ABSTRACT
Absorbed dose and transmission factors were determined for 6 MV X-ray fields applied in four conventional external radiation treatments where protection blocks are used to shield organs at risk. Studied treatments are: head and neck (cancer of the larynx), breast (breast cancer), brain (brain tumours) and pelvis (cervix-uterine cancer). Experimental determinations were made using ionization chambers and thermoluminescent dosimeters, at different locations in phantoms, for blocked and unblocked fields. Calculated absorbed doses, using the treatment planning system and Clarkson method, were compared to those measured. Measured transmission factor values ranged from 5% to 18%. It was found that the planning treatment system may underestimate the absorbed dose under the blocks, up to 35%.
Subject(s)
Neoplasms/radiotherapy , Radiation Protection/instrumentation , Radiotherapy, High-Energy , Absorption , Breast Neoplasms/radiotherapy , Cranial Irradiation , Dose-Response Relationship, Radiation , Female , Head and Neck Neoplasms/radiotherapy , Humans , Laryngeal Neoplasms/radiotherapy , Male , Particle Accelerators , Pelvic Neoplasms/radiotherapy , Radiation Injuries/prevention & control , Radiometry/methods , Radiotherapy DosageABSTRACT
The optically stimulated luminescence (OSL) response of Al2O3:C to high doses of gamma or beta irradiation can be used to predict the response of this material to charged particles as a function of particle fluence, particle energy and/or linear energy transfer (LET). In particular, it is predicted that track interaction effects at high particle fluences should result in linear-sublinear growth of the OSL signal. Similar considerations also predict a dependence of the fluence at which sublinearity starts upon the energy of the particles. In this work the OSL response of Al2O3:C to low-energy charged particles was investigated using protons (1, 2 and 4 MeV), carbon ions (13 MeV) and oxygen ions (10 MeV). The sublinear growth predicted above was qualitatively confirmed, but the energy dependence prediction was not. Furthermore, the efficiency of OSL production in the material after charged particle irradiation, compared to that obtained for gamma irradiation, is determined from the dose-response curves by fitting to a simple saturating exponential function. The efficiency values so obtained using this method are compared with those obtained from a conventional single-point measurement in the linear portion of the curve and found to be in good agreement. In general, the efficiency decreases as the LET of the particle increases. The present data are compared with published data obtained using high-energy charged particles and the results show that the efficiency is not a unique function of LET.
Subject(s)
Aluminum Oxide/chemistry , Aluminum Oxide/radiation effects , Beta Particles , Gamma Rays , Models, Chemical , Thermoluminescent Dosimetry/instrumentation , Thermoluminescent Dosimetry/methods , Computer Simulation , Dose-Response Relationship, Radiation , Equipment Design , Equipment Failure Analysis , Light , Linear Energy Transfer , Materials Testing , Radiation DosageABSTRACT
No disponible
Absorbed dose and transmission factors were determinedfor 6 MV X-ray fields applied in four conventionalexternal radiation treatments where protectionblocks are used to shield organs at risk. Studiedtreatments are: head and neck (cancer of the larynx),breast (breast cancer), brain (brain tumours) andpelvis (cervix-uterine cancer). Experimental determinationswere made using ionization chambers andthermoluminescent dosimeters, at different locationsin phantoms, for blocked and unblocked fields.Calculated absorbed doses, using the treatmentplanning system and Clarkson method, were comparedto those measured. Measured transmissionfactor values ranged from 5% to 18%. It was foundthat the planning treatment system may underestimatethe absorbed dose under the blocks, up to 35%
