Berbeco Ross I, Nishioka Seiko, Shirato Hiroki, Chen George T Y, Jiang Steve B
Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Phys Med Biol. 2005 Aug 21;50(16):3655-67. doi: 10.1088/0031-9155/50/16/001. Epub 2005 Jul 28.
Due to respiration, many tumours in the thorax and abdomen may move as much as 3 cm peak-to-peak during radiation treatment. To mitigate motion-induced irradiation of normal lung tissue, clinics have employed external markers to gate the treatment beam. This technique assumes that the correlation between the external surface and the internal tumour position remains constant inter-fractionally and intra-fractionally. In this work, a study has been performed to assess the validity of this correlation assumption for external surface based gated radiotherapy, by measuring the residual tumour motion within a gating window. Eight lung patients with implanted fiducial markers were studied at the NTT Hospital in Sapporo, Japan. Synchronized internal marker positions and external abdominal surface positions were measured during the entire course of treatment. Stereoscopic imaging was used to find the internal markers in four dimensions. The data were used retrospectively to assess conventional external surrogate respiratory-gated treatment. Both amplitude- and phase-based gating methods were investigated. For each method, three gating windows were investigated, each giving 40%, 30% and 20% duty cycle, respectively. The residual motion of the internal marker within these six gating windows was calculated. The beam-to-beam variation and day-to-day variation in the residual motion were calculated for both gating modalities. We found that the residual motion (95th percentile) was between 0.7 and 5.8 mm, 0.8 and 6.0 mm, and 0.9 and 6.2 mm for 20%, 30% and 40% duty cycle windows, respectively. Five of the eight patients showed less residual motion with amplitude-based gating than with phase-based gating. Large fluctuations (>300%) were seen in the residual motion between some beams. Overall, the mean beam-to-beam variation was 37% and 42% from the previous treatment beam for amplitude- and phase-based gating, respectively. The day-to-day variation was 29% and 34% from the previous day for amplitude- and phase-based gating, respectively. Although gating reduced the total tumour motion, the residual motion behaved unpredictably. Residual motion during treatment could exceed that which might have been considered in the treatment plan. Treatment margins that account for motion should be individualized and daily imaging should be performed to ensure that the residual motion is not exceeding the planned motion on a given day.
由于呼吸作用，胸部和腹部的许多肿瘤在放射治疗期间峰峰值移动幅度可能高达3厘米。为了减轻正常肺组织的运动诱导照射，临床机构采用外部标记物来控制治疗束。该技术假定外表面与内部肿瘤位置之间的相关性在分次治疗期间和单次治疗期间保持恒定。在这项工作中，通过测量门控窗口内的残余肿瘤运动，进行了一项研究以评估基于外表面的门控放射治疗中这种相关性假设的有效性。在日本札幌的NTT医院对8名植入基准标记物的肺癌患者进行了研究。在整个治疗过程中同步测量内部标记物位置和腹部外表面位置。使用立体成像在四维空间中找到内部标记物。这些数据被用于回顾性评估传统的外部替代呼吸门控治疗。研究了基于幅度和基于相位的门控方法。对于每种方法，研究了三个门控窗口，每个窗口的占空比分别为40%、30%和20%。计算了这六个门控窗口内内部标记物的残余运动。计算了两种门控方式下残余运动的束间变化和每日变化。我们发现，对于占空比为20%、30%和40%的窗口，残余运动（第95百分位数）分别在0.7至5.8毫米、0.8至6.0毫米和0.9至6.2毫米之间。8名患者中有5名基于幅度的门控比基于相位的门控显示出更少的残余运动。在一些束之间的残余运动中观察到大幅波动（>300%）。总体而言，基于幅度和基于相位的门控的平均束间变化分别比前一束治疗高37%和42%。基于幅度和基于相位的门控的每日变化分别比前一天高29%和34%。尽管门控减少了肿瘤的总体运动，但残余运动表现出不可预测性。治疗期间的残余运动可能超过治疗计划中所考虑的运动。考虑运动的治疗边界应个体化，并且应进行每日成像以确保残余运动在给定日期不超过计划的运动。
