De Wagter C, Colle C O, Fortan L G, Van Duyse B B, Van den Berge D L, De Neve W J
Division of Radiotherapy, University Hospital Gent, Belgium.
Radiother Oncol. 1998 Apr;47(1):69-76. doi: 10.1016/s0167-8140(97)00230-2.
This paper presents a method for interactive optimization of 3D conformal intensity-modulated radiotherapy plans employing a quadratic objective that also contains dose limitations in the organs at risk. This objective function is minimized by constrained matrix inversion (CMI) that follows the same approach as the gradient technique using matrix notation.
Sherouse's GRATIS radiotherapy design system is used to determine the outlines of the target volume and the organs at risk and to input beam segments which are given by the beam segmentation technique. This technique defines the beam incidences and the beam segmentation. The weights of the segments are then calculated using a quadratic objective function and CMI. The objective function to be minimized consists of two components based on the planning target volume (PTV) and the organ at risk (OAR) with an importance factor w associated with the OAR.
Optimization is tested for concave targets in the head and neck region wrapping around the spinal cord. For a predefined w-value, segment weights are optimized within a few seconds on a DEC Alpha 3000. In practice, 5-10 w-values have to be tested, making optimization a less than 5 min procedure. This optimization procedure predicts the possibility of target dose escalation for a tumour in the lower neck to 120-150 Gy without exceeding the spinal cord tolerance, whereas human planners could not increase the dose above 65-80 Gy.
Treatment plans optimized using a quadratic objective function and the CMI algorithm are superior to those which are generated by human planners. The optimization algorithm is very fast and allows interactive use. Quadratic optimization by CMI is routinely used by clinicians at the Division of Radiotherapy, U.Z.-Gent.
本文提出了一种用于三维适形调强放射治疗计划交互式优化的方法，该方法采用二次目标函数，该函数还包含对危及器官的剂量限制。通过约束矩阵求逆（CMI）将此目标函数最小化，CMI采用与使用矩阵表示法的梯度技术相同的方法。
使用Sherouse的GRATIS放射治疗设计系统来确定靶区体积和危及器官的轮廓，并输入由射束分割技术给出的射束段。该技术定义了射束入射和射束分割。然后使用二次目标函数和CMI计算各段的权重。要最小化的目标函数由基于计划靶区（PTV）和危及器官（OAR）的两个分量组成，其中与OAR相关联的重要性因子w。
对头颈部围绕脊髓的凹形靶区进行了优化测试。对于预定义的w值，在DEC Alpha 3000上几秒钟内即可优化段权重。在实际操作中，必须测试5 - 10个w值，使得优化过程不到5分钟。此优化过程预测下颈部肿瘤的靶区剂量可提升至120 - 150 Gy而不超过脊髓耐受剂量，而人工计划者无法将剂量提高到65 - 80 Gy以上。
使用二次目标函数和CMI算法优化的治疗计划优于人工计划者生成的计划。该优化算法非常快速且允许交互式使用。CMI的二次优化在根特大学医院放疗科的临床医生中常规使用。
