Suit Herman, Goldberg Saveli, Niemierko Andrzej, Trofimov Alexei, Adams Judith, Paganetti Harald, Chen George T Y, Bortfeld Thomas, Rosenthal Stanley, Loeffler Jay, Delaney Thomas
Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Acta Oncol. 2003;42(8):800-8. doi: 10.1080/02841860310017676.
With proton beam radiation therapy a smaller volume of normal tissues is irradiated at high dose levels for most anatomic sites than is feasible with any photon technique. This is due to the Laws of Physics, which determine the absorption of energy from photons and protons. In other words, the dose from a photon beam decreases exponentially with depth in the irradiated material. In contrast, protons have a finite range and that range is energy dependent. Accordingly, by appropriate distribution of proton energies, the dose can be uniform across the target and essentially zero deep to the target and the atomic composition of the irradiated material. The dose proximal to the target is lower compared with that in photon techniques, for all except superficial targets This resultant closer approximation of the planning treatment volume (PTV) to the CTV/GTV (grossly evident tumor volume/subclinical tumor extensions) constitutes a clinical gain by definition; i.e. a smaller treatment volume that covers the target three dimensionally for the entirety of each treatment session provides a clinical advantage. Several illustrative clinical dose distributions are presented and the clinical outcome results are reviewed briefly. An important technical advance will be the use of intensity modulated proton radiation therapy, which achieves contouring of the proximal edge of the SOBP (spread out Bragg peak) as well as the distal edge. This technique uses pencil beam scanning. To permit further progressive reductions of the PTV, 4-D treatment planning and delivery is required. The fourth dimension is time, as the position and contours of the tumor and the adjacent critical normal tissues are not constant. A potentially valuable new method for assessing the clinical merits of each of a large number of treatment plans is the evaluation of multidimensional plots of the complication probabilities for each of 'n' critical normal tissues/ structures for a specified tumor control probability. The cost of proton therapy compared with that of very high technology photon therapy is estimated and evaluated. The differential is estimated to be approximately 1.5 provided there were to be no charge for the original facility and that there were sufficient patients for operating on an extended schedule (6-7 days of 14-16 h) with > or = two gantries and one fixed horizontal beam.
对于大多数解剖部位，与任何光子技术相比，质子束放射治疗以高剂量水平照射的正常组织体积更小。这是由物理定律决定的，这些定律决定了光子和质子能量的吸收情况。换句话说，光子束的剂量在被照射物质中随深度呈指数下降。相比之下，质子具有有限的射程，且该射程与能量有关。因此，通过适当分布质子能量，剂量可以在靶区内均匀分布，在靶区深部以及被照射物质的原子组成部分基本为零。除了浅表靶区外，与光子技术相比，靶区近端的剂量更低。根据定义，由此产生的计划治疗体积（PTV）与临床靶体积/大体肿瘤体积（CTV/GTV，明显可见的肿瘤体积/亚临床肿瘤扩展）更接近构成了临床获益；也就是说，在每个治疗疗程的全过程中，一个在三维空间上覆盖靶区的较小治疗体积具有临床优势。文中给出了几个说明性的临床剂量分布，并简要回顾了临床结果。一项重要的技术进步将是使用强度调制质子放射治疗，它可以实现对扩展布拉格峰（SOBP）近端边缘以及远端边缘的轮廓描绘。该技术使用笔形束扫描。为了进一步逐步缩小PTV，需要进行四维治疗计划和投照。第四维是时间，因为肿瘤以及相邻关键正常组织的位置和轮廓并非恒定不变。一种评估大量治疗计划各自临床优点的潜在有价值的新方法是，针对特定的肿瘤控制概率，评估‘n’个关键正常组织/结构中每个组织的并发症概率的多维图。文中估计并评估了质子治疗与非常高科技的光子治疗相比的成本。如果原设施不收费，并且有足够的患者在延长的时间表（14 - 16小时的6 - 7天）下使用≥两个龙门架和一个固定水平束进行治疗，估计差价约为1.5 。
