Purpose: Motion management plays a critical role in stereotactic radiosurgery (SRS). In our SRS program, patients are aligned to treatment position using cone beam computed tomography (CBCT) imaging. This is repeated between each treatment field, leading to prolonged treatment times. Identify (Varian Medical Systems, Palo Alto) is a surface imaging guidance system. We evaluated the integration of Identify into our SRS workflow to enhance treatment delivery efficiency.

 

Methods: Identify- and CBCT-reported shifts were recorded for 14 SRS patients. A total of 27 treatment fields were included. The differences between the Identify- and CBCT-reported translational and rotational shifts were calculated for each treatment field, including intra-fraction and post-fraction imaging.

 

Results: The mean and standard deviations of the differences are: lateral = 0.1 ± 0.3 mm, longitudinal = 0.1 ± 0.3 mm, vertical = 0.0 ± 0.3 mm, rotation = 0.1 ± 0.2°, pitch = 0.0 ± 0.3°, and roll = 0.0 ± 0.2°. We require an additional CBCT if any discrepancy between the planning CT and CBCT exceeds 0.5 mm or 0.5°. The time spent on re-imaging can range from 15 to 25 minutes per treatment. The strong agreement between Identify and CBCT-reported shifts supports the feasibility of eliminating CBCT scans between treatment arcs.

 

Conclusions: Identify-based surface guidance measurements in SRS treatments align closely with CBCT-based positioning. This enables a reduction in the number of CBCT images during an SRS treatment, benefiting SRS patients through a reduction in imaging dose and faster treatment times.

Purpose: To enhance tumour perfusion in pancreatic cancer patients using neoadjuvant stereotactic ablative body radiotherapy (SABR) and monitor treatment response via computed tomography perfusion (CTP).

 

Methods: Patients with resectable (n=1) or borderline resectable (n=5) pancreatic cancer were treated with neoadjuvant SABR (27-30 Gy/3fx). CTP scans were acquired at baseline; 6 hrs after administering the first fraction of neoadjuvant SABR; and 3-4 weeks after completing SABR. For the borderline resectable patients, CTP scans were also taken post-chemotherapy prior to SABR. A deconvolution-based CTP software (GE HealthCare, Waukesha, USA) was used to calculate the tumour blood flow (BF), blood volume (BV), and permeability-surface area product (PS). The total contrast distribution volume (VD), extravascular volume (Ve), and intravascular volume (Vi) were also calculated (VD=Ve+Vi). A surrogate measure of tumour cell density (CD) was derived from the Ve.

 

Results: In all patients, tumour blood flow (BF) measured 6 hours after the first fraction (post-1st-fx) was significantly higher than baseline (median BF: baseline = 38.7 mL/min/100g, post-1st-fx = 71.6 mL/min/100g; p = 0.0312). However, tumour blood volume (BV) and permeability-surface area product (PS) did not exhibit statistically significant changes. Additionally, the total distribution volume (VD) and extravascular volume (Ve) increased by 3-4 weeks post-SABR compared to baseline. Conversely, cell density (CD) showed a progressive decline throughout treatment.

 

Conclusions: Neoadjuvant SABR could improve pancreatic tumour perfusion to potentially enhance the systemic delivery and biodistribution of systemic anticancer drugs. Additionally, CD may be a prominent biomarker that could help monitor patient response to standard-of-care therapy.

Purpose: Non-ionizing electrotherapy has been gaining traction as a potential treatment strategy for brain cancer. Intratumoral Modulation Therapy (IMT) is a sustained electrotherapy technique where low-intensity electric fields are applied to tumor regions through implanted electrodes. IMT application in-vitro leads to mild hyperthermia due the electrical properties of culture media and lack bioheat transfer present in the living brain. In this study we aim to isolate the effects from electric fields and hyperthermia on Glioblastoma cell survival in-vitro.

 

Methods: Patient-derived Glioblastoma cells transfected with Luciferase were used in this study to enable bioluminescence imaging (BLI) for cell viability quantification after 3-day treatment. Three scenarios were addressed: standard IMT (electric field + hyperthermia) at 1V/cm and 1.5V/cm, temperature adjusted IMT (electric field only) at 1V/cm and 1.5V/cm, and hyperthermia only at 39°C and 41°C.

