Association between Sternal Dosimetric Parameters and Acute Hematological Toxicity of Radiotherapy after Modified Radical Mastectomy for Breast Cancer

Abstract

To research the association between sternal dosimetric parameters and hematological toxicity of radiotherapy after modified radical mastectomy for breast cancer. We retrospectively analyzed the complete clinical data and radiotherapy data of 58 patients treated with radiotherapy after modified radical mastectomy. V5、V10、V20、V30、V40、Dmean、Dmax、D20、D40、D60、D80 of the sternum were recorded on dose-volume histogram. Collecting and sorting of patients with clinical parameters: such as ages, height, body weight, etc.14 indexes. The hematological indexes were recorded before and during radiotherapy; Hematological toxicity was graded according to (NCI-CTC)4.0. Simple linear correlation was used to test the relationship between clinical parameters, dosimetric parameters and blood cells nadir, and Logistic regression model was used to test the correlation between dosimetric parameters and the incidence of blood cell toxicity. The Receiver Operating Characteristic (ROC) curve is used to evaluate the cutoff values of dosimetric parameters to avoid hematological toxicity. Univariate factor Logistic analysis: sternum V20、V30、V40 were associated with increased risk ≥2 grade hematological toxicity; sternum V10、V20、V30、V40、D60、D80 was associated with increased risk≥2 grade leukopenia; Sternum V5 and V10 were associated with≥3 lymphocytopenia(P<0.1). Multivariate factor Logistic analysis: Sternum V30 is an independent risk factor for≥2 grade acute hematological toxicity (P = 0.031); Sternum V40 and D80 were independent risk factors for toxicity≥2 grade leukopenia (P = 0.009, P = 0.05). The cut-off point of V30 、V40、D80 was 24.38cm3、 6.48cm3、23.37Gy respectively. When sternal V30 ≥24.38cm3, the incidence of ≥grade 2 HT increased significantly (89%、37% P<0.001); when sternal V40 ≥ 6.48cm3, the incidence of ≥ 2 grade leukopenia increased significantly (64%、24% P = 0.003).When sternum D80 ≥23.37Gy, the incidence of ≥2 grade leukopenia increased significantly(75%、36% P = 0.008).In addition, clinical parameters related to hematological toxicity were also found. White blood cell and lymphocyte Count at baseline were associated with≥2 grade leukopenia and≥3 grade lymphocytopenia, respectively (P = 0.009、P = 0.005). Higher ki-67 and higher chemotherapy-radiotherapy time interval were more likely to cause grade≥2 neutropenia (P = 0.016、P = 0.025). Further studies on factors influencing sternal dose showed that Thoracic ratio and BMI were negatively correlated with sternal V40 (β = -0.304 P = 0.02、β = -0.259 P = 0.05). For patients receiving adjuvant radiotherapy after modified radical mastectomy for breast cancer, reducing the sternal dose can reduce the incidence of grade 2 or higher hematological toxicity. In addition, some clinical parameters such as baseline values of blood cells, ki-67, and time interval of chemoradiotherapy can also affect hematological toxicity, which should be paid enough attention.