Accelerator Room Research Articles

ARDUINO AND IOT-BASED OBSERVATION METHOD FOR MONITORING TEMPERATURE, HUMIDITY, AND AIR PRESSURE OF ELECTRON BEAM ACCELERATOR’S ROOM

The monitoring system for temperature, humidity and air pressure in the electron accelerator’s room has been designed. This research is based on operational environmental monitoring procedures in the accelerator room that must be carried out before the accelerator operates. We offer a simple and adaptable monitoring solution for the electron accelerator room. Parameter data can be monitored using a smart device. Operators do not need to go into the accelerator room to carry out environmental monitoring. The proposed system uses Arduino technology and the Internet of Things (IoT). Data acquisition programming was performed using Arduino IDE and ESP8266 NodeMCU as microcontrollers. The microcontroller then transmits temperature, humidity, and pressure data parameters to the cloud server, where they are then displayed on the smart device via the Blynk app. The results show that the system that has been designed is able to read and store parameter readings on the sensors used and the system has been able to make decisions in the form of notifications about whether the Electron Beam Machine is ready or not to be operated.

Improved compact representation method for Monte Carlo phase spaces

Phase space files used in particle Monte Carlo simulations can be large, and thereby awkward to distribute and slow to load into memory. To circumvent this, compact source models and phase space representations have been developed. In this study, the aim is to increase the versatility of a previously presented method, based on principal component analysis whitening, by evaluating several modifications to the method on simulated cone-beam computed tomography projection images. Scaling the phase space components before whitening was seen to give the largest improvement and allowed for accurate modelling of phase spaces with a shifted detector and/or a bowtie filter present, configurations where the original method struggled. The modified method reproduced results using the original phase space to within a few percent both in energy fluence on the detector and in simulated projection and scatter images of a patient pelvis, without obvious position-dependence of the errors. Hence, the modified method was deemed sufficiently accurate for most applications relying on cone-beam computed tomography simulations. The final aim is to use the more versatile method for a broader range of phase space-based applications such as linear accelerator beam simulations and room shielding calculations.

MONTE CARLO NEUTRON DOSE MEASUREMENT IN PROTON THERAPY FOR HEALTHCARE WORKER RADIATION SAFETY

Background: Proton therapy is an innovative and highly advanced external radiation therapy modality for cancer treatment that uses positively charged atomic particles. The usage of proton therapy facilities in Asia has been increasing and will be followed by Indonesia in the short-coming years. In line with its significant benefits, the application of proton therapy also requires radiation protection awareness due to its higher energy used by protons produces scattered photon and neutron radiation in proton interactions. Therefore, optimal verification is needed in the commissioning process for designing proton therapy shielding bunkers. Objective: This research aims to examine the effect of concrete density on proton shielding by calculating the equivalent dose H*(10) of neutrons in the treatment control room (TCR) and the door of the compact proton therapy facility (CPTC) using Particle and Heavy Ion Transport code System (PHITS) simulation software. Method: The proton facility modeled for this simulation uses a compact proton therapy type planned to be built at one of the radiotherapy facilities in Indonesia. The proton therapy bunker model consists of a synchrocyclotron accelerator room and an examination room with standard configurations, wall thicknesses, and modeling areas under compact proton therapy standards. The analysis is focused on assessing the suitability of concrete materials and wall thicknesses and determining the neutron exposure dose values in the TCR and CPTC doors. The geometry, radiation source, and type of concrete in the wall are simulated from a conservative assumption to a more realistic model. Result: At the designated points in the TCR and CPTC door, measurements are taken from the simulation, which indicates that the equivalent dose H*(10) value is below one mSv/year. Conclusion: This value indicates that the dose rate passing through the wall does not exceed the dose limit value already set at one mSv/year for the general public.

