Piotr Dubrowski is a Canadian trained and board-certified Therapy Medical Physicist. Throughout his career Piotr has had the opportunity to bring several new Cancer Clinics operational from the ground up, where he was able to hone a broad, systems-approach to Radiation Oncology. He was recently promoted to Associate Quality Director of Physics responsible for improving patient safety and workflow/technology improvements across a wide cancer care network. Piotr’s research interests focus mainly on improving the treatment planning process and increasing clinic safety through software development and hardware 3D-print prototyping. Additionally, Piotr has sought out opportunities to give back to the Global community with participation in the Stanford Global Radiation Oncology Outreach efforts expanding education and access to care in Tanzania and Kenya and throughout the developing world via online Radiation Therapy courses.

Academic Appointments

2023-24 Courses

All Publications

  • Chest wall pain after single-fraction thoracic stereotactic ablative Radiotherapy: Dosimetric analysis from the iSABR trial. Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology Lau, B., Wu, Y. F., Cui, S., Fu, J., Jackson, S., Pham, D., Dubrowski, P., Eswarappa, S., Skinner, L., Shirato, H., Taguchi, H., Gensheimer, M. F., Gee, H., Chin, A. L., Diehn, M., Loo, B. W., Moiseenko, V., Vitzthum, L. K. 2024: 110317


    Concerns over chest wall toxicity has led to debates on treating tumors adjacent to the chest wall with single-fraction stereotactic ablative radiotherapy (SABR). We performed a secondary analysis of patients treated on the prospective iSABR trial to determine the incidence and grade of chest wall pain and modeled dose-response to guide radiation planning and estimate risk.This analysis included 99 tumors in 92 patients that were treated with 25 Gy in one fraction on the iSABR trial which individualized dose by tumor size and location. Toxicity events were prospectively collected and graded based on the CTCAE version 4. Dose-response modeling was performed using a logistic model with maximum likelihood method utilized for parameter fitting.There were 22 grade 1 or higher chest wall pain events, including five grade 2 events and zero grade 3 or higher events. The volume receiving at least 11 Gy (V11Gy) and the minimum dose to the hottest 2 cc (D2cc) were most highly correlated with toxicity. When dichotomized by an estimated incidence of ≥ 20 % toxicity, the D2cc > 17 Gy (36.6 % vs. 3.7 %, p < 0.01) and V11Gy > 28 cc (40.0 % vs. 8.1 %, p < 0.01) constraints were predictive of chest wall pain, including among a subset of patients with tumors abutting or adjacent to the chest wall.For small, peripheral tumors, single-fraction SABR is associated with modest rates of low-grade chest wall pain. Proximity to the chest wall may not contraindicate single fractionation when using highly conformal, image-guided techniques with sharp dose gradients.

    View details for DOI 10.1016/j.radonc.2024.110317

    View details for PubMedID 38679202

  • A clinical solution for non-toxic 3D-printed photon blocks in external beam radiation therapy. Journal of applied clinical medical physics Schulz, J. B., Dubrowski, P., Gibson, C., Yu, A. S., Skinner, L. B. 2024: e14225


    A well-known limitation of multi-leaf collimators is that they cannot easily form island blocks. This can be important in mantle region therapy. Cerrobend photon blocks, currently used for supplementary shielding, are labor-intensive and error-prone. To address this, an innovative, non-toxic, automatically manufactured photon block using 3D-printing technology is proposed, offering a patient-specific and accurate alternative.The study investigates the development of patient-specific photon shielding blocks using 3D-printing for three different patient cases. A 3D-printed photon block shell filled with tungsten ball bearings (BBs) was designed to have similar dosimetric properties to Cerrobend standards. The generation of the blocks was automated using the Eclipse Scripting API and Python. Quality assurance was performed by comparing the expected and actual weight of the tungsten BBs used for shielding. Dosimetric and field geometry comparisons were conducted between 3D-printed and Cerrobend blocks, utilizing ionization chambers, imaging, and field geometry analysis.The quality assurance assessment revealed a -1.3% average difference in the mass of tungsten ball bearings for different patients. Relative dose output measurements for three patient-specific blocks in the blocked region agreed within 2% of each other. Against the Treatment Planning System (TPS), both 3D-printed and Cerrobend blocks agreed within 2%. For each patient, 6 MV image profiles taken through the 3D-printed and Cerrobend blocks agreed within 1% outside high gradient regions. Jaccard distance analysis of the MV images against the TPS planned images, found Cerrobend blocks to have 15.7% dissimilarity to the TPS, while that of the 3D-printed blocks was 6.7%.This study validates a novel, efficient 3D-printing method for photon block creation in clinical settings. Despite potential limitations, the benefits include reduced manual labor, automated processes, and greater precision. It holds potential for widespread adoption in radiation therapy, furthering non-toxic radiation shielding.

