Helical tomotherapy for total marrow and total skin irradiation : Optimisation, verification, and clinical results

Abstract: In modern cancer therapy, radiotherapy (RT) is a vital part of most treatments. Most RT treatments in Sweden are performed using intensity-modulated radiotherapy (IMRT) with fixed or dynamic arc delivery. The dose gradients outside the target are steep, the margins are small, and the treatment delivery is complicated. Complicated treatments increase the requirement for control of the uncertainties in planning and delivery. This requires robust treatments and mitigation of the various uncertainties. In addition, robust planning and rigorous quality assurance (QA) of the patient treatments that takes account of all types of uncertainties are essential. A TomoTherapy device (Accuray Inc., Madison, WI, USA) is an RT device with a linear accelerator mounted on a slip-ring construction, giving it the ability to irradiate while continuously rotating around the patient, very similar to a CT scanner but with megavoltage instead of X-ray energy generation. Since helical tomotherapy can entail long and complicated irradiations, new treatment types targeting RT to large parts of the body have emerged. These new techniques are challenging regarding the optimization and verification of the planning and treatment process. Recurring blood cancers (leukaemias) can be treated with RT and chemotherapy before stem cell transplantation. Traditionally, the patient is irradiated with whole-body irradiation using a conventional linac at a large distance. The treatment can be performed with helical tomotherapy to avoid organs at risks to a greater extent. Another emerging treatment with helical tomotherapy is irradiation of whole-body neoplastic skin lesions, such as mycosis fungoides. These patients were traditionally treated with electron irradiation in different positions, subsequently complemented with x-ray fields in ‘hard-to-reach’ sites. Delivering this treatment with photons is complex but opens the possibility for integrated boost treatments of lesions and simultaneously avoiding OAR and previously treated areas.The clinical follow-up illustrated the potential and usefulness of helical tomotherapy targeting the bone marrow, with more patients surviving without severe complications after one year, than with the previous technique. Further, we showed the possibility to implement irradiation of the entire skin with helical tomotherapy. Overall, we demonstrated the usefulness of helical tomotherapy, and solutions to overcome challenges in implementing large-target techniques.