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  4. Dosimetric Verification for Ultra-Small Intracranial Target Radiation Treatment Using Linac-Based Dynamic Conformal Arc Therapy

Dosimetric Verification for Ultra-Small Intracranial Target Radiation Treatment Using Linac-Based Dynamic Conformal Arc Therapy

Y Zheng*, Z Xu , D Mansur , M Machtay , G Pereira , University Hospitals Cleveland Medical Center, Cleveland, OH

Presentations

(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To assess the dosimetric accuracy of ultra-small intracranial target (< 2 cm³) radiation treatment using linac-based dynamic conformal arc therapy (DCAT) technique.

Methods: Three spherical targets with diameter of 0.6 cm (PTV1), 1.0 cm (PTV2), and 1.5 cm (PTV3) were created in the phantom center in Pinnacle³ (version 14.0) treatment planning system. 360° single arc DCAT plans were generated with 2 mm block margin and 6MV flattening filter free beam for each PTV. Field sizes were 1.0x1.0 cm², 1.4x1.5 cm², and 1.9x2.0 cm², respectively. All plans were delivered on an Elekta VersaHD linac with 5 mm wide leaves. Cone-beam CT and HexaPod 6D couch were used to position the phantom accurately before delivery. ArcCHECK, Gafchromic EBT3 film, and Exradin A14SL micro ion-chamber were used for absolute dose measurement and comparison. The reproducibility of the radiation delivery was verified by repeating the measurement with micro ion-chamber 3 times for the same plan.

Results: With 3%/2mm criteria, gamma analysis passing rates of ArcCHECK and film measurements for three targets using absolute dose comparison were 96.9%±0.9% and 97.4%±1.4%, respectively. Difference between the micro ion-chamber measurement and the calculated mean air cavity volume dose for PTV1-3 were -8.5%, -5.4%, and -2.1%, respectively. In addition, output factor for 1x1 cm² field size at 10 cm depth was measured with the micro-ion chamber and compared with the commissioning data, which was measured by SunNuclear EDGE detector. The micro ion-chamber measurement was found 6.1% low. Variations in the repeated ion-chamber measurements of each plan were less than 0.5%.

Conclusion: This study demonstrated the capability of linac-based DCAT technique for ultra-small intracranial target radiation treatment. Dosimetric accuracy and consistency of the radiation delivery were verified. A combination of ArcCHECK and high resolution film is recommended for dosimetric verification of plans with field sizes less than 2x2 cm².

Keywords

Stereotactic Radiosurgery

Taxonomy

TH- External beam- photons: intracranial stereotactic/SBRT

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