使用高能光子射束治療惡性腫瘤的病患時，因為輻射線是先穿越表皮後再照射到深處的腫瘤，所以皮膚表面會接受到無法避免的輻射劑量；另一方面,臨床治療上也常碰到腫瘤生長在表淺處；而此時我們卻希望表淺處要有足夠的劑量；所以此篇主要的目的是要探討在不同能量的光子下，不同的入射角度在假體表面上的增建區之輻射劑量改變的情況，以便在臨床上對腫瘤不同的生長部位或表皮劑量的分佈情況有一全面性的瞭解。在這實驗中我們使用自製的球形假體，GAF chromic 底片及TLD 進行增建區輻射劑量的量測；量測的結果顯示，大小不同能量的光子在增建區內的同一深度做比較時，隨著光子的能量愈小，增建區內的劑量有變大的趨勢；入射的角度越傾斜，則垂直於治療床的增建區處之百分深度劑量會變得愈大。在臨床治療上，因為入射的角度愈傾斜，則對患者的表皮傷害愈大；但對於腫瘤生長在較表淺處，則反而需要在表淺處覆蓋似組織物以便增加腫瘤的劑量；此結論是以此篇對臨床治療上最重要的貢獻。

The dose in the build-up region comprises a primary component from photons that originate in the x-ray target, head scattered photons, phantom scattered photons and electrons, and contamination electrons from the treatment head and volume of air between the treatment head and patient. The magnitude and importance of each of these components will vary with depth and, with the exception of the primary component, with field size and beam incidence angles.The purpose of this study was to measure the dose of build up region in ball phantom to imitate the dose in patients surface when receiving treatment. Elekta Precise medical linear ccelerator was adopted to deliver radiation dose in this experiment. GAF chromic EBT2 film were used for the dose measurement. The films must be cutted into little pieces in 3cm diameter compassed in a plastic water proof bag to be embedded into liquid for absolutely dose measurement. The conversion of raw scanner-signal and dose would be calibrated. This was achieved by placing 3 cm x 3 cm pieces of films at the thickness of 5 cm solid water phantom of field size 10 cm x 10 cm, Source Axis Distance (SAD) 100 cm, and were irradiated to dose ranges of 5, 10, 15,20,40, 60, 80,100,120,150 and 200 cGy. Epson XL 10000 scanner and associated software was employed for imaging the films. TLD was used only in ball phantom superficial dose check because TLD was unable to be inserted into phantom like film. A complicate calibration procedure both of TLD and film were done prior to do the dose verification and check. After film was irradiated by the same treatment planning design perform in ball phantom. The films optical density signal was read and converted to dose distribuation by adopting the H-D calibration curve. TLD glowing curve was read from the TLD Raxion UL-320 TLD reader and converted the dose by using the well calibrated TLD signal-dose calibration curve.
Results: The more gantry incidence angle, the more build up region dose performed. The film and TLD results showed good coincidence in superficial region while the results of superficial build up region showed poor coincidence with planning.