Working the Edge: The Emotional Experiences of Commissioning and Funding Arrangements for Service Leaders in the Sexual Violence Voluntary Sector

The specialist voluntary sector plays a crucial role in supporting survivors of sexual violence. However, in England, short-term funding underpins the sector's financial stability. This article examines sector leaders' ways of coping, resisting and being affected by funding practices. Using the concept of edgework, we show how funding and commissioning dynamics push individuals to the edge of service sustainability, job satisfaction, and emotional well-being. We examine how these edges are "worked," for example, by circumventing and remolding the edge. We offer an original way to theorize participants, make visible the emotional toll of service precarity and offer suggestions for support.

Evaluation of monte carlo to support commissioning of the treatment planning system of new pencil beam scanning proton therapy facilities

Objective. To demonstrate the potential of Monte Carlo (MC) to support the resource-intensive measurements that comprise the commissioning of the treatment planning system (TPS) of new proton therapy facilities.Approach. Beam models of a pencil beam scanning system (Varian ProBeam) were developed in GATE (v8.2), Eclipse proton convolution superposition algorithm (v16.1, Varian Medical Systems) and RayStation MC (v12.0.100.0, RaySearch Laboratories), using the beam commissioning data. All models were first benchmarked against the same commissioning data and validated on seven spread-out Bragg peak (SOBP) plans. Then, we explored the use of MC to optimise dose calculation parameters, fully understand the performance and limitations of TPS in homogeneous fields and support the development of patient-specific quality assurance (PSQA) processes. We compared the dose calculations of the TPSs against measurements (DDTPSvs.Meas.) or GATE (DDTPSvs.GATE) for an extensive set of plans of varying complexity. This included homogeneous plans with varying field-size, range, width, and range-shifters (RSs) (n= 46) and PSQA plans for different anatomical sites (n= 11).Main results. The three beam models showed good agreement against the commissioning data, and dose differences of 3.5% and 5% were found for SOBP plans without and with RSs, respectively. DDTPSvs.Meas.and DDTPSvs.GATEwere correlated in most scenarios. In homogeneous fields the Pearson's correlation coefficient was 0.92 and 0.68 for Eclipse and RayStation, respectively. The standard deviation of the differences between GATE and measurements (±0.5% for homogeneous and ±0.8% for PSQA plans) was applied as tolerance when comparing TPSs with GATE. 72% and 60% of the plans were within the GATE predicted dose difference for both TPSs, for homogeneous and PSQA cases, respectively.Significance. Developing and validating a MC beam model early on into the commissioning of new proton therapy facilities can support the validation of the TPS and facilitate comprehensive investigation of its capabilities and limitations.

Comparative evaluation of a surface-based respiratory monitoring system against a pressure sensor for 4DCT image reconstruction in phantoms

Four-dimensional computed tomography (4DCT), which relies on breathing-induced motion, requires realistic surrogate information of breathing variations to reconstruct the tumor trajectory and motion variability of normal tissues accurately. Therefore, the SimRT surface-guided respiratory monitoring system has been installed on a Siemens CT scanner. This work evaluated the temporal and spatial accuracy of SimRT versus our commonly used pressure sensor, AZ-733 V. A dynamic thorax phantom was used to reproduce regular and irregular breathing patterns acquired by SimRT and Anzai. Various parameters of the recorded breathing patterns, including mean absolute deviations (MAD), Pearson correlations (PC), and tagging precision, were investigated and compared to ground-truth. Furthermore, 4DCT reconstructions were analyzed to assess the volume discrepancy, shape deformation and tumor trajectory. Compared to the ground-truth, SimRT more precisely reproduced the breathing patterns with a MAD range of 0.37 ± 0.27 and 0.92 ± 1.02 mm versus Anzai with 1.75 ± 1.54 and 5.85 ± 3.61 mm for regular and irregular breathing patterns, respectively. Additionally, SimRT provided a more robust PC of 0.994 ± 0.009 and 0.936 ± 0.062 for all investigated breathing patterns. Further, the peak and valley recognition were found to be more accurate and stable using SimRT. The comparison of tumor trajectories revealed discrepancies up to 7.2 and 2.3 mm for Anzai and SimRT, respectively. Moreover, volume discrepancies up to 1.71 ± 1.62% and 1.24 ± 2.02% were found for both Anzai and SimRT, respectively. SimRT was validated across various breathing patterns and showed a more precise and stable breathing tracking, (i) independent of the amplitude and period, (ii) and without placing any physical devices on the patient's body. These findings resulted in a more accurate temporal and spatial accuracy, thus leading to a more realistic 4DCT reconstruction and breathing-adapted treatment planning.

Technical note: Commissioning of a linear accelerator producing ultra-high dose rate electrons

BACKGROUND

Ultra-high dose rate radiation (UHDR) is being explored by researchers in promise of advancing radiation therapy treatments.

PURPOSE

This work presents the commissioning of Varian's Flash Extension for research (FLEX) conversion of a Clinac to deliver UHDR electrons.

METHODS

A Varian Clinac iX with the FLEX conversion was commissioned for non-clinical research use with 16 MeV UHDR (16H) energy. This involved addition of new hardware, optimizing the electron gun voltages, radiofrequency (RF) power, and steering coils in order to maximize the accelerated electron beam current, sending the beam through custom scattering foils to produce the UHDR with 16H beam. Profiles and percent depth dose (PDD) measurements for 16H were obtained using radiochromic film in a custom vertical film holder and were compared to 16 MeV conventional electrons (16C). Dose rate and dose per pulse (DPP) were calculated from measured dose in film. Linearity and stability were assessed using an Advanced Markus ionization chamber.

RESULTS

Energies for 16H and 16C had similar beam quality based on PDD measurements. Measurements at the head of the machine (61.3 cm SSD) with jaws set to 10×10 cm2 showed the FWHM of the profile as 7.2 cm, with 3.4 Gy as the maximum DPP and instantaneous dose rate of 8.1E5 Gy/s. Measurements at 100 cm SSD with 10 cm standard cone showed the full width at half max (FWHM) of the profile as 10.5 cm, 1.08 Gy as the maximum DPP and instantaneous dose rate of 2.E5 Gy/s. Machine output with number of pulses was linear (R = 1) from 1 to 99 delivered pulses. Output stability was measured within ±1% within the same session and within ±2% for daily variations.

CONCLUSIONS

The FLEX conversion of the Clinac is able to generate UHDR electron beams which are reproducible with beam properties similar to clinically used electrons at 16 MeV. Having a platform which can quickly transition between UHDR and conventional modes (<1 min) can be advantageous for future research applications.

Characteristics of breathing-adapted gating using surface guidance for use in particle therapy: A phantom-based end-to-end test from CT simulation to dose delivery

To account for intra-fractional tumor motion during dose delivery in radiotherapy, various treatment strategies are clinically implemented such as breathing-adapted gating and irradiating the tumor during specific breathing phases. In this work, we present a comprehensive phantom-based end-to-end test of breathing-adapted gating utilizing surface guidance for use in particle therapy. A commercial dynamic thorax phantom was used to reproduce regular and irregular breathing patterns recorded by the GateRT respiratory monitoring system. The amplitudes and periods of recorded breathing patterns were analysed and compared to planned patterns (ground-truth). In addition, the mean absolute deviations (MAD) and Pearson correlation coefficients (PCC) between the measurements and ground-truth were assessed. Measurements of gated and non-gated irradiations were also analysed with respect to dosimetry and geometry, and compared to treatment planning system (TPS). Further, the latency time of beam on/off was evaluated. Compared to the ground-truth, measurements performed with GateRT showed amplitude differences between 0.03 ± 0.02 mm and 0.26 ± 0.03 mm for regular and irregular breathing patterns, whilst periods of both breathing patterns ranged with a standard deviation between 10 and 190 ms. Furthermore, the GateRT software precisely acquired breathing patterns with a maximum MAD of 0.30 ± 0.23 mm. The PCC constantly ranged between 0.998 and 1.000. Comparisons between TPS and measured dose profiles indicated absolute mean dose deviations within institutional tolerances of ±5%. Geometrical beam characteristics also varied within our institutional tolerances of 1.5 mm. The overall time delays were <60 ms and thus within both recommended tolerances published by ESTRO and AAPM of 200 and 100 ms, respectively. In this study, a non-invasive optical surface-guided workflow including image acquisition, treatment planning, patient positioning and gated irradiation at an ion-beam gantry was investigated, and shown to be clinically viable. Based on phantom measurements, our results show a clinically-appropriate spatial, temporal, and dosimetric accuracy when using surface guidance in the clinical setting, and the results comply with international and institutional guidelines and tolerances.

Practical experience commissioning MRI-compatible tandem and ring applicators for use with the Bravos HDR afterloader

Five complete MR-conditionally approved ring sets, including fifteen tandems, and two additional rings, were commissioned at an institution intending to use them in an MRI planning environment with a Bravos HDR brachytherapy remote afterloader. Channel length, radiograph, autoradiograph, ring offset, and treatment interrupt measurements were performed, and applicators were assessed in both CT and MRI. During commissioning, one ring was found to be defective and was returned to the manufacturer for a replacement. The eventual complete applicator suite (including the replacement ring) was found to follow the manufacturer-provided specifications, including those delineated in vendor-provided 3D virtual models and those defined within the manufacturer's instructions for use documentation. Based on this work, an offset correction of -0.4 cm will be used for all tested rings using the Bravos system's internal distal dwell position correction feature during treatment preparation. This study reiterated the requirement for careful commissioning of each applicator intended for clinical service considering the intended use and the planned clinical environment and work processes.

