| 1. |
- Knöös, Tommy, et al.
(författare)
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A method for conversion of hounsfield number to electron density and prediction of macroscopic pair production cross-sections
- 1986
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Ingår i: Radiotherapy and Oncology. - 1879-0887. ; 5:4, s. 337-345
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Tidskriftsartikel (refereegranskat)abstract
- A method for the determination of electron density using a narrow beam attenuation geometry is described. The method does not require that the elemental composition of the phantom materials is known. The Hounsfield numbers for the phantom materials used were determined using five different CT scanners. A relationship between Hounsfield number and electron density can thus be established, which is of considerable value in radiation therapy treatment planning procedures. Measurements of the ratio coherent/incoherent scattering of low energy photons in a certain geometry has proven valuable for determination of atomic number, which in its turn can be used for estimation of macroscopic pair production coefficients for high energy photons. The combination of knowledge of electron density with methods for determination of processes, dependent on atomic number, can form a base for adequate composition of phantom materials for purposes of testing dose calculation algorithms for photons and electrons.
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| 2. |
- Knöös, Tommy, et al.
(författare)
-
Comparison of measured and calculated absorbed doses from tangential irradiation of the breast
- 1986
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Ingår i: Radiotherapy and Oncology. - 1879-0887. ; 7:1, s. 81-88
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Tidskriftsartikel (refereegranskat)abstract
- Calculated absorbed dose distributions from tangential irradiation of the breast have been compared with TLD measurements in a anthropomorfic body-shaped phantom which has gone through all phases of the radiation treatment planning cycle, including mapping of electron densities with a CT scanner, simulation of beam set-up and several treatments with an accelerator. The absorbed doses, measured in the breast are 2-6% lower than those calculated with the clinically used treatment planning system. The deviation is slightly higher when wedges are used. The main source for this deviation is shown to be the limitations in the loss-of-scatter correction in the dose calculation algorithm used. It has also been noted that the variation of the absorbed dose in the target volume is in general smaller than predicted by the calculations.
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| 3. |
- Olsson, L E, et al.
(författare)
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Ferrous sulphate gels for determination of absorbed dose distributions using MRI technique : basic studies
- 1989
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 34:1, s. 43-52
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Tidskriftsartikel (refereegranskat)abstract
- Two gels have been found to be suitable to load with ferrous sulphate solution. In these soft tissue equivalent phantoms, the absorbed dose distribution can be measured after irradiation in clinically used MR imaging equipment. The present studies were carried out using a 0.25 T NMR analyser without imaging properties. A ferrous sulphate solution, 0.05 M with respect to sulphuric acid, can be gelled with 4% gelatin to give a dosemeter which has a response which is linearly correlated (r = 0.998) with the absorbed dose in the interval 0-40 Gy. Ferrous sulphate solution can also be gelled with 1% agarose, but this gel has to be purged with oxygen to obtain a linear relationship (r = 0.997) in the same absorbed dose interval. The ferrous sulphate loaded gels have a sensitivity which is a factor of 2.2 or 4.0 times higher for gelatin and agarose, respectively, than the ordinary dosemeter solution. Because the standard deviation of background measurements is higher for the gels than for the dosemeter solution, the minimum detectable absorbed dose is about the same, or 1.0 Gy, for the two gels and the dosemeter solution. The sensitivity of the ferrous sulphate loaded gels shows no dependence on dose rate if the mean dose rate and the absorbed dose per pulse are within the limits normally used by accelerators for radiotherapy.
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