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KMID : 1164220050170020155
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Journal of Korean Society for Radiotherapeutic Technology
2005 Volume.17 No. 2 p.155 ~ p.160
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A Study of Dose Stability at Low Monitor Unit Setting for Multiple Irradiated Field
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Kim Joo-Ho
Lee Sang-Kyu
Shin Hyun-Kyung
Lee Suk
Na Soo-Kyung
Cho Jeong-Hee
Kim Dong-Wook
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Abstract
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Purpose : Many authors have been introduced field in field technique and 3-D conformal radiotherapy that increased the tumor dose as well as decreased the dose of abutting critical organ. These technique have multiple beam direction and small beam segments even below 10 MU(monitor unit)for each field. we have confirmed the influence of low MU on dose output and beam stability.
Materials and Methods : To study the dose output, the dose for each field was always 90MU, but it divided into different segment size: 1, 2, 3, 5, 10, 15 segments, 90, 45, 30, 18, 9, 6 MU the measurements were carried out for X-ray energy 4 MV, 6 MV, 10 MV of three LINAC(Varian 600C, 2100C, 2100C, 2100C/D), in addition each measurement was randomly repeated three times for each energy. To study the field symmetry and flatness, X-omat V films were irradiated. After being developed, films were scanned and analyzed using densitometer.
Results : Influence of low MU on dose is slightly more increase output about in cGy/mu than 90MU, but may not changed beam quality(flatness or symmetry), Output stability depends on dose rate(PRF)rather than beam energy, field size.
Conclusion : Presented result are under the limits(out put<3%, flatness<, symmetry<2%). The 3 accelerators are safe to use and to perform conformal radiotherapy treatments in small segments, small MU around 10MU. but Even if the result presented here under the limits, continuous adjustments and periodic QA should be done for use of small MU
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KEYWORD
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monitor unit, multiple beam irradiation, quality assurance
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