To quantify the dosimetric gains from non-coplanar helical tomotherapy (HT) arcs for stereotactic body radiation therapy (SBRT) of lung cancer, we created oblique helical arcs by rotating patient’s CT images. Ten, 20 and 30 degrees of yaws were introduced in the treatment planning for a patient with a hypothetical lung tumor at the upper, middle and lower portion of the right lung, and the upper and middle left lung. The planning target volume (PTV) was 43 cm³. 60 Gy was prescribed to the PTV. Dose to organs at risk (OARs), which included the lungs, heart, spinal cord and chest wall, was optimized using a 2.5 cm jaw, 0.287 pitch and modulation factor of 2.5. Composite plans were generated by dose summation of the resultant plans. These plans were evaluated for its conformity index (R_x) and percentile volume of lung receiving radiation dose of x Gy (V_x). Conformity index was defined by the ratio of x percent isodose volume and PTV. The results show that combination of non-coplanar arcs reduced R₅₀ by 4.5%, R₂₀ by 26% and R₁₀ by 30% on average. Non-coplanar arcs did not affect V₂₀ but reduced V₁₀ and V₅ by 10% and 24% respectively. Composite of the non-coplanar arcs also reduced maximum dose to the spinal cord by 20-39%. Volume of chest wall receiving higher than 30 Gy was reduced by 48% on average. Heart dose reduction was dependent on the location of the PTV and the choice of non-coplanar orientations. Therefore we conclude that non-coplanar HT arcs significantly improve critical organ sparing in lung SBRT without changing the PTV dose coverage.

Key words: Tomotherapy; Rotational intensity modulated radiation therapy; Non-coplanar; Lung; SBRT.

This article can be cited as:
Yang, W., Jones, R., Lu, W., Geesey, C., Benedict, S., Read, P., Larner, J., Sheng, K. Feasibility of Non-Coplanar Tomotherapy for Lung Cancer Stereotactic Body Radiation Therapy Technol Cancer Res Treat. 10, 307-315 (2011).