Hypofraction radiotherapy of liver tumor using cone beam computed tomography guidance combined with active breath control by long breath-holding.

Abstract

To evaluate the feasibility and validity of cone beam computed tomography (CBCT) and active breath control (ABC) by long breath-holding in hypofraction radiotherapy of liver tumor. Twenty-four patients received hypofraction radiotherapy of liver tumor with long breath-holding at end-inhale; four prescriptions were used: 6 Gy×7 (n=8), 10 Gy×4 (n=7), 5 Gy×9 (n=6), 4 Gy×10 (n=3). For each fraction, all patients received pre-correction CBCT scans with ABC, some patients received post-correction and post-treatment CBCT. The interfraction and intrafraction liver positioning errors on medial-lateral (ML), cranial-caudal (CC) and anterior-posterior (AP) directions were obtained. The theoretic margin from clinical target volume (CTV) to planning target volume (PTV) was calculated based on post-treatment error. The dosimetric parameters of PTV and normal tissue were compared between ABC and free breathing (FB). The interfraction error in liver positioning showed system errors (Σ) of 3.18 mm (ML), 6.80 mm (CC) and 3.05 mm (AP); random error (σ) of 3.03 mm (ML), 6.78 mm (CC) and 3.62 mm (AP). These errors were significantly reduced with CBCT guided online correction. The intrafraction systematic error was 0.72 mm (ML), 2.21 mm (CC), 1.49 mm (AP), and random error was 2.30 mm (ML), 3.58 mm (CC), 2.49 mm (AP). Dosimetric parameters such as PTV, the liver's volume included by 23, 30 Gy isodose curve (V23, V30), mean dose to normal liver (MDTNL) and mean dose to cord were significantly larger for FB (P<0.05). Liver radiotherapy with long time breath-holding at end-inhale is an effective method to reduce liver motion, PTV and dose to normal tissue. Interfraction and intrafraction liver positioning errors were substantial. CBCT guided online correction of positioning error is recommended for liver radiotherapy with end-inhale ABC.