Repetitive Painting (REPEAT) Irradiation in Stereotactic Radiotherapy Using Helical Tomotherapy

Background/Aim: Stereotactic radiotherapy (SRT) for spine metastases with helical tomotherapy requires a long irradiation time due to the high dose per fraction. Since helical tomotherapy can neither confirm nor correct the position during irradiation, a plan with a long irradiation time cannot be used in actual clinical practice, given the intra-fractional motion error. To address this problem, we devised a method called REPEAT irradiation. Patients and Methods: REPEtitive pAinTing (REPEAT) irradiation is a method of dividing the irradiation for a given fraction per day into several sessions and performing the irradiation after position correction using mega-voltage computed tomography images for each session. In order to evaluate how REPEAT irradiation changes irradiation time and the dose-volume histogram (DVH), a planning study with helical tomotherapy was conducted using CT images of a patient with lumbar spine metastasis. Results: In this case, we found that dividing 3 irradiation fractions into 3 sessions per day (i.e., 9 fractions=9 sessions in 3 days) using REPEAT irradiation shortened the irradiation time per session and simultaneously improved dose-volume histogram parameters. Conclusion: Although the optimal number of sessions may differ depending on the patient's condition, the fixing method, the irradiation site, and the calculation parameters, REPEAT irradiation does not require any special equipment and is a simple practical treatment method.