ESTRO 2024 - Abstract Book

S3555

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

1 Sapienza, University of Rome, Institute of Basic and Applied Engineering Sciences, Rome, Italy. 2 National Institute of Nuclear Physics, INFN, Section of Rome I, Rome, Italy. 3 Sapienza, University of Rome, Physics, Rome, Italy. 4 S.I.T., Sordina IORT Technologies S.p.A, Aprilia, Italy. 5 Azienda Universitaria Ospedaliera Pisana, U.O.Fisica Sanitaria, Pisa, Italy. 6 Museo Storico della Fisica e Centro Studi e Ricerche, "E. Fermi", Roma, Italy. 7 Sapienza, University of Rome, Specialty School of Medical Physics, Rome, Italy. 8 University of Antwerp, Faculty of Medicine and Health Sciences, Antwerp, Belgium. 9 Iridium Netwerk, Radiation Oncology, Antwerp, Belgium. 10 National Institute of Nuclear Physics, INFN, Frascati National Laboratories (LNF), Frascati, Italy

Purpose/Objective:

Partial Breast Irradiation (PBI) [1,2] for the treatment of early-stage breast cancer patients can be performed by means of Intra Operative electron Radio Therapy (IOeRT) [3], which is a technique that, after the surgical tumor removal, delivers a dose of ionizing radiation directly to the primary tumor bed, reducing the risk of cancer recurrence. Within IOeRT, whenever needed and possible, temporarily beam modifiers like Radio-Protection disks (RP) are used to shield the underlying healthy tissues during the irradiation, and a PMMA hollow tube, know as applicator, is used for passive collimation. Currently there is a growing interest in the potential first clinical translation of the FLASH effect to IOeRT [4]. In particular, for PBI the FLASH effect represents an excellent opportunity, having the potential to re-define the treatments workflow allowing to place the applicator directly on the patient skin and avoiding the RP disk use. This advancement would make surgery less invasive and significantly improve patient quality of life. However, as for now, one of the main IOeRT limitations is the lack of a routinely used Treatment Planning System (TPS) which is an essential tool for ensuring accurate target coverage during irradiation [5], and will help enabling the FLASH irradiation in the clinical workflow. In addition an image guided applicator positioning tool could be used to minimize the risk of geographical miss, easing the treatment dose report calculation.

Aim of this contribution is to show how a fast Monte Carlo (MC) tool, called FRED [6], developed exploting the GPU hardware can be used to plan and optimize online a treatment delivered at conventional and FLASH rates.

Material/Methods:

An IOeRT TPS has been developed using a fast MC-GPU based tool and an ultrasound imaging system to provide, while the patient is still on the surgery bed, the best irradiation strategy (electron beam energy, position, irradiation angle and RP dimension and position) in both conventional and FLASH conditions. The study has been performed in silico, exploiting an MC simulation of a breast cancer treatment. Ultrasound like input has been used to compute the absorbed dose maps in different configurations and a quantitative comparison between the different options was carried out using Dose Volume Histogram (DVH) metrics.

Results:

Our system was capable of exploring different beam energies and applicator positions in less than five minutes, allowing to identify the best strategy with an overall computation time that was found to be completely compatible with a clinical implementation. The systematic uncertainty related to the tissue deformation during the treatment delivery with respect to the imaging acquisition was taken into account. The TPS is also capable of properly accounting for the Flash-Modifying Factor correction, opening the door to combining minimally invasive surgery strategies with ultra-high-dose rate irradiation.