Long-Term Results of Intraoperative Radiation Therapy for Early Breast Cancer Using a Nondedicated Linear Accelerator

To present the long-term results of intraoperative radiation therapy (IORT) for early breast cancer using a nondedicated linear accelerator. The eligibility criteria were biopsy-proven invasive carcinoma, age ≥40 years, tumor size ≤3 cm, and N0M0. We excluded multifocal lesions and sentinel lymph node involvement. All patients had previously undergone breast magnetic resonance imaging. Breast-conserving surgery with margins and sentinel lymph node evaluation using frozen sections were performed in all cases. If there were no margins or involved sentinel lymph nodes, the patient was transferred from the operative suite to the linear accelerator room, where IORT was delivered (21 Gy). A total of 209 patients who were followed up for ≥1.5 years from 2004 to 2019 were included. The median age was 60.3 years (range, 40-88.6), and the mean pT was 1.3 cm (range, 0.2-4). There were 90.5% pN0 cases (7.2% of micrometastases and 1.9% of macrometastases). Ninety-seven percent of the cases were margin free. The rate of lymphovascular invasion was 10.6%. Twelve patients were negative for hormonal receptors, and 28 patients were HER2 positive. The median Ki-67 index was 29% (range, 0.1-85). Intrinsic subtype stratification was as follows: luminal A, 62.7% (n=131); luminal B, 19.1% (n=40); HER2 enriched 13.4% (n=28); and triple negative, 4.8% (n=10). Within the median follow-up of 145 months (range, 12.8-187.1), the 5-year, 10-year, and 15-year overall survival rates were 98%, 94.7%, and 88%, respectively. The 5-year, 10-year, and 15-year disease-free rates were 96.3%, 90%, and 75.6%, respectively. The 15-year local recurrence-free rate was 76%. Fifteen local recurrences (7.2%) occurred throughout the follow-up period. The mean time to local recurrence was 145 months (range, 12.8-187.1). As a first event, 3 cases of lymph node recurrence, 3 cases of distant metastasis, and 2 cancer-related deaths were recorded. Tumor size >1 cm, grade III, and lymphovascular invasion were identified as risk factors. Despite approximately 7% of recurrences, we may infer that IORT may still be a reasonable option for selected cases. However, these patients require a longer follow-up as recurrences may occur after 10 years.

Assessment of Photon Beam Skyshine Dose Equivalent Rate of a 4 MeV Radiation Therapy Bunker Using Analytical and Monte Carlo Methods

Purpose: Skyshine radiation dose equivalent dose rate is known as scattered radiation by the room above air to points at the ground level points outside the Linear Accelerator (LINAC) room. Our aim was to estimate skyshine around the LINAC-based radiotherapy by a 4MV LINAC photon beam.
 Materials and Methods: Monte Carlo (MC) MCNP code calculation was conducted to skyshine at the control room, 60Co treatment room, physics, and simulator rooms. National Council on Radiation Protection and Measurements (NCRP) 151 was also used and it reported analytical formulation methods for photon beam calculation. A Flattering Filter (FF) equipped and Flattening Filter-Free (FFF) LINACs photon beams were derived and differences and agreements were discussed.
 Results: The results showed high skyshine for FF equipped relative to FFF LINACs. This effect may be attributed to photon beam hardening by FF in the LINAC head and higher transmission through the ceiling shield and more presence of photons on the roof above the air. NCRP 151 method results were higher than MC simulated photon beam skyshine dose equivalent dose rate and it may be the cause of the inflexible analytical method in contrast to MC simulation. Finally, FFF and FF-equipped LINACs result in skyshine compared and they compared to NCRP 151 report. MC simulation performed reasonably in estimation in different conditions.
 Conclusion: Our results showed that FF-equipped skyshine is higher than FFF LINAC and NCRP 151 is an inflexible method that does not take some effective parameters into account and calculates skyshine higher.

Single Institute Experience – Linear Accelerator Based Total Body Irradiation Using Volumetric Modulated Arc Therapy Planning in Standard Size Linear Accelerator Room

