Dynamic intensity-modulated non-coplanar arc radiotherapy (INCA) for head and neck cancer

Abstract 

Background and purpose

To define the potential advantages of intensity-modulated radiotherapy (IMRT) applied using a non-coplanar dynamic arc technique for the treatment of head and neck cancer.

Materials and methods

External beam radiotherapy (EBRT) was planned in ten patients with head and neck cancer using coplanar IMRT and non-coplanar arc techniques, termed intensity modulated non-coplanar arc EBRT (INCA). Planning target volumes (PTV1) of first order covered the gross tumor volume and surrounding clinical target volume treated with 68–70Gy, whereas PTV2 covered the elective lymph nodes with 54–55Gy using a simultaneous internal boost. Treatment plan comparison between IMRT and INCA was carried out using dose–volume histogram and “equivalent uniform dose” (EUD).

Results

INCA resulted in better dose coverage and homogeneity of the PTV1, PTV2, and reduced dose delivered to most of the organs at risk (OAR). For the parotid glands, a reduction of the mean dose of 2.9 (±2.0) Gy was observed (p=0.002), the mean dose to the larynx was reduced by 6.9 (±2.9) Gy (p=0.003), the oral mucosa by 2.4 (±1.1) Gy (p<0.001), and the maximal dose to the spinal cord by 3.2 (±1.7) Gy (p=0.004). The mean dose to the brain was increased by 3.0 (±1.4) Gy (p=0.002) and the mean lung dose increased by 0.2 (±0.4) Gy (p=0.87). The EUD suggested better avoidance of the OAR, except for the lung, and better coverage and dose uniformity were achieved with INCA compared to IMRT.

Conclusion

Dose delivery accuracy with IMRT using a non-coplanar dynamic arc beam geometry potentially improves treatment of head and neck cancer.

Keywords: Intensity-modulated radiotherapy, Non-coplanar arc therapy, External beam radiotherapy, Head and neck cancer, Toxicity, Xerostomia, IMRT