Purpose: To demonstrate that volumetric-modulated arc therapy (VMAT) presents a favorable dosimetric profile for patients with extensive skin field cancerization (ESFC) of the scalp.
Methods: Twelve ESFC patients treated with VMAT to the scalp were retrospectively analyzed for this study. The prescription (Rx) doses ranged from 45-50 Gy in 25 fractions for the ESFC with a simultaneous integrated boost of 50-55 Gy in 25 fractions to the defined lesions. A 10 mm 3D wax bolus (.decimal, Sanford, FL) was generated from the CT scan. The organ-at-risk (OAR) dose objectives and steep dose gradient between the planning target volume (PTV) and OARs were achieved using a combination of specialized ring and dose avoidance planning structures in the Eclipse planning system (Varian Medical Systems, Palo Alto, CA). All treatment plans were normalized such that at least 95% of the Rx dose covered 98% of the PTV. In-vivo dosimetry, using TLDs, ensured that treated skin surface doses did not differ from planned doses by more than +/-5%.
Results: For the PTVs, the volume was 351 +/- 99 cc (range: 120-512 cc), the mean dose was 48 +/- 3 Gy, the D98% was 43 +/- 5 Gy, the conformity index was 1.5 +/- 0.2 (range: 1.2 - 1.8), and the homogeneity index was 1.2 +/- 0.1. For the OARs, the mean brain dose was 6.0 +/- 2.2 Gy (range: 0.9 – 9.8 Gy), the maximum lens dose was 3.9 +/- 2.9 Gy (range: 0.2 – 9.3 Gy), and the normal tissue gradient index was 1.8 +/- 0.4.
Conclusion: This data demonstrates consistent PTV conformity, homogeneity, and OAR sparing using VMAT for ESFC of the scalp. The ability to conform to curved surfaces, combined with rapid treatment planning and dose delivery, make it a promising tool for scalable and precise widefield skin irradiation.
Treatment Planning, Conformal Radiotherapy, Inverse Planning
TH- External Beam- Photons: treatment planning/virtual clinical studies