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The Effect of Beam Interruption When Implementing Deep Inspiration Breath Hold During Volume Modulated Arc Stereotactic Body Radiation Therapy

S Oh

S Oh*, B Lewis , A Watson , S Kim , T Kim , Virginia Commonwealth University, Richmond, VA


SU-I-GPD-T-613 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To determine the dosimetric effect of beam interruption during partial-arcs of a volume modulated arc stereotactic body radiation therapy (SBRT) plan delivery. Clinical implementation of breath hold, utilizing an active breathing coordinator, during SBRT increases the probability of beam interruption during partial-arc delivery.

Methods: 10 SBRT plans were retrospectively selected, five using a 6 MV flattening filter free (FFF) beam, and five using a 10 MV FFF beam. All plans had four partial-arcs, with the exception of one, consisting of six partial-arcs, and were all delivered using a Varian Truebeam linear accelerator. The plans were delivered in three scenarios: The first with no partial-arc interruptions (0int), second with one interruption of each partial-arc (1int), and third with two interruptions of each partial-arc (2int). Dose was measured using the ArcCheck cylindrical 3D diode array. 2D global gamma evaluations and dose difference (DD) were calculated using the SNC Patient software suite. Delivered MU variations were evaluated at the beam interruption angles using the log files generated during beam delivery.

Results: The interruptions caused a total increase of 3.6±1.7 MU and 6.5±2.5MU for 1int and 2int, respectively, at the beam interruption angles. Total delivered MU per plan was 2450±472 MU for all plans. All plans for using 6 MV FFF and 10 MV FFF beams passed the clinical gamma analysis threshold of 3%/3mm for 90% of the measurement points. All plans delivered with the 1int and 2int scenarios were also within 3% DD of the 0int measured data.

Conclusion: Only minimal change was observed in gamma analysis, DD, and log file analysis with up to 12 interruptions occurring during treatment with SBRT. Delivering dose with multiple beam interruptions is clinically viable due to these small variations.

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