The Impact Of Different Definitions Of Lung Volume On The Dosimetry Of Radiotherapy In Lung Cancer

Purpose: To evaluate the impact of different definitions of lung volumeon the dosimetry of radiotherapy in lung cancer.Materials and MethodsPatient selection: This study was performed on retrospectively analysisof CT data of20consecutive patients treated in Fujian Cancer Hospitalin2010. All patients suffered from an inoperable or unresectable lungcancer without serious pulmonary diseases such as serious lung functiondisability or tuberculosis. Of the20patients,13were male, and7werefemale; the median age was59years (43-79years). The pathologydistribution referring to WHO classification included nine squamouscarcinomas, eight adenocarcinomas, and three small-lung cancers. Allpatients completed the radiotherapy.Simulation and radiation plans: The spiral CT scan was carried out forplanning purpose, The CT anatomical data were transferred to Pinnacle8.0m Planning System with three-dimensional reconstructions. Attendingphysicians delineated gross tumor volume (GTV), clinical target volume(CTV), planning target volume (PTV) of GTV and CTV and organs at risk (OAR).OARs including lung, esophagus, trachea, heart, liver, cord. Lung volumewas contoured according to four different definitions, which resulted infour groups of V20、V5and MLD. Group A: double lungs volume contains GTV;Group B: GTV was excluded from double lungs volume; Group C: CTV wasexcluded from double lungs volume; Group D: PTV-GTV was excluded fromdouble lungs volume. The comparisons of Group B with other three Groupson dosimetry were analyzed with paired t-test. The treatment plans weremade into IMRT (Intensity Modulated Radiation Therapy) plan with suchprescription:66Gy to GTV in2.2Gy daily fractions and54Gy to GTV in1.8Gy daily fractions. In consideration of adequate covering of GTV, PTVreceived at least95%of the treatment dose. Constrains were placed onthe dose to the spinal cord (45Gy), esophagus (V60<50%), heart (V40<50%),trachea（60Gy）, lung (V20<25%~30%; MLD<20Gy).Comparison of the lung-related parameters: Results were analyzed inpaired T-test (double sided, α﹦0.05) with SPSS statisticalsoftware(version13.0for windows). As the definition of group B is widelyuse], the analysis was based on the comparison of dosimetric parameters(V5、V20、MLD) obtained from Group B with Group A, Group C, Group D,respectively. The limit of significance for test was P<0.05.Results: Different definitions of lung volume caused obviously change onlung dosimetry (P<0.000).The rangeability was positively correlated withGTV. Moreover, the correlation with V20was greater than V5and MLD. WhenGTV/double lungs volume represents the GTV, the impact of the GTV to thelung dosimetric parameters could be better presented.Conclusions: There was statistical variation of lung-related parameterswith various definitions. As the variation hampers the comparison amongdifferent research institutes, the definition of lung volume should bestandardized. We recommend that the definition of the total lung volumeshould be both lung volumes minus the PTV, which might help to predictRP, because of preeminent representative of the actual exposure lungvolume. However, due to the constraint of dosimetric study, we plead forfurther perspective study designed for deciding which definition is morepreferable with relative recommendations on dosimetric parameters.