Kron T, Elliot A, Wong T, Showell G, Clubb B, Metcalfe P
Illawarra Cancer Care Centre, Department of Radiotherapy, Wollongong, NSW, Australia.
Med Phys. 1993 May-Jun;20(3):703-11. doi: 10.1118/1.597019.
Surface dose measurements in therapeutic x-ray beams are of importance in determining the dose to the skin of patients undergoing radiotherapy. Measurements were performed in the 6-MV beam of a medical linear accelerator with LiF thermoluminescence dosimeters (TLD) using a solid water phantom. TLD chips (surface area 3.17 x 3.17 cm2) of three different thicknesses (0.230, 0.099, and 0.038 g/cm2) were used to extrapolate dose readings to an infinitesimally thin layer of LiF. This surface dose was measured for field sizes ranging from 1 x 1 cm2 to 40 x 40 cm2. The surface dose relative to maximum dose was found to be 10.0% for a field size of 5 x 5 cm2, 16.3% for 10 x 10 cm2, and 26.9% for 20 x 20 cm2. Using a 6-mm Perspex block tray in the beam increased the surface dose in these fields to 10.7%, 17.7%, and 34.2% respectively. Due to the small size of the TLD chips, TLD extrapolation is applicable also for intracavity and exit dose determinations. The technique used for in vivo dosimetry could provide clinicians information about the build up of dose up to 1-mm depth in addition to an extrapolated surface dose measurement.
治疗性X射线束中的表面剂量测量对于确定接受放射治疗患者的皮肤剂量至关重要。使用固体水模体，采用氟化锂热释光剂量计（TLD）在医用直线加速器的6兆伏射束中进行测量。使用三种不同厚度（0.230、0.099和0.038克/平方厘米）的TLD芯片（表面积3.17×3.17平方厘米）将剂量读数外推至无限薄的氟化锂层。对面积范围从1×1平方厘米至40×40平方厘米的射野测量此表面剂量。发现对于5×5平方厘米的射野，相对于最大剂量的表面剂量为10.0%，对于10×10平方厘米的射野为16.3%，对于20×20平方厘米的射野为26.9%。在射束中使用6毫米厚的有机玻璃块托盘使这些射野中的表面剂量分别增加至10.7%、17.7%和34.2%。由于TLD芯片尺寸小，TLD外推法也适用于腔内剂量和出射剂量的测定。所采用的体内剂量测定技术除了能提供外推表面剂量测量结果外，还可为临床医生提供有关直至1毫米深度剂量积累的信息。
