| 1. |
- Blomquist, M, et al.
(author)
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Comparison between a conventional treatment energy and 50 MV photons for the treatment of lung tumours
- 2002
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In: Physics in Medicine and Biology. - 0031-9155 .- 1361-6560. ; 47:6, s. 889-897
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Journal article (peer-reviewed)abstract
- Radiation therapy in the thoracic region is difficult due to the presence of many dose-limiting structures and the large density differences that affect the dose distribution. Conventional irradiation techniques use low-energy photon beams to avoid build-up effects superficially in the tumour and increased lateral scattering of the beams. For deep-seated tumours higher beam energies could have lung-sparing properties that would enable dose escalation. A comparison was made for a conventional low photon energy (6 MV) and 50 MV photons for the treatment of a lung tumour. A representative patient geometry was selected, consisting of a small tumour semi-enclosed in lung tissue. Treatment plans were designed using a commercial 3D-pencil beam treatment planning system. The treatment beams designed in the TPS were simulated with the Monte Carlo code EGS4/BEAM and the dose distribution in the phantom created from the patients CT-data was calculated using MCDOSE with identical beam geometry for both energies. The intrinsic difference between the two photon energies implies a sparing effect of lung that can be utilized for dose escalation. For a treatment with two beams the mean total dose to the tumour could be increased by 5.3% for 50 MV, corresponding to 3.2 Gy for a prescription dose of 60 Gy, with the same complication probability for the treated lung as for 6 MV. In conclusion, high-energy beams have qualities that can be taken advantage of for irradiation of lung tumours. Optimum solutions would probably require the use of both high- and low-energy beams.
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| 2. |
- Blomquist, M, et al.
(author)
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Multileaf collimation of electrons-clinical effects on electron energy modulation and mixed beam therapy depending on treatment head design
- 2002
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In: Physics in Medicine and Biology. - 0031-9155 .- 1361-6560. ; 47:7, s. 1013-1024
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Journal article (peer-reviewed)abstract
- The aim Of this Study was to explore the possibilities of using multileaf-collimated electron beams for advanced radiation therapy with conventional scattering foil flattened beams. Monte Carlo simulations were performed with the aim to improve electron beam characteristics and enable isocentric multileaf collimation. The scattering foil positions, monitor chamber thickness, the MLC location and the amount of He in the treatment head were optimized for three common commercial accelerators. The performance of the three optimized treatment head designs was compared for different SSDs in air. at treatment depth in water and for some clinical cases. The effects of electron/photon beam matching including generalized random and static errors using Gaussian one-dimensional (1D) error distributions, and also electron energy modulation, were studied at treatment depth in beater, The modification of the treatment heads improved the electron beam characteristics and enabled the use of multileaf collimation in isocentric delivery of both electron and photon beams in a mixed beam IMRT procedure.
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| 3. |
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| 4. |
- Karlsson, M G, et al.
(author)
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Electron beam collimation with focused and curved leaf end MLCs - Experimental verification of Monte Carlo optimized designs
- 2002
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In: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 29:4, s. 631-637
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Journal article (peer-reviewed)abstract
- In general, electron beams, from conventional accelerators using applicators with lead alloy inserts are not suitable for advanced conformal radiation therapy. However, interesting electron treatments have been demonstrated on a few advanced accelerators. These accelerators have been equipped with helium filled treatment heads and computer controlled MLCs that produce clinically useful energy modulated electron beams or mixed photon electron beams in an automated sequence. This study analyzes the characteristics of different MLC designs, curved and focused leaf ends in helium filled treatment heads, with respect to their effect on electron beams. In addition, this study analyzes the effects that different treatment head designs have on the output factor due to collimator scattering and shielding of secondary sources during treatment. The investigation of the different treatment head designs was performed with the Monte Carlo package BEAM and was verified by experimental methods. The results show that the difference between curved leaf ends and focused ends is negligible in most practical cases. The results also show the importance of scattering foil optimization in the optimization of parameters such as penumbra. virtual source position, and in the reduction of the output variation. In all cases, the experimental data verifies the calculations. (C) 2002 American Association of Physicists in Medicine.
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