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Design of a compact high energy treatment unit combining narrow pencil beam scanning and multileaf collimation
Author(s) -
Svensson Roger
Publication year - 1998
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.598359
Subject(s) - isocenter , collimated light , collimator , microtron , optics , multileaf collimator , beam (structure) , photon , linear particle accelerator , physics , dosimetry , imaging phantom , nuclear medicine , laser , medicine
The thesis describes the design of scanned narrow photon beam in combination with a few optimally selected collimator settings delivered by a compact treatment machine to effectively produce a truly conformal treatment. The racetrack microtron generates moving photon beams by scanning the electron beam over a thin transmission target of low Z material, such as 3 mm beryllium. The transmitted electrons with an energy of about 49 MeV are removed by a strong purging magnet that will safely bend the beam to a dedicated electron stopper. The photon beam has a full width at half‐maximum of about 20 mm at a 70 cm source to the isocenter distance and the intensity in the forward direction is almost the same as from a full range target. The narrow photon beams are only scanned where the leaf collimator is open so the photons are effectively and safely used during the treatment. Only a few beam directions are needed to achieve almost optimal results. By using three fixed heads, it is possible to simultaneously scan three photon beams synchronously over the target volume. The increased instantaneous dose rate in the tumor enhances the biological effect. The mechanical construction will be very robust and of high mechanical stability since there are few moving parts. The compact size of the treatment heads and the whole gantry will make it an ergonomic and easy to handle unit. When biologically based optimized plans are delivered by such a compact machine, the highest possible complication free tumor control is nearly reached according to radiobiological models for treatment evaluation of intensity modulated beams. At the same time the treatment time will be short and the probability of tumor induction outside the target low. [References to the authors' papers on the thesis topic: Phys. Med. Biol. 39 , 37–61 (1994); Med. Phys. 22 , 1141–1156 (1995); Phys. Med. Biol. 41 , 1353–1397 (1996); Phys. Med. Biol. 43 , 1091–1112 (1998).]