Animal models of total-body irradiation (TBI) are used to elucidate normal tissue damage and evaluate the efficacy of medical countermeasures (MCM). The accuracy of these TBI models depends on the reproducibility of the radiation dose-response relationship for lethality, which in turn is highly dependent on robust radiation physics and dosimetry. However, the precise levels of radiation each organ absorbs can change dramatically when different photon beam qualities are used, due to the interplay between their penetration and the natural variation of animal sizes and geometries. In this study, we evaluate the effect of varying the radiation energy, namely cobalt-60 (Co-60); of similar penetration to a 4-MV polyenergetic beam), 6 MV and 15 MV, in the absorbed dose delivered by TBI to individual organs of eight Göttingen minipigs of varying weights (10.3–24.1 kg) and dimensions (17.5–25 cm width). The main organs, i.e. heart, lungs, esophagus, stomach, bowels, liver, kidneys and bladder, were contoured by an experienced radiation oncologist, and the volumetric radiation dose distribution was calculated using a commercial treatment planning system commissioned and validated for Co-60, 6-MV and 15-MV teletherapy units. The dose is normalized to the intended prescription at midline in the abdomen. For each animal and each energy, the body and organ dose volume histograms (DVHs) were computed. The results show that more penetrating photon energies produce dose distributions that are systematically and consistently more homogeneous and more uniform, both within individual organs and between different organs, across all animals. Thoracic organs (lungs, heart) received higher dose than prescribed while pelvic organs (bowel, bladder) received less dose than prescribed, due to smaller and wider separations, respectively. While these trends were slightly more pronounced in the smallest animals (10.3 kg, 19 cm abdominal width) and largest animals (>20 kg, ∼25 cm abdominal width), they were observed in all animals, including those in the 9–15 kg range typically used in MCM models. Some organs received an average absorbed dose representing <80% of prescribed dose when Co-60 was used, whereas all organs received average doses of >87% and >93% when 6 and 15 MV were used, respectively. Similarly, average dose to the thoracic organs reached as high as 125% of the intended dose with Co-60, compared to 115% for 15 MV. These results indicate that Co-60 consistently produces less uniform dose distributions in the Göttingen minipig compared to 6 and 15 MV. Moreover, heterogeneity of dose distributions for Co-60 is accentuated by anatomical and geometrical variations across various animals, leading to different absorbed dose delivered to organs for different animals. This difference in absorbed radiation organ doses, likely caused by the lower penetration of Co-60 and 6 MV compared to 15 MV, could potentially lead to different biological outcomes. While the link between the dose distribution and variation of biological outcome in the Göttingen minipig has never been explicitly studied, more pronounced dose heterogeneity within and between organs treated with Co-60 teletherapy units represents an additional confounding factor which can be easily mitigated by using a more penetrating energy.

使用全身辐射（TBI）的动物模型来阐明正常组织损伤并评估医学对策（MCM）的功效。这些TBI模型的准确性取决于致死性的辐射剂量-响应关系的可重复性，而后者又高度依赖于稳健的辐射物理学和剂量学。但是，由于使用不同的光子束质量，每个器官吸收的精确辐射水平可能会发生巨大变化，这是因为它们的穿透力与动物大小和几何形状的自然变化之间存在相互作用。在这项研究中，我们评估了改变辐射能的影响，即60号钴（Co-60）； 5号钴。与4 MV多能光束的穿透力相似），6 MV和15 MV，由TBI输送到八只不同重量（10.3-24.1千克）和尺寸（17.5-25厘米宽）的哥廷根小型猪的各个器官的吸收剂量。主要器官，即心脏，肺，食道，胃，肠，肝，肾和膀胱的轮廓由经验丰富的放射肿瘤学家绘制轮廓，并使用商业化的治疗计划系统对Co-60进行了验证，并计算了放射剂量分布，6-MV和15-MV远程治疗仪。将剂量标准化为腹部中线的预期处方。对于每只动物和每种能量，计算了身体和器官的剂量体积直方图（DVHs）。结果表明，更具穿透性的光子能量产生的剂量分布在系统上始终如一地更加均匀和均匀，在所有动物的单个器官内以及不同器官之间。胸腔器官（肺，心脏）的剂量比规定的要高，而盆腔器官（肠，膀胱）的剂量要比规定的要少，这是由于间隔较小和较宽。虽然这些趋势在最小的动物（10.3公斤，腹宽19厘米）和最大的动物（> 20公斤，腹宽约25厘米）中更为明显，但在所有动物中都观察到了这些趋势，包括9-15公斤的动物MCM模型中通常使用的范围。当使用Co-60时，一些器官的平均吸收剂量<处方剂量的80％，而当使用6和15 MV时，所有器官的平均吸收剂量分别> 87％和> 93％。同样，Co-60对胸腔器官的平均剂量高达预期剂量的125％，相比之下15 MV为115％。这些结果表明，与6和15 MV相比，Co-60在哥廷根小型猪中持续产生的均匀剂量分布较少。此外，Co-60剂量分布的异质性通过各种动物之间的解剖和几何变化而加剧，从而导致不同动物吸收到器官的吸收剂量不同。吸收辐射器官剂量的这种差异可能是由Co-60和6 MV的渗透率低于15 MV引起的，有可能导致不同的生物学结果。尽管从未明确研究过哥廷根小型猪的剂量分布与生物学结果变化之间的联系，