Low-dose radiotherapy to the lungs using an interventional radiology C-arm fluoroscope: Monte Carlo treatment planning and dose measurements in a postmortem subject.

Objective.The goal of this study was to use Monte Carlo (MC) simulations and measurements to investigate the dosimetric suitability of an interventional radiology (IR) c-arm fluoroscope to deliver low-dose radiotherapy to the lungs.Approach.A previously-validated MC model of an IR fluoroscope was used to calculate the dose distributions in a COVID-19-infected patient, 20 non-infected patients of varying sizes, and a postmortem subject. Dose distributions for PA, AP/PA, 3-field and 4-field treatments irradiating 95% of the lungs to a 0.5 Gy dose were calculated. An algorithm was created to calculate skin entrance dose as a function of patient thickness for treatment planning purposes. Treatments were experimentally validated in a postmortem subject by using implanted dosimeters to capture organ doses.Main results.Mean doses to the left/right lungs for the COVID-19 CT data were 1.2/1.3 Gy, 0.8/0.9 Gy, 0.8/0.8 Gy and 0.6/0.6 Gy for the PA, AP/PA, 3-field, and 4-field configurations, respectively. Skin dose toxicity was the highest probability for the PA and lowest for the 4-field configuration. Dose to the heart slightly exceeded the ICRP tolerance; all other organ doses were below published tolerances. The AP/PA configuration provided the best fit for entrance skin dose as a function of patient thickness (R2 = 0.8). The average dose difference between simulation and measurement in the postmortem subject was 5%.Significance.An IR fluoroscope should be capable of delivering low-dose radiotherapy to the lungs with tolerable collateral dose to nearby organs.

Monte Carlo simulations and phantom validation of low-dose radiotherapy to the lungs using an interventional radiology C-arm fluoroscope.

PURPOSE: To use MC simulations and phantom measurements to investigate the dosimetry of a kilovoltage x-ray beam from an IR fluoroscope to deliver low-dose (0.3-1.0 Gy) radiotherapy to the lungs. MATERIALS AND METHODS: PENELOPE was used to model a 125 kV, 5.94 mm Al HVL x-ray beam produced by a fluoroscope. The model was validated through depth-dose, in-plane/cross-plane profiles and absorbed dose at 2.5-, 5.1-, 10.2- and 15.2-cm depths against the measured beam in an acrylic phantom. CT images of an anthropomorphic phantom thorax/lungs were used to simulate 0.5 Gy dose distributions for PA, AP/PA, 3-field and 4-field treatments. DVHs were generated to assess the dose to the lungs and nearby organs. Gafchromic film was used to measure doses in the phantom exposed to PA and 4-field treatments, and compared to the MC simulations. RESULTS: Depth-dose and profile results were within 3.2% and 7.8% of the MC data uncertainty, respectively, while dose gamma analysis ranged from 0.7 to 1.0. Mean dose to the lungs were 1.1-, 0.8-, 0.9-, and 0.8- Gy for the PA, AP/PA, 3-field, and 4-field after isodose normalization to cover âˆ¼ 95% of each lung volume. Skin dose toxicity was highest for the PA and lowest for the 4-field, and both arrangements successfully delivered the treatment on the phantom. However, the dose distribution for the PA was highly non-uniform and produced skin doses up to 4 Gy. The dose distribution for the 4-field produced a uniform 0.6 Gy dose throughout the lungs, with a maximum dose of 0.73 Gy. The average percent difference between experimental and Monte Carlo values were -0.1% (range -3% to +4%) for the PA treatment and 0.3% (range -10.3% to +15.2%) for the 4-field treatment. CONCLUSION: A 125 kV x-ray beam from an IR fluoroscope delivered through two or more fields can deliver an effective low-dose radiotherapy treatment to the lungs. The 4-field arrangement not only provides an effective treatment, but also significant dose sparing to healthy organs, including skin, compared to the PA treatment. Use of fluoroscopy appears to be a viable alternative to megavoltage radiation therapy equipment for delivering low-dose radiotherapy to the lungs.

[The initial clinical probability in the diagnosis of the hospitalized pediatric patient]. / Probabilidad clínica inicial en el diagnóstico del paciente pediátrico hospitalizado.

OBJECTIVES: 1. To determine the degree of correlation among different physicians concerning their initial diagnosis and 2. identify the degree of correlation between the probability that physicians assing an initial diagnosis and the number of days the patient is hospitalized, laboratory test and X-rays taken of the patient. DESIGN: A comparative questionnaire. STUDY SITE: Pediatric hospitalization Unit of a third level medical care ward of the Mexican Social Security Institute. STUDY UNITS: All new admissions or non-programmed readmitted patients to the hospital during the months of November and December 1990. MAIN MEASUREMENTS: The treating physicians (Staff pediatricians (MB) and third (R3) and second (R2) year residents) were each asked to independently assign a probability (0 to 100) to each of the diagnosis emitted on the day the patient was admitted. When the patient was discharged, the number of days hospitalized as well as the number of laboratory tests and X-rays taken of the patient were added. RESULTS: 106 patients were evaluated, a correlation was gathered between MBs and R3s of 0.79 (P less than 0.001) and among MBs and R2s of 0.83 (P less than 0.001). The correlation between resident physicians was discretely less 0.60 (P less than 0.01). When relating the probability assigned by the physicians and the number of days the patients were hospitalized, associations were observed of 0.31 (P less than 0.05), 0.15 (P less than 0.05) and 0.19 (P = 0.04) for the MB, R3 and R2s respectively. In the case of laboratory test a correlation of 0.38, 0.06 and 0.04 (MB, R3, R2 respectively) was found. None of these correlations were statistically significant. The X-rays showed a significant correlation in cases of the MBs (0.50, P less than 0.05). CONCLUSIONS: The probabilities assigned by the staff physician as well as the resident doctors are closely related and a lesser grade of association is seen when comparing the residents among each other. No tendencies were identified in the correlation of the probability assigned by the residents and the variables analyzed. A consistent relation was seen between the staff physician and high probabilities, longer stays, and greater number of laboratory tests and X-rays.