Therapy Facility Research Articles

Optimization of synchrotron based ion beam therapy facilities for treatment time reduction, options and the MedAustron development roadmap.

A faster treatment reduces the risk of intra-fraction movement of organs, offers a more comfortable treatment to the patient, allows to treat lesion of larger volumes in a reasonable time and most of all expands the capacity of the facility. This work presents possible machine upgrades for synchrotron based ion beam therapy centers to shorten the irradiation time. The expected delivery times for each scenario are simulated for the study case of proton beams of MedAustron. The second part of the work focuses on the MedAustron development roadmap, where recently increase of ring fillings and delivered intensities were implemented for proton treatments achieving an average irradiation time of ~50% since start of operation.

Beam characterization and feasibility study for a small animal irradiation platform at clinical proton therapy facilities

A deeper understanding of biological mechanisms to promote more efficient treatment strategies in proton therapy demands advances in preclinical radiation research. However this is often limited by insufficient availability of adequate infrastructures for precision image guided small animal proton irradiation. The project SIRMIO aims at filling this gap by developing a portable image-guided research platform for small animal irradiation, to be used at clinical facilities and allowing for a precision similar to a clinical treatment, when scaled down to the small animal size. This work investigates the achievable dosimetric properties of different lowest energy clinical proton therapy beams, manipulated by a dedicated portable beamline including active focusing after initial beam energy degradation and collimation. By measuring the lateral beam size in air close to the beam nozzle exit and the laterally integrated depth dose in water, an analytical beam model based on the beam parameters of the clinical beam at the Rinecker Proton Therapy Center was created for the lowest available clinical beam energy. The same approach was then applied to estimate the lowest energy beam model of different proton therapy facilities, Paul Scherrer Institute, Centre Antoine Lacassagne, Trento Proton Therapy Centre and the Danish Centre for Particle Therapy, based on their available beam commissioning data. This comparison indicated similar beam properties for all investigated sites, with emittance values of a few tens of mm·mrad. Finally, starting from these beam models, we simulated propagation through a novel beamline designed to manipulate the beam energy and size for precise small animal irradiation, and evaluated the resulting dosimetric properties in water. For all investigated initial clinical beams, similar dosimetric results suitable for small animal irradiation were found. This work supports the feasibility of the proposed SIRMIO beamline, promising suitable beam characteristics to allow for precise preclinical irradiation at clinical treatment facilities.

Multidisciplinary Management of Radiation-Induced Salivary Gland Carcinomas in the Modern Radiotherapy Era.

Simple SummaryEtiopathogenesis of salivary gland cancers [SGCs] is largely unknown, even if exposition to ionizing radiation is a recognized risk factor for SGCs development. To date, exhaustive data to guide clinicians in managing patients with radiation-induced [ri] SGCs are scarce and their treatment remains challenging. The purpose of this work is to describe and to analyze clinical and histopathological features, delivered treatments, and outcome of a series of patients with ri-SGCs treated at two Italian cancer referral sites. Given the rarity of ri-SGCs, this retrospective analysis conducted on a case series of 13 patients adds further knowledge to the paucity of literature. The management of these malignancies is extremely complex requiring a multidisciplinary treatment approach.Clinical data of ri-SGCs patients treated between 2015 and 2019 at a tertiary cancer center and a national hadron therapy facility were reviewed. Latent time (LT) from first RT to ri-SGCs diagnosis, overall (OS), and disease-free survival (DFS) were assessed. Thirteen patients developed 14 ri-SGCs (one patient had 2 synchronous ri-SCGs), after a median LT of 23 years (range 16–34). Parotid was the primary site in 8 cases (57%) and salivary duct carcinoma was the most frequent histotype (29%). Nine patients (69%) underwent surgery (Sx). Among them, 4 patients (31%) underwent Sx alone, 5 received post-operative treatments: 3 (23%) photon-based (X) reRT, one (8%) protons and carbon ions, one (8%) carbon ions only. One patient (8%) received definitive XRT. The remaining 3 patients (23%) received androgen deprivation therapy. With a median follow-up of 48 months (range 24–72), median OS and PFS were 74 and 24 months, respectively. In the subgroup of AR+ ri-SGCs, median PFS and OS were 12 and 74 months, respectively. Given the rarity of ri-SGCs, this work adds further knowledge to the paucity of literature. The management of these malignancies is extremely complex requiring a multidisciplinary treatment approach.

