Evaluation of off-axis wedge correction factor using diode dosimeters for estimation of delivered dose in external radiotherapy
| Autor: | Mahmoud Allahverdi, Alireza Mohammadkarim, Mahbod Esfehani, Hasanali Nedaie, Alireza Shirazi, Ghazale Geraily |
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| Jazyk: | angličtina |
| Rok vydání: | 2012 |
| Předmět: | |
| Zdroj: | Journal of Medical Physics, Vol 37, Iss 1, Pp 32-39 (2012) |
| Druh dokumentu: | article |
| ISSN: | 0971-6203 1998-3913 |
| DOI: | 10.4103/0971-6203.92718 |
| Popis: | An in vivo dosimetry system, using p-type diode dosimeters, was characterized for clinical applications of treatment machines ranging in megavoltage energies. This paper investigates two different models of diodes for externally wedged beams and explains a new algorithm for the calculation of the target dose at various tissue depths in external radiotherapy. The values of off-axis wedge correction factors were determined at two different positions in the wedged (toward the thick and thin edges) and in the non-wedged directions on entrance and exit surfaces of a polystyrene phantom in 60 Co and 6 MV photon beams. Depth transmission was defined on the entrance and exit surfaces to obtain the off-axis wedge correction factor at any depth. As the sensitivity of the diodes depends on physical characteristics [field size, source-skin distance (SSD), thickness, backscatter], correction factors were applied to the diode reading when measuring conditions different from calibration situations . The results indicate that needful correction factors for 60 Co wedged photons are usually larger than those for 6 MV wedged photon beams. In vivo dosimetry performed with the proposed algorithms at externally wedged beams has negligible probable errors (less than 0.5%) and is a reliable method for patient dose control. |
| Databáze: | Directory of Open Access Journals |
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