| Analysis of the Imaging Dose for IGRT/Gated Treatments |
| Jung Suk Shin, Youngyih Han, Sang Gyu Ju, Eunhyuk Shin, Chae Seon Hong, Yong Chan Ahn |
1Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. youngyih@skku.edu
2Department of Nuclear Engineering, Hanyang University, Seoul, Korea. |
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| ABSTRACT |
PURPOSE:
The introduction of image guided radiation therapy/four-dimensional radiation therapy (IGRT/4DRT) potentially increases the accumulated dose to patients from imaging and verification processes as compared to conventional practice. It is therefore essential to investigate the level of the imaging dose to patients when IGRT/4DRT devices are installed. The imaging dose level was monitored and was compared with the use of pre-IGRT practice.
MATERIALS AND METHODS:
A four-dimensional CT (4DCT) unit (GE, Ultra Light Speed 16), a simulator (Varian Acuity) and Varian IX unit with an on-board imager (OBI) and cone beam CT (CBCT) were installed. The surface doses to a RANDO phantom (The Phantom Laboratory, Salem, NY USA) were measured with the newly installed devices and with pre-existing devices including a single slice CT scanner (GE, Light Speed), a simulator (Varian Ximatron) and L-gram linear accelerator (Varian, 2100C Linac). The surface doses were measured using thermo luminescent dosimeters (TLDs) at eight sites-the brain, eye, thyroid, chest, abdomen, ovary, prostate and pelvis.
RESULTS:
Compared to imaging with the use of single slice non-gated CT, the use of 4DCT imaging increased the dose to the chest and abdomen approximately ten-fold (1.74+/-0.34 cGy versus 23.23+/-3.67 cGy ). Imaging doses with the use of the Acuity simulator were smaller than doses with the use of the Ximatron simulator, which were 0.91+/-0.89 cGy versus 6.77+/-3.56 cGy, respectively. The dose with the use of the electronic portal imaging device (EPID; Varian IX unit) was approximately 50% of the dose with the use of the L-gram linear accelerator (1.83+/-0.36 cGy versus 3.80+/-1.67 cGy).
The dose from the OBI for fluoroscopy and low-dose mode CBCT were 0.97+/-0.34 cGy and 2.3+/-0.67 cGy, respectively.
CONCLUSION:
The use of 4DCT is the major source of an increase of the radiation (imaging) dose to patients. OBI and CBCT doses were small, but the accumulated dose associated with everyday verification need to be considered |
| Key Words:
Image Guide Radiation Therapy, 4-dimensional radiation therapy, Radiation dose |
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