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Dosimetric Effects On the Patient Setup Using Daily Vs Weekly CBCT in Treating Advanced Stage Lung Cancer: Preliminary Results

J Zhou*, G Lasio , A Gopal , S Lee , B Zhang , B Yi , Division of Medical Physics, Department of Radiation Oncology, Univ. of Maryland School Of Medicine, Baltimore, MD


(Sunday, 7/14/2019) 2:00 PM - 3:00 PM

Room: 221AB

Purpose: CBCT is regarded as one of the standard patient setup options of the IGRT. Daily CBCT may offer better setup accuracy but with added imaging dose and prolonged treatment time. This study aims to determine the optimal CBCT frequency by comparing the dosimetric effect of weekly CBCT patient setup protocol versus daily CBCT in treating advanced stage lung cancer.

Methods: The dataset consists of 64 daily CBCT images of randomly selected advanced stage lung patients. Daily orthogonal kV images were acquired followed by acquisition of daily CBCT, for all of the fractions. A weekly CBCT protocol was simulated by accepting the kV-based setup for 4 days and the kV followed by CBCT setup for 1 day per week. Dose distributions were calculated for the daily and the weekly CBCT schemes using CBCT’s of the treatment days. The Raystation (RaySearch Laboratories AB, Sweden) treatment planning system (TPS) was used together with in-house data processing scripts.

Results: The daily CBCT protocol achieved marginally higher target dose than the weekly CBCT. Ratios of D95 between delivered verse plan are 0.893±0.003, 0.883±0.002 (p=0.353) for daily and weekly, respectively. Those of mean dose are 0.995±0.0003, 0.988±0.0003 (p=0.055). None of the OAR such as lung, spinal cord and heart show noticeable dose changes.

Conclusion: Our results suggest that a protocol with daily kV imaging plus weekly CBCT has comparable deviations from the planned dose compared to a daily kV imaging plus daily CBCT protocol in advanced stage lung cancer, in the patient cohort we analyzed. To validate these preliminary results, a similar study with a larger sample size would be warranted.


Not Applicable / None Entered.


TH- RT Interfraction motion management : setup errors, immobilization, localization

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