ESTRO 2023 - Abstract Book

S1186

Digital Posters

ESTRO 2023

Conclusion To our knowledge, this is the first prospective study reporting the clinical outcomes of MRgSBRT for OMPC on a 1.5T MR LINAC. MRgSBRT was feasible, safe and well tolerated for both primary and metastases synchronously in OMPC pts. The encouraging preliminary clinical outcomes and low toxicities support further exploration of MRgSBRT for OMPC in clinical trials.

PO-1464 Novel treatment approach for inoperable bladder cancer: 1.5 Tesla MRI-guided online adaptive SBRT

G. Yavas 1 , C. Yavas 2 , E. Efe 2 , G. Arslan 2 , C. Onal 2,3

1 Ba ş kent University, Radition Oncology, Ankara, Turkey; 2 Ba ş kent University, Radiation Oncology, Ankara, Turkey; 3 Ba ş kent University, Adana Dr. Turgut Noyan Research and Treatment Center, Radiation Oncology, Adana, Turkey Purpose or Objective The purpose of this study was to report our initial experience with 1.5 T MRI-guided online adaptive stereotactic body radiotherapy (MRgRT) in patients with inoperable bladder cancer treated with definitive intent Materials and Methods Seven patients with inoperable muscle-invasive bladder cancer (MIBC) treated with 1.5T MRI-g-OA-SBRT (Unity® MR Linac System, Elekta AB, Stockholm, Sweden) were retrospectively evaluated. The treatment details and preliminary treatment outcomes were reported. Additionally the toxicity rates were reported Results The patients' median age was 86 years (range, 69-89 years). Except for the patient who received salvage second-course irradiation, the patients received 36 Gy in 6 fractions (30 Gy in 5 fractions). The median duration of follow-up was 14 months (range: 3-20 months). The average treatment time, including planning and delivery, was 46 minutes (range, 33-76 minutes). Only two of the patients were able to receive systemic treatment, while others were unable to do so due to co morbidities. Three months after treatment, there were three complete responses (CR), two partial responses (PR), and one progressive disease (PD). One patient who had CR after treatment died four months later from Covid-19 infection. One of the PR patients who could not receive systemic treatment died as a result of disease progression. All patients completed their MRgRT treatments on time, and the treatment was well tolerated, with no grade 2 or higher acute gastrointestinal or genitourinary system toxicities. Conclusion We demonstrated that the treatment of inoperable MIBC patients with MRgRT is both safe and efficacious, with reduced toxicity rates. Due to its high resolution, the 1.5-Tesla MR-LINAC allows for the modification of treatment planning and dose distribution in relation to bladder filling and the patient's daily anatomy. To better report treatment outcomes, survival rates, and late toxicity, however, a longer follow-up period is required.

PO-1465 5-year survival and toxicity results of SIB radiotherapy in (very) high-risk prostate cancer

I. Masson 1 , C. Guerin-Charbonnel 2 , D. Azria 3 , P. Pommier 4 , N. Mesgouez-Nebout 5 , P. Giraud 6 , D. Peiffert 7 , B. Chauvet 8 , P. Dudouet 9 , N. Salem 10 , G. Noel 11 , J. Khalifa 12 , I. Latorzeff 13 , M.A. Mahé 14 , S. Supiot 15 1 Institut de Cancérologie de l’Ouest René Gauducheau, Radiotherapy, Nantes , France; 2 Institut de Cancérologie de l'Ouest René Gauducheau, Clinical Trial Sponsor Unit/Biometry, Nantes, France; 3 Institut Régional du Cancer Montpellier (ICM), Fédération Universitaire d’Oncologie Radiothérapie (FOROM), Montpellier, France; 4 Léon Bérard Center, Radiotherapy, Lyon, France; 5 Institut de Cancérologie de l’Ouest Paul Papin, Radiotherapy, Angers, France; 6 Georges Pompidou European Hospital, Radiotherapy, Paris, France; 7 Lorraine Cancer Institute, Radiotherapy, Vandœuvre-lès-Nancy, France; 8 Sainte