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Title: Depth absorbed dose and LET distributions of therapeutic {sup 1}H, {sup 4}He, {sup 7}Li, and {sup 12}C beams

Abstract

The depth absorbed dose and LET (linear energy transfer) distribution of different ions of clinical interest such as {sup 1}H, {sup 4}He, {sup 7}Li, and {sup 12}C ions have been investigated using the Monte Carlo code SHIELD-HIT. The energies of the projectiles correspond to ranges in water and soft tissue of approximately 260 mm. The depth dose distributions of the primary particles and their secondaries have been calculated and separated with regard to their low and high LET components. A LET value below 10 eV/nm can generally be regarded as low LET and sparsely ionizing like electrons and photons. The high LET region may be assumed to start at 20 eV/nm where on average two double-strand breaks can be formed when crossing the periphery of a nucleosome, even though strictly speaking the LET limits are not sharp and ought to vary with the charge and mass of the ion. At the Bragg peak of a monoenergetic high energy proton beam, less than 3% of the total absorbed dose is comprised of high LET components above 20 eV/nm. The high LET contribution to the total absorbed dose in the Bragg peak is significantly larger with increasing ion charge as a naturalmore » result of higher stopping power and lower range straggling. The fact that the range straggling and multiple scattering are reduced by half from hydrogen to helium increases the possibility to accurately deposit only the high LET component in the tumor with negligible dose to organs at risk. Therefore, the lateral penumbra is significantly improved and the higher dose gradients of {sup 7}Li and {sup 12}C ions both longitudinally and laterally will be of major advantage in biological optimized radiation therapy. With increasing charge of the ion, the high LET absorbed dose in the beam entrance and the plateau regions where healthy normal tissues are generally located is also increased. The dose distribution of the high LET components in the {sup 7}Li beam is only located around the Bragg peak, characterized by a Gaussian-type distribution. Furthermore, the secondary particles produced by high energy {sup 7}Li ions in tissuelike media have mainly low LET character both in front of and beyond the Bragg peak.« less

Authors:
; ;  [1]
  1. Division of Medical Radiation Physics, Department of Oncology-Pathology, Karolinska Institutet and Stockholm University, Box 260, SE-171 76 Stockholm (Sweden)
Publication Date:
OSTI Identifier:
20853908
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 1; Other Information: DOI: 10.1118/1.2400621; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; BIOLOGICAL RADIATION EFFECTS; BRAGG CURVE; CARBON 12; DEPTH DOSE DISTRIBUTIONS; DOSIMETRY; HELIUM 4; ION BEAMS; LET; LIGHT IONS; LITHIUM 7; MONTE CARLO METHOD; NEOPLASMS; ORGANS; PROTON BEAMS; RADIATION DOSES; RADIOTHERAPY; SHIELDS; STOPPING POWER; STRAND BREAKS

