More and more attention tend to the application of intensity modulated radiation therapy (IMRT) treatment of malignant cancer.The accuracy of the radiotherapy is raising because of the increased radiosensitivity of bone marrow.Imaging modality quantified the distributions of bone marrow.,which could further reduce the volume to avoid.Bone marrow-sparing intensity-modulated radiotherapy can reduce the pelvic bone marrow irradiation volume,which may reduce the probability of acute bone marrow inhibit.It is worthy of application widely.

ObjectiveTo investigate the dosimetric difference in the application of RapidArc using 6 and 15 MV X-rays for radiotherapy of multiple hepatic malignancy.MethodsA total of 12 cases with multiple hepatic tumors ( primary 5 cases and secondary 7 cases) were selected.All patients underwent the three dimensional CT simulation in free breathing.For each patient,RapidArc plans with single or two 358° arcs using 6 or 15 MV X-rays were designed respectively,the prescription dose was 2Gy per fraction × 25 fractions.The dosimetric differences were compared among RapidArc plans.ResultsAll of RapidArc plans could meet the clinicalrequirement.There were no significant differences in the conformity index ( CI ),homogeneity index ( HI),the maximum dose and the minimum dose of PTV among RapidArc plans ( P ＞ 0.05).All the CI could get to 0.91 and HI could get to 0.88.In the RapidArc plans with two 358° arcs,the Vs,V10,V15 of normal liver were higher than with single arc,while V20,V25,V30,V35,V40 were lower than with single arc.There were no significant differences in the different radiation dose of normal liver,stomach,duodenum and spinal cord among different plans ( P ＞0.05 ).The monitor units of RapidArc plans using 6 MV X-rays increased 12％ compared to 15 MV averagely.CondusionThe 6 MV X-ray would be selected chiefly in the radiotherapy of multiple haptic tumor using RapidArc with whole arc(s).

Objective To compare and analyze the dosimetric characteristics of the intensity-modulated arc therapy (RapidArc) combined with active breathing coordinator (ABC) in the thoracic esophageal carcinoma radiation therapy. Methods Ten thoracic esophageal carcinoma patients undergoing radiotherapy were selected for this study.The CT simulations were performed under three breath patterns respectively:moderate deep inspiration breath-hold (mDIBH) with ABC aid; Set the trigger threshold to 80％ of the peak of the respiration curve; and free breathing (FB).Based on the corresponding CT image sets,three treatment plans were generated for each patient respectively:Arc-ABC( three small arcs),ArcFB (consisted of two coplanar full arcs) and IMRT-FB plan.The following dosimetric parameters were compared among different plans:D2％,D98％,V95,homogeneity index ( HI),conformal index ( CI ) the percentage of volume receiving dose of over x Gy (Vx),monitor unit (MU),control points and treatment time.Results The planning target volume ( PTV ) of FB was 376 cm3 which decreased to 260 cm3 after using ABC.For mDIBH and FB patients,the total lung volumes were 5964.6 cm3(35％ more than FB) and 3838.8 cm3 respectively; the heart volumes were 524.4 cm3 and 642.7 cm3 respectively. No significant difference was observed among Arc-ABC,IMRT-FB and Arc-FB in terms of D2,D98,V95,CI and HI.For Arc-ABC plans,there were significant decreases of radiation dose in total-lung's V10,V20,V30,V40 and mean lung dose ( F =4.38,5.34,4.07,3.89,4.28,P ＜0.05).Various dose decreases of heart V20,V3,V40,Dmean and spinal cord Dmax were observed,yet no statistically significant difference existed.The MUs and total control points of Arc-ABC plans were significantly lower than other plans ( F =26.86,12.56,P ＜ 0.05 ).Conclusions When thoracic esophageal carcinoma patients were treated with radiotherapy,the combined utilization of RapidArc and ABC can potentially decrease the volume of irradiated lung yet escalate the dose in target.