# Dynamic fluence map sequencing using piecewise linear leaf position functions

## TL;DR

This paper presents a novel approach for fluence map sequencing in IMRT and VMAT using piecewise linear leaf position functions and a two-loop optimization method to improve treatment delivery within limited time.

## Contribution

It introduces two modeling strategies with linear splines and smooth leaf blocking functions, along with a two-loop optimization framework for better fluence map matching.

## Key findings

- Effective modeling of leaf positions with linear splines.
- Improved fluence map matching within time constraints.
- Two-loop optimization enhances treatment planning accuracy.

## Abstract

Within the setting of intensity modulated radiation therapy (IMRT) and the fully continuous version of IMRT called volumetric modulated radiation therapy (VMAT), we consider the problem of matching a given fluence map as well as possible in limited time by the use of a linear accelerator (linac) with a multi-leaf collimator (MLC). We introduce two modeling strategies to manage the nonconvexity and the associated local minima of this problem. The first is the use of linear splines to model the MLC leaf positions as functions of time. The second is a progressively controllable smooth model (instead of a step function) of how the leaves block the fluence radiation. We propose a two part solution: an outer loop that optimizes the dose rate pattern over time, and an inner loop that given a dose rate pattern optimizes the leaf trajectories.