Dose homogeneity specification for reference dosimetry of nonstandard fields
Abstract
Purpose: To investigate the sensitivity of the plan-class specific correction factor to dose distributions in composite nonstandard field dosimetry. Methods: A cylindrical water-filled PMMA phantom was constructed at the center of which reference absorbed dose could be measured. Ten different TomoTherapy-based IMRT fields were created on the CT images of the phantom. The dose distribution for each IMRT field was estimated at the position of a radiation detector or ionization chamber. The dose in each IMRT field normalized to that in a reference 10 x 10 cm{sup 2} field was measured using a PTW micro liquid ion chamber. Based on the new dosimetry formalism, a plan-class specific correction factor k{sub Q{sub p{sub c{sub s{sub r,Q}{sup f{sub p}{sub c}{sub s}{sub r},f{sub r}{sub e}{sub f}}}}}} for each field was measured for two Farmer-type chambers, Exradin A12 and NE2571, as well as for a smaller Exradin A1SL chamber. The dependence of the measured correction factor on parameters characterizing dose distribution was analyzed. Results: Uncertainty on the plan-class specific correction factor measurement was in the range of 0.3%-0.5% and 0.3%-0.8% for the Farmer-type chambers and the Exradin A1SL, respectively. When the heterogeneity of the central region of the target volume was less than 5%,more »
- Authors:
-
- Medical Physics Unit, McGill University, Montreal General Hospital (L5-113), 1650 Cedar Avenue, Montreal, Quebec H3G 1A4 (Canada)
- Publication Date:
- OSTI Identifier:
- 22098726
- Resource Type:
- Journal Article
- Journal Name:
- Medical Physics
- Additional Journal Information:
- Journal Volume: 39; Journal Issue: 1; Other Information: (c) 2012 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 62 RADIOLOGY AND NUCLEAR MEDICINE; CAT SCANNING; CT-GUIDED RADIOTHERAPY; DELIVERY; EVALUATION; IONIZATION CHAMBERS; PHANTOMS; PMMA; RADIATION DOSE DISTRIBUTIONS; SENSITIVITY; SPECIFICATIONS
Citation Formats
Chung, Eunah, Soisson, Emilie, Seuntjens, Jan, Medical Physics Unit, McGill University and Department of Medical Physics, McGill University Health Centre, Montreal General Hospital, and Medical Physics Unit, McGill University, Montreal General Hospital. Dose homogeneity specification for reference dosimetry of nonstandard fields. United States: N. p., 2012.
Web. doi:10.1118/1.3669487.
Chung, Eunah, Soisson, Emilie, Seuntjens, Jan, Medical Physics Unit, McGill University and Department of Medical Physics, McGill University Health Centre, Montreal General Hospital, & Medical Physics Unit, McGill University, Montreal General Hospital. Dose homogeneity specification for reference dosimetry of nonstandard fields. United States. https://doi.org/10.1118/1.3669487
Chung, Eunah, Soisson, Emilie, Seuntjens, Jan, Medical Physics Unit, McGill University and Department of Medical Physics, McGill University Health Centre, Montreal General Hospital, and Medical Physics Unit, McGill University, Montreal General Hospital. 2012.
"Dose homogeneity specification for reference dosimetry of nonstandard fields". United States. https://doi.org/10.1118/1.3669487.
@article{osti_22098726,
title = {Dose homogeneity specification for reference dosimetry of nonstandard fields},
author = {Chung, Eunah and Soisson, Emilie and Seuntjens, Jan and Medical Physics Unit, McGill University and Department of Medical Physics, McGill University Health Centre, Montreal General Hospital and Medical Physics Unit, McGill University, Montreal General Hospital},
abstractNote = {Purpose: To investigate the sensitivity of the plan-class specific correction factor to dose distributions in composite nonstandard field dosimetry. Methods: A cylindrical water-filled PMMA phantom was constructed at the center of which reference absorbed dose could be measured. Ten different TomoTherapy-based IMRT fields were created on the CT images of the phantom. The dose distribution for each IMRT field was estimated at the position of a radiation detector or ionization chamber. The dose in each IMRT field normalized to that in a reference 10 x 10 cm{sup 2} field was measured using a PTW micro liquid ion chamber. Based on the new dosimetry formalism, a plan-class specific correction factor k{sub Q{sub p{sub c{sub s{sub r,Q}{sup f{sub p}{sub c}{sub s}{sub r},f{sub r}{sub e}{sub f}}}}}} for each field was measured for two Farmer-type chambers, Exradin A12 and NE2571, as well as for a smaller Exradin A1SL chamber. The dependence of the measured correction factor on parameters characterizing dose distribution was analyzed. Results: Uncertainty on the plan-class specific correction factor measurement was in the range of 0.3%-0.5% and 0.3%-0.8% for the Farmer-type chambers and the Exradin A1SL, respectively. When the heterogeneity of the central region of the target volume was less than 5%, the correction factor did not differ from unity by more than 0.7% for the three air-filled ionization chambers. For more heterogeneous dose deliveries, the correction factor differed from unity by up to 2.4% for the Farmer-type chambers. For the Exradin A1SL, the correction factor was closer to unity due to the reduced effect of dose gradients, while it was highly variable in different IMRT fields because of a more significant impact of positioning uncertainties on the response of this chamber. Conclusions: The authors have shown that a plan-class specific correction factor can be specified as a function of plan evaluation parameters especially for Farmer-type chambers. This work provides a recipe based on quantifying dose distribution to accurately select air-filled ionization chamber correction factors for nonstandard fields.},
doi = {10.1118/1.3669487},
url = {https://www.osti.gov/biblio/22098726},
journal = {Medical Physics},
issn = {0094-2405},
number = 1,
volume = 39,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2012},
month = {Sun Jan 15 00:00:00 EST 2012}
}