ESTRO 36 Abstract Book

S656 ESTRO 36 _______________________________________________________________________________________________

Purpose or Objective Stereotactic ablative radiotherapy (SABR) has been replacing the role of surgery in the management of operable stage I non-small cell lung cancer (NSCLC). We aim to assess the outcomes of SABR performed in these patients. Material and Methods Fifty-six patients with clinical stage I NSCLC who underwent SABR between Nov. 2006 and Jan. 2015 were analyzed retrospectively. Eligibility for SABR in our practice was tumor size less than 5cm and peripherally located tumors. Age ranged 54 to 87 (median 74) and male to female was 43 to13. ECOG score was 0 in 16, 1 in 25, and 2 in 15 patients, respectively. Adenocarcinoma was 24 and squamous cell carcinoma was 25. We defined the patients as medically inoperable based on the lung function (baseline FEV1 < 40% predicted, DLCO < 50% predicted), age > 75 yrs & PS >2. Intensity-modulated radiosurgery was planned and delivered consecutively with median 60 Gy (range, 55 – 64 Gy) in 3 to 8 fractions. Median follow-up time was 23.8 months (range, 1.9 - 93.5 months). Results The 3-year and 5-year overall (OS) rate of all 56 patients was 82.9% and 82.9% and progression free survival (PFS) was 54.8% and 45.6%, respectively. The possible prognostic parameters such as tumor size, tumor location (upper vs. lower lobe), gross tumor volume (GTV), SUVmax of the primary tumor, BED, and operability were entered into analysis regarding on OS or PFS. PFS was significantly dependent on the tumor location (p=0.047), tumor size (>3cm, p< 0.001), GTV (>19cm 3 , p=0.02), and operability. 5-yr PFS of operable (n=42) and inoperable (n=14) was 52.9% vs. 31.3% (p=0.022). OS was significantly dependent on the tumor size (p=0.046) and BED (>150 Gy, p=0.022). 5-yr OS of operable and inoperable patients was 90.1% vs. 67.7% (p=0.084), respectively. Conclusion SABR shows the survival outcomes similar to surgery in operable stage I NSCLC. Tumor size (>3cm) was the most significant prognostic factor affecting to OS. We need to increase the BED of SABR over 150 Gy in cases with tolerable lung compliances. EP-1215 Risk factors of radiation pneumonitis after SRT: the usefulness of the PTV to lung volume ratio. T. Ueyama 1 , T. Arimura 1 , K. Takumi 1 , F. Nakamura 1 , R. Higashi 1 , S. Ito 1 , Y. Fukukura 1 , T. Umanodan 1 , M. Nakajo 1 , C. Koriyama 2 , T. Yoshiura 1 1 Kagoshima University, Radiology, Kagoshima, Japan 2 Kagoshima University, Epidemiology, Kagoshima, Japan Purpose or Objective To investigate the risk factors of severe radiation pneumonitis (RP) after stereotactic radiation therapy We retrospectively evaluated 68 lung tumors in 63 patients treated with SRT between 2010 and 2015. RP was graded according to the National Cancer Institute- Common Terminology Criteria for Adverse Events (NCI-CTCAE) version.4.0. SRT was delivered at 7.0-12.0Gy fractions once daily to a total of 48-64Gy (median 50). Univariate and multivariate analyses were performed to assess patient- and treatment-related factors, including age, gender, smoking index, pulmonary function, tumor location, the value of serum Krebs von den Lungen-6 (KL- 6), and dose-volume metrics: V5, V10, V20, V30, V40, and VS5, V2 of contralateral lung, homogeneity index of PTV (HI), dose of PTV, mean lung dose (MLD), contralateral MLD, PTV volume, lung volume, the PTV/Lung volume ratio (PTV/Lung) . The value of PTV/Lung in predicting RP (SRT) for lung tumors. Material and Methods

was also analyzed with receiver operating characteristic (ROC) curves. Results The median follow-up was 21 months. Ten patients (14.7%) developed with RP of symptomatic grade2-5 after completing SRT and three patients (4.4%) died from RP. On univariate analysis, V10, V20, PTV volume, and PTV/Lung were significantly associated with occurrence of RP ≧ grade2 (P<0.05, respectively). On multivariate analysis, only PTV/Lung was statistically significant (P<0.05). ROC curves indicated that severe RP could be predicted using PTV/Lung (area under curve: 0.88, CI: 0.78-0.95, cut off value: 1.09, sensitivity: 90.0%, specificity: 72.4%) Conclusion PTV/Lung could well predict the risk for severe RP after SRT. EP-1216 Impact of the radiation dose on the pulmonary perfusion assessed using lung scintigraphy B. De Bari 1 , S. Godin 2 , M. Zeverino 3 , L. Deantonio 4 , T. Breuneval 2 , J. Prior 5 , J. Bourhis 2 , R. Moeckli 3 , M. Ozsahin 2 1 Hôpital Univ. Jean Minjoz, Radiation Oncology, Besançon, France 2 Centre Hospitalier Universitaire Vaudois, Radiation Oncology, Lausanne, Switzerland 3 Centre Hospitalier Universitaire Vaudois, Medical Physics, Lausanne, Switzerland 4 University Hospital "Maggiore della Carità-", Radiation Oncology, Novara, Italy 5 Centre Hospitalier Universitaire Vaudois, Nuclear Medicine, Lausanne, Switzerland Purpose or Objective We aimed at evaluating the impact of the dose of radiotherapy on lung function (LF). LF variations were evaluated by integrating SPECT/CT pulmonary perfusion before and after radiotherapy (RT) in patients treated with radiotherapy +/- chemotherapy for a lung tumor. Material and Methods Between 06.2014 and 09.2015, 15 pts presenting a primary (n = 11) or secondary (n = 4) lung cancer were treated with radiotherapy +/- chemotherapy (10x3 Gy, 1 pt; 13x3 Gy, 1 pt ; 6x8 Gy, 1 pt; 7x7.5 Gy, 1 pt; 3x18 Gy, 1 pt; 12x4.5 Gy, 1 pt; 5x11 Gy, 1 pt; 30x2Gy 4pts; 33x2Gy, 2 pts; 5x12Gy, 1pt; 12x5Gy, 1 pt). Three pts were treated in a context of re-irradiation. All patients received a SPECT/CT to evaluate the LF before and three months after radiotherapy, which was co-registered with the planning phase of the simulation CT-scan. For pts treated with hypo-fractionated regimens, the biological equivalent dose at 2 Gy/fraction (EQD2) was calculated (alpha / beta = 10 Gy for acute toxicity). Isodoses (5, 10, 20, 30, 40, 50, 60, 70, 80, and 90 Gy) were drawn. Then, we calculated the activity (MBq) in these volumes before and after treatment. Results Linear regression analysis showed a significant reduction in LF at three months, which was proportional to the increase of the radiation dose (p = 0.00017, Figure 1). Our analysis showed a reduction of 0.14% of the LF for each delivered gray. Even with the limits of the small population of this study, the linear equation showed a predictive value in predicting the loss of LF/Gy of 98% (R 2 = 0.9807). Conclusion SPECT/CT is a good imaging modality to assess changes in LF after thoracic irradiation. This analysis shows a functional decrease, which is proportional to the delivered dose, reflecting the functional acute toxicity. These function-based approaches could improve our knowledge about the response of the OARs to the radiation, and should be prospectively evaluated.