<h3>Purpose/Objective(s)</h3> To share experience of linear accelerator based total body irradiation (TBI) with volumetric modulated arc therapy (VMAT) in a standard size linear accelerator room <h3>Materials/Methods</h3> 30 patients aged 2-18 years (between 2018-2021) were treated with TBI as conditioning for bone marrow transplant (BMT)using VMAT based plan on our linear accelerator in a standard sized linear accelerator room. Indication of BMT was – acute lymphoblastic leukemia, acute myelogenous leukemia, chronic myeloid leukemia, myelodysplasia, aplastic anemia etc. Patient selection involved assessment regarding need of anesthesia, details of previous radiation, details of conditioning regimen for scheduling, organs dysfunction, adequate counselling and written consent from parents. With or without anesthesia, patients were immobilized using full body vacloc, head rest, brain orfit cast and knee rest. Position was supine, hands by side. Both head first (HF) and feet first (FF) scans were acquired if body length was more than 120 cm (for 120 cm, HF scan alone was acquired). A wire was placed on thigh to aid fusion of HF and FF scans for plan evaluation. Fiducials at three levels and optically stimulated luminescent dosimeter for dose monitoring were placed. Dose was 2-4 Gy single fraction and 12-13.2Gy/6 fractions (twice daily over 3 days, with 6 hours gap) based on chemotherapy conditioning regimen- delivered to 14 and 16 patients respectively. The planning objective was 90-100% coverage and dose max less than 120%. For multifraction plans, target was mean dose to lungs and kidney less than 10 Gy and 8Gy respectively. VMAT plans were generated with 3-5 iso-centers with fixed couch vertical and lateral values and changing longitudinal value, ensuring only longitudinal couch movement. Plan was made using 6MV energy and 5-9 arcs and 3 cm overlap between fields (avoid over joints to prevent effusion and over lungs to reduce lung dose) <h3>Results</h3> Mean PTV V95 – 93% (92-96%), Dmax – 115% mean (109%-120%). Mean lung dose (for 12-13.2Gy plans) was 9.4Gy/ (9-10 Gy), kidney mean dose was 7.8Gy (7.5-8 Gy). Mean monitor units in the plans were 1120 for complete arc and 690 for partial arcs. Treatment was delivered in strict aseptic precautions, under cover of steroids and antiemetics - in presence of radiation oncologist and physicist. Cone beam CT scan was used for position verification before and after treatment. The mean duration of treatment was 75 mins (range 60-90 minutes). 18 patients had grade 2 nausea and vomiting, one had knee joint effusion. No other side effects were reported. All transplants were successful except one reported graft versus host disease. <h3>Conclusion</h3> The procedure needs careful planning and delivery. It is feasible and possible to deliver TBI using VMAT in a standard sized linear accelerator room and should be offered to patients requiring the same.

Secondary and activated X($$\gamma$$) radiation of SPHIC particle therapy facility

We report the secondary X( $$\gamma$$ ) radiation from the accelerator in a normal operating state and activated X( $$\gamma$$ ) radiation from the accelerator devices when the accelerator stops operating in the cancer treatment facility of the Shanghai Proton and Heavy Ion Center (SPHIC). These radiation measurements show us the structural radiation distribution along the beam lines and devices inside the accelerator room when the beam is on and off and can support the radiation protection design of the accelerator facility used for cancer treatment and help evaluate the accumulated radiation dose in the case of an emergency, such as a personal safety system failure or a radiation accident. The radiation dose rate measured in this facility shows that the facility is safe from the radiation protection point. After shooting the quality assurance (QA) beam, the radiation dose rate in the treatment room was also measured to investigate the radiation dose space distribution and decay time dependence. In addition, the time period before safely entering the treatment room after determining the shooting of the QA beam is recommended to be approximately 5 min.

Decontamination Plan for the Concrete of the Activated Accelerator Room and Its Implementation: A Case Study in the Decommissioning of the PET Cyclotron Room at the Medical and Pharmacological Research Center Foundation

Decontamination Plan for the Concrete of the Activated Accelerator Room and Its Implementation: A Case Study in the Decommissioning of the PET Cyclotron Room at the Medical and Pharmacological Research Center Foundation

The patient experience of radiotherapy for breast cancer: A qualitative investigation as part of the SuPPORT 4 All study

