A method for incorporating organ motion due to breathing into 3D dose calculations

TLDR

The authors propose a method to incorporate intratreatment breathing‑induced organ motion into 3‑D dose calculations for liver cancer therapy. They convolve a static dose distribution with a one‑dimensional probability distribution function that models asymmetric breathing motion, and compare the resulting dose to static calculations and direct fraction‑by‑fraction simulations using dose‑difference displays and uninvolved‑liver volume metrics. Incorporating motion can alter the prescribed dose based on uninvolved‑liver volume, and a single convolution‑based calculation accurately predicts the dose distribution for the example plan.

Abstract

A method is proposed that incorporates the effects of intratreatment organ motion due to breathing on the dose calculations for the treatment of liver disease. Our method is based on the convolution of a static dose distribution with a probability distribution function (PDF) which describes the nature of the motion. The organ motion due to breathing is assumed here to be one‐dimensional (in the superior–inferior direction), and is modeled using a periodic but asymmetric function (more time spent at exhale versus inhale). The dose distribution calculated using convolution‐based methods is compared to the static dose distribution using dose difference displays and the effective volume of the uninvolved liver, as per a liver dose escalation protocol in use at our institution. The convolution‐based calculation is also compared to direct simulations that model individual fractions of a treatment. Analysis shows that incorporation of the organ motion could lead to changes in the dose prescribed for a treatment based on the of the uninvolved liver. Comparison of convolution‐based calculations and direct simulation of various worst‐case scenarios indicates that a single convolution‐based calculation is sufficient to predict the dose distribution for the example treatment plan given.