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

Satoshi Kodaira,Hisashi Kitamura,Eric R Benton,Mieko Kurano,Hajime Kawashima

doi:10.1038/s41598-019-39598-0

Abstract

The linear energy transfer (LET) spectrum, absorbed dose and dose equivalent from secondary particles of LET∞H2O ≥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.

Highlights

The benefits and advantages of ion beam radiotherapy have been well documented[1], one aspect of heavy ion beam radiotherapy that has received only limited attention is the absorbed dose and dose equivalent from nuclear target fragmentation interactions[2,3] between the primary protons and heavy ions of the radiotherapy beam, and the constituent heavy nuclei, mostly 12C and 16O nuclei, of the healthy tissue itself deposited in healthy tissue traversed by the plateau of the Bragg curve
To measure the contribution from proton and heavy ion induced target fragmentation secondaries to the absorbed dose and dose equivalent deposited in the plateau of the Bragg curve, CR-39 plastic nuclear track detector (PNTD) analyzed by means of AFM was used[9]
A uniform pattern of very small tracks can be seen in the 383 MeV/n Carbon exposure at δ = 90° that is not seen in any of the other images. These are the tracks from the primary C ions in the beam. They are not visible in the images from the proton and He beams, because the linear energy transfer (LET) of primary ions is too low to register in CR-39

Summary

Introduction

The benefits and advantages of ion beam radiotherapy have been well documented[1], one aspect of heavy ion beam radiotherapy that has received only limited attention is the absorbed dose and dose equivalent from nuclear target fragmentation interactions[2,3] between the primary protons and heavy ions of the radiotherapy beam, and the constituent heavy nuclei, mostly 12C and 16O nuclei, of the healthy tissue itself deposited in healthy tissue traversed by the plateau of the Bragg curve. We know of no treatment planning software that takes into account such nuclear target fragmentation contributions to dose in healthy tissue

Methods

Results

Conclusion