Contribution to dose in healthy tissue from secondary target fragments in therapeutic proton, He and C beams measured with CR-39 plastic nuclear track detectors

Abstract

The linear energy transfer (LET) spectrum, absorbed dose and dose equivalent from secondary particles of LET ∞ H 2 O ≥15 keV/μm deposited within the plateau of the Bragg curve in primary particle-induced nuclear target fragmentation reactions in tissue during proton and heavy ion radiotherapy were measured using CR-39 plastic nuclear track detectors and analyzed by means of atomic force microscopy. It was found that secondary target fragments contributed 20% to dose equivalent for primary protons (157 MeV), 13% for primary helium ions (145 MeV/n) and 4% for primary carbon ions (383 MeV/n), respectively. Little research has been done on the contribution from these particles to primary given dose. The smaller contribution measured for energetic carbon ion beams compared to proton beams can be considered an advantage of carbon ion radiotherapy over proton radiotherapy.

Secondary Radiation in Ion Therapy and Theranostics: A Review

“…At therapeutic energies, the target fragmentation rate was ∼3.62 times higher for carbon ion compared to that for proton beam [12]. But the absorbed dose and dose equivalent due to the secondary target fragments (STFs) were 0.22% and 4%, respectively, of the primary ion dose for 12 C, compared to 1.2% and 20%, respectively, for proton beam.…”

“…New beams like 4 He, 16 O are being studied to assess their possible advantages in ion beam therapy. 4 He ions might turn out to be a good choice, as projectile fragmentation and neutron production are expected to be lower than in the case of 12 C beams while having good localization of the energy deposition [12,13]. For 16 O, fragmentation is higher and in vitro studies had also provided a slightly larger RBE value [14,15] compared to 12 C, but carbon beam has a higher impact on cell survival.…”

“…4 He ions might turn out to be a good choice, as projectile fragmentation and neutron production are expected to be lower than in the case of 12 C beams while having good localization of the energy deposition [12,13]. For 16 O, fragmentation is higher and in vitro studies had also provided a slightly larger RBE value [14,15] compared to 12 C, but carbon beam has a higher impact on cell survival. However, in all the cases, actual volume which is exposed to primary and secondary radiation strongly depends on patient positioning and on anatomical variation of the target organ during treatment [5,6].…”

“…The contribution of the secondary fragments to the dose equivalent within the Bragg peak was ∼20%, 13%, and less than ∼8% of the total dose for 157 MeV proton, 145 MeV/u 4 He, and 219-383 MeV/u 12C beams, respectively [12,13,34]. Beyond the Bragg peak, the total dose was contributed by the secondary fragments only.…”

Are Further Cross Section Measurements Necessary for Space Radiation Protection or Ion Therapy Applications? Helium Projectiles

“…(6) In addition to projectile fragmentation, fragmentation of the target is also highly relevant for precise dose calculations in ion therapy [38].…”