Beyond TG‑43: A PRISMA-based systematic review on model-based dose-calculation algorithms in brachytherapy

The AAPM TG-43 formalism has long served as the clinical standard for brachytherapy dose calculation but assumes a homogeneous water equivalent medium, overlooking limited scattering conditions and tissue heterogeneities. Model-based dose-calculation algorithms (MBDCAs), including Monte Carlo (MC) simulations overcome these limitations by accounting for real tissue composition, scatter, and applicator attenuation. This systematic review evaluates TG-43, MBDCAs/MC methods in terms of dosimetric accuracy, validation strategies, computational feasibility, clinical implementation barriers, and emerging innovations.

A PRISMA-guided literature search was conducted using the Scopus database, identifying 284 records, of which 42 full-text studies met inclusion criteria. Eligible studies compared at least two of the three dose-calculation approaches (TG-43, MBDCAs and MCs) in pelvic, breast, or head-and-neck brachytherapy. Extracted data encompassed dosimetric discrepancies, validation approaches, computational performance, workflow integration, and enabling technologies.

Across anatomical sites, TG‑43 showed no consistent bias. Its differences from heterogeneity‑aware models depended on tissue composition, scatter conditions, and source geometry. In soft‑tissue regions with minimal heterogeneity, TG‑43 generally overestimated target coverage by about 0.5%-5%. Near low‑density interfaces or in reduced‑scatter configurations, TG‑43 could instead yield lower doses than Monte Carlo or MBDCAs. For OARs, discrepancies were site‑specific: skin dose was often overestimated, while other organs showed smaller or opposite variations. Overall, MBDCAs and Monte Carlo agreed with experimental or benchmark data within roughly 3% and produced more reliable biological metrics. GPU‑accelerated and deep‑learning engines reduced computation times from hours to seconds, shifting remaining challenges toward standardization, commissioning, and QA. Successful clinical adoption relied on TG‑186-aligned validation, staff training, and integrated automated workflows.

Evidence from the systematic review supports a clinical transition toward TG-186-compliant, heterogeneity-aware dose-calculation frameworks. MBDCAs/MC algorithms provide superior dosimetric and radiobiological accuracy and are increasingly compatible with adaptive and biologically guided planning. Broad implementation is now supported by established QA standards and benchmarking datasets, which connects dosimetric precision with patient outcomes. The transition beyond TG-43 marks a pivotal step toward precision, safety, and personalization in modern brachytherapy.