Citation Formats

Kempe, Johanna, Gudowska, Irena, and Brahme, Anders. Depth absorbed dose and LET distributions of therapeutic {sup 1}H, {sup 4}He, {sup 7}Li, and {sup 12}C beams. United States: N. p., 2007. Web. doi:10.1118/1.2400621.
Kempe, Johanna, Gudowska, Irena, & Brahme, Anders. Depth absorbed dose and LET distributions of therapeutic {sup 1}H, {sup 4}He, {sup 7}Li, and {sup 12}C beams. United States. doi:10.1118/1.2400621.
Kempe, Johanna, Gudowska, Irena, and Brahme, Anders. Mon . "Depth absorbed dose and LET distributions of therapeutic {sup 1}H, {sup 4}He, {sup 7}Li, and {sup 12}C beams". United States. doi:10.1118/1.2400621.
@article{osti_20853908,
title = {Depth absorbed dose and LET distributions of therapeutic {sup 1}H, {sup 4}He, {sup 7}Li, and {sup 12}C beams},
author = {Kempe, Johanna and Gudowska, Irena and Brahme, Anders},
abstractNote = {The depth absorbed dose and LET (linear energy transfer) distribution of different ions of clinical interest such as {sup 1}H, {sup 4}He, {sup 7}Li, and {sup 12}C ions have been investigated using the Monte Carlo code SHIELD-HIT. The energies of the projectiles correspond to ranges in water and soft tissue of approximately 260 mm. The depth dose distributions of the primary particles and their secondaries have been calculated and separated with regard to their low and high LET components. A LET value below 10 eV/nm can generally be regarded as low LET and sparsely ionizing like electrons and photons. The high LET region may be assumed to start at 20 eV/nm where on average two double-strand breaks can be formed when crossing the periphery of a nucleosome, even though strictly speaking the LET limits are not sharp and ought to vary with the charge and mass of the ion. At the Bragg peak of a monoenergetic high energy proton beam, less than 3% of the total absorbed dose is comprised of high LET components above 20 eV/nm. The high LET contribution to the total absorbed dose in the Bragg peak is significantly larger with increasing ion charge as a natural result of higher stopping power and lower range straggling. The fact that the range straggling and multiple scattering are reduced by half from hydrogen to helium increases the possibility to accurately deposit only the high LET component in the tumor with negligible dose to organs at risk. Therefore, the lateral penumbra is significantly improved and the higher dose gradients of {sup 7}Li and {sup 12}C ions both longitudinally and laterally will be of major advantage in biological optimized radiation therapy. With increasing charge of the ion, the high LET absorbed dose in the beam entrance and the plateau regions where healthy normal tissues are generally located is also increased. The dose distribution of the high LET components in the {sup 7}Li beam is only located around the Bragg peak, characterized by a Gaussian-type distribution. Furthermore, the secondary particles produced by high energy {sup 7}Li ions in tissuelike media have mainly low LET character both in front of and beyond the Bragg peak.},
doi = {10.1118/1.2400621},
journal = {Medical Physics},
number = 1,
volume = 34,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • Purpose: Modern clinical accelerators are capable of producing ion beams from protons up to neon. This work compares the depth dose distribution and corresponding dose averaged linear energy transfer (LET) distribution, which is related to the biological effectiveness, for different ion beams ({sup 1}H, {sup 4}He, {sup 6}Li, {sup 8}Be, {sup 10}B, {sup 12}C, {sup 14}N, and {sup 16}O) using multi-energetic spectra in order to configure spread-out Bragg peaks (SOBP). Methods: Monte Carlo simulations were performed in order to configure a 5 cm SOBP at 8 cm depth in water for all the different ion beams. Physical dose and dosemore » averaged LET distributions as a function of depth were then calculated and compared. The superposition of dose distribution of all ions is also presented for a two opposing fields configuration. Additional simulations were performed for {sup 12}C beams to investigate the dependence of dose and dose averaged LET distributions on target depth and size, as well as beam configuration. These included simulations for a 3 cm SOBP at 7, 10, and 13 cm depth in water, a 6 cm SOBP at 7 depth in water, and two opposing fields of 6 cm SOBP. Results: Alpha particles and protons present superior physical depth dose distributions relative to the rest of the beams studied. Dose averaged LET distributions results suggest higher biological effectiveness in the target volume for carbon, nitrogen and oxygen ions. This is coupled, however, with relatively high LET values--especially for the last two ion species--outside the SOBP where healthy tissue would be located. Dose averaged LET distributions for {sup 8}Be and {sup 10}B beams show that they could be attractive alternatives to {sup 12}C for the treatment of small, not deeply seated lesions. The potential therapeutic effect of different ion beams studied in this work depends on target volume and position, as well as the number of beams used. Conclusions: The optimization of beam modality for specific tumor cites remains an open question that warrants further investigation and clinically relevant results.« less
  • New experimental data on the cross sections for the yield of excited {sup 6}Li* and {sup 7}Li* nuclei and on their contributions to the production of {sup 4}He + {sup 2}H and {sup 4}He+{sup 3}H light dinuclear systems in {sup 16}O{sub p} collisions at a momentumof 3.25 A GeV/c per nucleon are presented.
  • We combine a recently developed ab initio many-body approach capable of describing simultaneously both bound and scattering states, the ab initio no-core shell model/resonating-group method (NCSM/RGM), with an importance-truncation scheme for the cluster eigenstate basis and demonstrate its applicability to nuclei with mass numbers as high as 17. By using soft similarity renormalization-group-evolved chiral nucleon-nucleon interactions, we first calculate nucleon-{sup 4}He phase shifts, cross sections, and analyzing powers. Next, we investigate nucleon scattering on {sup 7}Li, {sup 7}Be, {sup 12}C, and {sup 16}O in coupled-channel NCSM/RGM calculations that include low-lying excited states of these nuclei. We check the convergence ofmore » phase shifts with the basis size and study A=8,13, and 17 bound and unbound states. Our calculations predict low-lying resonances in {sup 8}Li and {sup 8}B that have not been experimentally clearly identified yet. We are able to reproduce reasonably well the structure of the A=13 low-lying states. However, we find that A=17 states cannot be described without an improved treatment of {sup 16}O one-particle-one-hole excitations and {alpha} clustering.« less