Helical tomotherapy for radiochemotherapy in esophageal cancer: a preferred plan?

T he addition of systemic chemotherapy to local radiation therapy in the non-surgical management of esophageal cancer has offered the opportunity for long-term survival (1). However, this survival benefit has come at the cost of increased side effects. The standard dose of radiation remains up to 50 Gy in the definitive or pre-operative setting despite previous attempts to dose escalate (2). Even at this modest dose, the majority of concurrent chemoradiation patients experience grade 3 or higher toxicities when utilizing conventional radiation techniques. When concurrent chemotherapy and radiation are delivered neoadjuvantly, the combination appears to increase resectability, produce tumor downstaging and may impact local control, disease-free survival, and overall survival (3-5). This tri-modality approach, while relatively effective, has been shown with peri-operative rates of toxicity of 11-12% (6). The esophagus is a centrally located structure, surrounded by the lungs, normal esophagus, heart and spinal cord. For the treating radiation oncologist, achieving adequate dose to the gross tumor volume and adjacent clinical targets while limiting dose to the surrounding critical normal tissues represents a therapeutic challenge. Emerging radiation technologies are aimed at improving that therapeutic ratio in this disease where the results remain modest at best, and morbidity is significant. Intensity modulated radiation therapy (IMRT) offer the opportunity to “shape”radiation dose, optimally sparing normal tissue while allowing adequate coverage to tumor volumes. Dosimetrically, the use of IMRT could be of benefit in the treatment of esophageal cancer where the target is surrounded by radiosensitive tissues. Helical tomotherapy is a form of IMRT delivered on a continuous helix, with the source being collimated to a fan beam which is modulated with a binary multi-leaf collimator (7). During treatment, the patient is moved through a ring gantry resulting in a helical beam delivery. Image-guidance is in the form of daily pre-treatment megavoltage CT. In this issue of the Journal of Thoracic Disease, Chen et al. report their results utilizing helical tomotherapy in the definitive and pre-operative management of patient with locally advanced esophageal cancer (8). To date, there is very limited published data on the use of tomotherapy in esophageal cancer. On the basis of dosimetric analysis, one previous study by Chen et al. found that based on isodose distributions and dose-volume histograms (DVHs), tomotherapy allowed for sharper dose gradients, more conformal coverage, and better homogeneity when compared with step-and-shoot IMRT or 3D-Conformal Radiotherapy (3D-CRT) (9). In addition the volume of lung receiving at least 20 Gy (V20) and the volume of heart receiving V30 and V45 were significantly reduced with tomotherapy. It is notable; however, that tomotherapy resulted in larger lung volume receiving V10 when compared to 3D-CRT. In the current study, 20 consecutive patients are treated with concurrent chemoradiation, with ten receiving definitive 10 patients receiving definitive therapy and 10 going on to surgery. The total dose to the gross disease was 50 Gy in standard fractionation, with 45 Gy delivered simultaneously to the regions of subclinical disease, while surrounding normal tissue limits were established prior to