Department of Oncology, University College London Hospitals NHS Foundation Trust, London, UK; Department of Medical Physics and Biomedical Engineering, University College London, London, UK.
Department of Radiotherapy Physics, University College London Hospitals NHS Foundation Trust, London, UK.
Clin Oncol (R Coll Radiol). 2021 Mar;33(3):e132-e142. doi: 10.1016/j.clon.2020.08.012. Epub 2020 Sep 19.
Pencil beam scanning (PBS) proton therapy is an increasingly used radiation modality for childhood malignancies due to its ability to minimise dose to surrounding organs. However, the dosimetry is extremely sensitive to anatomical and density changes. The aims of this study were to investigate if there is a dosimetric benefit or detriment with PBS for paediatric abdominal neuroblastoma, assess gastrointestinal air variability and its dosimetric consequences, plus identify if there are factors that could assist case selection for PBS referral.
Twenty neuroblastoma cases were double-planned with PBS and intensity-modulated arc therapy (IMAT). Cases were divided into unilateral, midline unilateral and midline bilateral locations in relation to the kidneys. Plans were recalculated after the gastrointestinal volume was simulated as air (Hounsfield Units -700) and water (Hounsfield Units 0), then compared with nominal plans (recalculated - nominal, ΔD). Forty-three weekly cone beam computed tomography scans were analysed to quantify gastrointestinal air variability during treatment.
PBS reduced the mean dose to normal tissues at all tumour locations, particularly unilateral tumours. However, 15% had better dosimetry with IMAT, all of which were midline tumours. Increased gastrointestinal air caused significant compromises to PBS versus IMAT plans for midline tumours [median/maximum ΔD95% clinical target volume (CTV) -2.4%/-15.7% PBS versus 1.4%/0% IMAT, P = 0.003], whereas minimal impact was observed for unilateral tumours (ΔD95% CTV -0.5%/-1.9% PBS versus 0.5%/-0.5% IMAT, P = 0.008). D95% CTV was significantly decreased in PBS plans if planning target volume (PTV) ≥400 cm (median -4.1%, P = 0.001) or PTV extension ≥60% anterior to vertebral body (-2.1%, P = 0.002). A larger variation in gastrointestinal air was observed in patients treated under general anaesthesia (median 38.4%) versus awake (11.5%); P = 0.004.
In this planning study, tumours at the unilateral location consistently showed improved dose reductions to normal tissue with minimal dose degradation from increased gastrointestinal air with PBS plans. Tumour location, PTV volume and anterior extension of PTV are useful characteristics in facilitating patient selection for PBS.
铅笔束扫描（PBS）质子治疗由于其能够最大限度地减少周围器官的剂量，因此是儿童恶性肿瘤越来越常用的放射治疗方式。然而，剂量学对解剖结构和密度变化非常敏感。本研究旨在探讨 PBS 治疗小儿腹部神经母细胞瘤是否有剂量学优势或劣势，评估胃肠道气腔变化及其剂量学后果，并确定是否存在有助于 PBS 转诊病例选择的因素。
对 20 例神经母细胞瘤病例进行 PBS 和强度调制弧形治疗（IMAT）的双规划。根据与肾脏的关系，将病例分为单侧、中线单侧和中线双侧位置。在将胃肠道体积模拟为空气（Hounsfield Units -700）和水（Hounsfield Units 0）后，重新计算计划，并与标称计划（重新计算-标称，ΔD）进行比较。分析了 43 个每周锥形束 CT 扫描，以量化治疗期间胃肠道气腔的变化。
PBS 降低了所有肿瘤部位的正常组织的平均剂量，特别是单侧肿瘤。然而，15%的病例采用 IMAT 治疗的剂量学更好，这些病例均为中线肿瘤。中线肿瘤的胃肠道气腔增加导致 PBS 与 IMAT 计划的显著差异[中位数/最大ΔD95%靶区（CTV）-2.4%/-15.7%PBS 对比 1.4%/0%IMAT，P=0.003]，而单侧肿瘤的影响较小（ΔD95%CTV-0.5%/-1.9%PBS 对比 0.5%/-0.5%IMAT，P=0.008）。如果计划靶区（PTV）≥400cm（中位数-4.1%，P=0.001）或 PTV 在前椎体前方向扩展≥60%，则 PBS 计划中 D95%CTV 显著降低。全身麻醉（中位数 38.4%）下的胃肠道气腔变化明显大于清醒状态（11.5%）；P=0.004。
在这项计划研究中，单侧位置的肿瘤始终显示出与 PBS 计划相关的正常组织剂量减少，而胃肠道气腔增加导致的剂量下降最小。肿瘤位置、PTV 体积和 PTV 前向扩展是帮助 PBS 转诊病例选择的有用特征。
