Commissioning of Aktina SRS cones and dosimetric validation of the RayStation photon Monte Carlo dose calculation algorithm.

Clinical implementation of SRS cones demands particular experimental care and dosimetric considerations in order to deliver precise and safe radiotherapy to patients. The purpose of this work was to present the commissioning data of recent Aktina cones combined with a 6MV flattened beam produced by an Elekta VersaHD linear accelerator. Additionally, the modelling process, and an assessment of dosimetric accuracy of the RayStation Monte Carlo dose calculation algorithm for cone based SRS was performed. There are currently no studies presenting beam data for this equipment and none that outlines the modelling parameters and validation of dose calculation using RayStation's photon Monte Carlo dose engine with cones. Beam data was measured using an SFD and a microDiamond and benchmarked against EBT3 film for cones of diameter 5-39 mm. Modelling was completed and validated within homogeneous and heterogeneous phantoms. End-to-end image-guided validation was performed using a StereoPHAN™ housing, an SRS MapCHECK and EBT3 film, and calculation time was investigated as a function of statistical uncertainty and field diameter. The TPS calculations agreed with measured data within their estimated uncertainties and clinical treatment plans could be calculated in under a minute. The data presented serves as a reference for others commissioning Aktina stereotactic cones and the modelling parameters serve similarly, while providing a starting point for those commissioning the same TPS algorithm for use with cones. It has been shown in this work that RayStation's Monte Carlo photon dose algorithm performs satisfactorily in the presence of SRS cones.

Nano X Image Guidance in radiation therapy: feasibility study protocol for cone beam computed tomography imaging with gravity-induced motion.

BACKGROUND: This paper describes the protocol for the Nano X Image Guidance (Nano X IG) trial, a single-institution, clinical imaging study. The Nano X is a prototype fixed-beam radiotherapy system developed to investigate the feasibility of a low-cost, compact radiotherapy system to increase global access to radiation therapy. This study aims to assess the feasibility of volumetric image guidance with cone beam computed tomography (CBCT) acquired during horizontal patient rotation on the Nano X radiotherapy system. METHODS: In the Nano X IG study, we will determine whether radiotherapy image guidance can be performed with the Nano X radiotherapy system where the patient is horizontally rotated while scan projections are acquired. We will acquire both conventional CBCT scans and Nano X CBCT scans for 30 patients aged 18 and above and receiving radiotherapy for head/neck or upper abdomen cancers. For each patient, a panel of experts will assess the image quality of Nano X CBCT scans against conventional CBCT scans. Each patient will receive two Nano X CBCT scans to determine the image quality reproducibility, the extent and reproducibility of patient motion and assess patient tolerance. DISCUSSION: Fixed-beam radiotherapy systems have the potential to help ease the current shortfall and increase global access to radiotherapy treatment. Advances in image guidance could facilitate fixed-beam radiotherapy using horizontal patient rotation. The efficacy of this radiotherapy approach is dependent on our ability to image and adapt to motion due to rotation and for patients to tolerate rotation during treatment. TRIAL REGISTRATION: ClinicalTrials.gov, NCT04488224. Registered on 27 July 2020.

Investigation of in vivo source tracking error thresholds for interstitial and intra-cavitary high-dose-rate cervical brachytherapy.

Purpose: The purpose of this study was to determine a comprehensive in vivo source tracking error thresholds in high-dose-rate (HDR) brachytherapy for cervical cancer. Achieving this enables the definition of an action level for imminent in vivo source tracking technologies and treatment monitoring devices, preventing clinically relevant changes to the applied dose. Material and methods: Retrospective HDR interstitial (n = 10) and intra-cavitary (n = 20) cervical brachytherapy patients were randomly selected to determine the feasibility of implementing in vivo source tracking error thresholds. A script was developed to displace all dwell positions in each treatment plan, along all major axes from their original position. Dose-volume histogram (DVH) indices were calculated without re-optimization of modified plans to determine the appropriate in vivo source tracking error thresholds in each direction. Results: In vivo source tracking error thresholds were directionally dependent; the smallest were found to be 2 mm in the anterior and posterior directions for both interstitial and intra-cavitary treatments. High-risk clinical treatment volume (HR-CTV) coverage was significantly impacted by displacements of 4 to 5 mm along each axis. Critically, there was a large variation in DVH metrics with displacement due to change in dwell weightings and patient anatomy. Conclusions: Determining the dosimetric impact of dwell position displacement provides a clinical benchmark for the development of pre-treatment verification devices and an action level for real-time treatment monitoring. It was established that an in vivo source tracking error threshold needs to be patient-specific. In vivo source tracking error thresholds should be determined for each patient, and can be conducted with extension of the method established in this work.

