ESTRO 2023 - Abstract Book

S879

Digital Posters

ESTRO 2023

prostate cancer (36 pts) as shown in fig.1. CIRT was used for patients with inoperable macroscopic disease, and/or when local control rates achievable with low LET radiation were considered suboptimal. In reirradiation CIRT was used according to radio-resistant histology (i.e.sarcoma, melanoma, salivary gland) or in high-risk clinical situations (example: early in field recurrence after high dose RT). Indication, dose prescription, and OARs constraints were determined in consideration of the available published data.

Materials and Methods In 44 cases we elected the moderately hypofractionated “German approach” with 3 Gy RBE per fraction delivered at 5 fractions per week. In the majority of pts those were H&N tumors treated with photons/protons elective nodal RT to 50/54 Gy RBE followed by carbon boost to 21-24 Gy RBE, skull base chordomas and chondrosarcomas treated with exclusive CIRT to 60-66 Gy RBE and re-irradiation at high risk of toxicity. In 288 patients we followed the “Japanese approach” with 4 fractions per week and higher doses per fraction. Those were B&STS (total dose 70.4-76.8 Gy RBE at 4.4-4.8 Gy RBE per fraction), H&N (total dose 65.6-68.8 Gy RBE at 4.1-4.3 Gy RBE per fraction) or prostate cancer (total dose 57.6 Gy RBE at 4.8 Gy RBE per fraction). Results A detailed subgroup analysis of this overall heterogeneous group of 350 patients will be presented. All clinical outcomes data were prospectively collected by enrollment of patients in either our prospective registry study (342/350 pts.) or participation in the international SACRO trial (8/350 pts). Two-year actuarial local control rates in 2 more homogenous disease groups were 89% for sacral chordomas and 80% for H&N mucosal melanoma ( fig 2). All outcomes data analyzed thus far are in accordance with best data published elsewhere. Severe toxicity was very limited with 7/350 pts. with G3 events – 6/7 occurring in the re-irradiation group (114 pts.). There was 1 G5 event with death due to pericardial effusion in a patient with recurrent sarcoma and evidence of infiltration of the pericardium prior to start of CIRT. 18 patients were treated with an innovative concept of hypo-fractionated partial tumor irradiation with sparing of the peri-tumoral immune microenvironment in the attempt to elicit an antitumor immune response. This concept is now being tested in a prospective trial.

Conclusion

Since 1 year beside the RBE LEM model which is used for dose prescription optimization and reporting, every plan is also recomputed with the alternative mMKM RBE model. To our knowledge, we are the first center that routinely uses multiple RBE models in a clinical setting.

PO-1098 ElectronFlash with triode-gun: an innovative device for the research on Flash radiotherapy

F. di martino 1 , D. del sarto 2 , J. pensavalle 2 , M. montefiori 3 , L. masturzo 2 , F. romano 4 , G. milluzzo 4 , M. marrale 5 , M.C. d'oca 5 , A. gonnelli 6 , N. giannini 6 , G. gadducci 6 , S. ursino 6 , F. paiar 6 , S. capaccioli 3 , L. giuliano 7 , M. marinelli 8 , G. verona rinati 9