Results: Standard 1V/cm and 1.5V/cm IMT reduced cell viability to 26±6% (n=12) and 7±3% (n=7) respectively, relative to sham conditions. Field only conditions reduced viability to 59±13% (n=4) and 46±4% (n=4) respectively for 1V/cm and 1.5V/cm. Hyperthermia only reduced viability to 41±6% (n=6) at 39°C and 12±2% at 41°C. IMT cell survival data followed the radiobiologic linear-quadratic model, with a linear electric field component, and a quadratic hyperthermic component.

 

Conclusions: We have shown the linear-quadratic model of cell survival can be applied to non-ionizing IMT, with linear and quadratic contributions from electric field and hyperthermia respectively. This IMT dose response model needs to be further tested with different cell lines to confirm its generality.

Intro: While maintaining full radiation medicine operations at an original location, a new comprehensive cancer centre was opened in October 2024. The new centre was a multi-year project that included installation of 10 linear accelerators (eight new, two transferred after opening), two MR-Linacs, two CT-Simulators (one a CT/PET), orthovoltage, and two MRI-sim - one uniquely integrated into a dual OR/afterloader brachytherapy suite.

Methods: Preparation for the transition included comprehensive commissioning, documentation, staff training and clinical development to ensure safety, quality and continuity in care. Minimal two-site operation (eight clinical workdays) was used to facilitate the clinical move.

Discussion: At the time of opening, all treatments available at the original location were fully operational. However, project delays, human health resource (HHR) limitations and logistical issues presented obstacles that required a high level of adaptability in project planning, management and staff response. Over fifty changes contemporaneous with the transition were cataloged that impacted the department and clinical operations, ranging from new equipment to clinical programs. Observations and staff feedback indicate change fatigue has impacted staff well-being and engagement due to these societal, organizational and project change stressors.

Conclusion: The initial transition was a success. The team has demonstrated remarkable resilience and adaptability in navigating shifting timelines and HHR challenges. However, we need to incorporate better data about change fatigue and staff burnout into future planning to ensure the success of the continued technology implementation and clinical development that is planned over the next couple of years.

Purpose: The dose rate of incident radiation could significantly affect gold nanoparticle (GNP)-induced radiosensitization. The purpose of this research is to compare GNP-induced radiosensitization between high-dose-rate brachytherapy (HDR-BT) and high-energy, external beam radiotherapy at variable dose rates.

Methods: HEC-1A cervical cancer cells were treated at a clinically translatable concentration of 10μg/mL with 11nm GNPs 24hrs before irradiation from either a 192-Ir HDR-BT source or a 6MV beam from a medical linear accelerator (LINAC). Radiosensitization was measured at two dose rates of 1.1 and 0.55Gy/min. Cellular survival post-irradiation was measured using clonogenic and DNA double-strand break (DSB) assays.

Results: Higher dose rates induced greater radiosensitization and loss in cellular viability at the same delivered dose compared to lower dose rates. GNP-induced dose enhancement increased from 1.19 to 1.37 and from 1.1 to 1.24 with higher dose rates from HDR-BT and LINAC irradiations, respectively. DNA damage was not significantly increased in GNP-treated cells at 0.55 Gy/min, but was at 1.1Gy/min by 34% (p < 0.01) and 26% (p < 0.05) for HDR-BT and LINAC irradiations, respectively.

Conclusion: We successfully demonstrated the first in vitro observation of a dose-rate dependency on GNP-induced radiosensitization from variable dose rates achieved from both high and low-energy irradiations. The results demand further investigation into incorporating GNPs into RT treatments where the dose rate varies significantly.

Purpose: This study sought to gather and analyse the latest information about CAMPEP-accredited graduate (MSc, PhD, Certificate) programs in Canada, to inform the discussion around planning for the future needs of the medical physics workforce. In particular, the study investigated the distribution of programs and faculty, and registration (matriculation) and graduation numbers, since 2019.

Methods: Data for this study were collected through two surveys. First, a survey was conducted with an online platform, circulated among directors of graduate and residency programs at Canadian universities. Second, the most recent data about program attendance were gathered from graduate program webpages for the years 2019–2024.

Results: There are currently 15 CAMPEP-accredited programs in Canada, of which 12 answered the survey. All 15 programs offer the PhD, while 12 offer the MSc, and six the certificate. The distribution of faculty in programs varies both in terms of total numbers (range 4–27), job category (e.g. university- vs. hospital-employes), and full-time equivalent (FTE) faculty. The survey of student numbers revealed a peak in new registrations in 2021, and increasing numbers of graduates until 2023. The number of students varies between programs and is strongly dependent on faculty FTE.

