Quality Control of IMRT Using Computer Radiography with the Oncology Cassette
M SETTI1*, F da CUNHA1, A GOUVEIA1, V LOPES1, R ARAUJO1, C de ALMEIDA2, (1) COT RADIOTERAPIA, Uberlandia, Minas Gerais,(2) UERJ - UNIVERSIDADE DO ESTADO DO RIO DE JANEIRO, Rio De Janeiro, Rio de JaneiroSU-E-T-89 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To evaluate the potential use of CR (Computer Radiography) as a Quality Control tool for IMRT.
Methods:A radiation oncology cassette was placed inside of a solid water phantom at a depth of 4.0cm with 5.0cm of back up material. This arrangement was irradiated using a 6 MV x-rays beam generated by a Clinac 600-C/D. The cassette was read by the Capsula X- Fujifilm CR. The beam uniformity was measured at an SSD of 156cm, and a field size of 30x30cm². The dose linearity was verified using a dose rate 400MU/min, a field size 8x8cm² and different exposure indexes S of 10,15,29,40,58,73, 92 and 115. The post-irradiation fading was verified for 1.41, 3.0, 5.0, 10.0, 15.0, 60.0, 180.0 and 360.0 min. For the dose profile, field sizes of 2x2cm², 5x5cm², 10x10cm², 15x15cm² and 30x30cm² were used different dose rates from 100 to 600MU/min. All radiation profiles were compared with the prescribed dose using S=29. In addition, 10 IMRT plans representing 60 fields were individually compared with a relative planned dose.
Results:A useful dose linearity region was found for each S value and the dose uniformity 98%(σ=1%). The maximum difference between the normalized measured and planned profiles was 4.4% for a field size of 2x2cm² consistent for all doses rates. The fading effect is not important if the cassette reading is done in less than 15min. Analyzing different IMRT plans, the mean gamma index values (4%/4mm) was 97%(σ=2%).
Conclusion:The CR high spatial resolution associated to its low cost and quick processing time has shown to be a useful tool for IMRT quality control if available. Since, the dose linearity region is limited, the slope of the linearity region must be known for each S value. We are also investigating its potential use for arc therapy
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