Back to the Future: Towards Ridge Filters in Clinical FLASH Proton Therapy Treatment Planning for Neuro-Oncological Targets

Master thesis (2021)

Authors

A.E. Meijer Applied Sciences

Contributors

D. Lathouwers RST/Reactor Physics and Nuclear Materials - AS (supervisor 1)
S. J.M. Habraken Erasmus MC (supervisor 1)
M.S. Hoogeman RST/Medical Physics & Technology - AS (supervisor 2)
M. Rohde RST/Reactor Physics and Nuclear Materials - AS (supervisor 2)
Faculty
Applied Sciences
Copyright: © 2021 Angeline Meijer
FLASH proton therapy Spread-out Bragg peak Ridge filter FLASH Energy modulation SOBP
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Published Date

24-06-2021

Language

English

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Faculty

Applied Sciences

Abstract

FLASH proton therapy is a growing field of research,
especially due to its biological benefits in radiation oncology: sparing
healthy tissue while delivering the treatment within a millisecond. However,
instead of sparing healthy tissue, the conventional FLASH approach, using
transmission beams, damages the tissue behind the distal edge of a tumour.
Therefore, this approach is less attractive in some clinical applications of
FLASH proton therapy. To solve this problem, the use of a ridge filter and
patient-specific range compensator, to shift the spread-out Bragg peak (SOBP)
of the proton beam to the tumour, is proposed. In this research, the clinical feasibility
and acceptability of FLASH-compatible treatment plans, optimized with multiple,
Monte Carlo-simulated ridge filter beams, is analysed. An SOBP-database is
generated using energy spectrum approximations and interpolations of energy
spectra retrieved from Monte Carlo simulations in TOPAS. To obtain optimized
FLASH-compatible treatment plans for neuro-oncological targets, this database
is implemented in the in-house treatment planning software of the Erasmus
Medical Center, iCycle.  The resulting treatment
plans show that it is possible to generate FLASH-compatible treatment plans
using a ridge filter. A FLASH enhancement ratio between 1.4 and 2.1 would
potentially give clinically acceptable plans for the three patients considered.
In some optimized plans, the homogeneity of the tumour dose is also increased. A
limitation of this research is that configuration of a stable ridge filter beam
treatment plan optimizer appears to be challenging. Besides this, the FLASH
enhancement ratio and the dose rate are not taken into account to find the
regions in the patient where the FLASH conditions (dose > 8 Gy, dose rate
> 40 Gy/s and treatment time < 0.1 s) are met.  Recommendations for future research include:
implementing the FLASH enhancement ratio and the dose rate optimization in
treatment plan optimization; investigating the influence of fractionation ofa
FLASH treatment plan on the tumour control and the healthy tissue irradiated;
study the relative biological effectiveness (RBE) and the biological character
of FLASH radiotherapy, and investigate the clinical potential of a combination
of FLASH and non-FLASH treatment.