Details

Autor(en) / Beteiligte

• Chan, Mark, PhD
• Grehn, Melanie, BS
• Cremers, Florian, PhD
• Siebert, Frank-Andre, PhD
• Wurster, Stefan, MD
• Huttenlocher, Stefan, MD
• Dunst, Jürgen, MD
• Hildebrandt, Guido, MD
• Schweikard, Achim, PhD
• Rades, Dirk, MD
• Ernst, Floris, PhD
• Blanck, Oliver, PhD

Titel

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

Ist Teil von

• International journal of radiation oncology, biology, physics, 2017-03, Vol.97 (4), p.839-848

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

2017

Quelle

MEDLINE

Beschreibungen/Notizen

• Abstract 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.