| Zugriffsnummer | 11564 |
| Dokumenttyp | Zeitschriftenartikel |
| Peer Review | unbekannt |
| Sprache | Englisch |
| Titel | Dose Determination with Plane-Parallel Ionization Chambers in Therapeutic Electron and Photon Beams: Investigation of the Accuracy of Procedures and Data in IAEA TRS-381 |
| Autor(in); Institution |
Roos, Martin; 6.23, Dosimetrie der Strahlung hoher Energie, PTB-Braunschweig
|
| Quelle/Jahr | SSDL Newsletter: 40 (1999), 11 - 12 |
| ISSN | 1011-2669 |
| Verlag | IAEA |
| Freie Schlagworte | therapy dosimetry ; electron dosimetry ; IAEA International Code of Practice TRS 381 ; ionization chambers ; plane-parallel chambers ; polarity effect ; saturation correction ; stopping power ratios |
| Zusammenfassung | The accuracy which is achievable with the new procedures and data of TRS 381 depends strongly on the performance characteristics of the ionization chambers commercially available. The present investigations include therefore the investigation of the dependence of response on the polarity (polarity effect) and the absolute value of the polarizing voltage (correlated with the saturation correction) of commercial plane-parallel chambers. Concerning the saturation correction, the uncertainties introduced by the application of the convenient Boag formula for volume recombination exclusively have been investigated and, in order to estimate the uncertainties introduced by the use of chambers not fulfilling the design requirements of TRS 381, the displacement of the effective point of measurement of the Markus chamber from that assumed in the code has been determined. Concerning the selection procedures of stopping power ratios, in the International Code of Practice IAEA TRS 381 the stopping power ratios water/air are selected according to the half-value depth and the depth of measurement. In the German Standard DIN 6800-2 a different procedure is recommended, which, in addition, takes the practical electron range into account. The stopping power data for monoenergetic beams from IAEA TRS 381 are used. Both procedures are compared with recent Monte Carlo calculations carried out for various beams of clinical accelerators. It turns out that the DIN procedure shows, in fact, a slightly better agreement. In addition, the stopping power ratios according to IAEA TRS 381 are compared with those according to DIN 6800-2 for the reference conditions of the beams from the PTB linac. The maximum deviation is not larger than 0.6%. (This research is carried out under the IAEA Coordinated Research Project E2.40.08, contract GFR 9927) |
