COMP Highlights - Salle de bal et foryer

June 24, 2022 from 8:30am EDT to 10:00am EDT

Scientific Session – Highlights
Friday, June 24, 2022, 8:30-10:00

Scientific Session Highlights – Presentation 1

Comparison of Clinician and Radiomic Analysis of Magnetic Resonance Imaging for Brain Metastasis Stereotactic Radiosurgery Prognosis

David DeVries, Frank Lagerwaard, Jaap Zindler, George Rodrigues, George Hajdok, Aaron Ward
Western University, Amsterdam UMC, Haaglanden Medical Centre

Purpose: Brain metastases (BMs) treated with stereotactic radiosurgery (SRS) may progress post-treatment, motivating the need for prognostic models. A previous study found a simple recursive partitioning analysis (RPA) model linking progression with a clinician-based score of BM appearance in T1w magnetic resonance imaging (MRI). MRI radiomics and machine learning (ML) have also successfully predicted SRS outcomes, but interpretability of these methods is lacking. This study therefore aims to directly compare these clinician and radiomics-based techniques.

Methods: A dataset of n=123 BMs was acquired containing clinical features, T1w MRI, appearance scores, and SRS outcomes. The RPA model with clinician-based appearance scores was used to stratify the BMs into progression risk groups. 28 MRI radiomic features were used to train ML classifiers to replicate the clinician-based appearance scoring, producing a second, radiomics-based RPA model. The radiomic and clinical features were used to train a final ML classifier to directly predict the progression probability, producing a third, non-RPA model. The three models were then compared using Kaplan-Meier analysis.

Results: All three models were shown to produce statistically significant risk stratifications. The clinician-based and radiomics-based RPA models were not identical, but the discrepancies were not detrimental to the stratification. The non-RPA model offered superior high-risk stratification at the expense of early versus late progression separation.

Conclusions: This study demonstrates that MRI radiomics can replicate the qualitative scoring performed by clinicians, providing valuable insights into radiomics-based systems. This study also shows the benefit of using more complex ML classifiers over RPA models for risk stratification.


Scientific Session Highlights – Presentation 2

Design of a patient-specific whole-breast 3D ultrasound device for point-of-care imaging

Claire Park, Jeffrey Bax, David Tessier, Lori Gardi, Aaron Fenster
Robarts Research Institute - Western University

Purpose: To develop a dedicated patient-specific 3D ultrasound (US) device for high-resolution whole-breast imaging using a point-of-care approach in women at high-risk for breast cancer.

Methods: We developed an innovative 3DUS device capable of supine automated whole-breast scanning with its apparatus affixed directly on the patient. The device is composed of a customized 3D-printed dam to conform to the patient, an adjustable compression assembly with a sonolucent TPX plate to immobilize the breast, and a motorized scanner and US cradle that can accommodate any US transducer. When affixed, hands-free automated whole-breast 3DUS scanning was performed. To expand the field-of-view, the US cradle can be shifted laterally to acquire multiple 3DUS images which are combined in real-time with a transformation and custom voxel-based fusion algorithm. Whole-breast 3DUS imaging was evaluated in a tissue-mimicking breast phantom with spherical structures and volumetric reconstruction error was assessed. The first proof-of-concept whole-breast 3DUS approach was performed in a healthy female volunteer study.

Results: Whole-breast 3DUS imaging was performed in the breast phantom allowing for dynamic multi-planar 3D viewing. Volumetric reconstruction error in the whole-breast 3DUS image was 1.98 ± 1.34% (N = 10) showing accurate multi-image registration and fusion. High-resolution whole-breast 3DUS images were acquired in the female volunteer study and anatomical features were clearly visualized and near seamlessly combined.

Conclusion: The developed 3DUS device shows potential as an alternative approach for automated supine whole-breast 3DUS imaging with the capability for accurate and efficient bedside point-of-care imaging.


Scientific Session Highlights – Presentation 3

A mail-able calorimeter for absolute dose determination in clinical beams

Malcolm McEwen, Bryan Muir, Stanislaw Szpala, Kirpal Kohli
National Research Council Canada, BC Cancer Agency

Purpose: To develop and commission a mail-able calorimeter that can be used in radiation beams by clinical medical physicists to address novel dosimetry problems.

Methods: A robust calorimeter design was constructed out of pure aluminum. To provide additional checks on performance in remote locations, the calorimeter is paired with an ionization chamber, also constructed from aluminum. The calorimeter and chamber are positioned at the same measurement depth (which can be adjusted) in aluminum alloy phantoms. Initial measurements were carried out in clinical photon and electron beams to determine the reproducibility of both detectors and evaluate the calorimeter/chamber ratio. A first test was then performed, with the system being shipped to a remote location for measurements in a range of photon beams. Technical support was provided via video-conferencing software, but otherwise the clinical medical physicist ran the software and obtained data alone.

Results: For a set of ten runs delivering 1.6 Gy per run, the standard deviation of the calorimeter-measured dose was 0.5 %. Polarity and recombination data agreed between “home” and “remote” locations. The calorimeter/chamber ratio showed variations at the 0.7 % level, demonstrating no significant impact of shipping on detectors. Feedback from the clinical site indicated that calorimeter operation was achievable and the overall uncertainty of 0.5 % was not significantly larger than reported for calorimeters operated at national laboratories.

