Meydanci Tülay P, Kemikler Gönül
Department of Radiation Oncology, Kocaeli Medical School, University of Kocaeli, Kocaeli, Turkey.
Radiat Med. 2008 Nov;26(9):539-44. doi: 10.1007/s11604-008-0271-6. Epub 2008 Nov 22.
The dose changes in the buildup region and beam attenuation by a carbon fiber tabletop were investigated for 6-and 18-MV photon beams.
Measurements were performed for 2 x 2 cm to 40 x 40 cm field sizes. The surface dose and percentage depth doses (PDD) were measured by a Markus parallel plate chamber. Attenuation measurements were made at the cylindrical phantom for 180 degrees rotation of the beam.
A carbon fiber tabletop increases the surface dose from 7.5% to 63.0% and from 4% to 43% for small fields at 6 and 18 MV, respectively. The increase was nearly fivefold for the 10 x 10 cm field and nearly twofold for the 40 x 40 cm field. Beam attenuation of the tabletop varies from 3.0% to 5.6% for 180 degrees and 120 degrees gantry angles for 6 MV.
The carbon fiber tabletop significantly decreases the skin-sparing effect. The dosimetric effect of the tabletop may be higher, especially for the intensity-modulated radiation therapy depending on the beam orientation. Attenuation should be considered and corrected such as any material under the patient at the treatment planning stage.
研究了6兆伏和18兆伏光子束在建成区的剂量变化以及碳纤维桌面的束流衰减情况。
对2×2厘米至40×40厘米的射野尺寸进行了测量。表面剂量和百分深度剂量（PDD）由马库斯平行板电离室测量。在圆柱形模体上进行了180度束流旋转的衰减测量。
对于6兆伏和18兆伏的小射野，碳纤维桌面分别将表面剂量从7.5%提高到63.0%以及从4%提高到43%。对于10×10厘米射野，增加近五倍；对于40×40厘米射野，增加近两倍。对于6兆伏，在180度和120度机架角度下，桌面的束流衰减在3.0%至5.6%之间变化。
碳纤维桌面显著降低了皮肤保护效应。桌面的剂量学效应可能更高，特别是对于调强放射治疗，这取决于束流方向。在治疗计划阶段，应像考虑患者下方的任何材料一样考虑并校正衰减。