Australia and New Zealand's responsibilities in improving oncology services in the Asia-Pacific: A call to action.

AIM: To review the expected increasing demand for cancer services among low and middle-income countries (LMICs) in the Asia-Pacific (APAC), and to describe ways in which Australia and New Zealand (ANZ) can provide support to improve cancer outcomes in our region. METHODS: We first review the current and projected incidence of cancer within the APAC between 2018 and 2040, and the estimated demand for chemotherapy, radiotherapy and surgery. We then explore potential ways in which ANZ can increase regional collaborations to improve cancer outcomes. RESULTS: We identify 6 ways that ANZ can collaborate with LMICs to improve cancer care in the APAC through the ANZ Regional Oncology Collaboration Strategy: Increasing education and institutional collaborations in the APAC region through in-country training, twinning partnerships, observerships and formalised training programs in order to increase cancer care quality and capacity. Promoting and assisting in the establishment and maintenance of population-based cancer registries in LMICs. Increasing research capacity in LMICs through collaboration and promoting high quality global oncology research within ANZ. Engaging and training Australian and New Zealand clinicians in global oncology, increasing awareness of this important career path, and increasing health policy engagement. Increasing web-based endeavours through virtual tumour boards, web-based advocacy platforms and web-based teaching programs. Continuing to leverage for funding through professional bodies, government, industry, not-for-profit organisations and local hospital funds. CONCLUSION: We propose the creation of an Australian and New Zealand Interest Group to provide formalised and sustained collaboration between researchers, clinicians and stakeholders.

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.

Pre-treatment and real-time image guidance for a fixed-beam radiotherapy system.

PURPOSE: A radiotherapy system with a fixed treatment beam and a rotating patient positioning system could be smaller, more robust and more cost effective compared to conventional rotating gantry systems. However, patient rotation could cause anatomical deformation and compromise treatment delivery. In this work, we demonstrate an image-guided treatment workflow with a fixed beam prototype system that accounts for deformation during rotation to maintain dosimetric accuracy. METHODS: The prototype system consists of an Elekta Synergy linac with the therapy beam orientated downward and a custom-built patient rotation system (PRS). A phantom that deforms with rotation was constructed and rotated within the PRS to quantify the performance of two image guidance techniques: motion compensated cone-beam CT (CBCT) for pre-treatment volumetric imaging and kilovoltage infraction monitoring (KIM) for real-time image guidance. The phantom was irradiated with a 3D conformal beam to evaluate the dosimetric accuracy of the workflow. RESULTS: The motion compensated CBCT was used to verify pre-treatment position and the average calculated position was within -0.3 ± 1.1 mm of the phantom's ground truth position at 0°. KIM tracked the position of the target in real-time as the phantom was rotated and the average calculated position was within -0.2 ± 0.8 mm of the phantom's ground truth position. A 3D conformal treatment delivered on the prototype system with image guidance had a 3%/2 mm gamma pass rate of 96.3% compared to 98.6% delivered using a conventional rotating gantry linac. CONCLUSIONS: In this work, we have shown that image guidance can be used with fixed-beam treatment systems to measure and account for changes in target position in order to maintain dosimetric coverage during horizontal rotation. This treatment modality could provide a viable treatment option when there insufficient space for a conventional linear accelerator or where the cost is prohibitive.

Total body irradiation in Australia and New Zealand: results of a practice survey.

Total body irradiation (TBI) is an important treatment modality for the preparation of patients for bone marrow transplants. It is technically challenging and the actual delivery may vary from clinic to clinic. Knowledge of the pattern of practice may be helpful for clinics to determine future practice. We carried out an email survey from April to September 2019 sending 48 TBI related questions to all radiotherapy clinics in Australia and New Zealand via the Australasian College of Physical Scientists in Medicine email distribution list. Centres not performing TBI were not expected to complete the survey and centres that had participated in a previous survey, or that were known to perform the treatment, were followed up if no response was received. Of a total of approximately 70 centres, 14 clinics responded to the survey. The vast majority of clinics use conventional lateral and/or anterior-posterior beams at extended SSD for TBI treatment delivery. However, treatment planning, ancillary equipment (used for immobilisation/modulation), beam energy and prescribed lung doses vary considerably-with some clinics delivering the prescription dose to the lungs and some aiming to deliver a lung dose which is lower than the prescription dose. Only one clinic reported using an advanced delivery technique with modulated arcs at extended SSD. Centres either said they had no access to outcome data or did not answer this question. Compared with an earlier survey from 2005, 3 clinics have lowered their linac dose rate and 7 are the same or similar. The TBI practice in Australia and New Zealand remains varied, with considerable differences in treatment planning, beam energy, accepted lung doses and delivered dose rates.

