Transfer line scattering model of therapeutic hadron beams and applications to nozzle and gantry optimization

M Palm,U Dorda,M Benedikt

doi:10.1103/physrevstab.16.014702

Abstract

The field of hadron therapy is growing rapidly with several facilities currently being planned, under construction or in commissioning worldwide. In the ``active scanning'' irradiation technique, the target is irradiated using a narrow pencil beam that is scanned transversally over the target while the penetration depth is altered with the beam energy. Together, the target dose can thereby be conformed in all three dimensions to the shape of the tumor. For applications where a sharp lateral beam penumbra is required in order to spare critical organs from unwanted dose, beam size blowup due to scattering in on-line beam diagnostic monitors, air gaps and passive elements like the ripple filter must be minimized. This paper presents a model for transverse scattering of therapeutic hadron beams along arbitrary multislab geometries. The conventional scattering formulation, which is only applicable to a drift space, is extended to not only take beam optics into account, but also non-Gaussian transverse beam profiles which are typically obtained from the slow resonant extraction from a synchrotron. This work has been carried out during the design phase of the beam delivery system for MedAustron, an Austrian hadron therapy facility with first patient treatment planned for the end of 2015. Irradiation will be performed using active scanning with proton and carbon ion beams. As a direct application of the scattering model, design choices for the MedAustron proton gantry and treatment nozzles are evaluated with respect to the transverse beam profile at the focal point; in air and at the Bragg peak.

Highlights

The goal of any radiotherapy, be it with hadron beams or photons, is to expose the tumor to a lethal dose, while minimizing the dose given to healthy tissue [1]
Beams of ions are attractive due to the following two properties: (1) the finite, well-defined penetration depth, which implies that little or no dose is given beyond the tumor, and (2) the Bragg peak behavior of the depth-dose curve, where each particle deposits a high dose at the end of the range
There are many cases where a narrow or sharp transverse beam profile is clinically motivated in order to spare critical organs or healthy tissue abutting the tumor from an unwanted dose: the sharper the beam profile, the better the dose can be conformed to the target

Summary

Introduction

The goal of any radiotherapy, be it with hadron beams or photons, is to expose the tumor to a lethal dose, while minimizing the dose given to healthy tissue [1]. Beams of ions are attractive due to the following two properties: (1) the finite, well-defined penetration depth, which implies that little or no dose is given beyond the tumor, and (2) the Bragg peak behavior of the depth-dose curve, where each particle deposits a high dose at the end of the range. Together, these advantages allow for higher dose in the target and/or lower dose at the entrance channel.

Methods

Results

Discussion

Conclusion