Analysis And Research Of Measurement Data For Different Detectors In IMRT Small Fields

Radiotherapy,surgery and chemotherapy are the three main ways of cancer treatment. the world health organization(WHO) announced the 5-year survival rate was about 55% of cancer In 2008,radiotherapy was 23%,surgery was 25%,and 7% of chemotherapy. The report published by WHO in 2014 pointed out that China’s cancer incidence is almost half of the world, Radiation therapy faced with an inevitable fact,although obvious advantages. It is a kind of local treatment,and with own limitations,destroy tumors may also cause damage to normal tissue.Intensity-modulated radiation therapy(IMRT) is a major technological change in the field of tumor radiotherapy,bascicked on 3 d- CRT technology,Well also follow the four principles of radiation: target dose accuracy,minimums dose of surrounding normal tissues,Protecting vital organs,Target dose distribution uniformity,therapy technology got highly promotion,also put forward higher request to the physical aspect,small volume dose measurement is a difficult problem for us,and also is focus in research of the physical,Accuracy physical model data is necessary for accuracy of intensity-modulated radiotherapy,then we will choose a more appropriate detector to finish the task.Our paper studied the difference by choosing differenced types of detectors(including finger ionization chamber PTW30010, PTW31010, semiconductor detector PTW60017,cusp ionization chamber PTW30016 and EBT2 films),with different size(0.6 cm x 0.6 cm,1.0 cm x 1.0 cm,1.0 cm x 2.0 cm,3.0 cm x 3.0 cm,3.0 cm x 4.0 cm and 5.0 cm x 5.0 cm) of the radiation field relative dose measurement. including percentage depth dose PDD,off-axis ratio curve profile and scattering factor(Scp). we analyzed the datas,and concluded that the result is diffent by the different detectors on the under the condition of the certain fixed radiation field. All datas are from SSD100 cm,measured under the conditions of 5 cm depth of water.Conclusion: there is no obvious difference for all detectors on 4.0 cm x 4.0 cm or larger field. there is obvious difference for on under 3.0 cm x 3.0 cm,0.6 cc finger ionization chamber cavity is larger,the volume effect and the lever effect,measurement data is difficult to trust,a small volume sensitive point ionization chamber andsemiconductor detector. For the 0.6 cm x 0.6 cm of small radiation field,even a small volume sensitive detector,the measured results also have obvious difference.Radiation field under 3.0 cm x 3.0 cm,the volume effect and the lever effect is diffent because 0.6 cc finger ionization chamber cavity is big. That is no diffent for a small volume sensitive point ionization chamber and semiconductor detector.For the 0.6 cm x 0.6 cm of small radiation field,even a small volume sensitive detector,the measured results is obvious difference. 0.125 cc ionization chamber detector measured value maximum,0.6 cc ionization chamber result is minimum the between difference is about 4.35%.The diffents between the maximum measured value and minimum measured values is 74.3% for 0.6 cm x 0.6 cm of small radiation field.