C Liu*, A Magnelli, Y Cho, L Angelov, E Balagamwala, S Chao, P Xia, Cleveland Clinic, Cleveland, OH

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  C Liu

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PO-GePV-T-415 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To compare four dose calculation algorithms and evaluate the dosimetric impact of the titanium implants in the spine for SBRT using three commercial treatment planning systems (TPSs).

Methods: Twenty patients with titanium implants treated with spinal SBRT in 2019-2021 at our institution were selected. The clinical plan for each patient was created in Pinnacle and subsequently imported into Eclipse (AAA and Acuros) and Raystation (CCC) for dose re-calculation. For each dose algorithm, two plans with and without density override (DO) to the titanium implant (4.43 g/cm3) were created per patient. The plans with DO were set to have the same tumor dose coverage as the plans without DO. Dose metrics of PTV such as maximum dose to 0.03 cc (Dmax), dose to 99% (D99%) and 90% (D90%) and dose limits for the spinal cord such as Dmax and 10 Gy (V10Gy) were evaluated.

Results: For the same algorithm, plans with and without DO had similar dose distributions. Differences in PTV metrics were <2% with slightly larger variations up to 5.58% in Acuros. Dmax of spinal cord for plans calculated with DO increased but the differences were insignificant for all algorithms (mean: 0.60%). Comparing to the clinical plans, the relative dose differences of PTV metrics between algorithms had an average of ~3% while two cases had the differences of >10%. Differences in Dmax of the spinal cord had an average of 4.1% while differences up to 11% were observed for smaller cord volumes. Due to the different partial volume interpretations, V10Gy (cc) of spinal cord were inconsistent among three TPSs depending on the spinal cord volume.

Conclusion: For all algorithms, the presence of titanium implants in the spine had minimal impact on dose distributions with and without DO. The partial volume effect from different TPSs can impact on V10Gy (cc).

Funding Support, Disclosures, and Conflict of Interest: Dr. Chao reports honorarium from Varian Medical Systems and research support from Blue Earth Diagnostics. Dr. Xia reports a research grant from Advanced Oncotherapy plc, London, UK. Other authors have nothing to disclose.

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