ESTRO 2023 - Abstract Book

S1204

Digital Posters

ESTRO 2023

Since October 2019, 1.5T MR-linac has been available in our department. A prospective observational study for the clinical use of MR-linac is currently ongoing in our department: patients affected by prostate adenocarcinoma, pancreatic cancer, oligometastases and patients requiring retreatments were included. Two different workflow were used depending on the OARs daily anatomy: Adapt To Position (ATP) where the reference plan position is adjusted rigidly to match the position of the targets and OARs, and Adapt To Shape (ATS) where a new plan is created to better match the anatomy of the day. Toxicity and quality of life were assessed at baseline and after treatment using the CTCAE v5.0. Patient-reported outcomes of prostate cancer patients were investigated by means IPSS, ICIQ-SF, IIEF-5, EPIC-26, EORTC-QLQ-C30 and PR-25 questionnaires. Results Between October 2019 and June 2022, 590 patients with 675 target sites were treated with MR-guided radiation therapy in 5000 total fractions. Median patient age was 70 years (39–86). Among 675 tumor sites, the most frequently treated region was pelvis (n=549, 81%). The most common diagnosis was prostate cancer (n=326). On–table adaptive radiation therapy was used at every treatment session: ATP workflow in 63 fractions (1%) and ATS workflow in 4937 fractions (99%), respectively. Median prescribed dose was 35 Gy (20–67.5 Gy) in median 5 fractions (5–30). Mean total treatment time was 43 minutes (20–56). Treatments were well-tolerated and no acute G>3 toxicities were reported. Concerning the PROMS, all questionnaires showed no relevant deterioration between the pre-, post-RT and follow-up evaluations. Conclusion MR-guided radiation treatment using 1.5T MR-linac has been successfully implemented into clinical routine at our department. The data reported support an optimal profile of tolerability of daily on-table adaptive radiation therapy in acceptable time slots. These results are confirmed by PROMs. Purpose or Objective The prostate bed is a virtual region in the close proximity to the rectum and the bladder. The volume of these organs can significantly change daily during the treatments. Thus, real time adaptive radiotherapy by means of 1.5T MR-Linac could be a promising choice in improving toxicity profile. Herein, we reported the evaluation of feasibility and acute toxicity related to postoperative moderately hypofractionated MR-guided adaptive radiotherapy on prostatic bed. Materials and Methods Fifty patients were treated on prostatic bed with daily adaptive radiotherapy by means of 1.5T MR-Linac inside an ethical committee approved protocol (MRI/LINAC n°23,748): 17 patients underwent adjuvant RT (total dose 66 Gy in 30 fractions) and 33 salvage RT (total dose 67.5 Gy in 30 fractions). Daily plan adaption was performed using one of the two workflows: adapt to shape (ATS, using contour adaptation and replanning) or adapt to position (ATP, rigid replanning onto the online anatomy with isocenter correction). Type of workflow, duration of treatments and acute toxicity were analyzed. Patient reported outcomes were investigated by means of IPSS, ICIQ-SF, IIEF-5, EPIC-26, EORTC-QLQ-C30 and PR-25 questionnaires. Results A total of 1500 fractions were successfully delivered on the MR-linac. No interruption occurred during each procedure. Median patient age was 66 years (47-77). In total, ATP was chosen in 97 (6.5%) and ATS in 1403 (93.5%) of fractions. Median total duration of all fractions was 41 (range 27-60) minutes. Acute toxicity (RTOG, CTCAEv5.0 and patient-reported outcomes) at the end of RT was mild with a tendency of recovery to baseline levels at 3 months post RT. No G3+ toxicity was scored. Concerning the PROMS, questionnaires showed only mild deterioration between the pre- and end-RT evaluations, but they fully recovered at first follow-up evaluations after 3 months. Conclusion In our experience daily adaptive post-operative RT on 1.5T MR-Linac appears well tolerated by the patients and achieved low rates of acute toxicity. Further studies are necessary in order to confirm a benefit in terms of long-term toxicity compared to conventional linac. PO-1486 Feasibility and tolerability of MR-guided adaptive RT on prostatic bed:mono-institutional experience M. RIGO 1 , N. Giaj-Levra 1 , R. Mazzola 1 , L. Nicosia 1 , F. Ricchetti 1 , E. Pastorello 1 , P. Ravelli 1 , A. De Simone 1 , D. Gurrera 1 , S. Naccarato 1 , G. Sicignano 1 , R. Ruggieri 1 , F. Alongi 1 1 IRCCS Sacro Cuore Don Calabria Hospital, Advanced Radiation Oncology Department, Negrar di Valpolicella (VR), Italy

PO-1487 Linac-based stereotactic radiotherapy for prostate cancer: preliminary analysis of a phase II trial

M.P. Ciliberti 1 , R. Carbonara 2 , F. Gregucci 2 , A. Surgo 2 , M. Scarcia 3 , M. Caliandro 2 , F.C. Di Guglielmo 2 , E. Paulicelli 4 , G.M. Ludovico 3 , I. Bonaparte 2 , A. Fiorentino 2 1 Generali Regional Hospital "Miulli", Radiation Oncology, Acquaviva delle fonti, Italy; 2 General Regional Hospital "Miulli", Radiation Oncology, Acquaviva delle fonti, Italy; 3 General Regional Hospital "Miulli", Urology, Acquaviva delle fonti, Italy; 4 General Regional Hospital "Miulli", Radiation Oncology, Acquaviva dlele fonti, Italy Purpose or Objective Extreme Hypofractionated Stereotactic Body Radiation Therapy (SBRT) is replacing prostatectomy mostly in case of low risk prostate cancer (PC). However, in some cases of high / intermediate risk disease, it may be considered a justified