| Purpose: Based on Monaco 3.20 plan system, this assay is about the research of segment parameters of Intensity-Modulated Radiotherapy for cervical and upper thoracic esophageal cancer. In the condition of selected the radiation field number(field 7) and angle of incidence(3600 average). Through fixing the adjacent sub-field area difference, minimal width of the field, we evaluate the impact of the sub-field minimum area, sub-field minimum MU of treatment plans quality. This study will make reference for the optional of the radiotherapy plan for the patients.Methods: A total of 8 patients who were diagnosed, histologically proven cervical and upper thoracic Esophageal squamous cell carcinoma in our research treated. All the patients were treated with IMRT planned by Monaco 3.20 treating planning system. The doses of the planning target volumes(PTV1、PTV2) were respectively 6000 cGy, 5100 cGy, respectively, delivered simultaneously over 30 fractions to every patients. Through fixing the adjacent sub-field area difference(3.0 cm2), minimal width of the field(0.6cm),and changing the sub-field minimum area, sub-field minimum MU: minimum segment area(cm2) 3, 4, 5, 6,7,8; minimum segment monitor unit(MU) 5,6,7,8,9,10.We had designed six plans for each patient. There were Six plans were made for every patient with different step-and-shoot IMRT segment parameters(A total of 48 plans). P(3,5) denote the plan with minimum segment area 3 cm2, minimum segment monitor unit 5 MU, the similar definition for P(4,6), P(5,7), P(6,8), P(7,9), P(8,10). After completed all IMRT plan, collect and analysis the data, compare the difference between the assessment parameters in different plans. The Excel、SPSS 13.0 statistical software was used for analysis data.Results:1. The dosimetric parameters in each IMRT plan had no significant difference(P>0.05). However, the target volume had the increasing trend(means homogeneity and conformity getting worse) with the segment parameters increasing.2. The volume parameters and dose parameters of PTV2 in each IMRT plan had no significant difference(P>0.05).3. Organs at risk: Compared with P57、P68、P79,the spinal cord,s D1 cc were more larger in P810(P <0.05).Compared with P35、P46、P57,the lung’s irradiated volume V20 were more larger in P810(P <0.05). The lung’s V5、V10、V30 and MLD had no significant difference in each plan(P> 0.05). The spinal cord and lung’s irradiated dose gets larger respectively with segment parameters increasing.4. Dmean(patient) in each IMRT plan had no significant difference(P>0.05).The Dmean(patient) gets bigger respectively with segment parameters increasing.5. The segment number and MU : P810 and P35, P46, P57 had significantly different(P <0.05), P810 and P68, P79 had no significant difference(P> 0.05). The segment number and MU gets more and longer respectively with segment parameters decreasing. Appropriate therapy-time will be shorten.Conclusions:1. Segment parameters(sub-field minimum area, sub-field minimum MU) have effect on dose distribution and delivering in Monaco-based Esophageal cancer IMRT plans, the smaller the segment parameters was, the more uniform targets dose(CI、HI)and the better sparing of normal tissue(spinal cord、lung、patient), but the longer delivery time. Regardless of the T stage、the size of the target volume, trends of the assessment parameters were consistent. The proper parameters should be adopted for different case in order to achieve good tradeoff between better dose distribution and shorter delivery time, then the biological effects will get better, the therapeutic effect will be better.2. For the cases that tumor invaded to the tissue near to spinal cord、lung, it was proper that the parameters of minimum segment area and minimum MU chose 3 cm2 and 5MU, respectively. For the other cases that all OARs located far away PTVs, the segment parameters could be increased properly. |
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