ESTRO 2020 Abstract Book

S535 ESTRO 2020

toxicity rates. Additional patient data and a longer follow- 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

SBRT. This update includes our first report of long-term outcomes and tolerances. Material and Methods We retrospectively analyzed consecutive patients with either primary lung cancer or oligometastatic disease treated with lung SBRT and CPAP between 6/2014- 8/2019. All patients received at least 40 Gray. After obtaining consent, patients underwent simulation and treatment with CPAP pressure set at 15 cmH2O for 15 minutes using either free breathing (FB) or deep inspiratory breath hold (DIBH) technique. Patient medical records were search for outcomes. Lung volume with and without CPAP were compared using Wilcoxon signed-rank test. Local control (LC) and progression free survival (PFS) were determined by CT or PET/CT, performed at 3-6- month intervals. Overall survival (OS) was determined according to national records. LC, PFS, and OS were estimated using Kaplan Meir. Data cutoff was on 10/2019. Results Sixty-one patients with either primary lung cancer 23 (25.8%) or oligometastatic disease 66 (74.6%) received treatment for 89 lung lesions using SBRT and CPAP (table 1). Indications for use of CPAP included disease in lower lobes 47 (52.8%) or presence of multiple lung lesion in 26 (29.2%). Mean radiation dose was 52 Gy (SD 4.39). CPAP was used with FB in 54 (60.7%) and DIBH in 35 (39.3%). CT simulations with and without CPAP were available for comparison of lung volumes in 51/61 patients. Use of CPAP increased mean lung volumes in both FB (3139 ml to 3927 ml, p= 0.0001) and DIBH (4913 ml to 5284 ml, p= 0.002). Most patients tolerated CPAP well. One patient suffered prolonged syncope before the first treatment and 2 patients were unable to tolerate the pressure increase. Median follow-up was 702 days; LC at 18 months: 80.1% (96% CI 67%-88%), and at 24 months was LC 68.5% (96% CI 50.5-80%) median not reached. LC did not differ according to DIBH or FB, tumor origin, tumor location or dose (Figure 1). PFS at 18 months was 45.6% (96% CI 30%-60%), and at 24 months was 35.3% (96% CI 20.5%-50.7%), median 526d. OS at 18 months was 77.7% (96% CI 62.4%-87.3%) and at 24 months 62.3% (96% CI 45.7%-75%), median survival not reached. PFS and OS were better for patients with primary lung cancer than for patients with metastatic disease (p=0.001).