ESTRO 38 Abstract book

S33 ESTRO 38

Material and Methods All patients treated for adrenal oligo-metastases on the MRIdian system (ViewRay Inc.) at our institution until June 2018 were included. The OAR and GTV’s were contoured on a breath-hold planning MR, and a planning target volume (PTV) was created by adding a 3mm margin to the GTV, but excluding luminal OAR’s (see figure). Relevant high dose OARs were stomach, bowel and ipsilateral kidney. A robust baseline plan was generated for daily adaptation. Our institutional protocol mandates accepting underdosage inside the PTV if deemed necessary to meet high dose OAR constraints (see figure). All patients underwent daily on-table MR-imaging before treatment, and to optimise delivery, a new on-table treatment plan was generated based on the anatomy-of-the-day. Gated SMART was delivered during repeated voluntary video- assisted breath-holds, with continuous tracking of the GTV and using the PTV as gating boundary. We analysed toxicity, local control (LC), disease free- and overall survival (DFS, OS).

Results 180 patients (M/F: 94/86); median age: 67, range 37-88) treated with SBRT for a total of 253 nodal recurrences were analyzed. Patients with different cancer types were included in the analysis, in particular the primary were: gynaecological (N°=49; 27.2%), prostatic (N°=38; 21.1%), gastrointestinal (N°=25; 13.9%), lung (N°=22;12.2%), breast (N°=16; 8.9%), genito-urinary (N°=12; 6.7%), head and neck (N°=11; 6.1%) and skin tumours (N°=7; 3.9%).The most common metastatic sites were the thorax (N°=92; 36.4%) and the pelvis (N°=88; 34.8%), followed by abdominal (N°=61; 24.1%) and neck regions (N°=12; 4.7%).The majority of lesions (79.8%) were treated with VMAT technique, while the former by 3DCRT or IMRT techniques. Dose prescription to the Planning Target Volume varied from 12 Gy/single fraction to 50 Gy/5 fractions. With a median follow-up of 21 months (2-124) no grade 3 acute or late toxicity was recorded. ORR based on CT/MRI/PET was 79.8 % (CI 95%: 73.3-85) with a complete response rate of 57.7% (CI 95%: 50.3-64.5). 24- and 48-months actuarial local control (freedom from progression in the irradiated site) was 81.3% and 69.6%, respectively. Conclusion These data on a large series of lymph node recurrences in oligometastatic patients demonstrate low risk of morbidity after SBRT and favourable long term local control OC-0072 Clinical outcomes of stereotactic MR-guided adaptive radiation therapy for adrenal oligo- metastases P. Cobussen 1 , M.A. Palacios 1 , F.O.B. Spoelstra 1 , I. Bahce 2 , A.M.E. Bruynzeel 1 , S.M.S. Hashemi 2 , A. Becker – Commissaris 2 , N.J. Haasbeek 1 , B.J. Slotman 1 , F.J. Lagerwaard 1 , S. Senan 1 1 VU University Medical Center, Radiation Oncology, Amsterdam, The Netherlands; 2 VU University Medical Center, Pulmonology, Amsterdam, The Netherlands Purpose or Objective Patients presenting with 1-5 distant metastases, so-called oligo-metastases, can have a survival benefit if all lesions are treated using stereotactic ablative radiotherapy (SABR). The delivery of SABR to adrenal metastases can be challenging due to respiration-induced organ motion and proximity of organs at risk (OAR). Consequently, lower radiation doses are often delivered to minimise the risk of toxicity, even though lower doses may be correlated with a worse local control. We implemented stereotactic magnetic resonance-guided adaptive radiation therapy (SMART) for abdominal tumors aiming for a BED 100 Gy 10 , and report on clinical outcomes in adrenal oligo- metastases.

Results Twenty-five patients underwent SMART for an adrenal oligo-metastasis (68% left-sided). Median patient age was 62 years, and the commonest primary tumor was lung cancer (72% NSCLC, 12% SCLC). The majority (64%) received a dose of 50 Gy in 5 fractions, with total doses