Purpose: Voluntary deep inspiration breath-hold (DIBH) is commonly used in radiation therapy (RT), but the short duration of a single breath-hold, estimated to be around 20-40 seconds (s), is a limitation. This prospective study aims to assess the feasibility and safety of using a simple preoxygenation technique with a Venturi mask to prolong voluntary DIBH. Methods and materials: The study included 33 healthy volunteers and 21 RT patients. Preoxygenation was performed using a Venturi mask with a 50% oxygen concentration. Paired t-tests compared the duration of a single DIBH in room air and after 5, 15, and 30 minutes of preoxygenation in healthy volunteers. Sustainability of breath-hold and tolerability of heart rate and blood pressure were assessed for multiple DIBH durations in both volunteers and patients. Results: In healthy volunteers, a 15-minute preoxygenation significantly prolonged the duration of a single DIBH by 24.95s compared to 5-minute preoxygenation (89 ± 27.76s vs. 113.95 ± 30.63s, p < 0.001); although there was a statistically significant increase in DIBH duration following 30-minute preoxygenation, it only extended by 4.95s compared to 15-minute preoxygenation (113.95 ± 30.63s vs. 118.9 ± 29.77s, p < 0.01). After 15-minute preoxygenation, a single DIBH lasted over 100s in healthy volunteers and over 80s in RT patients with no significant differences among six consecutive cycles of DIBH. Furthermore, there were no significant differences in heart rate, or blood pressure after DIBHs, including DIBH in room air and six consecutive DIBH after 15-minute preoxygenation (all p > 0.05). Conclusions: Preoxygenation with a 50% oxygen concentration for 15 minutes effectively prolongs the duration of six cycles of DIBH both in healthy volunteers and RT patients. The utilization of a Venturi mask to deliver 50% oxygen concentration provides a solution characterized by its convenience, good tolerability, and effectiveness.