Dose Calculation Using Dual Energy CT in Photon Radiation Therapy
Presentations
PO-GePV-M-140 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To investigate the dosimetric differences of dual energy CT (DECT) based treatment planning in photon radiation therapy, compared with the traditional single energy CT (SECT), using both AAA and AcurosXB algorithms.
Methods: Multi-Energy CT phantom (Sun Nuclear Corp) with 14 inserts was scanned on the Siemens SOMATOM CT scanner. Two protocols were executed: 120kVp SECT, and 80kVp/140kVp DECT. For the DECT protocol, a pseudo-monoenergetic 120kVp CT was reconstructed. The CT-to-electron density curves, and CT-to-mass density curves were extracted for both scans and imported into Eclipse treatment planning system. Patients were scanned using the same two protocols and assigned to their corresponding curves. Three sets of RapidArc (RA) plans were designed and calculated in Eclipse for three targets: target next to bone –“RA_bone”, target with metal inside – “RA_metal”, and prostate target with double hip prosthesis – “RA_pros”. For each target, MUs were kept the same between SECT and DECT plans. Both AAA and AcurosXB algorithms were used for calculation.
Results: CT numbers from the DECT and SECT differ the most in high density materials. For all plans, DECT target dose is consistently lower than SECT dose. The target dose difference is not clinically significant except for RA_metal plan (3.9%). 3D dose difference map revealed the largest discrepancies around the most superior and inferior ends of the PTV. AAA calculations resulted in bigger SECT-DECT dose difference than AcurosXB.
Conclusion: When adopting DECT into a photon clinic, most patient plans will not see significant dose differences. DECT dose to the target will be slightly colder, but only metals will show clinically significant under-dose. This effect is more prominent in AAA calculation than AcurosXB, suggesting that the CT-to-electron density curve is more affected by DECT than CT-to-mass density curve. Further study is warranted to investigate the dose calculation accuracy in DECT.
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