Elevated LET components in clinical proton beams
- 30 September 2011
- journal article
- Published by IOP Publishing in Physics in Medicine & Biology
- Vol. 56 (20), 6677-6691
- https://doi.org/10.1088/0031-9155/56/20/011
Abstract
This paper assesses the contribution of secondary particles to pencil and passively scattered proton beams, in particular when considering the dose-averaged linear energy transfer (LET(d)) in biological treatment planning. Proton Monte Carlo simulations are performed in water phantoms and for two patients, considering all primary and secondary particles, including recoils from inelastic nuclear interactions. Our results show that secondary protons exhibit LET(d) values up to a factor 10 higher than those of the primary protons at the same depth. Thus, secondary protons have a significant impact on the LET(d). Their contribution increases the LET(d) by ∼50% along the central axis and even >200% in the penumbra. Furthermore, the LET maximum after the peak changes from 12 to 15 keV µm(-1) when adding secondary protons to the primary contribution. This is important when modeling LET(d) with analytical methods. The contribution of recoils (A > 3) is observed to be 1.2% in the entrance region considering a prostate case. The degree of biological damage inflicted by recoils remains hard to quantify, but is discussed on the basis of detailed energy spectra. The results highlight the role of secondary protons in LET-based radiobiological effectiveness calculations for proton therapy and when analyzing radiobiological experiments. Furthermore, the findings demonstrate the impact of inhomogeneities on the LET and the subtle changes between the LET distributions of passively scattered and actively scanned beams.Keywords
This publication has 32 references indexed in Scilit:
- Frequency Distribution of Second Solid Cancer Locations in Relation to the Irradiated Volume Among 115 Patients Treated for Childhood CancerInternational Journal of Radiation Oncology*Biology*Physics, 2009
- Beyond the Bragg Peak: Hyperthermal Heavy Ion Damage to DNA ComponentsPhysical Review Letters, 2005
- Cell transformation by light charged particles : review of available dataRadiotherapy and Oncology, 2004
- Geant4—a simulation toolkitNuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003
- Cancer induction by radiotherapy: dose dependence and spatial relationship to irradiated volumeJournal of Radiological Protection, 2002
- Secondary neutron and photon dose in proton therapyRadiotherapy and Oncology, 1998
- Interspecies Differences in Bone Composition, Density, and Quality: Potential Implications for in Vivo Bone ResearchEndocrinology, 1998
- RBE-LET relationships for cell inactivation and mutation induced by low energy protons in V79 cells: further results at the LNL facilityInternational Journal of Radiation Biology, 1998
- Microdosimetry spectra of the Loma Linda proton beam and relative biological effectiveness comparisonsMedical Physics, 1997
- RBE-LET Relationship for the Survival of V79 Cells Irradiated with Low Energy ProtonsInternational Journal of Radiation Biology, 1989