Monte Carlo implementation of new algorithms for the evaluation of averaged-dose and -track linear energy transfers in 62 MeV clinical proton beams

We exploited the power of the Geant4 Monte Carlo toolkit to study and validate new approaches for the averaged linear energy transfer (LET) calculation in 62 MeV clinical proton beams. The definitions of the averaged LET dose and LET track were extended, so as to fully account for the contribution of secondary particles generated by target fragmentation, thereby leading to a more general formulation of the LET total. Moreover, in the proposed new strategies for the LET calculation, we minimised the dependencies in respect to the transport parameters adopted during the Monte Carlo simulations (such as the production cut of secondary particles, voxel size and the maximum steplength). The new proposed approach was compared against microdosimetric experimental spectra of clinical proton beams, acquired at the Italian eye proton therapy facility of the Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare (INFN-LNS, Catania, I) from two different detectors: a mini-tissue equivalent proportional chamber (TEPC), developed at the Legnaro National Laboratories of the National Institute for Nuclear Physics (LNL-INFN) and a silicon-on-insulator (SOI) microdosimeter with 3D sensitive volumes developed by the Centre for Medical Radiation Physics of Wollongong University (CMRP-UoW). A significant increase of the LET in the entrance region of the spread out Bragg peak (SOBP) was observed, when the contribution of the generated secondary particles was included in the calculation. This was consistent with the experimental results obtained.

Achromatic beamline design for a laser-driven proton therapy accelerator

A new laser-driven proton therapy facility is being designed by Peking University. The protons will be produced by laser--plasma interaction, using a 2-PW laser to reach proton energies up to 100 MeV. We hope that the construction of this facility will promote the real-world applications of laser accelerators. Based on the experimental results and design experience of existing devices in Peking University, we propose a beam transmission system which is suitable for the beam produced by laser acceleration, and demonstrate its feasibility through theoretical simulation. It is designed with two transport lines to provide both horizontal and vertical irradiation modes. We have used a locally-achromatic design method with new canted-cosine-theta (CCT) magnets. These two measures allow us to mitigate the negative effects of large energy spread produced by laser-acceleration, and to reduce the overall weight of the vertical beamline. The beamline contains a complete energy selection system, which can reduce the energy spread of the laser-accelerated beam enough to meet the application requirements. The users can select the proton beam energy within the range 40--100 MeV, which is then transmitted through the rest of the beamline. A beam spot with diameter of less than 15 mm and energy spread of less than 5% can be provided at the horizontal and vertical irradiation targets.

Proton vs Hyperarc™ radiosurgery: A planning comparison.

For many patients, stereotactic radiosurgery (SRS) offers a minimally invasive, curative option when surgical techniques are not possible. To date, the literature supporting the efficacy and safety of SRS treatment techniques uses photon beams. However, with the number of proton therapy facilities exponentially growing and the favorable physical properties of proton beam radiation therapy, there is an opportunity to develop proton therapy techniques for SRS. The goal of this paper is to determine the ability of clinical proton treatment planning systems to model small field dosimetry accurately and to compare various planning metrics used to evaluate photon SRS to determine the optimum beam configurations and settings for proton SRS (PSRS) treatment plans. Once established, these plan settings were used to perform a planning comparison on a variety of different SRS cases and compare SRS metrics between the PSRS plans and HyperArc™ (VMAT) SRS plans.

