Medical Physics Seminar - Seminario de Física Médica
Title: A patient is a spherical body of water submerged in an infinite water medium. Change my mind.
Author: Javier Vijande, PhD
Affiliation: IFIC / UV
absorbed dose in clinical brachytherapy have been reported by means of the well-known TG-43 formalism. However, such approach requires dose kernels obtained by means of Monte Carlo (MC) simulations assuming that the patient is made of water and immersed in an infinite volume of water. Therefore, effects like interseed attenuation, tissue heterogeneities, patient geometry or applicator materials are not explicitly considered when creating a clinical plan.
Fortunately, in the last years, new Model Based Dose Calculation Algorithms (MBDCAs) have been developed. However, the evaluation of the absorbed dose deposited on a patient following a pre-ordained clinical plan has undergone a renaissance during the last decade. The combined role played by increasingly powerful computational architectures together with new refined algorithms allows the clinical user to reach an accuracy only dreamed of during the last decades. Among the different radiation modalities, it is probably brachytherapy the one that has evolved more drastically in the last few years.
In 2012, AAPM, ESTRO, ABS, and ABG released a report, TG-186, to provide guidance for early adopters of MBDCAs for brachytherapy, and to ensure clinical practice uniformity. TG186 goes one-step further, defining MC as the gold standard to which any new dose calculation algorithms should be compared and commissioned. Therefore, any MBDCA algorithm has to be verified against state-of-the-art MC calculations to ensure: i) that it reproduces correctly the “true” absorbed dose as described by MC, ii) to evaluate possible discrepancies due to the unavoidable numerical approximations required, and iii) to guide the clinical user when moving away from the current TG-43 clinical planning.
It is evident that performing such complex numerical simulations is so time consuming and demanding that, in practice, it is usually beyond the capabilities of a regular clinical environment. This is the main reason why the ESTRO, AAPM, and ABG have created the working group on Model-Based Dose Calculation Algorithms in Brachytherapy. Its main aim being to facilitate such task to clinical user by creating and analyzing relevant test cases. In this talk, I will describe the new MBDCAs commercially available in clinical practice and their main properties. I will focus on their strong and weak points when dealing with clinical scenarios and I will establish the relevance of the proposed test cases in clinical practice.
Online link: https://conectaha.csic.es/b/fer-gny-a0x-omp. The room access code will be sent per e-mail.
Ana Ros y Fernando Hueso