Impact of CT tube voltage variation on calculated dose radiotherapy: A simulation and phantom study

Abstract

Background

Advanced radiotherapy techniques necessitate the use of precise treatment planning systems (TPSs) that account for tissue density differences. Modern TPSs require electron density to be defined for every tissue type and that is usually provided from computed tomographic images.

Objective

Changing the tube voltage used during CT acquisition can affect the CT number which consequently changes the derivation of tissue electron densities. This study measures the radio-therapeutic dose deviation caused by such variations.

Methods

A phantom with different tissue equivalent densities of material plugs is used in the study. We investigated the tube voltage influence on the dose attenuation coefficients percent (DACP) and equivalent path length (EPL) within the tissue phantom plugs. Monte Carlo was used to explore the influence of the tube voltage used in imaging on the dose distributions in a pelvic phantom.

Results

Our calculations show that the attenuation percentage in each phantom plug was highest in high-density materials. The maximum difference was 3.5% when comparing the attenuation percentage of 80 KV to 140 KV, while field size had no significant impact. Our simulation of a pelvic case revealed that switching from 140 KV to 80 KV could result in a 3% difference in a patient plan. However, it is highly dependent on the proximity to high-density materials. The study demonstrated that 140 KV images yield a much closer match between measured and theoretical equivalent path lengths compared to 80 KV images in high-density materials.

Conclusions

CT tube voltage variation has an impact on the dose calculations especially for high-density structures. The CT voltage variations influence can be small in most cases, but care should be taken in high dense bone situations especially in the vicinity of critical structures.