3D‐printable lung phantom for distal falloff verification of proton Bragg peak

Abstract

In proton therapy, the Bragg peak of a proton beam reportedly deteriorates when passing though heterogeneous structures such as human lungs. Previous studies have used heterogeneous random voxel phantoms, in which soft tissues and air are randomly allotted to render the phantoms the same density as human lungs, for conducting Monte Carlo (MC) simulations. However, measurements of these phantoms are complicated owing to their difficult‐to‐manufacture shape. In the present study, we used Voronoi tessellation to design a phantom that can be manufactured, and prepared a Voronoi lung phantom for which both measurement and MC calculations are possible. Our aim was to evaluate the effectiveness of this phantom as a new lung phantom for investigating proton beam Bragg peak deterioration. For this purpose, we measured and calculated the percentage depth dose and the distal falloff widths (DFW) passing through the phantom. For the 155 MeV beam, the measured and calculated DFW values with the Voronoi lung phantom were 0.40 and 0.39 cm, respectively. For the 200 MeV beam, the measured and calculated DFW values with the Voronoi lung phantom were both 0.48 cm. Our results indicate that both the measurements and MC calculations exhibited high reproducibility with plastinated lung sample from human body in previous studies. We found that better results were obtained using the Voronoi lung phantom than using other previous phantoms. The designed phantom may contribute significantly to the improvement of measurement precision. This study suggests that the Voronoi lung phantom is useful for simulating the effects of the heterogeneous structure of lungs on proton beam deterioration.

Investigation of the Bragg peak degradation caused by homogeneous and heterogeneous lung tissue substitutes: proton beam experiments and comparison to current clinical dose calculation

“…However, finding materials which fulfil all properties of real lung simultaneously was difficult, especially considering only non-biodegradable materials, which did not require a container. Lung substitutes produced with a 3D printer offer the possibility of controlling heterogeneity size and distribution as well as the proportion of material to air to match that of lung (roughly 75% air, 25% soft tissue) (Schneider et al 1996, Titt et al 2015, Koketsu et al 2019, Baumann et al 2019b, but usually do not fulfil the realistic elemental composition which in turn influences essentially the particle interactions. Therefore, cork, especially fine-grained cork, was identified a worthwhile choice for heterogeneous thoracic phantoms and the use of such lung substitutes for experimental validation in end-to-end test scenarios seems to be suitable.…”

Dosimetric characteristics of 3D-printed and epoxy-based materials for particle therapy phantoms

“…A comprehensive characterization of the elemental composition of human tissues [1] and the ICRU report 44 on "Tissue Substitutes in Radiation Dosimetry" are the foundation of modern surrogates [2]. Potential candidates to expand or improve the material library are investigated to this day [3][4][5][6].…”

The effect of voxelization in Monte Carlo simulation to validate Bragg peak characteristics for a pencil proton beam

“…Determination of characteristics of all radiation beams is vital. In proton therapy, the quality of a proton beam is mostly expressed in terms of its physical properties; the deposition of the major proportion of the dose within a few millimetres in a well-defined depth (BP), followed by a sharp dose fall-off and a subsequent negligible dose deposition thereafter, but one of the biggest factors affecting BP dosimetric characteristics is a geometrical collection efficiency [ 10 ], which can be defined as the partial volume effect associated with the process of voxelization [ 11 ]. BP is defined by its characteristics.…”