Technical Research On Adaptive Radiation Therapy Of Head And Neck Cancer Based On MVCT Images

Adaptive radiation therapy(ART) is a close-loop feedback process to evaluate patient-specific anatomic(such as tumor retraction,weight loss,or internal motion)and physiologic(such as hypoxia)changes by collecting the daily images of patients(such as CT,MRI,etc.)during treatment.The individualized radiation therapy can truly be done by analyzing the dose difference between the fractional and original plans of patient and modifying the delivered mode based on the variation of individual patient.For head and neck cancer,implementing ART has an important clinical value due to the significant anatomical changes in the target and its surrounding organs at risk during radiotherapy.The important obstacle to the clinical application of ART is the lack of a set of reasonable and efficient workflow and ART software tools.To get it,this thesis invovles the technical research on ART of head and neck cancer based on megavoltage computed tomotherapy(MVCT)images of tomotherapy,focusing on the dose effect of the images,the basic ART criteria and the method of fractional dose accumulation,in order to achieve the accurate delivery of radiotherapy for the evaluation and adjustment of treatment plans.The main work and contributions of the thesis include:1)The clinical experimental basis on dose calculation of MVCT during ART was established.The image value-to-density table(IVDT)was created and the influences of related factors on IVDT were evaluated by using the MVCT images of phantom and patient.The feasibility on MVCT images was verified during ART,and the errors of dose calculation based on MVCT for head and neck cancer could be kept within 3%.2)The basic criteria for the implementation of MVCT ART in head and neck cancer was first proposed.The change rule of CTN(CT Number)in the MVCT images of patients during radiotherapy was analyzed.The correlation between CTN decrease and the reduction of relative volume of tissue was found.It was revealed that the change of physiological signal besides anatomical structure could be used as a trigger indicator during ART.3)A set of software tools for implementation and evaluation of ART were developed.A set of deformable image registration(DIR)tools were used to solve the problems between planned kVCT and daily MVCT.The method of fractinal dose accumulation was achieved.The workflow and clinical guidelines of ART in head and neck cancer were formulated by assessing the cumulative dose.The clinical practice of head and neck cancer(i.e.nasopharyngeal carcinoma)patients was tested.It proves the validity and operability of ART technical process and specifications,and has a clinical significance.