Datta N R, Basu R, Das K J M, Rajasekar D, Pandey C M, Singh U, Ayyagari S
Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India.
Clin Oncol (R Coll Radiol). 2004 Apr;16(2):129-37. doi: 10.1016/j.clon.2003.10.011.
This study evaluates the consequences of point A as a dose prescription point during multiple high-dose-rate (HDR) intracavitary brachytherapy (ICBT) in cancer cervix.
Fifty patients who had received teletherapy were randomised into two groups of 25 to receive three HDR ICBT fractions of 6 Gy each at point A with either a flexible Ralstron (Shimadzu Corporation, Japan) or rigid Rotterdam (Nucletron, Netherlands) applicator. The orthogonal radiographs of the 150 applications were evaluated for applicator geometry and point A co-ordinates.
Irrespective of the nature and rigidity of the applicators, its various components exhibited a highly significant variation during multiple fractionated HDR ICBT. The Cartesian co-ordinates of point A (left and right) for the applicator geometry also showed significant variation during multiple HDR ICBT procedures. This resulted in an average shift of 9.5 mm (SD= +/-4.4) and 11.1 mm (SD= +/-6.4) in right point A, 10.2 mm (SD= +/-4.5) and 10.8 mm (SD= +/-6.6) in left point A for Ralstron and Rotterdam applicator, respectively, during the three HDR ICBT. Consequently, doses to both right and left point A's showed significant variation during multiple ICBT application and were independent of the applicator type.
Applicator variation in the components and spatial position in the pelvis during multiple HDR ICBT results in multiple point A's irrespective of the nature of applicator, leading to uncertainty in the dose prescription. These uncertainties, which have a bearing on clinical end points, could be minimised by shifting from point-based dose prescription to image-based target localisation and treatment planning in ICBT.
本研究评估了在宫颈癌多程高剂量率（HDR）腔内近距离放疗（ICBT）期间，将A点作为剂量处方点的后果。
50例接受远距离放疗的患者被随机分为两组，每组25例，分别使用可弯曲的Ralstron（日本岛津公司）或刚性的鹿特丹（荷兰核通公司）施源器，在A点接受3次每次6 Gy的HDR ICBT分割照射。对150次照射的正交X线片进行评估，以确定施源器几何形状和A点坐标。
无论施源器的性质和刚性如何，其各个组件在多程分割HDR ICBT期间均表现出高度显著的变化。施源器几何形状的A点（左右）笛卡尔坐标在多程HDR ICBT过程中也显示出显著变化。这导致在3次HDR ICBT期间，Ralstron施源器的右侧A点平均移位9.5 mm（标准差=±4.4），左侧A点平均移位11.1 mm（标准差=±6.4）；鹿特丹施源器的右侧A点平均移位10.2 mm（标准差=±4.5），左侧A点平均移位10.8 mm（标准差=±6.6）。因此，在多程ICBT应用期间，左右A点的剂量均显示出显著变化，且与施源器类型无关。
在多程HDR ICBT期间，施源器组件和盆腔内空间位置的变化会导致多个A点的出现，而与施源器的性质无关，从而导致剂量处方的不确定性。这些不确定性会影响临床终点，通过从基于点的剂量处方转变为ICBT中基于图像的靶区定位和治疗计划，可以将其降至最低。
