Premium
Dose contributions from large‐angle scattered particles in therapeutic carbon beams
Author(s) -
Kusano Yohsuke,
Kanai Tatsuaki,
Kase Yuki,
Matsufuji Naruhiro,
Komori Masataka,
Kanematsu Nobuyuki,
Ito Atsushi,
Uchida Hirohisa
Publication year - 2007
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2402328
Subject(s) - imaging phantom , percentage depth dose curve , pencil beam scanning , dosimetry , beam (structure) , irradiation , bragg peak , physics , pencil (optics) , optics , dose profile , transverse plane , gaussian , materials science , atomic physics , computational physics , nuclear medicine , ion , nuclear physics , ionization chamber , proton therapy , ionization , medicine , structural engineering , engineering , quantum mechanics
In carbon therapy, doses at center of spread‐out Bragg peaks depend on field size. For a small field of 5 × 5cm 2 , the central dose reduces to 96% of the central dose for the open field in case of 400 MeV ∕ n carbon beam. Assuming the broad beam injected to the water phantom is made up of many pencil beams, the transverse dose distribution can be reconstructed by summing the dose distribution of the pencil beams. We estimated dose profiles of this pencil beam through measurements of dose distributions of broad uniform beams blocked half of the irradiation fields. The dose at a distance of a few cm from the edge of the irradiation field reaches up to a few percent of the central dose. From radiation quality measurements of this penumbra, the large‐angle scattered particles were found to be secondary fragments which have lower LET than primary carbon beams. Carbon ions break up in beam modifying devices or in water phantom through nuclear interaction with target nuclei. The angular distributions of these fragmented nuclei are much broader than those of primary carbon particles. The transverse dose distribution of the pencil beam can be approximated by a function of the three‐Gaussian form. For a simplest case of mono‐energetic beam, contributions of the Gaussian components which have large mean deviations become larger as the depth in the water phantom increases.