A 4D-dosimeter and quality assurance phantom prototype was developed to quantify the effects of respiratory motion.

The dose distributions were measured using two-dimensional detectors that were mounted on a mobile platform capable of sinusoidal motion in one direction with different patterns using adjustable motion amplitude and frequency. The dose distributions were obtained from various treatment plans including conformal and intensity-modulated beams for both photon and proton therapy. Dose delivery and measurement were conducted using this 4D-dosimeter with the mobile phantom for different motion amplitudes (0–35 mm) and frequencies (0.25–0.33 Hz).

The increase in motion amplitude increased the blurring of the dose distributions at the beam edges along the direction of motion and led to large dose discrepancies. This produced larger dose deficits inside the treatment planning volume (PTV) and increasing dose deposition in the surrounding normal tissue with increasing motion amplitudes. For both the IMRT and VMAT-treatment plans, the dose profile for each increased amplitude increment showed a reproducible flattening of the penumbra at the beam edge, all changing around the 40–60% isodose line.

The 4D-dosimeter developed in this work provides a noble clinical tool to quantify the deviations in the dose distributions induced by respiratory motion.