Department of Chemistry and Konstanz Research School Chemical Biology, University of Konstanz, Konstanz, Germany.
Klinik und Praxis für Strahlentherapie am Klinikum Konstanz, Konstanz, Germany.
Radiat Oncol. 2021 Oct 30;16(1):209. doi: 10.1186/s13014-021-01938-8.
In-vivo dosimetry (IVD) is a patient specific measure of quality control and safety during radiotherapy. With regard to current reporting thresholds for significant occurrences in radiotherapy defined by German regulatory authorities, the present study examines the clinical feasibility of superficial electron paramagnetic resonance (EPR) IVD of cumulative total doses applied to breast cancer patients treated with helical intensity-modulated radiotherapy (tomotherapy).
In total, 10 female patients with left- or right-sided breast cancer were enrolled in this prospective IVD study. Each patient received a hypofractionated whole breast irradiation. A total median dose of 42.4 Gy in 16 fractions (5 fractions per week) was prescribed to the planning target volume. The treatments were completely delivered using helical tomotherapy and daily image guidance via megavoltage CT (MVCT). For each patient, three EPR dosimeters were prepared and placed at distinct locations on the patient's skin during the delivery of all fractions. Two dosimeters were placed next to the ipsilateral and contralateral mammilla and one dosimeter was placed ventrally to the thyroid (out-of-primary-beam). The total doses delivered to the dosimeters were readout after all fractions had been administered. The measured total dose values were compared to the planned dose values derived from the treatment planning system (TPS). Daily positional variations (displacement vectors) of the ipsilateral mammilla and of the respective dosimeter were analyzed with respect to the planned positions using the daily registered MVCT image.
Averaged over all patients, the mean absolute dose differences between measured and planned total dose values (± standard deviation (SD)) were: 0.49 ± 0.85 Gy for the ipsilateral dosimeter, 0.17 ± 0.49 Gy for the contralateral dosimeter and -0.12 ± 0.30 Gy for the thyroid dosimeter. The mean lengths of the ipsilateral displacement vectors (± SD) averaged over all patients and fractions were: 10 ± 7 mm for the dosimeter and 8 ± 4 mm for the mammilla.
Superficial EPR IVD is suitable as additional safeguard for dose delivery during helical tomotherapy of breast cancer. Despite positional uncertainties in clinical routine, the observed dose deviations at the ipsilateral breast were on average small compared to national reporting thresholds for total dose deviations (i.e. 10%/4 Gy). EPR IVD may allow for the detection of critical dose errors during whole breast irradiations.
体内剂量测定（IVD）是放射治疗期间患者质量控制和安全的特定措施。鉴于德国监管机构定义的放射治疗中重大事件的当前报告阈值，本研究检查了在接受螺旋强度调制放射治疗（螺旋断层放疗）的乳腺癌患者中应用于累积总剂量的浅表电子顺磁共振（EPR）IVD 的临床可行性。
总共纳入了 10 名左侧或右侧乳腺癌的女性患者进行这项前瞻性 IVD 研究。每位患者接受了左侧或右侧乳腺癌的hypofractionated 全乳房照射。计划靶区的中位总剂量为 42.4Gy，共 16 个分次（每周 5 个分次）。所有分次均采用螺旋断层放疗和每日兆伏 CT（MVCT）图像引导完成。对于每位患者，在所有分次治疗过程中，将三个 EPR 剂量计分别放置在患者皮肤的三个不同位置。两个剂量计分别放置在同侧和对侧乳晕旁，一个剂量计放置在甲状腺下方（主射束外）。在所有分次治疗完成后，读取剂量计所接受的总剂量。将测量的总剂量值与治疗计划系统（TPS）得出的计划剂量值进行比较。使用每日登记的 MVCT 图像分析同侧乳晕和相应剂量计的每日位置变化（位移向量）与计划位置的关系。
所有患者的平均剂量差异，测量的总剂量值与计划总剂量值（平均值±标准差（SD））之间：同侧剂量计为 0.49±0.85Gy，对侧剂量计为 0.17±0.49Gy，甲状腺剂量计为-0.12±0.30Gy。所有患者和分次的同侧位移向量的平均长度（平均值±SD）为：剂量计为 10±7mm，乳晕为 8±4mm。
浅表 EPR IVD 适合作为乳腺癌螺旋断层放疗中剂量传递的附加保障。尽管在临床常规中存在位置不确定性，但与总剂量偏差的国家报告阈值（即 10%/4Gy）相比，同侧乳房的观察到的剂量偏差平均较小。EPR IVD 可能允许在全乳房照射期间检测到临界剂量误差。
