ESTRO 2022 - Abstract Book

S1484

Abstract book

ESTRO 2022

Conclusion This study found that online adaption of palliative treatment plans that were initially generated using dCTs, was feasible using on-couch CBCT scans on the Ethos platform. We will now implement this workflow in our clinic, with expected benefits in both departmental logistics and patient experience.

PO-1685 Creating clinically competitive FLASH proton therapy treatment plans

N. Lovgren 1 , K. Petersson 1 , R. Labarbe 2 , L. Hotoiu 2 , I. Fagerström Kristensen 3

1 University of Oxford, Oncology, Oxford, United Kingdom; 2 Ion Beam Applications (IBA), IBA Research, Louvain-la-Neuve, Belgium; 3 Skåne University Hospital, Oncology, Lund, Sweden Purpose or Objective FLASH proton therapy (FLASH-PT) aims to use ultra-high dose rates ( ≥ 40 Gy/s) to induce a normal tissue sparing effect whilst maintaining the anti-tumour effectiveness of conventional dose rates. The beam delivery, dose rates, and fractionation schemes for FLASH-PT differ from standard radiotherapy. Hence, no guidelines exist regarding the development of treatment plans for this novel technique. The purpose of this study is to determine if FLASH-PT treatment plans can be developed and if the in silico results are comparable to the treatment plans produced for standard radiotherapy. Materials and Methods FLASH-PT and IMPT treatment plans were created using a novel research version of the MIROpt TPS developed by Ion Beam Applications SA from the open source version of UCLouvain. To produce conformal FLASH-PT plans the beam setup involved monoenergetic spot-scanned protons traversing through a conformal energy filter, a range shifter, and an aperture. The treatment plans were created for nine patient cases of bone (3), brain (3), and lung (3) metastases, all previously clinically treated with 3DCRT or VMAT. A dose rate of ≥ 40 Gy/s was included as an optimisation criterion for all FLASH-PT treatment plans for each patient case. Dose volume histograms (DVHs), boxplots, and the Wilcoxon Rank Sum Test were used to compare the FLASH-PT plans to the 3DCRT/VMAT and optimised IMPT plans. The statistical test was carried out with a 5% significance level and using DVH parameters V100%, V95%, V50%, D99%, D95%, and D2% for target and body structures. Results The qualitative and statistical comparisons yielded no significant differences between the optimised FLASH-PT plans and the clinical 3DCRT/VMAT and optimised IMPT plans. Conclusion The FLASH-PT treatment plans created in this study produced in silico results comparable to those of clinically competitive treatment plans. Future work involves the verification of the calculated dose against delivered dose and dose rate, to