Avanzo Michele, Trovo Marco, Stancanello Joseph, Jena Rajesh, Roncadin Mario, Toffoli Giulia, Zuiani Chiara, Capra Elvira
Medical Physics Department, CRO Aviano, 33081 Aviano, Italy.
Radiation Oncology Department, CRO Aviano, 33081 Aviano, Italy.
Phys Med. 2015 Dec;31(8):1022-1028. doi: 10.1016/j.ejmp.2015.08.016. Epub 2015 Oct 23.
To reduce the fraction number in Partial Breast Irradiation (PBI) with initial prescription of 40 Gy in 10 fractions using radiobiological models with specific focus on risk of moderate/severe radiation-induced fibrosis (RIF) and report clinical results.
68 patients (patient group A) were treated with 40 Gy in 10 fractions delivered by field-in-field, forward-planned IMRT. Isotoxic regimens with decreasing number of fractions were calculated using Biological Effective Dose (BED) to the breast. Risk for RIF in hypofractionated treatment was predicted by calculating NTCP from DVHs of group A rescaled to fractions and dose of novel regimens. Moderate/severe RIF was prospectively scored during follow-up. Various NTCP models, with and without incomplete repair correction, were assessed from difference to observed incidence of RIF. In order to verify the value for α/β of 3 Gy assumed for breast, we fitted α/β to observed incidences of moderate/severe RIF.
Treatments with 35 Gy/7f and 28 Gy/4f were selected for the fraction reduction protocol. 75 patients (group B) were treated in 35 Gy/7f. Incidence of moderate/severe RIF was 5.9% in group A, 5.3% in group B. The NTCP model with correction for incomplete repair had lowest difference from observed RIF. The α/β obtained from fitting was 2.8 (95%CIs 1.1-10.7) Gy.
The hypofractionated regimen was well tolerated. The model for NTCP corrected for incomplete repair was the most accurate and an assumed α/β value of 3 Gy is consistent with our patient data. The hypofractionation protocol is continuing with patients treated with 28 Gy/4f.
利用放射生物学模型，将初始处方为40 Gy分10次照射的部分乳腺照射（PBI）的分次次数减少，特别关注中度/重度放射性纤维化（RIF）的风险，并报告临床结果。
68例患者（A组）接受了适形野、正向计划调强放疗，分10次给予40 Gy。使用乳腺的生物等效剂量（BED）计算分次次数减少的等毒性方案。通过将A组的剂量体积直方图（DVH）重新调整为新方案的分次次数和剂量来计算超分割治疗中RIF的风险。在随访期间对中度/重度RIF进行前瞻性评分。根据RIF的观察发生率差异，评估了各种有或无不完全修复校正的正常组织并发症概率（NTCP）模型。为了验证乳腺假定的α/β值为3 Gy，我们将α/β值与中度/重度RIF的观察发生率进行拟合。
选择35 Gy/7次和28 Gy/4次的治疗方案进行分次减少方案。75例患者（B组）接受了35 Gy/7次的治疗。A组中度/重度RIF的发生率为5.9%，B组为5.3%。校正不完全修复的NTCP模型与观察到的RIF差异最小。拟合得到的α/β值为2.8（95%可信区间1.1 - 10.7）Gy。
超分割方案耐受性良好。校正不完全修复的NTCP模型最准确，假定的α/β值3 Gy与我们的患者数据一致。超分割方案正在继续用于接受28 Gy/4次治疗的患者。
