Session Item

MedAustron is a dual particle facility capable of delivering spot scanning particle therapy with both protons and carbon ions. From July 2019 to October 2022 350 patients have been treated using CIRT. The most common indications were inoperable bone and soft tissue sarcoma (103 pts), non SCC-H&N tumors (87 pts), re-irradiation (114 pts) and high risk 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.

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).

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.

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.