Jerimy C Polf and Wayne D Newhauser 2005 Phys. Med. Biol. 50 3859 doi:10.1088/0031-9155/50/16/014
Jerimy C Polf1 and Wayne D Newhauser1,2
Show affiliationsPassive beam spreading techniques have been used for most proton therapy treatments worldwide. This delivery method employs static scattering foils to spread the beam laterally and a range modulating wheel or ridge filter to spread the high dose region in depth to provide a uniform radiation dose to the treatment volume. Neutrons produced by interactions of the treatment beam with nozzle components, such as the range modulation wheel, can account for a large portion of the secondary dose delivered to healthy tissue outside the treatment volume. Despite this fact, little is known about the effects of range modulation on the secondary neutron exposures around passively scattered proton treatment nozzles. In this work, the neutron dose equivalent spectra per incident proton (H(E)/p) and total neutron dose equivalent per therapeutic absorbed dose (H/D) were studied using Monte Carlo techniques for various values of range modulation at 54 locations around a passive scattering proton therapy treatment nozzle. As the range modulator wheel step thickness increased from 1.0 to 11.5 cm, the peak values of H(E)/p decreased from approximately 1 × 10−17 mSv Gy−1 to approximately 2 × 10−18 mSv Gy−1 at 50 cm from isocentre along the beam's central axis. In general, H/D increased with increasing range modulation at all locations studied, and the maximum H/D exposures shifted away from isocentre.
Issue 16 (21 August 2005)
Received 24 February 2005, in final form 25 May 2005
Published 3 August 2005
Jerimy C Polf and Wayne D Newhauser 2005 Phys. Med. Biol. 50 3859
C. Scarlata et al. 2007 ApJS 172 494
T W Barbee III et al 1988 J. Phys. C: Solid State Phys. 21 5977
Kwok L Lam et al 2005 Phys. Med. Biol. 50 3849
A N F Aleixo et al 2003 J. Phys. A: Math. Gen. 36 11631
L Martina et al 2001 J. Phys. A: Math. Gen. 34 9243
Fèlix Casanova et al 2005 J. Phys. D: Appl. Phys. 38 3343
B J Fahey et al 2006 Phys. Med. Biol. 51 3785
Nelson Christensen et al 2004 Class. Quantum Grav. 21 S1747
Chad Clark et al 1999 Class. Quantum Grav. 16 3965