Breen S L, Battista J J
Physics Department, London Regional Cancer Center, Ontario Cancer Treatment and Research Foundation, Ontario, Canada.
Phys Med Biol. 1995 Dec;40(12):2065-77. doi: 10.1088/0031-9155/40/12/005.
Accurate measurements of dose in bone are required in order to improve the dosimetry of systemic radiotherapy for osseous metastases. Bone is an integrating dosimeter which records the radiation history of the skeleton. During irradiation, electrons become trapped in the crystalline component of bone mineral (hydroxyapatite). The traps are very stable; at room temperature, emptying of the traps occurs with a half-life of many years. The population of trapped unpaired electrons is proportional to the radiation dose administered to the bone and can be measured in excised bone samples using electron paramagnetic resonance (EPR). EPR spectra of synthetic hydroxyapatite, irradiated with Co-60, were obtained at room temperature and at 77 K. At room temperature, the radiation-induced signal, with a g-value of 2.001 +/- 0.001, increased linearly with absorbed dose above a lower threshold of 3 Gy, up to doses of 200 Gy. In contrast with pure hydroxyapatite, EPR spectra of excised human bone showed a broad "native' signal, due to the organic component of bone, which masks the dosimetrically important signal. This native signal is highly variable from sample to sample and precludes the use of EPR as an absolute dosimetry technique. However, after subtraction of the background signal, irradiated human bone showed a linear response with a lower limit of measurement similar to that of synthetic hydroxyapatite. Bone is an in vivo linear dosimeter which can be exploited to develop accurate estimates of the radiation dose delivered during systemic radiotherapy and teletherapy. However, improved sensitivity of the EPR dosimetry technique is necessary before it can be applied reliably in clinical situations.
为了改善骨转移系统性放疗的剂量测定，需要对骨中的剂量进行准确测量。骨是一种积分剂量计，可记录骨骼的辐射历史。在辐照过程中，电子被困在骨矿物质（羟基磷灰石）的晶体成分中。这些陷阱非常稳定；在室温下，陷阱排空的半衰期为许多年。被困的未成对电子数量与给予骨的辐射剂量成正比，可使用电子顺磁共振（EPR）在切除的骨样本中进行测量。在室温及77K下获得了用Co-60辐照的合成羟基磷灰石的EPR谱。在室温下，g值为2.001±0.001的辐射诱导信号，在3Gy的较低阈值以上随吸收剂量线性增加，直至200Gy的剂量。与纯羟基磷灰石不同，切除的人骨的EPR谱显示出由于骨的有机成分而产生的宽“天然”信号，该信号掩盖了剂量测定中重要的信号。这种天然信号在不同样本之间变化很大，排除了将EPR用作绝对剂量测定技术的可能性。然而，在减去背景信号后，辐照的人骨显示出线性响应，测量下限与合成羟基磷灰石相似。骨是一种体内线性剂量计，可用于准确估计系统性放疗和远距离治疗期间传递的辐射剂量。然而，在EPR剂量测定技术能够可靠地应用于临床情况之前，需要提高其灵敏度。
