S270 reports of practical oncology and radiotherapy 1 8 ( 2 0 1 3 ) S259-S274 delineated on 4 kilovoltage-CT: Inspiration, expiration and free-breath ± contrast by using Civco ® Pro-lok abdominal compression system, was the internal tumor volume (ITV). Planned treatment volume (PTV) consisted of 5-mm radial and a 10-mm craniocaudal expansion of ITV. The prescribed doses were: 3 × 20 Gy, 3 × 18 Gy, 8 × 7.5 Gy. Dose constraints to normal tissue were defined accord to RTOG 0236 protocol. To asses

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... ntrafraction tumor motion, megavoltage-CT (MVCT) scan was obtained prior to and at the end of each fraction (in patients receiving 18-20 Gy/fraction a MVCT was performed in the middle of the delivered treatment). The prior MVCT was matched with the kilovoltage-CT planning to check if corrections had to be done. Results. The mean fraction treatment time was 1Gy/1 min. In 2 patients multiple targets were simultaneously treated. To asses intra-fraction tumor motion we matched prior-MVCT, mid-MVCT and end-MVCT scan and we checked that PTVs were included within isodose of prescription dose in all cases. Mean correction after MVCT registration was 2 mm. One late fibrosis with transitory neuroalgic pain has been observed. All lesions are controlled at the time of analysis and one patient died by other causes and four patients are alive with disease. Conclusions. HT-SBRT is feasible and well tolerated treatment in lung tumors and image guidance with MVCT allowed daily position correction and precise treatment delivery. http://dx.