Characterization of a 6 MV photon beam in terms of primary and scattered dose components

The purpose of this work was to partition the 6 MV photon beam of a Philips SL75-5 linear accelerator into primary and scattered dose components in water. The two quantities that are necessary to define the primary beam component are a reference dose DR and a primary linear attenuation coefficient μ 0. DR describes the magnitude of the primary dose as a fraction of the total dose in a reference field at a reference depth, while μ 0 describes how the primary dose changes with depth in a medium. The scattered component is the difference between the primary and total dose. μ 0 for the beam in water was determined in four different ways, namely through the extrapolation of measured TMRs to zero field size, through linear attenuation measurements, through the fit of a convolution model to CAPDD data and through a method involving a central axis attenuator. The primary dose component was determined in two ways, namely by the extrapolation of the phantom scatter correction factor to zero field size and also by the central axis attenuator method. μ 0 varied from 0.0445 cm-1 to 0.0469 cm-1 with an average of 0.0455 +- 0.0012 cm-1. DR for a 10 cm x 10 cm field at the depth of maximum dose was found to vary between 0.933 Gy/ 100 MU and 0.935 Gy/ 100 MU, with an average of 0.934 Gy/ 100 MU. These values agree very well with values published in the literature. It has thus been shown that the 6 MV photon beam is separable into primary and scattered dose components

Implementation of carbon fibre treatment couches in the XiO® and Monaco® Treatment Planning Systems

CITATION: Van Reenen, C. J. & Trauernicht, C. J. 2020. Implementation of carbon fibre treatment couches in the XiO® and Monaco® Treatment Planning Systems, Polish Journal of Medical Physics and Engineering, 26(4):211-215, doi:10.2478/pjmpe-2020-0025.The original publication is available at https://www.sciendo.comPurpose: Carbon fibre treatment couches on linear accelerators provide a strong, rigid framework for patient support. Patient safety is a priority, therefore the dosimetric properties of treatment couches need to be accurately incorporated in treatment plans, to minimize differences between planned and delivered dose. This study aims to determine the attenuation effect of treatment couches for 3-D Conformal Radiotherapy (3-D CRT) and to validate the implementation thereof in the XiO and Monaco treatment planning systems (TPS). Material and methods: Attenuation measurements were performed on the ELEKTA Connexion couches of the ELEKTA Precise and Synergy-Agility linear accelerators. Measurements were made at 10° intervals in RMI-457 Solid water (30 cm x 30 cm x 30 cm) using a PTW Farmer-type ionization chamber (TW30013) positioned at the accelerator’s isocentre. The percentage attenuation was calculated as the ratio of the electrometer readings for parallelopposed fields. The Computed Tomography (CT) data sets of the set-ups were obtained on a Philips Big Bore 16-slice CT scanner and exported to the TPS. The individual couch structures were delineated and electron density (ED) values were assigned using the commissioned CT-to-ED curve. Test treatment plans were generated with 100MU per field at 10° gantry intervals. Results: The percentage attenuation was determined to be within 2% and 3% for beams perpendicular to the couch surface for XiO and Monaco, respectively. The maximum attenuation was observed for oblique fields which was significantly higher than the manufacturer specified values. TPS validation showed an agreement to 1% for XiO and Monaco. At extreme oblique angles, both planning systems overestimated this effect up to a maximum of 4%. Conclusions: Couch attenuation differs significantly with gantry angle and beam energy. As a result, the treatment couch models should be included in all treatment planning calculations.https://www.sciendo.com/article/10.2478/pjmpe-2020-0025Publisher's versio

Establishment of local diagnostic reference levels for CT colonography at a tertiary hospital

Background: Diagnostic reference levels (DRLs) are an important metric in identifying abnormally high radiation doses in diagnostic examinations. National DRLs for CT colonography do not currently exist in South Africa, but there are efforts to collect data for a national DRL project. Objectives: This study investigated radiation doses for CT colonography in adult patients at a large tertiary hospital in South Africa with the aim of setting local DRLs. Method: Patient data from two CT scanners (Philips Ingenuity and Siemens Somatom go.Top) in the period March 2020 – March 2023 were obtained from the hospital’s picture archiving and communication system (PACS) (n = 115). Analysis involved determining the median computed tomography dose index-volume (CTDIvol) and dose-length product (DLP) values. The findings were compared with DRLs established internationally. Results: Ingenuity median CTDIvol was 20 mGy and DLP was 2169 mGy*cm; Somatom median CTDIvol was 6 mGy and DLP was 557 mGy*cm. Ingenuity exceeded the United Kingdom’s (UK) recommended DRLs by 82% and 214%, respectively. Somatom median CTDIvol and DLP were 45% and 19% lower than UK NDRLs. Conclusion: Somatom’s tin filter and other dose reduction features provided significant dose reduction. These data were used to set DRLs for CT colonography at the hospital; CTDIvol: 6 mGy and DLP: 557 mGy*cm. Contribution: In addition to informing radiation protection practices at the level of the institution, the established local DRLs contribute towards implementing regional and national DRLs

