Servei d'Oncologia Radioteràpia (ICMHO), Hospital Clínic de Barcelona, Barcelona, Spain.
Servicio de Radiofísica y Protección Radiológica, Hospital Universitario Marqués de Valdecilla, Santander, Spain.
Phys Med Biol. 2022 Jul 29;67(15). doi: 10.1088/1361-6560/ac7d32.
Transitdosimetry methods monitor that the dose distribution is delivered as planned. However, they have a limited ability to identify and to quantify the cause of a given disagreement, especially those caused by position errors. This paper describes a proof of concept of a simpletechnique to infer a position error from a transit portal image (TPI).For a given treatment field, the impact of a position error is modeled as a perturbation of the corresponding reference (unperturbed) TPI. The perturbation model determines the patient translation, described by a shift vector, by comparing a givenTPI to the corresponding reference TPI. Patient rotations can also be determined by applying this formalism to independent regions of interest over the patient. Eight treatment plans have been delivered to an anthropomorphic phantom under a large set of couch shifts (<15 mm) and rotations (<10°) to experimentally validate this technique, which we have named Transit-Guided Radiation Therapy (TGRT).The root mean squared error (RMSE) between the determined and the true shift magnitudes was 1.0/2.4/4.9 mm for true shifts ranging between 0-5/5-10/10-15 mm, respectively. The angular accuracy of the determined shift directions was 12° ± 14°. The RMSE between the determined and the true rotations was 0.5°. The TGRT technique decoupled translations and rotations satisfactorily. In 96% of the cases, the TGRT technique decreased the existing position error. The detection threshold of the TGRT technique was around 1 mm and it was nearly independent of the tumor site, delivery technique, beam energy or patient thickness.TGRT is a promising technique that not only provides reliable determinations of the position errors without increasing the required equipment, acquisition time or patient dose, but it also adds on-line correction capabilities to existing methods currently using TPIs.
传输剂量学方法可监测剂量分布是否按计划进行。然而，它们识别和量化特定不一致的能力有限，尤其是由位置误差引起的不一致。本文描述了一种简单技术的概念验证，该技术可从传输门户图像（TPI）推断位置误差。对于给定的治疗野，位置误差的影响通过将相应的参考（未受扰）TPI 进行扰动作来建模。通过将给定的 TPI 与相应的参考 TPI 进行比较，扰模确定了患者平移，平移由移位矢量描述。还可以通过将此形式应用于患者上的独立感兴趣区域来确定患者旋转。已经向人体模型体模在大的一组治疗床移位（<15mm）和旋转（<10°）下输送了 8 个治疗计划，以实验验证该技术，我们将其命名为传输引导放射治疗（TGRT）。在真实移位幅度在 0-5/5-10/10-15mm 之间的情况下，确定的和真实的移位幅度之间的均方根误差（RMSE）分别为 1.0/2.4/4.9mm。确定的移位方向的角度精度为 12°±14°。确定的和真实旋转之间的 RMSE 为 0.5°。TGRT 技术可以很好地解耦平移和旋转。在 96％的情况下，TGRT 技术减小了现有位置误差。TGRT 技术的检测阈值约为 1mm，并且几乎与肿瘤部位、输送技术、射束能量或患者厚度无关。TGRT 是一种很有前途的技术，它不仅可以在不增加所需设备、采集时间或患者剂量的情况下提供可靠的位置误差确定，而且还为当前使用 TPI 的现有方法添加了在线校正功能。
