Dose-volume restriction analysis based on ≥grade II marrow suppression in radiotherapy for pelvic cancer

Objective To investigate the correlation between bone marrow suppression and the dose volume analysis of pelvic bone and provide reference for defining the parameters of bone volume-dose restriction during pelvic radiotherapy. Methods A retrospective analysis of 102 cases of cervical cancer, 53 cases of rectal cancer and 34 cases of prostate cancer in People′s Hospital of Xinjiang Uygur Autonomous Region from January 2013 to April 2016 was performed. All patients received pelvic irradiation at a dose of 50.0-50.4Gy, and a boost of 10-24 Gy was given for different types of tumors or tumor beds. Concurrent chemotherapy was carried out in patients with cervical cancer and colorectal cancer, and endocrine therapy was given to prostate cancer patients during radiotherapy. The parameters including the target bone volume, V10, V20, V30, V40, V50, and the grade of bone marrow suppression according to RTOG grading scale within 3 months after radiotherapy or 6 months post-radiotherapy were evaluated. The correlation between the irradiation bone volume and the grade of bone marrow suppression was assessed by univariate analysis. The relationship between the grade of bone marrow suppression and age, chemotherapy and radiotherapy dose was further analyzed by multivariate analysis. Results In patients with cervical, rectal and prostate cancer, the overall incidence rate of early bone marrow suppression was 77.5%, 79.2% and 70.6%, and 65.7%, 62.3% and 35.3% for ≥grade 2 bone marrow suppression, respectively. Late-stage bone marrow suppression occurred in 11 patients, grade Ⅱ in 7 cases, and the incidence rate of ≥grade 2 bone marrow suppression was 3.7%. The target bone volume in the cervical, rectal and prostate cancer groups was (746.30±27.84) cm3, (736.15±28.72) cm3 and (740.70±35.08) cm3(P=0.023), respectively. Univariate and multivariate analyses revealed that V10, V20, V30, V40 and CV10, CV20, CV30, CV40 were not significantly correlated with the grading of bone marrow suppression (all P>0.05), whereas V50 and CV50 were significantly correlated with bone marrow suppression (both P<0.05). ROC curve analysis demonstrated that V50=72.33 cm3 and CV50=9.42% were the diagnostic cut-off values for ≥grade 2 bone marrow suppression. Conclusions The incidence of bone marrow suppression is relatively high in pelvic radiotherapy, which is correlated with the irradiation bone volume and dose in the target area. At a total dose of 50 Gy, the incidence of ≥grade 2 bone marrow suppression is not associated with ≤V40 or absolute volume. Besides, it is not correlated with dose boost or whether chemotherapy is delivered, whereas it is associated with V50 and absolute volume. V50=10.23% and CV50=72.33 cm3 are the cut-off values for the incidence of ≥grade 2 bone marrow suppression. Key words: Pelvic neoplasm/radiotherapy; Bone marrow suppression; Pelvic bone; Dose restriction