ESTRO 37 Abstract book

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ESTRO 37

toxicity for both groups.

Conclusion 4D-image guided SBRT with small margin ITV-PTV provided good LC and survival rates with negligible toxicity. Interestingly, patients older than 78 had significantly better outcomes. EP-1388 The role of emphysema on lung toxicity and the feasibility of a “functional treatment plan” M. Maddalo 1 , G. Benecchi 1 , I. Moschini 2 , C. Grondelli 1 , R. Rossi 1 , E. Calabri 1 , F. Salaroli 3 , M. Manicone 3 , S. Andreani 3 , F. Ghetti 3 , S. Gianni 3 , R. Rossi 3 , S. Nurmahomed 3 , G. Ceccon 3 , P. Losardo 3 , C. Dell'Anna 3 , M. Bergamini 3 , C. Ghetti 1 , N. D'Abbiero 3 1 Azienda Ospedaliero Universitaria di Parma, Medical Physics Unit, Parma, Italy 2 Azienda AUSL Piacenza, Radiotherapy, Parma, Italy 3 Azienda Ospedaliero Universitaria di Parma, Radiotherapy, Parma, Italy Purpose or Objective Although the relationship between pulmonary emphysema (PE) and pneumonitis after radiotherapy has been investigated in recent years, it still remain controversial. The aim of this study was to retrospectively examine the role of PE on radiation- induced lung toxicity (RILT). The feasibility of a “functional treatment plan (FTP)”, designed to spare the functional volumes of the lungs (FLV), was also investigated. Material and Methods 34 patients with NSCLC who underwent radiotherapy has been retrospectively selected for this study. An expert radiologist analysed the first CT after-treatment and subdivided patients in two categories: RILT-1, 13 patients with no/low RILT; RILT-2, 21 patients with high RILT. Thresholds were applied on planning CT (before- treatment) to define PE (below -900 HU) and FLV (between -899 and -500 HU). Through the Mann-Whitney test, RILT-1 and RILT-2 were compared in terms of PE volumes and of dosimetric parameters V 5Gy and V 20Gy of both total (DP TL ) and functional lungs (DP FL ). For patients who had considerable PE volumes, FTPs were developed based on VMAT technique. To selectively spare the FLV, arc sectors which involved parts of FLV were avoided and high-weight constraints for FLV were applied in the VMAT Optimizer. Results PE volume was significantly higher in RILT-1 than in RILT- 2 (p<0.05). RILT-1 was characterised by significantly lower DP TL than RILT-2 and the difference become stronger when considering DP FL . The 66.7% of FTPs were not feasible because PE was irregularly distributed over the whole lungs volume. Regarding the remaining 33.3% of the FTPs, FLV D mean averagely decreased by 0.67Gy (0.25<ΔD mean <1.52Gy).

Figure 1: Overall survival according to irradiation schedule and age Conclusion No significant impact of the irradiation scheme was found for LC and acute toxicity. However, patients under 73 years old treated with the discontinuous schedule had a significant increase of OS. This result in favor of discontinuous scheme could be explained either by a lower toxicity or a better LC (tendency but not significant). Supplementary studies are warranted to confirm this findings and identify subgroups who could benefit from a discontinuous schedule of irradiation. EP-1387 High local control with 4D-IGRT based SBRT for stage I NSCLC: a retrospective study. S. Badellino 1 , J. Di Muzio 1 , A. Filippi 2 , A. Guarneri 1 , R. Ragona 1 , U. Ricardi 1 1 University of Torino, Radiation Oncology, Torino, Italy 2 San Luigi Gonzaga Hospital- University of Torino, Radiation Oncology, Orbassano, Italy Purpose or Objective To present Local Control (LC), Metastasis Free Survival (MFS) and Cancer Specific Survival (CSS) rates after Stereotactic Body Radiation Therapy (SBRT) with IGRT technique and small ITV-PTV margin (3 mm) for stage I Non Small Cell Lung Cancer. Material and Methods We retrospectively analyzed a cohort of two-hundred and two consecutive patients treated in a single Institution in the time interval 2010-2015. Patients were planned with frameless approach on 4D-CT scan, and PTV was generated from patients’ specific ITV adding only 3 mm isotropic margin; planning consisted of single arc VMAT delivered with daily cone-beam-CT guidance and a prescription BED 10Gy (at 80%) ranging from 75 to 150 Gy, in consecutive fractions. Results One-hundred fifty (74.25%) male and fifty two (25.75%) female with a median age of 78 years were included; 4 patients were lost at follow-up. 139 (68.8%) patients had a Stage IA NSCLC and 63 (31.2%) Stage IB, respectively; biopsy was performed in 105 (51.98%) of patients. With a median follow-up interval of 30.6 months, actuarial local control (LC) at 12 and 36 months was 96.7% and 84%, respectively (Figure 1). Metastasis-free survival (MFS) at 12 and 36 months was 86.1% and 70.5%, respectively, and Cancer Specific Survival (CSS) at 12 and 36 months was 96.5% and 80.7%, respectively (Figure 1). Median time to local recurrence was 24.7 months. At multivariate analysis, the only significant factor associated to outcome was age (patients older than 78 years had significantly better LC, MFS and CSS; p=0.05, = 0.058 and =0.05, respectively). Acute toxicity was very low, with 2,5% of RTOG > grade 3 pneumonitis.