ESTRO 2023 - Abstract Book

S1251

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ESTRO 2023

Hypofractionated radiotherapy caused a decline of most functions and worsening of symptoms, which mainly recovered to the baseline 3 months after RT and remained stable at 1 and 2 year at follow-up.

PO-1540 1.5T MR-guided daily-adapted SBRT on lymphnode oligometastases from prostate cancer

L. Nicosia 1 , G. Trapani 1 , M. Rigo 1 , M. Fiorini 1 , N. Giaj-Levra 1 , R. Mazzola 2 , E. Pastorello 3 , F. Ricchetti 1 , F. Cuccia 1 , V. Figlia 1 , R. Ruggieri 1 , F. Alongi 1 1 IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center, Advanced Radiation Oncology Department, Negrar, Italy; 2 IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center,, Advanced Radiation Oncology Department, Negrar, Italy; 3 IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center, Advanced Radiation Oncology Department, Negrar, Italy Purpose or Objective Lymphnode metastases are a particular site of prostate cancer (PCa) oligometastatic disease amenable of metastases directed therapy (MDT) and might identify a less severe degree of metastatic PCa. Despite image-guided radiotherapy significantly increased treatment accuracy, there might be some dosimetrical and imaging limitations when lesions are small or close organs at risk or vessels. Moreover, standard radiotherapy on conventional linac don’t allow clinicians to modify treatment plans in case of lesions displacement of when OARs (i.e. bowel loops) fall within the treatment field, as it may occur for abdominal targets. The aim of our study was to evaluate the efficacy and toxicity of a daily-adaptive MR guided SBRT on 1.5 T MR-linac in patients affected by lymphnode oligometastases from PCa. Materials and Methods The present study is a prospective observational study conducted in a single Institution (protocol n°: MRI / LINAC n. 23748). Patients with oligometastatic lymphnodes from PCa treated with daily-adaptive MR-guided SBRT on 1.5T MR-linac were included in the study. Minimum required follow-up of 3 months after SBRT. Primary end-point was local progression-free survival (LPFS). Secondary end-points were: nodal progression-free survival (NPFS), and progression-free survival (PFS), and toxicity. Results 118 lymphnode oligometastases from PCa were treated with daily-adaptive 1.5T MR-guided SBRT in 63 oligometastatic patients. 63.5% patients were oligoprogressive and 36.5% oligoprogressive. Two-year LPFS was 94.5%. Median NPFS was 22.3 months, and the 2-year NPFS was 46.5%. Having received hormone therapy before SBRT was correlated with lower NPFS at the multivariate analysis (1-y NPFS 87.1% versus 42.8%; p= 0.002 - HR 0.199, 95% CI 0.073-0.549). Furthermore, the oligorecurrent state during ADT was correlated with a lower NPFS than the oligoprogressive state. Median PFS was 10.3 months, the 2-year PFS was 32.4%. Patients treated with hormone therapy before SBRT had a significantly lower 1-year PFS the others (28% versus 70.4%; p= 0.01 - HR 0.259, 95% CI 0.117-0.574). No acute and late toxicities occurred during treatment. Conclusion The present is the largest prospective study of 1.5T lymphnode SBRT on MR-linac in patients with PCa. Lymphnode SBRT by 1.5T MR-linac provides high local control rates with an excellent toxicity profile. Treatment margin reduction seems not affecting local control and could be further explored. 1 Genesiscare UK, Radiation Oncology, Oxford, United Kingdom; 2 Genesiscare UK, Radiatiin Oncology, Oxford, United Kingdom Purpose or Objective Stereotactic MR-guided online adaptive radiotherapy (SMART) enables visualisation of inter-fractional changes of the clinical target volume (CTV) and nearby organs at risk (OARs) which leads to smaller planning target volume (PTV) margins, and finally the option to perform daily plan re-optimization. Materials and Methods A total of 180 patients (900 factions) with localised prostate cancer were treated with SMART since December 2019. Patients identified for treatment with SMART were assessed for eligibility against robust institutional criteria.SMART consisted of MR- and computed tomography (CT) simulation scan, inverse intensity-modulated radiotherapy (IMRT) treatment planning and daily plan re-optimization prior to treatment delivery with editing CTVs( as per daily variation) and OAR recontouring within the first 3 cm outside the PTV. Patient experiences with SMART were assessed using a patient-reported outcome questionnaire (PROMs) after completion of treatment. Results Patients were simulated on the MRIdian Linear accelerator to perform a 3-minute trueFISP MRI series. Fractional verification imaging was completed with the same image series that was used for simulations. Viewray software was used for both treatment planning and treatment delivery. A beam template of 21 beams of field-in-field intensity modulated radiotherapy (IMRT) with 60 to 80 segments was used for treatment delivery. After plan adaptation, the use of 2D-cine-MRI showed that 20% patients required an imaging correction due to the patient releasing gas or a 2D image shift during their radiotherapy course. Average duration of treatment was 44 minutes. PO-1541 Stereotactic MRguided adaptive radiotherapy in prostate cancer:Real life experience of 180 patients P. das 1 , C. Perna 2 , N. Dallas 2 , D. Ford 2 , A. Sabharwal 1 , P. Camilleri 1