ESTRO 2021 Abstract Book

S970

ESTRO 2021

RT doses ranged from 45 to 60 Gy (mean 55 Gy) in 15 or 20 fractions. The most frequent fractionation was 55Gy/20fr/4w (70.5%), followed by 60Gy/15fr/3w (19.7%). 49 patients (79%) received ChT, 24 sequentially and 25 concomitantly. 9 patients received durvalumab as maintenance treatment. Acute toxicity: 5 (8.2%) patients had radiodermitis G1, 9 (14.5%) experienced pneumonitis G2 and 23 (37.7%) had esophagitis, mostly G1 (15) and G2 (7) and only 1 G3 case. Late toxicity: only 4 cases (6.6%) with pneumonitis G2. With a median follow-up time of 8 months (range 1-35), of the 34 deaths recorded, 25 died from the tumor and 9 from other causes. Median overall survival (OS) of the entire serie was 12.3 months (95% CI 7.1 – 17.5). 1-yr OS was 50% and 2-yr OS was 21%. Median OS time was 21.8 months for stages I/II, 10.3 months for stage III and 7.3 months for stage IV. These differences were not statistically significant (p= 0.7).

Table 1. Patients and tumor characteristics Median age (years old) 67

Range 42-82

Performance Status at diagnosis 0-1

54 patients

2

6 patients

3

1 patient

Histology

Adenocarcinoma 25 tumors Squamous cell carcinoma 34 tumors Other 3 tumors

Stage (8th TNM edition)

I/II

6 tumors

III

45 tumors

IV

11 tumors

Conclusion Locally advanced NSCLC still represents an heterogeneus disease with high mortality. MHypoRT is an attractive strategy that allows to shorten the duration of RT without compromising survival or adding toxicity compared to conventional therapy and has been widely adopted during last year due to SARS-CoV-2 pandemic. PO-1169 30 Gy single dose stereotactic radiation therapy in a series of patients with lung oligometastasis D. Anzellini 1 , G. Scalabrino 1 , B. Campanella 1 , F. Perrone 1 , A.M. Ascolese 1 , M. Valeriani 1 , M.F. Osti 1 1 Sapienza Università di Roma, AOU Sant'Andrea Roma, UO Radioterapia Oncologica, ROMA, Italy Purpose or Objective To evaluate local control (LC), long term adverse effects and survival in a series of patients with oligometastatic to the lung disease who received 30Gy in single dose with stereotactic technique Materials and Methods Between December 2008 and March 2020, a total of 186 lung metastases in 147 patients affected by oligometastatic disease were treated, at our Institution, with stereotactic body radiotherapy (SBRT) delivered in a single dose of 30 Gy. The primary tumors in most cases were non small-cell lung cancer and colon-rectum cancer (48.2% and 30.7%, respectively). Prognostic factors were also assessed. Results The median follow-up was 56 months. 26 (13.9%) lesions in 25 patients progressed locally. Intra-thoracic progression (new lung lesions or thoracic lymph node metastases) occurred in 67 (36%) patients. Distant progression occurred in 49 (33.3%) patients after a median time of 21 months. The 3- and 5-year local relapse- free survival (LPFS) were 80.3% and 79.5% (median not reached), respectively. Late toxicity was evaluated in 141 patients (follow-up >6 months): 58 (41.1%) had grade ≤2 fibrosis, 11(7.8%) experienced grade 3 fibrosis. Two (1.4%) cases of rib fracture occurred. One case of toxic death (grade 5) has been reported. Prognostic factor at the univariate analysis was: lesion diameter ≤18 mm correlated significantly with a longer LPFS (p=0.001). Prognostic factors at the multivariate analysis was only lesion diameter. Conclusion Our results confirm the effectiveness and safety of stereotactic body radiation therapy 30 Gy schedule administered in selected oligometastatic patients. PO-1170 Between a rock and heart place – cardiac sparing in MRI-guided lung SBRT L. van der Pol 1 , M. Fast 1 , S. Hackett 1 , J. Verhoeff 1 , F. Mohamed Hoesein 2 , J. Pomp 1 , H. Ligtenberg 1 , L. Merckel 1 , L. Snoeren 1 1 UMC Utrecht, Radiotherapy, Utrecht, The Netherlands; 2 UMC Utrecht, Radiology, Utrecht, The Netherlands Purpose or Objective Survival differences of lung cancer patients in RTOG 0617 point to the importance of the heart as OAR in lung radiotherapy. Several retrospective studies have correlated higher dose to specific cardiac substructures (CS) with worse overall survival, but it remains unclear whether CS constraints are actionable in clinical practice. Online MRI-guidance potentially provides a route for daily CS identification, and subsequent CS sparing. In this study we investigate whether CS sparing is feasible for lung SBRT on the Unity MR-linac (Elekta AB, Stockholm, SE). Materials and Methods We included 34 lung SBRT patients (16 central / 8x7.5 Gy, 18 ultra-central / 12x5 Gy) in this treatment planning study. A mid-position CT scan, which was derived from 4D-CT using in-house deformable image