Craniospinal irradiation by volumetric modulated arc therapy technique on halcyon

Aims: Craniospinal irradiation (CSI) is a challenging task on halcyon due to its field size constraint (28 cm × 28 cm). CSI was planned by volumetric modulated arc therapy (VMAT) technique on Halcyon (6MV) linac with no junction shift with multiple arcs and numerous isocenter depending on the length of the patients. Methods and Materials: Planning CSI was achieved on Eclipse treatment planning system version 15.6 with anisotropic analytical algorithm and was optimized using autofeathering technique. Positioning accuracy was ensured by obtaining daily kvCBCT before radiation which ensured accurate field placement and avoidance of junctional errors. Pretreatment portal dosimetry was done to ensure the dose distribution calculated by the treatment planning system matches the dose delivered to the patient. Results: All VMAT CSI plans produced outstanding planning target volume (PTV) coverage with V95% >98% and gave acceptable doses to organ at risk in all CSI cases. Furthermore, the dose distributions were highly uniform, with homogeneity index values ≤0.1 and target conformity was equally excellent with values more than 0.95. In portal dosimetry, all of the composite images of CSI plans were evaluated, yielding good passing criteria of >98%. Conclusions: The remedy was straightforward to plan and deliver, thanks to autofeathering optimization. CSI plan was created with no junction shift which resulted in homogeneous and conformal doses to the PTV. The gamma analysis in the portal dosimetry composite image, which was utilized as a pretreatment verification, met all of the requirements and revealed a homogeneous and uniform junction dose.