AAPM Medical Physics Practice Guideline 8.b: Linear accelerator performance tests

The purpose of this guideline is to provide a list of critical performance tests to assist the Qualified Medical Physicist (QMP) in establishing and maintaining a safe and effective quality assurance (QA) program. The performance tests on a linear accelerator (linac) should be selected to fit the clinical patterns of use of the accelerator and care should be given to perform tests which are relevant to detecting errors related to the specific use of the accelerator. Current recommendations for linac QA were reviewed to determine any changes required to those tests highlighted by the original report as well as considering new components of the treatment process that have become common since its publication. Recommendations are made on the acquisition of reference data, routine establishment of machine isocenter, basing performance tests on clinical use of the linac, working with vendors to establish QA tests and performing tests after maintenance and upgrades. The recommended tests proposed in this guideline were chosen based on consensus of the guideline's committee after assessing necessary changes from the previous report. The tests are grouped together by class of test (e.g., dosimetry, mechanical, etc.) and clinical parameter tested. Implementation notes are included for each test so that the QMP can understand the overall goal of each test. This guideline will assist the QMP in developing a comprehensive QA program for linacs in the external beam radiation therapy setting. The committee sought to prioritize tests by their implication on quality and patient safety. The QMP is ultimately responsible for implementing appropriate tests. In the spirit of the report from American Association of Physicists in Medicine Task Group 100, individual institutions are encouraged to analyze the risks involved in their own clinical practice and determine which performance tests are relevant in their own radiotherapy clinics.

The NCS code of practice for the quality assurance of treatment planning systems (NCS-35)

A subcommittee of the Netherlands Commission on Radiation Dosimetry (NCS) was initiated in 2018 with the task to update and extend a previous publication (NCS-15) on the quality assurance of treatment planning systems (TPS) (Bruinviset al2005). The field of treatment planning has changed considerably since 2005. Whereas the focus of the previous report was more on the technical aspects of the TPS, the scope of this report is broader with a focus on a department wide implementation of the TPS. New sections about education, automated planning, information technology (IT) and updates are therefore added. Although the scope is photon therapy, large parts of this report will also apply to all other treatment modalities. This paper is a condensed version of these guidelines; the full version of the report in English is freely available from the NCS website (http://radiationdosimetry.org/ncs/publications). The paper starts with the scope of this report in relation to earlier reports on this subject. Next, general aspects of the commissioning process are addressed, like e.g. project management, education, and safety. It then focusses more on technical aspects such as beam commissioning and patient modeling, dose representation, dose calculation and (automated) plan optimisation. The final chapters deal with IT-related subjects and scripting, and the process of updating or upgrading the TPS.

PRIMO Monte Carlo software as a tool for commissioning of an external beam radiotherapy treatment planning system

Background

The purpose was to validate the PRIMO Monte Carlo software to be used during the commissioning of a treatment planning system (TPS).

Materials and methods

The Acuros XB v. 16.1 algorithm of the Eclipse was configured for 6 MV and 6 MV flattening-filter-free (FFF) photon beams, from a TrueBeam linac equipped with a high-definition 120-leaf multileaf collimator (MLC). PRIMO v. 0.3.64.1814 software was used with the phase space files provided by Varian and benchmarked against the reference dosimetry dataset published by the Imaging and Radiation Oncology Core-Houston (IROC-H). Thirty Eclipse clinical intensity-modulated radiation therapy (IMRT)/volumetric modulated arc therapy (VMAT) plans were verified in three ways: 1) using the PTW Octavius 4D (O4D) system; 2) the Varian Portal Dosimetry system and 3) the PRIMO software. Clinical validation of PRIMO was completed by comparing the simulated dose distributions on the O4D phantom against dose measurements for these 30 clinical plans. Agreement evaluations were performed using a 3% global/2 mm gamma index analysis.

Results

PRIMO simulations agreed with the benchmark IROC-H data within 2.0% for both energies. Gamma passing rates (GPRs) from the 30 clinical plan verifications were (6 MV/6MV FFF): 99.4% ± 0.5%/99.9% ± 0.1%, 99.8% ± 0.4%/98.9% ± 1.4%, 99.7% ± 0.4%/99.7% ± 0.4%, for the 1), 2) and 3) verification methods, respectively. Agreement between PRIMO simulations on the O4D phantom and 3D dose measurements resulted in GPRs of 97.9% ± 2.4%/99.7% ± 0.4%.

Conclusion

The PRIMO software is a valuable tool for dosimetric verification of clinical plans during the commissioning of the primary TPS.

AAPM WGDCAB Report 372: A joint AAPM, ESTRO, ABG, and ABS report on commissioning of model-based dose calculation algorithms in brachytherapy

The introduction of model-based dose calculation algorithms (MBDCAs) in brachytherapy provides an opportunity for a more accurate dose calculation and opens the possibility for novel, innovative treatment modalities. The joint AAPM, ESTRO, and ABG Task Group 186 (TG-186) report provided guidance to early adopters. However, the commissioning aspect of these algorithms was described only in general terms with no quantitative goals. This report, from the Working Group on Model-Based Dose Calculation Algorithms in Brachytherapy, introduced a field-tested approach to MBDCA commissioning. It is based on a set of well-characterized test cases for which reference Monte Carlo (MC) and vendor-specific MBDCA dose distributions are available in a Digital Imaging and Communications in Medicine-Radiotherapy (DICOM-RT) format to the clinical users. The key elements of the TG-186 commissioning workflow are now described in detail, and quantitative goals are provided. This approach leverages the well-known Brachytherapy Source Registry jointly managed by the AAPM and the Imaging and Radiation Oncology Core (IROC) Houston Quality Assurance Center (with associated links at ESTRO) to provide open access to test cases as well as step-by-step user guides. While the current report is limited to the two most widely commercially available MBDCAs and only for 192 Ir-based afterloading brachytherapy at this time, this report establishes a general framework that can easily be extended to other brachytherapy MBDCAs and brachytherapy sources. The AAPM, ESTRO, ABG, and ABS recommend that clinical medical physicists implement the workflow presented in this report to validate both the basic and the advanced dose calculation features of their commercial MBDCAs. Recommendations are also given to vendors to integrate advanced analysis tools into their brachytherapy treatment planning system to facilitate extensive dose comparisons. The use of the test cases for research and educational purposes is further encouraged.

Commissioning dose computation model for proton source in pencil beam scanning therapy by convolution neural networks

Objective. Proton source model commissioning (PSMC) is critical for ensuring accurate dose calculation in pencil beam scanning (PBS) proton therapy using Monte Carlo (MC) simulations. PSMC aims to match the calculated dose to the delivered dose. However, commissioning the 'nominal energy' and 'energy spread' parameters in PSMC can be challenging, as these parameters cannot be directly obtained from solving equations. To efficiently and accurately commission the nominal energy and energy spread in a proton source model, we developed a convolution neural network (CNN) named 'PSMC-Net.'Methods. The PSMC-Net was trained separately for 33 energies (E, 70-225 MeV with a step of 5 MeV plus 226.09 MeV). For eachE, a dataset was generated consisting of 150 source model parameters (15 nominal energies ∈ [E,E+ 1.5 MeV], ten spreads ∈ [0, 1]) and the corresponding 150 MC integrated depth doses (IDDs). Of these 150 data pairs, 130 were used for training the network, 10 for validation, and 10 for testing.Results. The source model, built by 33 measured IDDs and 33 PSMC-Nets (cost 0.01 s), was used to compute the MC IDDs. The gamma passing rate (GPRs, 1 mm/1%) between MC and measured IDDs was 99.91 ± 0.12%. However, when no commissioning was made, the corresponding GPR was reduced to 54.11 ± 22.36%, highlighting the tremendous significance of our CNN commissioning method. Furthermore, the MC doses of a spread-out Bragg peak and 20 patient PBS plans were also calculated, and average 3D GPRs (2 mm/2% with a 10% threshold) were 99.89% and 99.96 ± 0.06%, respectively.Significance. We proposed a nova commissioning method of the proton source model using CNNs, which made the PSMC process easy, efficient, and accurate.

Mental health needs in cancer - a call for change

There is continued under-recognition and underinvestment in the psychological and mental health aspects of care for cancer patients, despite the fact that increased patient survival rates in cancer mean that patients are living longer after diagnosis. In this article, we advocate for better integration and joint working between clinicians across all areas, including education and research, impacting positively on the outcomes and care of cancer patients.

Implementation of the Calypso system: a commissioning experience

Background

The aim of this study was to describe the clinical implementation of the Calypso system with its potential impact on the treatment delivery.

Materials and methods

The influence of the electromagnetic array was investigated on the kilovoltage cone beam computed tomography (kV-CBCT) image quality using the CATPHAN 504 CBCT images. Then, the QFix kVue Calypso couch top and the array attenuation, and their dosimetric influence on the Volumetric modulated arc therapy (VMAT) treatments of prostate was evaluated.

Results

Regarding the image quality, a significant increase of noise (p < 0.01) was detected with the array in place, resulting in a significant decrease in signal noise ratio (SNR) (p < 0.01). No difference in absolute contrast was observed. Finally, there was a significant decrease in contrast noise ratio (CNR) (p < 0.01) even if the deviation was only of 2.5%. For the dosimetric evaluation, the maximum attenuation of the couch was 12.02% and 13.19% for X6 and X6 flattening filter free (FFF), respectively (configuration of rails out). Besides, the mean attenuation of the array was 1.15% and 1.67% for X6 and X6 FFF, respectively. For the VMAT treatment plans, the mean dose was reduced by 0.61% for X6 and by 0.31% for X6 FFF beams when using the electromagnetic array.

Conclusions

The Calypso system does not affect significantly the kV-CBCT image quality and the VMAT plan dose distribution.

Delivery accuracy of VMAT on two beam-matched linacs provided by accelerated go live service

INTRODUCTION

Dosimetric accuracy is critical when a patient treated with volumetric modulated arc therapy (VMAT) is transferred to another beam-matched linac. To evaluate the performance of Accelerated Go Live (AGL) service, the measured beam characteristics and patient specific quality assurance (QA) results between two AGL-matched linacs were compared.