IntroductionBreast cancer is a global health problem with 2.09 million cases of breast cancer diagnosed worldwide in 2018. With an increase in breast cancer survival attention has now focussed on the impact treatment side effects can have on the quality of life for women during survivorship. The aim of the SuPPORT 4 All project is to develop a support bra for use during radiotherapy, that can reduce normal tissue toxicity (for women with larger breasts) and provide accuracy, dignity and modesty for all women. The first stage of the project involved a co-design process to understand the current patient experience where no support bra or modesty device is used. MethodA participatory co-design methodology was adopted. Workshops were held with patient representatives (n = 9) to seek understanding of experience during radiotherapy; a total of three workshops over 4 h. The workshops were audio recorded and framework analysis was adopted to identify key patient experiences. ResultsTwelve categories and twenty-six sub categories were identified specific to patient experience. Patient concerns focussed on information provision, Healthcare Practitioner (HCP) knowledge of breast lymphoedema, lack of choice, experiences of being naked, and feelings of disempowerment. ConclusionsA number of areas were identified that had negative effects on overall patient experience. Implications for practicePractitioners should consider patient dignity when configuring services to support patient needs regarding undressing, outside or inside the linear accelerator room. Additionally, practitioners should have an understanding of the impact permanent tattoos may have on some patients’ wellbeing and the impact that breast lymphoedema has on patient quality of life. Practitioners should also consider methods to encourage patient empowerment during radiotherapy; supporting patient self-monitoring of side-effects may be one way to facilitate this.

Determination of the photon spectrum of a therapeutic linear accelerator near the maze entrance: Comparison of Monte Carlo modeling and measurements using scintillation detectors corrected for pulse pile-up.

The determination of x-ray spectra near the maze entrance of linear accelerator (LINAC) rooms is challenging due to the pulsed nature of the LINAC source. Mathematical methods to account for pulse pile-up have been examined. These methods utilize the highly periodic pulsing structure of the LINAC, differing from the effects of high-intensity radioactive sources. Sodium iodide (NaI) and plastic scintillation detectors were used to determine the energy spectra at different points near the maze entrance of a medical LINAC. Monte Carlo calculations of the energy distribution of scattered photons were used to simulate the energy spectrum at the maze entrance. The proposed algorithm uses the Monte Carlo code, FLUKA, to calculate a response function for both detectors. To determine the effects of the pile-up in the spectra, the Poisson distribution was used, employing the average number of photons per pulse (μ) interacting with the detector. The quantity, μ, was obtained from the ratio of the number of events detected to the number of pulses delivered. The energy spectra at various distances from the maze entrance were measured using NaI and plastic scintillation detectors. From these measurements, the values of µ were calculated, and the pile-up probability was determined. The FLUKA Monte Carlo code was used to calculate the spectrum at the maze entrance and the response matrices of the NaI and plastic scintillation detectors. The algorithm based on the Poisson distribution was applied to calculate the spectrum. The agreement between the calculated and measured spectra was within the first standard deviation of the variance expected in µ. This agreement confirms that photons at the maze entrance have energies between 30 and 240keV for a maze with three turns, with an average energy of around 85keV. After pile-up correction, the range of the pulse height distribution with the plastic scintillation detector, which has a low atomic number, was decreased (0 to 140keV). In contrast, the range of the pulse height distribution with the NaI scintillation detector was closer to the photon spectrum (0 to 240keV). The corrected spectrum demonstrates that using a FLUKA Monte Carlo code and an algorithm based on the Poisson distribution are effective methods in removing the distortion due to the pile-up in LINAC spectra when measuring with NaI and plastic scintillation detectors. The agreement between the corrected and measured spectra indicates that Monte Carlo modeling can accurately determine the spectrum of a LINAC machine at the maze entrance.

Effect of intraoperative radiotherapy for early breast cancer on 10-year recurrence rates and overall survival.

The aim of this study was to evaluate 10-year local control and overall survival of IORT for early breast cancer treatment. We analyzed 68 patients submitted to breast conservative surgery and IORT, in the accelerator room of the Radiotherapy Service in South Brazil. In the long-term follow-up, we had 17.6% of patients with ipsilateral breast cancer recurrence, 2.9% with regional recurrence, 2.9% with contralateral breast recurrence, and 5.9% with distant metastasis. The 10-year overall survival was 82.8%. Our data show high local recurrence rates, however, good overall survival in early breast cancer patients treated with breast-conserving surgery and intraoperative radiotherapy with electron beams in the long-term follow-up.

