Pencil beam approach for correcting the energy dependence artifact in film dosimetry for IMRT verification Journal Article
| Authors: | Kirov, A. S.; Caravelli, G.; Palm, A.; Chui, C.; LoSasso, T. |
| Article Title: | Pencil beam approach for correcting the energy dependence artifact in film dosimetry for IMRT verification |
| Abstract: | The higher sensitivity to low-energy scattered photons of radiographic film compared to water can lead to significant dosimetric error when the beam quality varies significantly within a field. Correcting for this artifact will provide greater accuracy for intensity modulated radiation therapy (IMRT) verification dosimetry. A procedure is developed for correction of the film energy-dependent response by creating a pencil beam kernel within our treatment planning system to model the film response specifically. Film kernels are obtained from EGSnrc Monte Carlo simulations of the dose distribution from a 1 mm diameter narrow beam in a model of the film placed at six depths from 1.5 to 40 cm in polystyrene and solid water phantoms. Kernels for different area phantoms (50 × 50 cm 2 and 25 × 25 cm 2 polystyrene and 30 × 30 cm 2 solid water) are produced. The Monte Carlo calculated kernel is experimentally verified with film, ion chamber and thermoluminescent dosimetry (TLD) measurements in polystyrene irradiated by a narrow beam. The kernel is then used in convolution calculations to predict the film response in open and IMRT fields. A 6 MV photon beam and Kodak XV2 film in a polystyrene phantom are selected to test the method as they are often used in practice and can result in large energy-dependent artifacts. The difference in dose distributions calculated with the film kernel and the water kernel is subtracted from film measurements to obtain a practically film artifact free IMRT dose distribution for the Kodak XV2 film. For the points with dose exceeding 5 cGy (11% of the peak dose) in a large modulated field and a film measurement inside a large polystyrene phantom at depth of 10 cm, the correction reduces the fraction of pixels for which the film dose deviates from dose to water by more than 5% of the mean film dose from 44% to 6%. © 2006 American Association of Physicists in Medicine. |
| Keywords: | intensity modulated radiation therapy; reproducibility of results; algorithms; dose-response relationship, radiation; radiotherapy, intensity-modulated; artifact; radiometry; radiotherapy planning, computer-assisted; film dosimeter; ionization chamber; photon therapy; polystyrene; phantom; film dosimetry; photons; water; phantoms, imaging; energy; radiation dose distribution; artifacts; monte carlo method; thermoluminescence dosimetry; thermoluminescent dosimetry; polystyrenes |
| Journal Title: | Medical Physics |
| Volume: | 33 |
| Issue: | 10 |
| ISSN: | 0094-2405 |
| Publisher: | American Association of Physicists in Medicine |
| Date Published: | 2006-01-01 |
| Start Page: | 3690 |
| End Page: | 3699 |
| Language: | English |
| DOI: | 10.1118/1.2229425 |
| PUBMED: | 17089835 |
| PROVIDER: | scopus |
| DOI/URL: | |
| Notes: | --- - "Cited By (since 1996): 8" - "Export Date: 4 June 2012" - "CODEN: MPHYA" - "Source: Scopus" |
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