Clinical implementation and evaluation of stereotactic liver radiotherapy in inspiration breath-hold using nasal high-flow therapy and surface guidance

Objective. To evaluate 2 years of clinical experience with markerless breath-hold liver stereotactic radiotherapy (SBRT) using noninvasive nasal high-flow therapy (NHFT) for breath-hold prolonging and surface guidance (SGRT) for monitoring. Methods. Heated and humidified air was administered via a nasal cannula (40 L/min, 80% oxygen, 34 °C). Patients performed voluntary inspiration breath-holds with visual feedback. After a training session, 4-5 breath-hold CT scans were acquired to delineate an internal target volume (ITV) accounting for inter- and intra-breath-hold variations. Patients were treated in 3-8 fractions (7.5-20 Gy/fraction) using SGRT-controlled beam-hold. Patient setup was performed using SGRT and CBCT imaging. A posttreatment CBCT was acquired for evaluation purposes. Results. Fifteen patients started the training session and received treatment, of whom 10 completed treatment in breath-hold. Half of all 60-second CBCT scans were acquired during a single breath-hold. The average maximum breath-hold duration during treatment ranged from 47 to 108 s. Breath-hold ITV was on average 6.5 cm ^³/30% larger (range: 1.1-23.9 cm ^³/5%-95%) than the largest GTV. Free-breathing ITV based on 4DCT scans was on average 16.9 cm ^³/47% larger (range: −2.3 to 58.7 cm ³/−16% to 157%) than the breath-hold ITV. The average 3D displacement vector of the area around PTV for the posttreatment CBCT scans was 5.0 mm (range: 0.7-12.9 mm). Conclusions. Liver SBRT in breath-hold using NHFT and SGRT is feasible for the majority of patients. An ITV reduction was observed compared to free-breathing treatments. To further decrease the PTV, internal anatomy-based breath-hold monitoring is desired.