GEANT4 simulation of a range verification method using delayed γ spectroscopy of a ⁹²Mo marker

Abstract

In this work, we propose a novel technique for in-vivo proton therapy range verification. This technique makes use of a molybdenum hadron tumour marker, implanted at a short distance from the clinical treatment volume. Signals emitted from the marker during treatment can provide a direct measurement of the proton beam energy at the marker’s position. Fusion-evaporation reactions between the proton beam and marker nucleus result in the emission of delayed characteristic γ rays, which are detected off-beam for an improved signal-to-noise ratio. In order to determine the viability of this technique and to establish an experimental setup for future work, the Monte Carlo package GEANT4 was used in combination with ROOT to simulate a treatment scenario with the new method outlined in this work. These simulations show that the intensity of delayed γ rays produced from competing reactions yields a precise measurement of the range of the proton beam relative to the marker, with sub-millimetre uncertainty.

Range verification in heavy-ion therapy using a hadron tumour marker

“…This peak identification method is a possibility for heavy ion therapy due to the much larger stopping powers relative to proton therapy. In contrast, previous investigations of this method for proton therapy found that the reaction channels for the peaks of interest opened and closed over the span of several millimeters for a foil target similar to the one used in this experiment (Kasanda et al 2020). The beam range over which the channels of interest are open is also highly dependent on the thickness of the marker used, allowing the precision of the verification method to be adjusted based on the precision of marker positioning and irradiation techniques.…”

“…Due to the nonlinear nature of ion stopping powers within the Bragg Peak region, a small localized HTM marker situated near the distal edge of the treatment field will only produce the signal of interest for a small range of beam energies. Additionally, as described in Kasanda et al (2020) and Burbadge et al (2020), the prompt background present during treatment delivery tends to be quite large, but decays very quickly when the beam is stopped. Measuring the delayed HTM signal between beam pulses, or after treatment delivery (depending on the half-life of the reaction product) produces a much cleaner spectrum.…”

“…In this work, we investigate the application of the technique for in vivo PT RV, called hadron tumour marker (HTM) RV, to heavy-ion therapy. This technique was investigated for use in proton therapy through simulation (Kasanda et al 2020), and experiment (Burbadge et al 2020) using natural molybdenum as a marker and was found to provide measurements of the remaining beam range after the marker with sub-milimetre precision and with no model dependency. This technique involves the implantation of a small, metallic marker, called hadron tumour marker, in the beam path, at a short known distance from the clinical target volume (CTV).…”

Proton therapy range verification method via delayed γ-ray spectroscopy of a molybdenum tumour marker

“…Taking all these requirements into account, molybdenum was chosen as an HTM material, which we have shown by simulations to be well suited for our RV technique (Kasanda et al 2020). nat Mo has a high (p, xn) reaction cross section to Tc isotopes, on the order of 100 mb for clinical proton beam energies (Uddin et al 2004, Uddin and Baba 2008, Takács et al 2002, Khandaker et al 2007, Alharbi et al 2011.…”

“…The work presented here experimentally demonstrates the feasibility of a new method to measure the remaining range of a proton beam after it passes through a hadron tumour marker (HTM) (Kasanda et al 2020), a small metal marker that would be implanted or injected very close to the tumour prior to treatment. The HTM responds to proton activation by undergoing nuclear reactions and producing characteristic γ rays.…”