Conclusions: A calorimeter/chamber system has been demonstrated, which can be used in clinical situations to investigate dosimetry problems requiring an absolute dose determination.


Scientific Session Highlights – Presentation 4

Development of an HDR emergency response simulator using optical tracking methods

Alasdair Syme, Kathleen MacLean, Michel Ladouceur, Krista Chytyk-Praznik
Dalhousie University

Purpose: To develop a system to evaluate the doses received by responders (particularly physicians) during a stuck source emergency in high dose rate brachytherapy.

Methods: A motion capture system was configured to record detailed positional information about both the Ir-192 HDR source and various anatomical regions of a responder from the time they enter the room until the time the source is deposited in a shielding container. Models were created for both prostate and gynecological (ring and tandem) treatments. Dose calculations were based on a simple application of the gamma constant, where the distances used in the calculations were those calculated from the time-dependent 3-dimensional positional information of a particular anatomical landmark and the source. Radiation Oncologists (2 residents, 1 staff) and a Medical Physics resident participated.

Results: Responders with no previous brachytherapy training (clinical or emergency response – 1 RO resident, 1 MP resident) had the highest doses: hands: 89 mGy (high dose hand) and 47 mGy (low dose hand); eyes: 6 mGy; torso: 2.8 mGy. Excluding those cases, average doses [prostate , gynecological] were: high dose hand: [14.4 , 22.9] mGy; low dose hand: [7.0 , 3.1] mGy; eyes: [0.3 , 0.5] mGy; torso: [0.3 , 0.4] mGy.

Conclusions: The system was able to precisely record the position of the source and anatomy. Calculated doses provide useful information to inform responders about doses they are likely to receive during the intervention. Basic training with realistic applicator removal significantly reduces responder doses.


Scientific Session Highlights – Presentation 5

Fusion of three-dimensional ultrasound images for the guidance of gynecological brachytherapy treatments

Tiana Trumpour, Jessica Rodgers, Lucas Mendez, Kathleen Surry, Aaron Fenster
Robarts Research Institute, Queens University, London Regional Cancer Program

Purpose: High dose rate brachytherapy is a common treatment technique for gynecological malignancies.

This method uses specialized applicators and, in some cases, interstitial needles to deliver radiation locally to the cancerous volume. To ensure accurate dose delivery and positive treatment outcome, identification of the applicator and needle tips is necessary. We propose the use of three-dimensional (3D) ultrasound (US) image fusion to overcome limitations in intra-operative visualization of important structures.

Methods: An anthropomorphic female pelvic phantom was created with a brachytherapy applicator and seven interstitial needles embedded. The phantom was imaged using 3D transrectal US and 3D transabdominal US, individually. The resultant images were rigidly registered based on a physical model of the applicator and were combined using a voxel overlap technique. Registration validation was completed using the target registration error (TRE) and fiducial localization error (FLE) of the embedded needle tips. The fused 3D US image was also qualitatively compared to a magnetic resonance (MR) image.

Results: All seven needle tips, applicator, and anatomical structures were visible in the fused 3D US image.

Registration error resulted in a mean TRE of 2.48±0.32 mm and a mean FLE of 0.22±0.09 mm. The fused image depicted similar needle placement to the MR image.

Conclusions: We developed a technique to fuse 3D US images for the identification of gynecological brachytherapy applicators and needle tips. This method has the potential for use as an intra-operative image guidance technique to aid physicians in radiation placement during treatment.


Scientific Session Highlights – Presentation 6

Optimizing the Deliverability of Trajectory Optimization Technologies for Multi-metastases Cranial SRS/SRT

Eva Lee, Lee MacDonald, Christopher Thomas, Alasdair Syme
Dalhousie University

Purpose: A novel treatment technique, CODA-iABC, for multi-metastases cranial SRS/SRT has been shown to be superior to VMAT with respect to OAR dose sparing and MU efficiency. This study focuses on validating the delivery and optimizing the dose fidelity of CODA-iABC in which dynamic couch, collimator, and gantry trajectories are used with periodic binary target collimation.

Methods: Seven plans were studied and each consisted of a full gantry arc and two 180o couch arcs. A transition window (TW) between control points (CPs) defines the fraction of a CP dedicated to the transition of binary MLC. The size of the TW is marked by two additional motion points (MP) around a CP, where the transition of binary MLC motion starts at the first MP and completes at the next MP. Plans were delivered with six TW widths: 20%, 40%, 60%, 80%, 100% (continuous arc delivery), and 0% (step-and-shoot delivery). Delivery accuracy was evaluated with an Octavius detector. The total beam-on-time was manually recorded.

Results: Gamma passing rate and beam-on time decreased as a function of TW width. Five plans delivered at both 0% and 20% TWs have a pass rate above 95%. At a 60% TW width, three plans maintained a pass rate above 95%, two plans had rates between 90% and 95%, and the remaining two plans were around 86%.

