Department of Radiation Oncology, Robert H. Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Northwestern Memorial Hospital, Chicago, IL, 60611, USA.
Med Phys. 2017 Dec;44(12):6706-6714. doi: 10.1002/mp.12637. Epub 2017 Nov 13.
To characterize the dosimetric impact of using different sizes of spherical applicators in Intrabeam™ Intraoperative Radiation Therapy (IB-IORT) to treat unicentric cancer lesions after breast-conserving lumpectomy.
Using the commissioned depth dose rates, the three-dimensional dosages of the 3.5, 4.0, 4.5, and 5.0 cm spherical applicators of the IB-IORT PRS400 machine were established. Five different cancer cell infiltration depths of unicentric breast lesions were formulated by a linearly declining cancer cell density distribution from the surgical surface. The equivalent uniform dose (EUD), which is the dosage of a homogeneous dose treatment for killing the same amount of cancer cells as IB-IORT in the same target volume, was then calculated using the modified linear quadratic model (MLQ). The radiobiological response of two types of cancer cell lines and three types of normal tissues in the TARGIT-A clinical trial of 20 Gy dose was estimated. The study was carried out for an acutely responding breast cancer cell line with an α/β ratio of 10 and a slow responding breast cancer cell line with an α/β ratio of 3.85, respectively. The cancer cell density at the surgical excision surface was assumed to be 0.01%, 0.1%, 1%, and 10%, respectively. The three types of normal tissue are radiosensitive, moderate radiosensitive, and radioresistant, respectively. The therapeutic ratio (TR), which was defined by a ratio between the survival fractions of normal tissue cells respectively in IB-IORT and in homogeneous dose treatments, was calculated.
The EUDs are moderately dependent on the applicator size (increasing from 1 to 10% depending on the cancer infiltrating depth when increasing diameter by 0.5 cm), not on the cancer cell radiosensitivity (differing by less than 1.30% between two cancer cell lines), and not dependent on the cancer cell population density at the surgical excision surface (differing by 0% among the tested surface densities). The EUDs decrease with the cancer cell maximum infiltrating depth. EUD of a 10 mm spherical shell target volume is about 50% of EUD of a 1 mm spherical shell. TRs are dependent on the applicator size, cancer cell infiltrating depth, and the radiosensitivities of cancer cells and normal tissue. A smaller size of applicator was found to produce a greater TR for a shallowly seated lesion (<5 mm), while a large size of applicator is better to treating a deeply seated lesion (>5 mm).
The applicator size has a moderate impact on the EUDs, a greater size of applicator will deliver a greater EUD at the same cancer cell infiltrating depth, but a smaller size of applicator is seen to produce a greater TR for the shallow lesions (depth <5 mm). In addition, a greater size of applicator is preferred for treating a deeply seated lesion (depth >5 mm) because it produces a greater TR and EUD than a smaller size of applicator. IB-IORT is a preferable alternative to uniform dose treatment when treating unicentric breast cancer at smaller infiltration depths.
描述在保乳手术后使用不同大小的球形施源器进行 Intrabeam™术中放射治疗（IB-IORT）治疗单中心癌症病变时，剂量学的影响。
使用委托的深度剂量率，建立了 IB-IORT PRS400 机器的 3.5、4.0、4.5 和 5.0cm 球形施源器的三维剂量。通过从手术表面呈线性下降的癌细胞密度分布，制定了五个不同的单中心乳腺癌病变的癌细胞浸润深度。使用改良的线性二次模型（MLQ）计算等效均匀剂量（EUD），即同质剂量治疗杀死与同一靶体积中的 IB-IORT 相同数量的癌细胞的剂量。估计了 TARGIT-A 临床试验中 20Gy 剂量的两种癌细胞系和三种正常组织的放射生物学反应。研究了具有 10 的α/β比的急性反应性乳腺癌细胞系和具有 3.85 的α/β比的缓慢反应性乳腺癌细胞系。假设手术切除表面的癌细胞密度分别为 0.01%、0.1%、1%和 10%。三种正常组织分别为辐射敏感、中度辐射敏感和辐射抗性。治疗比（TR）是通过 IB-IORT 和同质剂量治疗中正常组织细胞存活分数的比值定义的。
EUD 与施源器大小中度相关（当直径增加 0.5cm 时，取决于癌细胞浸润深度，增加 1%至 10%），与癌细胞放射敏感性无关（两种癌细胞系之间相差小于 1.30%），也与手术切除表面的癌细胞种群密度无关（在测试的表面密度之间相差 0%）。EUD 随癌细胞最大浸润深度而降低。10mm 球形壳靶体积的 EUD 约为 1mm 球形壳的 50%。TR 取决于施源器大小、癌细胞浸润深度以及癌细胞和正常组织的放射敏感性。较小的施源器尺寸发现对于较浅的病变（<5mm）产生更大的 TR，而较大的施源器尺寸对于较深的病变（>5mm）更好。
施源器尺寸对 EUD 有中度影响，较大的施源器在相同的癌细胞浸润深度下会提供更大的 EUD，但较小的施源器尺寸会对较浅的病变（深度<5mm）产生更大的 TR。此外，对于较深的病变（深度>5mm），较大的施源器尺寸优于较小的施源器尺寸，因为它产生的 TR 和 EUD 大于较小的施源器尺寸。当治疗较小浸润深度的单中心乳腺癌时，IB-IORT 是同质剂量治疗的较好替代方法。
