Image-guided helical tomotherapy for localized prostate cancer: technique and initial clinical observations

The purpose of the present study was to implement a technique for daily computed tomography (CT)-based image-guided radiation therapy and to report observations on treatment planning, imaging, and delivery based on the first 2 years of clinical experience. Patients with previously untreated stage T1-T3 biopsy-proven adenocarcinoma of the prostate were considered eligible for treatment with daily CT-guided helical tomotherapy. The prostate was targeted daily using megavoltage CT (MVCT) images that were fused with treatment-planning CT images based on anatomic alignments. All patients were treated at 2 Gy per fraction to 76-78 Gy (mean: 76.7 Gy). As part of this study, 33 prostate patients were planned, imaged, and treated with a total of 1266 CT-guided fractions. The prostate, rectum, bladder, femoral heads, and pubis symphysis were visible in one or more slices for all 1266 MVCT image sets. The typical range of measured prostate displacement relative to a 3-point external laser setup in this study was 2-10 mm [3.4 mm standard deviation (SD)] in the anterior-posterior direction, 2-8 mm (3.7 mm SD) in the lateral direction, and 1-6 mm (2.4 mm SD) in the superior-inferior direction. The obese patients in this study had a substantially larger lateral variation (8.2 mm SD) attributable to mobility of skin marks. The prostate, seminal vesicles, rectum, and bladder anatomy were used to position the patient relative to the desired treatment position without the use of implanted markers. Acute toxicities were within the expected range given the number of patients treated and the dose level.