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Purpose: Neutron peripheral contamination in high-energy radiotherapy implies an increase of secondary radiation-induced cancer risk. Although peripheral neutron dose (PND) has been evaluated in organs, few studies have been performed regarding patient size. This work aims to improve an existing methodology for adult patient PND estimations to generalize it to young and children, for its implementation in treatment planning systems (TPS)., Methods: As a first step, we aimed to generalize the previous model to be usable with any thermal neutron detector. Then, taking into account total neutron spectra and dose-to-point thermal neutron fluence measurements for three phantom sizes (adult, teen and child) and two common treatment locations (H&N and abdomen), the new model was proposed. It represents an upgraded parameterization and extension of the existing one, including patient anatomy. Finally, comparison between estimations and measurements, as well as validation against the original model, was carried out for 510 measured patients., Results: Concordance found between experimental and theoretical estimations makes us confident about later implementation in treatment planning systems. Comparison among the previous and upgraded models shows no significant differences for the adult case. However, an important underestimation (34.1% on average) can be observed regarding child case for the original one., Conclusions: An improved generalization of an existing PND model, considering patient anatomy has been validated and used in real patients. The final methodology is easily implementable in clinical routine and TPS thanks to the ready availability of input parameters (patient height and weight, high-energy MU and facility characterization)., (Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

The increasing interest of the medical community to radioinduced second malignancies due to photoneutrons in patients undergoing high-energy radiotherapy, has stimulated in recent years the study of peripheral doses, including the development of some dedicated active detectors. Although these devices are designed to respond to neutrons only, their parasitic photon response is usually not identically zero and anisotropic. The impact of these facts on measurement accuracy can be important, especially in points close to the photon field-edge. A simple method to estimate the photon contribution to detector readings is to cover it with a thermal neutron absorber with reduced secondary photon emission, such as a borated rubber. This technique was applied to the TNRD (Thermal Neutron Rate Detector), recently validated for thermal neutron measurements in high-energy photon radiotherapy. The positive results, together with the accessibility of the method, encourage its application to other detectors and different clinical scenarios., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Active thermal neutron detectors are used in a wide range of measuring devices in medicine, industry and research. For many applications, the long-term stability of these devices is crucial, so that very well controlled neutron fields are needed to perform calibrations and repeatability tests. A way to achieve such reference neutron fields, relying on a 3 MV Tandem Pelletron accelerator available at the CNA (Seville, Spain), is reported here. This paper shows thermal neutron field production and reproducibility characteristics over few days., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Purpose: Knowing the contribution of neutron to collateral effects in treatments is both a complex and a mandatory task. This work aims to present an operative procedure for neutron estimates in any facility using a neutron digital detector., Methods: The authors' previous work established a linear relationship between the total second cancer risk due to neutrons (TR(n)) and the number of MU of the treatment. Given that the digital detector also presents linearity with MU, its response can be used to determine the TR(n) per unit MU, denoted as m, normally associated to a generic Linac model and radiotherapy facility. Thus, from the number of MU of each patient treatment, the associated risk can be estimated. The feasibility of the procedure was tested by applying it in eight facilities; patients were evaluated as well., Results: From the reading of the detector under selected irradiation conditions, m values were obtained for different machines, ranging from 0.25 × 10(-4)% per MU for an Elekta Axesse at 10 MV to 6.5 × 10(-4)% per MU for a Varian Clinac at 18 MV. Using these values, TR(n) of patients was estimated in each facility and compared to that from the individual evaluation. Differences were within the range of uncertainty of the authors' methodology of equivalent dose and risk estimations., Conclusions: The procedure presented here allows an easy estimation of the second cancer risk due to neutrons for any patient, given the number of MU of the treatment. It will enable the consideration of this information when selecting the optimal treatment for a patient by its implementation in the treatment planning system.

