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 ×10 及 20 × 20 cm ?斯奶T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 cm ?揹氶A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 85.2 ％。 當照射範圍為 10 × 10 cm ?揹氶A 體表相對劑量由100 ％減為 93.7 ％。 當照射範圍為 20 × 20 cm ?揹氶A 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。

　　　　　Purpose: The existence of an air gap between the bolus material and theskin surface is often encountered in electron beam therapy. This studyinvestigated the perturbation effect of air gaps under bolus material on thesurface dose.Materials and Methods: The surface dose was measured for air gaps from adistance of 0.0 cm to 2.0 cm using 6, 9, 12, 16 and 20 MeV electron beams andvarious available cone sizes from 6 × 6, 10 × 10, and 20 × 20 cm ?? on alinear accelerator.Results: In this cases of 6 × 6 cm ?? cone size with different thickness ofboluses and electron energy, the relative surface dose decreased from 100% to85.2% as the air gap was increased. In 10 × 10 cm ?? cone size the relativesurface dose decreased from 100% to 93.7%. In 20 × 20 cm ?? cone size therelative surface dose decreased from 100% to 97.1%.Conclusions: These measurements showed that there was a tendency of relativelydecreasing surface dose by lower electron energies, smaller field sizes, largerair gaps, and thicker boluses. It is necessary to correct the problem withindividual dosimetry.