Neutron measurements with ultra-thin 3D silicon sensors in a radiotherapy treatment room using a Siemens PRIMUS linac

Abstract

The accurate detection and dosimetry of neutrons in mixed and pulsed radiation fields is a demanding instrumental issue with great interest both for the industrial and medical communities. In recent studies of neutron contamination around medical linacs, there is a growing concern about the secondary cancer risk for radiotherapy patients undergoing treatment in photon modalities at energies greater than 6 MV. In this work we present a promising alternative to standard detectors with an active method to measure neutrons around a medical linac using a novel ultra-thin silicon detector with 3D electrodes adapted for neutron detection. The active volume of this planar device is only 10 µm thick, allowing a high gamma rejection, which is necessary to discriminate the neutron signal in the radiotherapy peripheral radiation field with a high gamma background. Different tests have been performed in a clinical facility using a Siemens PRIMUS linac at 6 and 15 MV. The results show a good thermal neutron detection efficiency around 2% and a high gamma rejection factor.

Improving the neutron-to-photon discrimination capability of detectors used for neutron dosimetry in high energy photon beam radiotherapy

“…This equivalence does not depend on the primary photon field energy, since the out-of-axis photon spectrum is invariably composed by photons below 0.5 MeV (D'Mellow et al, 2007;Chofor et al, 2012). In addition, due to the high neutron capture cross section of 10 B, the borated rubber acts as an efficient neutron absorber (Guardiola et al, 2013; http:// www.johncaunt.com/shielding/neutron-shielding/jc238/), with a nominal thermal neutron transmission factor of 3.8  10 À 3 . Two layers of Flex-boron s (dimensions 0.32 cm  5 cm  20 cm) were used to shield on both sides the detectors used here.…”

“…Since dosimetric methods for photon doses are well-known Taddei et al, 2013), our group has focused on the neutron component, and established a methodology to estimate peripheral neutron doses (Sánchez-Doblado et al, 2012;Expósito et al, 2013;Romero-Expósito et al, 2015;VazquezLuque et al, 2013). Although this procedure was developed for a particular thermal neutron detector (Gómez et al, 2010), could be applicable to any other (Guardiola et al, 2013;Bedogni et al, 2014). Specifically, one of these detectors, named TNRD (Thermal Neutron Rate Detector), designed and developed by Bedogni et al, was characterized for peripheral neutron dose measurements in radiotherapy environments, according to the methodology described in Sánchez-Doblado et al (2012).…”

Proposed linear energy transfer areal detector for protons using radiochromic film

“…Specifically, current techniques measure LET use tissue-equivalent proportional counters, 4 solid-state spectrometers, 5 and other methods. [6][7][8] Preliminary proof of principle studies 9,10 used a BANG gel to explore the possibility of measuring LET over extended volumes. This study discusses a possible method to measure the LET deposited by a proton beam over extended areas using a film dosimeter (radiochromic Gafchromic EBT2 film).…”

“…The SND calculation used the registered images of the absolute planned dose and the detected dose and then related to the LET according to Eq. (8). To validate this approach, Monte Carlo simulations (magenta in Figure 2) were generated to emulate the experimental setup.…”

Semiconductor neutron detectors

“…The reported efficiency was of 6.3% for a single layer compared the 4.90% obtained with a reference planar detector. Among other interesting devices based on micro-machining are ultra thin 3D sensors with a planar converter coating ( 10 B 4 C) proposed by CNM Barcelona (Spain) to minimize the γ-ray sensitivity [20][21] [22]. Moreover, SINTEF (Oslo, Norway) developed sensors with pyramidal grooves with a relative efficiency of up to 38% higher compared to planar [23].…”