The New Method Of Target Breathing Movement Controlling Used In Precise Radiotherapy For Tumor

With the fast development of computer technology, the tumour radio-therapy technology has continually gain significant development, at present, the three-dimension conformal precise radio-therapy(3D-CRT) technology of tumour has replaced traditional lagging two-dimension radio-therapy technology and become the main stream of radio-therapy technology in nowadays. According to precise radio-therapy, which is characterized by "precise location、precise treatment、precise planning", should demand for the "high accuracy, high dosage, high treatment efficiency and low common tissue damage "(three "high" and one "low").However, the breathing movement of human body leads to the displacement of tumour target compared with the static radiation field, so in order to make sure that tumour can always locate in the high dosage region during the radio-therapy time, our traditional method is to enlarge the edge of "clinical target" to satisfy the high dosage demand, but at the same time more normal tissue and organ would get the higher dosage.So breathing movement of tumour target has become the "bottle neck" which has limited the treatment efficiency of precise radio-therapy. In order to eliminate or reduce the bad effect to the high efficiency of the precise radio-therapy which is caused by the breathing movement, many professors have introduced several methods which are used to control the breathing movement of tumour target in large amount of papers, these methods can be described as follows:1 Deep inspiration breath-hold technique 2 the technology of utilizing pressure device 3 Active breathing Control method 4 respiratory gated irradiation system 5 real-time tumour tracking radiotherapy and so on, all of these methods can reduce the breathing movement displacement in some extend or make the tumour target be static to the radiotherapy field. However, there are some defaults exist in these methods, for example, the method 1,2,3, patient breathing movement should be restrained during the radiotherapy time, which are not suitable for some lung tumour patients; although method 4 can make the patient keep breathing during the whole radio-therapy time,but accelerator can only emit the X ray at the particular time and in other time the X ray beam should be shut down, so in this situation the whole treatment time would be largely prolonged,and the switch of X ray beam should be turn on and shut down frequently, which may do harm to machine’s function. The fifth method can be achieved by the main stream machine-cyber-knife, which can drive the radiation field to track the location of tumour target, but the tracking method of cyber knife is achieved through real-time tracking the metal marks which are put on the body skin,so this tracking method would unavoidable bring certain errors.On the base of the above analysis, this paper proposes a new method which can effectively reduce the breathing movement displacement,this method need to be achieved by limiting the patients’breathing movement, meanwhile need not weaken the influence of tumour targets’ breathing movement by interrupting the X ray beam,compared with the above five methods, this method seems to be more superior to some extend. The core idea of this method is "inversely tracking", which is achieved by designing a whole mechanical system drove by stepper motor, the movement platform(tracking platform) of the mechanical system drives the patient body to move inversely relative to the tumour target in real-time during the radiotherapy time, so do this can we reduce the breathing movement displacement relative to the static radiation field. In order to achieve the goal of precisely and inversely tracking the tumour target in real-time, this paper mainly introduces two available schemes, the first scheme is to achieve displacement of tumour target in default interval through the image-guide manner, and then utilize relative software to transform the displacement into the pulse controlling signal of stepper motor to drive the tracking platform, which make the inverse displacement of tracking platform equal to the breathing movement displacement of tumour target. The first idea is achieved depending on the manner of X-ray image, which would lead to make patient receive more extra X-ray dosage, then in this situation this paper propose another scheme which indirectly achieve patients’ breathing movement signal through the breathing air flow sensors, in the light of the hypothesis that the breathing air flow signal is synchronous to the breathing movement signal of tumour target so this air flow signal can be transformed to the controlling signal to drive the tracking platform to inversely track the tumour target.This paper analysed the concrete course of the two schemes in detail, when adopt the second scheme, although the patient can avoid absorbing extra X-ray dose, the displacement signal of tumour target can not be achieved during the treatment time, so it is necessary to build the "displacement-time" math function model before the treatment, the definite course is as follows:to scan the human body tissue through CT-scanner with CINE mode, in order to achieve the transverse section images sequence, which is reconstructed into coronal section, and then adopt the "Snake" algorithm and "block match" algorithm used to track the moving target, these two algorithms can be combined to perfectly construct breathing movement function model of the target. The fourth chapter of this paper mainly analysis the mechanical structure design which is the hardware part of the inversely tracking system and the design of inverse tracking main controlling circuit module, the main part of the mechanical structure is the two-dimension linear movement platform model drove by the stepper motor, the main controlling circuit module adopts the 89S52 SCM as the core chip, which receives the breathing movement signal of human body extracted from the thermal circuit;then the analogy breathing movement signal is converted into the discrete digital pulse signal which can be used to control the running speed and running direction of stepper motor through C programming manner, in the end, the stepper motor can drive the tracking platform to inversely track the tumour target. The chapter 5 of this paper show the physical model of the circuit part and mechanical part included in the tracking system and the "the intelligent controlling software system on the base of "VC++" programme environment ", besides, at the end of this chapter we test and verify the accuracy of the "Snake" algorithm and "block match" algorithm used to track the moving target through "video image tracking for the periodic motion law of spring oscillator " experiment.The method that inversely track the breathing movement of tumour target,can effectively reduce breathing movement displacement of the target, but we still have to solve many problems, and in the end,this paper gives an overview and puts forward the issues to do in the future.