| Background and Objectives:Thoracic malignancies, such as lung cancer and esophageal cancer, are among themain life-threatening diseases. Lung cancer, in particular, is one of the most commonmalignancies worldwide. The incidence and mortality rate of lung cancer in China ranksfirst among all the malignancies in the urban areas. Generally, more than70%lung cancerpatients are treated with radiation therapy. Whether lymph node metastasis occurs in thelung cancer patient, especially whether mediastinal lymph nodes are involed, largely affectsthe treatment planning and prognosis of the patient. The principle of radiation therapy is tokill tumor cells by ionizing radiation (X-rays), but consequently, some normal tissues andorgans will be inevitably damaged by the X-rays in the treatment process. Therefore, inpractice, radiation therapy is basically to irradiate the tumor area with a precise butsufficient therapeutic dose leaving as less irradiation to the surrounding normal tissuesand organs as possible, which will hopefully improve tumor control probability (TCP) andreduce normal tissue complication probability (NTCP) of radiotherapy. In view of this, toperform lung cancer radiotherapy, it is very important to study the spatial positions andradiation dose distribution of lung lesions, mediastinal lymph nodes and organs at risk (OR),which cannot be measured directly by instruments. Therefore, it is essrntial to develop anew method to monitor the spatial position and the radiation dose distribution of organs inthe human body.The Chinese visible human (CVH) chest dataset forms a visible basis for calculatingradiotherapy dose in lung cancer with a Chinese human body model. In the treatmentplanning system (TPS), the spatial position of each organ in the human body can be betterobserved and the tissue dose distribution can be simulated and calculated using the digital model. In this way, a more reasonable radiotherapy program can be developed and moreprecise dose distribution can be achieved so as to improve the curative effects of the lungcancer radiotherapy and reduce the radiation complications. In lung cancer radiotherapy,monitoring the actual exposure doses of lung lesions, mediastinal lymph nodes and OR isinseparable from the irradiated human chest simulation model. As a substitute for thehuman body, irradiated simulation phantom can be used to simulate the exposure situationunder actual irradiation conditions, the environment of various tissues and the sensitiveorgans of the body. The actual exposure dose can be monitored effectively by installingdetection equipment, which has become an important tool in modern radiotherapy. Thephantom and its mathematical model have been advised by ICRU Report No.48to beapplied to treatment. Combining computer graphics and digital simulation with the realphysical models in studying the radiation doses in the target areas and OR is a typicalexample of combining the digitized radiation therapy model with the radiation simulationphantom.In our study, advanced digital technologies, such as digitized visible human datasets inthe Third Military Medical University and Chengdu Dosimetric Phantom (CDP) of XinqiaoHospital’s radiotherapy center, are fully utilized and integrated with multidisciplinaryknowledge, such as medical image reconstruction, image format conversion, registrationand fusion. First of all, three-dimensional reconstruction of mediastinal lymph nodes willbe realized and then combined with CDP to monitor the actual exposure dose in themediastinal lymph nodes, target areas and OR so as to evaluate the dose distribution indifferent lung cancer radiotherapy modes. Eventually, the radiation treatment planningoptimization program can be realized, which takes into account the effects of radiotherapyand complications.Methods1. The thoracic section (from the pleura to the diaphragm) of the first CVH femaledataset was selected for the study. The cross-sectional contours of mediastinal lymph nodesand the adjacent structures were outlined and defined using Adobe Photoshop, and then thethree-dimensional reconstruction and visualization of these structures were realized usingthe Amira software program.2. Based on the construction of the three-dimensional anatomical model of mediastinal lymph nodes and the adjacent structures, the digital human body data, with advantages ofhigh definition, high resolution and high recognition, were combined with the CT data ofthe same sample to convert the digital human chest data into standard DICOM data usingthe Matlab software program. In the Eclipse treatment planning system, the two types ofdata image were registered and fused, characterizing CT data with high recognition. On thefusion image, the mediastinal lymph nodes, simulated lung lesions and OR were outlined,and the radiation treatment planning was developed under three kinds of radiotherapymodes (3D-CRT, IMRT, VMAT). The spatial position and the radiation dose distribution oflung lesions, mediastinal lymph nodes and OR in the human body were observed, and thena comparison was made between the radiation dose distribution of target areas and ORunder these three kinds of radiotherapy mode.3. Chengdu Dosimetric Phantom was adopted in this study. The central points of thedistribution areas of the mediastinal lymph nodes and the center of OR were accuratelydrilled, and then CDP was scanned by CT simulation. Based on the elastic deformation ofMIM software, the digitized anatomical model data image of mediastinal lymph nodes