Molecular Radiotherapy

Molecular radiotherapy (MRT) may be defined as the delivery of radiation to malignant tissue via the interaction of a radiopharmaceutical with molecular sites and receptors. This is a rapidly evolving discipline, particularly with regard to quantification of uptake in normal and malignant tissue. Internal dosimetry is essential to the future development of MRT.

Of interest are the radiopharmaceuticals ¹³¹I-mIBG and ¹⁷⁷Lu-DOTATATE.

Metaiodobenzylguanidine (mIBG) is highly sensitive and specific for neuroblastoma (a form of childhood cancer), concentrating in >90% of tumours. It may be labelled to ¹²³I as a routine tool for neuroblastoma gamma camera and SPECT-CT imaging. Patients eligible for treatment may be treated with ¹³¹I-mIBG, often in combination with a radiosensitiser such as Topotecan. Therapies are performed on an in-patient basis in one of the radionuclide therapy rooms within UCLH. Response rates are monitored using imaging techniques within INM.

Further work with mIBG involves using ¹²⁴I-mIBG as a novel PET radiotracer, with the ability to offer improved spatial resolution and quantification. We aim to compare ¹²⁴I-mIBG PET/CT to ¹²³I-mIBG scintigraphy in their ability to detect lesions in metastatic neuroblastoma.

Another well-established technique is ⁶⁸Ga-DOTATATE PETCT imaging. This is a useful diagnostic tool to determine disease extent and evaluate patients for targeted ¹⁷⁷Lu-DOTATATE therapy. A phase 2 trial is currently underway to evaluate ¹⁷⁷Lu-DOTATATE therapy in the treatment of refractory or relapsed neuroblastoma. Key components of the trial are evaluating ⁶⁸Ga-DOTATATE uptake correlation with response and a dosimetry study to investigate tumour and normal organ dose.