Study of the time and space distribution of beta+ emitters from 80 MeV/u carbon ion beam irradiation on PMMA

TL;DR

This study investigates the spatial and temporal distribution of positron emitters produced by 80 MeV/u carbon ion beams in PMMA, aiming to improve real-time dose monitoring in carbon ion therapy.

Contribution

It provides the first detailed measurement of beta+ emitter rates and their depth distribution from carbon ion irradiation in PMMA, highlighting the dominance of $^{11}C$ and comparing observed depths with simulations.

Findings

$^{11}C$ is the dominant positron emitter.

Measured positron emission depth is 5.3 mm, less than the simulated Bragg peak at 11.0 mm.

Fraction of carbon ions activating beta+ emitters is approximately 1.03%.

Abstract

Proton and carbon ion therapy is an emerging technique used for the treatment of solid cancers. The monitoring of the dose delivered during such treatments and the on-line knowledge of the Bragg peak position is still a matter of research. A possible technique exploits the collinear $511\ \kilo\electronvolt$ photons produced by positrons annihilation from $\beta^+$ emitters created by the beam. This paper reports rate measurements of the $511\ \kilo\electronvolt$ photons emitted after the interactions of a $80\ \mega\electronvolt / u$ fully stripped carbon ion beam at the Laboratori Nazionali del Sud (LNS) of INFN, with a Poly-methyl methacrylate target. The time evolution of the $\beta^+$ rate was parametrized and the dominance of $^{11}C$ emitters over the other species ($^{13}N$, $^{15}O$, $^{14}O$) was observed, measuring the fraction of carbon ions activating $\beta^+$ emitters $A_0=(10.3\pm0.7)\cdot10^{-3}$. The average depth in the PMMA of the positron annihilation from $\beta^+$ emitters was also measured, $D_{\beta^+}=5.3\pm1.1\ \milli\meter$, to be compared to the expected Bragg peak depth $D_{Bragg}=11.0\pm 0.5\ \milli\meter$ obtained from simulations.