Session Item

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.

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.

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. Treatment was generally well tolerated. PROMs showed that SMART has high level of patients satisfaction and grade 2 and above toxicities are relatively low.

Our experience indicates that SMART is a safe and well tolerated system for delivery of SBRT in localised prostate cancer.