Purpose: To determine if coplanar treatment plans generated for craniopharyngioma patients on a magnetic resonance (MR) guided linac can achieve the same dosimetric objectives used for non-coplanar treatment plans on conventional linacs.
Methods: Nine patients were treated for craniopharyngioma in our clinic between 2016 and 2021 using 3-4 non-coplanar conformal dynamic arcs with 4-6 additional IMRT beams with 6MV photon beams on a Varian Truebam Stx Linac. The clinical images and structures were used to create coplanar treatment plans in the Viewray MRIdian treatment planning system using the same dose fractionation of 54Gy in 30 fx and organ-at-risk (OAR) objectives: PTV D99%>95%, PTV D0.03cc<105%, Brainstem D0.03cc<60Gy, Chiasm D0.03cc<56Gy, Optic NervesD0.03cc<58cGy, Retina D0.03cc< 50Gy, Lens D0.03cc<10Gy, Cochlea D0.03cc<40Gy, and Spinal Cord D0.03cc<55Gy. MR-linac plans used 20-22 coplanar beams with 6FFF photons, and were normalized to PTV V100%=95%. Conformity index (CI) was calculated by taking the ratio of the prescription isodose volume to the PTV, the goal in planning was CI< 1.5. All generated plans were delivered to a 3D diode array for verification QA using 3%/2mm, 10% dose threshold, gamma criteria of >95% measurement points gamma index <1.
Results: All plans met the OAR objectives and had an overall maximum dose <105%. The average conformity index was 1.26 and the range was 1.1-1.4. Plan delivery time, which includes gantry motion, MLC motion, and beam delivery, was 4.7 minutes on average with a range of 3.9-5.7 minutes. All plans passed verification QA.
Conclusion: Co-planar treatment plans generated for craniopharyngioma patients using an MR-guided linac are clinically feasible, meeting all planning objectives with deliverable plans and less than 6 minute treatment times.
Dosimetry, MR, Treatment Planning
IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined (general)