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Author Chan, Mark ♦ Grehn, Melanie ♦ Cremers, Florian ♦ Siebert, Frank-Andre ♦ Wurster, Stefan ♦ Huttenlocher, Stefan ♦ Dunst, Jürgen ♦ Hildebrandt, Guido ♦ Schweikard, Achim ♦ Rades, Dirk ♦ Ernst, Floris
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword RADIOLOGY AND NUCLEAR MEDICINE ♦ ANGULAR CORRELATION ♦ ERRORS ♦ LIVER ♦ NEOPLASMS ♦ RADIATION DOSE DISTRIBUTIONS ♦ RADIOTHERAPY ♦ RESPIRATION ♦ SAFETY MARGINS
Abstract Purpose: Although the metric precision of robotic stereotactic body radiation therapy in the presence of breathing motion is widely known, we investigated the dosimetric implications of breathing phase–related residual tracking errors. Methods and Materials: In 24 patients (28 liver metastases) treated with the CyberKnife, we recorded the residual correlation, prediction, and rotational tracking errors from 90 fractions and binned them into 10 breathing phases. The average breathing phase errors were used to shift and rotate the clinical tumor volume (CTV) and planning target volume (PTV) for each phase to calculate a pseudo 4-dimensional error dose distribution for comparison with the original planned dose distribution. Results: The median systematic directional correlation, prediction, and absolute aggregate rotation errors were 0.3 mm (range, 0.1-1.3 mm), 0.01 mm (range, 0.00-0.05 mm), and 1.5° (range, 0.4°-2.7°), respectively. Dosimetrically, 44%, 81%, and 92% of all voxels differed by less than 1%, 3%, and 5% of the planned local dose, respectively. The median coverage reduction for the PTV was 1.1% (range in coverage difference, −7.8% to +0.8%), significantly depending on correlation (P=.026) and rotational (P=.005) error. With a 3-mm PTV margin, the median coverage change for the CTV was 0.0% (range, −1.0% to +5.4%), not significantly depending on any investigated parameter. In 42% of patients, the 3-mm margin did not fully compensate for the residual tracking errors, resulting in a CTV coverage reduction of 0.1% to 1.0%. Conclusions: For liver tumors treated with robotic stereotactic body radiation therapy, a safety margin of 3 mm is not always sufficient to cover all residual tracking errors. Dosimetrically, this translates into only small CTV coverage reductions.
ISSN 03603016
Educational Use Research
Learning Resource Type Article
Publisher Date 2017-03-15
Publisher Place United States
Journal International Journal of Radiation Oncology, Biology and Physics
Volume Number 97
Issue Number 4


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