Purpose: To investigate the ability of helical tomotherapy (HT) to spare critical organs immediately adjacent to the tumor target in stereotactic body radiation therapy (SBRT) for centrally located lung lesions.
Methods and materials: HT SBRT plans for 10 patients with centrally located lesions or lesions immediately adjacent to a critical structure were generated. A total of 70 Gy in 10 fractions was prescribed to the planning target volume (PTV) to satisfy a target volume coverage of ≥95% PTV receiving 70 Gy and an established set of dose constraints for the organs at risk (OARs). Quality assurance (QA) of the HT plans was performed with both ion chamber and film measurements.
Results: The PTV coverage criteria was met with 95% of the PTV receiving 70.68 ± 0.33 Gy for all cases even though the OARs immediately adjacent to the PTV ranged from 0.38 to 0.85 cm away. The mean lung dose (MLD), and V(20) were 7.15 ± 1.44 Gy, and 11.93 ± 3.24 % for the total lung, respectively. The dose parameters of MLD, V(5), V(10), and V(20) for the contralateral lung were significantly lower than those for the ipsilateral lung (p < 0.05). An average dose fall off from the PTV periphery to the edge of the immediately adjacent OAR was 47.6% over an average distance of 4.87 mm. Comparison of calculated and measured doses with the ion chamber showed an average of 1.85% point dose error, whereas an average mean gamma and the area with a gamma larger than 1 of 0.20 and 0.94% were observed, respectively.
Conclusion: HT allows the sparing of critical structures immediately adjacent to the tumor target, thus making SBRT for these centrally located lesions feasible.
Copyright © 2011 Elsevier Inc. All rights reserved.