Journal
RADIOTHERAPY AND ONCOLOGY
Volume 115, Issue 2, Pages 279-283Publisher
ELSEVIER IRELAND LTD
DOI: 10.1016/j.radonc.2015.04.007
Keywords
LET; RBE; Fe-plot; Survival parameters; Spread-out Bragg peak
Funding
- Heavy Ions at the National Institute of Radiological Sciences-Heavy-ion Medical Accelerator in Chiba (NIRS-HIMAC)
- Grants-in-Aid for Scientific Research [15K09986] Funding Source: KAKEN
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Background and purpose: Carbon-ion radiotherapy uses spread-out Bragg peaks (SOBP) to produce uniform biological effects within a target volume. The relative biological effectiveness is determined by the in vitro cell kill after a single dose is employed to design the SOBP. A question remains as to whether biological effects for in vivo tissues after fractionated doses are also uniform within the SOBP. Material and methods: Mouse foot skin was irradiated with fractionated doses of carbon ions at various linear energy transfer (LET) values. A new ridge filter was designed based on alpha and beta values for each LET to cause moderate skin reaction, and was studied concerning its uniformity. Results: The reciprocal total doses of intermediate-LET carbon ions and of reference gamma rays linearly increased with an increase of a dose per fraction in Fe-plots. As the single total dose of higher LET run off linearity, data obtained from 2 to 6 fractions were used to design a new ridge filter. The physical dose distribution of the new ridge filter was almost identical to, and indistinguishable from, the ridge filter designed based on the in vitro cell kill. Conclusions: The LET dependence of alpha is a principle of the biological factor to be used for designing spread-out Bragg peaks of carbon-ion radiotherapy. (C) 2015 Elsevier Ireland Ltd. All rights reserved.
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