MATERIALS AND METHODS

Two VersaHD linacs were installed using the AGL service. After the installation, the beam data such as percentage depth dose (PDD), lateral profiles and output factors for all photon beams were measured. Relative doses were also measured as a function of the multi-leaf collimator (MLC) leaf gap width. Subsequently, VMAT plans were created for prostate, pelvis, head and neck, liver, lung cancers and multiple brain metastases. Dose distributions and point doses were measured by multi-dimensional detectors and ionization chambers for patient specific quality assurance, and comparisons were made between the two linacs.

RESULTS

Dose differences in PDDs were all within ± 1% except the entrance region, and the averaged gamma indices of the lateral profiles were within 0.3. The differences in doses as a function of the MLC leaf gap width between the two linacs were within ±0.5%. For all the plans, gamma passing rates were all higher than 95% with criteria of 2%/2 mm. The average and the SD of dose differences on the multi-dimensional detector between both measurements was 0.06 ± 2.12%, and the average of point dose differences was -0.03 ± 0.33%.

CONCLUSION

We have evaluated the AGL performance in the context of beam characteristics and patient specific QA. It was demonstrated that the AGL service provides an accurate VMAT treatment reproducibility for many tumor sites with gamma pass rates greater than 95% under criteria of 2%/2 mm.

A MC-based anthropomorphic test case for commissioning model-based dose calculation in interstitial breast 192-Ir HDR brachytherapy

PURPOSE

To provide the first clinical test case for commissioning of ¹⁹² Ir brachytherapy model-based dose calculation algorithms (MBDCAs) according to the AAPM TG-186 report workflow.

ACQUISITION AND VALIDATION METHODS

A computational patient phantom model was generated from a clinical multi-catheter ¹⁹² Ir HDR breast brachytherapy case. Regions of interest (ROIs) were contoured and digitized on the patient CT images and the model was written to a series of DICOM CT images using MATLAB. The model was imported into two commercial treatment planning systems (TPSs) currently incorporating an MBDCA. Identical treatment plans were prepared using a generic ¹⁹² Ir HDR source and the TG-43-based algorithm of each TPS. This was followed by dose to medium in medium calculations using the MBDCA option of each TPS. Monte Carlo (MC) simulation was performed in the model using three different codes and information parsed from the treatment plan exported in DICOM radiation therapy (RT) format. Results were found to agree within statistical uncertainty and the dataset with the lowest uncertainty was assigned as the reference MC dose distribution.

DATA FORMAT AND USAGE NOTES

The dataset is available online at http://irochouston.mdanderson.org/rpc/BrachySeeds/BrachySeeds/index.html,https://doi.org/10.52519/00005. Files include the treatment plan for each TPS in DICOM RT format, reference MC dose data in RT Dose format, as well as a guide for database users and all files necessary to repeat the MC simulations.

POTENTIAL APPLICATIONS

The dataset facilitates the commissioning of brachytherapy MBDCAs using TPS embedded tools and establishes a methodology for the development of future clinical test cases. It is also useful to non-MBDCA adopters for intercomparing MBDCAs and exploring their benefits and limitations, as well as to brachytherapy researchers in need of a dosimetric and/or a DICOM RT information parsing benchmark. Limitations include specificity in terms of radionuclide, source model, clinical scenario, and MBDCA version used for its preparation.

An integrated care model for mental health in diabetes: Recommendations for local implementation by the Diabetes and Mental Health Expert Working Group in England

CONTEXT

In 2019, NHS England and Diabetes UK convened an Expert Working Group (EWG) in order to develop a Model and recommendations to guide commissioning and provision of mental health care in diabetes pathways and diabetes care in mental health pathways. The recommendations are based on a combination of evidence, national guidance, case studies and expert opinion from across the UK and form other long term conditions.

THE CASE FOR INTEGRATION

There is good the evidence around the high prevalence of co-morbidity between diabetes and mental illness of all severities and, the poorer diabetes and mental health outcomes for patients when this co-morbidity exists. Detecting and managing the mental health co-morbidity improves these outcomes, but the evidence suggests that detection of mental illness is poor in the context of diabetes care in community and acute care settings and that when it is detected, the access to appropriate mental health resource is variable and generally inadequate.

THE MODEL OF INTEGRATED CARE FOR DIABETES

The EWG developed a one-page Model with five core principles and five operational work-streams to support the delivery of integration, with examples of local case studies for local implementation. The five core principals are: Care for all-describing how care for all PWD needs to explore what matters to them and that emotional wellbeing is supported at diagnosis and beyond; Support and information-describing how HCPs should appropriately signpost to mental health support and the need for structured education programmes to include mental healthcare information; Needs identified-describing how PWD should have their mental health needs identified and acted on; Integrated care-describing how people with mental illness and diabetes should have their diabetes considered within their mental health care; Specialist care-describing how PWD should be able to access specialist diabetes mental health professionals. The five cross cutting work-streams for operationalising the principles are: Implementing training and upskilling of HCPs; Embedding mental health screening and assessment into diabetes pathways; Ensuring access to clear, integrated local pathways; Ensuring addressing health inequalities is incorporated at every stage of service development; Improving access to specialist mental health services through commissioning.

DISCUSSION AND CONCLUSIONS

The Model can be implemented in part or completely, at an individual level, all the way up to system level. It can be adapted across the life span and the UK, and having learnt from other long term conditions, there is a lot of transferability across all long term conditions There is an opportunity for ICBs to consider economies of scale across multiple long term conditions for which there will be a significant overlap of patients within the local population. Any local implementation should be in co-production with experts by experience and third sector providers.

Logistical, technical, and radiation safety aspects of establishing a radiopharmaceutical therapy program: A case in Lutetium-177 prostate-specific membrane antigen (PSMA) therapy

Prostate-specific membrane antigen (PSMA) is a cell surface protein highly expressed in nearly all prostate cancers, with restricted expression in some normal tissues. The differential expression of PSMA from tumor to non-tumor tissue has resulted in the investigation of numerous targeting strategies for therapy of patients with metastatic prostate cancer. In March of 2022, the FDA granted approval for the use of lutetium-177 PSMA-617 (Lu-177-PSMA-617) for patients with PSMA-positive metastatic castration-resistant prostate cancer (mCRPC) who have been treated with androgen receptor pathway inhibition and taxane-based chemotherapy. Therefore, the use of Lu-177-PSMA-617 is expected to increase and become more widespread. Herein, we describe logistical, technical, and radiation safety considerations for implementing a radiopharmaceutical therapy program, with particular focus on the development of operating procedures for therapeutic administrations. Major steps for a center in the U.S. to implement a new radiopharmaceutical therapy (RPT) program are listed below, and then demonstrated in greater detail via examples for Lu-177-PSMA-617 therapy.

A roadmap for implementation of kV-CBCT online adaptive radiation therapy and initial first year experiences

PURPOSE

Online Adaptive Radiation Therapy (oART) follows a different treatment paradigm than conventional radiotherapy, and because of this, the resources, implementation, and workflows needed are unique. The purpose of this report is to outline our institution's experience establishing, organizing, and implementing an oART program using the Ethos therapy system.

METHODS

We include resources used, operational models utilized, program creation timelines, and our institutional experiences with the implementation and operation of an oART program. Additionally, we provide a detailed summary of our first year's clinical experience where we delivered over 1000 daily adaptive fractions. For all treatments, the different stages of online adaption, primary patient set-up, initial kV-CBCT acquisition, contouring review and edit of influencer structures, target review and edits, plan evaluation and selection, Mobius3D 2nd check and adaptive QA, 2nd kV-CBCT for positional verification, treatment delivery, and patient leaving the room, were analyzed.

RESULTS

We retrospectively analyzed data from 97 patients treated from August 2021-August 2022. One thousand six hundred seventy seven individual fractions were treated and analyzed, 632(38%) were non-adaptive and 1045(62%) were adaptive. Seventy four of the 97 patients (76%) were treated with standard fractionation and 23 (24%) received stereotactic treatments. For the adaptive treatments, the generated adaptive plan was selected in 92% of treatments. On average(±std), adaptive sessions took 34.52 ± 11.42 min from start to finish. The entire adaptive process (from start of contour generation to verification CBCT), performed by the physicist (and physician on select days), was 19.84 ± 8.21 min.

CONCLUSION

We present our institution's experience commissioning an oART program using the Ethos therapy system. It took us 12 months from project inception to the treatment of our first patient and 12 months to treat 1000 adaptive fractions. Retrospective analysis of delivered fractions showed that the average overall treatment time was approximately 35 min and the average time for the adaptive component of treatment was approximately 20 min.

Keeping track: An intra-UK comparison of orthodontic commissioning and treatment outcome assessments

INTRODUCTION

Across the United Kingdom (UK), National Health Service (NHS) orthodontic treatment is commissioned differently across the devolved nations. There is a relative paucity in the literature describing the way in which the orthodontic services in each country are commissioned and treatment outcomes measured.

OBJECTIVE

To highlight the differences in the following: commissioning of primary care orthodontic services across the UK; assessment of treatment outcomes; and the potential impacts these differences have on contractors, performers and patient care.

MATERIALS AND METHODS

Data were collected using an online mixed-methods approach. Systematic content analysis was used to extract the required information from the websites and guidance documents of orthodontic service providers, which was then catalogued and verified electronically by senior dental advisors in the four devolved UK nations.

RESULTS

The Index of Orthodontic Treatment Need (IOTN) is a mandatory needs assessment tool used across all four nations, with an agreed minimum threshold of a dental health component (DHC) score of 3 and an aesthetic component (AC) score of 6 for NHS treatment. While the peer assessment rating (PAR) is the most utilised method of assessing post-treatment outcomes, it is applied differently by each country.