Artificial Intelligence-Based Radiotherapy Contouring and Planning to Improve Global Access to Cancer Care.

PURPOSE: Increased automation has been identified as one approach to improving global cancer care. The Radiation Planning Assistant (RPA) is a web-based tool offering automated radiotherapy (RT) contouring and planning to low-resource clinics. In this study, the RPA workflow and clinical acceptability were assessed by physicians around the world. METHODS: The RPA output for 75 cases was reviewed by at least three physicians; 31 radiation oncologists at 16 institutions in six countries on five continents reviewed RPA contours and plans for clinical acceptability using a 5-point Likert scale. RESULTS: For cervical cancer, RPA plans using bony landmarks were scored as usable as-is in 81% (with minor edits 93%); using soft tissue contours, plans were scored as usable as-is in 79% (with minor edits 96%). For postmastectomy breast cancer, RPA plans were scored as usable as-is in 44% (with minor edits 91%). For whole-brain treatment, RPA plans were scored as usable as-is in 67% (with minor edits 99%). For head/neck cancer, the normal tissue autocontours were acceptable as-is in 89% (with minor edits 97%). The clinical target volumes (CTVs) were acceptable as-is in 40% (with minor edits 93%). The volumetric-modulated arc therapy (VMAT) plans were acceptable as-is in 87% (with minor edits 96%). For cervical cancer, the normal tissue autocontours were acceptable as-is in 92% (with minor edits 99%). The CTVs for cervical cancer were scored as acceptable as-is in 83% (with minor edits 92%). The VMAT plans for cervical cancer were acceptable as-is in 99% (with minor edits 100%). CONCLUSION: The RPA, a web-based tool designed to improve access to high-quality RT in low-resource settings, has high rates of clinical acceptability by practicing clinicians around the world. It has significant potential for successful implementation in low-resource clinics

A risk assessment of automated treatment planning and recommendations for clinical deployment

CITATION: Kisling, K. et al. 2019. A risk assessment of automated treatment planning and recommendations for clinical deployment. Medical Physics, 46(6): 2567-2574. doi:10.1002/mp.13552The original publication is available at https://aapm.onlinelibrary.wiley.com/journal/24734209Purpose: To assess the risk of failure of a recently developed automated treatment planning tool, the radiation planning assistant (RPA), and to determine the reduction in these risks with implementation of a quality assurance (QA) program specifically designed for the RPA. Methods: We used failure mode and effects analysis (FMEA) to assess the risk of the RPA. The steps involved in the workflow of planning a four-field box treatment of cervical cancer with the RPA were identified. Then, the potential failure modes at each step and their causes were identified and scored according to their likelihood of occurrence, severity, and likelihood of going undetected. Additionally, the impact of the components of the QA program on the detectability of the failure modes was assessed. The QA program was designed to supplement a clinic's standard QA processes and consisted of three components: (a) automatic, independent verification of the results of automated planning; (b) automatic comparison of treatment parameters to expected values; and (c) guided manual checks of the treatment plan. A risk priority number (RPN) was calculated for each potential failure mode with and without use of the QA program. Results: In the RPA automated treatment planning workflow, we identified 68 potential failure modes with 113 causes. The average RPN was 91 without the QA program and 68 with the QA program (maximum RPNs were 504 and 315, respectively). The reduction in RPN was due to an improvement in the likelihood of detecting failures, resulting in lower detectability scores. The top-ranked failure modes included incorrect identification of the marked isocenter, inappropriate beam aperture definition, incorrect entry of the prescription into the RPA plan directive, and lack of a comprehensive plan review by the physician. Conclusions: Using FMEA, we assessed the risks in the clinical deployment of an automated treatment planning workflow and showed that a specialized QA program for the RPA, which included automatic QA techniques, improved the detectability of failures, reducing this risk. However, some residual risks persisted, which were similar to those found in manual treatment planning, and human error remained a major cause of potential failures. Through the risk analysis process, we identified three key aspects of safe deployment of automated planning: (a) user training on potential failure modes; (b) comprehensive manual plan review by physicians and physicists; and (c) automated QA of the treatment plan.https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.13552Publisher’s versio

