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New strategy of a lung compensating technique with STR for total body irradiation
Yuya Yanagi1,2, Hajime Monzen1, Mikoto Tamura1
1Department of Medical Physics, Graduate School of Medical Sciences, Kindai University, Osakasayama, Osaka, Japan.
Purpose:
To determine the thickness of a soft variable shape tungsten rubber (STR) as a lung compensating filter in total body irradiation.
Methods:
A tough water (TW) phantom and tough lung (TL) phantom were used as water and lung-equivalent phantoms. The TW with a thickness of 3 cm simulating the thoracic wall was used (upper layer). The TW or TL with a thickness from 1 to 15 cm (1 cm increments) was placed beneath the upper layer (middle layer). The TW with a thickness of 5 cm simulating the mediastinum was placed beneath the middle layer (lower layer), and a farmer ionization chamber was placed beneath this layer. The relative doses of a 10 MV X-rays were then measured. The TL was compensated in 1 mm increments from 1 to 11 mm of the STR, and the thickness of the STR at the same dose of TW (water equivalent) was obtained.
Results:
The compensating ability of STR increased as the thickness of the TL increased, and an STR with a thickness of 1 mm reduced the dose by 2%-4%, depending on the thickness of lung. The STR thickness as an equivalent dose of TW per cm of TL was approximately linear, and the thickness was 0.62 mm/cm of TL.
Conclusion:
The STR can be used as a lung compensating filter for a water equivalent dose with 0.62 mm of STR per cm of lung.
