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Dosimetric Impact of Hysteresis On Lung Cancer Tomotherapy

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K Zhang

K Zhang*, JR Dai , ZH Hu , CM Niu , National Cancer Center / Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China


SU-I-GPD-T-267 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This study investigates the dosimetric impact of hysteresis on lung cancer tomotherapy.

Methods: MapCheck was sandwiched between array calibration fixture and film alignment template and then fixed on XY4D motion simulation table to form the phantom combination. Phantom plans were based on the MVCT image of the phantom combination. The structures and optimization parameters were from patient plans and the DQA plan`s prescription was reduced to 200cGy. Each plan was measured three times with a random starting phase in the static state and five hysteresis states (hysteresis 0, π/32, π/16, π/8, and π/4); the average of the three values was used in the analyses. The SNC Patient software imported the DICOMRT structure file modified by an in-house-developed MATLAB program and displayed and analyzed globally and each structure in the measurement plane. The absolute dose difference (DD) local normalization with a dose difference threshold of 6cGy was adopted in the analysis of each hysteresis vs. static state and for non-zero vs. zero hysteresis. The thresholds were 10% for all analyses.

Results: For the DD analysis of each hysteresis vs. static state, the passing rate differed depending on the structure but was similar between different hysteresis states for globally and most structures. For the DD analysis of non-zero vs. zero hysteresis (H0(non-zero)), the passing rate changed slightly with increasing hysteresis when hysteresis was not π/4 and was lowest during maximum hysteresis both globally and for all structures. The differences for H0(π/4) vs. H0(π/32), H0(π/16), and H0(π/8) were significant globally and for the target, left lung, and chest wall.

Conclusion: In this study, the impact of hysteresis for each hysteresis vs. static state differed depending on the structure but was similar between different hysteresis states. For non-zero vs. zero hysteresis, remarkable effects were only seen for structures directly related to the target.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by the national key project of research and development of china (2016YFC0904600). The authors report no conflicts of interest with this study.

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