CONCLUSION

While NHS orthodontic services across the UK share mutual elements of service delivery, there are significant differences in the prior approval process and assessment of treatment outcomes. More research is required to assess the economic feasibility of orthodontic treatment from the associated treatment outcomes.

Clinical commissioning of the first point-of-care spectral photon-counting CT for the upper extremities

BACKGROUND

Acceptance testing and quality assurance (QA) of computed tomography (CT) scans are of great importance to ensure the appropriate performance of the systems. However, current standards and guidelines do not include a dedicated QA program for spectral photon-counting CT (SPCCT), nor adapted tolerance levels.

PURPOSE

To evaluate the technical performance, in terms of image quality and radiation dose, of the first point-of-care SPCCT for the upper extremities (MARS Extremity 5X120, MARS Bioimaging Ltd., Christchurch, New Zealand) and to establish a comprehensive QA program.

METHODS

The specific dimensions of the scanner with a 125 mm diameter gantry and a small voxel size of 0.1 × 0.1 × 0.1 mm³ require the use of suitable phantoms and evaluation techniques. Indicators such as CT number accuracy, image noise, uniformity, and slice thickness were assessed to characterize the image quality. The in-plane and longitudinal spatial resolutions were evaluated by means of the modulation transfer function (MTF). Noise power spectra (NPS) were calculated to further evaluate the image noise. Material identification capabilities were assessed using clinically relevant high-Z materials (iodine, gold, gadolinium, and calcium). A 100-mm diameter CTDI-like phantom was used to measure the dose indices. A complete radiation survey was carried out to measure the radiation exposure at different points around the scanner.

RESULTS

The proposed QA program is based on international and local recommendations as well as practical experience. It includes standardised CT tests and SPCCT-specific methods. Additional methodologies to further assess the system performance are also presented. Tolerance levels are discussed and revised when appropriate. Both in-plane and longitudinal high spatial resolutions were evidenced by the MTF measurements with 1.8 lp· mm^-1 and 5.0 lp· mm^-1 at 10%, respectively. The calculated effective slice thickness ranged between 0.15 and 0.16 mm for the five energy bins and for a reconstructed voxel size of 0.1 × 0.1 × 0.1 mm³ . Reference values of the linear attenuation coefficient of water have been calculated and used to assess the CT number uniformity of water. Evaluation of the CT number accuracy and stability of various clinically relevant materials showed excellent spectral correlation and linearity between HU values and concentrations (r² > 0.99). The NPS showed less noise correlation between slices than within transverse slice, as well as a systematic increase at low spatial frequencies. The volume CT dose index (CTDI v o l $_{vol}$ ) for a custom-made 100 mm diameter phantom was 9.32 mGy. Radiation measurements around the scanner showed that it is completely shielded except for the access port, and that no additional protective measures are necessary for the patient.

CONCLUSIONS

A routine QA framework for SPCCT systems has been proposed. Image quality and radiation dose were assessed using newly designed phantoms, relevant metrics, and automated algorithms. Baseline values were established and tolerance levels discussed for the MARS SPCCT scanner based on collected data and international recommendations.

Commissioning of helium ion therapy and the first patient treatment with active beam delivery

PURPOSE

Helium ions offer intermediate physical and biological properties to the clinically used protons and carbon ions. This work presents the commissioning of the first clinical treatment planning system (TPS) for helium ion therapy with active beam delivery to prepare the first patients' treatment at the INSTITUTION-XXX METHODS: : Through collaboration between RaySearch Laboratories and INSTITUTION-XXX, absorbed and relative biological effectiveness (RBE)-weighted calculation methods were integrated for helium ion beam therapy with raster-scanned delivery in the TPS RayStation. At INSTITUTION-XXX, a modified Microdosimetric Kinetic biological Model was chosen as reference biological model. TPS absorbed dose predictions were compared against measurements with several devices, using phantoms of different complexities, from homogeneous to heterogeneous anthropomorphic phantoms. RBE and RBE-weighted dose predictions of the TPS were verified against calculations with an independent RBE-weighted dose engine. The patient specific quality-assurance of the first treatment at INSTITUTION-XXX using helium ion beam with raster-scanned delivery is presented considering standard patient-specific measurements in a water phantom and two independent dose calculations with a Monte-Carlo or an analytical-based engine.

RESULTS

TPS predictions were consistent with dosimetric measurements and independent dose engines computations for absorbed and RBE-weighted doses. The mean difference between dose measurements to the TPS calculation was 0.2% for spread-out Bragg peaks in water. Verification of the first patient treatment TPS predictions against independent engines for both absorbed and RBE-weighted doses presents differences within 2% in the target and with a maximum deviation of 3.5% in the investigated critical regions of interest.

CONCLUSION

Helium ion beam therapy has been successfully commissioned and introduced into clinical use. Through comprehensive validation of the absorbed and RBE-weighted dose predictions of the RayStation TPS, the first clinical TPS for helium ion therapy using raster-scanned delivery was employed to plan the first helium patient treatment at INSTITUTION-XXX.

Transitioning from a COMS-based plaque brachytherapy program to using eye physics plaques and plaque simulator treatment planning system: A single institutional experience

The aim of this work is to describe the implementation and commissioning of a plaque brachytherapy program using Eye Physics eye plaques and Plaque Simulator treatment planning system based on the experience of one institution with an established COMS-based plaque program. Although commissioning recommendations are available in official task groups publications such as TG-129 and TG-221, we found that there was a lack of published experiences with the specific details of such a transition and the practical application of the commissioning guidelines. The specific issues addressed in this paper include discussing the lack of FDA approval of the Eye Physics plaques and Plaque Simulator treatment planning system, the commissioning of the plaques and treatment planning system including considerations of the heterogeneity corrected calculations, and the implementation of a second check using an FDA-approved treatment planning system. We have also discussed the use of rental plaques, the analysis of plans using dose histograms, and the development of a quality management program. By sharing our experiences with the commissioning of this program this document will assist other institutions with the same task and act as a supplement to the recommendations in the recently published TG-221.

Validation of pencil beam scanning proton therapy with multi-leaf collimator calculated by a commercial Monte Carlo dose engine

This study aimed to evaluate the clinical beam commissioning results and lateral penumbra characteristics of our new pencil beam scanning (PBS) proton therapy using a multi-leaf collimator (MLC) calculated by use of a commercial Monte Carlo dose engine. Eighteen collimated uniform dose plans for cubic targets were optimized by the RayStation 9A treatment planning system (TPS), varying scan area, modulation widths, measurement depths, and collimator angles. To test the patient-specific measurements, we also created and verified five clinically realistic PBS plans with the MLC, such as the liver, prostate, base-of-skull, C-shape, and head-and-neck. The verification measurements consist of the depth dose (DD), lateral profile (LP), and absolute dose (AD). We compared the LPs and ADs between the calculation and measurements. For the cubic plans, the gamma index pass rates (γ-passing) were on average 96.5% ± 4.0% at 3%/3 mm for the DD and 95.2% ± 7.6% at 2%/2 mm for the LP. In several LP measurements less than 75 mm depths, the γ-passing deteriorated (increased the measured doses) by less than 90% with the scattering such as the MLC edge and range shifter. The deteriorated γ-passing was satisfied by more than 90% at 2%/2 mm using uncollimated beams instead of collimated beams except for three planes. The AD differences and the lateral penumbra width (80%-20% distance) were within ±1.9% and ± 1.1 mm, respectively. For the clinical plan measurements, the γ-passing of LP at 2%/2 mm and the AD differences were 97.7% ± 4.2% on average and within ±1.8%, respectively. The measurements were in good agreement with the calculations of both the cubic and clinical plans inserted in the MLC except for LPs less than 75 mm regions of some cubic and clinical plans. The calculation errors in collimated beams can be mitigated by substituting uncollimated beams.

Elekta Unity MR-linac commissioning: mechanical and dosimetry tests

We report the commissioning results of Elekta Unity for the dosimetric performance and mechanical quality assurance (QA), and propose additional commissioning procedures. Mechanical tests included multi-leaf collimator (MLC) positional accuracy, radiation isocenter diameter at the center and off-center position, and coincidence between the magnetic resonance (MR) image center and radiation isocenter. Comparisons between the measurements and calculations of the simple irradiated field, intensity modulated radiation therapy (IMRT) commissioning, MLC output factor ratio, validation of independent dose calculation software and end-to-end testing were performed to evaluate dosimetric performance. The average values of the MLC positional accuracy for film- and imaging device-based analysis were −0.1 and 0.3 mm, respectively. The measured radiation isocenter size was 0.41 mm, and the off-center results were within 1 mm. The coincidence was −0.21, −1.19 and 0.49 mm along the x-, y- and z-axes, respectively. The calculated percent depth doses (PDD) and profiles agreed with the measurements. The results of independent dose calculation were within the action level recommended by American Associations of Physicist in Medicine. The gamma passing rate (GPR) for IMRT commissioning was 98.6 ± 0.9%, and end-to-end testing of adapted plans showed agreement within 2% between the measurement and calculation. We reported the results of mechanical and dosimetric performances of Elekta Unity, and proposed novel commissioning procedures. Our results should provide knowledge to the physics community for enhancing the QA programs.