Purpose: Peripheral dose in radiotherapy treatments represents a potential source of secondary neoplasic processes. As in the last few years, there has been a fast-growing concern on neutron collateral effects, this work focuses on this component. A previous established methodology to estimate peripheral neutron equivalent doses relied on passive (TLD, CR39) neutron detectors exposed in-phantom, in parallel to an active [static random access memory (SRAMnd)] thermal neutron detector exposed ex-phantom. A newly miniaturized, quick, and reliable active thermal neutron detector (TNRD, Thermal Neutron Rate Detector) was validated for both procedures. This first miniaturized active system eliminates the long postprocessing, required for passive detectors, giving thermal neutron fluences in real time., Methods: To validate TNRD for the established methodology, intrinsic characteristics, characterization of 4 facilities [to correlate monitor value (MU) with risk], and a cohort of 200 real patients (for second cancer risk estimates) were evaluated and compared with the well-established SRAMnd device. Finally, TNRD was compared to TLD pairs for 3 generic radiotherapy treatments through 16 strategic points inside an anthropomorphic phantom., Results: The performed tests indicate similar linear dependence with dose for both detectors, TNRD and SRAMnd, while a slightly better reproducibility has been obtained for TNRD (1.7% vs 2.2%). Risk estimates when delivering 1000 MU are in good agreement between both detectors (mean deviation of TNRD measurements with respect to the ones of SRAMnd is 0.07 cases per 1000, with differences always smaller than 0.08 cases per 1000). As far as the in-phantom measurements are concerned, a mean deviation smaller than 1.7% was obtained., Conclusions: The results obtained indicate that direct evaluation of equivalent dose estimation in organs, both in phantom and patients, is perfectly feasible with this new detector. This will open the door to an easy implementation of specific peripheral neutron dose models for any type of treatment and facility.

Purpose: Second cancer, as a consequence of a curative intent radiotherapy (RT), represents a growing concern nowadays. The unwanted neutron exposure is an important contributor to this risk in patients irradiated with high energy photon beams. The design and development by our group of a neutron digital detector, together with the methodology to estimate, from the detector readings, the neutron equivalent dose in organs, made possible the unprecedented clinical implementation of an online and systematic neutron dosimetry system. The aim of this study was to systematically estimate neutron equivalent dose in organs of a large patient group treated in different installations., Patients and Methods: Neutron dosimetry was carried out in 1377 adult patients at more than 30 different institutions using the new neutron digital detector located inside the RT room. Second cancer risk estimates were performed applying ICRP risk coefficients., Results: Averaged equivalent dose in organs ranges between 0.5 mSv and 129 mSv depending on the type of treatment (dose and beam-on time), the distance to isocenter and the linac model. The mean value of the second cancer risk for our patient group is 1.2%. Reference values are proposed for an overall estimation of the risks in 15 linac models (from 2.8 × 10(-5) to 62.7 × 10(-5)%/MU)., Conclusions: The therapeutic benefit of RT must outweigh the second cancer risk. Thus, these results should be taken into account when taking clinical decisions regarding treatment strategy choice during RT planning., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Neutron peripheral contamination in patients undergoing high-energy photon radiotherapy is considered as a risk factor for secondary cancer induction. Organ-specific neutron-equivalent dose estimation is therefore essential for a reasonable assessment of these associated risks. This work aimed to develop a method to estimate neutron-equivalent doses in multiple organs of radiotherapy patients. The method involved the convolution, at 16 reference points in an anthropomorphic phantom, of the normalized Monte Carlo neutron fluence energy spectra with the kerma and energy-dependent radiation weighting factor. This was then scaled with the total neutron fluence measured with passive detectors, at the same reference points, in order to obtain the equivalent doses in organs. The latter were correlated with the readings of a neutron digital detector located inside the treatment room during phantom irradiation. This digital detector, designed and developed by our group, integrates the thermal neutron fluence. The correlation model, applied to the digital detector readings during patient irradiation, enables the online estimation of neutron-equivalent doses in organs. The model takes into account the specific irradiation site, the field parameters (energy, field size, angle incidence, etc) and the installation (linac and bunker geometry). This method, which is suitable for routine clinical use, will help to systematically generate the dosimetric data essential for the improvement of current risk-estimation models.