The study focus on thermoluminescence (TL) response of five different diameters ~120, 241, 362, 483 and 604 μm of 8 mol% Ge-doped optical fibres. The irradiation was performed using Linear Accelerator (LINAC) Model Primus MLC Siemens provided by the Hospital Sultan Ismail, Johor Bahru at 6 MV photon irradiation with delivered doses ranging from 0.5 – 4.0 Gy. The results show the linear dose response against TL signals up to 4 Gy. The diameter of 483 μm optical fibre shows the highest in TL dose response and sensitivity compared to other fibres. The sensitivity of 483 µm optical fibre are almost 1.6 times  more than 604 µm. The linear dose response at low dose makes this optical fibre suitable to be used in radiation dosimetry application.