Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA, USA.
Mary Bird Perkins Cancer Center, Baton Rouge, LA, USA.
J Appl Clin Med Phys. 2020 Dec;21(12):131-145. doi: 10.1002/acm2.13079. Epub 2020 Nov 18.
This project determined the range of island block geometric configurations useful for the clinical utilization of intensity-modulated bolus electron conformal therapy (IM-BECT).
Multiple half-beam island block geometries were studied for seven electron energies 7-20 MeV at 100 and 103 cm source-to-surface distance (SSD). We studied relative fluence distributions at 0.5 cm and 2.0 cm depths in water, resulting in 28 unique beam conditions. For each beam condition, we studied intensity reduction factor (IRF) values of 0.70, 0.75, 0.80, 0.85, 0.90, and 0.95, and hexagonal packing separations for the island blocks of 0.50, 0.75, 1.00, 1.25, and 1.50 cm, that is, 30 unique IM configurations and 840 unique beam-IM combinations. A combination was deemed acceptable if the average intensity downstream of the intensity modulator agreed within 2% of that intended and the variation in fluence was less than ±2%.
For 100 cm SSD, and for 0.5 cm depth, results showed that beam energies above 13 MeV did not exhibit sufficient scatter to produce clinically acceptable fluence (intensity) distributions for all IRF values (0.70-0.95). In particular, 20 MeV fluence distributions were unacceptable for any values, and acceptable 16 MeV fluence distributions were limited to a minimum IRF of 0.85. For the 2.0 cm depth, beam energies up to and including 20 MeV had acceptable fluence distributions. For 103 cm SSD and for 0.5 cm and 2.0 cm depths, results showed that all beam energies (7-20 MeV) had clinically acceptable fluence distributions for all IRF values (0.70-0.95). In general, the more clinically likely 103 cm SSD had acceptable fluence distributions with larger separations (r), which allow larger block diameters.
The geometric operating range of island block separations and IRF values (block diameters) producing clinically appropriate IM electron beams has been determined.
本项目旨在确定适用于强度调制 bolus 电子适形治疗（IM-BECT）临床应用的岛形块几何形状范围。
在源皮距（SSD）为 100 和 103cm 处，对七种电子能量 7-20MeV 的多个半束岛形块几何形状进行了研究。我们研究了水深处 0.5cm 和 2.0cm 的相对剂量分布，产生了 28 种独特的射束条件。对于每种射束条件，我们研究了强度降低因子（IRF）值为 0.70、0.75、0.80、0.85、0.90 和 0.95，以及岛形块的六边形间隔为 0.50、0.75、1.00、1.25 和 1.50cm，即 30 种独特的 IM 配置和 840 种独特的射束-IM 组合。如果调制器下游的平均强度在 2%以内，则认为组合是可接受的，并且剂量分布的变化小于±2%。
在 SSD 为 100cm 和 0.5cm 深度的情况下，结果表明，高于 13MeV 的束能没有足够的散射来产生所有 IRF 值（0.70-0.95）的临床可接受的剂量分布。特别是，20MeV 的剂量分布对于任何值都是不可接受的，而 16MeV 的可接受剂量分布仅限于最小 IRF 值为 0.85。在 2.0cm 深度处，直到包括 20MeV 的所有束能都具有可接受的剂量分布。在 SSD 为 103cm 以及 0.5cm 和 2.0cm 深度处，结果表明，所有束能（7-20MeV）对于所有 IRF 值（0.70-0.95）都具有临床可接受的剂量分布。一般来说，更可能临床应用的 SSD 为 103cm，其具有较大的分离度（r），允许更大的块直径。
已经确定了产生临床合适的 IM 电子束的岛形块分离和 IRF 值（块直径）的几何操作范围。