Healthcare Equity and Commissioning: A Four-Year National Analysis of Portuguese Primary Healthcare Units

Equal and adequate access to healthcare is one of the pillars of Portuguese health policy. Despite the controversy over commissioning processes' contribution to equity in health, this article aims to clarify the relationship between socio-economic factors and the results of primary healthcare (PHC) commissioning indicators through an analysis of four years of data from all PHC units in Portugal. The factor that presents a statistically significant relationship with a greater number of indicators is the organizational model. Since the reform of PHC services in 2005, a new type of unit was introduced: the family health unit (USF). At the time of the study, these units covered 58.1% of the population and achieved better indicator results. In most cases, the evolution of the results achieved by commissioning seems to be similar in different analyzed contexts. Nevertheless, the percentage of patients of a non-Portuguese nationality and the population density were analyzed, and a widening of discrepancies was observed in 23.3% of the cases. The commissioning indicators were statistically related to the studied context factors, and some of these, such as the nurse home visits indicator, are more sensitive to context than others. There is no evidence that the best results were achieved at the expense of worse healthcare being offered to vulnerable populations, and there was no association with a reduction in inequalities in healthcare. It would be valuable if the Portuguese Government could stimulate the increase in the number of working USFs, especially in low-density areas, considering that they can achieve better results with lower costs for medicines and diagnostic tests.

Treatment planning with a 2.5 MV photon beam for radiation therapy

PURPOSE

The shallow depth of maximum dose and higher dose fall-off gradient of a 2.5 MV beam along the central axis that is available for imaging on linear accelerators is investigated for treatment of shallow tumors and sparing the organs at risk (OARs) beyond it. In addition, the 2.5 MV beam has an energy bridging the gap between kilo-voltage (kV) and mega-voltage (MV) beams for applications of dose enhancement with high atomic number (Z) nanoparticles.

METHODS

We have commissioned and utilized a MATLAB-based, open-source treatment planning software (TPS), matRad, for intensity-modulated radiation therapy (IMRT) dose calculations. Treatment plans for prostate, liver, and head and neck (H&N), nasal cavity, two orbit cases, and glioblastoma multiforme (GBM) were performed and compared to a conventional 6 MV beam. Additional Monte Carlo calculations were also used for benchmarking the central axis dose.

RESULTS

Both beams had similar planning target volume (PTV) dose coverage for all cases. However, the 2.5 MV beam deposited 6%-19% less integral doses to the nasal cavity, orbit, and GBM cases than 6 MV photons. The mean dose to the heart in the liver plan was 10.5% lower for 2.5 MV beam. The difference between the doses to OARs of H&N for two beams was under 3%. Brain mean dose, brainstem, and optic chiasm max doses were, respectively, 7.5%-14.9%, 2.2%-8.1%, and 2.5%-19.0% lower for the 2.5 MV beam in the nasal cavity, orbit, and GBM plans.

CONCLUSIONS

This study demonstrates that the 2.5 MV beam can produce clinically relevant treatment plans, motivating future efforts for design of single-energy LINACs. Such a machine will be capable of producing beams at this energy beneficial for low- and middle-income countries, and investigations on dose enhancement from high-Z nanoparticles.

Commissioning and Dosimetric Results of an Indigenously Developed Intra-Vaginal Template for Interstitial Plus Intracavitary High dose Rate Image-Guided Brachytherapy of Advanced Cervix Cancer

Aim

The goal of this study is to discuss the commissioning and dosimetric parameters achieved during the clinical implementation of an indigenously developed intracavitary (IC) plus interstitial (IS) template for high dose rate (HDR) image-guided brachytherapy (IGBT) in cancer (Ca) cervix. We want to discuss our achieved values of cumulative equi-effective doses (EQD2) for high-risk clinical target volume (HRCTV) and organ at risk (OAR) and compare it with available published results.

Materials and Methods

Medanta anterior oblique/lateral oblique template has a total of 19 needles including the central tandem. For commissioning the template with needles, the indigenously made acrylic phantom was used. Oblique and straight needles were placed inside the acrylic phantom and a computed tomography (CT) scan was performed. Sixteen patients were treated in HDR IGBT using this template after external-beam radiotherapy. The IGBT plans were evaluated based on EQD2 of target coverage i.e., dose received by 98% (D98%_HRCTV), 90% (D90%_HRCTV), and 50% (D50%_HRCTV) volume of HRCTV, and dose received by 2 cc (D2cc) and 0.1 cc (D0.1cc) of OAR using linear quadratic (LQ) radiobiological model.

Results

The autoradiographic in radiochromic film shows that the distance between the needle tip and the middle of the source position is 6 mm. The mean D98%_HRCTV and D90%_HRCTV was 76.8 Gy (range: 70-87.7 Gy, P < 0.01) and 84.49 Gy (range: 76.6-96.7 Gy, P < 0.01), respectively. Mean EQD2 of D2cc of the bladder, rectum, and sigmoid was 85.6 Gy (range: 77.5-99.6 Gy, P < 0.03), 74.3 Gy (range: 70.9-76.7 Gy, P < 0.05), and 58.3 Gy (range: 50.6-67.9 Gy, P = 0.01), respectively. The mean total reference air kerma at a 1 m distance is 0.489cGy (range: 0.391-0.681cGy).

Conclusions

The indigenously developed template could attain satisfactory standards in terms of set parameters for commissioning and acceptable dose volume relations in our clinical use for treating the advanced Ca cervix patients who need IC + IS type of HDR IGBT. The comparative analysis with contemporary applicators was acceptable.

Commissioning and validation of RayStation treatment planning system for CyberKnife M6

Background

RaySearch (AB, Stockholm) has released a module for CyberKnife (CK) planning within its RayStation (RS) treatment planning system (TPS).

Purpose

To create and validate beam models of fixed, Iris, and multileaf collimators (MLC) of the CK M6 for Monte Carlo (MC) and collapsed cone (CC) algorithms in the RS TPS.

Methods

Measurements needed for the creation of the beam models were performed in a water tank with a stereotactic PTW 60018 diode. Both CC and MC models were optimized in RS by minimizing the differences between the measured and computed profiles and percentage depth doses. The models were then validated by comparing dose from the plans created in RS with both single and multiple beams in different phantom conditions with the corresponding measured dose. Irregular field shapes and off‐axis beams were also tested for the MLC. Validation measurements were performed using an A1SL ionization chamber, EBT3 Gafchromic films, and a PTW 1000 SRS detector. Finally, patient‐specific QAs with gamma criteria of 3%/1 mm were performed for each model.

Results

The models were created in a straightforward manner with efficient tools available in RS. The differences between computed and measured doses were within ±1% for most of the configurations tested and reached a maximum of 3.2% for measurements at a depth of 19.5‐cm. With respect to all collimators and algorithms, the maximum averaged dose difference was 0.8% when considering absolute dose measurements on the central axis. The patient‐specific QAs led to a mean result of 98% of points fulfilling gamma criteria.

Conclusions

We created both CC and MC models for fixed, Iris, and MLC collimators in RS. The dose differences for all collimators and algorithms were within ±1%, except for depths larger than 9 cm. This allowed us to validate both models for clinical use.

Variations in policies for accessing elective musculoskeletal procedures in the English National Health Service: A documentary analysis

OBJECTIVE

The overall aim of this study was to investigate how commissioning policies for accessing clinical procedures compare in the context of the English National Health Service. Our primary objective was to compare policy wording and categorise any variations identified. Our secondary objective was to explore how any points of variation relate to national guidance.

METHODS

This study entailed documentary analysis of commissioning policies that stipulated criteria for accessing eight elective musculoskeletal procedures. For each procedure, we retrieved policies held by regions with higher and lower rates of clinical activity relative to the national average. Policies were subjected to content and thematic analysis, using constant comparison techniques. Matrices and descriptive reports were used to compare themes across policies for each procedure and derive categories of variation that arose across two or more procedures. National guidance relating to each procedure were identified and scrutinised, to explore whether these provided context for explaining the policy variations.

RESULTS

Thirty-five policy documents held by 14 geographic regions were included in the analysis. Policies either focused on a single procedure/treatment or covered several procedures/treatments in an all-encompassing document. All policies stipulated criteria that needed to be fulfilled prior to accessing treatment, but there were inconsistences in the evidence cited. Policies varied in recurring ways, with respect to specification of non-surgical treatments and management, requirements around time spent using non-surgical approaches, diagnostic requirements, requirements around symptom severity and disease progression, and use of language, in the form of terms and phrases ('threshold modifiers') which could open up or restrict access to care. National guidance was identified for seven of the procedures, but this guidance did not specify criteria for accessing the procedures in question, making direct comparisons with regional policies difficult.

CONCLUSIONS

This, to our knowledge, is the first study to identify recurring ways in which policies for accessing treatment can vary within a single-payer system with universal coverage. The findings raise questions around whether formulation of commissioning policies should receive more central support to promote greater consistency - especially where evidence is uncertain, variable or lacking.

Beam commissioning of the first clinical biology-guided radiotherapy system

This study reports the beam commissioning results for the first clinical RefleXion Linac.

Methods: The X1 produces a 6 MV photon beam and the maximum clinical field size is 40 × 2 cm² at source‐to‐axis distance of 85 cm. Treatment fields are collimated by a binary multileaf collimator (MLC) system with 64 leaves with width of 0.625 cm and y‐jaw pairs to provide either a 1 or 2 cm opening. The mechanical alignment of the radiation source, the y‐jaw, and MLC were checked with film and ion chambers. The beam parameters were characterized using a diode detector in a compact water tank. In‐air lateral profiles and in‐water percentage depth dose (PDD) were measured for beam modeling of the treatment planning system (TPS). The lateral profiles, PDDs, and output factors were acquired for field sizes from 1.25 × 1 to 40 × 2 cm² field to verify the beam modeling. The rotational output variation and synchronicity were tested to check the gantry angle, couch motion, and gantry rotation.

Results: The source misalignments were 0.049 mm in y‐direction, 0.66% out‐of‐focus in x‐direction. The divergence of the beam axis was 0.36 mm with a y‐jaw twist of 0.03°. Clinical off‐axis treatment fields shared a common center in y‐direction were within 0.03 mm. The MLC misalignment and twist were 0.57 mm and 0.15°. For all measured fields ranging from the size from 1.25 × 1 to 40 × 2 cm², the mean difference between measured and TPS modeled PDD at 10 cm depth was −0.3%. The mean transverse profile difference in the field core was −0.3% ± 1.1%. The full‐width half maximum (FWHM) modeling was within 0.5 mm. The measured output factors agreed with TPS within 0.8%.

