A. van Baardwijk

Analysis of the relative deformation of lung lobes before and after surgery in patients with NSCLC.

An accurate assessment of the extent of the tumor is critical for successful local treatment of lung cancer by surgery and/or radiotherapy. Guidelines to establish the extent of treatment margins may be derived from correlation studies between pre-treatment imaging and histopathology. Deformations occur, however, between in-vivo CT imaging and ex-vivo pathology due to the softness of lung tissue and pathology processing. The first aim of this study was to quantify these deformations in tissue around non-small cell lung cancer. The second aim was to explore factors associated with the magnitude of the deformations. The study was performed in 25 patients who underwent lobectomy after preoperative CT. Non-rigid registration was employed to evaluate tissue deformations around the gross tumor volume (GTV), taking into account potential differences in elasticity between tumor and healthy lung tissue. Tissue was found to be compacted by approximately 60% depending on circularity of the tumor and orientation of the specimen on the pathology table during processing. The deformations give rise to potential underestimation of the treatment margins in pathology studies that do not take this aspect into account.

PD-0097: Impact of new Dutch guideline on patient selection for WBRT in a large lung cancer cohort

local control (LC), regional control (RC) and metastasis-free survival (MFS). A strong correlation between total lymph node tumour volume and Nstage was found (Rs=0.93, P<0.01). MFS was worse with involvement of the lower neck levels (Rs=0.345, P<0.01). Patients with larger total lymph node tumour volumes had poorer RC and MFS rates, independent of treatment regimen. For total lymph node volumes up to 3.5 cm, MFS can be improved by ARCON (P<0.01). Conclusions: The strong prognostic value of T-stage and primary tumour volume, observed in retrospective analyses was not confirmed in patients treated in a prospective randomised trial with accelerated radiotherapy with or without carbogen breathing and nicotinamide. Results of this study indicate that (biological) factors other than primary tumour volume and T-stage are needed to select patients with laryngeal cancer for treatment intensification.

O-146 Effects of radiotherapy planning with a dedicated combined PET-CT-simulator of patients with non-small cell lung cancer on dose limiting normal tissues and radiation dose-escalation: A planning study

BACKGROUND AND PURPOSE To investigate the effect of radiotherapy planning with a dedicated combined PET-CT simulator of patients with locally advanced non-small cell lung cancer. PATIENTS AND METHODS Twenty-one patients underwent a pre-treatment simulation on a dedicated hybrid PET-CT-simulator. For each patient, two 3D conformal treatment plans were made: one with a CT based PTV and one with a PET-CT based PTV, both to deliver 60Gy in 30 fractions. The maximum tolerable prescribed radiation dose for CT versus PET-CT PTV was calculated based on constraints for the lung, the oesophagus, and the spinal cord, and the Tumour Control Probability (TCP) was estimated. RESULTS For the same toxicity levels of the lung, oesophagus and spinal cord, the dose could be increased from 55.2+/-2.0Gy with CT planning to 68.9+/-3.3Gy with the use of PET-CT (P=0.002), with corresponding TCPs of 6.3+/-1.5% for CT and 24.0+/-5.6% for PET-CT planning (P=0.01). CONCLUSIONS The use of a combined dedicated PET-CT-simulator reduced radiation exposure of the oesophagus and the lung, and thus allowed significant radiation dose escalation whilst respecting all relevant normal tissue constraints.