2232 - Dose Prescription with Very High Energy Electron (VHEE): The Clinical Dosimetric Approach Applied to Challenging Cases in Conventional and Flash Delivery Scenarios
D. Carlotti1, A. De Gregorio2, M. Fiore1,3, G. Franciosini2, T. Insero1, M. Marafini4, V. Marè1, A. Muscato2, V. Patera5, S. Ramella1,3, A. Schiavi2, M. Toppi2, G. Traini2, A. Trigilio6, and A. Sarti5; 1Radiation Oncology, Fondazione Policlinico Universitario Campus Bio-Medico, Rome, Italy, 2INFN Sezione di Roma I, Rome, Italy, 3Radiation Oncology, Department of Medicine and Surgery, Università Campus Bio-Medico di Roma, Rome, Italy, 4Museo Storico della Fisica e Centro Studi e Ricerche “E. Fermi”, Rome, Italy, 5Dipartimento di Scienze di Base e Applicate per l’Ingegneria, Sapienza Università di Roma, Rome, Italy, 6INFN Sezione di LNF, Frascati, Italy
Purpose/Objective(s): According to the most recent report of the American Cancer Society, the 5-year overall survival for pancreatic and lung cancer is respectively 44% and 63% for localized lesions, respectively, highlighting the need for improved tumor control [1]. The FLASH effect, recently discovered and being investigated in the context of a real implementation in the clinical workflow, has a clear potential to contribute to this challenge. Promising radiobiological results have already been obtained with low energy electron beams (6 MeV), which has stimulated our interest in studying the potential of VHEE (70-130 MeV) with the aim of quantifying the main dosimetric advantages compared to the current state of the art clinical solutions (VMAT, at conventional rates). By applying the FLASH effect to the VHEE plans, it is possible to quantify the organ-at-risk sparing and the possible increase in target prescriptions to improve tumor control. In this paper, we investigate the comparison between VMAT and VHEE and the potential increase in prescribing to improve overall survival for these challenging diseases, taking into account the FLASH effect. Materials/
Methods: The selected cancers for the dosimetric comparison are: pancreatic adenocarcinoma and NSCLC. For pancreatic cancer, 3 patients with primary neoplasia were enrolled for stereotactic tumor ablation. Radical radiotherapy was chosen aiming to induce tumor necrosis. In this case, the main limitation is imposed by duodenal sparing: the maximum dose should not exceed a total of 35 Gy in 0.1 cm^3 in 5 treatment sessions to avoid serious adverse events for the patients. The 2 selected lung cancer cases are medically inoperable early stage I-II NSCLC primary neoplasms. Current RTOG guidelines recommend three, four or five-fraction SBRT. For all the patients, we have planned a treatment using an in-house developed treatment planning system that uses dose maps derived from FRED software. Results: The prescription used for VMAT pancreatic cases is less than 7 Gy for 5 fractions due to the duodenal sparing. Comparing the VHEE results for these cases with the FLASH model applied, it can be seen that the duodenal sparing allows a dose escalation up to 8 Gy in 5 fractions. For the lung cases, the VHEE plans with the FLASH model applied show a sparing effect on the high dose region around the CTV. When compared to the conventional VMAT schedule, the VHEE FLASH irradiation of lung cancer can reduce the number of sessions and increase the dose per fraction: the first case studied showed that it will be possible to go from 12 Gy in 4 fractions to 15 Gy in 3 fractions achieving the same level of toxicity. Conclusion: For a clinical translation of the presented in silico results, radiobiological experiments on human tissues and a better understanding of FLASH activation in a clinical setting are needed. The results obtained suggest a high potential for FLASH electron irradiation and strongly support research efforts in this area. [1] American Cancer Society: Cancer Facts and Figures 2024.
