Radiological Physics & Advisory Division, Bhabha Atomic Research Centre, CTCRS Building, Anushaktinagar, Mumbai-400094, India.
Phys Med. 2012 Jan;28(1):54-60. doi: 10.1016/j.ejmp.2011.03.001. Epub 2011 Apr 12.
A universal wedge filter of 15W × 20 cm(2) and 60° nominal wedge angle is designed and placed between the collimating jaws and penumbra trimmers inside the treatment head. A pneumatically driven actuating mechanism toggles the wedge between the wedge IN position and wedge OUT position. The effective wedge angles were determined using an analytical formula. An accumulated wedge profile at a depth of 10 cm which was measured using a 2D profiler and dose values at depths of 10 cm and 20 cm for the same experimental setup were used as input parameters in the formula used for determining effective wedge angles. The relationship between the wedge beam weight and effective wedge angle was established. The planned wedge angles were compared with the measured wedge angles and the differences are found to be less than 2° throughout the range of field sizes. Planned doses for various field sizes and wedge angles were measured for verification and the differences were found to be less than 1.8%. This study established that the relationship between the beam weights and effective wedge angles implemented for the motorized wedge filter of medical linacs is not directly applicable for the motorized wedge filter of Telecobalt.
设计并放置了一个 15W×20cm(2)、标称楔角 60°的通用楔形滤光片，位于准直器夹和治疗头内的半影修剪器之间。一个气动驱动的致动机构在楔形 IN 位置和楔形 OUT 位置之间切换楔形滤光片。有效楔角是使用解析公式确定的。使用二维轮廓仪在 10cm 深度处测量累积楔形轮廓，并将相同实验设置在 10cm 和 20cm 深度处的剂量值作为确定有效楔角的公式的输入参数。建立了楔形光束权重与有效楔角之间的关系。计划的楔形角与测量的楔形角进行了比较，结果发现整个射野尺寸范围内的差异小于 2°。为验证目的测量了各种射野尺寸和楔形角的计划剂量，发现差异小于 1.8%。这项研究表明，为医用直线加速器的电动楔形滤光片实施的光束权重与有效楔形角之间的关系并不直接适用于钴-60 远距离治疗机的电动楔形滤光片。
