Influence of phantom material and phantom size on radiographic film response in therapy photon beams Journal Article
| Authors: | Palm, A.; LoSasso, T. |
| Article Title: | Influence of phantom material and phantom size on radiographic film response in therapy photon beams |
| Abstract: | The energy dependence of radiographic film can introduce dosimetric errors when evaluating photon beams. The variation of the film response, which is attributed to the changing photon spectrum with depth and field size, has been the subject of numerous publications in recent years. However, these data show large unexplained differences in the magnitude of this variation among independent studies. To try to resolve this inconsistency, this study assesses the dependence of radiographic film response on phantom material and phantom size using film measurements and Monte Carlo calculations. The relative dose measured with film exposed to 6 MV x rays in various phantoms (polystyrene, acrylic, Solid Water, and water; the lateral phantom dimensions vary from 25 to 50 cm square; backscatter thickness varies from 10 to 30 cm) is compared with ion chamber measurements in water. Ranges of field size (5 × 5 to 40 × 40 cm2) and depth (dmax to 20 cm) are studied. For similar phantom and beam configurations, Monte Carlo techniques generate photon fluence spectra from which the relative film response is known from an earlier study. Results from film response measurements agree with those derived from Monte Carlo calculations within 3%. For small fields (≤ 10 × 10 cm 2) and shallow depths (≤10 cm) the film response variation is small, less than 4%, for all phantoms. However, for larger field sizes and depths, the phantom material and phantom size have a greater influence on the magnitude of the film response. The variation of film response, over the ranges of field sizes and depths studied, is 50% in polystyrene compared with 30% in water. Film responses in Solid Water and water phantoms are similar; acrylic is between water and polystyrene. In polystyrene the variation of film response for a 50 cm square phantom is nearly twice that observed in a 25 cm square phantom. This study shows that differences in the configuration of the phantoms used for film dosimetry can explain much of the inconsistency for film response reported in the literature. © 2005 American Association of Physicists in Medicine. |
| Keywords: | radiation dose; sensitivity and specificity; reproducibility of results; radiotherapy dosage; dose-response relationship, radiation; dosimetry; measurement; radiography; radiotherapy planning, computer-assisted; radiotherapy, conformal; polystyrene; phantom; film dosimetry; photons; water; phantoms, imaging; liquid; energy; photon; monte carlo method; calculation; solid; x ray film; equipment failure analysis; materials testing; beam therapy; poly(methyl methacrylate); materials |
| Journal Title: | Medical Physics |
| Volume: | 32 |
| Issue: | 8 |
| ISSN: | 0094-2405 |
| Publisher: | American Association of Physicists in Medicine |
| Date Published: | 2005-08-01 |
| Start Page: | 2434 |
| End Page: | 2442 |
| Language: | English |
| DOI: | 10.1118/1.1949747 |
| PUBMED: | 16193772 |
| PROVIDER: | scopus |
| DOI/URL: | |
| Notes: | --- - "Cited By (since 1996): 19" - "Export Date: 24 October 2012" - "CODEN: MPHYA" - "Source: Scopus" |
Altmetric
Citation Impact
BMJ Impact Analytics
Related MSK Work