Mean excitation energy determination for Monte Carlo simulations of boron carbide as degrader material for proton therapy.

Boron carbide is a material proposed as an alternative to graphite for use as an energy degrader in proton therapy facilities, and is favoured due to its mechanical robustness and promise to give lower lateral scattering for a given energy loss. However, the mean excitation energy of boron carbide has not yet been directly measured. Here we present a simple method to determine the mean excitation energy by comparison with the relative stopping power in a water phantom, and from a comparison between experimental data and simulations we derive a value for it of 83.1±2.8eV suitable for use in Monte-Carlo simulation. This is consistent with the existing ICRU estimate (84.7eV with 10-15% uncertainty) that is based on indirect Bragg additivity calculation, but it has a substantially smaller uncertainty. The method described can be readily applied to predict the ionisation loss of other boron carbide materials in which the atomic constituent ratio may vary, and allows this material to be reliably used as an alternative to graphite, diamond or beryllium.

Design of the input power coupler for Boron Neutron Capture Therapy Drift Tube Linac

An accelerator-based Boron Neutron Capture Therapy (BNCT) facility has been built at the campus of China Spallation Neutron Source (CSNS). To upgrade it, a Drift Tube Linac (DTL) is designed to provide a 40 mA, 25% duty factor, 10.1 MeV beam for the target. Two opposing power couplers are employed to deliver forward peak power up to 640 kW for the beam and DTL cavity. A new coaxial power coupler with a single Tristan type window is designed to meet the power and coupling coefficient requirements. In this paper, the detailed RF optimization process of the coupler is described. According to the RF simulation results, the multipacting (MP) phenomenon at critical locations is simulated by the CST PS (Particle Studio). Simulations of thermal and mechanical are also carried out, the cooling design to provide a large margin for RF heating is performed based on the simulation results.

A Simple Approach for Experimental Characterization and Validation of Proton Pencil Beam Profiles

A precise characterization of therapeutic proton pencil beams is essential for commissioning of any treatment planning system (TPS). The dose profile characterization includes measurement of the beam lateral dose profile in the beam core and far from the beam core, in the so called low-dose envelope, and requires a sophisticated detection system with a few orders of magnitude dynamic range. We propose to use a single-quantum sensitive Minipix Timepix detector, along with an in-house designed holder to perform measurements of the pencil beam dose profile in air and in water. We validated the manufacturer calibration of the Minipix Timepix detector in proton beams of various energies and compared the deposited energy spectra to Monte Carlo (MC) simulations. The precision of the lateral dose profile measurements has been systematically validated against Krakow proton facility commissioning data and dose profile simulations performed with MC codes Gate/Geant4 and Fred. We obtained an excellent agreement between Minipix Timepix measurements and simulations demonstrating the feasibility of the system for a simple characterization and validation of proton pencil beams. The proposed approach can be implemented at any proton therapy facility to acquire experimental data needed to commission and validate analytical and MC based TPS.

Technical Note: 4D cone-beam CT reconstruction from sparse-view CBCT data for daily motion assessment in pencil beam scanned proton therapy (PBS-PT).

