ESTRO 2020 Abstract Book

S658 ESTRO 2020

irradiation for bone metastases of breast cancer. It is most in demand at treatment of HER2-positive patients. PO-1250 Palliation of vertebral metastases and cord compressions: single field or VMAT? N. West 1 , R.A. Pearson 1 , A. Hashmi 1 , X. Jiang 1 , A. Ogilvie 1 , T. Simmons 1 1 Newcastle upon Tyne Hospitals Trust, Northern Centre for Cancer Care, Newcastle upon Tyne, United Kingdom Purpose or Objective In spite of advances in treatment planning and delivery, radiotherapy techniques for palliation of vertebral bone metastases or metastatic spinal cord compression have not evolved. Modern, more sophisticated VMAT approaches are often deemed unfeasible for this cohort of patients due to contouring and planning burdens. With more effective therapies, patients are living longer and the risk of retreatment is higher. We propose, and dosimetrically evaluate a pragmatic, semi-automated technique to treat vertebral metastases with VMAT. Material and Methods Fifteen cases (n=11 patients) who received radiotherapy to vertebral metastases for pain (n=11) or cord compression (n=4) between 2010 and 2018 were randomly selected for the study. Primary sites included lung (n=6), prostate (n=4) and breast (n=1). Target vertebra determined by patient’s history and CT/MRI imaging of the spine; with a single posterior field defined to encompass the target and a margin of one to two vertebral bodies above and below, prescribing dose at target depth as is convention (SCORAD III Clinical Trial). For the study, a new VMAT plan was generated for each case. Clinicians defined target vertebrae according to diagnostic information and original treatment intent using an automated technique with manual editing to generate a pseudo CTV, growing to a PTV (isotropic 1.5cm for the single field plan and 1.0cm for the VMAT plan). The previously delivered single field plan was recalculated and a VMAT plan generated. Treatment delivery times were calculated for both plans. Results Dosimetric differences between a single posterior field and a VMAT plan are displayed in Figure 1 and analysed in Table 1.

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 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.