| 1. |
- Slatkin, Daniel, et al.
(författare)
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Microbeam Radiation Therapy
- 1992
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405 .- 2473-4209. ; 19, s. 1395-1400
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Tidskriftsartikel (refereegranskat)abstract
- It is proposed to carry out radiotherapy and radiosurgery for brain lesions by crossfiring an array of parallel, closely spaced microbeams of synchrotron-generated x rays several times through an isocentric target, each microbeam in the array having an 25-µm-wide adjustable-height rectangular cross section. The following inferences from the known tissue sparing of 22-MeV deuteron microbeams in the mouse brain and the following exemplary Monte Carlo computations indicate that endothelial cells in the brain that are lethally irradiated by any microbeam in an array of adequately spaced microbeams outside an isocentric target will be replaced by endothelial cells regenerated from microscopically contiguous, minimally irradiated endothelium in intermicrobeam segments of brain vasculature. Endothelial regeneration will prevent necrosis of the nontargeted parenchymal tissue. However, neoplastic and/or nonneoplastic targeted tissues at the isocenter will be so severely depleted of potentially mitotic endothelial and parenchymal cells by multiple overlapping microbeams that necrosis will ensue. The Monte Carlo computations simulate microbeam irradiations of a 16-cm diameter, 16-cm-long cylindrical human head phantom using 50-, 100-, and 150-keV monochromatic x rays.
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| 2. |
- 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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| 3. |
- Karlsson, Mikael
(författare)
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A multileaf delineator system for a radiotherapy simulator
- 1994
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 21:1, s. 83-84
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Tidskriftsartikel (refereegranskat)abstract
- Multileaf collimators are offered as an accessory to many accelerators for conformal radiotherapy and the dose planning systems are capable of calculating multileaf collimated beams. There is further a frequent desire to verify the radiation fields on a radiotherapy simulator prior to the actual treatment. For this purpose,an accessory to the simulator was developed (the multileaf delineator). With this unit the front end of the individual leaves are indicated both on the skin of the patient and in the x-ray image. All anatomical structures both outside and inside the field edge are, however, still fully visible.
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| 4. |
- Karlsson, Mikael, et al.
(författare)
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Electron beam characteristics of the 50-MeV racetrack microtron
- 1992
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 19:2, s. 307-315
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Tidskriftsartikel (refereegranskat)abstract
- Electron beams in the MM50 racetrack microtron are generated by computer controlled scanning of a well-focused electron pencil beam. The treatment head is optimized to give a minimum of scatter between the source position and the collimator plane by a general minimization of all scattering material in the beam and by replacement of the air in the treatment head by helium, which has a much lower linear scattering power than air. A double-focused multileaf collimator with a 31-cm collimator to patient distance is used both for electron and photon collimation. In general, no extra electron collimation is needed for the standard SSD of 100 cm. To make irregular field collimation at a distance this far from the patient possible, a number of requirements have to be fulfilled regarding the virtual source position and the spatial and angular distribution of the initial electron beam. The virtual source position has been found to be at a fixed position for different irradiation parameters. This is important for the use of the light field in electron beam treatment but also for achieving a high degree of accuracy in the dosimetry. Scatter from the multileaf collimator has not been found to give any significant contribution to the radiation field or to the monitor output factor of the MM50. Experimental dose distribution data on the MM50 have been compared to data both from other types of treatment units and to Monte Carlo simulations.
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| 5. |
- Karlsson, Mikael, et al.
(författare)
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Photon beam characteristics on the MM50 racetrack microtron and a new approach for beam quality determination
- 1993
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 20:1, s. 143-149
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Tidskriftsartikel (refereegranskat)abstract
- The photon beams of the MM50 racetrack microtron have special characteristics which make them more suitable than conventional photon beams for precision radiation therapy with good dosimetric control. The beam flattening is obtained by the scanning of an elementary beam instead of using a flattening filter. This will give a number of advantages such as the possibility to optimize field flattening to individual field forms and field sizes. The radiation quality is the same across the whole beam, which gives smaller changes in dose profiles with depth and also makes it easier to perform careful dose planning. Beam collimation is mainly performed by a multileaf collimator and the special design of the treatment head gives nearly ideal characteristics for dose determination in an arbitrary point in the treatment fields. The output factor has been shown to depend almost solely on scattering within the treatment field. The conventional methods for beam quality characterization have been found less suitable at high energies and a new method based on HVL measurements in water is proposed.
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| 6. |
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