Browsing by Author "Shankar, A"

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Low-dose radiotherapy to the lungs using an interventional radiology C-arm fluoroscope: Monte Carlo treatment planning and dose measurements in a postmortem subject
(Institute of Physics, 2022) Leon, S; Paucar, O; Correa, N; Glassell, M; Gonzales, A; Olguin, E; Shankar, A; Moskvin, V; Schwarz, B; Alva-Sanchez, M; Moyses, H; Hamrick, B; Sarria, GR; Li, B; Tajima, T; Necas, A; Guzman, C; Challco, R; Montoya, M; Meza, Z; Zapata, M; Gonzales, A; Marquina, J; Quispe, K; Chavez, T; Castilla, L; Moscoso, J; Ramirez, J; Marquez ,F; Neira, R; Vilca, W; Mendez, J; Hernandez, J; Roa, D
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
Monte Carlo simulations and phantom validation of low-dose radiotherapy to the lungs using an interventional radiology C-arm fluoroscope
(Associazione Italiana di Fisica Medica, 2022) Roa, D; Leon, S; Paucar, O; Gonzales, A; Schwarz, B; Olguin, E; Moskvin, V; Alva-Sanchez, M; Glassell, M; Correa, N; Moyses, H; Shankar, A; Hamrick, B; Sarria, GR; Li, B; Tajima, T; Necas, A; Guzman, C; Challco, R; Montoya, M; Meza, Z; Zapata, M; Marquez, F; Neira, R; Vilca, W; Mendez, J; Hernandez, J
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 ∼ 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.