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Titolo:
Beam characteristics and clinical possibilities of a new compact treatmentunit design combining narrow pencil beam scanning and segmental multileaf collimation
Autore:
Svensson, R; Lind, B; Brahme, A;
Indirizzi:
Karolinska Inst, Dept Med Radiat Phys, S-17176 Stockholm, Sweden Karolinska Inst Stockholm Sweden S-17176 Phys, S-17176 Stockholm, Sweden Stockholm Univ, S-17176 Stockholm, Sweden Stockholm Univ Stockholm Sweden S-17176 Univ, S-17176 Stockholm, Sweden
Titolo Testata:
MEDICAL PHYSICS
fascicolo: 12, volume: 25, anno: 1998,
pagine: 2358 - 2369
SICI:
0094-2405(199812)25:12<2358:BCACPO>2.0.ZU;2-F
Fonte:
ISI
Lingua:
ENG
Soggetto:
RADIATION-THERAPY; CONFORMAL RADIOTHERAPY; PHOTON BEAMS; OPTIMIZATION; COMPENSATION; GENERATION; ALGORITHM; PROFILES; BREMSSTRAHLUNG; DOSIMETRY;
Keywords:
scanned beams; intensity modulation; radio biological optimization; treatment units; bremsstrahlung targets;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Clinical Medicine
Life Sciences
Citazioni:
38
Recensione:
Indirizzi per estratti:
Indirizzo: Svensson, R Karolinska Inst, Dept Med Radiat Phys, POB 260, S-17176 Stockholm, Sweden Karolinska Inst POB 260 Stockholm Sweden S-17176 holm, Sweden
Citazione:
R. Svensson et al., "Beam characteristics and clinical possibilities of a new compact treatmentunit design combining narrow pencil beam scanning and segmental multileaf collimation", MED PHYS, 25(12), 1998, pp. 2358-2369

Abstract

Not until the last decade has flexible intensity modulated three-dimensional dose delivery techniques with photon beams become a clinical reality, first in the form of heavy metal transmission blocks and other beam compensators, then in dynamic and segmented multileaf collimation, and most recentlyby scanning high-energy narrow electron and photon beams. The merits of various treatment unit and bremsstrahlung target designs for high-energy photon therapy are investigated theoretically for two clinically relevant target sites, a cervix and a larynx cancer both in late stages. With an optimized bremsstrahlung target it is possible to generate photon beams with a half-width of about 3 cm at a source to axis distance (SAD) of 100 cm and an initial electron energy of 50 MeV. By making a more compact treatment head and shortening the SAD, it is possible to reduce the half-width even further to about 2 cm at a SAD of 70 cm and still have sufficient clearance betweenthe collimator head and the patient. One advantage of a reduced SAD is that the divergence of the beam for a given field size on the patient is increased, and thus the exit dose is lowered by as much as 1%/cm of the patient cross section. A second advantage of a reduced SAD is that the electron beam on the patient surface will be only about 8 mm wide and very suitable forprecision spot beam scanning. It may also be possible to reduce the beamwidth further by increasing the electron energy up to about 60 MeV to get a photon beam of around 15 mm half-width and an electron beam as narrow as 5 mm. The compact machine will be more efficient and easy to work with, due tothe small gantry and the reduced isocentric height. For a given target volume and optimally selected static multileaf collimator, it is no surprise that the narrowest possible scanned elementary bremsstrahlung beam generatesthe best possible treatment outcome. In fact, by delivering a few static field segments with individually optimized scan patterns, it is possible to combine the advantage of being able to fine tune the fluence distribution by the scanning system with the steeper dose gradients that can be deliveredby a few static multileaf collimator segments. It is demonstrated that in most cases a few collimator segments are sufficient and often a single segment per beam portal may suffice when narrow scanned photon beams are employed, and they can be delivered sequentially with a negligible time delay. A further advantage is the increase of therapeutically useful photons and improved patient protection, since the pencil beam is only scanned where the leaf collimator is open. Consequently, some of the problems associated with dynamic multileaf collimation such as the tongue and groove and edge leakage effects are significantly reduced. Fast scanning beam techniques combinedwith good treatment verification systems allow interesting future possibilities to counteract patient and;internal organ motions in real time. (C) 1998 American Association of Physicists in Medicine. [S0094-2405(98)01112-2].

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 04/12/20 alle ore 22:32:17