Effect of Pelvic Bone Marrow-Sparing on Acute Hematologic Toxicity in Rectal Cancer Patients Undergoing Chemoradiotherapy

Abstract

To investigate whether pelvic bone marrow sparing (PBMS) could reduce the incidence of acute hematologic toxicity in rectal cancer patients undergoing chemo-radiotherapy. 84 rectal cancer patients were selected and divided into the IMRT Group (42 cases) and the PBMS-IMRT Group (42 cases). All patients underwent concurrent chemo-radiotherapy. The PTV was prescribed with a total dose of 50∼50.4Gy in 1.8∼2Gy fractions. Capecitabine combined was administered concurrently with pelvic radiation. The pelvic bone was contoured both for the PBMS-IMRT and IMRT groups. Only the pelvic bone in PBMS-IMRT group was prescribed by:V10≤85%,V20≤65%,V30≤45%.The mean dose (Dmean) and the volume of each organ at risk (OAR) with dose range from 5 to 50Gy (e.g., V 5, V10, V15, V20, V25, V30, V35, V40, V45, andV50) was calculated for all the patients from the two groups. The patient acute hematologic toxicity (e.g. patient with symptoms of leukopenia, neutropenia, anemia, or thrombocytopenia) was recorded according to RTOG scoring scale. Independent sample t test were applied for the dose-volume parameters, and card square analysis for clinical parameters. In terms of the OAR dose-volume parameters, the V5∼V35 and Dmean for the pelvic bone, left femoral head and the right femoral head significantly (p<0.05) decreased for the PBMS-IMRT Group compared with the IMRT group. There was no significant difference in any dose-volume parameters for the bladder. As for PTV dose distribution, there was a significant (p=0.001) improvement of the target conformity in the PBMS-IMRT group. In addition, the dose homogeneity was also improved by 14.5% for this group, although not significantly (P=0.108). For the following acute hematologic toxicity observation, the numbers of the patients with grade 0, 1, 2, 3, 4 were 12, 6, 14, 10, and 0 respectively for the IMRT group. Meanwhile the corresponding numbers were 10, 19, 12, 1, and 0 for PBMS-IMRT group. The incidence of grade 2 or upper acute hematologic toxicity in the PBMS-IMRT group was significantly reduced (31%, 13/42 vs. 57.1%, 24/42, p=0.027). There was no incidence of grade 2 or upper acute cystitis in both of the two groups. The marrow-sparing of the pelvic bone significantly reduces its dosage as well as the left and right femoral head. Patients with pelvic bone marrow-sparing had lower incidence of the grade 2 or upper acute hematologic toxicity compared with those without marrow-paring. Pelvic bone marrow-sparing can benefit patients with rectal cancer undergoing chemo-radiotherapy.