Comparison of Response of Passive Dosimetry Systems in Scanning Proton Radiotherapy—a Study Using Paediatric Anthropomorphic Phantoms

Abstract

Proton beam therapy has advantages in comparison to conventional photon radiotherapy due to the physical properties of proton beams (e.g. sharp distal fall off, adjustable range and modulation). In proton therapy, there is the possibility of sparing healthy tissue close to the target volume. This is especially important when tumours are located next to critical organs and while treating cancer in paediatric patients. On the other hand, the interactions of protons with matter result in the production of secondary radiation, mostly neutrons and gamma radiation, which deposit their energy at a distance from the target. The aim of this study was to compare the response of different passive dosimetry systems in mixed radiation field induced by proton pencil beam inside anthropomorphic phantoms representing 5 and 10 years old children. Doses were measured in different organs with thermoluminescent (MTS-7, MTS-6 and MCP-N), radiophotoluminescent (GD-352 M and GD-302M), bubble and poly-allyl-diglycol carbonate (PADC) track detectors. Results show that RPL detectors are the less sensitive for neutrons than LiF TLDs and can be applied for in-phantom dosimetry of gamma component. Neutron doses determined using track detectors, bubble detectors and pairs of MTS-7/MTS-6 are consistent within the uncertainty range. This is the first study dealing with measurements on child anthropomorphic phantoms irradiated by a pencil scanning beam technique.

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

“…The data for the bubble detectors placed inside a water tank irradiated with an energy range between 62.7 and 89.8 meV used for eye treatments (Ciocca et al 2019) suggest that H is about ten times lower than those obtained in the present study for a similar primary proton energy used for the lung treatment. Unexpectedly, for a brain tumor of 65 cm 3 volume located inside a paediatric phantom irradiated with proton PBS of energies in the range 70-140 meV (Knežević et al 2018), the H measured with track-etched detectors showed similar values as the ones simulated in the present study for the lung tumour with a target volume twice as large and much lower primary proton energy. In addition, the H measured with track-etched detectors by Stolarczyk et al (2018), for a 1000 cm 3 target volume located inside a water tank irradiated with proton PBS at an energy range of 120-170 meV, is comparable to the H measured with the same detector type in an adult human phantom treated for prostate cancer (Hälg et al 2014), and to the H simulated in the present study for the prostate tumour, despite a five times bigger target volume and slightly lower primary proton energy.…”

“…The available literature on dose measurements in proton radiotherapy using a human phantom shows that the most studied cases involve tumours located in the head and that doses to other organs were not given (La Tessa et al 2012), or where data on the mean organ distance to the target volume were not given (Stolarczyk et al 2011). Furthermore, a comparison of the results obtained in the present study could not be done with those obtained by (Knežević et al 2018) because the phantom used by these authors was of another size.…”

“…nuclear track detectors or via simulations (Takam et al 2009). Such a conversion factor was recently elaborated by Knežević et al (2018) based on the net MTS-6-MTS-7 signal and the H measured by the nuclear track detectors inside a child phantom irradiated with proton PBS at energies between 70 and 140 meV. The conversion factor was found to be equal to unity.…”

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

“…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.…”

“…Pairs of 6 LiF/ 7 LiF thermoluminescence detectors are used in dosimetry to discriminate between neutron and gamma-ray doses. The difference in response between 6 LiF and 7 LiF detectors, caused by the higher 6 Li cross section in the Li(n,α)T reaction, is expressed in terms of the gamma-equivalent neutron dose, D n (Knežević et al 2018). However, this quantity cannot be used to infer neutron dose equivalent because the dose in tissue is predominately produced by high energy neutrons whereas 6 Li reacts mainly with thermal neutrons.…”