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SU‐FF‐T‐250: Impact of Pulse Forming Network (PFN) and Injection Current (IC) Parameters On Output and Energy Variations of Helical TomoTherapy
Author(s) -
Shi C,
Gutiérrez A,
Liu Y,
Zhai Y,
Papanikolaou N
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3181726
Subject(s) - tomotherapy , wedge (geometry) , nuclear medicine , imaging phantom , materials science , voltage , dose rate , energy (signal processing) , physics , biomedical engineering , mathematics , medicine , optics , statistics , radiation therapy , quantum mechanics , medical physics
Purpose: To quantity evaluate the impact of pulse forming network (PFN) and injection current (IC) parameters on the output and energy variations of a helical TomoTherapy (HT) unit. Method and Materials: Tomotherapy quality assurance (TQA™) platform, especially the step wedge phantom and step wedge static module, was used for the whole measurement. PFN and IC voltage values were coarsely sampled from 3.0 to 5.0 V in 0.2 V increments, and finely sampled ( 4.0 < = V PFN < = 4.1 and 3.5 < = V IC < = 3.7 ) in 0.02 V increments. Results: Five working zones were found for different combination of PFN and IC voltage values: low dose rate zone, normal dose rate zone, dose rate failure during treatment zone, high dose rate zone, inoperable dose rate zone . It was noted that a 1.0% increase in V IC yields an average 1.4% increase in the average dose rate. Additionally, a 0.02 V increase in V PFN yields an average 1.0% increase in the average dose rate. A 1.0% increase in the V IC value yielded an average 0.3% decrease in the energy ratio. Furthermore, changes in the energy ratio were more dependent on V IC than V PFN based on the fact that only a 0.5% variation in energy was noted when varying the V PFN from 4.00 to 4.10 V while a 2.0% change was noted when varying the V IC from 3.5 to 3.7 V. Conclusions: In this study, several working zones based on the V PFN and V IC parameter setting were found to exist for a HT unit. Inside the normal dose rate zone, the output and energy vary linearly with V IC and V PFN parameter values. The results of this study may provide a quick guide for physicists to adjust their HT unit V PFN and V IC values in order to reset the radiation beam output and energy back to within the tolerance of the commissioned baseline.