Wheldon T E, O'Donoghue J A, Barrett A, Michalowski A S
Department of Radiation Oncology, University of Glasgow, CRC Beatson Laboratories, U.K.
Radiother Oncol. 1991 Jun;21(2):91-9. doi: 10.1016/0167-8140(91)90080-z.
A mathematical model has been used to investigate the relationship of curability to tumour size and cell number for spherical tumours treated with targeted 131I or 90Y, assuming uniform uptake of radionuclide throughout the tumour. The analysis shows that, for any given cumulated activity per unit mass of tumour, cure probability is greatest for tumours whose diameter is close to an optimum value which depends on the path length of the emitted beta-particle. Smaller tumours are less curable because of inefficient absorption of radiation energy, and larger tumours are less curable because of greater clonogenic cell number. The lesser curability of very small tumours is a feature of targeted radiotherapy using long-range beta-emitters which does not occur with external beam irradiation. The predicted inefficiency of sterilisation of microscopic tumours poses a problem for targeted radiotherapy which is analogous to "geographic miss" in conventional radiotherapy. The implication is that small micro-metastases could escape sterilisation by radionuclides administered at activity levels sufficient to eradicate larger tumours. It is suggested that single agent targeted radiotherapy should not be used for treatment of disseminated malignancy when multiple tumours of differing size, including micrometastases, may be present. The analysis implies that an advantage might result from the use of a panel of several radionuclides (including short-range emitters) or from combining targeted radiotherapy using long-range beta-emitters with external beam irradiation or some other modality to which microscopic tumours are preferentially vulnerable.
采用数学模型研究了用靶向¹³¹I或⁹⁰Y治疗球形肿瘤时，治愈率与肿瘤大小和细胞数量之间的关系，假设整个肿瘤内放射性核素摄取均匀。分析表明，对于任何给定的单位质量肿瘤累积活度，直径接近取决于发射β粒子路径长度的最佳值的肿瘤，治愈概率最大。较小的肿瘤治愈率较低是因为辐射能量吸收效率低，而较大的肿瘤治愈率较低是因为克隆原性细胞数量较多。极小肿瘤治愈率较低是使用长程β发射体进行靶向放射治疗的一个特点，而外照射不会出现这种情况。预测对微小肿瘤进行杀菌的效率低下给靶向放射治疗带来了一个问题，这类似于传统放射治疗中的“摆位误差”。这意味着，对于足以根除较大肿瘤的活度水平下给予的放射性核素，小的微转移灶可能无法被清除。建议当可能存在大小不同的多个肿瘤（包括微转移灶）时，不应将单药靶向放射治疗用于播散性恶性肿瘤的治疗。分析表明，使用一组几种放射性核素（包括短程发射体），或者将使用长程β发射体的靶向放射治疗与外照射或微小肿瘤优先易受影响的其他某种方式相结合，可能会带来优势。