Thermal neutron profile inside J-PARC main ring tunnel

Abstract To estimate the beam losses and activation in the J-PARC main ring (MR) tunnel, thermal neutron distribution was measured using gold foil activation detectors with the Cd difference method. Hundred pairs of bare and Cd-covered gold foils were prepared to cover the entire area of the MR tunnel. The relative and absolute activities of the gold foils were measured using an imaging plate and an HP-Ge detector for some reference foils, respectively. A total of 97% of the thermal neutrons were detected in the injection section, where a beam collimation system was installed to localize the beam loss in the MR tunnel. The thermal neutron fluxes were compared with the calculation results from a Monte Carlo simulation code, PHITS. The calculation results were generally in good agreement with the experimental thermal neutron flux distribution. Furthermore, we investigated a simple empirical formula, ϕ th = C Q ∕ S , to estimate the thermal neutron flux in the accelerator room, where Q is the neutron source intensity and S is the total surface area of the room. A coefficient C of 1.61 ± 0.15 was deduced in the MR tunnel, which is within the error range of the previous value measured in the CERN CHARM facility using a 24 GeV/c proton beam despite the different projectile energies and room shapes. The γ dose rates at the same positions as the gold foils were measured as well. A strong correlation was observed between the thermal neutron fluxes and γ dose rates with respect to the surrounding concrete types. This result suggests that the dose rate on the concrete wall can be used to estimate the distribution of the thermal neutron fluxes and the amount of beam loss in the MR.

Measurement and calculation of thermal neutrons induced by the 24 GeV/c proton bombardment of a thick copper target

Abstract The CERN High-Energy AcceleRator Mixed field (CHARM) facility provides a secondary particle field, produced by irradiating a thick target with 24 GeV/c protons supplied by the proton synchrotron. In order to investigate the thermalization process of secondary neutrons in the CHARM facility, we measured the thermal neutrons using the gold foil activation method. Bare and Cd-covered gold foils were placed at 35 positions to deduce the thermal neutron distribution in the CHARM facility. The 197Au(n, γ )198Au reaction rates and thermal neutron fluxes measured in this study were compared with the Monte Carlo simulation codes, PHITS, FLUKA, and MARS. The comparison between the measured and simulated values gives an agreement better than a factor of two. Besides, we investigated the simple empirical formula to estimate a thermal neutron flux in the accelerator room, ϕ th = CQ / S , where Q is the neutron source intensity and S is the total surface area of a room. The coefficient C estimated in this study did not significantly depend on the incident proton beam energy.

New Beam lines for the NUMEN experiment at INFN-LNS

The NUMEN experiment at INFN-LNS demands an upgrade of the Superconducting Cyclotron (CS) to deliver beam with power up to 10 kW for ions with mass A < 40 amu. To transport these high power beams, it is mandatory to build a new extraction beam line from the CS and to upgrade the existing beam transport lines to maintain the beam losses below 100 W, both in the accelerator room and along the beam transport areas. Moreover, a new fragment in-flight separator will be built to produce radioactive ion beams, but also to perform energy selection of the beam extracted from the cyclotron, to be delivered to the MAGNEX spectrometer with an energy spread below 0.1% FWHM. The use of a 10 kW ion beam implies also to redesign of the beam transport line inside the MAGNEX experimental room to allow the installation of a new large and well shielded beam dump beyond the apparatus.

Monte Carlo study and design of system for implementation of Rotational Total Skin Electron Irradiation technique