    View details for DOI 10.1002/acm2.14225

    View details for PubMedID 38213084

  • Tungsten filled 3D printed lung blocks for total body irradiation. Practical radiation oncology Capaldi, D. P., Gibson, C., Villa, A., Schulz, J. B., Ziemer, B. P., Fu, J., Dubrowski, P., Yu, A. S., Fogh, S., Chew, J., Boreta, L., Braunstein, S. E., Witztum, A., Hirata, E., Morin, O., Skinner, L. B., Nano, T. F. 2023


    Lung blocks for total-body-irradiation (TBI) are commonly used to reduce lung dose and prevent radiation pneumonitis. Currently, molten Cerrobend containing toxic materials, specifically lead and cadmium, is poured into molds to construct blocks. Here, we propose a streamlined method to create 3D-printed lung block shells and fill them with tungsten ball-bearings (BBs) to remove lead and improve overall accuracy in the block manufacturing workflow.3D-printed lung block shells were automatically generated using an inhouse software, printed, and filled with 2-3mm diameter tungsten BBs. Clinical Cerrobend blocks were compared to the physician drawn blocks as well as our proposed tungsten filled 3D-printed blocks. Physical and dosimetric comparisons were performed on a linac. Dose transmission through the Cerrobend and 3D-printed blocks were measured using point dosimetry (ion-chamber) and the on-board Electronic-Portal-Imaging-Device (EPID). Dose profiles from the EPID images were used to compute the full-width-half-maximum (FWHM) and to compare with the treatment-planning-system (TPS). Additionally, the coefficient-of-variation (CoV) in the central 80% of FWHM was computed and compared between Cerrobend and 3D-printed blocks.The geometric difference between TPS and 3D-printed blocks was significantly lower than Cerrobend blocks (3D: -0.88±2.21mm, Cerrobend: -2.28±2.40mm, p=0.0002). Dosimetrically, transmission measurements through the 3D-printed and Cerrobend blocks for both ion-chamber and EPID dosimetry were between 42-48%, as compared to the open field. Additionally, CoV was significantly higher in 3D-printed blocks versus Cerrobend blocks (3D: 4.2±0.6%, Cerrobend: 2.6±0.7%, p<0.0001).We designed and implemented a tungsten filled 3D-printed workflow for constructing TBI lung blocks, which serves as an alternative to the traditional Cerrobend based workflow currently used in clinics. This workflow has the capacity of producing clinically useful lung blocks with minimal effort in an attempt to facilitate the removal of toxic materials from the clinic.

    View details for DOI 10.1016/j.prro.2023.11.003

    View details for PubMedID 37981253

  • Shaping success: clinical implementation of a 3D-printed electron cutout program in external beam radiation therapy. Frontiers in oncology Schulz, J. B., Gibson, C., Dubrowski, P., Marquez, C. M., Million, L., Qian, Y., Skinner, L., Yu, A. S. 2023; 13: 1237037


