Analysis Of Dosimetric Factors For Acute Radiation-induced Small Bowel Damage Following Intensity-modulated Radiotherapy In Patients With Abdominal-and-pelvic Tumor

Objective: To study acute radiation-induced small bowel damage in patients with abdominal-and-pelvic tumor radiation therapy, in order to explore the clinical and dosimetric factors associated with grade≥2 acute radiation-induced small bowel damage in abdominal-and-pelvic cancer patients treated with intensity-modulated radiotherapy(IMRT).Methods: 63 patients with abdominal-and-pelvic tumor receiving intensity-modulated radiation therapy from January 2010 to October 2013 at Third Hospital of Hebei Medical University were retrospectively reviewed, from which male and female patients were 37 and 26, respectively. The median age was 61 years, and 28 patients were abdominal cancer, 35 patients were pelvic cancer. With or without prior abdominal surgery were 43 and 20. They were scanned with 5mm layer spacing CT, and CT images were transmitted to CMS Xio4.4 planning systems. Target dose distribution and small bowel exposure doses were analyzed by treatment planning systems. Irradiation was delivered at 1.8-2.0Gy, 5 times per week to a total dose of 45-66 Gy. Acute radiation-induced small bowel damage was graded by using the Common Terminology Criteria for Adverse Events version 3.0. Analyze the correlations between the clinical characteristics parameters and dose volume parameters[absolute small bowel volume received ≥5Gy、10Gy、15Gy、20Gy、25Gy、30Gy、 35Gy、40Gy、45Gy、50Gy、55Gy、60Gy(V5、V10、V15、V20、V25、V30、 V35、V40、V45、V50、V55、V60)and Dmax 、 Dmin 、 Dmean 、 D2 cc 、 D5 cc ] and grade 2(and above) acute radiation-induced small bowel damage. SPSS 19.0 software package was used for statistical analysis. T-test or chi-square test was used to univariate analysis of the clinical characteristics parameters and dose volume parameters associated with acute radiation-induced small bowel damage. For multivariate analysis of meaningful factors, we used logistic regression analysis to Select statistical significance of the independent factors. Using logistic regression model and ROC curve to evaluate dose volume parameters predictors associated with acute radiation-induced small bowel damage.Results: All of the patients after the IMRT in acute observation period, the total incidence rate of acute radiation-induced small bowel damage was 34.92%(22/63), Grade ≥2 small bowel toxicity occurred in 20.63%(13/63) of patients in the study. 9 cases were 1 grade, 11 cases were 2 grade, 2 cases were 3 grade and 4 grade or above level of acute radiation-induced small bowel damage was not found. Patients with various clinical factors such as gender, age, with or without abdominal pelvic surgery, Whether chemotherapy during radiation therapy or position of the target were not significantly associated with acute radiation-induced small bowel damage(P>0.05). On univariate analysis, grade≥2 acute radiation-induced small bowel damage was associated with absolute small bowel volume(cm3)receiving a dose of at least 20-60Gy( V20-60Gy), D2 cc and D5cc( P < 0.05). Multivariable analysis found that the absolute small bowel volume V20, V55 were independent factors of grade ≥2 acute radiation-induced small bowel damage(P = 0.025 and 0.004). In order to find the radiation tolerance dose of the small bowel, ROC curve analysis was used, the results showed that the areas under the curve of V20, V55 were 0.831 and 0.975, respectively. Appropriate threshold for V20, V55 ROC curve to predict in patients with abdominal and pelvic radiotherapy cancer, V20, V55 area under the ROC curve were 0.831, 0.975(P = 0.000). The accuracy of prediction was high, boundary values were 183cm3 and 2cm3. The incidence of grade ≥2 acute radiation-induced small bowel damage in patients with V20<183cm3 was 4.76%(2/42), significantly lower than of patients with V20 > 183cm3 52.38%(11/22). The incidence of grade ≥2 acute radiation-induced small bowel damage in patients with V55 < 2 cm3 was 4.00%(2/50), significantly lower than 84.62%(11/13) of patients with V55>2cm3(P = 0.000). When using V20、V55 as tolerated dose to predict acute radiation-induced small bowel damage the sensitivity was 0.846, the specificity was 0.800、0.960, respectively.Conclusions:1 The patients with abdominal or pelvic tumor after intensity-modulated radiation therapy, acute radiation-induced small bowel damage was grade 1-2,in this study, ≥grade 2 acute radiation-induced small bowel damage developed in 20.63%.2 Clinical factors were no significant correlation with ≥grade 2 acute radiation-induced small bowel damage.3 The V20-60, D2cm3 and D5cm3 of small bowel were important dosimetry parameters of acute radiation-induced small bowel damage factor, could better predict the occurrence of acute radiation-induced small bowel damage.4 The absolute small bowel volume of 20 Gy and 55 Gy were probably the most valuable predictor for patients with acute radiation-induced small bowel damage, when V20 > 183 cm3 and V55 > 2 cm3, the incidence of ≥ grade 2 acute radiation-induced small bowel damage would be increased significantly.5 When we evaluate the treatment planning, V20 = 183cm3 and V55 = 2cm3 can serve as radiation tolerance dose of the small bowel, should be restricted them in the appropriate range.