ESTRO 2022 - Abstract Book

S1203

Abstract book

ESTRO 2022

Conclusion A dose response was observed by HAS injection: highest volumes of HAS dissolute most swiftly. A ratio of HA:HAS of 1:2 has already a decrease of half of volume on the second day. This is of special interest while using the HA in clinical practice when wrongly positioned, and dissolution is urgently needed.

PO-1419 Early Outcomes with Linac-based Dose-escalated Prostate SBRT and Real-Time Electromagnetic Tracking

R. Lucchini 1,2 , D. Panizza 3 , R.R. Colciago 1,2 , P. Caricato 4 , V. Faccenda 4 , S. Arcangeli 5,2

1 University of Milan Bicocca, School of Medicine and Surgery, Milan, Italy; 2 ASST Monza, Radiation Oncology Department, Monza, Italy; 3 ASST Monza, Monza, Medical Physics Department, Monza, Italy; 4 ASST Monza, Medical Physics Department, Monza, Italy; 5 University of Milan Bicocca, School of Medicine and Surgery, Monza, Italy Purpose or Objective To investigate treatment outcomes and compliance in patients with organ-confined prostate cancer treated with dose- intensified Linac-based SBRT using a novel electromagnetic transmitter-based tracking system to account for intra- fractional organ motion Materials and Methods Thirteen patients with intermediate unfavorable (70%) and selected high-risk prostate cancer (30%) underwent dose- escalated SBRT in 4 or 5 fractions (BED 1.5 = 279 Gy and 253 Gy, respectively). ADT was prescribed concomitantly, as per standard of care. The VMAT treatment consisted in two 6FFF or 10FFF arcs optimized to have the 95% isodose covering at least 95% of the PTV (2 mm isotropic expansion of the CTV). The beam delivery was interrupted whenever the real time tracking registered a displacement that exceeded 2 mm to promptly correct the prostate motion. The incidence of treatment-related genitourinary (GU) and gastrointestinal (GI) toxicity, patient QOL, and IPSS scores were computed from the start of treatment to the last follow-up date. Results All patients (median age 77 years) completed the treatment in the expected time and their compliance to the procedure was excellent. At a median follow up 6 months, only one patient developed a G2 acute rectal toxicity. No other acute nor late Grade 2 or higher GI (rectal) and GU side effects were observed. EPIC-26 scores in the urinary domain decreased from a median baseline of 86 pre-treatment to 79 at one-month, and returned to baseline at a later timepoint (median score of 85 at 6 months). The same features for EPIC-26 scores in the bowel domains were 92, 80 and 91, respectively. The median IPSS increased from 8 at baseline to 12 one-month after treatment, and settled to 6 thereafter. Conclusion Our preliminary findings show that Linac-based Dose-intensified SBRT for unfavorable prostate tumors does not come at the cost of an increased toxicity, provided that a reliable technique for real time prostate monitoring is ensured. These observations need to be confirmed on a larger scale and a longer follow up. F. Teunissen 1 , J. de Boer 1 , W. Eppinga 1 , E. de Groot-van Breugel 1 , J. Hes 1 , J. van der Velden 1 , R. Wortel 2 , J. van der Voort van Zyp 1 1 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands; 2 University Medical Center Utrecht, Urology, Utrecht, The Netherlands Purpose or Objective The ERECT-trial is a single-arm study assessing the effect of neurovascular sparing on erectile function in 5 x 7.25 Gy magnetic resonance-guided adaptive radiotherapy (MRgRT) for intermediate-risk localized prostate cancer (PCa). The 1.5T MR-linac used in our study allows for daily recontouring and plan optimization for all relevant structures (adapt to shape workflow, or ATS). The quality of the obtained MR scans allows for visualization of the neurovascular structures, in contrast to cone-beam CT. This study aims to assess the dosimetric difference for the neurovascular bundle (NVB) and internal pudendal artery (IPA) between an ATS approach and a rigid translation workflow (adapt to position, or ATP) similar to a couch shift. Materials and Methods The first 5 trial patients completed treatment and were included in this study. Per patient 1 offline pre-treatment plan and 5 online pre-treatment ATS plans of each fraction were available. To simulate an ATP workflow, we matched the daily online MRI with the offline planning MRI. Subsequently, the daily adjusted ATS contours of the NVB and IPA were rigidly propagated onto the offline pre-treatment plan, to simulate the planned dose that would have been delivered to the NVB and IPA in an ATP setting. Planned ATS and simulated planned ATP mean D0.1cc were compared using paired T-tests. Results The NVB was spared bilaterally for 1 patient and unilaterally for 4 patients. The IPA was spared bilaterally for all patients. The mean D0.1cc for the spared NVBs was significantly lower in the ATS plans compared to the simulated ATP plans (32.90 Gy vs. 33.51 Gy; p < 0.001) (Fig. 1). The mean D0.1cc for the spared IPAs was not significantly different (16.63 Gy vs. 17.60 PO-1420 Better neurovascular sparing by daily contouring and plan optimization in MRgRT for prostate cancer