The grid-dose-spreading algorithm for dose distribution calculation in heavy charged particle radiotherapy

TL;DR

The paper introduces the grid-dose spreading (GDS) algorithm, a faster and more efficient method for dose calculation in heavy charged particle radiotherapy, improving computational speed and realism in treatment planning.

Contribution

It presents the GDS algorithm as a novel, faster variant of the pencil-beam method, with implementation in a carbon-ion radiotherapy system for realistic beam modeling.

Findings

GDS algorithm is 1.4 times faster than broad-beam algorithms.

Mathematically equivalent to pencil-beam for coplanar beams.

Dose deformation within 3 mm for angled proton beams.

Abstract

A new variant of the pencil-beam (PB) algorithm for dose distribution calculation for radiotherapy with protons and heavier ions, the grid-dose spreading (GDS) algorithm, is proposed. The GDS algorithm is intrinsically faster than conventional PB algorithms due to approximations in convolution integral, where physical calculations are decoupled from simple grid-to-grid energy transfer. It was effortlessly implemented to a carbon-ion radiotherapy treatment planning system to enable realistic beam blurring in the field, which was absent with the broad-beam (BB) algorithm. For a typical prostate treatment, the slowing factor of the GDS algorithm relative to the BB algorithm was 1.4, which is a great improvement over the conventional PB algorithms with a typical slowing factor of several tens. The GDS algorithm is mathematically equivalent to the PB algorithm for horizontal and vertical coplanar beams commonly used in carbon-ion radiotherapy while dose deformation within the size of the pristine spread occurs for angled beams, which was within 3 mm for a single proton pencil beam of $30^\circ$ incidence, and needs to be assessed against the clinical requirements and tolerances in practical situations.