Secondary absorbed doses from light ion irradiation in anthropomorphic phantoms representing an adult male and a 10 year old child

• 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.

Ämnesord

NATURVETENSKAP  -- Fysik -- Annan fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Other Physics Topics (hsv//eng)

Nyckelord

Medical Radiation Physics

medicinsk strålningsfysik

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)