Dosimetric Implications of Residual Tracking Errors during Robotic SBRT of Liver Metastases

Type of publication:  Artikel
Publikationsstatus: Akzeptiert
Zeitschrift: International Journal of Radiation Oncology • Biology • Physics
Jahr: 2016
Monat: Dezember
Seiten: accepted
Verlag: Elsevier
ISSN: 0360-3016
DOI: 10.1016/j.ijrobp.2016.11.041
Abriss: Purpose While the metric precision of robotic stereotactic body radiation therapy (SBRT) in the presence of breathing motion is widely known, we investigated the dosimetric implications of breathing phase-related residual tracking errors. Methods and Material: From 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 ten breathing-phases. The average breathing phase errors were used to shift and rotate the CTV/PTV for each phase to calculate a pseudo 4D error dose distribution for comparison with the original planned dose distribution. Results The median systematic directional correlation, prediction, and absolute aggregate rotation errors were 0.3mm (0.1–1.3mm), 0.01mm (0.00–0.05mm), and 1.5° (0.4°–2.7°). Dosimetrically, 44%, 81%, and 92% of all voxels differed less than 1%, 3%, and 5% of the planned local dose. Median coverage reduction for the PTV was 1.1% (-7.8%–+0.8%), significantly depending on correlation (p=0.026) and rotational (p=0.005) error. With a 3mm PTV margin, the median coverage change for the CTV was 0.0% (-1.0%–+5.4%), not significantly depending on any investigated parameter. In 42% of patients, the 3mm margin did not fully compensate for the residual tracking errors, resulting in a CTV coverage reduction of 0.1%–1.0%. Conclusions For liver tumors treated with robotic SBRT, a safety margin of 3mm is not always sufficient to cover all residual tracking errors. Dosimetrically, this translates only into small CTV coverage reductions.
Autoren: Chan, Mark
Grehn, Melanie
Cremers, Florian
Siebert, Frank-Andre
Wurster, Stefan
Huttenlocher, Stefan
Dunst, Jürgen
Hildebrandt, Guido
Schweikard, Achim
Rades, Dirk
Ernst, Floris
Blanck, Oliver