Joint Department of Physics, Institute of Cancer Research, Sutton, London, SM2 5NG, UK,
Eur J Nucl Med Mol Imaging. 2013 Oct;40(10):1532-41. doi: 10.1007/s00259-013-2451-6. Epub 2013 Jun 6.
(32)P-chromic phosphate colloid treatments of astrocytoma and craniopharyngioma cystic brain tumours in paediatric patients are conventionally based on a sphere model under the assumption of uniform uptake. The aims of this study were to determine the distribution of the absorbed dose delivered by (32)P on a patient-specific basis and to evaluate the accuracy with which this can be predicted from a pretherapy administration of (99m)Tc-Sn colloid.
Three patients were treated with (32)P-chromic phosphate colloid following (99m)Tc-Sn colloid administrations. Convolution dosimetry was performed using pretherapy and posttherapy sequential SPECT imaging, and verified with EGSnrc Monte Carlo radiation transport simulations. Mean absorbed doses to the cyst wall and dose-volume histograms were also calculated and compared with those obtained by the sphere model approach.
Highly nonuniform uptake distributions of both the (99m)Tc and (32)P colloids were observed and characterized by dose-volume histograms to the cyst wall. Mean absorbed doses delivered to the cyst wall, obtained with the convolution method, were on average 21 % (SD 18 %) and 50 % (SD 30 %) lower than those predicted by the (99m)Tc distribution and the uniform assumption of the sphere model, respectively.
Absorbed doses delivered to the cyst wall by (32)P are more accurately predicted from image-based patient-specific convolution dosimetry than from simple sphere models. These results indicate the necessity to perform personalized treatment planning and verification for intracavitary irradiation of cystic brain tumours treated with radiocolloids. Patient-specific dosimetry can be used to guide the frequency and levels of repeated administrations and would facilitate data collection and comparison to support the multicentre trials necessary to progress this therapy.
（32）P-放射性胶体磷酸铬治疗小儿脑星形细胞瘤和颅咽管瘤囊性脑肿瘤，传统上基于均匀摄取假设的球体模型。本研究旨在确定（32）P 对患者的吸收剂量分布，并评估从预治疗（99m）Tc-Sn 胶体给药预测其准确性。
3 名患者在（99m）Tc-Sn 胶体给药后接受（32）P-放射性胶体磷酸铬治疗。使用预治疗和治疗后 SPECT 成像进行卷积剂量测定，并通过 EGSnrc 蒙特卡罗辐射传输模拟进行验证。还计算了囊壁的平均吸收剂量和剂量体积直方图，并与球体模型方法获得的结果进行了比较。
观察到（99m）Tc 和（32）P 胶体的摄取分布极不均匀，并通过囊壁的剂量体积直方图进行了描述。使用卷积方法获得的囊壁平均吸收剂量，平均比（99m）Tc 分布和球体模型的均匀假设分别低 21%（SD 18%）和 50%（SD 30%）。
通过基于图像的患者特异性卷积剂量测定，比简单的球体模型更准确地预测（32）P 对囊壁的吸收剂量。这些结果表明，需要对放射性胶体治疗的囊性脑肿瘤进行腔内照射进行个体化治疗计划和验证。患者特异性剂量测定可用于指导重复给药的频率和水平，并有助于数据收集和比较，以支持推进该治疗的多中心试验。
