Purpose: To analyze the stereotactic radiotherapy (SRT) plans in terms of internal target volume (ITV) and organs at risk (OARs).
Methods and materials: Treatment planning and dose distributions were analyzed using dose-volume histograms (DVHs) of ITV and OARs in 37 patients, who were treated for a solitary lung tumor with SRT. The stereotactic body frame (SBF) was used for immobilization and accurate setup. Prescription dose was 48 Gy in four fractions at the isocenter.
Results: Use of SBF limits the extent of the noncoplanar beam directions to prevent a collision with the Linac gantry. DVH analyses showed that the homogeneity index, defined as the ratio of maximum and minimum dose to ITV, ranged from 1.03 to 1.25 (mean, 1.12). The volume irradiated with 20 Gy or more (V(20)) of the lung ranged from 0.3 to 11.6% (mean, 4.4%) of the whole lung volume. The maximum dose to the other OARs ranged from 0 to 11.8 Gy (mean, 0.5-2.7) per fraction. No clinically significant complications were encountered.
Conclusions: Despite the limitation of the beam arrangement, a homogeneous target dose distribution, while avoiding high doses to normal tissues, was obtained.