The increasing complexity of modern radiotherapy, including stereotactic radiosurgery (SRS), single-isocenter multitarget (SIMT) techniques, Gamma Knife systems, and online adaptive MR-Linacs, demands robust and independent end-to-end verification. Patient-specific motion management, high geometric precision, and adaptive workflows introduce uncertainties that conventional QA methods may not fully capture.
RTsafe has focused on developing anthropomorphic phantoms and remote dosimetry audit solutions that enable commissioning, benchmarking, periodic end-to-end testing, and research applications across advanced treatment platforms. Recent scientific projects demonstrate how such tools can support clinical validation and standardization.
Dosimetric and positional validation of Gamma Knife Icon motion management
In collaboration with clinical partners, the RTsafe PRIME phantom incorporating radiochromic film was used to assess the dosimetric and geometric performance of Gamma Knife Icon plan adaptation and high-definition motion management (HDMM). (Han et al 2019) Thirteen motion and setup scenarios were investigated, including near-threshold displacements, coughing events, treatment interruptions requiring adaptation, and pitch errors up to 20°.
Results showed reliable dosimetric accuracy even under challenging motion conditions, supporting the robustness of the HDMM system and demonstrating the value of controlled, reproducible end-to-end testing for motion-sensitive SRS treatments.
Multicenter evaluation of SIMT SRS practices
A second project involved a multicenter study of 23 radiotherapy centers across Germany, Austria, and Switzerland to evaluate variations in infrastructure, planning, delivery, and QA for SIMT SRS. (Thomann et al 2025) Using a standardized PRIME phantom configuration with ionization chamber and polymer gel dosimetry and a common reference case, inter-institutional performance was compared.
The study revealed substantial variability in planning criteria, motion control, QA approaches, and platform usage. While consensus existed on high-resolution imaging and 6DoF setups, differences in execution highlighted the need for harmonized guidelines to improve reproducibility and safety. The work illustrates how standardized phantom-based testing can facilitate benchmarking and best-practice development across institutions.
End-to-end geometric accuracy of an adaptive MR-Linac workflow
For online adaptive MR-guided radiotherapy, three-dimensional dosimetry becomes essential to assess geometric accuracy. Using a gel-filled PRIME phantom and film inserts, investigators evaluated the adapt-to-shape workflow of a Unity MR-Linac. (Oolbekkink et al 2024) Three-dimensional gel measurements quantified spatial offsets, while film provided independent verification.
The system achieved high agreement between planned and delivered dose distributions, with a global 3%/3 mm gamma passing rate of 98.2% and sub-millimeter geometric accuracy (0.3 mm with gel, 0.6 mm with film). These findings support 3D gel dosimetry as a practical and precise method for comprehensive MR-Linac end-to-end validation.
Supporting safer, standardized radiotherapy
Together, these scientific projects demonstrate how independent, realistic phantom-based methodologies can strengthen commissioning, auditing, and research in contemporary radiotherapy. By enabling reproducible end-to-end verification across platforms, such approaches contribute to safer treatments, improved confidence, and greater standardization across the medical physics community.
References
adaptation and high-definition motion management system with a motorized anthropomorphic head phantom J. Radiosurgery SBRT 6 217 Online: https://pmc.ncbi.nlm.nih.gov/articles/PMC6774480/
Oolbekkink S, Wolthaus J W H, van Asselen B and Raaymakers B W 2024 3D gel dosimeter assessment for end-to-end geometric accuracy determination of the online adaptive workflow on the 1.5 T MR-linac Phys. Imaging Radiat. Oncol. 32 100664
Thomann B, Fechter T, Fischer J, Runz A, Roers J, Ludwig U, Grehn M, Grohmann M, Ziemann C, Judge M, Baus W, Grahle M, Walke M, Bathen B, Köhn J, Käthner P, Shariff M, Matthis R, Fleckenstein J, Großmann S, Streller T, Howitz S, Priegnitz M, Weigel R, Winkler P, Blanck O, Schmitt D, Beck J, Machein M, Pappas E, Popp I, Reiner M, Karger C P, Moustakis C, Bock M, Grosu A L and Baltas D 2025 Multicenter multiplatform pattern-of-practice analysis of single-isocenter multitarget stereotactic radiosurgery Strahlenther. Onkol. 201 953–62 Online: https://pubmed.ncbi.nlm.nih.gov/40637729/
AUTHOR
Emmanouil Zoros
Medical Physicist – Product Manager
Emmanouil is responsible for product management, data analysis, and film dosimetry at RTsafe. He has a Diploma in Applied Mathematics & Physics from the National Technical University of Athens, a Master of Science and a Ph.D. in Medical Physics from the National and Kapodistrian University of Athens. His research interests focus on radiation therapy with emphasis on quality assurance in stereotactic radiosurgery, experimental and computational dosimetry using Monte Carlo simulation techniques.