D Lee¹*, S Oh¹, D Pavord¹, A Colonias¹, R Fuhrer¹⁵, J Sohn^1,2, (1) Allegheny Health Network, Pittsburgh, PA, (2) Drexel University College of Medicine, Philadelphia, PA

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  D Lee

PO-GePV-M-78 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: This study aims to test the daily dose accumulation of online adaptive plans using commercially available MiM (MiM Software; Cleveland, OH) and RayStation (RaySearch; Stockholm, Sweden) for Elekta Unity MR-Linac. Dose accumulation is essential to validate delivered dose to tumor and surrounding organs, which can be a prerequisite for further re-planning and/or an additional fraction.

Methods: This study utilized a CT and 5 daily MR datasets of a prostate cancer patient to develop a reference plan (37.5Gy in 5 fractions with 7-fields and a 7FFF Unity® beam) and simulate two plan adaptations using an offline MRL Monaco (v5.40.01). In the first and second simulations, (1) five adapt-to-position(s) (ATP), rigidly registering CT-to-MR(s), were performed and (2) three ATP(s) for Day1, Day3 and Day5 MR(s) and two adapt-to-shape(s) (ATS) for Day2 and Day4 MR(s), deformably registering CT-to-MR or MR-to-MR, were performed for composite doses. MiM (Ver 7.0.6) and RayStation (Ver 9A) were used for rigid and deformable image registration for composite doses. Composite doses were compared in mean dose and 3D gamma analysis using an in-house software.

Results: We found a minimal difference of mean dose for ATP plans (MiM<0.1% and RayStation<0.3% for PTV (Prostate+SeminalVes+5mm margin)) and slightly higher for ATS plans (MiM<0.3% and RayStation<2.5% for PTV). The 3D gamma analysis resulted in 91.1% and 93.3% for ATP plans, and 90.6% and 89.9% for ATS plans across MiM and RayStation, respectively.

Conclusion: This is the first that we demonstrated the dose accumulation of ATP and ATS using MiM and RayStation across rigid and deformable registration. In addition, generating a composite plan in adaptive radiation therapy process can be achievable to validate delivered cumulative doses. Further investigations will need to include an improvement of 3D dose accumulation and speed for real-time process whilst optimizing image registrations and adapting daily target organ contours.

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