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J Korean Soc Ther Radiol Oncol > Volume 27(2); 2009 > Article
The Journal of the Korean Society for Therapeutic Radiology and Oncology 2009;27(2): 103-110. doi: https://doi.org/10.3857/jkstro.2009.27.2.103
Superficial Dosimetry for Helical Tomotherapy
Song Yih Kim, Sei Hwan You, Taesoo Song, Yong Nam Kim, Ki Chang Keum, Jae Ho Cho, Chang Geol Lee, Jinsil Seong
Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea. kckeum@yumc.yonsei.ac.kr
ABSTRACT
PURPOSE:
To investigate the feasibility of helical tomotherapy on a wide curved area of the skin, and its accuracy in calculating the absorbed dose in the superficial region.
MATERIALS AND METHODS:
Two types of treatment plans were made with the cylinder-shaped 'cheese phantom'. In the first trial, 2 Gy was prescribed to a 1-cm depth from the surface. For the other trial, 2 Gy was prescribed to a 1-cm depth from the external side of the surface by 5 mm. The inner part of the phantom was completely blocked. To measure the surface dose and the depth dose profile, an EDR2 film was inserted into the phantom, while 6 TLD chips were attached to the surface.
RESULTS:
The film indicated that the surface dose of the former case was 118.7 cGy and the latter case was 130.9 cGy. The TLD chips indicated that the surface dose was higher than these, but it was due to the finite thickness of the TLD chips. In the former case, 95% of the prescribed dose was obtained at a 2.1 mm depth, while the prescribed does was at 2.2 mm in the latter case. The maximum dose was about 110% of the prescribed dose. As the depth became deeper, the dose decreased rapidly. Accordingly, at a 2-cm depth, the dose was 20% of the prescribed dose.
CONCLUSION:
Helical tomotherapy could be a useful application in the treatment of a wide area of the skin with curvature. However, for depths up to 2 mm, the planning system overestimated the superficial dose. For shallower targets, the use of a compensator such as a bolus is required.
Key Words: Helical tomotherapy, Tangential beam, Skin dose, Surface dose, Cheese phantom
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