ESTRO 2020 Abstract book

S706 ESTRO 2020

was reported, using a questionary in telephone consultation, at 4 and 8 weeks after treatment. Treatment outcome was scored as a benefit when patients reported positive on the question if radiotherapy of the whole brain did relieve their complaints.

Minimum doses to PTV (D98%) are inferior with a single field (p<0.005) and prescription dose was only achieved to D50% in 2 out of 15 cases. Maximum doses in the PTV (D2%) were greater (p<0.005), escalating up to 140% of the prescription dose in normal tissues.

Conclusion Retrospective analysis suggests a single posterior field may not deliver the prescribed dose for vertebral metastases palliation. Furthermore, this technique leads to an inadequate dose distribution due to compromise between target coverage and overdosing proximal and distal normal tissues. Improved IGRT will now facilitate and justify tighter margins and smaller treatment fields. Adoption of complex planning and delivery methods, for palliative treatments has been slow within the radiation oncology community. We propose using semi-automated contouring tools and simple optimisation as a feasible treatment option to deliver superior dose distributions and enable faster treatment delivery. Ongoing work will compare delivered dose to retreatment rates and associated toxicities in a larger cohort of patients. PO-1251 Whole brain radiotherapy: to treat or not to treat? L. Otto-Vollaard 1 , S. Quint 2 , I. De Pree 2 , I. Steinvoort 3 , O. Tims 2 , J.J. Nuyttens 2 1 ErasmusMC, Radiotherapy, Rotterdam, The Netherlands ; 2 Erasmus MC, Radiotherapy, Rotterdam, The Netherlands ; 3 Erasmus MC, Radioltherapy, Rotterdam, The Netherlands Purpose or Objective To determine overall survival and prognostic factors for patients with brain metastases treated with whole brain radiotherapy (WBRT) in a prospective cohort. Material and Methods From september 2015 until march 2019, 162 patients were treated with WBRT with a dose of 5x4 Gy using a plan- parallel technique. The target volume included the whole brain (109 patients), and whole brain with an extension to C2 for patients with leptomeningeal metastases (53 patients). The patient characteristics are listed in table 1. The median follow up was 2 months. Treatment outcome

Results Forty-three patients died within 2 months (27%). Fifty- eight of the remaining 119 patients (48.7%) did report to have benefit of the treatment. Patients who were alive after 2 months and did benefit from treatment had a median survival of 8.1 months compared to 2.9 months for patients who reported no benefit. The median overall survival was 3.5 months (range 0.3-41.8). On univariate analysis of the whole patient population (Cox regression) the following parameters were significant: dose dexamethasone prior to WBRT (Hazard Ratio (HR): 0.628), Karnofsky score (HR: 1.509) and treatment options after