Effect of the Air Gap between the Skin Surface and Bolus Material on the Relative Surface Dose in Electron Beam Therapy

目的：在電子射線治療中，使用的Bolus與病患體表常無法密合而產生空氣間隔。此研究即探討不同的空氣間隔對皮膚表面劑量所造成之影響。材料與方法：本實驗使用平行板游離腔測量體表相對劑量，空氣間隔由0公分至2公分，電子射線能量為6、9、12、16及20百萬電子伏特等五種，照射範圍有6×6、10×l0及20×20 平方公分斤等三種，Bolus的厚度有0.5和1.0公分二種。結果：當照射範圍為6×6平方公分時，體表相對劑量會隨不同 Bolus 厚度，空氣間隔及電子射線能量由100％減為852％。當照射範圍為l0×10平方公分時，體表相對劑量由100％減為937％。當照射範圍為20×20平方公分時，體表相對劑量由100％減為97.1%。結論：根據實驗結果，我們發現當電子射線能量愈低，照射範圍愈小，體表與 Bolus 的空氣間隔愈大，及Bolus愈厚，會對電子射線相對表面劑量的影響愈大，個別的測量做適度的修正是必要的。

關鍵字

電子線治療；空氣間隔

並列摘要

Purpose: The existence of an air gap between the bolus material and the skin surface is often encountered in electron beam therapy. This study investigated the perturbation effect of air gaps under bolus material on the surface dose. Materials and Methods: The surface dose was measured for air gaps from a distance of 0.0cm to 2.0cm using 6, 9, 12, 16 and 20 MeV electron beams and various available cone sizes from 6×6, 10×l0, and 20×20 cm^2 on a linear accelerator Results: In the case of 6×6 cm^2 cone size with different thickness of boluses and electron energy, the relative surface dose decreased from 100% to 85.2% as the air gap was increased. In l0×l0 cm^2cone size the relative surface dose decreased from 100% to 93.7%. In 20×20 cm^2 cone size the relative surface dose decreased from 100% to 97.1%. Conclusions: These measurements showed that there was a tendency of relatively decreasing surface dose by lower electron energies, smaller field sizes, larger air gaps, and thicker boluses. It is necessary to correct the problem with individual dosimetry.

並列關鍵字

Electron beam therapy ； Air gap ； Bolus

國際替代計量

Effect of the Air Gap between the Skin Surface and Bolus Material on the Relative Surface Dose in Electron Beam Therapy

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