Organs at risk dose constraints in carbon ion radiotherapy at MedAustron: Translations between LEM and MKM RBE models and preliminary clinical results

Sarah Grosshagauer; Piero Fossati; Mansure Schafasand; Antonio Carlino; Karin Poljanc; Tobias Radakovits; Markus Stock; Eugen Hug; Petra Georg; Maciej Pelak; Joanna Góra

doi:10.1016/j.radonc.2022.08.008

Organs at risk dose constraints in carbon ion radiotherapy at MedAustron: Translations between LEM and MKM RBE models and preliminary clinical results

Radiother Oncol. 2022 Oct:175:73-78. doi: 10.1016/j.radonc.2022.08.008. Epub 2022 Aug 8.

Authors

Affiliations

¹ MedAustron Ion Therapy Center, Austria; Technical University of Vienna, Austria.
² MedAustron Ion Therapy Center, Austria.
³ MedAustron Ion Therapy Center, Austria; Medical University of Vienna, Austria.
⁴ Technical University of Vienna, Austria.
⁵ MedAustron Ion Therapy Center, Austria. Electronic address: joanna.gora@medaustron.at.

PMID: 35952977
DOI: 10.1016/j.radonc.2022.08.008

Abstract

Background: Carbon ion radiotherapy (CIRT) treatment planning is based on relative biological effectiveness (RBE) weighted dose calculations. A large amount of clinical evidence for CIRT was collected in Japan with RBE estimated by the modified microdosimetric kinetic model (MKM) while all European centres apply the first version of the local effect model (LEM). Japanese schedules have been used in Europe with adapted prescription dose and organs at risk (OAR) dose constraints. Recently, less conservative adapted LEM constraints have been implemented in clinical practice. The aim of this study was to analyse the new set of LEM dose constraints for brain parenchyma, brainstem and optic system considering both RBE models and evaluating early clinical data.

Material and methods: 31 patients receiving CIRT at MedAustron were analysed using the RayStation v9A planning system by recalculating clinical LEM-based plans in MKM. Dose statistics (D1cm³, D5cm³, D0.1cm³, D0.7cm³, D10%, D20%) were extracted for relevant critical OARs. Curve fitting for those values was performed, resulting in linear quadratic translation models. Clinical and radiological toxicity was evaluated.

Results: Based on derived fits, currently applied LEM constraints matched recommended MKM constraints with deviations between -8% and +3.9%. For particular cases, data did not follow the expected LEM vs MKM trends resulting in outliers. Radiological (asymptomatic) toxicity was detected in two outlier cases.

Conclusion: Respecting LEM constraints does not automatically ensure that MKM constraints are met. Constraints for both RBE models need to be fulfilled for future CIRT patients at MedAustron. Careful selection of planning strategies is essential.

Keywords: Carbon ion radiotherapy; Head and neck cancer; Organs at risk; Relative biological effectiveness.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Carbon / therapeutic use
Heavy Ion Radiotherapy* / methods
Humans
Organs at Risk*
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Relative Biological Effectiveness

Substances

Carbon