    The integration of 3D-printing technology into radiation therapy (RT) has allowed for a novel method to develop personalized electron field-shaping blocks with improved accuracy. By obviating the need for handling highly toxic Cerrobend molds, the clinical workflow is significantly streamlined. This study aims to expound upon the clinical workflow of 3D-printed electron cutouts in RT and furnish one year of in-vivo dosimetry data.3D-printed electron cutouts for 6x6 cm, 10x10 cm, and 15x15 cm electron applicators were designed and implemented into the clinical workflow after dosimetric commissioning to ensure congruence with the Cerrobend cutouts. The clinical workflow consisted of four parts: i) the cutout aperture was extracted from the treatment planning system (TPS). A 3D printable cutout was then generated automatically through custom scripts; ii) the cutout was 3D-printed with PLA filament, filled with tungsten ball bearings, and underwent quality assurance (QA) to verify density and dosimetry; iii) in-vivo dosimetry was performed with optically stimulated luminescence dosimeters (OSLDs) for a patient's first treatment and compared to the calculated dose in the TPS; iv) after treatment completion, the 3D-printed cutout was recycled.QA and in-vivo OSLD measurements were conducted (n=40). The electron cutouts produced were 6x6 cm (n=3), 10x10 cm (n=30), and 15x15 cm (n=7). The expected weight of the cutouts differed from the measured weight by 0.4 + 1.1%. The skin dose measured with the OSLDs was compared to the skin dose in the TPS on the central axis. The difference between the measured and TPS doses was 4.0 + 5.2%.The successful clinical implementation of 3D-printed cutouts reduced labor, costs, and removed the use of toxic materials in the workplace while meeting clinical dosimetric standards.

    View details for DOI 10.3389/fonc.2023.1237037

    View details for PubMedID 37621682

    View details for PubMedCentralID PMC10445153

  • An affordable platform for virtual reality-based patient education in radiation therapy. Practical radiation oncology Schulz, J. B., Dubrowski, P., Blomain, E., Million, L., Qian, Y., Marquez, C., Yu, A. S. 2023


    The goal of this study is to develop and assess the effectiveness of an affordable smartphone-based Virtual Reality (VR) patient education platform with 360-degree videos produced depicting a first-person patient perspective during the radiation therapy (RT) care path to reduce patient anxiety.and Materials Three disease site-specific (breast, pelvis, head and neck) VR-videos were filmed using a 360-degree camera to portray the first-person perspective of a patient's standard RT appointments: including a Computed Tomography (CT) simulation and the first RT treatment session. Instruction is given for possible clinical implementation. Patient participation was divided into two groups: 1) Group-A (n=28) included patients participating before simulation and later after the first treatment, and 2) Group-B (n=33) included patients participating only while undergoing treatment. Patients viewed their disease site-specific video using an inexpensive cardboard VR-viewer and their smartphone, emulating an expensive VR-headset. Surveys were administered assessing patient anxiety, comfort, satisfaction, and knowledge of RT on a 5-point Likert-type scale.Patients in Group-A and Group-B while undergoing treatment both selected their anxiety "decreased a little" in the survey, after watching the VR-video (Group-A, median on a 5-point Likert-type scale, 4 [interquartile range {IQR}, 4-5]; Group-B, 4 [IQR 4-4]). The VR aspect of the videos was especially liked by patients while undergoing treatment, with 96.4% in Group-A and 90.9% in Group-B reporting that the VR aspect of the videos was helpful. All Group-A participants believed that the VR-videos would be beneficial to new patients.Our affordable VR patient education platform effectively immerses a patient in their care path from simulation through initial treatment delivery, reducing anxiety and increasing familiarity with the treatment process.

    View details for DOI 10.1016/j.prro.2023.06.008

    View details for PubMedID 37482182

  • Learning image representations for content-based image retrieval of radiotherapy treatment plans. Physics in medicine and biology Huang, C., Vasudevan, V., Pastor-Serrano, O., Islam, M. T., Nomura, Y., Dubrowski, P., Wang, J. Y., Schulz, J. B., Yang, Y., Xing, L. 2023


    In this work, we propose a content-based image retrieval (CBIR) method for retrieving dose distributions of previously planned patients based on anatomical similarity. Retrieved dose distributions from this method can be incorporated into automated treatment planning workflows in order to streamline the iterative planning process. As CBIR has not yet been applied to treatment planning, our work seeks to understand which current machine learning models are most viable in this context.Our proposed CBIR method trains a representation model that produces latent space embeddings of a patient's anatomical information. The latent space embeddings of new patients are then compared against those of previous patients in a database for image retrieval of dose distributions. All source code for this project is available on github.The retrieval performance of various CBIR methods is evaluated on a dataset consisting of both publicly available image sets and clinical image sets from our institution. This study compares various encoding methods, ranging from simple autoencoders to more recent Siamese networks like SimSiam, and the best performance was observed for the multitask Siamese network.Our current results demonstrate that excellent image retrieval performance can be obtained through slight changes to previously developed Siamese networks. We hope to integrate CBIR into automated planning workflow in future works.