PurposeThe number of pencil beam scanned proton therapy (PBS‐PT) facilities equipped with cone‐beam computed tomography (CBCT) imaging treating thoracic indications is constantly rising. To enable daily internal motion monitoring during PBS‐PT treatments of thoracic tumors, we assess the performance of Motion‐Aware RecOnstructiOn method using Spatial and Temporal Regularization (MA‐ROOSTER) four‐dimensional CBCT (4DCBCT) reconstruction for sparse‐view CBCT data and a realistic data set of patients treated with proton therapy.MethodsDaily CBCT projection data for nine non‐small cell lung cancer (NSCLC) patients and one SCLC patient were acquired at a proton gantry system (IBA Proteus® One). Four‐dimensional CBCT images were reconstructed applying the MA‐ROOSTER and the conventional phase‐correlated Feldkamp‐Davis‐Kress (PC‐FDK) method. Image quality was assessed by visual inspection, contrast‐to‐noise ratio (CNR), signal‐to‐noise ratio (SNR), and the structural similarity index measure (SSIM). Furthermore, gross tumor volume (GTV) centroid motion amplitudes were evaluated.ResultsImage quality for the 4DCBCT reconstructions using MA‐ROOSTER was superior to the PC‐FDK reconstructions and close to FDK images (median CNR: 1.23 [PC‐FDK], 1.98 [MA‐ROOSTER], and 1.98 [FDK]; median SNR: 2.56 [PC‐FDK], 4.76 [MA‐ROOSTER], and 5.02 [FDK]; median SSIM: 0.18 [PC‐FDK vs FDK], 0.31 [MA‐ROOSTER vs FDK]). The improved image quality of MA‐ROOSTER facilitated GTV contour warping and realistic motion monitoring for most of the reconstructions.ConclusionMA‐ROOSTER based 4DCBCTs performed well in terms of image quality and appear to be promising for daily internal motion monitoring in PBS‐PT treatments of (N)SCLC patients.

Association Between Travel Distance and Use of Post-Operative Radiation Therapy Among Men With Prostate Cancer: Does Geography Influence Treatment Decisions?

Following radical prostatectomy (RP), men with a persistent post-operative PSA and select men with adverse pathologic features are candidates for postoperative radiation therapy (PORT). However, travel distance to radiation therapy facilities may negatively affect patient access to PORT. In this study, we investigated disparities in rates of PORT in men with high risk prostate cancer according to their distance from the treatment facility. Using the National Cancer Database, we identified 510,665 men with prostate cancer diagnosed 2004-2015 who have received RP. Multivariable logistic regression defined adjusted odds ratios (AORs) with 95% confidence intervals (95CI) of receiving PORT as the primary dependent variable and distance from the treatment facility as the primary independent variable. Patients were defined as living “far” from the treatment facility if they lived beyond the median distances of 9.1 miles for metro counties, 38.1 miles for urban counties, and 52.9 miles for rural counties; all others were categorized as “near.” Analyses were stratified by the presence of adverse pathologic features (pT3 disease or positive surgical margins) and type of county (rural vs urban vs metro). Patients living far from the treatment facility received PORT less frequently than those living near a treatment facility (3.98% vs 6.33%, AOR 0.58, 95CI 0.56-0.60, P<0.001). These trends persisted in patients with adverse features (far vs near: 11.36% vs 17.94%, AOR 0.58, 95CI 0.56-0.60, P<0.001) and those with no adverse features (1.51% vs 2.62%, AOR 0.58, 95CI 0.55-0.60, P<0.001). When stratifying by county type, patients living far from a treatment facility had lower rates of PORT compared to those living near a treatment facility in metro (4.10% vs 6.16%, AOR 0.62, 95CI 0.61-0.64, P<0.001), urban (3.39% vs 7.42%, AOR 0.39, 95CI 0.36-0.42, P<0.001), and rural (3.26% vs 6.87%, AOR 0.41, 95CI 0.34-0.50, P<0.001) counties. For men with prostate cancer managed with surgery, patients living farther from their treatment facility were 38-61% less likely to receive PORT relative to those living near the treatment facility, regardless of the presence of adverse pathologic features and county type. While the decision to use PORT depends on many patient-specific factors, these findings raise the possibility that the geographic availability of radiation treatment facilities influences the treatment decision. As alternative payment models in radiation oncology are being explored, attention should be given to supporting community-based radiation treatment centers to ensure accessibility of care for patients with prostate cancer.Tabled 1Abstract 2941; TableOR95% CIP>|z|% PORTFarNearMetro0.620.610.640.0004.16.16Urban0.390.360.420.0003.397.42Rural0.410.340.500.0003.266.87 Open table in a new tab

Evaluation of GATE-RTion (GATE/Geant4) Monte Carlo simulation settings for proton pencil beam scanning quality assurance.

