Optical Surface-guided Radiotherapy for Upper and Lower Limb Sarcomas: An Analysis of Setup Errors and CTV-PTV Margins: Optical Surface-guided Radiotherapy for Sarcomas

Purpose To assess the clinical benefits of surface-guided radiotherapy (SGRT) in terms of setup error, positioning time, and clinical target volume-to-planning target volume (CTV-PTV) margin in extremity soft tissue sarcoma (STS). Methods and Materials Fifty consecutive patients treated with radiotherapy were retrospectively selected. Treatment setup was performed with either laser-based imaging only (control group), or with laser-based and daily optical surface-based imaging (SGRT group). Pre-treatment cone beam computed tomography images were acquired daily for the first 3 – 5 fractions and weekly thereafter, with the frequency adjusted as necessary. Translational and rotational errors were collected. CTV-PTV margin was calculated using the formula, 2.5Σ + 0.7σ. Results Each group consisted of 10 and 15 upper and lower limb STSs, respectively. For patients with upper limb sarcomas, the translation errors were (1.64 ± 1.34) mm, (1.10 ± 1.50) mm, and (1.24 ± 1.45) mm in SGRT group, and (1.48 ± 3.16) mm, (2.84 ± 2.85) mm, and (3.14 ± 3.29) mm in control group in the left-right (LR), supero-inferior (SI), and antero-posterior (AP) directions, respectively. Correspondingly, for patients with lower limb sarcomas, the translation errors were (1.21 ± 1.65) mm, (1.39 ± 1.71) mm, and (1.48 ± 2.10) mm in SGRT group, and (1.81 ± 2.60) mm, (2.93 ± 3.28) mm, and (3.53 ± 3.75) mm in control group, respectively. The calculated CTV-PTV margins of SGRT group and control group were 5.0 mm, 3.8 mm, 4.1 mm vs. 5.9 mm, 9.1 mm, 10.1 mm for upper limb sarcomas; and 4.2 mm, 4.7 mm, 5.2 mm vs. 6.3 mm, 9.6 mm, 11.4 mm for lower limb sarcomas in the LR, SI, and AP directions, respectively. Conclusion Daily optical surface guidance can effectively improve the setup accuracy of extremity STS patients, and safely reduce the required CTV-PTV margins.