    View details for DOI 10.1088/1361-6560/accdb0

    View details for PubMedID 37068492

  • Pancreatic Stereotactic Body Radiation Therapy with or without Hypofractionated Elective Nodal Irradiation. International journal of radiation oncology, biology, physics Miller, J. A., Toesca, D. A., Baclay, J. R., Vitzthum, L. K., Dubrowski, P., Pollom, E. L., Chang, D. T. 2021


    PURPOSE/OBJECTIVES: Pancreatic stereotactic body radiation therapy (SBRT) is limited to gross tumor without elective coverage for subclinical disease. Given a better understanding of recurrence patterns, we hypothesized that the addition of elective nodal irradiation (ENI) to pancreatic SBRT would be tolerable and would decrease locoregional progression.MATERIALS/METHODS: We conducted a retrospective 1:2 propensity-matched cohort study to compare toxicity and locoregional progression among patients treated with pancreatic SBRT with or without ENI. In the SBRT+ENI cohort, an elective target volume was delineated per RTOG guidelines and treated to 25 Gy in 5 fractions alongside 40 Gy in 5 fractions to gross disease. The primary outcome was the cumulative incidence of locoregional progression, with death as a competing risk.RESULTS: Among 135 candidate controls treated with SBRT alone, 100 were propensity-matched to 50 patients treated with SBRT+ENI. All patients completed SBRT. Median potential radiographic follow-up was 28 months. The incidence of late and serious acute toxicity were similar between matched cohorts. However, SBRT+ENI was associated with a statistically significant increase in acute grade 1-2 nausea (60% vs. 20%, p<0.001). The 24-month cumulative incidences of locoregional progression with and without ENI were 22.6% (95% confidence interval [CI]: 10.0-35.1%) vs. 44.6% (95% CI: 34.8-54.4%, multivariable-adjusted hazard ratio 0.39, 95% CI 0.18-0.87, p=0.021). This was stable in sensitivity analyses of uniform prescription dose, multiagent chemotherapy, and resectability. There were fewer peripancreatic (0% vs. 7%), porta hepatis (2% vs. 7%), and peri-aortic/aortocaval (5% vs. 12%) recurrences after SBRT+ENI, but no difference in survival.CONCLUSIONS: Pancreatic SBRT+ENI was tolerable and did not increase late or serious acute toxicity relative to a matched cohort undergoing SBRT alone, but did increase acute grade 1-2 nausea. The addition of ENI to SBRT was associated with decreased locoregional progression but not improved survival. Further studies are warranted to determine if ENI offers meaningful benefit.

    View details for DOI 10.1016/j.ijrobp.2021.07.1698

    View details for PubMedID 34348171

  • A Longitudinal Telehealth Curriculum for Radiation Oncology Centers in Low and Middle-Income Countries Transitioning from 2D to 3D External Beam Radiation Therapy Yang, F., Carter, R., Ahmed, S., Plautz, T., Dubrowski, P., Wadi-Ramahi, S., Ashmeg, S., Ascoli, F., Wakefield, D., Adamson, J., Li, B. AMER ASSOC CANCER RESEARCH. 2021
  • CT-less electron radiotherapy simulation and planning with a consumer 3D camera. Journal of applied clinical medical physics Skinner, L., Knopp, R., Wang, Y., Dubrowski, P., Bush, K. K., Limmer, A., Trakul, N., Million, L., Marquez, C. M., Yu, A. S. 2021