Geant4 is a multi-purpose Monte Carlo simulation tool for modeling particle transport in matter. It provides a wide range of settings, which the user may optimize for their specific application. This study investigates GATE/Geant4 parameter settings for proton pencil beam scanning therapy. GATE8.1/Geant4.10.3.p03 (matching the versions used in GATE-RTion1.0) simulations were performed with a set of prebuilt Geant4 physics lists (QGSP_BIC, QGSP_BIC_EMY, QGSP_BIC_EMZ, QGSP_BIC_HP_EMZ), using 0.1mm-10mm as production cuts on secondary particles (electrons, photons, positrons) and varying the maximum step size of protons (0.1mm, 1mm, none). The results of the simulations were compared to measurement data taken during clinical patient specific quality assurance at The Christie NHS Foundation Trust pencil beam scanning proton therapy facility. Additionally, the influence of simulation settings was quantified in a realistic patient anatomy based on computer tomography (CT) scans. When comparing the different physics lists, only the results (ranges in water) obtained with QGSP_BIC (G4EMStandardPhysics_Option0) depend on the maximum step size. There is clinically negligible difference in the target region when using High Precision neutron models (HP) for dose calculations. The EMZ electromagnetic constructor provides a closer agreement (within 0.35mm) to measured beam sizes in air, but yields up to 20% longer execution times compared to the EMY electromagnetic constructor (maximum beam size difference 0.79mm). The impact of this on patient-specific quality assurance simulations is clinically negligible, with a 97% average 2%/2mm gamma pass rate for both physics lists. However, when considering the CT-based patient model, dose deviations up to 2.4% are observed. Production cuts do not substantially influence dosimetric results in solid water, but lead to dose differences of up to 4.1% in the patient CT. Small (compared to voxel size) production cuts increase execution times by factors of 5 (solid water) and 2 (patient CT). Taking both efficiency and dose accuracy into account and considering voxel sizes with 2mm linear size, the authors recommend the following Geant4 settings to simulate patient specific quality assurance measurements: No step limiter on proton tracks; production cuts of 1mm for electrons, photons and positrons (in the phantom and range-shifter) and 10mm (world); best agreement to measurement data was found for QGSP_BIC_EMZ reference physics list at the cost of 20% increased execution times compared to QGSP_BIC_EMY. For simulations considering the patient CT model, the following settings are recommended: No step limiter on proton tracks; production cuts of 1mm for electrons, photons and positrons (phantom/range-shifter) and 10mm (world) if the goal is to achieve sufficient dosimetric accuracy to ensure that a plan is clinically safe; or 0.1mm (phantom/range-shifter) and 1mm (world) if higher dosimetric accuracy is needed (increasing execution times by a factor of 2); most accurate results expected for QGSP_BIC_EMZ reference physics list, at the cost of 10-20% increased execution times compared to QGSP_BIC_EMY.

Contraception Choice among HIV-Positive Women Utilizing Family Planning Services Integrated with HIV Care at the Antiretroviral Therapy Clinic of Jos University Teaching Hospital, Nigeria

