Davis Anne T, Muscat Sarah, Palmer Antony L, Buckle David, Earley James, Williams Matthew G J, Nisbet Andrew
Department of Medical Physics, Portsmouth Hospitals NHS Trust, Portsmouth, UK.
Department of Medical Physics, Royal Berkshire NHS Foundation Trust Reading, UK.
BJR Open. 2019 Jul 30;1(1):20190023. doi: 10.1259/bjro.20190023. eCollection 2019.
The reconstruction kernel used for a CT scan strongly influences the image quality. This work investigates the changes in Hounsfield units (HUs) which can arise when altering the image reconstruction kernel for planning CT images and the associated changes in dose in the radiotherapy treatment plan if the treatment planning system (TPS) is not re-calibrated.
Head and neck, prostate and lung CT images from four centres were used. For a specific scan, the base image was acquired using the original reconstruction kernel (used when the TPS was calibrated) and the treatment plan produced. The treatment plan was applied to all images from the other reconstruction kernels. Differences in dose-volume metrics for the planning target volume (PTV) and organs at risk (OARs) were noted and HU differences between images measured for air, soft tissue and bone.
HU change in soft tissue had the greatest influence on dose change. When within ±20 HU for soft tissue and ±50 HU for bone and air the dose change in the PTV and OAR was within ±0.5% and ±1% respectively.
When imaging parameters were changed, if HU change was within ±20 HU for soft tissue and ±50 HU for bone and air, the change in the PTV and OAR doses was below 1%.
The degree of dose change in the treatment plan with HU change is demonstrated for current TPS algorithms. This adds to the limited evidence base for recommendations on HU tolerances as a tool for radiotherapy CT protocol optimization.
CT扫描所使用的重建内核会对图像质量产生重大影响。本研究探讨了在规划CT图像时改变图像重建内核可能导致的亨氏单位（HU）变化，以及如果治疗计划系统（TPS）未重新校准，放射治疗计划中剂量的相关变化。
使用了来自四个中心的头颈部、前列腺和肺部CT图像。对于特定扫描，使用原始重建内核（TPS校准时所使用的）获取基础图像并生成治疗计划。将该治疗计划应用于来自其他重建内核的所有图像。记录了计划靶体积（PTV）和危及器官（OAR）的剂量体积指标差异，并测量了空气、软组织和骨骼图像之间的HU差异。
软组织中的HU变化对剂量变化影响最大。当软组织的HU变化在±20 HU以内，骨骼和空气的HU变化在±50 HU以内时，PTV和OAR中的剂量变化分别在±0.5%和±1%以内。
当成像参数改变时，如果软组织的HU变化在±20 HU以内，骨骼和空气的HU变化在±50 HU以内，则PTV和OAR剂量的变化低于1%。
针对当前的TPS算法，展示了治疗计划中剂量随HU变化的程度。这为作为放射治疗CT协议优化工具的HU耐受性建议增加了有限的证据基础。
