ESTRO 2023 - Abstract Book

S782

Monday 15 May 2023

ESTRO 2023

is ideally suited for the development of novel SGRT solutions such as that needed to replace immobilisation masks. When the two are used in conjunction to measure H&N motion, they can achieve near submillimetre accuracy.

OC-0935 Patient selection for DIBH radiotherapy of locally advanced non-small cell lung cancer K. Fjellanger 1,2 , L. Rossi 3 , B.J.M. Heijmen 3 , H.E.S. Pettersen 1 , I.M. Sandvik 1 , S. Breedveld 3 , T. Husevåg Sulen 1 , L.B. Hysing 1,2 1 Haukeland University Hospital, Department of Oncology and Medical Physics, Bergen, Norway; 2 University of Bergen, Institute of Physics and Technology, Bergen, Norway; 3 Erasmus MC Cancer Institute, Department of Radiotherapy, Rotterdam, The Netherlands Purpose or Objective Deep inspiration breath hold (DIBH) during radiotherapy treatment can reduce the risk of radiation pneumonitis (RP) and 2-year mortality compared to treatment in free breathing (FB) for patients with locally advanced non-small cell lung cancer (LA-NSCLC). DIBH is not commonly used for this patient group, although the equipment to perform DIBH is available in many clinics. The extra time needed for imaging, comparative planning and treatment in DIBH could be a factor preventing its use in busy clinics. This study investigates if specific patient and tumor characteristics predict the benefit of DIBH, in order to prioritize the patients with the greatest benefit. Materials and Methods In a prospective study, 4DCTs and DIBH CTs were acquired at treatment planning for 37 patients with LA-NSCLC. Treatment plans in FB and DIBH were generated without manual intervention, using a system for automated multi-criterial planning. Normal tissue complication probabilities (NTCPs) for radiation pneumonitis (RP) grade ≥ 2 and 2-year mortality were calculated for each technique using validated models. Correlations between the ∆ NTCPs between FB and DIBH and the following patient characteristics were investigated: primary tumor location in right vs. left lung and upper vs. lower lobes, expansion of the lungs with DIBH (relative increase in lung volume compared to FB) and cranio-caudal motion extension of the primary tumor in FB (breathing motion). The Wilcoxon signed-rank test was used for related samples and linear regression was used to test correlations between two continuous variables. p-values ≤ 0.05 were considered statistically significant. Results The NTCP for RP was significantly lower with DIBH than FB regardless of tumor position (Figure 1), and there was no correlation between Δ NTCP and tumor motion in FB (p = 0.1) or lung expansion with DIBH (p = 0.2). For 2-year mortality, the benefit of DIBH depended on tumor location. 83%, 79% and 80% of the patients with tumors in the left upper lobe, right upper lobe and left lower lobe, respectively, had a lower NTCP for 2-year mortality with DIBH than FB ( Δ NTCP range -4.6 to 0.6 pp). This benefit was seen only for 43% of the patients with tumors in the right lower lobe ( Δ NTCP range -1.2 to 3.7 pp) (Figure 2). No correlation was found between Δ NTCP and tumor motion in FB (p = 0.3) or lung expansion with DIBH (p = 0.9).