A comparison of intensity modulated radiation therapy (IMRT) and HybridArc (TM) treatment plans for spinal tumours

Abstract

Aim: HybridArc™ (Brainlab, AG) is a treatment technique blending aperture-enhanced dynamic conformal arc therapy with discrete IMRT beams. This study dosimetrically compares HybridArc with IMRT in Stereotactic Body Radiotherapy (SBRT) for spinal tumours. Method: In a retrospective study of 10 patients with metastatic thoracic or lumbar spinal disease, the dosimetric results of a 7 field IMRT distribution were compared against a single 320–340 degree HybridArc™ distribution containing three to four fixed-port IMRT fields. Planning was performed using the Brainlab iPlan RT Dose 4.5.3 platform. Treatment plans were designed to deliver a homogeneous dose of 40 Gy to Planning Target Volume (PTV) Spine with a simultaneous integrated-boost to the tumour to a total dose of 50 Gy. Planning objectives were 90% of prescribed dose to cover 100% of PTVs, while minimising the maximum spinal cord point dose to 34 Gy. A comparison of target and Organ At Risk dose volume histograms, maximum and minimum target dose, and conformity index was used to evaluate each planning technique. Planning time, mean beam-on time and Monitor Units were also analysed. Results: Both IMRT and HybridArc™ produced clinically acceptable treatment plans; HybridArc™ incorporating 4 IMRT beams generally produced superior results when compared to HybridArc™ incorporating 3 IMRT beams. Superior PTV coverage and lower maximum dose was achieved more often with IMRT plans compared with HybridArc™. The conformity index for the IMRT distributions was generally lower, correlating to improve sparing of normal tissues. Planning times were less for IMRT plans due to the time taken to optimise both aperture and IMRT beams for HybridArc™. Conclusion: Epworth Radiation Oncology will continue to use IMRT as its modality of choice for SBRT of spinal tumours as the dosimetric qualities are generally superior to HybridArc™, and efficiencies are achieved in the planning process.