Development of a defacing algorithm to protect the privacy of head and neck cancer patients in publicly-accessible radiotherapy datasets

Kayla O'Sullivan-Steben; Luc Galarneau; John Kildea

doi:10.1002/mp.70160

Home/Archive/arXiv

arXiv · 2508.13914

Development of a defacing algorithm to protect the privacy of head and neck cancer patients in publicly-accessible radiotherapy datasets

Kayla O'Sullivan-Steben·Luc Galarneau·John Kildea

View original source ↗Read source document ↗Export metadata ↓

Abstract

Introduction: The rise in public medical imaging datasets has raised concerns about patient reidentification from head CT scans. However, existing defacing algorithms often remove or distort Organs at Risk (OARs) and Planning Target Volumes (PTVs) in head and neck cancer (HNC) patients, and ignore DICOM-RT Structure Set and Dose data. Therefore, we developed and validated a novel automated defacing algorithm that preserves these critical structures while removing identifiable features from HNC CTs and DICOM-RT data. Methods: Eye contours were used as landmarks to automate the removal of CT pixels above the inferior-most eye slice and anterior to the eye midpoint. Pixels within PTVs were retained if they intersected with the removed region. The body contour and dose map were reshaped to reflect the defaced image. We validated our approach on 829 HNC CTs from 622 patients. Privacy protection was evaluated by applying the FaceNet512 facial recognition algorithm before and after defacing on 3D-rendered CT pairs from 70 patients. Research utility was assessed by examining the impact of defacing on autocontouring performance using LimbusAI and analyzing PTV locations relative to the defaced regions. Results: Before defacing, FaceNet512 matched 97% of patients' CTs. After defacing, this rate dropped to 4%. LimbusAI effectively autocontoured organs in the defaced CTs, with perfect Dice scores of 1 for OARs below the defaced region, and excellent scores exceeding 0.95 for OARs on the same slices as the crop. We found that 86% of PTVs were entirely below the cropped region, 9.1% were on the same slice as the crop without overlap, and only 4.9% extended into the cropped area. Conclusions: We developed a novel defacing algorithm that anonymizes HNC CT scans and related DICOM-RT data while preserving essential structures, enabling the sharing of HNC imaging datasets for Big Data and AI.

Explore related subjects

physics.med-ph

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Kayla O'Sullivan-Steben, Luc Galarneau, John Kildea. 2025-08-19. Development of a defacing algorithm to protect the privacy of head and neck cancer patients in publicly-accessible radiotherapy datasets. https://doi.org/10.1002/mp.70160

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Fingertip Micro-Motion as a Source of Respiratory Information During Sleep Using Triaxial Accelerometers

Objective: Triaxial accelerometers (TAAs) are widely used in home care medicine. This study investigates whether TAA signals recorded at the fingertip encode respiratory information, particularly instantaneous respiratory rate (IRR) and respiratory effort, during sleep. Method: We propose an antiderivative-based nonlinear transformation to convert TAA signals into a respiratory surrogate, termed TAA-resp. To quantify the embedded respiration-induced oscillation, a modern time-frequency analysis tool is applied to derive an index, referred to as the {\em respiratory motion index} (RMI). The proposed TAA-resp and RMI are validated on two datasets comprising 39 Asians and 10 white or African Americans with full-night recordings from simultaneous polysomnography (PSG) and a fingertip TAA measurement. Criteria for labeling TAA-resp signal quality as good, moderate, or poor are established, and two experts' independent annotations with consensus are obtained. Result: On average, TAA-resp encodes high-quality respiratory information in over 21.25%$\pm$16.11% of full-night recordings, reaching up to 58.33% in some cases. TAA-resp shows stronger correlation with thoracic and abdominal motion than with airflow, indicating predominant capture of respiratory effort. High-quality TAA-resp segments offer an accurate IRR estimate with root mean square error $0.027\pm 0.022$ Hz. RMI is higher for high-quality segments and lower for poor-quality segments, and its distribution aligns with physiology, with higher values during REM, N2, and N3 sleep and in the absence of apnea or hypopnea events. In leave-one-subject-out cross-validation, RMI predicts quality labels with 0.84 sensitivity and 0.88 specificity. Conclusion: Fingertip-mounted TAAs encode meaningful respiratory information intermittently, and our method recycles underutilized respiratory information.

physics.med-ph↗

arXiv2026

Characterization and Mitigation of Boundary Sampling Artifacts in Electron Phase Space Generation for Clinical FLASH-RT Deployment

Applicator-specific phase space (PHSP) files recorded at the aperture exit reduce Monte Carlo dose calculation time by 30-50% for electron FLASH radiotherapy. However, positioning PHSP scoring planes coincident with the applicator-air interface introduces boundary sampling artifacts. This study characterizes these artifacts in Geant4-based simulations and demonstrates their mitigation. PHSP files were generated using GAMOS 6.2.0 for a 9 MeV Mobetron UHDR model across twelve clinical aperture configurations (2.5-10 cm diameter). Three scoring plane positions were evaluated relative to the physical aperture exit: coincident with the interface, 0.1 mm downstream, and 1 mm downstream. Scoring at the exact interface produced proximal R50 shifts of up to 2.2 mm and Distance-to-Agreement (DTA) values of 4-6 mm, exceeding clinical acceptance criteria. Artifact severity scaled inversely with aperture diameter, with the smallest configurations most severely affected. A 0.1 mm offset partially restored the primary electron energy spectrum but failed to recover the bremsstrahlung tail. A 1 mm offset fully resolved all artifacts, achieving mean DTA values within 2.0 mm, equivalent to or better than linac-exit references. These artifacts arise from the degenerate behavior of the fUseSafety step-limitation algorithm when safety equals zero at exact material boundaries, producing incomplete secondary electron equilibration and suppressed bremsstrahlung production. Angular distribution analysis revealed a near-forward particle pileup in the 0 mm PHSP and a deficit of large-angle secondaries recovered by the 1 mm offset. A 1 mm downstream offset fully mitigates these artifacts while introducing negligible perturbation to primary beam characteristics. This requirement applies to any Geant4-based framework (including TOPAS and GATE) scoring PHSP files at material exit surfaces.

physics.med-ph↗

arXiv2026

Melanin- and linewidth-corrected pulse-oximetry

Current pulse oximeters tend to overestimate arterial saturation in darkly pigmented patients, increasing occult hypoxemia rates. One proposed mechanism is spectral coloring: melanin contributes to reshaping the detected spectrum of a broad-linewidth source, making the wavelength-dependent parameters behind calibration skin-tone-dependent. Diffuse optics theory allows for a melanin- and linewidth-corrected calibration equation, which to our knowledge has never been tested in vivo. In this work, we fit the empirical linear equation, the diffuse optics theoretical equation, and its corrected form to the public OpenOximetry Repository---considering 98 patients with paired arterial blood-draws, raw photoplethysmograms, and skin reflectance spectra. Accuracy is practically indistinguishable between the three approaches, yet the saturation error's dependence on melanin falls from +2.8 to +1.2 to +0.1 percentage points per unit melanin volume fraction---consistent with the spectral-coloring theory. None of these dependencies on melanin are statistically resolved here---a cohort roughly ten times larger is needed---so the correction is backed by theory and its expected direction. All three calibration approaches carry two degrees of freedom: the theoretical equation drops into existing calibration procedures, and its melanin-aware form needs a per-patient skin-tone measurement. This work demonstrates how the theoretical pulse oximetry model can be applied in calibration.

physics.med-ph↗