Open Collections

McKeown, Dakota

University of British Columbia

Purpose: Clinical brachytherapy is typically performed using TG43 formalism, which assumes a homogeneous water medium and does not account for factors such as interseed attenuation or tissue inhomogeneities. Monte Carlo (MC) model-based dose calculation algorithms (MBDCA) provide improved dosimetric accuracy. The purpose of this work was to quantify the impact of eb_gui, a Canadian developed, user-friendly MC MBDCA, on plan evaluation with 80 low dose rate (LDR) breast brachytherapy patients and 76 LDR prostate brachytherapy patients. Methods: Dosimetry of 80 breast brachytherapy cases treated with Pd-103 seeds (TheraSeed200, 2.3-2.8 U, 90 Gy prescription dose) and 76 prostate cases treated with I-125 seeds (AgX100, 0.354-0.493 U, 144 or 110 Gy prescription doses) were simulated using the MC program and doses were calculated using two methods: 1) water-equivalent MC and 2) material-assigned MC. The clinical dose-volume histogram metrics of the targets and organs at risk (OAR) for both simulations were extracted and compared across the two patient cohorts. Results: Breast target volumes showed a slight overestimation of dose by water-equivalent MC of 1% for the CTV V₁₀₀ and 6% for the ETV V₁₀₀ compared to the median material-assigned MC results (p < 0.05). Water-equivalent MC significantly underestimated the skin D₀ꓸ₂꜀ₘ₃ by 20.3% compared to material-assigned MC (p < 0.05). In prostate patients, water-equivalent MC overestimated CTV V₁₀₀ by 4.4% compared to material-assigned MC (p < 0.05). The only potentially clinical significant result for a prostate OAR is the urethra D₁꜀ₘ₃ , where dose was overestimated by 6.3% by water-equivalent MC (p < 0.05). Conclusion: MC simulation of 80 breast and 76 prostate LDR patients were performed. Slight overestimation of dose in target volumes and prostate OARs and potentially clinically significant underestimation of dose in skin were seen using the standard TG43 calculations when compared to the more accurate MBDCA. These differences motivate the future adoption of eb_gui as a valuable tool for LDR breast and prostate treatments in clinical practices.

Text; Still Image

2023-09-07

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/85815

Medical Physics

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/