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Session: Therapy General ePoster Viewing [Return to Session]

Stereotactic Body Radiotherapy On a Ring-Gantry Based Linac with Novel Image Guiding System (Reflexion): Plan Quality Comparison with TrueBeam and Tomotherapy

B Liu1*, C Han1, T Reilly1, Y Dorsainvil1, K Qing1, Y Chen1, T Williams1, A Liu1, (1) City of Hope National Medical Center, Duarte, CA


PO-GePV-T-290 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Reflexion X1 (RFX) is a new ring-gantry based external beam radiotherapy machine with novel imaging guidance system (kV-CT and PET). This study aims to evaluate the dosimetric performance of RFX equipped with 6MV-FFF photon beam in planning for Liver and Lumbar Spine SBRT, compared to TrueBeam with high definition MLC (TB) and Helical TomoTherapy (HT).

Methods: Three patients for each site were retrospectively included in the treatment planning study. For each patient, four plans were developed: TB plan using 10MV FFF photon beam, HT plan with 2.5-cm jaw size, RFX plan with 20-mm jaw size and with 10-mm jaw size. The dose prescription is 40Gy in 5 fractions for all liver patients, 27Gy in 3 fractions for two spine patients and 24Gy in 2 fractions for one spine patient. Clinical planning objectives were followed per NRG LU-002 and Timmerman guidelines 2018 protocol. Dosimetric parameters were compared among different machines.

Results: On average, 15 dosimetric parameters (range: 11-22) were analyzed for each patient. In all plans, prescription dose covers no less than 95% of the planning target volume (PTV). The maximum dose of RFX plans is within 2% from those of TB and HT plans. Organ-at-risk dose constraints were met consistently in all three machines. For Spine SBRT, the Cauda Equina D0.03cc is 20.1Gy±3.6Gy, 19.9Gy±3.5Gy, 20.6Gy±3.4Gy and 20.5Gy±3.3Gy for TB, HT, RFX-20mm and RFX-10mm plans respectively. For Liver SBRT, Liver minimal spared volume of 21Gy is 1504cc±310cc, 1458cc±316cc, 1483cc±314cc, 1495cc±310cc for TB, HT, RFX-20mm and RFX-10mm plans respectively. The conformity index and dose drop-off of TB and RFX-10mm are comparable, and are superior to HT and RFX-20mm.

Conclusion: This retrospective treatment planning study suggested that the new RFX system achieved comparable plan quality in Liver and Spine SBRT compared to TB and HT.


Treatment Planning, Radiation Therapy


Not Applicable / None Entered.

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