A method to estimate radiobiological effectiveness at a very low surviving level of cells

An estimation method of radiobiological effectiveness at very low-survival (or high-dose) region on a malignant melanoma cells was investigated, for a treatment planning of eye melanoma at HIMAC, where high-dose exposure per each fractionation is required. Survival fractions were obtained using X-rays and heavy-ions at LET values among 13 - 300 keV/_m by colony formation methods for single-cells (low-dose region) and multicellular spheroids (high-dose region) of HMV-I cells. The linear-quadratic (LQ) equation and the multi-target single-hit (MS) equation together with a combined (LMS) equation, S = exp(-aD)[1-{1-exp(-D/Do)}n ], obtained from the linear part of the LQ equation and the MS equation were used for survival data fitting. Survival data obtained from single-cells and spheroids were combined each other. The LQ equation fits well for the combined survival data at lower dose region or single-cells survival data. The MS equation fits well combined survival data at higher dose region of spheroid data. The LMS equation fits well for the combined survival data for all dose region tested. We estimated the RBE values of the ion-beams from low to high dose regions by using the combined survival data with LMS equation. The RBE values at very high survival level (> 50 %) were ~3.7 at 300 keV/mm or ~1.8 at 13 keV/mm, decreased with survival level quickly at higher (~ 10 %) survival level and converged at very low survival level to be ~1.5 for ion-beams at LET value 13 - 300 keV/_m.The 2nd International Workshop on Space Radiation Researc

Estimation of RBE Values for Carbon-Ion Beams at High-Dose Region Using Multicellular Spheroids of HMV-I Cells

(Introduction) Heavy-ion beams have good dose distribution for tumor. Carbon beams, accelerated by HIMAC in National Institute of Radiological Sciences (NIRS), is a candidate for use in hypofractionated radiotherapy of tumors included malignant melanoma of choroid, non-small cell lung cancer or hepatocellular carcinoma. In this case, relative biological effectiveness (RBE) at high dose region (low survival level) must be considered however, the RBE is calculated physically and not verified biologically. (Purpose) The purpose of this study is to estimate RBE at high dose range as well as low dose range using monolayer cells and multicellular spheroids. (Materials and Methods) One human malignant melanoma cell line, HMV-I was used for this study. We used the 96 wells spheroid plates (SUMILOM MS-0096S) for making the multicellular spheroids. Cells were irradiated with 290 MeV/u carbon ions, 490 MeV/u silicon ions or 500 MeV/u argon ions with a dose-averaged about 13, 35, 100 and 300keV/um LET and X-rays. (Results) Surviving fractions of cells exposed to carbon beams and X-rays at a lower dose range (0-8 Gy) and a higher range (8-15 Gy) were obtained using monolayer cells and multicellular spherooids, respectively. The lenear-quadratic (LQ) equation fits well in survival data of monolayer cultures after both radiation at lower dose region. The multi-target single-hit (MT) equation fits well in those of spheroids at higher dose region. In addition, we could fit with a formula combined MT equation and initial slope part of LQ equation as well as multi-process (MP) equation, to survival data. This equation has good fitting for survival data in wide dose range when both monolayer and spheroid data was combined. (Conclusion) We could estimate RBE values of carbon beams from low to high dose range by converting the surviving fractions of spheroids into monolayer cells using the MP equation. RBE values at high dose range converged on the fixed values at 1.1-1.4, but varied in LET values at very low dose range (0-4 Gy).The 13th International Congress of Radiation Researc

Estimation of RBE values for accelerated carbon-ion beams in the wide dose range using multicellular spheroids of HMV-I cells

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