| BackgroundThe Development and Current Situation of the Radiotherapy As the continuous progress of modern radiation physics and radiation therapy technology, precise radiation therapy technology is becoming mature day by day. At the beginning of1990s, from the development of three dimensional conformal radiation therapy (3D-CRT) to intensity modulated radiation therapy (IMRT), precise radiotherapy has stood on the mainstream of radiotherapy, including Image-Guided Radiation Therapy (IGRT), Volumetric Modulated Arc Therapy (VMAT), Tomotherapy (TOMO) and True Beam Image-Guided Radiation Therapy and so on. All the equipment and technologies of beam is still an important part of radiotherapy in modern period.High Energy Electron Beam Therapy Medical high energy electron beam is produced by a linac, energy for the mega-Volt level. From the early1950s, high energy electron beam has been applied to radiotherapy, mainly on raying the shift of superficial lymph nodes, hemangioma cults, scar tissue and so on. It is counted that high energy electron beam is more or less applied to patients about fifteen percent in the whole process of radiotherapy at domestic superior radiotherapy center. When it comes to the treatment of superficial and eccentric lesion, compared to high energy X-ray, an advantage of high energy electron beam, is that by use of electron beam single field to ray, the maximum doses are lies on lesion tissue while the doses being rayed are very few on the tissues and organs of block.High Energy Electron Beam Lead Block The conformal radiation therapy of tumor formed by high electron beam is realized through plumbum lead. Lead block can convert regular exposure field into irregular one, making the radiation range shape consistent with the target shape’s shadow, which can protect some vital tissues and organs within the portal.The Dose Compensation of High Energy Electron Beam Therapy When lesion tissue is on the surface of skin, and moreover, the thick of lesion tissue is smaller than activating thick (the thick of the maximum dose point) of high energy electron beam, the maximum dose area of electron beam lies in the back of lesion tissue. The dose exposure on lesion tissue is lower, so some substances should be put on the surface of skin lesion area to compensate for tissue which means playing an activating part and making the whole lesion tissue covered by the maximum dose area. ObjectiveIn radiotherapy work, those tows methods are all in use. But no literature reported this research. In the research, we use the MatriXX to verify the radiation field dose, which is from the different Lead block methods to make a test. Its method and result has great guiding significance towards radiotherapy. Traditional finger ionization chamber operation is tedious to use, can only single point dose measurement. The two-dimensional air ionization chamber MatriXX is one of the most progressive IMRT real-time two-dimensional authentication system, it can get the complicated Two-dimensional dose data quickly, easy to use and large massages. This research by using MatriXX on electron beam radiation dose’s verification, proved the MatriXX’s superiority in electron beam dose’s verification. Through the three validation techniques, treatment planning system (TPS), finger-type ionization chamber and the two-dimensional ion chamber matrix, to compare the four materials, plexiglass panels, wet medical gauze, colloidal compensatory material, Vaseline compensation flat’s compensation effects towards electron beam radiation fields. And the Vaseline compensation flat is made on our own. Vaseline compensation flat has some good physical and chemical properties:the character is stable, easy to get materials, easy to make, cheap and practical. Through this study to find out if we can call for use in the radiotherapy work.Methods1. Using MatriXX to compare beam dose of two lead block methodsRadiation field formed by integrative lead block By setting angle of racks0°helps beam expose vertically on the surface of two-dimensional air ionization chamber MatriXX. Put electron beam calimator10*10cm on the tray of treatment head and integrative electron beam hollow block under the lowest bottom of. On the treatment bed put MatriXX flat, on which lays a plexiglass plate with thickness of1.5cm. And then adjust the height of treatment bed to a source skin distance of100cm and the place of MatriXX until its center is in accordance with radiation range’s. Moreover, the frame of rectangular field in the center of10cm*8cm should match with electron beam exposure field’s, meaning that radiation field area formed by integrative lead block is10cm*8cm and long molecular axis of radiation field matches with long molecular axis, Y-axis, of treatment and width axis of radiation field matches with the left and right, X-axis, of treatment bed.Radiation field formed by activities lead block By setting angle of racks0°helps beam expose vertically on the surface of the MatriXX. Put electron beam calimator10*10cm on the tray of treatment head and integrative electron beam hollow block under the lowest bottom of. On the treatment bed put MatriXX flat, on which lays a plexiglass plate with thickness of1.5cm. And then adjust the height of treatment bed to a source skin distance of100cm, put