| Objective:Preliminary inquiredthe method and technology of the adaptive technique applied in the nasopharyngeal carcinoma radiotherapy. According to the problems we meet during the research process, explored its rationality, necessity and feasibility to give some clinical advice.Trydifferent adaptive approach to evaluate and eliminate all kinds of changes in the process of nasopharyngeal carcinoma radiotherapy and the effects they leaded to dosimetry. Methods: 1. Using cone beam CT technology by appropriate period to conventional intensity-modulated radiotherapy of nasopharyngeal carcinoma with the setup error correction. Record the online setup offset of the whole course of radiotherapy, and calculate the dosimetry caused by the setup error and the deviation from the original plan; 2. By using periodic cone beam CT image during the course of nasopharyngeal carcinoma radiotherapy offline to study the quantified analysis of anatomy structure changes.Then summarized its change rule and trend and calculated the dosimetry deviation caused by the deformable of the anatomy structure from the original plan; 3. After a period of the radiotherapy in nasopharyngeal carcinoma, start a CT scan to the patient again. Using two types of registration toevaluate the actual implementation of irradiation dose and deviation statistics of the comparisonwith the original plan. Then exploredhow to set the planning methods to achieve a expected effect. Results: 1.Using 10 cases of nasopharyngeal carcinoma(NPC) patients with online adaptive radiation treatment to explore for the setup error of the three direction. Turned out to be 0.180 +/- 0.119 cm in left and right; 0.136 +/- 0.112 cm in foot and head; 0.136 +/- 0.084 cm in before and after respectively. Its dosimetry deviation in target areas,such as D95 deviation reached to 2.27%, the dosimetry effect of the targetare no more than 5%; The rise of the dose of organ at risk for dose accounts for about 47.86%, some mainly organs such as brain stem have the Dmax variation of 3.28%(39~385cGy); Spinal cord have the Dmax variation of 4.53%(40~487cGy); Parotid gland have the Dmean variation of 6.58%(323-323cGy). 2. Through 18 cases of patients with nasopharyngeal carcinoma(NPC) using off-line adaptive scheme to found outthat patients with nasopharyngeal carcinoma using radiotherapy has obvious anatomy structure change.During the whole course the parotid gland volume have an average drop of 7.33 cm3(30.04%). The brain stem and spinal cord with random position deviation, about 3~4 mm of average.The skin has anobvious progressive shrinkage in the neck site. The average dosimetry deviation caused by anatomical changes of parotid gland is of 289.56 cGy(23.13%). 3.Using CBCT position correction weekly and CT after 20 fractions fortwopatients so that we can re-contouring and re-planning for the RT plan.Using deformation registration to get the actual delivered dose to get a comprehensive adaptive scheme to get the target dose compensation of 1% ~5% and about 8%~16% dose fall in normal tissues such as parotid gland. Conclusion: For the radiotherapy of nasopharyngeal carcinoma, there are many kinds of uncertainty factors during the course, such assetuperror, anatomical structure deformable, which will affect the dosimetry in the body. During the course, the accumulation of these effects will affectthe treatment and cause some irreversible change. Appropriate using of the adaptive technology during the course of radiation therapy to get the correction and the compensation of the individualized uncertainty and more preciseof the nasopharyngeal carcinoma radiotherapy is very necessary.For patients,the various solutions of adaptive radiotherapy, the reliability of the corresponding hardware and software technology are all need to be study further. The further application need more quantity and deeper research and development, which can make the adaptive technology better, more efficient and popularization innasopharyngeal carcinoma(NPC) radiotherapy. |
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