Beach J L, Kelsey C A
Br J Radiol. 1975 Feb;48(566):134-40. doi: 10.1259/0007-1285-48-566-134.
Tissue air ratios (TAR) and scatter air ratios (SAR) for collimated beams of 14 MeV neutrons were determined from depth dose curves measured in air and water using a tissue equivalent proportional counter. Central axis depth dose data were obtained as a function of field size and depth in a water phantom for an SSD or 125 cm. The collimator was composed of steel and polyethylene and was continuously variable from a 3 times 3 cm to a 20 times 20 cm field size at 125 cm SSD. The field scans for this collimator were flat within plus or minus 2 per cent over 80 per cent of the field dimension in air and were reduced to 20 per cent of the central axis dose at 1-2 field radii in air. Relative depth dose data in air and phantom were measured with an accuracy of plus or minus 2 per cent and were used for the TAR and SAR calculations. The resulting scatter air ratios for 14 MeV neutrons have roughly the same characteristics as 60-Co SAR, but are 60 per cent larger at maximum build-up and reach that maximum at about 60 per cent of the peak depth for 60-Co for all field sizes. The effects of collimator throat scatter on the central axis depth dose characteristics of this particular collimator design are discussed in detail using the measured tissue and scatter air ratios.
使用组织等效正比计数器，根据在空气和水中测量的深度剂量曲线，确定了14兆电子伏中子准直束的组织空气比（TAR）和散射空气比（SAR）。在水模体中，针对源皮距（SSD）为125厘米的情况，获取了中心轴深度剂量数据作为射野大小和深度的函数。准直器由钢和聚乙烯组成，在125厘米SSD下，射野大小可在3×3厘米至20×20厘米之间连续变化。该准直器的射野扫描在空气中80%的射野尺寸范围内，平坦度在±2%以内，在空气中1 - 2个射野半径处，降至中心轴剂量的20%。在空气和模体中的相对深度剂量数据测量精度为±2%，并用于TAR和SAR的计算。所得到的14兆电子伏中子的散射空气比与60钴的SAR大致具有相同的特性，但在最大建成区大60%，并且对于所有射野大小，在达到60钴峰值深度的约60%处达到最大值。利用测量得到的组织空气比和散射空气比，详细讨论了准直器颈部散射对这种特定准直器设计的中心轴深度剂量特性的影响。
