Medical Physics Unit, CHR Metz-Thionville, Metz, France.
Université de Lorraine, CNRS, CRAN, F-54000, Nancy, France.
Med Phys. 2021 Jul;48(7):3453-3458. doi: 10.1002/mp.14841. Epub 2021 Jul 7.
A common dosimetric quality assurance (QA) method in stereotactic body radiation therapy (SBRT) of lung tumors is to use lung phantoms with radiochromic film. However, in most phantoms, the film moves with the tumor, leading to the blurring effect. This technical note presents the QA performance of a novel phantom in which the film is fixed; this phantom can be used for both patient-specific QA and end-to-end testing.
Lung tumor motion was simulated with the CIRS Model 008A phantom. A lung-equivalent insert that consisted of a fixed radiochromic film around which a 2-cm tumor moved in the inferior/superior direction (i.e., mimicking respiration-induced tumor motion) was generated by 3D printing. Two common SBRT plans [dynamic conformal arc (DCA) and volumetric-modulated arc therapy (VMAT)] were calculated on the average intensity projection (AIP) image set in Varian Eclipse using the dose calculation algorithm Acuros XB. The plans were delivered by a Varian TrueBeam STx accelerator using 6-MV flattening filter-free energy. EBT3 films were used for treatment-dose verification. The measured and planned dose distributions were compared by using the local gamma index at 3% and 2 mm.
Mean gamma pass rates of film and planned dose distributions were all ≥95%. DCA and VMAT plans did not differ in gamma pass rates. Planned and measured dose distributions agreed well, as did planned and measured gamma maps.
With this new insert, measured and planned dose distributions were very similar, which supports the current view in the field that dose calculations on AIP image sets account sufficiently for tumor motion during treatment. The phantom also performed well despite challenging breathing parameters (large tumor amplitude and slow breathing rate) and the application of a complex treatment technique (VMAT). This phantom could facilitate clinical and end-to-end film-based dosimetric QA for lung SBRT.
Twenty-seven TH- Radiation dose measurement devices. Eleven Phantoms for dosimetric measurement.
在肺部肿瘤立体定向体放射治疗（SBRT）中，一种常用的剂量学质量保证（QA）方法是使用带有辐射显色胶片的肺部体模。然而，在大多数体模中，胶片随肿瘤移动，导致模糊效应。本技术说明介绍了一种新型体模的 QA 性能，该体模的胶片是固定的；这种体模既可以用于患者特定的 QA，也可以用于端到端测试。
使用 CIRS 模型 008A 体模模拟肺部肿瘤运动。通过 3D 打印生成了一个肺等效插入物，该插入物由固定的辐射显色胶片组成，胶片周围有一个 2cm 的肿瘤，可在下方/上方方向移动（即模拟呼吸引起的肿瘤运动）。使用瓦里安 Eclipse 中的平均强度投影（AIP）图像集，通过 Acuros XB 剂量计算算法计算了两种常见的 SBRT 计划[动态适形弧（DCA）和容积调制弧治疗（VMAT）]。使用瓦里安 TrueBeam STx 加速器，以 6-MV 无均整过滤器能量进行计划交付。EBT3 胶片用于治疗剂量验证。通过使用 3%和 2mm 的局部伽马指数，比较测量和计划的剂量分布。
胶片和计划剂量分布的平均伽马通过率均≥95%。DCA 和 VMAT 计划的伽马通过率没有差异。计划和测量的剂量分布吻合良好，计划和测量的伽马图也吻合良好。
使用这种新的插入物，测量和计划的剂量分布非常相似，这支持了目前该领域的观点，即在治疗过程中，基于 AIP 图像集的剂量计算足以考虑肿瘤运动。尽管呼吸参数具有挑战性（肿瘤幅度大、呼吸速度慢），且应用了复杂的治疗技术（VMAT），该体模仍表现良好。这种体模可以促进肺部 SBRT 的临床和端到端胶片剂量学 QA。
二十七项 TH- 辐射剂量测量设备。十一项剂量测量体模。
