Langmuir V K, Sutherland R M
University of Rochester Cancer Center, University of Rochester Medical Center, New York 14642.
Med Phys. 1988 Nov-Dec;15(6):867-73. doi: 10.1118/1.596169.
Tumor therapy using radiolabeled antibodies presents a challenging problem in absorbed dose determination. The purpose of this study is to evaluate the effect of tumor size on the absorbed dose distribution from beta-emitters when the radiolabeled antibody is not uniformly distributed throughout the tumor. Two theoretical dosimetry models are constructed, one for nonvascularized micrometastases and the other for vascularized tumors. All calculations assume no penetration of radionuclide into the tumor. These are compared to an even distribution of radionuclide throughout the tumor. In micrometastases of 1-mm diameter or less, emitters of low energy such as 131I give higher dose rates than emitters of higher energy because less energy is lost outside the target volume. However, even with 131I, a significant proportion of the energy is not absorbed in the tumor and, as a result, the concentration of radionuclide necessary for a therapeutic radiation dose becomes higher as the tumor diameter gets smaller. Because it may be impossible to achieve these concentrations in very small tumors (less than 0.5-mm diameter), alpha-emitters may be useful in combination with beta-emitters for therapy of micrometastatic disease. In vascularized tumors, higher energy emitters such as 90Y yield higher doses because of overlapping dose distributions from multiple vascular sources. This also produces a more even dose distribution across a tumor, even when there is poor penetration of the radiolabeled antibody. Thus tumor size, antibody penetration, and tumor vascularity all influence the choice of radionuclide and, depending on the circumstances, alpha-emitters, low-energy beta-emitters, high-energy beta-emitters, or some combination of the three may be most efficacious.
使用放射性标记抗体进行肿瘤治疗在吸收剂量测定方面存在一个具有挑战性的问题。本研究的目的是评估当放射性标记抗体在肿瘤内分布不均匀时，肿瘤大小对β发射体吸收剂量分布的影响。构建了两个理论剂量学模型，一个用于无血管的微转移灶，另一个用于有血管的肿瘤。所有计算均假设放射性核素不穿透肿瘤。将这些模型与放射性核素在肿瘤内均匀分布的情况进行比较。在直径为1毫米或更小的微转移灶中，低能发射体（如131I）比高能发射体产生更高的剂量率，因为在靶体积外损失的能量较少。然而，即使使用131I，仍有很大一部分能量未被肿瘤吸收，因此，随着肿瘤直径变小，达到治疗辐射剂量所需的放射性核素浓度会变得更高。由于在非常小的肿瘤（直径小于0.5毫米）中可能无法达到这些浓度，α发射体可能与β发射体联合用于微转移疾病的治疗。在有血管的肿瘤中，高能发射体（如90Y）由于多个血管来源的剂量分布重叠而产生更高的剂量。这也会在整个肿瘤中产生更均匀的剂量分布，即使放射性标记抗体的穿透性较差。因此，肿瘤大小、抗体穿透性和肿瘤血管生成都会影响放射性核素的选择，根据具体情况，α发射体、低能β发射体、高能β发射体或三者的某种组合可能最为有效。
