Department of Medical Radiation Physics, Karolinska Institutet and Stockholm University, Stockholm (Sweden).
Phys Med. 2006 January-March;22(1):3-15. doi: 10.1016/S1120-1797(06)80005-0.
The purpose of this study was to investigate the optimal coplanar beam directions when treating an early breast cancer with locoregional lymphatic spread with a few radiobiologically optimized intensity modulated beams. Also to determine the increase in the probability of complication-free cure with the number of beam portals and the smallest number required to perform a close to optimal treatment for this tumour site. Four test patients with stage II left-sided breast cancer were studied with heart, lung and contralateral breast as principal organs at risk. The clinical target volume consisted of the breast tissue remaining after surgery, the axillary, the internal mammary as well as the supraclavicular lymph nodes. Through an exhaustive search of all possible beam directions the most effective coplanar beams with one to four intensity modulated photon beam portals were investigated. Comparisons with uniform beam treatment techniques and up to 12 intensity modulated beams were also made. The different plans were optimized using the probability of complication-free tumour cure, P(+), as biological objective function. When using two intensity modulated beam directions three major sets of suitable directions were identified denoted by A, P and T. A corresponds to an anterior oblique pair of beams around 25 degrees and 325 degrees , P is a perpendicular lateral pair at around 50 degrees and 130 degrees whereas T is a more conventional tangential pair at around 155 degrees and 300 degrees . Interestingly, these configurations identify simply three major effective beam directions namely at 30 degrees +/-20 degrees , 145 degrees +/-20 degrees and 310 degrees +/-15 degrees . For the three intensity modulated beam technique a combination of these three effective beam directions generally covered the global maximum of the probability of complication-free tumour control. The improvement in complication-free cure probability with two optimally selected intensity modulated beams is around 10% when compared to a uniform beam technique with three to four beam portals. This increase is mainly due to a reduction by almost 1% in the probability of injury to the heart and an increase of 6% in the probability of local tumour control. When three or four biologically optimized beam portals are used a further increase in the probability of complication-free cure of about 6% can often be obtained. This improvement is caused by a small decrease in the probability of injury to the heart, left lung and other surrounding normal tissue, as well as a slight further increase in the probability of tumour control. The increase in the treatment outcome is minimal when more than four intensity modulated beams are employed. A small increase in dose homogeneity in the target volume and a slight decrease in the normal tissue volume receiving high dose may be seen, but without appreciably improving the complication-free cure probability. For a stage II breast cancer, three and in more complex cases four optimally oriented beams are sufficient to reach close to the maximum probability of complication-free tumour control when biologically optimized intensity modulated dose delivery is used. Angle of incidence optimization may then be advantageous starting from the given most effective three beam directions.
本研究的目的是探讨在局部区域淋巴扩散的早期乳腺癌中，使用少数放射生物学优化的强度调制射束时，最佳共面射束方向。还确定了增加无并发症治愈率的可能性，方法是增加射束端口的数量，并确定为该肿瘤部位进行接近最佳治疗所需的最少数量。对 4 名患有左侧 II 期乳腺癌的测试患者进行了研究，主要的危险器官有心、肺和对侧乳房。临床靶区包括手术后残留的乳腺组织、腋窝、内乳以及锁骨上淋巴结。通过对所有可能的射束方向进行详尽的搜索，研究了最多具有 1 到 4 个强度调制光子射束端口的最有效共面射束。还对均匀射束治疗技术和最多 12 个强度调制射束进行了比较。使用并发症无肿瘤治愈率 P(+)作为生物目标函数，对不同的方案进行了优化。当使用两个强度调制射束方向时，确定了三个主要的合适射束方向集，分别用 A、P 和 T 表示。A 对应于大约 25 度和 325 度的前斜对射束，P 是大约 50 度和 130 度的垂直侧对射束，而 T 是更传统的大约 155 度和 300 度的切线对射束。有趣的是，这些配置仅简单地标识了三个主要的有效射束方向，即大约 30 度 +/-20 度、145 度 +/-20 度和 310 度 +/-15 度。对于三个强度调制射束技术，这三个有效射束方向的组合通常可以覆盖无并发症肿瘤控制的全局最大值。与使用三到四个射束端口的均匀射束技术相比，两个最佳选择的强度调制射束的无并发症治愈率提高了约 10%。这种提高主要是由于心脏损伤概率降低了近 1%，局部肿瘤控制概率增加了 6%。当使用三个或四个生物优化射束端口时，通常可以获得约 6%的无并发症治愈率的进一步提高。这种提高是由于心脏、左肺和其他周围正常组织损伤概率的微小降低，以及肿瘤控制概率的轻微进一步增加。当使用超过四个强度调制射束时，治疗效果的提高最小。在靶区中可以看到剂量均匀性的微小提高，以及接受高剂量的正常组织体积的轻微减少，但无并发症治愈率没有明显提高。对于 II 期乳腺癌，当使用生物优化强度调制剂量输送时，三个射束，在更复杂的情况下为四个最佳定向射束足以达到接近无并发症肿瘤控制的最大概率。从给定的最有效三个射束方向开始，入射角优化可能是有利的。
