Secondary neutron dose measurement for proton eye treatment using an eye snout with a borated neutron absorber

Abstract

BackgroundWe measured and assessed ways to reduce the secondary neutron dose from a system for proton eye treatment.MethodsProton beams of 60.30 MeV were delivered through an eye-treatment snout in passive scattering mode. Allyl diglycol carbonate (CR-39) etch detectors were used to measure the neutron dose in the external field at 0.00, 1.64, and 6.00 cm depths in a water phantom. Secondary neutron doses were measured and compared between those with and without a high-hydrogen–boron-containing block. In addition, the neutron energy and vertices distribution were obtained by using a Geant4 Monte Carlo simulation.ResultsThe ratio of the maximum neutron dose equivalent to the proton absorbed dose (H(10)/D) at 2.00 cm from the beam field edge was 8.79 ± 1.28 mSv/Gy. The ratio of the neutron dose equivalent to the proton absorbed dose with and without a high hydrogen-boron containing block was 0.63 ± 0.06 to 1.15 ± 0.13 mSv/Gy at 2.00 cm from the edge of the field at depths of 0.00, 1.64, and 6.00 cm.ConclusionsWe found that the out-of-field secondary neutron dose in proton eye treatment with an eye snout is relatively small, and it can be further reduced by installing a borated neutron absorbing material.

In‐field and out‐of‐field microdosimetric characterisation of a 62 MeV proton beam at CATANA

“…Moving a further 2 mm, the value obtained drops significantly to 184.0 mSv/Gy. This drop off past 2 mm of the edge of the field agrees well with previous work by Cuttone et␣al, 25 which quotes a lateral fall‐off of <1.5 mm for SOBP primary protons. 2 mm further away this value significantly reduces to a value of 19.0 mSv/Gy and continues reducing to a value of 1.27 mSv/Gy at 27 mm from isocentre, 12 mm from the edge of the field.…”

Measurement of stray radiation within a scanning proton therapy facility: EURADOS WG9 intercomparison exercise of active dosimetry systems

“…Indeed, WENDI-II shows a factor of 7.9 over-response at 2 MeV, a factor of 2 under-response at 20 MeV, and a factor of 1.86 over-response at 5 GeV. 15 The very good agreement with extended-range BSS H * (10) values, observed at all measurement positions (14), is mainly due to the fact that neutron fluence peak values (see Figs. 2 and 3) fall at energy ranges where the performance of the WENDI-II is appropriate.…”

“…5,8,10,11 Neutron organ dose measurements have also been conducted using passive detectors such as superheated emulsions (bubble detectors), thermoluminescent detector (TLD), and solid state nuclear track detector (SSNTD) mainly. 3,8,[12][13][14] On the one hand, all these studies have shown that stray neutron radiation involved in proton therapy is not negligible (up to 10 mSv/proton Gy outside the clinical target volume), is facility dependent (with major effects arising from beam line elements and shielding design), and implicates neutrons of high energy (equal to the proton beam energy). On the other hand, these studies have confirmed that measuring stray radiation and estimating patients' exposure remain very challenging owing to the complexity of the radiation field.…”

Monte Carlo modeling of proton therapy installations: a global experimental method to validate secondary neutron dose calculations

“…Proper evaluation of the risks related to proton therapy treatments requires assessment of the secondary doses delivered to normal tissues. Since in vivo organ dose measurements are practically impossible to perform, Monte Carlo (MC) simulations have proven to be a very useful tool that allows neutron dose calculations (Agosteo et al 1998, Zheng et al 2007, Zacharatou-Jarlskog et al 2008, Kim et al 2013. The modeling of the treatment facility is based on original manufacturer and engineering drawings of both the beam line elements and the bunker.…”

“…However, to guarantee accurate dose calculations in routine clinical conditions, the main challenge is the validation of the MC models with respect to both the proton beam (prescription dose) and the simulation of secondary neutrons (secondary dose) present inside the treatment room. Measurements in a water-tank phantom of proton depth dose distributions and profiles represent a good and widely used method to validate MC models with respect to the prescription dose (Paganetti et al 2004, Hérault et al 2005, Fontenot et al 2005, Tayama et al 2006, Kim et al 2013. However, the validation of the MC model with respect to secondary neutrons is far more challenging owing to the complex neutron dosimetry.…”