    PURPOSE: Electron radiation therapy dose distributions are affected by irregular body surface contours. This study investigates the feasibility of three-dimensional (3D) cameras to substitute for the treatment planning computerized tomography (CT) scan by capturing the body surfaces to be treated for accurate electron beam dosimetry.METHODS: Dosimetry was compared for six electron beam treatments to the nose, toe, eye, and scalp using full CT scan, CT scan with Hounsfield Unit (HU) overridden to water (mimic 3D camera cases), and flat-phantom techniques. Radiation dose was prescribed to a depth on the central axis per physician's order, and the monitor units (MUs) were calculated. The 3D camera spatial accuracy was evaluated by comparing the 3D surface of a head phantom captured by a 3D camera and that generated with the CT scan in the treatment planning system. A clinical case is presented, and MUs were calculated using the 3D camera body contour with HU overridden to water.RESULTS: Across six cases the average change in MUs between the full CT and the 3Dwater (CT scan with HU overridden to water) calculations was 1.3% with a standard deviation of 1.0%. The corresponding hotspots had a mean difference of 0.4% and a standard deviation of 1.9%. The 3D camera captured surface of a head phantom was found to have a 0.59mm standard deviation from the surface derived from the CT scan. In-vivo dose measurements (213±8cGy) agreed with the 3D-camera planned dose of 209±6cGy, compared to 192±6cGy for the flat-phantom calculation (same MUs).CONCLUSIONS: Electron beam dosimetry is affected by irregular body surfaces. 3D cameras can capture irregular body contours which allow accurate dosimetry of electron beam treatment as an alternative to costly CT scans with no extra exposure to radiation. Tools and workflow for clinical implementation are provided.

    View details for DOI 10.1002/acm2.13283

    View details for PubMedID 34042253

  • A robotically assisted 3D printed quality assurance lung phantom for Calypso. Physics in medicine and biology Capaldi, D. P., Skinner, L. B., Dubrowski, P. n., Zhang, H. n., Xing, L. n., Chuang, C. F., Loo, B. W., Bush, K. K., Fahimian, B. P., Yu, A. S. 2021


    Purpose:Radiation dose delivered to targets located near the upper-abdomen or in the thorax are significantly affected by respiratory-motion. Relatively large-margins are commonly added to compensate for this motion, limiting radiation-dose-escalation. Internal-surrogates of target motion, such as a radiofrequency (RF) tracking system, i.e. Calypso® System, are used to overcome this challenge and improve normal-tissue sparing. RF tracking systems consist of implanting transponders in the vicinity of the tumor to be tracked using radiofrequency-waves. Unfortunately, although the manufacture provides a universal quality-assurance (QA) phantom, QA-phantoms specifically for lung-applications are limited, warranting the development of alternative solutions to fulfil the tests mandated by AAPM's TG142. Accordingly, our objective was to design and develop a motion-phantom to evaluate Calypso for lung-applications that allows the Calypso® Beacons to move in different directions to better simulate true lung-motion.Methods and Materials:A Calypso lung QA-phantom was designed, and 3D-printed. The design consists of three independent arms where the transponders were attached. A pinpoint-chamber with a buildup-cap was also incorporated. A 4-axis robotic arm was programmed to drive the motion-phantom to mimic breathing. After acquiring a four-dimensional-computed-tomography (4DCT) scan of the motion-phantom, treatment-plans were generated and delivered on a Varian TrueBeam® with Calypso capabilities. Stationary and gated-treatment plans were generated and delivered to determine the dosimetric difference between gated and non-gated treatments. Portal cine-images were acquired to determine the temporal-accuracy of delivery by calculating the difference between the observed versus expected transponders locations with the known speed of the transponders' motion.Results:Dosimetric accuracy is better than TG142 tolerance of 2%. Temporal accuracy is greater than, TG142 tolerance of 100ms for beam-on, but less than 100ms for beam-hold.Conclusions:The robotic QA-phantom designed and developed in this study provides an independent phantom for performing Calypso lung-QA for commissioning and acceptance testing of Calypso for lung treatments.

