ESTRO 2020 Abstract book

S110 ESTRO 2020

OC-0199 Cardiac sparing in advanced stage NSCLC patients: at what cost? R. Van Der Bel 1 , B. Stam 1 , D. Eekhout 1 , A. Tijhuis 1 , K. Kiers 1 , G. Wortel 1 , J. Belderbos 1 , S. Jan‐Jakob 1 , T. Janssen 1 , E. Damen 1 1 Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective Cardiac toxicity is of increasing concern in lung radiotherapy. However, given current clinical practice regarding organ at risk constraints, it remains to be seen how much room there is for cardiac sparing. Therefore, we investigate the effects of more stringent heart constraints on heart dose in relation to other OAR and PTV dose parameters. How much room is there for heart sparing and what is the expected effect of it on lung toxicity and survival from possible cardiac toxicity? Material and Methods We retrospectively replanned 98 locally advanced stage NSCLC patients, receiving concurrent chemo‐radiotherapy 66/58.08 Gy (tumour/involved lymph nodes) in 24 fractions using IMRT and Philips Auto‐Planning in Pinnacle 3 . Patients were treated from 2015 to 2017 and selected based on consistent delineation. For each patient two Auto‐Plans were created, one with minimal cardiac sparing (mean heart dose (MHD) <20 Gy EQD2) – mimicking the manual plan ‐ and the second with more stringent objectives on the heart (MHD <8 ‐ 12 Gy EQD2 and V 5Gy <35%). Differences in dose parameters between plans were tested using paired t‐tests. Using NTCP models for overall survival based on MHD at 2 years, and pneumonitis based on mean lung dose (MLD) [Kwa et al. 1998], we assessed the effect of the decreased cardiac dose on overall survival, and increased MLD on pneumonitis risk using paired t‐tests. Results Compared to the original plans, the Auto‐Plans’ PTV coverage was slightly improved, V 90% was 0.4% higher, OAR doses were comparable. The added heart constraints did not significantly impair OAR doses (including lung), target coverage, target dose inhomogeneity or conformity. All DVH parameters remained within clinically acceptable ranges between different Auto‐Plans. The average decrease in MHD was 0.41 Gy (range ‐2.34 – 7.44 Gy), in heart V 5Gy was 0.67% (range ‐14.8 ‐ 20.2%). Cardiac sparing of ≥1 Gy was achieved in 14.3 % of patients. The average increase in MLD was 0.01 Gy (range ‐0.99 – 0.94 Gy) in the entire group and 0.34 Gy (range ‐0.29 – 0.94 Gy) in the responding 14.3% of patients. (Fig. 1) This translates to a significant expected increase in overall survival at 2 years of 0.5% (range ‐3 – 9%), p‐value: 0.003, and a non‐significant increased grade ≥2 pneumonitis risk of 0.02% (range ‐1 – 2%).

Conclusion This automated planning study revealed that with a MHD constraint below 8 ‐ 12 Gy (EQD2) for locally advanced NSCLC treated with radical intent a substantial expected increase in overall survival can be achieved without a relevant increase in pneumonitis risk. Cardiac sparing should be implemented in routine clinical practice for locally advanced stage NSCLC patients. OC-0200 Heart dose constraints do not predict for cardiac death in radiotherapy for lung cancer K. Banfill 1 , A. McWilliam 1 , A. Abravan 1 , F. Sun 2 , K. Franks 2 , M. Van Herk 1 , C. Faivre‐Finn 1 1 University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom ; 2 Leeds Cancer Centre, Clinical Oncology, Leeds, United Kingdom Purpose or Objective Following the results of RTOG 0617, there have been a number of studies investigating the relationship between heart dose and survival in patients undergoing RT for lung cancer. Few of these studies record data on cause of death. The aim of this study is to investigate the ability of conventional heart dosimetric parameters to predict death due to cardiac causes using data from the UK national Data on cancer diagnosis, treatment and cause of death following radical lung cancer RT were obtained from Public Health England for all patients treated at a UK cancer centre between 1/1/10 and 31/12/16. Ethical approval to use patient information was granted by NHS Health Research Authority. Individuals with metastatic disease at time of RT, those who received multiple courses of thoracic RT or concurrent chemoradiotherapy where excluded. All patients who received > 45Gy in 20 – 25 fractions were included. Cardiac cause of death was defined as the following death certificate ICD‐10 codes: cause of death registry. Material and Methods

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