ESTRO 2023 - Abstract Book

S384

Sunday 14 May 2023

ESTRO 2023

A. Muscato 1 , L. Arsini 2,3 , L. Campana 4,5 , D. Carlotti 6,7 , A. De Gregorio 8,6 , F. De Felice 9 , C. Di Felice 10 , M. Fischetti 11,12 , M. Fiore 7,13 , G. Franciosini 14,6 , M. Marafini 14,15 , V. Marè 16 , I. Mattei 17 , M. Pacilio 18 , V. Patera 8,19 , S. Ramella 16,20 , A. Schiavi 19,8 , A. Sciubba 14,19 , M. Schwarz 21 , M. Toppi 19 , G. Traini 22 , A. Trigilio 8,6 , A. Sarti 8,19 1 University La Sapienza of Rome, Department of Scienze e Biotecnologie medico-chirurgiche, Rome, Italy; 2 University La Sapienza of Rome, Physics Department, Rome, Italy; 3 INFN,Isituto Nazionale Fisica Nucleare, Section of Rome 1 , Rome, Italy; 4 INFN, Istituto Nazionale Fisica Nucleare , Section of Rome 1 , Rome, Italy; 5 University La Sapienza of Rome, Department of Scienze e Biotecnologie medico-chirurgiche, Rome , Italy; 6 University La Sapienza of Rome, Physics Department , Rome, Italy; 7 Fondazione Policlinico Universitario Campus-Bio Medico, Operative Research Unit of Radiation Oncology, Rome, Italy; 8 INFN, Istituto Nazionale Fisica Nucleare, Section of Rome 1, Rome, Italy; 9 Azienda Ospedaliero Universitaria Policlinico Umberto I, Department of Radiological,Oncological and Pathological Sciences, Rome, Italy; 10 Azienda Ospedaliero-Universitaria Policlinico Umberto I, Unità di Fisica Sanitaria , Rome, Italy; 11 University La Sapienza of Rome, Department of Scienze di Base e Applicate per l'Ingegneria, Rome, Italy; 12 INFN,Istituto Nazionale Fisica Nucleare, Section of Rome 1 , Rome, Italy; 13 University Campus-Bio Medico of Rome, Research Unit of Radiation Oncology, Department of Medicine and Surgery , Rome, Italy; 14 INFN, Istituto Nazionale Fisica Nucleare, Section of Rome 1 , Rome, Italy; 15 Museo Storico della Fisica e Centro Studi e Ricerche “E.Fermi”, -, Rome, Italy; 16 Fondazione Policlinico Universitatio Campus-Bio Medico, Operative Research Unit of Radiation Oncology, Rome, Italy; 17 INFN, Istituto Nazionale Fisica Nucleare, Section of Milan , Milan, Italy; 18 Azienda Ospedaliero-Universitaria Policlinico Umberto I, Unità di Fisica Sanitaria, Rome, Italy; 19 University La Sapienza of Rome, Department of Scienze di Base e Applicate per l’Ingegneria, Rome, Italy; 20 Università Campus Bio-Medico of Rome, Research Unit of Radiation Oncology, Department of Medicine and Surgery, Rome, Italy; 21 Fred Hutch Cancer Center, Radiation Oncology Department , Seattle, USA; 22 INFN, Istituto Nazionale Fisica Nucleare , Section of Rome 1, Rome, Italy Purpose or Objective External beam radiotherapy is currently performed with either photons (RT), protons (PT) or heavier ions like 12C. VHEE beams (100-200 MeV) for the treatment of deep seated tumors are now being considered as well due to the developments in the field of the C-band electron acceleration and FLASH radiotherapy. Compact accelerators with high gradients (~50 MeV/m) will provide ultra-high dose rate (UHDR) beams (>40 Gy/s) suitable for clinical implementation. We investigated how VHEE could be used in the treatments of deep seated tumors, working on head and neck and pancreatic cancer cases, and compared them with conventional RT or PT. Materials and Methods We implemented and developed a VHEE treatment plan using an accurate Monte Carlo simulation of the electrons interaction with the patient tissues and included the FLASH effect modelling as a function of the absorbed dose. We studied in detail the feasibility of treating patients with VHEE with kinetic energies in the 70 – 130 MeV range. From the results obtained, based on a set of beam delivery parameters and reasonable assumptions on the conditions that have to be met to trigger the FLASH effect, we computed the absorbed dose rate taking into account a Flash Modifying Factor (FMF) accounting also for the dose rate dependence [1]. For calculating the latter, the Average Dose Rate (ADR) definition was used [2]. [1] doi: 10.1016/j.ijrobp.2022.05.038 [2] doi:10.1002/mp.14456 Results Even without assuming a dose modification factor due to FLASH, VHEE dose distributions are competitive with respect to PT and RT when it comes to both target coverage and organs at risk (OARs) sparing: in Fig 1 (right, solid line – pancreatic cancer) and Fig 2 (bottom right – head and neck district) FMF 1 was used. FLASH effect helps the duodenum sparing in the case of pancreatic cancer in comparison with standard VMAT RT as shown in Fig 1 (right). Such results were obtained with a reasonable treatment hypofractionation (6 Gy/fr) and beam delivery strategy. The implemented thresholds on the dose and on the ADR to enable the FLASH sparing were 4 Gy and 40 Gy/s, respectively.

Figure 1: DVH of a treatment of pancreatic cancer. (left) VMAT treatment delivered to the patient (right) VHEE treatment. Solid line implies FMF = 1. Results with FMF in the 0.6 – 0.9 range are shown by dashed and dotted lines.