ESTRO 2022 - Abstract Book

S1208

Abstract book

ESTRO 2022

Our model provided a promising performance in fitting and forecasting post-EBRT PSA values. We identified three model- based metrics enabling an early detection of tumor recurrence with respect to standard practice, and whose definition emanates from the mechanisms of PCa response to EBRT in our model. In the future, we plan to validate our model and metrics in larger cohorts with a higher proportion of tumor recurrences.

PO-1424 SBRT for clinically localized prostate cancer in men with hip replacements: a cautionary note

D. Conroy 1 , A. Pepin 2 , H. Tsou 1 , H. Rashid 1 , M. Ayoob 1 , M. Danner 1 , T. Yung 1 , B. Collins 1 , P. Krishnan 3 , S. Lei 1 , S. Suy 1 , S. Kataria 4 , N. Aghdam 5 , S. Collins 1 1 MedStar Georgetown University Hospital, Radiation Medicine, Washington, DC, USA; 2 University of Pennsylvania, Radiation Medicine, Philadelphia, PA, USA; 3 MedStar Georgetown University Hospital, Radiology, Washington, DC, USA; 4 Virginia Hospital Center, Radiation Medicine, Arlington, VA, USA; 5 Beth Israel Deaconess Medical Center, Radiation Medicine, Boston, MA, USA Purpose or Objective SBRT has been established as a safe and effective treatment for prostate cancer. SBRT requires high accuracy to reduce treatment margins. Metal hip prostheses create image artifacts, distorting pelvic imaging and potentially decreasing the accuracy of target/organ at risk identification and radiation dose calculations. Data on the safety and efficacy of SBRT after hip replacement is limited. This single-institution study sought to evaluate the safety and local control following SBRT for prostate cancer in men with hip replacements. Materials and Methods Twenty-four patients with localized prostate cancer and a history of pre-treatment hip replacement, treated with SBRT from 2007-2017 at MedStar Georgetown University Hospital, were included in this retrospective analysis. Minimum follow- up was three years. Treatment was delivered using the CyberKnife with doses of 35-36.25 Gy in 5 fractions. The target and OARs were identified and contoured by a single experienced Radiation Oncologist. In treatment planning, care was taken to avoid treatment beams that directly traversed the hip replacement(s). Toxicities were recorded and scored using the Common Terminology Criteria for Adverse Events version 4.0. Local recurrence was confirmed by magnetic resonance imaging and/or prostate biopsy. Results The median follow-up was 8 years. The patients were elderly (Median age = 71.5 years) with a high rate of comorbidities (Carlson Comorbidity Index > 2 in 25%). Four patients had bilateral hip replacements. The majority were low to intermediate risk (91.7%) according to the D’Amico classification. Median pre-treatment PSA was 6.3 ng/mL. 12.5% received upfront ADT. Ten were treated with 35 Gy and 14 were treated with 36.25 Gy. The rates of late > Grade 3 GU toxicity and late > Grade 2 GI toxicity were 8.3% and 4.2%, respectively, with no Grade 4 or 5 toxicities. Six patients (25%) developed a local recurrence at a median time of 7.5 years. Of these six patients, four had unilateral hip replacements and two had bilateral. Three underwent salvage cryotherapy and three received salvage ADT. Conclusion Local recurrence and high-grade late toxicity are uncommon following prostate SBRT in the general population. However, in this cohort of patients with prior hip replacements, prostate SBRT had higher than expected rates of both. In the opinion of the authors, such patients should be counseled on these elevated risks and treatment alternatives. Brachytherapy, with its ultrasound guidance, circumvents CT image artifact interference, while moderately-hypofractionated/conventionally- fractionated IMRT utilizes larger treatment margins and is therefore less susceptible to target miss. Both represent preferable radiation options in this patient population. If these patients are treated with SBRT, they should be monitored for local recurrence so early salvage can be performed. It is hoped that recent advances in metal artifact reduction techniques and dose-calculation algorithms will improve future outcomes.

PO-1425 SBRT in patients with oligometastatic renal cell carcinoma: A multi-institutional analysis

O.C. Guler 1 , P. Hurmuz 2 , G. Ozyigit 2 , C. Onal 1

1 Baskent University, Radiation Oncology, Adana, Turkey; 2 Hacettepe University, Radiation Oncology, Ankara, Turkey

Purpose or Objective To investigate the effects of stereotactic body radiotherapy (SBRT) on local control or survival in oligometastatic renal cell cancer (RCC) patients in the era of immunotherapy. Materials and Methods A total of 33 patients and 63 lesions treated between March 2013 and October 2020. Twenty patients (60.6%) had de novo oligometastasis and 11 patients (33.4%) had oligoprogression during treatment or follow-up. Only patients with bone metastasis included this retrospective study with the aim of homogenous group. The diagnosis of metastasis was based on imaging studies. Histopathological verification was not mandatory. The local control (LC), overall survival (OS), and progression-free survival (PFS) rates were calculated using Kaplan-Meier analyses.

Results