## 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 150-MeV proton pencil beam of 30° incidence, and needs to be assessed against the clinical requirements and tolerances in practical situations.

Original language | English |
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Pages (from-to) | 602-607 |

Number of pages | 6 |

Journal | Medical Physics |

Volume | 35 |

Issue number | 2 |

DOIs | |

Publication status | Published - 2008 |

## Keywords

- Dose calculation
- Heavy-ion radiotherapy
- Pencil-beam algorithm
- Proton radiotherapy

## ASJC Scopus subject areas

- Biophysics
- Radiology Nuclear Medicine and imaging