This thesis explores the development of upright radiotherapy, from its origins in the first external beam

radiotherapy treatments to a modern solution. Unlike conventional supine radiotherapy, where a linear

accelerator within a gantry rotates around a patient in the supine position, upright radiotherapy rotates

a patient upright (perched or seated) with a fixed-beam linac. To explore the uncertainties associated

with a conventional gantry (C-arm) linac due to rotation. Using a platform to eliminate gantry sag, the

rotational output dose uncertainty was shown to be 1 %. However, when rotating around a cylindrical

phantom, this output uncertainty was less than 0.5 %. These mechanical uncertainties are not found in a

fixed-beam linac. Monte Carlo simulations were performed to predict dose distributions from the linac

head. The EGSnrc and TOPAS toolkits were used to improve the designs of the primary collimator and

the entire linac head. An idealised shape for a primary collimator was found to be a conical frustum.

This is an improvement over the conventional cylinder used in most radiotherapy linacs. This thesis

presents a method for comparing shielding components, in collaboration with the engineering team from

Leo Cancer Care™, to optimise the design collimation for a fixed-beam linac. The linac head design

was simulated and adjusted to reduce (radiation) leakage. This resulted in a design which exceeds the

regulatory requirement of 10^-3 of the primary beam. Measurements and Monte Carlo TOPAS simulations

were performed on the multileaf collimator, including the leaf guide through which the primary beam was

attenuated. These simulations quantified the effect of the leaf guide in respect to the spectrum. Dosimetric

measurements and Monte Carlo simulations were undertaken and validated with one another. Initial

measurements on the multileaf collimator explored the attenuation through the bank, maximum interleaf

leakage, leakage due to abutting ends and further measurements of the leaf guide. These measurements

were undertaken with geometric challenges, yet the results could still be compared to industry standards.

Measurements of the open field also highlighted the impact of the leaf guide. A physiological study was

also performed on healthy participants to explore the differences in lung volumes and chest and abdomen

surface measurements. This study demonstrated that vital capacity, expiratory reserve volume, peak

expiratory flow and forced expiration in one second (p < 0.05) were all larger in the upright position. In

contrast, inspiratory capacity was larger in the supine position (p < 0.05). These findings demonstrate

the change in physiology due to changing patient position from the supine to the upright position and the

potential superior option for thoracic treatments.