Key Issues In Protection Of Organs At Risk In Lung Cancer Radiotherapy

Radiation therapy has become one of the main methods for treatment of all states of lung cancer.How to reduce and accurately evaluate the irradiated dose to organs at risk is one of the key issues.However,there still occurred several factors which led to more irradiated dose to the organs at risk or difficulty to accurately assess their irradiated dose,such as the irradiated dose caused by margins for consideration of geometric uncertainty of target,and the difficulty to choose the proper treatment technique,and the changes of anatomy structure or tumor volume in treatment of central type lung cancer using stereotactic body radiation therapy.The main contributions are listed as following:(1)A systematic research has been done on the robust optimization method based on geometric uncertainty analysis.The geometric uncertainty model of the clinical tumor volume,which was considered as an object function in optimization,was used to reduce the irradiated dose to organs at risk instead of using the planning target volume margin based on analysis of the characteristics of random errors in image-guided radiotherapy.The dosimetry of tumor and normal tissues was compared with that of the traditional method using margins.The result showed that the new method could effectively reduce the irradiated dose to the normal tissues in lung cancer radiotherapy,which was potentially valuable in clinical practice.The impact of the variations of geometric uncertainties on dosimetry of tumor and normal tissues was analyzed,and the results showed that dosimetry of lung and other normal tissues was sensitive to the geometric errors,which suggested that more attention should be paid to the delivery of volumetric modulated arc therapy plans.(2)The ratio of lung volume to tumor volume(LTR)was proposed as the metric to help to determine a proper treatment technique to decrease the lung dose,which was difficult for the variety of patient characteristics,including tumor volume,shape,location,and lung volume.The correlation between LTR and the mean lung dose(MLD)was investigated in current standard radiotherapy techniques.And it was found that there were different power-law correlations between averaged LTR and averaged MLD for the three techniques.The correlation was fitted to test if it was also existed in individual patients in adaptive radiation therapy by using their planning data.The findings suggested that LTR was a useful patient characteristic in determining a proper treatment mode.(3)A dose tracking technique using cone beam computed tomography and hybrid deformation registration was proposed in order to accurately evaluate the irradiated dose to organs at risk due to changes of tumor size or body structure in central type lung cancer using stereotactic body radiation therapy.The results showed that the hybrid deformation registration could effectively reduce the influence of image scattering using cone beam computed tomography.This technique was indicated to be valuable in accurate dose assessment of organs at risk and tumor,avoiding their unnecessary radiation damage and target leakage.