No abstract

BackgroundTo evaluate pancreatic tumor motion and its dynamics during respiration.Methods and materialsThis retrospective study includes 20 patients with unresectable pancreatic cancer who were treated with stereotactic ablative radiotherapy. An online respiratory tumor tracking system was used. Periodical maximum and minimum tumor positions with respiration in superior-inferior (SI), latero-lateral (LL), and anterior-posterior (AP) directions were collected for tumor motion evaluation. The predictability of tumor motion in each axis, based on reference measurement, was analyzed.ResultsThe use of a 20-mm and 5-mm constant margins for SI and LL/AP directions, avoids target underdosage, without the need for reference measurement. Pearson’s correlation coefficient indicated only a modest correlation between reference and subsequent measurements in the SI direction (r = 0.50) and no correlation in LL (r = 0.17) and AP (r = 0.35) directions. When margins based on the reference measurement of respiratory tumor motion are used, then 30% of patients have a risk zone of underdosage >3 mm (in average). ITV (internal target volume) optimization based on the reference measurement is possible, but allows only modest margin reduction (approximately from 20 mm to 16-17 mm) in SI direction and no reduction in AP and LL directions.ConclusionOur results support the use of 20-mm margin in the SI direction and 5-mm margins in the LL and AP directions to account for respiratory motion without reference measurement. Single measurement of tumor motion allows only modest margin reduction. Further margin reduction is only possible when there is on-line tumor motion control according to internal markers.

Hyperfractionated stereotactic re-RT is a reasonable treatment option for patients with recurrent/second primary HNSCC who were previously exposed to high-dose irradiation and who are not candidates for systemic treatment or hypofractionation.

HARTCIB (75 Gy in 5 weeks) is feasible for patients deemed unsuitable for chemoradiation. Acute toxicity was lower than predicted from radiobiological models; duration of dysphagia and confluent mucositis were particularly short. Better conformity of radiotherapy allows the use of more intensive altered fractionation schedules compared with older studies. These results suggest that further dose escalation might be possible when highly conformal techniques (e.g., stereotactic radiotherapy) are used.

BT remains to be the best method for dose escalation. Due to the significant organ-sparing effect of CK, patients that are not candidates for BT could benefit from stereotaxis more than from classical external beam radiotherapy.