Measured and calculated dose distributions in the “claws” – a specially designed gold applicator loaded with I-125 seeds

Introduction: The “Claws” is a unique gold applicator for whole-eye radiotherapy that was designed at Groote Schuur Hospital. It is used to treat retinoblastoma. Under general anaesthesia, a pericorneal ring is attached to the four extraocular muscles, and four legs, each loaded with I125 seeds, are inserted beneath the conjunctiva in-between each pair of muscles and attached anteriorly to the ring. The four legs that are now sutured onto the ring give it a claw-like appearance, hence the name for the applicator. The applicator was designed in such a way that the dose is directed towards the middle of the eye, while sparing surrounding tissues. The dose to the organs at risk could never be determined accurately, because the treatment planning system (TPS) is not able to take into account the gold shielding. Additionally, the TPS approximates each seed as a point source and not as a line source, therefore not taking any anisotropy into account. Aims: The first aim of this project was to accurately determine various dosimetric and physical characteristics of a single I-125 seed and to then compare these to published data. Spectral measurements of the OncoSeed 6711 using various detectors were also done. The next aim was to formalize the model of the “Claws” so that the applicator can potentially also be manufactured elsewhere. The next aim was to describe the “Claws” dosimetrically. This was done - Using thermoluminescent dosimeters in a solid water phantom - Using gafchromic film in a solid water phantom - Using treatment planning systems TheraPlan Plus and BrachyVision - Using Monte Carlo simulations – egs_brachy The final aim of the thesis was the comparison of measured and calculated data. The Monte Carlo simulations take into account the seed anisotropy as well as the gold shielding; therefore the relative dose to critical structures can be estimated more reliably. Method and Materials: Gafchromic film and thermoluminescent dosimeters (TLDs) were used for measurements in various specially designed phantoms to determine the seed parameters, as well as dose distributions in the eye. Dose distributions were calculated on two treatment planning systems. A CAD drawing of the “Claws” was created and used to create the input file for Monte Carlo simulations using egs_brachy. The final Monte Carlo calculation simulated 64.000.000.000 particle histories at voxel sizes of 0.1 mm x 0.1 mm x 0.1 mm. Results: Measured seed data matched published seed data. Significant dose distribution changes were found when comparing measured and Monte Carlo data to planned data, especially near the periphery of the eye between adjacent legs. The Monte Carlo calculated dose to the optic nerve is 64.8 % of the central dose in the eye, while the planned dose is 93.7 %. The Monte Carlo lens dose varies from 72.0 % - 86.1 %, while the planned dose varies from 73.0 % - 84.3 %. Monte Carlo calculated dose to the bony orbit is 11.3 %, while the planned dose is 54.7 %. Conclusion: Measured seed data matched published seed data. The “Claws” were formalized with CAD drawings. Measured and Monte Carlo simulated dose distributions matched well, while planned dose distributions showed discrepancies in certain regions of the eye and outside of the eye. This clearly indicates that the gold shielding of the applicator walls must be taken into account during dose calculations. It can be concluded that the “Claws” were extensively described and characterized in this work

Model for Estimating Power and Downtime Effects on Teletherapy Units in Low-Resource Settings

Purpose: More than 6,500 megavoltage teletherapy units are needed worldwide, many in low-resource settings. Cobalt-60 units or linear accelerators (linacs) can fill this need. We have evaluated machine performance on the basis of patient throughput to provide insight into machine viability under various conditions in such a way that conclusions can be generalized to a vast array of clinical scenarios. Materials and Methods: Data from patient treatment plans, peer-reviewed studies, and international organizations were combined to assess the relative patient throughput of linacs and cobalt-60 units that deliver radiotherapy with standard techniques under various power and maintenance support conditions. Data concerning the frequency and duration of power outages and downtime characteristics of the machines were used to model teletherapy operation in low-resource settings. Results: Modeled average daily throughput was decreased for linacs because of lack of power infrastructure and for cobalt-60 units because of limited and decaying source strength. For conformal radiotherapy delivered with multileaf collimators, average daily patient throughput over 8 years of operation was equal for cobalt-60 units and linacs when an average of 1.83 hours of power outage occurred per 10-hour working day. Relative to conformal treatments delivered with multileaf collimators on the respective machines, the use of advanced techniques on linacs decreased throughput between 20% and 32% and, for cobalt machines, the need to manually place blocks reduced throughput up to 37%. Conclusion: Our patient throughput data indicate that cobalt-60 units are generally best suited for implementation when machine operation might be 70% or less of total operable time because of power outages or mechanical repair. However, each implementation scenario is unique and requires consideration of all variables affecting implementation

