Relative biological effectiveness of single and split helium ion doses in the rat spinal cord increases strongly with linear energy transfer. (May 2022)

• Record Type: Journal Article
• Authors: Hintz, Lisa; Glowa, Christin; Saager, Maria; Euler-Lange, Rosemarie; Peschke, Peter; Brons, Stephan; Grün, Rebecca; Scholz, Michael; Mein, Stewart; Mairani, Andrea; Debus, Jürgen; Karger, Christian P.
• Is Part Of: Radiotherapy and oncology. Volume 170(2022)
• Page Start: 224
• Page End: 230
• Publication Date: 2022-05
• Subjects: CL confidence limit -- CNS central nervous system -- DCE-MRI dynamic contrast-enhanced MRI -- Fx Fractions -- HIT Heidelberg Ion-Beam Therapy Center -- LBL Lawrence Berkeley Laboratory -- LEM local effect model -- LET linear energy transfer -- LQ linear-quadratic -- mMKM modified microdosimetric kinetic model -- MRI magnetic resonance imaging -- NIRS National Institute of Radiological Sciences -- PMMA polymethyl-methacrylate -- RBE relative biological effectiveness -- SD standard deviation -- SE standard error -- SOBP Spread-out Bragg-peak -- TD iso-effect dose -- TPS treatment planning system -- TRiP treatment planning for particles; Helium ion radiotherapy -- Protons -- Relative biological effectiveness (RBE) -- Linear energy transfer (LET) -- Rat spinal cord -- Myelopathy -- Late normal tissue effects -- Local effect model (LEM) -- Modified Microdosimetric kinetic model (mMKM); Oncology -- Periodicals; Radiotherapy -- Periodicals; Tumors -- Periodicals; Medical Oncology -- Periodicals; Neoplasms -- radiotherapy -- Periodicals; Radiotherapy -- Periodicals; Radiothérapie -- Périodiques; Cancérologie -- Périodiques; Tumeurs -- Périodiques; Electronic journals; 616.9940642
• DOI: 10.1016/j.radonc.2022.03.017
• Languages: English
• ISSNs: 0167-8140

Abstract

Highlights: The RBE of helium ions increases strongly with LET. The RBE at the distal edge increases more for helium ions than for protons. At high doses, the RBE of helium ions is independent of fractionation. Agreement of model-predictions with measured RBE is LET and dose-level dependent. Abstract: Background and purpose: Determination of the relative biological effectiveness (RBE) of helium ions as a function of linear energy transfer (LET) for single and split doses using the rat cervical spinal cord as model system for late-responding normal tissue. Material and methods: The rat cervical spinal cord was irradiated at four different positions within a 6 cm spread-out Bragg-peak (SOBP) (LET 2.9, 9.4, 14.4 and 20.7 keV/µm) using increasing levels of single or split doses of helium ions. Dose-response curves were determined and based on TD50 -values (dose at 50% effect probability using paresis II as endpoint), RBE-values were derived for the endpoint of radiation-induced myelopathy. Results: With increasing LET, RBE-values increased from 1.13 ± 0.04 to 1.42 ± 0.05 (single dose) and 1.12 ± 0.03 to 1.50 ± 0.04 (split doses) as TD50 -values decreased from 21.7 ± 0.3 Gy to 17.3 ± 0.3 Gy (single dose) and 30.6 ± 0.3 Gy to 22.9 ± 0.3 Gy (split doses), respectively. RBE-models (LEM I and IV, mMKM) deviated differently for single and split doses but described the RBE variation in the high-LET region sufficiently accurate. Conclusion: This study established the LET-dependence of the RBE for late effects in the central nervous system after single and split doses of helium ions. The results extend the existing database for protons and carbon ions and allow systematic testing of RBE-models. While the RBE-values of helium were generally lower than for carbon ions, the increase at the distal edge of the Bragg-peak was larger than for protons, making detailed RBE-modeling necessary.