Figure 3. Typical arrangement of four treatment fields for nasopharyngeal carcinoma in the 1940s together with isodose distributions. The isodose curves numbered 4, 8, 12, 16 and 20 are in units of roentgen min^-1. Displaying the dose distributions in sagittal and coronal planes is an early attempt at trying to produce a three-dimensional (3D) view [35]. Even in the late 1960s manual calculation (maybe using an analogue computing device as distinct from a digital computer) in two or three orthogonal planes was the only way of showing a 3D distribution.