King Abdulaziz City for Science and Technology (KACST), Riyadh, Saudi Arabia.
J Radiol Prot. 2020 Jun;40(2):393-409. doi: 10.1088/1361-6498/ab703c. Epub 2020 Jan 27.
The dose length product (DLP) provides a measurement related to energy imparted from a computed tomography (CT) scan. The DLP is based on the volume-averaged CT dose index (CTDI ), which is designed for fan beams. The aims of this study were to investigate the use of DLP for scans with wide beams used in cone beam CT (DLP ) in radiotherapy that would be analogous to the DLP of fan beam scans (DLP ), and to compare the efficiencies of DLP and DLP in reporting the total energy imparted in patients. A validated Monte Carlo model of a kV imaging system integrated into a Varian TrueBeam linac was employed. The DLP was assessed by multiplying the CTDI for a 20 mm fan beam by scan length, and the DLP determined through multiplying the CTDI , estimated for wide beams using a correction factor based on free-in-air measurements, by the beam width. Two scan protocols for head and body were investigated for tube potentials between 80 and 140 kV and a range of scan lengths/widths. Efficiency values were estimated by normalising the DLP and DLP with respect to the corresponding dose profile integrals (DPIs), which were evaluated within 900 mm long phantoms. The results show that the DLP values were within 1% of those for DLP of similar length performed on the same system, and the efficiencies decrease with tube potential. However, whereas DLP values for fan beams are approximately proportional to scan length, those for wide beams decrease by ∼2% between beam widths of 20 and 320 mm. As a result, while the DLP efficiency is similar over all scan lengths, that for DLP increases slightly with beam width. The DLP and DLP underestimated the total energy imparted by comparable amounts with efficiencies within the range of 80-81% and 80-83% for the head scans, and 71-76% and 70-77% for the body scans, respectively. The results indicate that the DLP can be considered as an analogous dose index to the DLP . It could, therefore, be used for quantification of doses from imaging in radiotherapy and provide a valuable tool to aid optimisation.
剂量长度乘积（DLP）提供了与 CT 扫描所传递能量相关的测量值。DLP 基于体积平均 CT 剂量指数（CTDI），旨在用于扇形束 CT。本研究旨在探讨使用宽束锥形束 CT（DLP）的扫描，该扫描类似于扇形束扫描的 DLP（DLP），并比较 DLP 和 DLP 在报告患者所接受的总能量方面的效率。采用已验证的 Monte Carlo 模型，该模型将千伏成像系统集成到瓦里安 TrueBeam 直线加速器中。通过将 20mm 扇形束的 CTDI 乘以扫描长度来评估 DLP ，并通过将基于自由空气测量的校正因子估算的宽束 CTDI 乘以束宽来确定 DLP 。研究了 80 至 140kV 管电压和一系列扫描长度/宽度的头部和身体两种扫描协议。通过将 DLP 和 DLP 相对于相应剂量分布积分（DPI）进行归一化来估计效率值，这些积分是在 900mm 长的体模内评估的。结果表明，DLP 的值与在同一系统上进行的相似长度的 DLP 的值相差在 1%以内，且效率随管电压降低而降低。然而，扇形束的 DLP 值与扫描长度大致成正比，而宽束的 DLP 值在 20 至 320mm 的束宽之间减小约 2%。因此，尽管所有扫描长度的 DLP 效率相似，但 DLP 随着束宽的增加略有增加。对于头部扫描，DLP 和 DLP 对总能量的估计都有类似的低估，效率分别为 80-81%和 80-83%，对于身体扫描，效率分别为 71-76%和 70-77%。结果表明，DLP 可视为与 DLP 类似的剂量指数。因此，它可用于放射治疗成像剂量的定量，并提供有价值的工具以辅助优化。
