O. van Wulfften Palthe, Massachusetts General Hospital, Boston, MA, USA K.-W. Jee, Y.-L. E. Chen, Department of Radiation Oncology, Massachusetts General Hospital-Harvard Medical School, Boston, MA, USA J. A. M. Bramer, Department of Orthopaedic Surgery, Academic Medical Center, Amsterdam, Amsterdam, The Netherlands F. J. Hornicek, Harvard Medical School, Orthopaedic Oncology Service, Massachusetts General Hospital-Harvard Medical School, Boston, MA, USA J. H. Schwab, Department of Orthopaedic Surgery, Orthopaedic Oncology Service, Spine Surgery Service, Massachusetts General Hospital-Harvard Medical School, Boston, MA, USA.
Clin Orthop Relat Res. 2018 Mar;476(3):520-528. doi: 10.1007/s11999.0000000000000063.
Effects of high-dose radiation using protons and photons on bone are relatively unexplored, but high rates of insufficiency fractures are reported, and the causes of this are incompletely understood. Imaging studies with pre- and postradiation scans can help one understand the effect of radiation on bone.
QUESTIONS/PURPOSES: The purpose of this study was to assess the effects of high-dose radiation on the trabecular density of bone in the sacrum using CT-derived Hounsfield units (HU).
Between 2009 and 2015, we treated 57 patients (older then 18 years) with sacral chordoma. Fourteen (25%) of them were treated with radiation only. The general indication for this approach is inoperability resulting from tumor size. Forty-two (74%) patients were treated with transverse sacral resections and high-dose radiotherapy (using either protons or photons or a combination) before surgery and after surgery. During this time period, our indication for this approach generally was symptomatic sacral chordoma in which resection would prevent further growth and reasonable sacrifice of nerve roots was possible. Of those patients, 21 (50%) had CT scans both before and after radiation treatment. We used HU as a surrogate for bone density. CT uses HU to derive information on tissue and bone quantity. A recent study presented reference HU values for normal (mean 133 ± 38 HU), osteoporotic (101 ± 25 HU), and osteopenic bone (79 ± 32 HU). To adjust for scanning protocol-induced changes in HU, we calculated the ratio between bone inside and outside the radiation field rather than using absolute values. To assess the effect of radiation, we tested whether there was a difference in ratio (sacrum/L1) before and after radiation. A control measurement was performed (L2/L1) and also tested for a difference before and after radiation. Statistical analyses were performed using the paired t-test.
The effects of radiation appeared confined to the intended field, because the bone density outside the treated field was not observed to decrease. The ratio of HU (a surrogate for bone density) in L2 relative to L1 did not change after radiotherapy (preradiation mean: 0.979 ± 0.009, postradiation mean: 0.980 ± 0.009, mean difference outside the radiation field: -0.001, 95% confidence interval [CI], -0.009 to 0.007, p = 0.799). The ratio of HU within the radiation field relative to L1 decreased after radiotherapy (preradiation mean: 0.895 ± 0.050, postradiation mean: 0.658 ± 0.050, mean difference inside the radiation field: 0.237, 95% CI, 0.187-0.287, p < 0.001), suggesting the bone density stayed the same outside the radiation field but decreased inside the radiation field.
Trabecular bone density decreased after high-dose radiation therapy in a small group of patients with sacral chordoma. High-dose radiation is increasingly gaining acceptance for treating sacral malignancies; further long-term prospective studies using calibrated CT scanners and preferably bone biopsies are needed.
Level IV, therapeutic study.
使用质子和光子进行高剂量辐射对骨骼的影响尚未得到充分研究，但据报道，骨不愈合的发生率很高，其原因尚不完全清楚。有研究表明，在进行辐射治疗前后进行影像学检查有助于了解辐射对骨骼的影响。
问题/目的：本研究旨在使用 CT 衍生的亨氏单位（HU）评估高剂量辐射对骶骨骨小梁密度的影响。
在 2009 年至 2015 年期间，我们治疗了 57 名（年龄大于 18 岁）骶骨脊索瘤患者。其中 14 名（25%）仅接受了放射治疗。这种治疗方法的一般适应证是由于肿瘤大小导致无法手术。42 名（74%）患者在手术前和手术后接受了横切骶骨切除术和高剂量放疗（使用质子或光子或两者的组合）。在此期间，我们一般对有症状的骶骨脊索瘤患者采用这种治疗方法，这种治疗方法可以防止肿瘤进一步生长，并可以合理地牺牲神经根。其中 21 名（50%）患者在接受放射治疗前后都进行了 CT 扫描。我们使用 HU 作为骨密度的替代物。CT 使用 HU 来获取有关组织和骨量的信息。最近的一项研究提出了正常（平均 133 ± 38 HU）、骨质疏松（101 ± 25 HU）和骨质减少（79 ± 32 HU）的参考 HU 值。为了调整因扫描方案引起的 HU 变化，我们计算了骨内与骨外辐射场之间的比值，而不是使用绝对值。为了评估辐射的影响，我们测试了骨密度比值（sacrum/L1）在辐射前后是否有差异。还进行了对照测量（L2/L1），并测试了辐射前后的差异。使用配对 t 检验进行统计学分析。
辐射的影响似乎仅限于预期的治疗区域，因为未观察到治疗区域外的骨骼密度下降。L2 相对于 L1 的 HU 比值（骨密度的替代物）在放射治疗后没有改变（放射治疗前平均值：0.979 ± 0.009，放射治疗后平均值：0.980 ± 0.009，治疗区域外的平均差值：-0.001，95%置信区间[CI]，-0.009 至 0.007，p = 0.799）。放射治疗后，治疗区域内的 HU 比值（相对于 L1）降低（放射治疗前平均值：0.895 ± 0.050，放射治疗后平均值：0.658 ± 0.050，治疗区域内的平均差值：0.237，95%CI，0.187-0.287，p < 0.001），表明治疗区域外的骨密度保持不变，但治疗区域内的骨密度降低。
一小部分患有骶骨脊索瘤的患者在接受高剂量放射治疗后，骨小梁密度降低。高剂量放疗越来越被接受用于治疗骶骨恶性肿瘤；需要进一步进行长期前瞻性研究，使用校准 CT 扫描仪，最好使用骨活检。
IV 级，治疗研究。
