\({}^{1}\) Departement of Basic Medical Sciences for Damages, National Institutes for Quantum and Radiological Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan; [EMAIL_ADDRESS] (M.P.) \({}^{1}\) Departement of Basic Medical Sciences for Damages, National Institutes for Quantum and Radiological Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan; [EMAIL_ADDRESS] (T.N.) \({}^{1}\) Departement of Basic Medical Sciences for Damages, National Institutes for Quantum and Radiological Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan; [EMAIL_ADDRESS] (M.P.) \({}^{1}\) Departement of Basicof ion beams have been exploited in depth to deliver sufficient doses to tumours and to reduce doses to organs at risk [1; 2; 3; 4; 5]. Meanwhile, in ion beam therapy, the biological effects of the beams, besides their physical properties, have to be considered, as the biological effects of ion beams vary with depth along the BP or spread-out Bragg peak (SOBP). In order to accurately estimate the biological effect of ion beams, reliable biological models have been developed, and the mixed beam model (i.e., the Kanai model), local effect model, and microdosimetric kinetic (MK) model have been introduced and used in clinical practice [6; 7; 8; 9; 10]. The National Institute for Quantum and Radiological Science and Technology (QST) has recently announced a research project called the Quantum Scalpel to reduce the cost and size of heavy ion beam therapy systems as well as to improve clinical results for radioresistant tumours [11]. Multi-ion therapy is one of the main projects expected to achieve favourable treatment outcomes by optimizing the linear energy transfer (LET) distribution in addition to dose distribution using \({}^{4}\)He-, \({}^{12}\)C-, \({}^{16}\)O-, and \({}^{20}\)Ne-ion beams. Recent publications have confirmed the concept of multi-ion therapy through in silico studies and cell irradiation experiments [12; 13; 14; 15]. [PERSON] et al. [15] proved that the biological model developed for multi-ion therapy reproduced the survival fractions (SFs) of the human salivary gland tumour (HSGc-C5) and human pancreatic cancer cells exposed to these ions. In ion beam therapy, one important issue is the prediction of biological effects by physical measurements. In particular, a silicon-on-insulator (SOI) microdosimeter and a MicroPlus probe developed at the Centre for Medical Radiation Physics (CMRP), University of Wollongong, would be useful for such measurements in conjunction with a dedicated biophysical model, i.e., the MK model. The SOI microdosimeter consists of an array of 3D micrometer-sized cylindrical silicon sensitive volumes (SVs) to imitate the sizes of cells [16; 17]. The SOI microdosimeter measures the stochastic energy deposited for the primary or secondary charged particle in SVs [18; 19], which enables the biological responses of ion beams to be estimated. This microdosimeter has been demonstrated to precisely measure the lineal energy spectra of passively scattered and scanned proton, carbon, nitrogen, and oxygen ions in [20; 21] and [22], respectively. In our previous work, we demonstrated that the biological effects of pancreatic cancer cells calculated by treatment planning software (TPS) can be well reproduced from the measured microdosimetric lineal energy spectra in conjunction with the MK model [22]. In this study, as part of the initial phase of the Quantum Scalpel project, the SF, relative biological effectiveness (RBE), and RBE-weighted dose of HSGc-C5 cells irradiated independently in the SOBPs of \({}^{4}\)He-, \({}^{12}\)C-, \({}^{16}\)O-, and \({}^{20}\)Ne-ion scanning beams were predicted based on the measurements of microdosimetric spectra with the SOI MicroPlus-mushroom microdosimeter in conjunction with the MK model. This study demonstrated that the SOI MicroPlus-mushroom microdosimeter can be used to validate the biological effect across the target volume exposed independently to these beams calculated by the TPS.