
--
通讯作者：
Spalding AC
中科院分区：
文献类型：
--
作者：
Shields LB;Bond C;Odom A;Sun DA;Spalding AC
无框架固定允许强度调制放射外科（IM-SRS）计划的规划和质量保证。我们测试了这样一个假设，即与异质性校正算法相比，采用均匀组织密度校正的IM-SRS计划会导致剂量不准确。15例垂体或海绵窦肿瘤患者接受了无框架IM-SRS。获得治疗计划CT和MRI扫描并融合以描绘肿瘤、视神经、视交叉和脑干。使用笔形射束（PB）、分析各向异性（AAA）和Acuros XB（AXB）算法，使用静态机架IM-SRS场开发该计划。我们评估了每种算法的目标覆盖率以及危及器官（OAR）的剂量。我们比较了PTV与OAR重叠（n = 10）和OAR与PTV不重叠（n = 5）情况下每种算法的结果。利用胶片剂量测定法，我们测量了每个算法的剂量分布，通过一个均匀密度的目标，一个随机体模与非均匀密度的空气，组织和骨骼。通过DMaxPTV、DMinPTV、D95%PTV或覆盖95% PTV的等剂量面（IDS）测量的靶区覆盖率无差异，与算法无关。然而，OAR的剂量存在差异。PB预测脑干、视交叉、右侧视神经和左侧视神经的Dmax较高（p < 0.05）。在PTV与视神经重叠的病例中（n = 7），PB无法将剂量限制在8 Gy，同时实现PTV覆盖（PB 855 cGy vs. AAA 769 cGy，p = 0.05 vs. AXB 658 cGy，p = 0.03）。在随机体模中，PB和AAA算法高估了窦骨-组织-空气界面中输送的剂量（+17%），而AXB算法准确预测了通过不均匀组织输送的实际剂量（最大+/-1%，p < 0.05）。当病变位于组织密度变化很大且接近关键正常结构（如颅底）的区域时，接受无框架SRS的患者可从异质性校正剂量计划中获益。胶片剂量测定证实，AXB剂量计算算法比PB或AAA剂量计算算法更准确地预测通过不同密度组织输送的实际剂量。
Frameless immobilization allows for planning and quality assurance of intensity-modulated radiosurgery (IM-SRS) plans. We tested the hypothesis that IM-SRS planning with uniform tissue density corrections results in dose inaccuracy compared to heterogeneity-corrected algorithms. Fifteen patients with tumors of the pituitary or cavernous sinus underwent frameless IM-SRS. Treatment planning CT and MRI scans were obtained and fused to delineate the tumor, optic nerves, chiasm, and brainstem. The plan was developed with static gantry IM-SRS fields using a pencil beam (PB), analytical anisotropic (AAA), and Acuros XB (AXB) algorithms. We evaluated measures of target coverage as well as doses to organs at risk (OAR) for each algorithm. We compared the results of each algorithm in the cases where PTV overlapped OAR (n = 10) to cases without overlapping OAR with PTV (n = 5). Utilizing film dosimetry, we measured the dose distribution for each algorithm through a uniform density target to a rando phantom with non-uniform density of air, tissue, and bone. There was no difference in target coverage measured by DMaxPTV, DMinPTV, D95%PTV, or the isodose surface (IDS) covering 95 % of the PTV regardless of algorithm. However, there were differences in dose to OAR. PB predicted higher (p < 0.05) Dmax for the brainstem, chiasm, right optic nerve, and left optic nerve. In cases of PTV overlapping an optic nerve (n = 7), PB was unable to limit dose to 8Gy while achieving PTV coverage (PB 855 cGy vs. AAA 769 cGy, p = 0.05 vs. AXB 658 cGy, p = 0.03). Within the rando phantom, the PB and AAA algorithms over-estimated the dose delivered in the bone-tissue-air interface of the sinus (+17 %), while the AXB algorithm closely predicted the actual dose delivered through the inhomogeneous tissue (+/- 1 % max, p < 0.05). Patients undergoing frameless SRS benefit from heterogeneity corrected dose plans when the lesion lies in areas of widely varying tissue density and near critical normal structures such as the skull base. Film dosimetry confirms that the AXB dose calculation algorithm more accurately predicts actual dose delivered though tissues of varying densities than PB or AAA dose calculation algorithms.