ESTRO 2020 Abstract book

S580 ESTRO 2020

Senan 1 1 Amsterdam University Medical Centers VUmc location, Department of Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective Magnetic resonance (MR-)guided stereotactic ablative radiotherapy (SABR) was performed for lung tumor patients in whom treatment delivery was challenging due to pulmonary comorbidity, tumor location or motion. Given the complexity of the stereotactic MR-guided adaptive radiation therapy (SMART) approach, we evaluated early clinical outcomes in this high-risk patient cohort. Material and Methods Fifty consecutive patients (54 lung tumors) underwent SMART between 2016 - 2018 for either a primary lung cancer (n = 29 patients) or for lung metastases (n = 21). Risk-adapted dose fractionation was used to deliver 60 Gy in 8 fractions (n = 28), 55 Gy in 5 fractions (n = 23), 54 Gy in 3 fractions (n = 2), and 60 Gy in 12 fractions (n = 1). All patients had ≥1 factors predisposing to toxicity, including a central tumor location (n = 30 patients), previous thoracic radiotherapy (n = 17), synchronous multiple lung tumors (n = 9), or interstitial lung disease (n = 7). After acquisition of a daily 17-second breath-hold MR scan in treatment position, on-table plan adaptation was performed using the anatomy-of-the-day. Gated SABR delivery was performed during repeated breath-holds under continuous MR-guidance. Local control, overall (OS) and disease-free survival (DFS) were estimated using the Kaplan-Meier method. Results All but one patient completed the planned SMART schedule. With use of daily plan adaptation, a biologically equivalent dose (BED 10Gy ) ≥100Gy to 95% of the planning target volume was delivered in 50 tumors (93%), with prioritized organ at risk sparing in the other cases. Median patient follow-up was 20.9 months (95%CI, 17.2-27.0). Local control, OS and DFS at 12 months were 95.4% (95%CI, 89.4-100.0), 88.0% (95%CI, 79.4-97.5) and 63.5% (95%CI, 51.4-78.5), respectively (Fig. 1). Local failures developed in 2 patients who were re-irradiated for a post-SABR local recurrence of squamous cell carcinoma, and in another 2 patients treated for colorectal metastases. Overall rates of any grade ≥2 and ≥3 toxicity were 32% and 8%, respectively. Commonest toxicities were grade ≥2 radiation pneumonitis (12%) and chest wall pain (8%). No treatment-related deaths were noted.

up are needed to precisely define the benefits of MR- guided SABR in different high-risk subgroups. PO-1003 Preliminary results of SRS for a lung tumor: a single-arm phase 2 study in a single institute T. Yamamoto 1 , N. Kadoya 1 , H. Matsushita 1 , R. Umezawa 1 , K. Ito 1 , Y. Ishikawa 1 , N. Takahashi 1 , Y. Katagiri 1 , K. Takeda 1 , S. Tasaka 1 , Y. Suzuki 1 , K. Kawabata 1 , K. Kishida 1 , S. Teramura 1 , S. Omata 1 , K. Jingu 1 1 Tohoku University Hospital, Radiation Oncology, Sendai, Japan Purpose or Objective Stereotactic radiosurgery (SRS) for a lung tumor with a de- escalated radiation dose compared to that in the RTOG 0915 trial might be beneficial. The strategy of a risk- adapted and de-escalated radiation dose would contribute to the maintenance of a high level of local control and to the prevention of hesitation by radiation oncologists to fully contour the (internal) gross tumor volume. The purpose of this phase 2 study was to demonstrate the efficacy of this strategy. The primary endpoint of this study was irradiated tumor control and the secondary endpoints were overall survival, marginal recurrence and toxicities. Material and Methods Patients who were unfit for surgery or who refused surgery for early stage non-small cell lung cancer or solitary pulmonary oligometastasis was included. The eligible patients fulfilled the following criteria: performance status of 2 or less, forced expiratory volume in 1 second of 700 mL or more, and tumor not located in central or attached to the chest wall. Primary lung tumors with diameters of 3 cm or less were treated with 28 Gy and primary lung tumors with diameters of 3.1-5 cm or pulmonary oligometastasis were treated with 30 Gy. Radiation doses were prescribed to cover 95% of the PTV using VMAT. Results Eighteen patients were enrolled in this study from 2016. Four patients were operable and 14 patients were medically inoperable. The patients included 7 patients with adenocarcinoma, 1 patient with squamous cell carcinoma, 1 patient with oligometastasis and 9 patients with clinical diagnosis. The median tumor diameter was 1.9 cm and median PTV was 27.3 cc. SRS was prescribed at 28 Gy for 15 tumors and 30 Gy for 3 tumors. The median follow-up period was 12.7 months. During follow-up, there was no irradiated tumor failure or marginal recurrence. Disease progression occurred in 2 patients: lymph node metastasis in one patient with lung cancer and liver metastases in one oligometastatic patient. Two patients died: one from primary disease and the other from comorbidity. There was no grade 3 or higher toxicity. Grade 2 radiation pneumonitis occurred in only in 1 patients and Grade 1 chest wall pain occurred in 2 patients. Conclusion SRS with a risk-adapted moderate radiation dose showed excellent local control and minimal toxicity. This strategy would be beneficial, although further enrollment and follow-up are needed. PO-1004 Continuous Positive Airway Pressure (CPAP) use for Motion management in Lung SBRT S. Appel 1 , Z. Symon 1 , Y. Lawrence 1 , J. Goldstein 1 , D. Alezra 1 , M. Ben-Ayun 1 , T. Kushnir 1 , S. Felder 1 , G. Jacobson 1 , D. Swissa 1 , T. Katzman 1 , I. Sadeski 1 , S. Dubinski 1 , N. Honig 1 , L. Tzvang 1 1 Chaim Sheba Medical Center, Radiation Oncology, Ramat Gan, Israel Purpose or Objective Our institution uses CPAP to reduce respiratory motion when treating primary and metastatic lung lesions with

Conclusion Use of the SMART approach in a cohort of high-risk lung tumors resulted in adequate early local control and low toxicity rates. Additional patient data and a longer follow-