ESTRO 2020 Abstract Book

S226 ESTRO 2020

after RT, with 48% of the subjects reporting increased breathlessness at 24-months. Based on radiological findings, we recognised two patterns of RILD evolution: patients whose normal lung volume shrinkage peaked at 6 months and then improved, indicative of abating acute inflammation (Group A, n=24), and patients whose radiological findings continued to deteriorate up to 24 months (Group B, n=21). The MRC scores of patients in Group A showed an early deterioration whereas in Group B, the MRC scores showed a gradual but unremitting deterioration. A similar evolution pattern was seen with FEV 1 /FVC% (Figure 2). These findings are indicative of an evolution of RILD from an early acute inflammation phase, characterised by reversible parenchymal change, into chronic inflammation, characterised by progressive lung volume loss and anatomical distortion.

Conclusion margin reduction does not underdoes clinical target volume in the majority of patients. GTV of primary tumour demonstrated a mean shrinkage of 48%. These two observation lead us to explore the implementation of a complete adaptive replanning strategy in the second or third week of treatment, with the aim of a better target coverage, sparing lung tissue and, if so, attempt to a isotoxic dose escalation. PD-0417 The evolution of radiation-induced lung damage following dose-escalated chemo-radiotherapy E. Chandy 1 , J. Jacob 2 , N. Yip 2 , A. Szmul 2 , D. Landau 1 , J.R. McClelland 2 , C. Veiga 2 1 University College London, UCL Cancer Institute, London, United Kingdom ; 2 University College London, Centre for Medical Image Computing, London, United Kingdom Purpose or Objective Radiation-induced lung damage (RILD) is a common consequence of lung cancer radiotherapy (RT) but its evolution over time is unclear. We investigate and quantify how RILD evolves during the 24-months after RT using CT imaging and breathing function tests. Material and Methods CT images were available pre-RT and at 3, 6, 12 and 24- months following RT for forty-five subjects enrolled in IDEAL-CRT; a stage I/II clinical trial of isotoxic, dose- escalated radiotherapy for locally advanced non-small cell lung cancer. Patients were treated with 5 or 6 fractions a week and all received concurrent chemotherapy. To investigate how RILD appears and develops, radiological findings were quantified using a suite of CT-based imaging biomarkers (previously developed by our group) over serial time-points. The biomarkers are representative of parenchymal, pleural and lung volume change, and anatomical distortions after RT. Medical Research Council (MRC) dyspnoea scores and formal pulmonary function tests (PFTs) were also available for the majority of the subjects included. Results Radiological findings and breathing function vary according to time since RT. Figure 1 shows temporal change of selected biomarkers and breathing function. Parenchymal damage was common at 3-months and peaked at 6-months. From 6 to 24-months, the volume of consolidated parenchyma reduced and the normal lung volume in the treated lung progressively reduced. Anatomical distortions increased over time, peaking at 12 to 24-months. Pleural change was common at all time- points and demonstrated variable evolution across the cohort. FEV 1 /FVC % and MRC scores progressively declined

Figure 1.

Figure 2.

Conclusion This study investigates the evolution of RILD using quantitative information on a set of homogeneously treated patients. The use of objective measures is advantageous as the evolution of RILD is not easily quantifiable by human observers. Radiological findings may allow identification of subgroups with differing patterns of RILD evolution and this information could potentially be harnessed to help predict a particular patient’s late response to RT. PD-0418 Dose on cardiac (sub)structures as predictor for OS in early stage NSCLC patients treated with SBRT M. Duijm 1 , D. Pezzulla 1 , W. Schillemans 1 , J. Nuyttens 1 1 Erasmus MC Cancer Institute, Radiation Oncology, Rotterdam, The Netherlands Purpose or Objective Although the cardiac dose is related to an increased mortality risk in patients with advanced NSCLC, this relation is unclear in stereotactic body radiation therapy (SBRT). The cardiac dosimetry within SBRT is markedly different, because of high radiation doses in small volumes of the heart. Within this analyses we investigated possible clinical and dosimetric cardiac factors prognostic for OS after SBRT. Material and Methods We analyzed 306 patients with early stage NSCLC treated with SBRT. For each patient the pericardium, the heart and 10 cardiac substructures were contoured on the planning CT scan following the RTOG guidelines. Of each contoured structure the maximum and minimum point dose (D max , D min ), mean dose (D mean ), dose to 2% / 50% / 98%