Recently, cancer patients continues to increase, and the proportion of the radiation therapy is increasing.
IGRT(Image Guided Radiation Therapy) in radiation therapy is a very useful technique to improve the setup accuracy of patient and position reproducibility.
Tomotherapy is an innovative means of delivering IMRT (Intensity-Modulated Radiation Therapy) using a device that merges features of a linear accelerator and a helical computed tomography scanner. The Tomotherapy unit can generate MVCT images from the megavoltage radiation and use these for treatment as often as needed during a course of radiation therapy.
Although Tomotherapy not only increases accuracy of setup to take IGRT, but alos verify accuracy of Image guided treatment, radiation exposure increases in patients due to the MVCT.
IGRT approaches in Tomotherapy setup up the patient and localize the target within 1.0mm. When MVCT using Tomotherapy phantom for QA, QC be taken, exposure dose is Fine(2mm Slice thickness) 3cGy, Normal(4mm Slice thickness) 1.5cGy, Corse(6mm Slice thickness) 1.0cGy. (L-Gram using film 8.0cGy, EPID 3.0cGy)
Measurement value of spatial resolution using AAPM CT performance phantom didn''t cause a big difference. But Corse was the most poorly measured and Fine was measured normal to the relatively good.
As a result, ability of IGRT in Tomotherapy is very accurate. We appropriate dose management based on ALARA(As Low As Reasonably Achievable) principle is required. While obtaining image for IGRT, we should minimize expose range because patient''s be exposed to radiation. We should make an effort to do accurate radiation therapy to minimize exposure of patient by selecting the appropriate thickness of MVCT depending on patient''s body and treat area.