Author: Issra Rashed, Jennie Wilder, Jingeng Zhu 👨🔬
Affiliation: Rush Riverside Cancer Institute, Advanced Oncology Solutions (AOS) Varian, a Siemens Healthineers company 🌍
Purpose: Develop a method to plan and deliver homogeneous dose to Craniospinal(CS) irradiation on Linear Accelerator.
Methods: Three treatment planning volumes (PTV) are created in sequence from superior to inferior of the CS structure to accommodate the Linear Accelerator field size limits. PTV1 from top of the head to the lower end of the cervical spine, PTV2 from the lower end of cervical spine to the middle of the Thoracic spine, PTV3 from the middle of the Thoracic spine to the end of CNS. Each PTV overlaps the abutting PTV(s) by 8-10cm. Two VMAT arc beams are defined at the center of PTV1, one VMAT arc beam each is defined at center of PTV2 and PTV3. The three isocenters are set with the same lateral and vertical coordinates and only use longitudinal shifts. Multiple targets VMAT arc beam optimization is used to achieve conformal dose distribution to the targets. Single extended CBCT on Varian true beam is used for patient position and verification. Treatment of the entire CS structure is sequentially delivered by moving patient in the longitudinal direction only.
Results: This method creates an homogenesis radiation dose to the Craniospinal treatment target with minimum and maximum doses at 95% to110% of the prescribed dose. Single extended CBCT and moving patient in the longitudinal direction only during the treatment promises an accurate radiation delivery.
Conclusion: The developed method can achieve homogeneous dose to craniospinal irradiation on Linear Accelerator. Therefore, it overcomes the difficulty of geometric radiation field matching and dosimetry feathering of the craniospinal irradiation.