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Dosimetric Performance of a New Ring Gantry Linear Accelerator for the Stereotactic Body Radiation Therapy Treatment of Prostate Cancer

F Li*, P Teo , R Lalonde , D Clump , D Heron , M Huq , UPMC Hillman Cancer Center, University of Pittsburgh School of Medicine, Pittsburgh, PA


(Sunday, 7/29/2018) 4:30 PM - 5:00 PM

Room: Exhibit Hall | Forum 7

Purpose: To investigate the dosimetric performance of a novel ring gantry linear accelerator for the treatment of prostate stereotactic body radiation therapy (SBRT) patients.

Methods: Using a test version of Eclipse V15.5.11 (Varian), fourteen patients with early stage prostate cancer, previously planned in Eclipse (AAA V11.0.31) and treated on TrueBeamᵀᴹ (TB) STx, were re-planned with the same optimization objectives using Varian Halcyon as the delivery system. Two to four beam VMAT plans were generated for each patient. Same set of patient were also re-planned with 9 beams IMRS. The prescription was 36.25Gy to PTV and 40.0Gy to GTV in five fractions. At least 95% of the PTV and GTV were covered by the prescription isodose line; rectum V100 was limited to 5%, bladder V100 limited to 10%. Plans were generated by utilizing a dual-level MLC. The evaluated dosimetric parameters include PTV/GTV coverage, conformity index (CI), treatment times, total MU, number of MLC segments and organ-at-risk (OAR) sparing.

Results: Average CI of 1.08, 1.08 and 1.11 is obtained for Halcyon VMAT, TB VMAT and Halcyon IMRS plans respectively. Similar level of organ sparing is achieved while maintaining the same level of PTV/GTV coverage across the plans. Total MU were 2923, 2877 and 4831 for Halcyon-VMAT, TB and Halcyon-IMRS plans, respectively. Corresponding beam on times are 3.6 min for Halcyon-VMAT, 2.1 min for TB and 6min for Halcyon-IMRS. Average number of MLC segments is about 500 for both Halcyon-VMAT and TB plans, and 1500 for Halcyon-IMRS.

Conclusion: Halcyon VMAT/IMRS plans have similar plan quality as TB plans. Plan conformity and delivery time are comparable. Halcyon could potentially be used for SRS/SBRT treatment.


Not Applicable / None Entered.


TH- External beam- photons: extracranial stereotactic/SBRT

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