Monte Carlo calculations of positron emitter yields in proton radiotherapy

Abstract

Positron emission tomography (PET) is a promising tool for monitoring the three-dimensional dose distribution in charged particle radiotherapy. PET imaging during or shortly after proton treatment is based on the detection of annihilation photons following the ß(+)-decay of radionuclides resulting from nuclear reactions in the irradiated tissue. Therapy monitoring is achieved by comparing the measured spatial distribution of irradiation-induced ß(+)-activity with the predicted distribution based on the treatment plan. The accuracy of the calculated distribution depends on the correctness of the computational models, implemented in the employed Monte Carlo (MC) codes that describe the interactions of the charged particle beam with matter and the production of radionuclides and secondary particles. However, no well-established theoretical models exist for predicting the nuclear interactions and so phenomenological models are typically used based on parameters derived from experimental data. Unfortunately, the experimental data presently available are insufficient to validate such phenomenological hadronic interaction models. Hence, a comparison among the models used by the different MC packages is desirable. In this work, starting from a common geometry, we compare the performances of MCNPX, GATE and PHITS MC codes in predicting the amount and spatial distribution of proton-induced activity, at therapeutic energies, to the already experimentally validated PET modelling based on the FLUKA MC code. In particular, we show how the amount of ß(+)-emitters produced in tissue-like media depends on the physics model and cross-sectional data used to describe the proton nuclear interactions, thus calling for future experimental campaigns aiming at supporting improvements of MC modelling for clinical application of PET monitoring.

Determination of elemental tissue composition following proton treatment using positron emission tomography

“…For example, the integration of the proton energy fluence with the cross sections, 12 C(p,pn) 11 C and 16 O(p,αpn) 11 C gave rise to α and α', respectively. The MCNPX technique used by Seravalli et al 2012 was followed for this Monte Carlo simulation. All cross sections used for Monte Carlo simulations were obtained from the semi-empirical equation developed by Nishio et al 2005, 2008, which is in agreement with the experimental data (Iljinov et al 1994) available at the EXFOR library from Brookhaven National Laboratory National Nuclear Data Center (http://www.nndc.bnl.gov/exfor/exfor00.htm).…”

Shaping and monitoring of the mini-beam structures for the spatially fractionated hadron radiation therapy

“…Design of collimators and their effectiveness were evaluated by Monte Carlo simulations in the framework of a software package for medical physics «Gate_v.6.2» based on Geant4 version [19,20]. Ideal rectangular (0.7 mm wide) beam of protons with angular spreading of Gaussian shape was assumed passing through water phantom of cylindrical shape with 16 cm height and 16 cm diameter.…”

“…Dose was calculated for voxels with the size of (0.01  1  1) mm 3 in each fractional part as the sum of the contributions from every individual minibeam to cover required irradiation field. The ionization potential for water was assumed to be 75 eV (as recommended in [20,21]). As figure of merit, percentage (peak and valley) depth dose curves, penumbras, and central value of the PVDR have been calculated for various collimators, incident ions and their energies.…”

Imaging-Based Treatment Adaptation in Radiation Oncology

“…As a consequence, PET is a noninvasive means for almost instantaneous image-guidance in hadron therapy, with an accuracy of below a few millimeters for estimating the range of proton and carbon ion beams (58). However, biologic washout and patient motion challenge the accuracy of range verification with PET (59).…”