Automated treatment planning of postmastectomy radiotherapy

CITATION: Kisling, K., et al. 2019. Automated treatment planning of postmastectomy radiotherapy. Medical physics, 46(9), 3767–3775. https://doi.org/10.1002/mp.13586The original publication is available at https://aapm.onlinelibrary.wiley.com/journal/24734209Purpose: Breast cancer is the most common cancer in women globally and radiation therapy is a cornerstone of its treatment. However, there is an enormous shortage of radiotherapy staff, especially in low- and middle-income countries. This shortage could be ameliorated through increased automation in the radiation treatment planning process, which may reduce the workload on radiotherapy staff and improve efficiency in preparing radiotherapy treatments for patients. To this end, we sought to create an automated treatment planning tool for postmastectomy radiotherapy (PMRT). Methods: Algorithms to automate every step of PMRT planning were developed and integrated into a commercial treatment planning system. The only required inputs for automated PMRT planning are a planning computed tomography scan, a plan directive, and selection of the inferior border of the tangential fields. With no other human input, the planning tool automatically creates a treatment plan and presents it for review. The major automated steps are (a) segmentation of relevant structures (targets, normal tissues, and other planning structures), (b) setup of the beams (tangential fields matched with a supraclavicular field), and (c) optimization of the dose distribution by using a mix of high- and low-energy photon beams and field-in-field modulation for the tangential fields. This automated PMRT planning tool was tested with ten computed tomography scans of patients with breast cancer who had received irradiation of the left chest wall. These plans were assessed quantitatively using their dose distributions and were reviewed by two physicians who rated them on a three-tiered scale: use as is, minor changes, or major changes. The accuracy of the automated segmentation of the heart and ipsilateral lung was also assessed. Finally, a plan quality verification tool was tested to alert the user to any possible deviations in the quality of the automatically created treatment plans. Results: The automatically created PMRT plans met the acceptable dose objectives, including target coverage, maximum plan dose, and dose to organs at risk, for all but one patient for whom the heart objectives were exceeded. Physicians accepted 50% of the treatment plans as is and required only minor changes for the remaining 50%, which included the one patient whose plan had a high heart dose. Furthermore, the automatically segmented contours of the heart and ipsilateral lung agreed well with manually edited contours. Finally, the automated plan quality verification tool detected 92% of the changes requested by physicians in this review. Conclusions: We developed a new tool for automatically planning PMRT for breast cancer, including irradiation of the chest wall and ipsilateral lymph nodes (supraclavicular and level III axillary). In this initial testing, we found that the plans created by this tool are clinically viable, and the tool can alert the user to possible deviations in plan quality. The next step is to subject this tool to prospective testing, in which automatically planned treatments will be compared with manually planned treatments.https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.13586Publisher’s versio

Addressing the Global Expertise Gap in Radiation Oncology: The Radiation Planning Assistant

PURPOSEAutomation, including the use of artificial intelligence, has been identified as a possible opportunity to help reduce the gap in access and quality for radiotherapy and other aspects of cancer care. The Radiation Planning Assistant (RPA) project was conceived in 2015 (and funded in 2016) to use automated contouring and treatment planning algorithms to support the efforts of oncologists in low- and middle-income countries, allowing them to scale their efforts and treat more patients safely and efficiently (to increase access).DESIGNIn this review, we discuss the development of the RPA, with a particular focus on clinical acceptability and safety/risk across jurisdictions as these are important indicators for the successful future deployment of the RPA to increase radiotherapy availability and ameliorate global disparities in access to radiation oncology.RESULTSRPA tools will be offered through a webpage, where users can upload computed tomography data sets and download automatically generated contours and treatment plans. All interfaces have been designed to maximize ease of use and minimize risk. The current version of the RPA includes automated contouring and planning for head and neck cancer, cervical cancer, breast cancer, and metastases to the brain.CONCLUSIONThe RPA has been designed to bring high-quality treatment planning to more patients across the world, and it may encourage greater investment in treatment devices and other aspects of cancer treatment