A scanning dynamic collimator for spot-scanning proton minibeam production

Marios Sotiropoulos,Yolanda Prezado

doi:10.1038/s41598-021-97941-w

Abstract

In proton minibeam radiation therapy, proton minibeams are typically produced by modulating a uniform field using a multislit collimator. Multislit collimators produce minibeams of fixed length and width, and a new collimator has to be manufactured each time a new minibeam array is required, limiting its flexibility. In this work, we propose a scanning dynamic collimator for the generation of proton minibeams arrays. The new collimator system proposed is able to produce any minibeam required on an on-line basis by modulating the pencil beam spots of modern proton therapy machines, rather than a uniform field. The new collimator is evaluated through Monte Carlo simulations and the produced proton minibeams are compared with that of a multislit collimator. Furthermore, a proof of concept experiment is conducted to demonstrate the feasibility of producing a minibeam array by repositioning (i.e. scanning) a collimator. It is concluded that besides the technical challenges, the new collimator design is producing equivalent minibeam arrays to the multislit collimator, whilst is flexible to produce any minibeam array desired.

Highlights

In proton minibeam radiation therapy, proton minibeams are typically produced by modulating a uniform field using a multislit collimator
Contrary to conventional proton therapy, Proton Minibeam radiation therapy (pMBRT) uses multiple coulomb scatting to its advantage: proton minibeams get increasingly wider as a function of depth, which may result in a homogeneous target dose c overage[1], while normal tissues at the entrance will benefit from the spatial fractionation of the dose
The new collimator design introduces the concept of a scanning dynamic collimator for the production of a minibeam array

Summary

Introduction

In proton minibeam radiation therapy, proton minibeams are typically produced by modulating a uniform field using a multislit collimator. The new collimator system proposed is able to produce any minibeam required on an on-line basis by modulating the pencil beam spots of modern proton therapy machines, rather than a uniform field. The generation method influences the shape and size of minibeams, the peak-to-valley dose ratio (PVDR) but as well potential neutron contamination[11,12]. All of these aspects have an impact on the biology r esponse[4]. The main advantage of minibeam generation with multislit collimators is that it enables its implementation at any proton therapy c entre[15]. The main drawbacks are their inefficiency, inflexibility (a custom collimator may have to be fabricated for each case) and introduce a source of secondary neutrons close to the patient[12,16]

Methods

Discussion

Conclusion