Conclusions: This work demonstrates the feasibility of CODA-iABC delivery. Shorter TWs result in increased delivery accuracy, but longer delivery time. The tradeoff between delivery accuracy and time should be optimized.


Scientific Session Highlights – Presentation 7

Preliminary Comparison of Organic Electret-Style Devices on Silicon and Flexible Plastic Substrates as Ionizing Radiation Dosimeters

Alexandria Mitchell, Irina Valitova, Ian G. Hill, Alasdair Syme
Dalhousie University, Nova Scotia Health Authority

Purpose: Evaluate the response of electret-style organic thin film transistors (OTFTs) as an ionizing radiation dosimeter in wired and wireless configurations. Assess energy dependence and reusability of silicon OTFTs and compare sensitivity of devices on silicon and polyethylene terephthalate (PET) substrates.

Methods: These devices were exposed to 100 kVp photons from an orthovoltage treatment unit and 6 MV photons from a TrueBeam linear accelerator. In wireless mode, a high gate voltage was applied to program the device prior to irradiation and after each delivered dose, devices were scanned to readout the amount of erased charges by monitoring the drain current change. For real-time readout in a wired configuration the drain current was measured with constant drain and gate voltage applied. Different dose rates were used to quantify the sensitivity of the device to changes in dose rate.

Results: The wireless silicon transistors showed a linear increase in current with increasing dose. The sensitivities for different energies were 60 ± 5 nA/Gy at 6 MV and 80 ± 10 nA/Gy at 100 kVp. The sensitivity of silicon detectors tested in a wired configuration was 8.1 nA/s and the sensitivity of the PET devices was 4.0 nA/s at a dose rate of 600 MU/min.

Conclusions: OTFTs with an electret have demonstrated potential in radiation dosimetry applications. Silicon devices in a wireless configuration possess excellent linearity at both kilovoltage and megavoltage X-ray energies. In wired mode Si devices had sensitivities that were approximately twice those of the PET.


Scientific Session Highlights – Presentation 8

On the orientation independence of the HYPERSCINT scintillation dosimetry research platform in a MR-linac environment.

Benjamin Cote, Bas Raaymakers, Simon Woodings, Prescilla Uijtewaal, Wilfred de Vries, Simon Lambert-Girard, François Therriault-Proulx, Martin Fast
Medscint, UMC Utrecht

Purpose: The purpose of this work was to characterize the Hyperscint scintillation dosimetry research platform in a MR-linac environment, particularly with respect to its orientation. 

Methods: The detector, composed of a single point 1 X 1 mm2 plastic scintillator, was tested in a 7 MV photon beam at a 1.5 T Elekta Unity MR-linac. This work presents its characterization in terms of repeatability, dose linearity, dose rate dependency and orientation dependency of the output factors (3x3 cm² to 20x20 cm²) for five perpendicular and parallel orientations compared to the magnetic and radiation fields. 

Results: The repeatability (0.06%), dose linearity (R² > 0.999), and dose rate dependency (0.3%) were found to be excellent. Orientation dependence on the output factors was shown to be smaller than ±1 % over all orientations. These levels of performance are supported by the stem effect removal technique accounting for different physical mechanisms independently (scintillation, Cerenkov, fluorescence, optical fiber attenuation).

Conclusion: Unlike other detectors, this study shows that the HYPERSCINT scintillation dosimetry platform can be used regardless of its orientation in a magnetic field environment. Together with its linearity to dose and dose-rate, the detector shows great promises for development of dosimetry solutions dedicated to the MR-Linac environment.


Scientific Session Highlights – Presentation 9

Development of an Open Source Cardiac Phantom Capable of Coupled Cardiac and Respiratory Motion

Ishaan Kohli, Don Ta, Justin Poon, Steven Thomas
BC Cancer Agency

Purpose: Assessing treatment fidelity becomes increasingly difficult for technologies addressing conditions such as ventricular tachycardia or cancers near the heart, as cardiac motion negatively affects the accuracy of radiosurgery. Most current commercial phantoms do not couple cardiac and respiratory motion simultaneously. We present an open-source, cost-effective method to build a development and evaluation platform for respiratory/cardiac motion management technologies.

Methods: Since many institutions already have access to the QUASAR respiratory phantom, we designed an add-on module for this device to add cardiac motion functionality, which can be 3D printed and assembled in-house. This module can drive a 3D printed insert containing gafchromic film and a fiducial marker according to a user specified motion trajectory in the mediolateral and ventral-dorsal axis using a linear actuator.  The module was filled with silicone for water equivalency. The module motion was assessed using a LIDAR sensor.

Results: The device is capable of generating user defined cardiac motion that could be adjusted for amplitudes between 1 and 14 mm at 20 to 120 beats per minute. The device was able to replicate the cardiac motion profile to sub millimeter accuracy up to 120 bpm. The module was measured to be between 155 and 163 HU.

Conclusion: The phantom successfully replicates cardiac motion, however further testing is required for cardiac motions above 120 bpm. By making this device open-source, we hope to accelerate timelines for development and adoption of novel cardiac-related technologies around the world, and make it easier to assess treatment fidelity.