Program Information
The Influence of Time of Day On Set-Up Errors in External Beam Radiotherapy
V Valakh*, E Day , Allegheny Health Network, Pittsburgh, PA
Presentations
SU-I-GPD-J-53 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: The impact of operator-dependent factors on the accuracy of positioning for radiotherapy is not well described. We carried out an exploratory study of influence of time of day, which may potentially be a measure of therapist fatigue, on daily set-up.
Methods: With approval from IRB, 346 consecutive set-up error measurements from 15 patients were retrospectively collected. Fractionated pelvic radiotherapy was administered prone with a mechanical small bowel displacement device. After positioning on LINAC couch according to tattooed skin marks, kilovoltage CBCT’s were obtained prior to treatment delivery. Alignment to bone produced couch translations in 3 orthogonal directions. Translations recorded on day of verification were excluded to limit impact of systematic errors, and chief component of translations collected was that from random inter-fraction set-up errors.
Results: Mean set-up error (± SD, range) in right-left, superior-inferior, and anterior-posterior directions was 0.47 cm (± 0.41, 0 – 3.02), 0.48 cm (± 0.31, 0 – 1.9), and 0.51 cm (± 0.5, 0 – 2.93), respectively. Largest error in either direction during each treatment fraction was on average 0.85 cm (± 0.48, 0.09 - 3.02). Female sex, African-American race, age > 60, obesity, on-treatment weight loss, radiotherapy interruptions, and non-IMRT plans were strongly associated with larger set-up errors. Potential influence of time of day was noted for errors in superior-inferior, anterior-posterior directions, and for largest error in either direction during each fraction. Largest error was on average 0.78 cm from 6:30 am to 9:00 am, 0.99 cm from 9:05 am to 11:55 am, and 0.81 cm from 1:00 pm to 4:00 pm after lunch break.
Conclusion: This study demonstrated possible impact of time of day on set-up errors. Therapist fatigue may be one of explanations. If findings are confirmed by a planned larger study, workflow measures to improve accuracy of set-up may be considered.
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