Helical tomotherapy for solitary lung tumor: feasibility study and dosimetric evaluation of treatment plans

The purpose of this study is to evaluate the feasibility of and treatment plans for helical tomotherapy (HT) for solitary lung tumors. Nine patients with stage IA non-small-cell lung cancer (NSCLC) and three patients with solitary lung metastasis were treated with HT. All patients were immobilized with the BodyFIX system, and the target volume shown on computed tomography in the 3 respiration phases were superimposed onto the 3-dimensional radiation treatment planning system to represent the internal target motion. All patients were treated with 54-60 Gy in 12 fractions over 8 to 13 days. The median follow-up time was 14 months (range: 3-16 months). The overall response rate was 92%. The local control rate at 1 year was 100% with no difference between NSCLC and metastasis. Of 12 patients, one patient experienced Grade 2 radiation pneumonitis (RP), and the other patient with severe interstitial pneumonia and emphysema experienced Grade 5 RP. The mean lung dose (MLD) and the dose-volume histogram (DVH) for the normal lung volumes were converted into normalized total dose with an alpha/beta ratio of 3 Gy. The DVH of the normal lung volumes demonstrated that the mean volumes of V(10), V(30), V(50), and V(70) were 40.4 +/- 9.4%, 21.3 +/- 6.4%, and 12.8 +/- 4.6%, and 9.3 +/- 4.2% in all patients, 28.8%, 18.7%, 12.3%, and 10.5% in the patient with Grade 2 RP, and 29.3%, 17.9%, 7.7%, and 5.4% in the patient with Grade 5 RP. The mean MLD of all patients was 13.5 +/- 3.9 Gy, and those values of patients with Grade 2 and 5 RP were 12.9 and 21.8 Gy, respectively. Our study found that only the MLD was significantly correlated with RP >Grade 2 (p = 0.030) using the Student's t-test. Our study found the conformity index value of 1.48 +/- 0.15 and the homogeneity index value of 1.066 +/- 0.023, which suggested the feasibility of using HT to treat lung tumors with hypofractionation. In conclusion, HT is a feasible non-invasive technique for treating solitary lung tumors and achieves high accuracy in terms of dose conformity and homogeneity. The decision of the indications for HT might be required caution in cases in which a severe pulmonary toxicity is predicted from the high MLD, especially in cases involving a severe pulmonary comorbidity.