VALIDITY OF TRANSITION-ZONE DOSIMETRY AT HIGH ATOMIC-NUMBER INTERFACES IN MEGAVOLTAGE PHOTON BEAMS

被引:37
作者
DAS, IJ
KASE, KR
MEIGOONI, AS
KHAN, FM
WERNER, BL
机构
[1] YALE UNIV,MED CTR,DEPT THERAPEUT RADIOL,NEW HAVEN,CT 06510
[2] UNIV MINNESOTA HOSP & CLIN,DEPT THERAPEUT RADIOL,MINNEAPOLIS,MN 55455
关键词
chamber response; electron spectrum in; high-Z interface; Monte Carlo at interface; photon beam; transition zone dosimetry;
D O I
10.1118/1.596553
中图分类号
R8 [特种医学]; R445 [影像诊断学];
学科分类号
1002 ; 100207 ; 1009 ;
摘要
Measurement of dose or dose perturbation factors at high atomic number interfaces are usually performed with a thin-window parallel-plate ion chamber. In a transition region, under nonequilibrium conditions, accuracy of ion chamber readings for the dose measurements has often been questioned. This paper critically analyzes the factors (stopping power ratio and charge collection) for the dose measurements at interfaces. Monte Carlo simulations were performed to investigate the secondary electron spectrum produced by photon beams and to calculate the stopping power ratios at the point of measurement. The validity of dose measurements was studied for the photon beams in the range of Co-60 gamma rays to 24-M V x rays at bone and lead interfaces with polystyrene, using thermoluminescent dosimeters, extrapolation chamber and several types of commercially available parallel-plate ion chambers. It is observed that for energies >10 MV most parallel-plate chambers can be used to measure dose accurately. At lower energies, however significant differences between measured doses with different detectors were noticed. It is suggested that at high-Z interfaces and lower energies, the dose measurements should be performed with ultrathin-window parallel-plate ion chambers or extrapolation chambers. © 1990, American Association of Physicists in Medicine. All rights reserved.
引用
收藏
页码:10 / 16
页数:7
相关论文
共 29 条
[1]   STOPPING-POWER RATIO FOR A PHOTON SPECTRUM AS A WEIGHTED SUM OF THE VALUES FOR MONOENERGETIC PHOTON BEAMS [J].
ANDREO, P ;
NAHUM, AE .
PHYSICS IN MEDICINE AND BIOLOGY, 1985, 30 (10) :1055-1065
[2]   STOPPING POWER DATA FOR HIGH-ENERGY PHOTON BEAMS [J].
ANDREO, P ;
BRAHME, A .
PHYSICS IN MEDICINE AND BIOLOGY, 1986, 31 (08) :839-858
[3]  
Attix FH., 1986, INTRO RADIOLOGICAL P, P358
[4]   PERTURBATION CORRECTION FOR THE IONOMETRIC DETERMINATION OF ABSORBED DOSE IN A GRAPHITE PHANTOM FOR CO-60 GAMMA-RAYS [J].
BOUTILLON, M .
PHYSICS IN MEDICINE AND BIOLOGY, 1983, 28 (04) :375-388
[5]   THE DEPENDENCE OF MASS-ENERGY ABSORPTION-COEFFICIENT RATIOS ON BEAM SIZE AND DEPTH IN A PHANTOM [J].
CUNNINGHAM, JR ;
WOO, M ;
ROGERS, DWO ;
BIELAJEW, AF .
MEDICAL PHYSICS, 1986, 13 (04) :496-502
[6]   BACKSCATTER DOSE PERTURBATION AT HIGH ATOMIC-NUMBER INTERFACES IN MEGAVOLTAGE PHOTON BEAMS [J].
DAS, IJ ;
KAHN, FM .
MEDICAL PHYSICS, 1989, 16 (03) :367-375
[7]  
DAS IJ, 1988, THESIS U MINNESOTA
[8]  
DUTREIX A, 1985, RAD DOSIMETRY IONIZI, V1
[9]  
DUTREIX J, 1964, Ann Radiol (Paris), V7, P233
[10]   DOSIMETRY AT INTERFACES FOR HIGH ENERGY X AND GAMMA RAYS [J].
DUTREIX, J ;
BERNARD, M .
BRITISH JOURNAL OF RADIOLOGY, 1966, 39 (459) :205-&