inDICOM format and the CT positioning data image of CDP were registered and fused. Onthe fusion image, the radiation treatment planning was developed under three kinds ofradiotherapy modes (3D-CRT, IMRT, VMAT), under which the radiation dose distributionof lung lesions, mediastinal lymph nodes and OR in the human body were observed. Dosemonitoring equipment was installed in the distribution area of mediastinal lymph nodes, thepunch points of OR and the center of simulated lung lesions in CDP to performradiotherapy. Next, the actual exposure doses of mediastinal lymph nodes, lung lesions, andOR were monitored and a comparison was made between the actual and theoreticalradiation doses under different radiation patterns.Results:1. The three-dimensional reconstruction of mediastinal lymph nodes and the adjacentstructures was established. The reconstructed digital model clearly demonstrated the shapesof mediastinal lymph nodes and the adjacent structures and their spatial relationship. Thereconstructed structures were able to be displayed separately or as a whole, and rotated orcut at any angle.2. Digitized visible human data was converted to standard DICOM format data, and integrated with CT data image in the mediastinal area and double lungs. On the fusionimage, ten kinds of lesions in different parts of the lung and positive mediastinal lymphnodes in the lung cancer patients were outlined and the radiation treatment planningoptimization program was designed under different radiotherapy modes. Dose-volumehistogram (DVH) was observed and statistical analysis of dose distribution in the targetareas and OR was performed. Significant difference was found in the target areas, OR andconformity index (CI)(p <0.05), but not in homogenity index (HI)(p>0.05) underdifferent radiotherapy modes. In view of PTV,3D-CRT had higher D2, D98, and DmeanthanIMRT and VMAT, while there was no significant difference between IMRT and VMATexcept in D98. CI was high in IMRT and VMAT, but low in3D-CRT. In regard to OR, IMRThad the lowest irradiation value in V20, V30, and Vmeanof double lungs and spinal cord,while3D-CRT had the highest, with VMAT in the middle.3. The central points of the second, fourth and seventh areas of the mediastinal lymphnodes in CDP were accurately punched, and the devices for monitoring radiation dose wereinstalled, leading to the establishment of an irradiation simulation model for monitoring thedose of mediastinal lymph nodes. Digitized visible human chest data images and the CTpositioning data images of CDP were registered and fused in double lungs and mediastinalregion based on the elastic deformation of MIM software. On the fusion image, threeradiation treatment planning programs were worked out. After exposure under theirradiation simulation model5times, the actual exposure doses of target areas and OR weremonitored. The actual and theoretical adiation doses were compared, and then statisticalanalysis was performed. We found a close value between the second area and the lunglesions, but an obvious deviation in other districts and OR, suggesting that appropriateamendments should be taken to be in accordance with the actual dose when designing theradiation treatment planning.Conclusion:1. By building the digital model of mediastinal lymph nodes, the distribution of themediastinal lymph nodes and their spatial relationship with the adjacent importantstructures are displayed clearly, thus providing a morphological basis for better anatomyteaching, clinical surgery, lung cancer staging and radiotherapy.2. IMRT is the preferred procedure in lung cancer radiotherapy planning and optimization, especially in the radical radiotherapy using digital model of mediastinallymph nodes. In terms of both dose distribution in target areas and protection of normallung tissues, IMRT has more advantages than3D-CRT and VMAT.3. In lung cancer radiotherapy, the actual exposure doses in target areas and OR aremonitored by the irradiation simulation model which monitors the dose of mediastinallymph nodes in thoracic radiotherapy. Under the three kinds of radiation modes, the actualand theoretical radiation doses have some deviations in other areas of mediastinal lymphnodes and OR except the second area and the lung lesions. Therefore, the radiotherapyplanning should be appropriately modified in different radiotherapy modes.Research significance:1. Dosimetry simulation of the digital model of mediastinal lymph nodes in radiationtreatment planning optimization has been realized, which lays the foundation for anin-depth dose study of the lung cancer radiotherapy and also provides references forcarrying out dosimetry simulation work in other tissues or organs in the human body usingsimilar methods.2. Although the irradiated simulation phantom is a standard human body model, thebody tissue-equivalent materials of the simulator and the elastic deformation of the MIMsystem can be used to realize the simulation of individualized radiotherapy planoptimization in cancer patients.3. This study can change the monitoring defects of actual radiation dose in the tissuesand organs in the modern radiotherapy and achieve accuracy, objectivity and repeatabilityin radiation dose monitoring. This can help to further improve the reality and efficiency ofclinical radiotherapy research so as to improve the efficacy of radiotherapy, reducecomplications, and ultimately improve the prognosis and quality of life of cancer patients. |
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