K. De Jaeger

Portal imaging to assess setup errors, tumor motion and tumor shrinkage during conformal radiotherapy for non-small cell lung cancer

PURPOSE To investigate patient set-up, tumor movement and shrinkage during 3D conformal radiotherapy for non-small cell lung cancer. MATERIALS AND METHODS In 97 patients, electronic portal images (EPIs) were acquired and corrected for set-up using an off-line correction protocol based on a shrinking action level. For 25 selected patients, the orthogonal EPIs (taken at random points in the breathing cycle) throughout the 6-7 week course of treatment were assessed to establish the tumor position in each image using both an overlay and a delineation technique. The range of movement in each direction was calculated. The position of the tumor in the digitally reconstructed radiograph (DRR) was compared to the average position of the lesion in the EPIs. In addition, tumor shrinkage was assessed. RESULTS The mean overall set-up errors after correction were 0, 0.6 and 0.2 mm in the x (left-right), y (cranial-caudal) and z (anterior-posterior) directions, respectively. After correction, the standard deviations (SDs) of systematic errors were 1.4, 1.5 and 1.3 mm and the SDs of random errors were 2.9, 3.1 and 2.0 mm in the x-, y- and z-directions, respectively. Without correction, 41% of patients had a set-up error of more than 5 mm vector length, but with the set-up correction protocol this percentage was reduced to 1%. The mean amplitude of tumor motion was 7.3 (SD 2.7), 12.5 (SD 7.3) and 9.4 mm (SD 5.2) in the x-, y- and z-directions, respectively. Tumor motion was greatest in the y-direction and in particular for lower lobe tumors. In 40% of the patients, the projected area of the tumor regressed by more than 20% during treatment in at least one projection. In 16 patients it was possible to define the position of the center of the tumor in the DRR. There was a mean difference of 6 mm vector length between the tumor position in the DRR and the average position in the portal images. CONCLUSIONS The application of the correction protocol resulted in a significant improvement in the set-up accuracy. There was wide variation in the observed tumor motion with more movement of lower lobe lesions. Tumor shrinkage was observed. The position of the tumor on the planning CT scan did not always coincide with the average position as measured during treatment.

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.