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Dosimetric Evaluation of Gated and Non-Gated IMRT Treatments Using Portal Dose Image Prediction Software

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K Karunakaran

Kaviarasu Karunakaran1*, Arunai Nambi Raj2, K Krishna Murthy1, Ananda Giri Babu 1, B Durga Prasad1, (1)Krishna Institute of Medical Sciences, Secunderabad, Andhra Pradesh,(2) Vellore Institute of Technology, Vellore, Tamilnadu

SU-E-T-178 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The aim of the study is to compare the planar dose of IMRT fields on RPM gated delivery (for different duty cycles) with non-gated delivery.

Methods: Clinac NovalisTx Linear Accelerator equipped with Real-Time Position Management (RPM) gating system is used to deliver the gated treatments. Varian Eclipse Treatment Planning System is used to perform the IMRT Planning. Quality Assurance of IMRT fields are performed on Electronic Portal Imaging Detector (aS1000) with Portal Dosimetry software. Portal Dose Image Prediction software is used to analyze the gamma of planar doses for gated to the reference of non-gated IMRT delivery.
In this retrospective study, 60 IMRT fields from various IMRT plans were analyzed and compared for three different duty cycles (20%, 30% & 40% Duty cycle, which are generally used for treatment) of gated delivery with that of non-gated delivery. The measured dose planes were analyzed for gamma agreement with criteria of 1% to 1mm. In addition to that, the measured dose planes of gated & non-gated delivery are compared with the TPS Calculated dose planes for gamma with criteria of 3% to 3mm.

Results:The mean values of average area gamma greater than one for measured planar doses for 60 IMRT fields of 20%, 30% and 40% duty cycles were 1.50, 0.79 and 0.58 respectively for the gated delivery to the reference of non-gated delivery.

Conclusion:The Gamma results suggest that the gated deliveries for various duty cycles are comparable with the normal non-gated delivery. The result exhibits that the increase in duty cycle reduces the deviation between the gated and non-gated delivery. This deviation is attributed due to the frequent breakage of beam for 20% duty cycles compared with the 30% and 40% duty cycles.

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