Harrison R M
Regional Medical Physics Department, Newcastle General Hospital, Newcastle-upon-Tyne, UK.
Br J Radiol. 1997 Sep;70(837):946-9. doi: 10.1259/bjr.70.837.9498916.
Percentage depth dose data acquired during the revision of BJR Supplement 17: Central Axis Depth Dose Data for Use in Radiotherapy have been reviewed. Coverage of the half value layer (HVL) and field diameter rang was broad, although gaps were apparent at HVLs of 3-5 and 6-7 mm A1 and field diameters > 14 cm. Comparisons of submitted data with that in Supplement 17 indicate a generally even spread of data about the existing PDD values. Most data agreed to within +/- 5% at 2 cm and +/- 15% at 10 cm depth. Systematic discrepancies may be due to the use of different phantom materials. There is evidence that the spread of data is at least partially due to the problems of beam quality specification. The inadequacy of the first HVL as a specifier of beam quality is a well known and a more realistic specifier might be defined in terms of a broad beam dose ratio at defined depths, for a given beam geometry.
在《英国放射学杂志》增刊17修订版：放射治疗中使用的中心轴深度剂量数据期间获取的百分深度剂量数据已得到审查。半值层（HVL）和射野直径范围的覆盖很广，尽管在3 - 5mm铝和6 - 7mm铝的半值层以及射野直径>14cm时存在明显差距。提交的数据与增刊17中的数据比较表明，现有百分深度剂量（PDD）值的数据分布总体较为均匀。大多数数据在2cm深度处的偏差在±5%以内，在10cm深度处的偏差在±15%以内。系统差异可能是由于使用了不同的模体材料。有证据表明，数据的离散至少部分是由于射束质量规范问题。第一个半值层作为射束质量指标的不足是众所周知的，对于给定的射束几何形状，更现实的指标可能根据在规定深度处的宽束剂量比来定义。