Conclusions: This study summarizes our specific experience commissioning the first novel RefleXion linac, which may assist future users of this technology when implementing it into their own clinics.

Determination of commissioning criteria for multileaf-collimator, stereotactic radiosurgery treatments on Varian TrueBeam and Edge machines using a novel anthropomorphic phantom

An anthropomorphic phantom has been developed by Varian Medical Systems for commissioning multileaf‐collimator (MLC), stereotactic radiosurgery (SRS) treatments on Varian TrueBeam and Edge linear accelerators. Northwest Medical Physics Center (NMPC) has collected end‐to‐end data on these machines, at six independent clinical sites, to establish baseline dosimetric and geometric commissioning criteria for SRS measurements with this phantom. The Varian phantom is designed to accommodate four interchangeable target cassettes, each designed for a specific quality assurance function. End‐to‐end measurements utilized the phantom to verify the coincidence of treatment isocenter with a hidden target in a Winston‐Lutz cassette after localization using cone‐beam computed tomography (CBCT). Dose delivery to single target (2 cm) and single‐isocenter, multitarget (2 and 1 cm) geometries was verified using ionization chamber and EBT3 film cassettes. A nominal dose of 16 Gy was prescribed for each plan using a site's standard beam geometry for SRS cases. Measurements were performed with three Millennium and three high‐definition MLC machines at beam energies of 6‐MV and 10‐MV flattening‐filter‐free energies. Each clinical site followed a standardized procedure for phantom simulation, treatment planning, quality assurance, and treatment delivery. All treatment planning and delivery was performed using ARIA oncology information system and Eclipse treatment planning software. The isocenter measurements and irradiated film were analyzed using DoseLab quality assurance software; gamma criteria of 3%/1 mm, 3%/0.5 mm, and 2%/1 mm were applied for film analysis. Based on the data acquired in this work, the recommended commissioning criteria for end‐to‐end SRS measurements with the Varian phantom are as follows: coincidence of treatment isocenter and CBCT‐aligned hidden target < 1 mm, agreement of measured chamber dose with calculated dose ≤ 5%, and film gamma passing > 90% for gamma criteria of 3%/1 mm after DoseLab auto‐registration shifts ≤ 1 mm in any direction.

The commissioning of infant mental health services in the United Kingdom: A study of stakeholder views

CONTEXT

Infant regulatory disturbances are common and stable over time and can compromise infant outcomes across a range of developmental domains. Many such problems have their origins within the parent-infant relationship and specialized parent-infant relationship teams provide support and intervention that is explicitly aimed at addressing such relationship difficulties. However, there are currently only around 27 such teams across the United Kingdom, and just under half of CAMHS do not accept referrals of children under 2 years of age.

AIM

The current research aimed to examine the views of commissioners of children's services regarding the reasons for commissioning (or not) infant mental health services.

METHOD

Fourteen in-depth interviews were conducted with a range of stakeholders involved in commissioning children's services across 14 areas of England, half of which were commissioning specialized infant mental health services. A thematic analysis was undertaken.

RESULTS

A total of five themes emerged from the data as being key factors in the commissioning of infant mental health services: pressure from local practitioners, policy transfer through policy networks, opportunity for long-term cost reduction, potential to embed the service model within existing services and perinatal mental health funding.

CONCLUSION

As with commissioning more widely, the commissioning of infant mental health services is a complex process, with a range of factors influencing whether such services are commissioned or not, and data to suggest that the process is currently driven by informal and contingent factors, as much as by the evidence regarding what works.

A novel methodology for the optimization of transmission and dosimetric leaf gap parameters

PURPOSE

Optimization of dosimetric leaf gap (DLG) and transmission is commonly performed through a manual trial and error process, which can lead to sub-optimal values. The purpose of this work is to create an alternative automated optimization process that provides the optimal DLG and transmission pair for use in a clinical setting.

METHODS

Utilizing the treatment planning system application programming interface, a phase space of clinically viable DLG and transmission pairs was generated. The phase space contained 51,051 dose planes for DLGs between 0.0  and 2.5 mm and transmission values between 0.01% and 2.5%. Thirteen plans were measured for multiple multileaf collimator types and nominal beam energies. The optimization minimized the mean γ-index and maximized the γ-index pass rate. The optimized values were validated using five plans excluded from the optimization.

RESULTS

Of the nominal beam energies and multileaf collimator system (MLC)-type combinations tested, 6/7 showed an increase in γ-index pass rate and a decrease in mean γ-index signifying better agreement between measurement and calculation. When comparing the optimized DLG and transmission values to the clinically implemented values identified via an iterative method, 5/7 energy, and MLC type combinations showed no statistically significant changes. In addition, the optimized values were benchmarked against three Task Group 119 plans with published γ-index pass rates, which had been held out of the optimization. For those plans, the optimized DLG and transmission values provided the same or better γ-index pass rates.

CONCLUSION

We presented a novel and viable automated alternative to current approaches of selecting the DLG and transmission parameters. This method will reduce the time required to determine the clinically acceptable DLG and transmission parameters and ensure optimality for the plans included in the optimization.

Technical Note: Commissioning of an ultrasound-compatible surrogate vaginal cylinder for transvaginal ultrasound-based gynecologic high-dose-rate brachytherapy

PURPOSE

To provide a comprehensive set of commissioning tests for clinical implementation of three-dimensional transvaginal ultrasound (3D TVUS) as a replacement of computed tomography (CT) for applicator reconstruction in gynecologic intracavitary high-dose-rate brachytherapy with a multi-channel vaginal cylinder.

METHODS

We introduce an ultrasound-compatible "surrogate" vaginal cylinder (SVC) for reconstruction of Elekta's CT-MR Multi Channel Applicator (MCVC) in 3D TVUS. The MCVC is digitized over the SVC in 3DUS using digital library model overlay. Consulting guidelines from various sources (CPQR, GEC-ESTRO, AAPM), we identify and describe three tests specific to commissioning the SVC: 1) verification of SVC outer dimensions, 2) source position accuracy of MCVC digitization over the SVC in 3D TVUS, and 3) MRI/US registration error.

RESULTS

The SVC outer dimensions (diameter and A-D marker locations) were well matched to the MCVC, however a 0.6 mm discrepancy in length between cylinder tips was observed. Source position accuracy was within 1 mm (tolerance recommended by CPQR) when reconstructing the MCVC in 3D TVUS. Dice similarity coefficients and target registration error for MRI/3D TVUS registration was similar to MRI/CT registration, which is the clinical standard.

CONCLUSIONS

These commissioning tests are performed using institutional equipment but provide the framework for any practitioners to repeat in their own setup, to demonstrate safe adoption of the 3D TVUS system for patient treatments. We demonstrate that MRI/US-based workflow achieves similar source position accuracy and image registration error as standard MRI/CT, which is consistent with standard tolerances. This is a critical step towards replacement of CT with US in gynecologic high-dose-rate brachytherapy treatments with the MCVC. This article is protected by copyright. All rights reserved.

No wrong door: addressing injustices and achieving better mental healthcare provision for under-18s in acute physical healthcare settings

The distressing reality that mental healthcare for children and young people in acute trust settings in the UK is woefully underprovided is not news. But with acute trust debts being written off, hospital trusts and commissioners of services have a timely opportunity to address this age- and condition-based discrimination.Delivering a just service for under-18s depends on attitude, resources and adequate knowledge of the tasks involved. This article aims to describe the current landscape, summarise the arguments for better integrating mental healthcare into physical healthcare settings, articulate the tasks involved and the challenges for commissioning and providing, and finally share examples of current service models across the country.Ultimately, commissioning and provider choices will be constrained by resource pressures, but this article aims to underscore why commissioning and providing a portmanteau 'no wrong door' hospital service for children, young people and families is worth the headache of thinking outside old commissioning and provider boxes.

Rethinking Accessibility in Light of the Orange Declaration: Applying a Socio-Ecological Lens to Rural Mental Health Commissioning

The prevalence of mental illness is a critical public health issue. In Australia, the prevalence of mental illness is similar across all settings, however, people living in rural and remote areas experience worse outcomes than their urban counterparts. Access to mental health services is critical, however, the notion of accessibility needs to be understood in the context of the uniqueness and variability of the rural experience. The Orange Declaration on Rural and Remote Mental Health recognized that rural areas face a series of interconnected challenges and called for place-specific responses and new funding models that reward collaboration and local partnerships. In this paper, we argue that recent mental health planning, policy and service development uses a narrow interpretation of the notion of accessibility that is out of step with current thinking on the heterogeneity of the rural experience. We use some examples of our own research and experience in rural Western Australia to argue that the current commissioning model is not aligned with the Orange Declaration, and remains largely metro-centric and reliant on a narrow conceptualization of service accessibility. We argue that what is needed is a dynamic, responsive, context-sensitive understanding of accessibility that is informed by the distinctiveness of rural adversity, and recognizes the heterogeneity and variability of the rural experience whilst acknowledging rural agency and social capital, and we suggest that applying a socio-ecological approach to the development of new commissioning models provides a way forward.

Validation of Monte Carlo dose calculation algorithm for CyberKnife multileaf collimator

PURPOSE

To commission and evaluate the Monte Carlo (MC) dose calculation algorithm for the CyberKnife equipped with a multileaf collimator (MLC).

METHODS

We created a MC model for the MLC using an integrated module of the CyberKnife treatment planning software (TPS). Two parameters could be optimized: the maximum energy and the source full width at half-maximum (FWHM). The optimization was performed by minimizing the differences between the measured and the MC calculated tissue phantom ratios and profiles. MLC plans were calculated in the TPS with the MC algorithm and irradiated on different phantoms. The dose was measured using an A1SL ionization chamber and EBT3 Gafchromic films, and then compared to the TPS dose to obtain dose differences (ΔD). Finally, patient-specific quality assurances (QA) were performed with global gamma index criteria of 3%/1 mm.