Conclusions: This study gathered data on graduate education in medical physics in Canada over the past 6 years. FTE effort appears to be split evenly between academic faculty and clinical physicists. New registrations in graduate programs appeared to reach a peak in 2021, while graduate numbers appear to increase until 2023.

Purpose: Total body irradiation requires the entirety of the patient's body to be irradiated, and treatment methods vary greatly across treatment centres. For many of these techniques, little is known about the heterogeneity of dose delivered to the circulating blood. To enable investigation of the dose to blood, a full body blood flow simulation, including explicit modelling of major vessels, has been created.

Methods: By combining one-dimensional flow modelling in vessels and zero-dimensional compartments, based on human body reference values, a complete closed network was produced. The model is composed of 94 vessel segments and 28 compartments. It simulates 10E5 blood volumes (BVs) which are tracked with a time resolution of 2 ms. Some of the modelled vessels feed regions of dispersed tissue that are not part of the reference human body. Time spent within the compartments needed to be tuned to ensure the distribution of BVs across the model is physiologically realistic. The maximum change in distribution was used to determine how many periods are required for the system to arrive at a steady state.

Results: After tuning the model to achieve a match with the reference values, it was determined that after 100 periods the mean change in blood volume distribution percentages varies by <0.5 %.
Conclusions: With the model verified and quantified, it is now ready to be combined with dose deposition data to calculate dose heterogeneity within the circulating blood volume for a range of TBI techniques.

Purpose: Culturing cancer cells in 3D tumor spheroids influences radiation response and provides a more physiologically relevant model of patient tumors compared to conventional 2D monolayer culture. Volumetric imaging of spheroids with dynamic optical coherence tomography (dOCT) may contribute spatial information and complement alternative methods like proliferation assay to clonogenic assay, the gold standard method for measuring radiation survival. Clonogenic assay requires spheroids to be disaggregated and plated in 2D for longitudinal observation of colony formation, but the geometry of cell culture following treatment also influences radiation response. Thus, motivation to replace clonogenic assay measurement with an alternative is particularly salient with respect to spheroid investigation.

Methods: Prostate tumor spheroids were irradiated and 24 hours later evaluated for: clonogenic survival by clonogenic assay; average cellular proliferation by Alamar Blue (AB) proliferation assay; live and dead cell visualization by fluorescence microscopy (FM); and sub-cellular dynamic motion by volumetric dOCT imaging.

Results: Radiation effect measured by dOCT demonstrated excellent quantitative and qualitative agreement with AB proliferation assay and FM respectively. Measurement of radiation survival by dOCT and AB was significantly higher than measurement by clonogenic assay, likely by quantifying cellular activity related to post-treatment radiation repair. In contrast, clonogenic assay captured delayed reproductive death induced by radiation through longitudinal observation.

Conclusions: The acquisition of multiple dOCT measurements in the week after treatment to quantify delayed radiation effects could potentially complement clonogenic assay by eliminating the need for spheroid disaggregation and uniquely retaining the spatial effect of radiation throughout the heterogenous spheroid.

Purpose: This study evaluates early and late gastrointestinal (GI) toxicity following prostate stereotactic ablative body radiotherapy (SABR) delivered at prescription doses of 36.25 Gy and 40 Gy.

Methods: Patients from a prospective, province-wide SABR registry who completed both 6-8 week (n = 378) and 1-year (n = 317) follow-up were analyzed. Univariate analysis was conducted using Fisher’s exact tests and student’s t-tests to compare patient features and GI toxicity. Factors evaluated included dose metrics, age, staging, Gleason score, prescription dose (with/without nodal coverage), use of rectal spacer gel, and more.

Results: Incidence of physician-graded RTOG/SOMA GI toxicity grade 2+ was low at both 6–8 weeks (1.1%) and 1 year (1.8%). In the non-spacer cohort, the mean (median) rectal V36 Gy was 1.02 cc (0.89 cc) compared to 0.27 cc (0.09 cc) for the spacer group. For rectum V18 Gy, the rectal spacer group achieved a mean (median) of 17.5% (12.5%) versus 30.4% (35.8%) for the non-spacer group. Differences in rectum V36 Gy and V18 Gy were significant (p ≪ 0.05). The rectal spacer group also achieved lower grade 1+ GI toxicity after one year (odds ratio = 2.2, p = 0.07). Notably, only one patient with rectal spacer experienced grade 2 GI toxicity after one year.

Conclusions: Prostate SABR at 40 Gy and below yields very low GI toxicity. Future work will involve multivariate analysis and longer-term follow-up to further elucidate toxicity predictors.