a piece of rectangular solid block lead(14*14cm) on the limit of electron beam calimator top. A solid block of lead long axis is consistent with the treatment of long axis of the bed, and get on the calimator on the left side of the place, adjust the location of the solid block of lead until the activity lead block formation of the radiation field size is10cm x8cm, and adjust the place of MatriXX until its center is in accordance with radiation range’s. Moreover, the frame of rectangular field in the center of10cm*8cm should match with electron beam exposure field’s, meaning that radiation field area formed by integrative lead block is10cm*8cm and long molecular axis of radiation field matches with long molecular axis, Y-axis, of treatment and width axis of radiation field matches with the left and right, X-axis, of treatment bed.Two methods of lead block radiation field dose verification Parameter: energy6MeV; exposure dose100cGy; dosage rate400cGy/min; source skin distance:100cm. Use the same exposure condition, irradiating the two radiation fields respectively. Two-dimensional air ionization chamber array Matrix to verify the dose distribution of those tow radiation fields. Using the computer which is links with the MatriXX to gather, show and analyze in time. Using the OmniPro I’mRT to figure out dose distribution curve on X axis and Y axis’and dose distribution curve of irradiation field in two methods. 2. Applying TPS to Compare the Compensation Effect of Four Varieties of MaterialsPutting respectively the same thickness plexiglass panels of1.5cm, wet medical gauze, colloidal compensatory material, Vaseline compensation flat on the surface of two dimensional air ionization chamber MatriXX; Using the GE64-CT machine to position and scan them separately, and then transmit the CT image to the TPS, and set irradiation parameters:high energy electron beam;6MeV energy;100Cgy dose; the angle of incidence0degree, the radiation field10×10cm,source skin distance100cm. Rebuilding CT photos and analyzing dose of these four varieties materials by using TPS. Applying the finger-type ionization chamber to compare the Compensation Effect of Four Varieties of Materials3. Applying the finger-type ionization chamber to Compare the Compensation Effect of Four Varieties of MaterialsPut respectively the same thickness plexiglass panels of1.5cm, wet medical gauze, colloidal compensatory material, Vaseline compensation flat on the surface of the finger-type ionization chamber, irradiating them with a linear accelerator. The irradiation conditions are:high energy electron beam;6MeVenergy;100cGy dose; dose rate:400cGy/min; rack angle:0degree; source skin distance:100cm; the radiation field10×10cm. And then work out the compensation does of a variety of materials by PTM dosimeter which is connected at a finger-type ionization chamber.4. Applying MatriXX to Compare the Compensation Effect of Four Varieties of MaterialsPut respectively the same thickness plexiglass panels, wet medical gauze, colloidal compensatory material, Vaseline compensation flat on the surface of MatriXX, irradiating with a linear accelerator. The irradiation conditions are:high energy electron beam;6MeV energy,100cGy dose,400cGy/min dose rate, the radiation field10×10cm, source skin distance100cm, radiation range area:10cm*10cm. Through an exclusive computer connected to MatriXX on the four doses of material compensation for real-time capture, display and analysis, and mapping out the dose distribution curve.Result1. Two methods of lead block radiation field dose have very large differenceThe shape and area of the radiation field formed by a removable lead block are the same:10*10cm. Using the IB A I’mRT Matrix to figure out dose distribution curve, X axis and Y axis’dose distribution curve of irradiation field in two methods, the symmetric axis of the integrative lead block is symmetrical with that of the dose distribution curve which is located at the X axis, the curve is symmetric distribution right and left, the dose maximum is located at the X=0axis’Y axis, the dose maximum is located in the middle of the radiation field, dose curve’s axis of symmetry is the same as the radiation field’s axis of symmetry. The high dose of plateau of the X axis direction is distributes between x=-4cm to x=4cm, high dose plateau’s two border and radiation field’s two border is very close, which is come near to the actual width of the of the radiation field:8cm. Curve’s dose drop zone is symmetrical with the x axis’s polluted area at the Y axis that is locating at X=0. Radiation field’s outer edge dose is sharp drop to nearly zero. The symmetric axis of the activities lead block is symmetrical with that of the dose distribution curve which is located at the X axis, curve is not completely symmetrical the dose maximum is located at the X=-1, axis’Y axis. It means the dose maximum is not located in the middle of the radiation field. The high dose of plateau of the X axis direction is distributes between x=-4cm to x=4cm, high dose plateau’s two border and radiation field’s two border is very close, which is come near to the actual width of the of the radiation field:8cm.Curve’s dose drop zone is symmetrical with the x axis’s polluted area at the Y axis that is locating at X=0. Radiation field’s outer