Purpose or learning objective
Carbon ion beams used in radiotherapy have a distinct physical characteristic for radiation dosimetry compared to photon beams. When carbon ions pass through beam modulating human tissue, they produce nuclei fragmented from the projectile and the target nuclei. Many kinds of atomic nuclei are present, all with different energy distributions.
On the other hand, water is used as the reference medium for measurements of absorbed dose in carbon ion beams. Those fragmentations of projectiles and targets affect considerably the biological response to carbon ion beams...
Methods or background
A Monte Carlo simulation application was used to model the radiation field produced by carbon ion beams in various human tissue-like phantoms.
The geometry of the beamline is shown in Figure 1. The dose along with the phantom depth for each type of nuclear fragment was calculated using the Monte Carlo simulation code (PHITS 3.20). The characteristics of the radiation field produced by incident carbon ions were studied in phantoms. Table 1 shows the median of the phantoms (ICRU-44).
Results or findings
The output of the simulation consisted of the energy deposition in the phantom as well as the position of secondary particles generated within the phantom.
The energy deposition derived from the incident Carbon(C) ion beam and from the secondary nuclear fragments, such Proton, Helium (He), Lithium (Li), Beryllium (Be), and Boron (B), was tallied spatial resolution.
Table 2 and Figure 2 show the depth of Bragg peak for various media.
Figure 3 shows the distribution of spread-out Bragg peak of 350 MeV/n carbon beams.
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Conclusion
We present a method with four tissue types. The tissue media are shown to be a key parameter for dose distribution with carbon ion beams.
The contribution of total depth dose deposition behind the Bragg peak is 100% due to the secondary nuclear fragments. Energy deposition tail cannot be neglected as side effects may be located in this position behind the Bragg Peak.
Carbon ion therapy is measured to investigate the secondary fragments outside of the therapeutic field.
References
Tatsuhiko Sato, Yosuke Iwamoto, Shintaro Hashimoto, Tatsuhiko Ogawa, Takuya Furuta, Shin-ichiro Abe, Takeshi Kai, Pi-En Tsai, Norihiro Matsuda, Hiroshi Iwase, Nobuhiro Shigyo, Lembit Sihver and Koji NiitaFeatures of Particle and Heavy Ion Transport code System (PHITS) version 3.02, J. Nucl. Sci. Technol. 55(5-6), 684-690 (2018)