A Modified VMAT Technique for the Treatment of Diffuse and Extensive Involvement of the Skull By Various Malignancies 📝

Author: Edward D. Brandner, Weihua Fu, M. Saiful Huq, Ronald John Lalonde, Kiran Mehta, Hima Bindu Musunuru, Yongqian Zhang 👨‍🔬

Affiliation: UPMC Hillman Cancer Center and University of Pittsburgh School of Medicine, Department of Radiation Oncology, University of Pittsburgh School of Medicine and UPMC Hillman CancerCenter 🌍

Abstract:

Purpose: Treatment of diffuse and extensive involvement of the skull by malignancy presents a difficult challenge for radiation therapy. This study reports preliminary experience of a modified volumetric modulated arc therapy (VMAT) planning technique to deliver homogeneous dose to the planning target volume (PTV) while minimizing the doses to critical structures.

Methods: Eleven patients with extensive involvement of the skull by malignancy were retrospectively analyzed. A modified VMAT with Jaw-offset (JO-VMAT) was created and compared to the clinical plan with Jaw-tracking technique. Various dosimetric parameters, including PTV coverage, conformity index (CI), and doses to the normal brain were compared between the two techniques. The same dose parameters were used for JO-VMAT and Jaw-tracking plans in plan optimization.

Results: PTV coverage in JO-VMAT plans was consistent with clinical plans. There were no significant differences in the conformity index between the two techniques. However, JO-VMAT demonstrated superior sparing of normal brain tissue, significantly reducing the maximum dose (Dmax) from 10.24±7.79 Gy to 7.15±9.19 Gy, the volume receiving 10Gy (V10Gy) from 347.29±380.70 cc to 263.62±288.96 cc and the volume receiving 5Gy (V5Gy) from 556.46±405.37 cc to 428.93±371.65 cc.

Conclusion: This study explored the dosimetric benefits of the JO-VMAT technique for the treatment of diffuse and extensive involvement of the skull by malignancy. This technique provides comparable target coverage and conformity index to Jaw-tracking VMAT while significantly reducing brain doses, including Dmax, V10Gy, and V5Gy. These results highlight JO-VMAT’s potential as a brain-sparing approach in this challenging clinical scenario.