Dose verification for liver target volumes undergoing respiratory motion.

Respiratory motion has a significant impact on dose delivered to abdominal targets during radiotherapy treatment. Accurate treatment of liver tumours adjacent to the diaphragm is complicated by large respiratory movement, as well as differing tissue densities at the lung-liver interface. This study aims to evaluate the accuracy of dose delivered to superior liver tumours using passive respiratory monitoring, in the absence of gating technology, for a range of treatment techniques. An in-house respiratory phantom was designed and constructed to simulate the lung and liver anatomy. The phantom consisted of adjacent slabs of lung and liver equivalent materials and a cam drive system to emulate respiratory motion. A CC04 ionisation chamber and Gafchromic EBT3 film were used to perform point dose and dose plane measurements respectively. Plans were calculated using an Elekta Monaco treatment planning system (TPS) on exhale phase study sets for conformal, volume modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) techniques, with breathing rates of 8, 14 and 23 bpm. Analysis confirmed the conformal delivery protocol currently used for this site within the department is suitable. The experiments also determined that VMAT is a viable alternative technique for treatment of superior liver lesions undergoing respiratory motion and was superior to IMRT. Furthermore, the measurements highlighted the need for respiratory management in these cases. Displacements due to respiration exceeding planned margins could result in reduced coverage of the clinical target volume and much higher doses to the lung than anticipated.

Development and commissioning of a full-size prototype fixed-beam radiotherapy system with horizontal patient rotation.

PURPOSE: Compared to conventional linacs with rotating gantries, a fixed-beam radiotherapy system could be smaller, more robust and more cost-effective. In this work, we developed and commissioned a prototype x-ray radiotherapy system utilizing a fixed vertical radiation beam and horizontal patient rotation. METHODS: The prototype system consists of an Elekta Synergy linac with gantry fixed at 0° and a custom-built patient rotation system (PRS). The PRS was designed to immobilize patients and safely rotate them about the horizontal axis. The interlocks and emergency stops of the linac and PRS were connected. Custom software was developed to monitor the system status, control the motion of the PRS and modify treatment plans for the fixed-beam configuration. Following installation, the prototype system was commissioned for three-dimensional (3D) conformal therapy based on guidelines specified in AAPM TG-45 and TG-142, with modifications for the fixed-beam geometry made where necessary. RESULTS: The system and control software was tested in a variety of machine states and executed motion, stop and beam gating commands as expected. Interlocks and emergency stops of the linac and PRS were found to correctly stop PRS motion and both kV and MV radiation beams when triggered. For 3D conformal treatments, the prototype system met all AAPM TG-45 and TG-142 specifications for geometric and dosimetric accuracy. Motion of the PRS was within 0.6 ± 0.3 mm and 0.10° ± 0.07° of input values for translation and rotation respectively. The axis of rotation of the PRS was coincident with the radiation beam axis to less than 1 mm. End-to-end treatment verification for 6 MV conformal treatments showed less than 2% difference between planned and delivered dose for all fields. CONCLUSION: In this work, we have developed and commissioned a radiotherapy system that utilizes a fixed vertical radiation beam and horizontal patient rotation. This system is a proof-of-concept prototype for a fixed-beam treatment system without a rotating gantry. Fixed-beam systems that are smaller and more cost-effective could help in improving global access to radiotherapy.

Functional imaging equivalence and proof of concept for image-guided adaptive radiotherapy with fixed gantry and rotating couch.