Total skin electron irradiation technique is used in treatment of the mycosis fungoid. The implementation of this technique requires non-standard measurements and complex dosimetry methods. Depending on the linear accelerator (Linac) type, bunker size, room dimensions and dosimetry equipment, the design of instruments for appropriate set up and implementation of TSEI in different radiation therapy centers varies. The studies which have been done in this article provide an introduction to the implementing of this method for the first time in Iran and its results can be used for the centers with similar specifications in the world. This article determined the electron beam characteristic of TSEI for the only electron accelerator, located at the radiation center of the Seyed Alshohada Hospital of Isfahan (NEPTUN 10PC), by performing Monte Carlo simulations and using EGSnrc-based codes (BEAMnrc and DOSXYZnrc). For the best uniformity of the vertical profile, the optimal angle of gantry was defined at SSD=350 cm. The effect of the degrader plane that is located at a distance of 20 cm from the patient surface, was evaluated on the amount of energy reduction of the beam, the opening of the electron beam field and the homogeneity of the dose distribution. The transversal dose distribution from the whole treatment with Stanford technique (six dual fields) and Rotational technique was simulated in a CT-based anthropomorphic phantom. Also, the percentage depth dose in the head, neck, thorax, abdomen and legs was obtained for both methods. The simulation results show that the 20̂ angle between the horizontal and the beam central axis is optimal in order to provide the best vertical dose uniformity. The mean energy decreases from 6.1 MeV (the exit window) to 3 MeV (the treatment surface) by placing a degrader with 0.8 cm thickness in front of the treatment plane. FWHM of the angular distribution of the electron beam increased from 15̂ at SSD=100 cm to more than 30̂ on the treatment surface by traversing the PMMA degrader. The MC calculated percentage depth dose curves in different organs of anthropomorphic phantom for RTSEI indicates that the depth of maximum dose is on the surface of the phantom and Isodose curve of 80% is formed at a depth less than 4 mm. the results also show, with the degrader plane in front of the patient, the degree of homogeneity of the dose distribution for both Stanford and rotational techniques is the same.

A versatile program for the calculation of linear accelerator room shielding

This work aims at designing a computer program to calculate the necessary amount of shielding for a given or proposed linear accelerator room design in radiotherapy. The program (Shield Calculation in Radiotherapy, SCR) has been developed using Microsoft Visual Basic. It applies the treatment room shielding calculations of NCRP report no. 151 to calculate proper shielding thicknesses for a given linear accelerator treatment room design. The program is composed of six main user-friendly interfaces. The first enables the user to upload their choice of treatment room design and to measure the distances required for shielding calculations. The second interface enables the user to calculate the primary barrier thickness in case of three-dimensional conventional radiotherapy (3D-CRT), intensity modulated radiotherapy (IMRT) and total body irradiation (TBI). The third interface calculates the required secondary barrier thickness due to both scattered and leakage radiation. The fourth and fifth interfaces provide a means to calculate the photon dose equivalent for low and high energy radiation, respectively, in door and maze areas. The sixth interface enables the user to calculate the skyshine radiation for photons and neutrons. The SCR program has been successfully validated, precisely reproducing all of the calculated examples presented in NCRP report no. 151 in a simple and fast manner. Moreover, it easily performed the same calculations for a test design that was also calculated manually, and produced the same results. The program includes a new and important feature that is the ability to calculate required treatment room thickness in case of IMRT and TBI. It is characterised by simplicity, precision, data saving, printing and retrieval, in addition to providing a means for uploading and testing any proposed treatment room shielding design. The SCR program provides comprehensive, simple, fast and accurate room shielding calculations in radiotherapy.

Abstract ID: 30 Facility shielding evaluation using Monte Carlo simulation for proton therapy

The secondary neutrons generated as a result of interaction with protons and material in the beam path introduces a significant radiological hazard. The radiation shielding must be designed to protect workers in close proximity to the therapy equipment and the general public in aspect of radiation protection. Therefore, this study evaluated the shielding wall design using Monte Carlo code in proton facility. In this study, several terms are assumed for the conservative calculation and simplification of calculation. First, the direction of proton beam loss is fixed in the accelerator room and the gantry room. Second, the neutron spectrum has been generated by using Monte Carlo method at the specific condition of reference target composition (80% of Fe and 20% of C) with 235 MeV incident proton beam and the simple geometry. Also, we assumed that every evaluation point is full occupancy and the workload safety factor is 1.5 for the conservative result. The dose evaluation places for the effective dose were selected as places at where the dose is considered highly among various places that can be accessible to people when the proton facility is operated. In this study, the radiation transport was simulated with the Monte-Carlo code such as ANISN, MCNPX and FLUKA. And then, the neutron dose at evaluation point is got by the calculated value using the simulation value and the neutron dose coefficient (ICRT-74). In all evaluation points, annual dose calculated with Monte Carlo method is under a factor of 10 than the annual dose limit of 20 mSv/yr in the Korea regulation based on ICRP 60. And, the most of result of MCNPX and FLUKA showed a smaller value than result of ANISN in Monte Carlo simulation using the complicated geometry. Based on this calculation result, we assigned areas that cannot be allowed during the proton facility operation time, routinely occupied by workers involved directly for operation, and accessible to members of the general public.

