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652 Background: Radiotherapy (RT) outcome depends on accurate delineation of gross tumor volume (GTV) regarding tumor size and position. CT and MRI are standard image modalities as they provide the necessary structural information. Positron emission tomography with flourodeoxyglucose (FDG-PET) visualizes glucose metabolism in active tumor tissue. The main objective was to explore the intra-observer and inter-modality variation of the GTV delineated on CT, MRI and PET images. Methods: Between November 2006 and July 2009, 22 patients with biopsy-proven anal carcinoma stage T1-T4/N0-3/M0-1 scheduled for curative RT were included in the study. All patients underwent FDG-PET/contrast enhanced CT and MRI. The delineations of GTV were done twice for each imaging modality with a minimum of 3 months in between. Delineations on the CT and MRI were done by routine methods. For the PET part three different cut-off values were used: SUV 2.5, 40% and 50% of maximum SUV. Non-overlap was calculated by subtracting the intersection from the union of two sets both regarding intra-observer variation and inter-modality variation. The GTV were compared for size, intra-observer variation and non-overlap using Wilcoxon rank sum test, where p < 0.05 was considered significant. Results: Volume size: the median GTV-CT was 25.6 cm3 which was significantly larger compared to GTV-MRI (7.2 cm3) and the GTV from the different PET cut offs (6.2 cm3, 10.6 cm3 and 7.0 cm3). Intra-observer variation: the median GTV delineated on CT, MRI and PET did not vary significant between delineation number 1 and 2. Non-overlap: the non-overlapping regions in GTV between delineation 1 and 2 using CT and MRI (20.5% and 22.5%) were significantly different from the PET cut offs (5.5% , 6.4% and 5.8%). Conclusions: Delineation of anal tumors is difficult; CT gives rise to the largest GTV with considerable intra-observer variation. MRI has the same degree of inaccuracy, but smaller GTV. PET-GTVs are the smallest with significant smaller intra-observer uncertainty.

e11583 Background: Loco-regional recurrences of breast cancer may cause considerable discomfort due to ulceration, oozing, bleeding and pain. Electrochemotherapy (ECT) is a local treatment using electric pulses to permeabilize cell membranes, augmenting uptake of chemotherapy. For bleomycin, the effect is enhanced several hundred fold, enabling one or few treatments. ECT has proven efficient for small cutaneous tumours, but has not previously been systematically investigated for large cutaneous tumours. Methods: We conducted a phase II, non randomized trial for patients with loco-regional recurrences of breast cancer larger than 3 cm with no further standard treatment available. Primary endpoint was response evaluated with measurement of lesion extension. Secondary endpoints included response evaluated with PET/CT. All treatments were given in general anaesthesia with iv. injection of bleomycin (15000 IU/m2) followed by application of trains of 8 high-voltage pulses of 1 ms. Up to 4 treatments could be gi...

3573 Background: Weekly (q1w) cetuximab (cet) is effective in all lines treatment of metastatic colorectal cancer (mCRC). Cet at 500 mg/m2 every second week (q2w) has similar pharmacokinetics to 25...

e11509 Background: By applying short electric pulses to cells, the cell membranes can become permeabilised. This can be used to augment the effect of chemotherapy, by providing direct access to the...