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N14 Could the effect of therapy depend on the prostate movements during irradiation?

      Introduction and Objectives

      Prostate could change localization during fractionated irradiation. We want to estimate the displacements of prostate position during radiotherapy and we want to check if the effect of therapy depend on those displacements.

      Material and Methods

      The study is based on 40 patients treated with radical radiotherapy for localized prostate cancers between October 2004 and May 2006. Thermoplastic Orfit masks and Orfit HP System Leg Support and Foot Support were used. The PTVs included prostates with reasonable margins. All patients were treated conformally, using high energy photons. The total dose was 74Gy, delivered in 37 fractions, 7.5 weeks. The positions of prostate were evaluated once a week using CT scans. CTs, all planning procedures and irradiation were performed using the same positioning system. Prostates were delineated and the changes in their positions were measured using appropriate device the ‘Eclipse’ program. All procedures were performed by the same experienced two radiation oncologists and three radiation technologists. The patients have been observed after therapy every 3 months for the first two years after treatment and every 6 months for next years.

      Results

      We observed major prostate displacements first of all in anterior-posterior (AP) axis. The mean of prostate movement in AP axis was 4.6 mm and ranged between 0.0 mm and 30.1 mm. We find that only 19 (47.5%) patients had all measured displacements smaller than 10 mm. Displacements larger than 20 mm were observed in 5 patients (25%). Two patients died 29 and 32 months after treatment without recurrence. 38 patients are being observed still. Median follow-up was 41 months. We have found biochemical relapse in 3 patients (7%), all of whom had major displacements: two of them had the largest prostate displacement (median 14.0 and 12.1 mm) and the third one had the fourth largest displacements (median 11.9 mm). We have not found any clinical relapse.

      Conclusions

      Prostate displacements seem to be the main reason of biochemical relapse in analyzed group.