April 6, 2010 - Helical TomoTherapy delivers continuous arc-based intensity-modulated radiation therapy (IMRT) that gives high conformality and excellent dose homogeneity for the target volume, concluded a study published online March issue of the Internal Journal of Radiation Oncology Biology Physics.
The study, entitled “Standard and Nonstandard Craniospinal Radiotherapy Using Helical TomoTherapy, conducted at McGill University Health Centre, applied helical TomoTherapy technology in a variety of cases requiring craniospinal irradiation (CSI) in children and young adults.
Researchers focused on four patients, three of whom had complicating circumstances, such as unusual anatomy, prior radiation treatment or multiple boost targets. The first was a standard case of CSI in a 19-year-old patient with recurrent myxopapillary ependymoma (MPE). Two other patients received non-standard CSI via differential dosing. One of them was a seven-year-old with recurrent medulloblastoma who had been treated before and required a simultaneous dose reduction to the posterior fossa, and the other was a 14-year-old with metastatic tumors throughout the craniospinal axis from MPE who required concurrent boosting of multiple sites. The fourth patient was a 21-year-old with neurofibromatosis and pronounced scoliosis who needed treatment of the whole spine for recurrent MPE.
Clinicians were able to extend the length of the radiation fields up to 60 cm to 90 cm with TomoTherapy technology, compared to field lengths of up to only 40 cm for standard radiation therapy solutions. This capability of the TomoTherapy system to create long fields means the entire craniospinal axis can be treated with a single set-up, thereby “obviating the risks associated with use of abutting fields, junctions and beam gaps,” as the study reported. In addition, accurate patient setup via integrated MVCT imaging enables a margin reduction, which enables sparing of more healthy tissue.
All patients in the study received treatment while lying on their back, with a standard thermoplastic mask used for immobilization. Beam-on time ranged from 10-15.7 minutes and total time on the treatment table was typically 45 minutes for adult patients and 30 minutes for children. This is similar to, or less than, conventional treatment times.
The researchers concluded: "Helical TomoTherapy allows for differential dosing of multiple targets resulting in very elegant dose distributions. By its conformal nature, IMRT is very sensitive to improper patient setup. The use of pretreatment megavoltage CT (MVCT) imaging with helical TomoTherapy allows for increased precision with respect to patient positioning and use of a reduced planning target volume (PTV) margin."
They also reported finding the technique very reproducible.