| 1. |
- Ahnesjö, Anders, et al.
(författare)
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Application of the convolution method for calculation of output factors for therapy photon beams
- 1992
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Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 19:2, s. 295-301
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Tidskriftsartikel (refereegranskat)abstract
- The output factor for a therapy photon beam is defined as the dose per monitor unit relative to the dose per monitor unit in a reference field. Convolution models for photon dose calculations yield the dose in units normalized to the incident energy fluence with phantom scatter intrinsically modeled. Output factors calculated with the convolution method as the dose per unit energy fluence relative to the calculated dose per unit energy fluence in a reference field could deviate as much as 5% if corrections are not made for perturbations due to treatment head scatter. Significant perturbations are particles backscattered from the collimators to the monitor and photons forward scattered from the filter and collimators in the treatment head. The forward scatter adds an "unmonitored" contribution to the total energy fluence of the beam. A model is developed that describes the field size dependence of these perturbations for conversion of output factors, calculated with the convolution method, to machine output factors as an integrated part in treatment planning. The necessary machine characteristics are derived from measurements of the output in air for a limited set of field sizes. The method has been tested using five different multileaf collimated irregular fields at 6 MV and for a large set of rectangular fields at 5, 6, and 18 MV and found to predict output factors with an accuracy better than 1%.
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| 2. |
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| 3. |
- Knöös, Tommy, et al.
(författare)
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Which depth dose data should be used for dose planning when wedge filters are used to modify the photon beam?
- 1991
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 36:2, s. 255-267
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Tidskriftsartikel (refereegranskat)abstract
- The use of beam data for open photon fields when calculating absorbed dose distributions for beams with wedge filters has been studied. The depth doses for beams with wedge filters are changed through beam hardening and the dose maximum can be shifted; both these changes result in errors in the final dose calculations of several per cent if open beam data are used. The errors are larger for 6 MV than for 18 MV x-rays. The depth of measurement for determining the wedge factor and the influence of other beam modifying devices are discussed. It is recommended that the reference depth be used instead of the dose maximum for these kinds of measurements since the influence of contaminating electrons in the beam will then be avoided and the wedge factor will be correct at a clinically relevant depth.
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| 4. |
- Lindholm, C E, et al.
(författare)
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Arterial rupture after microwave-induced hyperthermia and radiotherapy. With reference to two patients treated for recurrence in previously operated and irradiated areas
- 1990
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Ingår i: International Journal of Hyperthermia. - : Informa UK Limited. - 0265-6736 .- 1464-5157. ; 6:3, s. 499-509
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Tidskriftsartikel (refereegranskat)abstract
- Two patients who developed frank arterial bleeding after combined microwave-induced hyperthermia and radiotherapy are described. One patient received re-irradiation and hyperthermia for recurrent metastatic neck nodes of a mesopharyngeal carcinoma. Full course radiotherapy had been given 6 years previously and a right-sided radical neck node dissection had been performed 4 months earlier because of recurrent neck node metastases. Six weeks after the combined therapy for a second recurrence, which achieved complete remission, a fatal rupture of the carotid artery occurred. The other patient received re-irradiation and hyperthermia for a chest wall recurrence of a breast carcinoma, treated 5.5 years previously by sector resection and tangential beam radiotherapy, and treated again 2 years earlier with extensive surgery for a local recurrence. A frank arterial bleeding from the treated region was seen after 7 months, but could be arrested with surgery. This important complication in combined hyperthermia and radiotherapy does not seem to have been recognized before. Different explanations are discussed, such as the previous local treatment as well as high temperature and atherosclerosis per se.
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| 5. |
- Nilsson, M, et al.
(författare)
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Application of the Fano theorem in inhomogeneous media using a convolution algorithm
- 1992
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 37:1, s. 69-83
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Tidskriftsartikel (refereegranskat)abstract
- For photon fields, separate dose distribution kernels have been generated for charged particles produced in the first interaction, for single and multiple scattered photons, including bremsstrahlung and annihilation. These kernels are applied in absorbed dose calculations for radiotherapy treatment planning using a convolution technique. The vast amount of kernel data required for 3D calculations can be accurately generated out of a small subset, due to rotational symmetry. Due to the discrete sampling of both the irradiated object and the dose distribution kernels, application of the Fano theorem and O'Connor's scaling theorem is not possible without difficulties. The scaling process has been thoroughly investigated and a density dependent correction factor applied to the central kernel value has been derived. The calculated absorbed dose distributions were found to agree well with Monte Carlo calculated data using the EGS4 program.
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