Delineating Biological Target Volume On PET-CT Image For Lung Cancer

Background:Although some phantom and clinical studies on the delineation of biological target volume(BTV) for lung cancer by PET-CT have been investigated, the influence of respiratory movement during PET-CT acquisition is still problematic. Researchers have paid much attention on how to draw BTV.Objective:To evaluate clinical values and to assess the optimal selection of threshold as well as influence factors of BTV delineation for lung cancer on PET-CT image.Method:The BTV delineation for radiotherapy(RT) by conventional nuclear medicine and PET,PET-CT was investigated based on the survey of nuclear medicine in Beijing.In order to confirm the usefulness of BTV delineation for lung cancer by PET-CT,a Meta analysis was performed according to the data cited from the foreign published studies.Phantom and clinical studies of BTV delineation for lung cancer by PET-CT were conducted in our hospital for the choice of threshold as well as the discussion of influence factors.Results:PET/CT can reduce the variation between observers and hardware fusion is superior to software fusion.A varied threshold of 40-50%which was concordant with the CT level of lung should be adopted.The indicators of ADV(Absolute Different Value) and ADV/ASV(Absolute Different Value/ Absolute Sum Value) between GTV_PET-CT and GTV_CT can be adopted to identify the difference between the subsets of GTV.The influence factors of BTV delineation using PET-CT are positively related to the total counts of ROI,background level(or the ratio of target/ background) and the diameter of the lesion.The equations of threshold-Area-B/S, which can be used to guide the choice of the threshold,were deived accurately based on phantom and PET/CT respiratory gating images.Furthermore,respiratory movement can influence the size and shape of the area,as well as SUV value on PET images with 2.04cm² of the average range of area between respiratory phases under the different thresholds.Biological target volume on PET and CT was clinically proved significantly different.Therefore,an ideal threshold for a given lesion should be modified according to the slice number,background and SUV of the images on PET/CT.Conclusion:BTV delineation for lung cancer by PET-CT has a great value in radiotherapy but China is still in the preliminary stage.Varied threshold and optimal CT level should be adopted in the BTV delineation on PET-CT images.Delineation of biological target volume for lung cancer by PET-CT can significantly change the strategy of radiotherapy planning and reduce the variation between observers.Uses of relevant equations of threshold-Area-B/S under different adaptive conditions and PET-CT respiratory gating method have special clinical significance in radiotherapy planning.