Dose distribution of secondary radiation in a water phantom for a proton pencil beam—EURADOS WG9 intercomparison exercise

Abstract

Systematic 3D mapping of out-of-field doses induced by a therapeutic proton pencil scanning beam in a 300 × 300 × 600 mm water phantom was performed using a set of thermoluminescence detectors (TLDs): MTS-7 (LiF:Mg,Ti), MTS-6 (LiF:Mg,Ti), MTS-N (LiF:Mg,Ti) and TLD-700 (LiF:Mg,Ti), radiophotoluminescent (RPL) detectors GD-352M and GD-302M, and polyallyldiglycol carbonate (PADC)-based (CHO) track-etched detectors. Neutron and gamma-ray doses, as well as linear energy transfer distributions, were experimentally determined at 200 points within the phantom. In parallel, the Geant4 Monte Carlo code was applied to calculate neutron and gamma radiation spectra at the position of each detector. For the cubic proton target volume of 100 × 100 × 100 mm (spread out Bragg peak with a modulation of 100 mm) the scattered photon doses along the main axis of the phantom perpendicular to the primary beam were approximately 0.5 mGy Gy at a distance of 100 mm and 0.02 mGy Gy at 300 mm from the center of the target. For the neutrons, the corresponding values of dose equivalent were found to be ~0.7 and ~0.06 mSv Gy, respectively. The measured neutron doses were comparable with the out-of-field neutron doses from a similar experiment with 20 MV x-rays, whereas photon doses for the scanning proton beam were up to three orders of magnitude lower.

Modelling and measurements of distributions in an adult human phantom undergoing proton scanning beam radiotherapy: lung- and prostate-located tumours

“…7, the mean conversion factor from the γ-equivalent neutron dose to H was found in the present study to be 1.03 ± 0.32, showing a very good agreement with the results by (Knežević et al 2018). However, the values of the conversion coefficient are not always equal to unity as was reported in (Stolarczyk et al 2018).…”

Out-of-field doses for scanning proton radiotherapy of shallowly located paediatric tumours—a comparison of range shifter and 3D printed compensator

“…The uncertainties can be calculated as the uncertainty of the average value using values for particular counters from table 1 in the supplementary data. difference is proportional to the thermal neutron fluence at the position of the detector (Stolarczyk et al 2018). The dose values obtained in this way require a conversion to be comparable with neutron doses obtained by reading BD (see section 4.1.…”

“…Neutron ambient dose equivalent H * (10) measurements were performed using five different neutron monitors presented in this section, which-except REM-2 and GW2 ionization chambers-are described in details in the previous EURADOS WG9 article (Stolarczyk et al 2018). The REM-2 and GW2 chambers are cylindrical parallel-plate recombination chambers with an active volume of about 1800 cm 3 .…”

“…RPLs were calibrated in terms of kerma free-in-air, K air , using a 60 Co source and then converted to D w using experimentally determined factors (Knežević et al 2013). For determining the uncertainty of dose calculation for TLDs and RPLs, the same procedures were used as presented in Knežević et al (2013Knežević et al ( , 2018 and Stolarczyk et al (2018). Particular calculated uncertainties are presented in the table 2 in the supplementary data.…”

High CT doses return to the agenda

“…These problems have prompted efforts to model the combined dose from radiotherapy and imaging using Monte Carlo techniques and to test the results experimentally by simulating the treatment using anthropomorphic phantoms loaded with thermoluminescence (TL) and other passive dosemeters. This is, for example, outlined by the European Radiation Dosimetry Group (EURA-DOS), building upon previous experimental studies of out-of-field doses in radiotherapy (Majer et al 2017;Stolarczyk et al 2018;Knesevic et al 2018). A summary of recent findings of these efforts can be found in Rühm et al (2019).…”