A novel approach to infectious disease control and radiotherapy risk management.

BACKGROUND: Infectious disease outbreaks have always presented challenges to the operation of healthcare systems. In particular, the treatment of cancer patients within Radiation Oncology often cannot be delayed or compromised due to infection control measures. Therefore, there is a need for a strategic approach to simultaneously managing infection control and radiotherapy risks. PURPOSE: To develop a systematic risk management method that uses mathematical models to design mitigation efforts for control of an infectious disease outbreak, while ensuring safe delivery of radiotherapy. METHODS: A two-stage failure mode and effect analysis (FMEA) approach is proposed to modify radiotherapy workflow during an infectious disease outbreak. In stage 1, an Infection Control FMEA (IC-FMEA) is conducted, where risks are evaluated based on environmental parameters, clinical interactions, and modeling of infection risk. occupancy risk index (ORI) is defined as a metric for infection transmission risk level in each room, based on the degree of occupancy. ORI, in combination with ventilation rate per person (Rp ), is used to provide a broad infection risk assessment of workspaces. For detailed IC-FMEA of clinical processes, infection control failure mode (ICFM) is defined to be any instance of disease transmission within the clinic. Infection risk priority number (IRPN) has been formulated as a function of time, distance, and degree of protective measures. Infection control measures are then systematically integrated into the workflow. Since the workflow is perturbed by infection control measures, there is a possibility of introducing new radiotherapy failure modes or increased likelihood of existing failure modes. Therefore, in stage 2, a conventional radiotherapy FMEA (RT-FMEA) should be performed on the adjusted workflow. RESULTS: The COVID-19 pandemic was used to illustrate stage 1 IC-FMEA. ORI and Rp values were calculated for various workspaces within a clinic. A deep inspiration breath hold (DIBH) CT simulation was used as an example to demonstrate detailed IC-FMEA with ICFM identification and IRPN evaluation. A total of 90 ICFMs were identified in the DIBH simulation process. The calculated IRPN values were found to be progressively decreasing for workflows with minimal, moderate, and enhanced levels of protective measures. CONCLUSION: The framework developed in this work provides tools for radiotherapy clinics to systematically assess risk and adjust workflows during the evolving circumstances of any infectious disease outbreak.

Effect of ethmoid sinus cavity on dose distribution at interface and how to correct for it: magnetic field with photon beams.

Recent work proposed the use of magnetic field as a solution to reduce the undesirable effect of air cavities on dose after the air/tissue interface. In contrast to the published work that looks into the problem with slab geometries, in this work we use actual anatomy based on CT images and the magnetic flux from a Helmholtz coil-pair configuration to investigate the problem and to evaluate the efficacy of the proposed solution. The EGS4 phantom was created using CT scans of the head at the level of the ethmoid sinus. The sinus measures 1.95 x 2.18 x 2.00 cm3. The grid size used is 0.15 x 0.15 x 0.4 cm3. Three different radiation beams, 1 x 1, 2 x 2, and 4 x 4 cm2, all 6 MV irradiate the phantom in two different configurations: single beam and parallel opposed. The magnetic field has three different strengths: 0.0, 0.5, and 1.0 T. These represent the maximum strength achieved in the middle of the configuration, between the two coils. The depth of the second buildup region in the absence of the magnetic field was used as the normalization point for the purpose of analysis. Dose was then scored at 0.23 cm after the air/tissue interface. A second phantom, very similar to the CT-based phantom, was created, but with the sinus cavity filled with unit-density tissue; everything else remained the same. This phantom provides a base to investigate the effect of the air cavity on dose. The phantom was termed the phantom without air, or PWA for short. We use the terms "dose reduction ratio" (DRR), defined as one minus the ratio of the dose in PWA to the dose with the presence of the cavity multiplied by 100% and the "dose improvement ratio" (DIR), defined as the ratio of dose with B to that without B, to evaluate the reduction in dose due to the cavity and the improvement in dose with magnetic field, respectively. For single beam geometry, the reduced dose ranged from 41% (1 x 1 cm2 beam) to less than 2% (4 x 4 cm2 beam). For the same single beam geometry, DIR ranged from 1.13 to 1.00 (DIR = 1 indicates no change) with 0.5 T, whereas it ranged from 1.44 to 1.05 for 1.0 T magnets. When an opposing beam was used, the reduced dose was not as severe, such that DRR ranged from 24% to less than 2%. Whereas the dose improvement ranged from 1.08 to 1.00 for 0.5 T, and from 1.23 to 1.01 for 1.0 T.