The Impact of a Cyberattack at a Radiation Oncology Department: Immediate Response and Future Preparedness.

Cyberattacks are increasing year after year and many organizations, including hospitals, are becoming targets. Radiation oncology is especially vulnerable because of the reliance on computer and network capabilities to transfer relevant patient information for safe and effective patient treatment. In early 2019, our institution was hit by a ransomware attack that brought down our oncology information system (OIS). Although we were not fully prepared for such an attack, a total of 69 treatment fractions occurred without our OIS thanks to the quick development of a contingency plan and the ability to restore the patients' records. The OIS was recovered by the manufacturer 4 days after the attack. We also have developed a contingency plan and outline important considerations for institutions trying to prepare for unexpected downtime such as a cyberattack.

The Operation of Canada's Only Virtually Operated Radiation Oncology Service During the COVID-19 Pandemic.

PURPOSE: Our institution operates a remote radiation oncology service in Northern Ontario, Canada. Since the start of the coronavirus disease 2019 pandemic, this center has operated without radiation oncologists on site owing to safety precautions, and this study seeks to understand the effect of this shift. METHODS AND MATERIALS: Departmental level data reports were used to investigate differences in metrics between April to May of 2019 and April to May 2020. These metrics include the total number of referrals received, average wait time from referral to consult, the number of cases that underwent peer review before beginning treatment, the total number of fractions given over each period, patient-reported outcomes, and patient satisfaction. We also examined the importance of physical examinations and the use of SABR treatment. RESULTS: There was an observed decrease in the number of referrals received, total number of fractions administered, and number of patients providing patient-reported outcomes. We observed no change in patient wait times, cases undergoing peer review before commencing treatment, or overall patient satisfaction. Challenges were identified in the collection of patient- reported outcomes and the conduction of physical examinations. CONCLUSIONS: This paper provides proof of concept that a radiation clinic can function entirely virtually in the short term without sacrificing patient satisfaction, efficiency, or safety.

Tissue segmentation-based electron density mapping for MR-only radiotherapy treatment planning of brain using conventional T1-weighted MR images.

PURPOSE: Magnetic resonance imaging (MRI) is the primary modality for targeting brain tumors in radiotherapy treatment planning (RTP). MRI is not directly used for dose calculation since image voxel intensities of MRI are not associated with EDs of tissues as those of computed tomography (CT). The purpose of the present study is to develop and evaluate a tissue segmentation-based method to generate a synthetic-CT (sCT) by mapping EDs to corresponding tissues using only T1-weighted MR images for MR-only RTP. METHODS: Air regions were contoured in several slices. Then, air, bone, brain, cerebrospinal fluid (CSF), and other soft tissues were automatically segmented with an in-house algorithm based on edge detection and anatomical information and relative intensity distribution. The intensities of voxels in each segmented tissue were mapped into their CT number range to generate a sCT. Twenty-five stereotactic radiosurgery and stereotactic ablative radiotherapy patients' T1-weighted MRI and coregistered CT images from two centers were retrospectively evaluated. The CT was used as ground truth. Distances between bone contours of the external skull of sCT and CT were measured. The mean error (ME) and mean absolute error (MAE) of electron density represented by standardized CT number was calculated in HU. RESULTS: The average distance between the contour of the external skull in sCT and the contour in coregistered CT is 1.0 ± 0.2 mm (mean ± 1SD). The ME and MAE differences for air, soft tissue and whole body voxels within external body contours are -4 HU/24 HU, 2 HU/26 HU, and -2 HU/125 HU, respectively. CONCLUSIONS: A MR-sCT generation technique was developed based on tissue segmentation and voxel-based tissue ED mapping. The generated sCT is comparable to real CT in terms of anatomical position of tissues and similarity to the ED assignment. This method provides a feasible method to generate sCT for MR-only radiotherapy treatment planning.

Static and rotational step-and-shoot IMRT treatment plans for the prostate: a risk comparison study.