RESULTS

The maximum energy and source FWHM showing the best agreement with measurements were 6.4 MeV and 1.8 mm. The output factors calculated with these parameters gave an agreement within ±1% with measurements. The ΔD showed that MC model systematically underestimated the dose with an average of -1.5% over all configurations tested. For depths deeper than 12 cm, the ΔD increased, up to -3.0% (maximum at 15.5 cm depth).

CONCLUSIONS

The MC model for MLC of CyberKnife is clinically acceptable but underestimates the delivered dose by an average of -1.5%. Therefore, we recommend using the MC algorithm with the MLC only in heterogeneous regions and for shallow-seated tumors.

Weight loss interventions on health-related quality of life in those with moderate to severe obesity: Findings from an individual patient data meta-analysis of randomized trials

The relationship between BMI and health-related quality of life (HRQoL) critically affects regulatory approval of interventions for weight loss, but evidence of the association is inconsistent. A higher standard of evidence than that available was sought with an IPD meta-analysis of 10,884 people enrolled in five randomized controlled trials of intentional weight loss interventions. Cross-sectional and longitudinal associations of BMI and HRQoL were estimated in mixed effects models specifying a latent variable for HRQoL. Spline regressions captured nonlinear associations across the range of BMI. In cross-sectional spline regressions, BMI was not associated with HRQoL for people with a BMI < 30 kg/m² but was for those with a higher BMI. In longitudinal spline regressions, decreases in BMI were positively associated with HRQoL for people with a BMI ≥ 25 kg/m² . The impact of change in BMI was larger for people with higher BMIs than for those with BMIs under 30 kg/m² . Lower BMI and decreases in BMI were related to higher HRQoL for people living with obesity but not in the population without excess weight. HRQoL gains from weight loss are greater for more severe obesity. Commissioners should use these estimates for future decision making.

Interinstitutional beam model portability study in a mixed vendor environment

A 6 MV flattened beam model for a Varian TrueBeamSTx c‐arm treatment delivery system in RayStation, developed and validated at one institution, was implemented and validated at another institution. The only parameter value adjustments were to accommodate machine output at the second institution. Validation followed MPPG 5.a. recommendations, with particular attention paid to IMRT and VMAT deliveries. With this minimal adjustment, the model passed validation across a broad spectrum of treatment plans, measurement devices, and staff who created the test plans and executed the measurements. This work demonstrates the possibility of using a single template model in the same treatment planning system with matched machines in a mixed vendor environment.

What do senior genitourinary medicine physicians think of the future of the speciality? A national survey

Genitourinary Medicine (GUM) is a specialty that has undergone significant change over the past decade. Multiple factors have contributed to this including changes in service models and commissioning landscapes, health service leadership, medical education and changes in the spectrum of our clinical work. The Joint Specialist Committee for GUM at the Royal College of Physicians (RCP) conducted a national survey in December 2019 - January 2020 to understand the changing scope of work for GUM consultants. The survey indicated an increase in clinical complexity alongside a decline in registrar recruitment, staff shortages and service fragmentation. Funding cuts have impacted many services and the majority of consultants feel a return to an NHS commissioning model would be preferable. Despite the many challenges, GUM physicians consider the specialty 'unique, dynamic, friendly and open-minded'. It is clear that senior doctors value the wider clinical, academic and educational opportunities within the specialty.

Stereotactic radiosurgery commissioning and QA test cases-A TG-119 approach for Stereotactic radiosurgery

PURPOSE

To develop a standardized set of representative clinical treatment cases that pose a range of optimization problems for evaluating the plan quality and dosimetric accuracy within the commissioning process for linac-based stereotactic radiosurgery (SRS).

METHODS

Five test cases with increasing complexity were created to validate delivery accuracy in SRS commissioning similar to the approach used by AAPM TG-119 in developing a test suite for IMRT commissioning. Standardized structure sets, planning goals, and delivery requirements were specified for each case including a small sphere target, irregular target, irregular target placed off-axis, multi-target, and abutting organs-at-risk (OARs). Various VMAT field arrangements including a single arc, two coplanar arcs, full arc and vertex half arc, and four noncoplanar arcs were tested to generate clinically appropriate treatment plans.

RESULTS

The small spherical target was 1.0 cm in diameter. The irregular target was a clinical cavity (2.3 × 2.2 × 1.4 cm³) and was shifted 4.5 cm for the irregular target off-axis case. The multi-target case used the irregular target and four spherical targets representing metastases ranging 0.9 to 1.6 cm in diameter, placed up to 7.5 cm off-axis. The abutting OARs case included an acoustic neuroma and target placed near the optic nerve. All spherical targets received 24 Gy and the cavity received 18 Gy. The abutting OAR cases included a 3.74 cc lesion adjacent to the brainstem receiving 13 Gy and a 1.11 cc lesion adjacent to the optic nerve receiving 12 Gy. All plans used a single-isocenter placed at the target center or geometric center of multiple targets. Planning goals for all cases included constraints for the target and brain minus PTV, along with brainstem and optic nerve where applicable. Deliverability was assessed through ion chamber measurements, in addition to composite and per-field planar measurements on Gafchromic film and small-field diode array. A mean and SD for measured versus planned doses of 101.0% ± 2.9% was observed over the 14 ion chamber measurements. Mean and SD for gamma pass rates were 98.5% ± 2.2% and 97.1% ± 4.9% for film and diode array, respectively, for gamma criteria of 2% and 1 mm.

CONCLUSION

These cases could provide the preliminary groundwork for a novel benchmark for institutions to evaluate linac-based SRS commissioning and delivery accuracy prior to clinical implementation. The rapid widespread implementation of linac-based SRS, the complexity associated with dosimetry and delivery, and high-profile treatment deviations that have already resulted from its use, highlight the importance of such a benchmark test suite. Comprehensive dosimetric measurements from this standardized set of SRS optimization problems were used to fine-tune and understand the limitations of our SRS planning and delivery system and establish a set of baseline data for comparison with other delivery platforms.

Joining the dots: Day to day challenges for practitioners in delivering integrated dementia care

Despite the increasing policy focus on integrated dementia care in the UK, little is known about the opportunities and challenges encountered by practitioners charged with implementing these policies on the ground. We undertook an extensive, mixed-methods analysis of how a contemporary multidisciplinary dementia pathway in the UK was experienced and negotiated by service providers. Our pragmatic mixed methods design incorporated three types of research interaction with practitioners: (a) Semi-structured interviews (n = 31) and focus group discussions (n = 4), (b) Practitioner 'shadowing' observations (n = 19), and (c) Service attendance and performance metrics reviews (n = 8). Through an abductive analysis of practitioner narratives and practice observations, we evidenced how inter-practitioner prejudices, restrictive and competitive commissioning frameworks, barriers to effective data sharing and other resource constraints, all challenged integrative dementia care and led to unintended consequences such as practice overlap and failure to identify and respond to people's needs. In order to more successfully realise integrated dementia pathways, we propose innovative commissioning frameworks which purposefully seek to diffuse power imbalances, encourage inter-provider respect and understanding, and determine clear lines of responsibility.

Asia-Pacific Special Interest Group: The first ten years

INTRODUCTION

The Asia-Pacific Special Interest Group (APSIG) was formed in 2009 by the Australian College of Physical Scientists and Engineers in Medicine (ACPSEM) to support radiation oncology services in low-to-middle income countries in our region. In 2017, APSIG moved to the ACPSEM's charity, the Better Healthcare Technology (BHT) Foundation, enabling improvement in fundraising, marketing and partnerships with like-minded organizations.

METHODS

APSIG's main activity is to recruit certified medical physicists as volunteers to train local staff in countries such as Vietnam, Cambodia, Myanmar and Mongolia. APSIG also supports remote mentoring, coordinates the delivery of donated radiotherapy equipment, and brings Asia-Pacific medical physicists to Australia and New Zealand for conferences and hospital training.

RESULTS

The number of APSIG volunteer assignments has been steadily increasing over the last decade. Challenges include the limited number of ACPSEM certified medical physics volunteers, the limited opportunities to train the local physicists due to their heavy workloads, and language barriers. The COVID-19 pandemic has halted volunteer assignments for now but a range of alternative means of assistance such as webinars, online tutorials and virtual meetings are planned to continue APSIG's activities.

CONCLUSION

APSIG will continue to provide a support service to radiation oncology staff in the Asia-Pacific region. APSIG and the BHT Foundation's work promotes quality health care by supporting medical physicists in Asia-Pacific countries and championing better radiotherapy technology access and treatment knowledge sharing.

Monte Carlo framework for commissioning a synchrotron-based discrete spot scanning proton beam system and treatment plan verification

This study aimed to develop a Monte Carlo (MC) framework for commissioning the narrow proton beams (spot size sigma, 5.2 mm 2 mm at isocenter for 69.4 MeV-221.3 MeV for the main beam option and 4.1 mm 1.3 mm for the minibeam option respectively) of a synchrotron-based proton therapy system and design an independent absolute dose calculation engine for intensity-modulated proton treatments. A proton therapy system (Hitachi PROBEAT-V) was simulated using divergent and convergent beam models at the nozzle entrance. The innovative source weighting scheme for the MC simulation with TOPAS (TOol for PArticle Simulations) was implemented using dose output data for the absolute dose calculations. The results of the MC simulation were compared to the experimental data, analyzed and used to commission the treatment planning system. Two MC models, divergent and convergent beams were implemented. The convergent beam model produced a high level of agreement when MC and measurements were analyzed. The beam ellipticity did not result in significant differences between MC simulated and treatment planning system calculated doses. A model of a synchrotron-based spot scanning proton therapy system has been developed and implemented in the TOPAS MC transport code framework. The dose computation engine is useful for treatment plan verification with primary and minibeam beam option.

