Session Item

(1) To explore the association between clinical and dosimetric parameters with acute hematologic toxicity (HT) in locally advanced rectal cancer (LARC) patients treated with Fluorouracil (5-FU) -based preoperative concurrent chemoradiation (CRT); (2) To provide potential predictors for HT in pelvic CRT planning; (3) To ascertain the dosimetric benefits in bone marrow sparing (BMS)-VMAT  compared with 3DCRT in the treatment of LARC.

Data from 68 LARC patients treated with 5-FU based neoadjuvant CRT were investigated. The pelvic bone marrow (PBM), including lumbosacral (LSBM), iliac (IBM) and lower pelvic (LPBM), were contoured and dose-volume parameters were extracted. Blood cell nadir involving hemoglobin, white blood cell (WBC), platelet and absolute neutrophil count (ANC) were collected and HT was graded according to CTCAE v5. Association between clinical and dosimetric variables and HT grade 2 or above (> 2) were tested using logistic regression analysis. P-value < 0.05 indicated statistically significance. 20 patients were further selected for dosimetric comparison between BMS-VMAT and 3DCRT generated using Eclipse planning system. Conformity index (CI) and homogeneity index (HI) to planning target volume (PTV) were analyzed. DV parameters to PTVs, PBM, bladder, bowel space (BS) and femoral heads (FH) were compared using Wilcoxon Signed-Ranks Test and statistical significance was considered when p <0.05.

The incidence of anemia ≥2, leukopenia ≥2 and neutropenia ≥2 were 20.6%, 35.4% and 26.5%, respectively. Sex and PBM-V40 was found associated with leukopenia ≥ 2 and anemia > 2 respectively. Female patients were more likely to have leukopenia > 2. Increased PBM-V40 was correlated with a higher likelihood to develop anemia > 2. In dosimetric comparison of BMS-VMAT and 3DCRT, similar dose coverage and HI of PTVs were obtained (p> 0.05) while CI was found significantly higher in BMS-VMAT (p<0.05). Moreover, dose to PBM, bladder, BS and FHs were significantly reduced in BMS-VMAT compared with 3DCRT (p<0.05). Dose to PBM-V40 decreased by 48% in BMS-VMAT which was believed to lower the risk of anemia > 2 development (p <0.05). 

Gender was found to be associated with the risk of having leukopenia > 2 whereas PBM V40 was shown to be a potential predictor for anemia > 2 since there were correlation between PBM V40 and anemia > 2. This study also demonstrated that BMS-VMAT could be effectively reduce the dose to pelvic bone marrows, bladder, bowel space and femoral heads. Therefore, BMS-VMAT was recommended for reducing bone marrow dose in neoadjuvant concurrent CRT.