Improving Gated Delivery Efficiency Using Brief Breath Holds at Both Inhale and Exhale
S Geneser1*, B Fahimian2, L Xing2, (1) University of California San Francisco, San Francisco, CA, (2) Stanford University, School of Medicine, Stanford, CASU-E-T-399 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: Respiration-gated intensity modulated radiation therapy (IMRT) and volumetric modulated radiation therapy (VMAT) deliver the treatment beam at a single phase to reduce dose uncertainties resulting from respiratory-induced organ motion. In some cases, gating can significantly prolong treatment times, leading to increased patient discomfort, treatment duration, and dose uncertainty due to patient postural shifts. To decrease treatment duration without increasing dose uncertainty, we propose dual-gating in conjunction with with alternating coached five to ten second breath holds at inhale and exhale. In this study, we examine the feasibility of maintaining reproducible inhale and exhale RPM marker positions in a healthy volunteer and compare the expected dual-gated delivery speedup over the free breathing case.
Materials/Methods: Varian Real-Time Position Management (RPM) respiratory signals from a volunteer were recorded during free breathing and during alternating ten second inspiration and exhalation breath hold coaching. The signals were then processed to examine the volunteer's ability to consistently reproduce RPM marker position during subsequent breath holds. Conventionally-gated and dual-gated treatment times were simulated for a given treatment plan under both normal and alternating breath hold conditions and compared.
Results: Dual-gated delivery under free breathing increases the duty cycle from 30.3% to 58.3% as compared with gating at exhale only. Alternated breath hold coaching further improves the duty cycle to 85.1%. Treatment delivery requiring 29.05 minutes to complete under normal exhale gating conditions is reduced to 16.58 minutes for dual-gating during free breathing and only 5.88 minutes with dual-gated alternated breath holds. RPM marker reproducibility was within 8% over the course of the delivery time.
Conclusion: While additional improvements and testing are necessary, dual-gated treatment delivery during alternated breath hold coaching is a feasible method for increasing duty cycle and thus improving treatment efficiency for tumors undergoing respiratory-motion.