Commissioning and quality assurance of HalcyonTM 2.0 linear accelerator

BACKGROUND

Varian Medical Systems has introduced a new medical linear accelerator called HalcyonTM 2.0, which is based on the ring delivery system (RDS). It is a true IGRT machine having 6MV FFF photon energy. In addition to the planar and MV-CBCT imaging techniques it also has an option of ultra-fast kV-iCBCT which enhances the image reconstruction and improves the visualization of soft tissue. The field portals are shaped by a unique dual layer MLC with special stacked and staggered design which enables high modulation with low radiation leakage. Recently, we have commissioned our first Halcyon 2.0 machine. The aim of this work was to systematically investigate various parameters of a newly installed HalcyonTM 2.0 linear accelerator.

MATERIALS AND METHODS

Detailed measurements were conducted as per various guidelines. Also, the measurements were performed to fulfil the national regulatory requirements. Commissioning data of Halcyon 6 MV-FFF beam was performed in a water tank. For absolute measurements, a 0.6-cc waterproof Farmer chamber and electrometer were used. All relative measurements (PDDs, in-line, cross-line and angular profiles) were performed with 0.0125 cc point chamber.

RESULTS

All the tests were within the acceptable limit. Measured data were compared with factory data as well as the existing medical linear accelerator of the same category. The obtained results were quite satisfactory.

CONCLUSIONS

This study summarizes the commissioning experience with Halcyon linear accelerator. Evaluation of mechanical, radiation safety and dosimetric parameters were performed. The obtained parameters were well below the specified tolerance limits.

Investing to prevent: Description of an innovative approach to commissioning a supervised toothbrushing programme across multiple local authorities in England

INTRODUCTION

The NHS Long Term Plan prioritises NHS action to reduce health inequalities and give children a good start in life. A Sustainability and Transformation Partnership (STP) is a collaborative working arrangement between local authorities and the NHS covering a defined population and geography. Within the STP in Devon, England, all three local authorities had separate supervised toothbrushing programmes; all were precariously funded. Devon has limited access to routine NHS dentistry and children in deprived areas have high rates of general anaesthetics for dental extractions. Consolidating the supervised toothbrushing programmes presented an opportunity to address oral health inequalities across Devon STP.

OBJECTIVES

1. Reduce oral health inequalities for children in deprived areas. 2. Reduce treatment need for children who have limited access to routine NHS dentistry. 3. Invest in prevention.

METHODS

A proposal, supported by local authorities in Devon STP, was developed for a targeted supervised toothbrushing programme at early years sites across the most deprived 50% of areas in Devon. Return on investment was estimated using a national resource. Methods are described for identifying eligible sites and defining procurement lots. The NHS dental services commissioner agreed to support this proposal using an innovative approach to commissioning.

RESULTS

Three lots, totalling 525 sites, were awarded to two providers. Mobilisation over summer 2019 led to implementation from September 2019.

CONCLUSION

Partnership working and innovative commissioning can enable NHS England to invest in prevention at scale where options to increase dental access are limited. Implementation across a large geographical area creates challenges but facilitates equitable programme delivery.

Commissioning of an ultra-high dose rate pulsed electron beam medical LINAC for FLASH RT preclinical animal experiments and future clinical human protocols

PURPOSE

To present the acceptance and the commissioning, to define the reference dose, and to prepare the reference data for a quality assessment (QA) program of an ultra-high dose rate (UHDR) electron device in order to validate it for preclinical animal FLASH radiotherapy (FLASH RT) experiments and for FLASH RT clinical human protocols.

METHODS

The Mobetron^® device was evaluated with electron beams of 9 MeV in conventional (CONV) mode and of 6 and 9 MeV in UHDR mode (nominal energy). The acceptance was performed according to the acceptance protocol of the company. The commissioning consisted of determining the short- and long-term stability of the device, the measurement of percent depth dose curves (PDDs) and profiles at two different positions (with two different dose per pulse regimen) and for different collimator sizes, and the evaluation of the variability of these parameters when changing the pulse width and pulse repetition frequency. Measurements were performed using a redundant and validated dosimetric strategy with alanine and radiochromic films, as well as Advanced Markus ionization chamber for some measurements.

RESULTS

The acceptance tests were all within the tolerances of the company's acceptance protocol. The linearity with pulse width was within 1.5% in all cases. The pulse repetition frequency did not affect the delivered dose more than 2% in all cases but 90 Hz, for which the larger difference was 3.8%. The reference dosimetry showed a good agreement within the alanine and films with variations of 2.2% or less. The short-term (resp. long-term) stability was less than 1.0% (resp. 1.8%) and was the same in both CONV and UHDR modes. PDDs, profiles, and reference dosimetry were measured at two positions, providing data for two specific dose rates (about 9 Gy/pulse and 3 Gy/pulse). Maximal beam size was 4 and 6 cm at 90% isodose in the two positions tested. There was no difference between CONV and UHDR mode in the beam characteristics tested.

CONCLUSIONS

The device is commissioned for FLASH RT preclinical biological experiments as well as FLASH RT clinical human protocols.

Public perspectives of social prescribing

BACKGROUND

There is a strong national drive within the UK government and National Health Service for social prescribing. Previous research studies have mainly focused on service user perspectives and evaluating their experiences. There is limited evidence on how the general public perceive and understand what social prescribing is and how these views could influence service planning and delivery. This paper seeks to understand perceptions of social prescribing within the wider community.

METHODS

Semi-structured focus groups were conducted with 37 members of the public in four areas in north-west England. We explored public awareness and understanding of social prescribing.

RESULTS

Limited knowledge of the term social prescribing was found amongst participants as well as limited involvement in community discussions of the topic. Concerns were raised about the short-term nature of activities and the need for adequate resourcing to support continuity of service provision. The social prescribing link worker was considered to be important in supporting engagement with services and it was preferred this role was undertaken by people with local knowledge.

CONCLUSIONS

The findings provide evidence of public perspectives on social prescribing and highlight how wider community perceptions can supplement service user feedback to support social prescribing service planning, commissioning and delivery.

The relationship between alcohol-related hospital admission and specialist alcohol treatment provision across local authorities in England since passage of the Health and Social Care Act 2012

To our knowledge no previous studies have been conducted at the local authority level assessing relationships between alcohol-related hospital admission, specialist alcohol treatment provision and socioeconomic deprivation since the UK government passed the Health and Social Care Act in 2012. Our results, using publicly available national data-sets, suggest that the local authority areas in England most in need of adequately funded specialist alcohol treatment, because of high prevalence of alcohol dependence and deprivation, are not receiving targeted increased funding, and that the national rise in alcohol-related hospital admissions may be fuelled by local authority funding cuts to specialist alcohol treatment.

Application of radiochromic gel dosimetry to commissioning of a megavoltage research linear accelerator for small-field animal irradiation studies

PURPOSE

To develop and implement an efficient and accurate commissioning procedure for small-field static beam animal irradiation studies on an MV research linear accelerator (Linatron-M9) using radiochromic gel dosimetry.

MATERIALS

The research linear accelerator (Linatron-M9) is a 9 MV linac with a static fixed collimator opening of 5.08 cm diameter. Lead collimators were manually placed to create smaller fields of 2 × 2 cm² , 1 × 1 cm² , and 0.5 × 0.5 cm² . Relative dosimetry measurements were performed, including profiles, percent depth dose (PDD) curves, beam divergence, and relative output factors using various dosimetry tools, including a small volume ionization chamber (A14), GAFCHROMIC™ EBT3 film, and Clearview gel dosimeters. The gel dosimeter was used to provide a 3D volumetric reference of the irradiated fields. The Linatron profiles and relative output factors were extracted at a reference depth of 2 cm with the output factor measured relative to the 2 × 2 cm² reference field. Absolute dosimetry was performed using A14 ionization chamber measurements, which were verified using a national standards laboratory remote dosimetry service.

RESULTS

Absolute dosimetry measurements were confirmed within 1.4% (k = 2, 95% confidence = 5%). The relative output factor of the small fields measured with films and gels agreed with a maximum relative percent error difference between the two methods of 1.1 % for the 1 × 1 cm² field and 4.3 % for the 0.5 × 0.5 cm² field. These relative errors were primarily due to the variability in the collimator positioning. The measured beam profiles demonstrated excellent agreement for beam size (measured as FWHM), within approximately 0.8 mm (or less). Film measurements were more accurate in the penumbra region due to the film's finer resolution compared with the gel dosimeter. Following the van Dyk criteria, the PDD values of the film and gel measurements agree within 11% in the buildup region starting from 0.5 cm depth and within 2.6 % beyond maximum dose and into the fall-off region for depths up to 5 cm. The 2D beam profile isodose lines agree within 0.5 mm in all regions for the 0.5 × 0.5 cm² and the 1 × 1 cm² fields and within 1 mm for the larger field of 2 × 2 cm² . The 2D PDD curves agree within approximately 2% of the maximum in the typical therapy region (1-4 cm) for the 1 × 1 cm² and 2 × 2 cm² and within 5% for the 0.5 × 0.5 cm² field.

CONCLUSION

This work provides a commissioning process to measure the beam characteristics of a fixed beam MV accelerator with detailed dosimetric evaluation for its implementation in megavoltage small animal irradiation studies. Radiochromic gel dosimeters are efficient small-field relative dosimetry tools providing 3D dose measurements allowing for full representation of dose, dosimeter misalignment corrections and high reproducibility with low inter-dosimeter variability. Overall, radiochromic gels are valuable for fast, full relative dosimetry commissioning in comparison to films for application in high-energy small-field animal irradiation studies.