SU-F-T-06: Development of a Formalism for Practical Dose Measurements in Brachytherapy in the German Standard DIN 6803

Purpose: In the steep dose gradients in the vicinity of a radiation source and due to the properties of the changing photon spectra, dose measurements in Brachytherapy usually have large uncertainties. Working group DIN 6803-3 is presently discussing recommendations for practical brachytherapy dosim...

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Bibliographic Details
Published in:Medical physics (Lancaster) 2016-06, Vol.43 (6), p.3462-3462
Main Authors: Hensley, F, Chofor, N, Schoenfeld, A, Harder, D
Format: Article
Language:English
Subjects:
60 APPLIED LIFE SCIENCES
ABSORBED RADIATION DOSES
Absorption spectra
ALGORITHMS
BRACHYTHERAPY
COBALT 60
COMPUTERIZED SIMULATION
CORRECTIONS
DOSIMETRY
Electromagnetic radiation detectors
ENERGY DEPENDENCE
Error analysis
Group theory
MONTE CARLO METHOD
PHANTOMS
Photons
Radiation detectors
RADIATION DOSE DISTRIBUTIONS
RADIATION SOURCES
RADIOLOGY AND NUCLEAR MEDICINE
Radiotherapy sources
RECOMMENDATIONS
SPECTRA
Spectral properties
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Summary:Purpose: In the steep dose gradients in the vicinity of a radiation source and due to the properties of the changing photon spectra, dose measurements in Brachytherapy usually have large uncertainties. Working group DIN 6803-3 is presently discussing recommendations for practical brachytherapy dosimetry incorporating recent theoretical developments in the description of brachytherapy radiation fields as well as new detectors and phantom materials. The goal is to prepare methods and instruments to verify dose calculation algorithms and for clinical dose verification with reduced uncertainties. Methods: After analysis of the distance dependent spectral changes of the radiation field surrounding brachytherapy sources, the energy dependent response of typical brachytherapy detectors was examined with Monte Carlo simulations. A dosimetric formalism was developed allowing the correction of their energy dependence as function of source distance for a Co-60 calibrated detector. Water equivalent phantom materials were examined with Monte Carlo calculations for their influence on brachytherapy photon spectra and for their water equivalence in terms of generating equivalent distributions of photon spectra and absorbed dose to water. Results: The energy dependence of a detector in the vicinity of a brachytherapy source can be described by defining an energy correction factor kQ for brachytherapy in the same manner as in existing dosimetry protocols which incorporates volume averaging and radiation field distortion by the detector. Solid phantom materials were identified which allow precise positioning of a detector together with small correctable deviations from absorbed dose to water. Recommendations for the selection of detectors and phantom materials are being developed for different measurements in brachytherapy. Conclusion: The introduction of kQ for brachytherapy sources may allow more systematic and comparable dose measurements. In principle, the corrections can be verified or even determined by measurement in a water phantom and comparison with dose distributions calculated using the TG43 dosimetry formalism. Project is supported by DIN Deutsches Institut fuer Normung
ISSN:0094-2405
2473-4209
DOI:10.1118/1.4956140