    View details for DOI 10.1088/1361-6560/abebaa

    View details for PubMedID 33657537

  • An integrated quality assurance phantom for frameless single-isocenter multitarget stereotactic radiosurgery. Physics in medicine and biology Capaldi, D. P., Skinner, L. B., Dubrowski, P. n., Yu, A. S. 2020


    Purpose:Brain stereotactic-radiosurgery (SRS) treatments require multiple quality-assurance (QA) procedures to ensure accurate and precise treatment delivery. As single-isocenter multitarget SRS treatments become more popular, the quantification of off-axis accuracy of the linear-accelerator is crucial. In this study, a novel brain SRS integrated phantom was developed and validated to enable SRS QA with a single phantom to facilitate implementation of a frameless single-isocenter, multitarget SRS program. This phantom combines the independent verification of each positioning system, the Winston-Lutz, off-axis accuracy evaluation (i.e. off-axis Winston-Lutz), and the dosimetric accuracy utilizing both point-dose-measurements as well as film-measurement, without moving the phantom.Methods and Materials:A novel 3D-printed phantom, coinedOneIso, was designed with a movable insert which can switch between the Winston-Lutz test target and dose measurement without moving the phantom itself. For dose verification, eight brain SRS clinical-treatment-plans with 10MV Flattening-Filter-Free (FFF) beams were delivered on a Varian TrueBeam with a high-definition-multi-leaf-collimator (HD-MLC). Radiochromic film and pinpoint ion chamber comparison measurements were made between the OneIso and solid water (SW) phantom setups. For the off-axis Winston-Lutz measurements, a row of off-axis ball-bearings (BBs) was integrated into the OneIso. To quantify the spatial accuracy versus distance from isocenter, two-dimensional displacements were calculated between the planned and delivered BB locations relative to their respective MLC defined field border.Results:OneIso and the SW phantoms agree within 1%, for both film and point-dose measurements. OneIso identified a reduction in spatial accuracy further away from isocenter. Differences increased as distance from isocenter increased exceeding recommended SRS accuracy tolerances at 3-4cm away from isocenter.Conclusions:OneIso provides a streamlined, single-setup workflow for single-isocenter multitarget frameless linac-based SRS QA. Additionally, with the ability to quantify off-axis spatial-discrepancies, we can determine limitations on the maximum distance between targets to ensure a single-isocenter multitarget SRS program meets recommended guidelines.

    View details for DOI 10.1088/1361-6560/ab8534

    View details for PubMedID 32235050

  • A novel-integrated quality assurance phantom for radiographic and nonradiographic radiotherapy localization and positioning systems. Medical physics Yu, A. S., Fowler, T. L., Dubrowski, P. 2018


    PURPOSE: Various localization and positioning systems utilizing radiographic or nonradiographic methods have been developed to improve the accuracy of radiation treatment. Each quality assurance (QA) procedure requires its own phantom and is independent from each other, so the deviation between each system is unavailable. The purpose of this work is to develop and evaluate a single-integrated QA phantom for different localization and positioning systems.METHODS: The integrated phantom was designed in three-dimensional (3D) CAD software and 3D printed. The phantom was designed with laser alignment marks, a raised letter "S" on the anterior surface for optical surface monitoring system registration, a core for radiofrequency (RF) tracking system alignment, eight internal fiducials for image alignment, and an isocentric bearing for Winston-Lutz test. Tilt legs and rotational stage were designed for rotational verification of optical surface mapping system and RF tracking system, respectively. The phantom was scanned using a CT scanner and a QA plan was created. This prototype phantom was evaluated against established QA techniques.RESULTS: The QA result between the proposed procedure and established QA technique are 1.12 ± 0.31 and 1.14 ± 0.31 mm, respectively, for RF tracking system and 0.18 ± 0.06 and 0.18 ± 0.05 mm for Winston-Lutz test. There is no significant difference for the QA results between the established QA and proposed procedure (P > 0.05, t test). The accuracy of rotational verification for surface mapping system and RF tracking system are less than 0.5 and 1° compared the predefined value. The isocenter deviation of each location system is around l mm.CONCLUSION: We have designed and evaluated a novel-integrated phantom for radiographic and nonradiographic localization and positioning systems for radiotherapy. With this phantom, we will reduce the variation in measurements and simplify the QA procedures.

    View details for PubMedID 29730884