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Secondary absorbed doses from light ion irradiation in anthropomorphic phantoms representing an adult male and a 10 year old child
Stockholm University, Faculty of Science, Department of Physics. (Medicinsk strålningsfysik)
Stockholm University, Faculty of Science, Department of Physics. (Medicinsk strålningsfysik)
2010 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 55, no 22, 6633-6653 p.Article in journal (Refereed) Published
Abstract [en]

Secondary organ absorbed doses were calculated by Monte Carlo simulations with the SHIELD-HIT07 code coupled with the mathematical anthropomorphic phantoms CHILD-HIT and ADAM-HIT. The simulated irradiations were performed with primary 1H, 4He, 7Li, 12C and 16O ion beams in the energy range 100–400 MeV/u which were directly impinging on the phantoms, i.e. approximating scanned beams, and with a simplified beamline for 12C irradiation. The evaluated absorbed doses to the out-of-field organs were in the range 10−6 to 10−1 mGy per target Gy and with standard deviations 0.5–20%. While the contribution to the organ absorbed doses from secondary neutrons dominated in the ion beams of low atomic number Z, the produced charged fragments and their subsequent charged secondaries of higher generations became increasingly important for the secondary dose delivery as Z of the primary ions increased. As compared to the simulated scanned 12C ion beam, the implementation of a simplified beamline for prostate irradiation with 12C ions resulted in an increase of 2–50 times in the organ absorbed doses depending on the distance from the target volume. Comparison of secondary organ absorbed doses delivered by 1H and 12C beams showed smaller differences when the RBE for local tumor control of the ions was considered and normalization to the RBE-weighted dose to the target was performed.

General scientific summary. During light ion therapy, the production of nuclear fragments results in a complex secondary radiation field which the organs and normal tissues of the patient are exposed to. In the present work, the absorbed doses to out-of-field organs and the energy distribution of secondary particle fluences in anthropomorphic phantoms have been simulated by the Monte Carlo code SHIELD-HIT07 for brain tumor and prostate irradiation with approximated scanned beams of 1H, 4He, 7Li, 12C and 16O ions in the energy range 100–400 MeV/u, as well as with a simplified beam line for 12C irradiation. The evaluated organ absorbed doses were in the range 10−6 to 10−1 mGy per target Gy. The absorbed dose contribution from secondary neutrons dominated in the ion beams of low atomic number Z, while the produced charged fragments and their subsequent charged secondaries became increasingly important for the secondary dose delivery as Z of the primary ion increased.

Place, publisher, year, edition, pages
2010. Vol. 55, no 22, 6633-6653 p.
National Category
Other Physics Topics
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-64294DOI: 10.1088/0031-9155/55/22/004OAI: oai:DiVA.org:su-64294DiVA: diva2:456784
Available from: 2011-11-15 Created: 2011-11-15 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Secondary absorbed dose distributions and radiation quality in light ion therapy
Open this publication in new window or tab >>Secondary absorbed dose distributions and radiation quality in light ion therapy
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Radiotherapy with light ions offers the possibility of achieving a dose distribution which is highly conformed to the target volume while sparing normal tissues. For ions heavier than protons, an additional advantage is the increased Relative Biological Effectiveness (RBE) as compared to conventional photon and electron beams. During light ion therapy, nuclear fragments are produced in nuclear inelastic collisions of the projectile and the atomic nuclei in the material. In a cascade of events, the nuclear fragments in turn produce secondaries during their transport. The organs of the patient are thus exposed to a complex secondary radiation field and secondary doses can be delivered to normal tissues both close to and relatively far from the treated volume. In this thesis, secondary doses were evaluated in anthropomorphic phantoms which were developed for simulations with the Monte Carlo code SHIELD-HIT. Simulations of lung tumor, prostate and brain tumor irradiation with 1H, 4He, 7Li, 12C and 16O ion beams in the energy range 80-400 MeV/u were performed with SHIELD-HIT. The simulated organ absorbed doses were in the range 10-6-10-1 mGy per treatment Gy. In general, the organ absorbed doses decreased with increasing distance from the target volume and increased with increasing atomic number of the primary ions.

The produced nuclear fragments also influences the radiation quality in the target volume and thus the biological effectiveness of the beam. The dose-mean lineal energy, <yD>, was studied in a 290 MeV/u 12C beam by simulating the energy distributions of both primary and secondary ions and weighting their relative dose fractions with the corresponding energy-dependent <yD> which were obtained by ion-track simulations with PITS99 coupled with the electron transport code KURBUC. <yD> were evaluated in the target volume for object diameters 10-100 nm and were used in estimations of clinically useful weighting factors.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2011. 54 p.
Keyword
secondary doses, light ion therapy, radiation quality, Monte Carlo simulation
National Category
Physical Sciences
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-64302 (URN)978-91-7447-412-1 (ISBN)
Public defence
2011-12-20, Föreläsningssalen, Cancercentrum Karolinska, R8:00, Karolinska universitetssjukhuset, Solna, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.

Available from: 2011-11-28 Created: 2011-11-16 Last updated: 2016-01-18Bibliographically approved

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