PURPOSE: The purpose of this article is to present the first imaging experiments to demonstrate the functional equivalence between a conventional rotational gantry and a fixed-beam imaging geometry, and the feasibility of an iterative image-reconstruction technique under gravitational deformation. METHODS AND MATERIALS: Experiments were performed using an Elekta Axesse with Agility MLC and XVI, a custom-built rotating phantom stage, a Catphan QA phantom, and a porcine heart. For the imaging equivalence, a conventional cone beam computed tomography (CBCT) of the Catphan was acquired, as well as a set of 660 x-ray projections with a static gantry and rotating Catphan. Both datasets were reconstructed with the Feldkamp-Davis-Kress (FDK) algorithm, and the resultant volumetric images were compared using standard metrics. For imaging under gravitational deformation, a conventional CBCT of the Catphan and a set of 660 x-ray projections with a static gantry and rotating Catphan were also acquired with a porcine heart. The conventional CBCT was reconstructed using FDK. The projections that were acquired with the heart rotating were sorted into angular bins and reconstructed with prior image constrained compressed sensing using a deformation-blurred FDK prior. Deformation was quantified with B-spline transformation-based deformable image registration. RESULTS: For imaging equivalence, the difference between the two Catphan images was consistent with Poisson noise. For imaging under gravitational deformation, the conventional CBCT porcine heart image (ground truth at 0 degrees) matched the static gantry, rotating heart reconstruction with a mean magnitude of <3 mm and maximum magnitude of <5 mm of the deformation vector field. The mean deformation of the rotating heart was 3.0 to 8.9 mm, up to 16.1 mm maximum deformation. Deformation was mainly observed in the direction of gravity. CONCLUSIONS: We have demonstrated imaging equivalence in cone beam CT reconstructions between rigid phantom images acquired with a conventional rotating gantry and with a fixed-gantry and rotating phantom. We have presented a method for image reconstruction under a fixed-beam imaging geometry using a deformable phantom.

Characterization of small-field stereotactic radiosurgery beams with modern detectors.

To derive accurate beam models for stereotactic radiosurgery (SRS) planning it is necessary to characterize the beam with dosimetric measurements. The aim of this study is to identify the best detectors for each task in the characterization process. Output ratios, beam profiles and percentage depth doses were measured for SRS cone diameters of 5-45 mm. Commercially available and emerging detectors were used: Gafchromic EBT2 film, an air-core fibre optic dosimeter (FOD) (developed at Royal Prince Alfred Hospital, Sydney), an IBA stereotactic field diode, a PTW 60012 electron diode and an IBA cc01 small volume thimble ion chamber. Analysis of the measured data supported by baseline Monte Carlo simulation data, led to the following recommendations: (1) water-equivalent detectors (Gafchromic EBT2 film or FOD) are the preferred choice for SRS dosimetry, (2) ion chambers (including small volume chambers with high-density central electrodes) should be avoided due to volume averaging effects and energy dependence, (3) if diodes are used, corrections must be made to account for their over-response in small fields.

In vivo real-time dosimetric verification in high dose rate prostate brachytherapy.

PURPOSE: To evaluate the performance of a diode array in the routine verification of planned dose to points inside the rectum from prostate high dose rate (HDR) brachytherapy using a real-time planning system. METHODS: A dosimetric study involving 28 patients was undertaken where measured doses received during treatment were compared to those calculated by the treatment planning system (TPS). After the ultrasound imaging required for treatment planning had been recorded, the ultrasound probe was replaced with a geometric replica that contained an 8 mm diameter cylindrical cavity in which a PTW diode array type 9112 was placed. The replica probe was then positioned inside the rectum with the individual diode positions determined using fluoroscopy. Dose was then recorded during the patients' treatment and compared to associated coordinates in the planning system. RESULTS: Factors influencing diode response and experimental uncertainty were initially investigated to estimate the overall uncertainty involved in dose measurements, which was determined to be +/- 10%. Data was acquired for 28 patients' first fractions, 11 patients' second fractions, and 13 patients' third fractions with collection dependent upon circumstances. Deviations between the diode measurements and predicted values ranged from -42% to +35% with 71% of measurements experiencing less than a 10% deviation from the predicted values. If the +/- 10% measurement uncertainty was combined with a tolerated dose discrepancy of +/- 10% then over 95% of the diode results exhibited agreement with the calculated data to within +/- 20%. It must also be noted that when large dose discrepancies were apparent they did not necessarily occur for all five diodes in the one measurement. CONCLUSIONS: This technique provided a method that could be utilized to detect gross errors in dose delivery of a real-time prostate HDR plan. Limitations in the detection system used must be well understood if meaningful results are to be achieved.