Neutron dose distribution in the treatment room for an accelerator in the flattening filter‐free mode

AbstractObjectiveTo provide specific data and to make recommendations for radiation protection for clinical applications, the neutron cumulative dose, and exposure time in the treatment room around an accelerator operating at 10 MV in the conditions of both a conventional dose rate (with a flattening filter [FF] mode) and an ultra‐high dose rate (flattening filter‐free [FFF] mode) were measured and analyzed.MethodsIn the accelerator treatment room, the data were collected from four representative sites: the therapist's operating location, the distal end of the couch in the patient plane, the proximal maze, and the protective door. The field sizes were 5 × 5 cm2, 10 × 10 cm2, and 30 × 30 cm2; the output doses were 500 MU, 1000 MU, and 2000 MU; the solid water phantom simulating the patient's body was put on the isocenter; the dose rate in FF mode was a 10‐MV X‐ray at 600 MU/min; and the dose rate in FFF mode was 2400 MU/min. Under the same conditions, data were collected outside the selected area measuring three positions: the protective door, operating room, and center of the main protective wall position.ResultsThe neutron cumulative dose was negatively correlated with the field size; the closer to the target, the larger the neutron cumulative dose. The neutron cumulative dose was the largest at the distal end of the couch, and the neutron cumulative dose in FF mode was almost threefold as large as that in FFF mode. The neutron exposure time was positively correlated with the output dose. The FF mode takes slightly longer than the FFF mode. No neutron dose was read outside the accelerator room.ConclusionsOperating the accelerator in FFF mode will benefit both the patients and radiation therapists by reducing the neutron cumulative dose and exposure time. The current anti‐neutron accelerator room design is equally applicable to an ultra‐high‐dose rate (FFF) mode accelerator.

Shielding analyses of an AB-BNCT facility using Monte Carlo simulations and simplified methods

Accurate Monte Carlo simulations and simplified methods were used to investigate the shielding requirements of a hypothetical accelerator-based boron neutron capture therapy (AB-BNCT) facility that included an accelerator room and a patient treatment room. The epithermal neutron beam for BNCT purpose was generated by coupling a neutron production target with a specially designed beam shaping assembly (BSA), which was embedded in the partition wall between the two rooms. Neutrons were produced from a beryllium target bombarded by 1-mA 30-MeV protons. The MCNP6-generated surface sources around all the exterior surfaces of the BSA were established to facilitate repeated Monte Carlo shielding calculations. In addition, three simplified models based on a point-source line-of-sight approximation were developed and their predictions were compared with the reference Monte Carlo results. The comparison determined which model resulted in better dose estimation, forming the basis of future design activities for the first ABBNCT facility in Taiwan.

Shielding calculations for industrial 5/7.5MeV electron accelerators using the MCNP Monte Carlo Code

High energy X-rays from accelerators are used to irradiate food ingredients to prevent growth and development of unwanted biological organisms in food, and by that extend the shelf life of the products. The production of X-rays is done by accelerating 5 MeV electrons and bombarding them into a heavy target (high Z). Since 2004, the FDA has approved using 7.5 MeV energy, providing higher production rates with lower treatments costs. In this study we calculated all the essential data needed for a straightforward concrete shielding design of typical food accelerator rooms. The following evaluation is done using the MCNP Monte Carlo code system: (1) Angular dependence (0-180°) of photon dose rate for 5 MeV and 7.5 MeV electron beams bombarding iron, aluminum, gold, tantalum, and tungsten targets. (2) Angular dependence (0-180°) spectral distribution simulations of bremsstrahlung for gold, tantalum, and tungsten bombarded by 5 MeV and 7.5 MeV electron beams. (3) Concrete attenuation calculations in several photon emission angles for the 5 MeV and 7.5 MeV electron beams bombarding a tantalum target. Based on the simulation, we calculated the expected increase in dose rate for facilities intending to increase the energy from 5 MeV to 7.5 MeV, and the concrete width needed to be added in order to keep the existing dose rate unchanged.