PURPOSE: For certain clinical applications, rotational intensity modulated radiation therapy (R-IMRT) techniques such as volumetric modulated arc therapy (VMAT) are capable of improved target dose coverage and shorter delivery time when compared to static, step-and-shoot IMRT. The authors performed a risk comparison study for two standard step-and-shoot IMRT plans and two step-and-shoot Rotational IMRT plans that were designed specifically for a Siemens Primus linear accelerator. METHODS: CT images of a RANDO phantom were used to generate R-IMRT and static IMRT plans. One simple and one complex prostate cases were created to investigate these techniques. The R-IMRT plans consisted of 72 single-segmented 6 MV beams, equally spaced with beam angle separations of 5°. The static IMRT plans employed seven multisegmented 6 MV beams. Both types of plans were optimized in Pinnacle(3) with the direct machine parameter optimization (DMPO) algorithm using the same set of optimization objectives. The plans were delivered to a RANDO phantom and thermoluminescent diode (TLD) dose measurements were performed at various locations throughout the phantom. Risk coefficients and organ weightings as defined by International Commission on Radiological Protection (ICRP) Publication 103 were used to calculate the resulting effective doses to various organs at risk, as well as the overall risk estimate for both techniques. RESULTS: For the simple prostate case, the R-IMRT technique provided a higher dose to organs at risk within the CT volume and a lower overall peripheral dose to remaining organs. The R-IMRT plan had a risk estimate of 4.56% when compared to the IMRT risk of 4.78%. For the complex prostate case, there was no significant difference in the lifetime risks of the IMRT (5.73%) and R-IMRT (5.74%) plans. CONCLUSIONS: R-IMRT is an approximation to VMAT and it was found that there is no clinically significant difference between lifetime risk estimates between R-IMRT and standard seven-beam IMRT for the prostate.

An analytical approach to estimating the first order x-ray scatter in heterogeneous medium.

X-ray scatter estimation in heterogeneous medium is a challenge in improving the quality of diagnostic projection images and volumetric image reconstruction. For Compton scatter, the statistical behavior of the first order scatter can be accurately described by using the Klein-Nishina expression for Compton scattering cross section provided that the exact information of the medium including the geometry and the attenuation, which in fact is unknown, is known. The authors present an approach to approximately separate the unknowns from the Klein-Nishina formula and express the unknown part by the primary x-ray intensity at the detector. The approximation is fitted to the exact solution of the Klein-Nishina formulas by introducing one parameter, whose value is shown to be not sensitive to the linear attenuation coefficient and thickness of the scatterer. The performance of the approach is evaluated by comparing the result with those from the Klein-Nishina formula and Monte Carlo simulations. The approximation is close to the exact solution and the Monte Carlo simulation result for parallel and cone beam imaging systems with various field sizes, air gaps, and mono- and polyenergy of primary photons and for nonhomogeneous scatterer with various geometries of slabs and cylinders. For a wide range of x-ray energy including those often used in kilo- and megavoltage cone beam computed tomographies, the first order scatter fluence at the detector is mainly from Compton scatter. Thus, the approximate relation between the first order scatter and primary fluences at the detector is useful for scatter estimation in physical phantom projections.

An analytical approach to estimating the first order scatter in heterogeneous medium. II. A practical application.

Recently, the authors proposed an analytical scheme to estimate the first order x-ray scatter by approximating the Klein-Nishina formula so that the first order scatter fluence is expressed as a function of the primary photon fluence on the detector. In this work, the authors apply the scheme to experimentally obtained 6 MV cone beam CT projections in which the primary photon fluence is the unknown of interest. With the assumption that the higher-order scatter fluence is either constant or proportional to the first order scatter fluence, an iterative approach is proposed to estimate both primary and scatter fluences from projections by utilizing their relationship. The iterative approach is evaluated by comparisons with experimentally measured scatter-primary ratios of a Catphan phantom and with Monte Carlo simulations of virtual phantoms. The convergence of the iterations is fast and the accuracy of scatter correction is high. For a sufficiently long cylindrical water phantom with 10 cm of radius, the relative error of estimated primary photon fluence was within +/- 2% and +/- 4% when the phantom was projected with 6 MV and 120 kVp x-ray imaging systems, respectively. In addition, the iterative approach for scatter estimation is applied to 6 MV x-ray projections of a QUASAR and anthropomorphic phantoms (head and pelvis). The scatter correction is demonstrated to significantly improve the accuracy of the reconstructed linear attenuation coefficient and the contrast of the projections and reconstructed volumetric images generated with a linac 6 MV beam.

Analytically derived weighting factors for transmission tomography cone beam projections.

Weighting factors, which define the contributions of individual voxels of a 3D object to individual projection elements (pixels) on the detector, are the basic elements required in iterative tomographic reconstructions from transmission projections. Exact or as accurate as possible values for weighting factors are required in high-resolution reconstructions. Geometric complexity of the problem, however, makes it difficult to obtain exact weighting factor values. In this work, we derive an analytical expression for the weighting factors in cone beam projection geometry. The resulting formula is validated and applied to reconstruction from mega and kilovoltage x-ray cone beam projections. The reconstruction speed and accuracy are significantly improved by using the weighting factor values.

Estimation of the focal spot size and shape for a medical linear accelerator by Monte Carlo simulation.

The focal spot size and shape of a medical linac are important parameters that determine the dose profiles, especially in the penumbral region. A relationship between the focal spot size and the dose profile penumbra has been studied and established from simulation results of the EGSnrc Monte Carlo code. A simple method is proposed to estimate the size and the shape of a linac's focal spot from the measured dose profile data.