An Update of Couch Effect on the Attenuation of Megavoltage Radiotherapy Beam and the Variation of Absorbed Dose in the Build-up Region

Purpose: Fiber carbon is the most common material used in treating couch as it causes less beam attenuation than other materials. Beam attenuation replaces build-up region, reduces skin-sparing effect and causes target volume under dosage. In this study, we aimed to evaluate beam attenuation and variation of build-up region in ۵۵۰ TxT radiotherapy couch. Materials and Methods: In this study, we utilized cylindrical PMMA Farmer chamber, DOSE-۱ electrometer and set PMMA phantom in isocenter of gantry and the Farmer chamber on the phantom. Afterwards, the gantry rotated ۱۰°, and attenuation was assessed. To measure build-up region, we used Markus chamber, Solid water phantom and DOSE-۱ electrometer. Doing so, we set Solid water phantom on isocenter of gantry and placed Markus chamber in it, then we quantified the build-up region at ۰° and ۱۸۰° gantry angels and compared the obtained values.Results: Notable attenuation and build-up region variation were observed in ۵۵۰ TxT treatment table. The maximum rate of attenuation was ۵.۹۵% for ۶ MV photon beam, at ۵×۵ cm۲ field size and ۱۳۰° gantry angle, while the maximum variation was ۷ mm for ۶ MV photon beam at ۱۰×۱۰ cm۲ field size.Conclusion: Fiber carbon caused beam attenuation and variation in the build-up region. Therefore, the application of fiber carbon is recommended for planning radiotherapy to prevent skin side effects and to decrease the risk of cancer recurrence.

کلیدواژه ها:

Beam Attenuation ، Carbon Fiber ، Couch Insert ، Surface Dose ، Megavoltage Radiotherapy