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Analysis of Modulation Factor to Reduce the Delivery Time of Head and Neck Cases in Helical Tomotherapy
H Shimizu1*, K Sasaki2 , H Tachibana1 , N Tomita1 , C Makita5 , K Nakashima6 , K Yokoi1 , T Kubota1 , T Iwata1 , T Kodaira1 , (1) Aichi Cancer Center Hospital, Nagoya, Aichi, (2) Gunma Prefectural College of Health Sciences, Maebashi, Gunma
Presentations
MO-RPM-GePD-TT-1 (Monday, July 31, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Theater
Purpose: The purpose of this study was to reduce the delivery time of head and neck cases in helical tomotherapy using initial values and the upper limit values of modulation factor (MF).
Methods: First, patients with head and neck cancer (293 cases) treated between June 2011 and July 2015 were included in the analysis of MF values. We hypothesized that the histogram of MF values would show normal distribution, so the average of MF value was defined as initial MF value (MFinitial). In addition, the value that added double of the standard deviation of MF value to the average MF value was defined as the upper limit of the MF value (MFUL). Next, a treatment plan was designed for patients with head and neck cancer (62 cases) treated between December 2015 and June 2016 by using MFinitial value. If the dose distribution was not good, we increased the MF value up to MFUL step by step in intervals of 0.1 or 0.2
Results: The average MF value for the nasopharynx, oropharynx, and hypopharynx cases decreased from 2.1 to 1.9 (p = 0.0006), 1.9 to 1.6 (p < 0.0001), and 2.0 to 1.7 (p < 0.0001) by adapting the MFinitial and the MFUL values, respectively. For the post-adaptation of MFUL, the percentage of the MF values less than the MFinitial values in nasopharynx, oropharynx, and hypopharynx cases were 84.2%, 100.0%, and 92.3%, respectively. The average delivery time for the nasopharynx, oropharynx, and hypopharynx cases also decreased from 19.9 s/cm to 16.7 s/cm (p < 0.0001), 15.0 s/cm to 13.9 s/cm (p = 0.025), and 15.1 s/cm to 13.8 s/cm (p = 0.015), respectively.
Conclusion: The delivery time was shortened by the adaptation of MFinitial and MFUL values with a reduction in the average MF value for head and neck cancer cases.
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