Transmission of Human Immunodeficiency Virus from a pregnant HIV-infected woman to her unborn child is one of the ways through which new HIV infections can be acquired. Utilization of contraceptives among HIV-positive women can prevent unintended pregnancies, and the use of dual methods reduces the risk of transmission of sexually transmitted infections including HIV, hence the need to support contraception in them. This study sought to describe the various choices of contraception used by women accessing family planning services integrated with the antiretroviral therapy facility of Jos University Teaching Hospital. In a retrospective study, relevant information was extracted from the records of all women who had sought contraception in the Family Planning unit of the facility from 1st March 2019 – 29th February 2020. The data obtained was analysed using EPI info 7 statistical software. Results: A total of 137 records were reviewed. The most frequent choice of contraception was hormonal implants (61.3%), while the least frequent choice was using condoms alone (1.5%). Less than half (46.7%) of them used dual contraception. Secondary and tertiary educational status, as well as disclosure of HIV-positive status to partner were significantly associated with utilization of dual contraceptive methods (P value =0.0010 and 0.0245 respectively; Odds ratio =5.8199 and 4.3307 respectively). Conclusion: Integration of family planning services with HIV care as a strategy for the prevention of unintended pregnancy is promoted in this facility but there is need to improve the uptake particularly of dual method of contraception. There is also need for inclusion of IUCD in the choices of contraception offered as this method is highly effective, long lasting and has been proven to be safe in well selected HIV patients. Furthermore, screening the clients to identify unmet needs and implementing strategies to meet those needs would enhance the impact of family planning.

Impact of COVID-19 on patient\u2013doctor interaction in a complex radiation therapy facility

PurposeIn the last months, Italy faced a COVID-19 emergency and implemented preventive measures in order to protect patients and healthcare providers from a disease outbreak. The pandemic control strategies impacted patient experience directly. Questionnaires evaluating patients reported measures (PREMs) may assess critical issues and represent a helpful tool to measure the patient perception of healthcare service. Our aim was to prospectively assess patient satisfaction about doctor–patient interaction in a high-volume radiation therapy and oncology center during the COVID-19 pandemic.MethodsCancer patients receiving either systemic and/or radiation treatment underwent a survey. Two validated questionnaires (EORTC QLQ-C30, FACIT-TS-G version 1) and 14 specific questions evaluating patients’ perception of COVID-19 measures were administered.ResultsOne hundred twenty-five patients admitted to our department from 1–30 April 2020 completed the questionnaires. The majority (66.4%) of patients were women and the most common disease was breast cancer (40%). The average Global Health Status (GHS) of EORTC QLQ-C30 was 61.67. Emotional functioning, social, and cognitive domains obtained scores of 75.48, 80.13, and 84.67, respectively. FACIT-TS-G results revealed 120 patients rated the treatments effective and 108 patients thought the side effects were the same as expected or better. Most (89.6%) rated their treatment good, very good, or excellent. Concerning COVID-19-related questions, patients reported overall very good level of information.ConclusionsDespite the introduction of strict COVID-19 control measures, there was a high level of cancer outpatient satisfaction. The satisfaction levels may influence compliance, continuity of treatments, and patient–doctor communication, impacting the quality of clinical care in the next phases of the pandemic.

Two Bacillus isolates recovered from a radiation therapy facility differ greatly in their ability to attach to four immobilization masks

BackgroundThermoplastic immobilization masks used during radiation therapy treatment have been shown to harbor several different types of bacteria. Recovered bacteria included Staphylococcus aureus, Enterococcus species, Gram-negative rods, coagulase-negative staphylococci, and several different Bacillus species. Two of the recovered Bacillus bacteria were examined for their ability to attach to and survive over time on patient head-only masks from four different manufacturers. B. halosaccharovorans was recovered from a treatment facility's water bath while B. cereus was recovered from a patient mask in the same facility. Bacillus bacteria were chosen for this study due to their capability to form dormant spores. MethodsInoculums containing either B. halosaccharovorans or B. cereus bacteria were seeded onto predesignated areas of each test mask. Masks were subsequently sampled at intervals of 1-h, 1 week, 2 weeks, 3 weeks, and 4 weeks. Recovered bacterial numbers at each sampling interval were determined using the direct plate count method. Spore stains were made of both bacterial isolates and number of detected spores were enumerated. ResultsB. halosaccharovorans attached to each mask type after a 1-h contact time at a number 3X greater than B. cereus. B. halosaccharovorans was also recovered at a number 8.5X greater than B. cereus after 4 weeks. Variation was seen in the attachment capability of each bacterium on tested mask types. Both bacilli were recovered from all 4 masks at each sampling interval including week 4. Examination of spore stains of each bacteria demonstrated nearly a 25:1 ratio of B. halosaccharovorans spores over B. cereus. DiscussionThe large variation seen between B. halosaccharovorans and B. cereus capability to attach to each of the four tested masks is revealing, especially when it is combined with determined spore numbers. It suggests that spores play a role in mediating their attachment to mask surfaces. Moreover, the recovery of both bacteria from stored masks after 4 weeks indicates a continued presence of dormant spores since growth-supportive nutrients are lacking. It also implies the potential for their transfer to a patient wearing a contaminated mask during a treatment session. ConclusionThe demonstrated ability of these two Bacillus bacteria to attach to and reside on patient masks presents a dilemma. Routine cleaning with approved disinfectants may not be sufficient to eliminate dormant spores on masks surfaces. This matter requires further investigation. For now, a small modification to the routine mask cleaning procedure before its application may help to reduce the possibility of spore transfer.