edge dose is sharpdrop to nearly zero. The symmetric axis of the activities lead block is symmetricalwith that of the dose distribution curve which is located at the X axis, curve is notcompletely symmetrical. The dose maximum is located at the X=-1, axis’Y axis. Itmeans the dose maximum is not located in the middle of the radiation field. Dosecurve’s axis of symmetry is not the same as the radiation field’s axis of symmetry.The high dose of plateau of the X axis direction is distributes between x=-4cm tox=4cm, it is not symmetrical with the x=0’Y axis. High dose plateau’s two borderand radiation field’s two border is not close at all. The dosage of the radiation field isvery inhomogenous, the dose of the radiation field, at the left side is higher than thatat right. On the left of the radiation field’s dose is closed between x=4to x=0, but theright side, it decrease to45055cGy from82081cGy between x=0to x=4. Curve’sdose drop zone is not symmetrical with the x axis’s polluted area at the Y axis that islocating at X=0. Radiation field’s left outer edge dose X=-4cm to x=-6cm is closedto zero. Radiation field’s right outer edge dose decrease to45055cGy from82081cGy between x=0to x=4. Curve’s dose drop zone is not symmetrical with thex axis’s polluted area at the Y axis that is locating at X=0.Radiation field’s left outeredge dose X=-4cm to x=-6cm is closed to zero. The left of the radiation field’s doseis decrease to14.55cGy from19.95cGy between x=4cm to x=6cm. There is adecrease in the dose, but is not closed to zero, namely activity type target outer edge’ordinary tissue is shined, radiation dose is about54.97%to18.04%of the total dose,radiation area is about25%of the total dose.2. The difference of the compensation dose made by this four materials afterverified by TPS Through the TPS to get four compensation doses, MatriXX’s surface dose, themaximum dose point and its depth. TPS method is used to test, put four materials on the face of MatriXX, the dose it make have Statistical differences in total. Compare with the Bonferroni, find out the measured data of moist medical gauze has a large difference from other three materials (p>0.05), While the measured data among the Perspex sheet, colloidal compensatory material and Vaseline compensation is close (p<0.001).There is difference of the compensation dose made by these four materials after verified by TPS.3. The difference of the compensation dose made by this four materials after verified by the finger-type ionization chamberAfter verified by the finger-type ionization chamber, find out the measured data of dose has a large difference, compare with the Bonferroni, find out the measured data of moist medical gauze has a large difference from other three materials(p>0.05), While the measured data among the Perspex sheet, colloidal compensatory material and Vaseline compensation is close(p<0.001). The measured date of compensation and Vaseline compensation matter is approximate, plexiglass panels, colloidal compensatory material, Vaseline compensation flat is phase approaching and the wet medical gauze is lower than those three obviously, the compensatory discrepancy is about10%. There is difference of the compensation dose made by those four materials, after verified by the finger-type ionization chamber.4. The difference of the compensation dose made by those four material after verified by MatriXX.Through the MatriXX’s Validation, get a dose distribution graph. The result is that, find out the measured data of dose has a large difference, compare with the Bonferroni, find out the measured data of moist medical gauze has a large difference from other three materials(p>0.05), While the measured data among the Perspex sheet, colloidal compensatory material and Vaseline compensation is close(p<0.001). ConclusionThe two-dimensional air ionization chamber MatriXX is one of the most progressive IMRT real-time two-dimensional authentication system, it can get the complicated Two-dimensional dosimetry data quickly, easy to use and large massages. Traditional finger ionization chamber operation is tedious to use, can only single point dose measurement. In radiotherapy works, those tows methods are all in use. But no literature reported this research. In the research, we use the MatriXX to verify the radiation field dose, which is from the different Lead block methods to make a test, its method and result has great guiding significance towards radiotherapy. The activities lead block’s size of the radiation field is the same as the integrative lead block, but the dose distribution is not totally similar. In practical work it must be in strict accordance with the plan and the doctor’s advice, using integrative lead block which is compatible with the plan. Radiation field dose verification results of TPS, plexiglass panels, colloidal compensatory material, Vaseline compensation flat is closed, but the wet medical gauze is different with those three materials. And the Vaseline compensation flat is made by ourselves. Vaseline compensation flat has some good physical and chemical properties:the character is stable, easy to get materials, easy to make, cheap and practical. Through this study to find out if we can call for use in the radiotherapy work. |
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