臨床上治療時，如何適當選用等效組織補償物來減少皮膚免除（Skin-Sparing)效應，增加皮膚表面的劑量 達到最適化之治療效果，製作良好的輔具以提升皮膚表面劑量爲重要課題。本實驗主要在利用改變等效組織補償 物的厚度來測量回散射所提供對治療皮膚表淺性腫瘤時的相對關係影響。利用6、8、12 cm的固態水假體模擬治 療下肢端，採左右對照治療人體表淺性腫瘤時來探討受照體，不同等效組織塡充物（0、2、3、5、7、10、20、 30、40、5 mm)、不同照野（5x5、10x10、15x15、20x20、25x25 cm2)及不同射束能量（鈷六十治療機及直線 加速器）對回散射補償貢獻比例並比較其差異。
實驗結果量測6 cm、8 cm、12 cm三個厚度回散射再以不加等效組織材料厚度時和加九種厚度及各照野互相 做比較發現，厚度愈厚回散射愈小，鈷六十射線，其測得的回散射比直線加速器大。補償效應隨照野增大而更趨 顯著，在小照野內所提供的劑量較多，而在直線加速器此現象較不明顯。在量測補償效應時，不同厚度的等效組 織塡充物所造成的回散射補償效應因照野愈小愈不明顯，且穿透的厚度愈薄，回散射補償作用影響愈大。在10 mm 厚度以內的等效組織塡充物所造成的回散射補償作用影響甚鉅，而大於此厚度後，其補償效應趨緩，故於臨床應 用時，建議至少增加10 mm的等效組織塡充物以提供足夠的回散射補償。

Tissue-equivalent compensable materials (TECMs) are often used to deliver a homogenous dose throughout the extremities and effectively eliminate the skin sparing effect in the treatment of optimal thickness of TECMs to ensure that the extremities are receiving enough skin doses is of particular interest. This study examined the effect of back-scatter electron on surface dose while changing the thickness of TECMs. The solid water phantom of different dimension of 6 cm, 8 cm, 12 cm was used to simulate the lower extremity and it was placed at the isocenter of a parallel-opposed filed arrangement. Different field size of 5x5、10x10、15x15、20x20、25x25 cm2 was employed. This study also examined the dosimetry of these field arrangements for different photon beam energies (Co-60 machine, Linac), and different thickness of TECMs (0, 2, 3, 5, 7, 10, 20, 30, 40, 50 mm) to compensate for contributions of back-scatter radiation.
According to our findings, no matter in 6 MV Lianc or Co-60 machine, the compensatory effects were more profound with the larger field size and thicker TECMs in all three different thicknesses of phantoms. Furthermore, the back-scatter radiation becomes the less significant when the thickness becomes thicker. In addition, the much more uneven dose distribution phenomenon of Co-60 compared to Linac with smallest field size (5x5 cm2) may be attributed to the effect of penumbra. Due to the smaller field size, the influence of TECMs on compensatory effects from back-scatter radiation was less profound; moreover, the thinner the penetration, the more significant the compensatory effects will be. In addition, the compensatory effects change dramatically when the thickness of TECMs was below 10 mm. And greater than this thickness, the compensatory effects tend toward plateau. Therefore, we suggest that should add to at least 10 mm of TECMs to provide sufficient compensatory effects to improve the outcome of radiotherapy in clinical.