| Objective:Preoperative concurrent radiochemotherapy has become a standard treatment for patients with Stage II / III resectable rectal cancer [1,2]. Compared with postoperative concurrent radiochemotherapy, the preoperative concurrent radiochemotherapy not only can further reduce the local recurrence rate of rectal cancer, but also can reduce the adverse effects of radiotherapy.But compared with radiotherapy alone, concurrent radiochemotherapy increased efficacy, while acute hematologic toxicity in patients(hematologic toxicity, HT) also significantly increased, thereby increasing the use of the opportunity of colony-stimulating factor for patient during treatment, and severe bone marrow(bone marrow, BM) suppression can increase the opportunity of hospital infection, blood transfusions and antibiotic use, can result in the delay of concurrent radiochemotherapy, the interruption of radiotherapy and the dose reduction or termination of chemotherapy, can cause reduced efficacy of patients and increased hospital costs [3,4]. It has been reported that the volume of pelvis and lumbar BM accepted 10Gy(Gray), 20 Gy irradiation(V10, V20) was significantly associated with acute HT [5]. Based on this, we studied preoperative concurrent radiochemotherapy on colorectal cancer radiotherapy of bone marrow protection IMRT. Comparing the bone marrow IMRT(bone marrow-sparing intensity-modulated radiotherapy, BMS-IMRT) with not limited to bone marrow traditional three-dimensional radiation therapy(three Dimensional Conformal Radiotherapy, 3D-CRT), found their differences in target volume coverage and organs at risk(organ at risk, OAR) protection, exploring the advantages of BMS-IMRT dosimetry and the protect value on the bone marrow protection. Methods:Selected 10 patients with Stage II / III resectable colorectal cancer in Tai’an City Cancer hospital who accepted preoperative concurrent radiochemotherapy between February 2012 and February 2013, designed BMS-IMRT treatment planning and without limited to the bone marrow with conventional three-dimensional radiation therapy(three Dimensional Conformal Radiotherapy, 3D-CRT) scheme for comparison. According to the definition of ICRU(International Commission on Radiation Units and Measurements) Reports 50 & 62, we outlined the target volume and the organs at risk for the selected patients. The traditional three-dimensional radiation treatment plans without limiting to bone marrow were used forward design, and the BMS-IMRT plans were used reverse design. The prescription dose were all 50Gy/25f/5w.The chemotherapy regimen was capecitabine 1600mg/m2/d, successive for 2 weeks and stop 1 week for 4 weeks, beginning the first day of radiotherapy orally. The treatment plans were evaluated by average dose(Dmean), maximum dose(Dmax), minimum dose(Dmin), conformity index(CI), heterogeneity index(HI), the extent coverage of isodose curve and Dose-Volume Histogram(DVH). The evaluation criteria were: 1.PTV dose requirements include: a.V100% ≥ 95%; b.V93% ≥ 99%; c.V110% <1%; 2. organs at risk: bladder: V50 <50%; small intestine: V50 <30%, Dmax ≤ 50Gy; femoral: V50 <5%; 3. The accepted dose of bone marrow must follow the requirements of A V5<90%-95%; b.V10 <80%-85%; c.V20 <60-65%; d.V30 <40%-50%. The statistical analysis of the data was used by SPSS19.0 software.Results:10 cases of BMS-IMRT plans and 3D-CRT plans came up to the required standard of PTV dose. Target volume conformity index(CI) of BMS-IMRT was the best. Instead, the target volume heterogeneity index(HI) was 3D-CRT3F> BMS-IMRT. The target conformity and uniformity of BMS-IMRT plans were better than 3D-CRT plans. Compared with conventional 3D-CRT plans, the accepted dose of bladder, small intestine in BMS-IMRT plans were significantly reduced, the small intestine V50 is 4.79 ± 0.07; bladder V50 was 33.91 ± 2.97; femoral V50 was 0.09 ± 0.25. Compared with conventional 3D-CRT plans, the bone marrow dose in BMS-IMRT plans were also significantly reduced, the V5, V10, V20 and V30 of bone marrow in BMS-IMRT plans were 93.12%±1.07%, 83.40%±1.12%,63.09%±1.06%and 46.78%±1.95% respectively, which in conventional 3D-CRT plans were 95.95%±2.70%, 87.16%±2.67%, 69.94% ± 3.77% and53.51%±4.99%.Conclusions:Compared with the conventional 3D-CRT plans, bone marrow-sparing intensity-modulated radiotherapy(BMS-IMRT) which take limitation to bone marrow can exploit the dosimetric advantages to reduce the radiation volume and the low dose volume of bone marrow significantly, under the conditions of certifying the target volume coverage and not reducing the limitation standard on organs at risk. BMS-IMRT can reduce the incidence and severity of HT and improve the tolerance of preoperative concurrent radiochemotherapy obviously. |
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