A wireless diminutive inertial sensor being developed at Lancaster is capable of measuring position and orientation about three orthogonal axes. A real-time algorithm determines the six degree-of-freedom (6DOF) sensor posture, consisting of three components of dimensional position (heave, sway, and surge) and three components of rotational orientation (pitch, yaw, and roll). The objective of this study is to design an ultra-miniaturised version of this sensor that could be potentially implanted into tumours in order to help medical physicists track the motion of tumours and target the radiation accordingly.