Feasibility report of stereotactic body radiotherapy with tomotherapy for early stage medically inoperable lung cancer using extreme hypofractionation

Abstract

17097 Background: This is a report on the technical feasibility, dosimetric aspects, and daily image-guidance capability with megavoltage computed tomography (MvCT) imaging of stereotactic body radiotherapy (SBRT) using tomotherapy for patients with medically inoperable early stage non-small cell lung cancer (NSCLC). Methods: Treatment planning was performed using 4D PET-CT in a BodyFix device. A pilot group of 4 patients with <5 cm T1/2, N0 tumors, was treated using IMRT (tomotherapy), utilizing daily image guidance with MvCT. Patients received 60 Gy within 10 days, delivered in five 12Gy fractions. The primary endpoint of this study was evaluation of acute and sub-acute treatment related toxicities. The secondary endpoint was radiographic evaluation for objective tumor response. Results: All 20 fractions were successfully delivered. MvCT provided excellent tumor visualization for daily image guidance. No significant tumor regression was observed in any patient during the 2 weeks of therapy, using volumetric contouring on MvCT images. The relevant dosimetric aspects, measured as median normalized total dose (NTD) were as follows: tumor = 116.5 Gy10; whole lung = 6.8 Gy3. Maximum fraction-size equivalent dose (FED) demonstrated median values as follows: esophagus = 4.04 Gy3; spinal cord = 6.53 Gy3. All patients are alive at a median follow-up of 6 months, with no grade 2 or higher acute pulmonary toxicities. Early radiographic follow-up demonstrates all 4 patients experienced a partial response. The mean tumor regression is 79% (range 64–85%). Conclusions: 4D PET-CT permits precise target delineation. In this, the first reported clinical experience, IMRT delivery of SBRT using tomotherapy is feasible, safe and free of major acute toxicities. The conformality which is obtained by helical delivery of the therapeutic dose makes it well-suited for dose escalation through extreme hypofractionation, with extremely low mean NTD to normal tissue. The ability to obtain on-treatment megavoltage CT scans to confirm tumor localization is a substantial advantage. Further studies and longer follow-up are warranted to evaluate the efficacy of this treatment modality. [Table: see text]