A dosimetric comparison between two intensity-modulated radiotherapy techniques: tomotherapy vs dynamic linear accelerator.

This manuscript describes a direct comparison between radiation treatment plans in terms of dosimetric outcomes created by two different IMRT systems: TomoTherapy HiArt and dynamic linac intensity-modulated radiotherapy (dIMRT). Three patient cases were selected (with disease in different anatomical areas): vertebral metastasis re-treatment, radical prostate therapy and an ethmoid sarcoma re-treatment. Each case presents significant and varying dosimetric difficulties with respect to avoidance of adjacent organs. The patients were each planned and treated at the Cromwell Hospital (London, UK) using the TomoTherapy HiArt system, with planning replicated at St Bartholomew's Hospital (London, UK) using Eclipse Treatment Planning System and a 6EX linac with a 120-leaf multileaf collimator (Varian Medical Systems). For both modalities, all treatment plans conformed to the stringent clinical dose constraints set. For the vertebral body re-treatment, both techniques demonstrated adequate and similar planning target volume (PTV) coverage and sparing of the spinal cord. The critical structure sparing and PTV coverage for the prostate treatment was again similar for both modalities. For re-treatment of the paediatric ethmoid sarcoma, tomotherapy was able to produce slightly better organ sparing whilst producing PTV coverage similar to linac dIMRT. The data presented in this manuscript demonstrate subtle dosimetric differences between the two techniques but no marked advantage with either system. Therefore, other factors may need to be considered when making a decision between tomotherapy and linac dIMRT.