Radiotherapy Research Today is a free monthly online journal that collates and summarizes the latest research about Radiotherapy, including details on cancer treatment, side effects. | ||||||||
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Strategy for online correction of rotational organ motion for intensity-modulated radiotherapy of prostate cancer.Rijkhorst EJ, van Herk M, Lebesque JV, Sonke JJ Department of Radiation Oncology, The Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands. PURPOSE: To develop and evaluate a correction strategy for prostate rotation using gantry and collimator angle adjustments. METHODS AND MATERIALS: Gantry and collimator angle adjustments were used to correct for prostate rotation without rotating the table. A formula to partially correct for left-right (LR) rotations was derived through geometric analysis of rotation-induced clinical target volume (CTV) beam's-eye-view shape changes. For 10 prostate patients, intensity-modulated radiotherapy (IMRT) plans with different margins were created. Simulating CTV LR rotation and correcting each beam by a collimator rotation, the corrected CTV dose was compared with the original and uncorrected dose. Effects of residual geometric uncertainties were assessed using a Monte Carlo technique. A large number of treatments representative for prostate patients were simulated. Dose probability histograms of the minimum CTV dose (D min) were derived, with and without online correction, resulting in a more realistic margin estimate. RESULTS: Dosimetric analysis of all IMRT plans showed that, with rotational correction and a 2-mm margin, D min was constant to within 3% for LR rotations up to +/-15 degrees . The Monte Carlo dose probability histograms showed that, with correction, a margin of 4 mm ensured that 90% of patients received a D min >or=95% of the prescribed dose. Without correction a margin of 6 mm was required. CONCLUSIONS: We developed and tested a practical method for (online) correction of prostate rotation, allowing safe and straightforward implementation of margin reduction and dose escalation. Published 23 November 2007 in Int J Radiat Oncol Biol Phys, 69(5): 1608-17.
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