Catalent extends in gene therapy and ADCs

Catalent says it will spend $130 million to add five manufacturing suites to its gene therapy facility in Harmans, Maryland. The pharmaceutical services firm is in the midst of a project to add 10 ...

Impact of Radiation Therapy Facility Volume on Survival Among Patients with Cancer

Impact of Radiation Therapy Facility Volume on Survival Among Patients with Cancer

Catalent to produce vaccine for AstraZeneca

AstraZeneca has contracted with Catalent to produce its adenovirus vector–based COVID-19 vaccine candidate, AZD1222, at Catalent’s gene therapy facility in Harmans, Maryland. Catalent is preparing ...

Conceptual Shield Design for Boron Neutron Capture Therapy Facility Using Monte Carlo N-Particle Extended Simulator with Kartini Research Reactor as Neutron Source

The research aims to measure the radiation dose rate over the radiation shielding which is made of paraffin and aluminium and to determine the best shield material for the safety of radiation workers. The examination used MCNP (Monte Carlo N-Particle) simulator to model the BNCT neutron source and the shield. The shield should reduce radiation to less than the dose limit of 10.42 µSv/h, which is assumed to be the most conservative limit when the duration of workers is 1920 h. The first design resulted in a radiation dose rate which was still greater than the limit. Therefore, optimization was done by adding the lead on the outer part of the shield. After optimization by adding the lead with certain layers, the radiation dose rate decreased, with the largest dose being 57.60 µSv/h. Some locations over the limit could be overcome by other radiation protection aspects such as distance and time. The paraffin blocks were covered by aluminium to keep the shield structure. The lead was used to absorb the gamma ray which resulted from the interaction between the neutrons and aluminium.

Layout optimization of corrector magnets for a proton therapy beamline via genetic algorithm

Proton therapy is one of the most effective radiotherapy methods for cancer and the dose distribution of protons on patients is superior to conventional rays. However, it is likewise more sensitive to the beam misalignment raised from errors in the magnets, girders and beam diagnostic devices. According to the clinical treatment guidelines, beam position accuracy at the iso-center should be controlled within ±0.5 mm. While the response matrix method is widely used in beam orbit correction, the correction performance relies largely on the locations of corrector magnets. This paper introduces an optimization approach for the layout of corrector magnets by using the multi-objective genetic algorithm NSGA-II and this technique is applied to a cyclotron-based proton therapy facility. All potential locations of the corrector magnets are encoded with an integer sequence. After 300 generations of crossover, mutation and selection, seventeen Pareto-front solutions were obtained and the best configuration was selected by taking the overall beam misalignment along the beamline into considerations. Finally, the maximum deviation of the corrected beam orbit in the beamline is less than 4.5 mm and the beam position at the iso-center can be optimized within ±0.3 mm, fulfilling the clinical requirement.