ESTRO 2022 - Abstract Book

S1167

Abstract book

ESTRO 2022

adaptive fraction, a comparative non-adaptive equivalent was generated from the pre-treatment reference plan. Acute toxicity was then assessed at three months following completion of treatment with EORTC Toxicity Criteria. Results A total of 313 fractions were clinically delivered to 9 patients. Pre-treatment reference plans met all CTV and OAR criteria. CTV coverage criteria of D98%>70Gy was met in 85.2% of MRgART fractions compared to 41.54% of non-adaptive fractions. Bladder V50Gy<50% was met in 85.16% of MRgART fractions compared to 76.18% for non-adaptive plans. Rectum V40Gy<60% was met in 98.13% of MRgART fractions compared to 85.78% of non-adaptive fractions. 3-month EORTC genitourinary and gastrointestinal acute toxicity was absent in most patients, and mild-to-moderate in a minority of patients (Grade 2 GI toxicity in 1 patient and Grade 1 GU toxicity in 1 patient). Conclusion Daily MRgART treatment consistently met planning criteria more often than non-adaptive comparison. Target volume variability in prostate bed treatment can be mitigated by using MRgART and delivers satisfactory coverage of CTV whilst minimising dose to adjacent OARs and reducing toxicity. 1 Seoul National University Hospital , Radiation Oncology , Seoul, Korea Republic of; 2 Seoul National University Bundang Hospital , Nuclear Medicine, Seongnam, Korea Republic of; 3 Seoul National University Bundang Hospital , Urology, Seongnam, Korea Republic of; 4 Seoul National University Bundang Hospital , Radiation Oncology , Seongnam, Korea Republic of Purpose or Objective The optimal condition for clinical application of 18F-fluorocholine Positron Emission Tomography–Computed Tomography (FCH-PET/CT) to detect recurrence sites in prostate specific antigen (PSA) failure remains unclear due to the heterogeneity of prostate cancer PSA failure. We aimed to evaluate the detection rate of FCH-PET/CT in prostate cancer patients with PSA failure and determine the optimal PSA level to take FCH-PET/CT. Materials and Methods FCH-PET/CT was conducted in 89 patients diagnosed with PSA failure after radical treatment (radical prostatectomy in 75 and definitive radiotherapy in 14) between November 2018 and May 2021. Detection rates were examined by receiver operating characteristic (ROC) analysis and multivariable logistic regression was performed to identify factors affecting the positive findings on FCH-PET/CT. We also did subgroup analyses according to the response after the radical treatment; persistent high PSA (N=48) and biochemical recurrence (BCR) (N=41). Results Of all patients, FDG-PET/CT demonstrated 59.6% of overall detection rates and the optimal PSA threshold for detecting positive findings was ≥ 1.00 ng/ml at the time of imaging. On multivariable analysis, PSA higher than 1.00 ng/ml (P<0.001) was a significant factor to affect detection rates on FCH-PET/CT, especially to find positive findings of distant bone metastases (P<0.001) and recurrence outside the pelvis (P<0.001). In a subgroup analysis of patients with BCR after initial radical treatment, the area under ROC curve was 0.82 and the PSA level of 1.75 ng/ml or higher was the optimal value for positive FDG-PET/CT findings. This PSA value also was correlated with significantly higher distant bone metastases and outside pelvis metastasis detection rates (P<0.001, both respectively). Conclusion FCH-PET/CT is a clinically useful tool for detecting tumor recurrence sites in prostate cancer patients with PSA failure if PSA has exceeded a certain value at the time of imaging. In particular, higher AUC values were observed when FCH-PET/CT was performed in patients with BCR after initial treatment. O. Muñoz Muñoz 1 , A.M. Burgueño Caballero 2 , E. Gomis Selles 3 , P. Cabrera Roldan 3 , D.M. Muñoz Carmona 4 , B.D. Delgado León 3 1 Hospital Universitario Virgen del Rocio , Oncology Radiation Therapy, Seville, Spain; 2 Hospital Universitario Virgen del Rocio, Oncology Radiation Therapy , Sevilla, Spain; 3 Hospital Universitario Virgen del Rocio, Oncology Radiation Therapy, Sevilla, Spain; 4 Hospital Universitario Virgen del Rocio , Oncology Radiation Therapy, Sevilla, Spain Purpose or Objective High dose (HD) radiotherapy (RT), with radical intent, is used more and more in prostate cancer (PCa) oligometastatic patients (pts) with good outcomes and low toxicity profile. This retrospective study evaluated at the tolerability and outcomes of stereotactic body radiation therapy (SBRT) in patients with oligometastatic PCa treated in our center. Materials and Methods Pts with 1-2 bone or 1-5 lymph node metastases, treated with radical doses, were considered for this analysis. Between October 2017 to May 2021, 37 patients with oligometastatic PCa were treated in our institute. RT was delivered with helical PO-1375 Detection of recurrence sites using FCH PET/CT in prostate cancer patients with PSA failure D. Kim 1 , W. Lee 2 , S. Byun 3 , J. Kim 4 PO-1376 The role of Stereotactic Body Radiation Therapy in Oligometastatic Prostate Cancer