ESTRO 2022 - Abstract Book

S1247

Abstract book

ESTRO 2022

Materials and Methods A retrospective review of patients treated with LTR from January 2019 to June 2021 has been analyzed. Patients and treatment characteristics are shown on table 1. VMAT plans were employed in all cases and treatments were guided by CBCT on each fraction. RTOG scales of toxicity have been employed. Results 12 patients with median age of 50 years (42 to 81) were found to receive LTR. The tumor volume ranged from 310cc to 2511cc with a median of 5 lattice vertices (2 to 13) placed within the GTV representing a median of 0,8% of its volume. Lung tumor was the most frequent site (41,6%). 3 patients received a total dose (EQD2) >60Gy. Image evaluation post LRT was performed in 5 patients, showing volume reduction in all cases. With a median follow up of 3 months (2 to 27) no mortality or toxicity Grade 2-3 related to LTR was found. Conclusion LTR appears to be a safe modality to treat bulky tumors without significant morbidity directly related to RT treatment. Further develop of treatment protocols to standardize LTR are required. M. Loi 1 , I. Bonucci 2 , L. Masi 2 , R. Doro 3 , G. Francolini 1 , V. Di Cataldo 3 , P. Bonomo 1 , L. Visani 3 , M. Tempobono 3 , N. Bellosi 3 , S. Pazzaglini 3 , M. Cassinelli 3 , G. Simontacchi 1 , D. Greto 1 , I. Desideri 4 , S. Lucidi 4 , M. Aquilano 4 , L. Livi 4 1 Azienda Ospedaliero-Universitaria Careggi, Radiation Oncology, Florence, Italy; 2 Istituto Fiorentino di Cura e Assistenza (IFCA) , Radiation Oncology, Florence, Italy; 3 Istituto Fiorentino di Cura e Assistenza (IFCA), Radiation Oncology, Florence, Italy; 4 University of Florence, Radiation Oncology, Florence, Italy Purpose or Objective Robotic Stereotactic Body Radiotherapy (SBRT) employs radiopaque fiducial markers implanted near the tumor for real- time tracking. Fiducials are usually placed before simulation in a dedicated interventional radiology platform. This represents a limitation to treatment availability and may result in potential treatment delay. In our Institution, an in-house percutaneous CT-guided fiducial placement procedure was implemented for pelvic SBRT. The aim of our study is to evaluate the performance and side effects of in-house fiducial placement. Materials and Methods Patients underwent percutaneous fiducial insertion with a 18 G needle under CT guidance, using a radiopaque skin marker to calculate the depth of target location from body surface (Figure 1). Careful skin asepsis and local anaesthesia was obtained at the insertion site. A >2 cm spacing between fiducials was advised. One week after placement, simulation CT and orthogonal X-ray imaging were acquired to verify fiducial usability for SBRT tracking. Data from a consecutive cohort of patients treated with fiducial-guided, robotic-arm pelvic SBRT were collected from January 2018 to September 2021. Success rate was defined as the implanted/tracked fiducials ratio. Kruskal Wallis-test was used to compare median success rate over time. PO-1469 CT-GUIDED FIDUCIAL PLACEMENT FOR ROBOTIC STEREOTACTIC BODY RADIOTHERAPY: EFFICACY AND SAFETY

Results In the observed time frame, 282 patients underwent CT-guided fiducial placement, accounting for 883 implanted fiducials (median 3, range 1-4). Target sites were the prostate bed, extra-spinal bones and pelvic lymph nodes in 158 (56%), 37 (13%) and 87 (31%) patients, respectively. Side effects consisted of minor bleeding at the insertion site and transient pain requiring medication after 24 hours in 5 patients (2%). No grade >2 toxicity was observed, particularly infectious or haemorrhagic complications. Overall success rate was 86% (719/833); median success rate per procedure was 100% (range 50-100%). Among the 114 fiducials rejected for tracking, failure was due to migration in 63 cases (55%) and misplacement in 51 cases (45%). In the subset of patients receiving ≥ 3 fiducials (n=161), at least 3 fiducials were used for tracking in 80% (n=129) of patients. Overall success rate increased across the observed time window from 2018 (53/73, 74%) to 2019 (245/293, 84%) to 2020 (246/272, 90%) to 2021 (175/195, 90%) (Figure 2). A consistent, statistically significant improvement in median success rate was observed over time from 2018 (75%, Interquartile Range, IQR 67-100%) to 2019 (100%, IQR 75-100%) to 2020 (100%, IQR 75-100%) to 2021 (100%, IQR 100-100%) : p= 0.0008.

Conclusion