Datasheet1_MRI visibility and displacement of elective lymph nodes during radiotherapy in head and neck cancer patients.pdf

Background and purposeTo decrease the impact of radiotherapy to healthy tissues in the head and neck region, we propose to restrict the elective neck irradiation to elective lymph nodes at risk of containing micro metastases instead of the larger lymph node volumes. To assess whether this new concept is achievable in the clinic, we determined the number, volume changes and displacement of elective lymph nodes during the course of radiotherapy.
Materials and methodsMRI scans of 10 head and neck cancer (HNC) patients were acquired before radiotherapy and in week 2, 3, 4 and 5 during radiotherapy. The weekly delineations of elective lymph nodes inside the lymph node levels (Ib/II/III/IVa/V) were rigidly registered and analyzed regarding number and volume. The displacement of elective lymph nodes was determined by center of mass (COM) distances, vector-based analysis and the isotropic contour expansion of the lymph nodes of the pre-treatment scan or the scan of the previous week in order to geographically cover 95% of the lymph nodes in the scans of the other weeks.
ResultsOn average, 31 elective lymph nodes in levels Ib-V on each side of the neck were determined. This number remained constant throughout radiotherapy in most lymph node levels. The volume of the elective lymph nodes reduced significantly in all weeks, up to 50% in week 5, compared to the pre-treatment scan. The largest median COM displacements were seen in level V, for example 5.2 mm in week 5 compared to the pre-treatment scan. The displacement of elective lymph nodes was mainly in cranial direction. Geographical coverage was obtained when the lymph node volumes were expanded with 7 mm in case the pre-treatment scan was used and 6.5 mm in case the scan of the previous week was used.
ConclusionElective lymph nodes of HNC patients remained visible on MRI and decreased in size during radiotherapy. The displacement of elective lymph nodes differ per lymph node level and were mainly directed cranially. Weekly adaptation does not seem to improve coverage of elective lymph nodes. Based on our findings we expect elective lymph node irradiation is achievable in the clinic.

背景与目的：为减轻放疗对头颈部正常组织的损伤，我们提出将选择性颈部放疗的靶区限定为存在微转移风险的选择性淋巴结，而非更大范围的淋巴结体积。为评估这一新理念在临床中是否可行，我们明确了放疗过程中选择性淋巴结的数量、体积变化及位移情况。
材料与方法：本研究纳入10名头颈癌（Head and Neck Cancer, HNC）患者，分别于放疗前及放疗第2、3、4、5周采集磁共振成像（Magnetic Resonance Imaging, MRI）扫描数据。对淋巴结分区（Ib/II/III/IVa/V）内的选择性淋巴结进行每周勾画，并经刚性配准后分析其数量与体积变化。通过质心（Center of Mass, COM）距离、基于向量的分析，以及对放疗前扫描或前一周扫描的淋巴结实施各向同性轮廓扩张，以覆盖其余各周扫描中95%的淋巴结区域，以此定量评估淋巴结的位移情况。
结果：双侧颈部Ib-V区平均共检出31枚选择性淋巴结。多数淋巴结分区的淋巴结数量在整个放疗过程中保持稳定。与放疗前扫描结果相比，所有随访周次的选择性淋巴结体积均出现显著缩小，第5周时体积最大可缩减至原体积的50%。V区的中位质心位移最大，例如与放疗前扫描相比，第5周时位移达5.2mm。选择性淋巴结的位移主要朝向颅侧。若采用放疗前扫描的淋巴结进行7mm各向同性扩张，或采用前一周扫描的淋巴结进行6.5mm扩张，即可实现95%的淋巴结覆盖度。
结论：头颈癌患者的选择性淋巴结在MRI上仍可显影，且在放疗过程中体积逐渐缩小。不同淋巴结分区的选择性淋巴结位移存在差异，且主要朝向颅侧。每周进行靶区适配似乎并不能提升选择性淋巴结的覆盖度。基于本研究结果，我们认为选择性淋巴结放疗在临床中具备可行性。