Prescribed Activity of 131I Therapy in Differentiated Thyroid Cancer

Know thy tumour: Biomarkers to improve treatment of molecular radionuclide therapy

Molecular radionuclide therapy (MRT) is an effective treatment for both localised and disseminated tumours. Biomarkers can be used to identify potential subtypes of tumours that are known to respond better to standard MRT protocols. These enrolment-based biomarkers can further be used to develop dose-response relationships using image-based dosimetry within these defined subtypes. However, the biological identity of the cancers treated with MRT are commonly not well-defined, particularly for neuroendocrine neoplasms. The biological heterogeneity of such cancers has hindered the establishment of dose-responses and minimum tumour dose thresholds. Biomarkers could also be used to determine normal tissue MRT dose limits and permit greater injected doses of MRT in patients. An alternative approach is to understand the repair capacity limits of tumours using radiobiology-based biomarkers within and outside patient cohorts currently treated with MRT. It is hoped that by knowing more about tumours and how they respond to MRT, biomarkers can provide needed dimensionality to image-based biodosimetry to improve MRT with optimized protocols and personalised therapies.

Tailoring morphologies of mesoporous polydopamine nanoparticles to deliver high-loading radioiodine for anaplastic thyroid carcinoma imaging and therapy

Anaplastic thyroid carcinoma (ATC), as one of the most aggressive human malignancies, cannot be cured by ¹³¹iodine (¹³¹I) internal radiotherapy (RT) because the tumor cells cannot effectively take up ¹³¹I and are resistant to radiotherapy. In this study, a facile and simple method was proposed to synthesize mesoporous polydopamine nanoparticles (MPDA) and tailor their morphologies by component-adjusting Pluronic micelle-guided polymerization. Then, MPDA were used not only as nanocarriers to radiolabel ¹³¹I, but also as photothermal conversion agents for photothermal therapy (PTT) to promote RT. The iodine-labeling capacity and photothermal conversion efficiency of MPDA can be enhanced by optimizing their morphologies. It was found that MPDA NPs with a cerebroid pore channel structure (CPDA) showed the highest iodine-carrying capacity and a higher photothermal conversion efficiency as a result of their maximum specific surface area and unique morphology. In subsequent experiments in vitro and in vivo, our ATC animal models showed impressive therapeutic responses to CPDA-¹³¹I NPs because of the synergistic effect of PTT and RT. Additionally, CPDA-¹²⁵I NPs can be utilized to obtain high-quality SPETC/CT images of tumors, which can guide clinical therapy for ATC. Considering their great biosafety, these radioiodine-labeled CPDA NPs may serve as a promising tool in combined therapy and diagnosis in ATC.

Pre-Therapeutic Measurements of Iodine Avidity in Papillary and Poorly Differentiated Thyroid Cancer Reveal Associations with Thyroglobulin Expression, Histological Variants and Ki-67 Index

Papillary thyroid cancer (PTC) and poorly differentiated thyroid cancer (PDTC) are treated with radioiodine to reduce recurrence and to treat the spread of disease. Adequate iodine accumulation in cancer tissue, iodine avidity, is important for treatment effect. This study investigated which clinical and histological tumour characteristics correlate with avidity. To quantify avidity in cancer tissue, tracer amounts of iodine-131 were given to 45 patients with cytologically confirmed thyroid cancer. At pathology grossing, representative samples of tumour and lymph nodes were taken and subjected to radioactivity quantification ex vivo to determine avidity. Afterwards, samples underwent extended pathology work-up and analysis. We found that tumoural Tg expression and Ki-67 index were correlated with avidity, whereas tumour size and pT stage were not. The histological variant of thyroid cancer was also correlated with iodine avidity. Variants associated with worse clinical prognoses displayed lower avidity than variants with better prognoses. This work provides new information on which tumours have low iodine avidity. Lower avidity in aggressive histological PTC variants may explain their overall poorer prognoses. Our findings also suggest that radioiodine dosage could be adapted to Tg expression, Ki-67 index or histological variant instead of pT stage, potentially improving the efficacy of radioiodine therapy.

Radiotheragnostics Paradigm for Radioactive Iodine (Iodide) Management of Differentiated Thyroid Cancer

This review of radioactive iodide treatment (RAIT) extends from historical origins to its modern utilization in differentiated thyroid cancer (DTC). The principles embedded in the radiotheragnostics (RTGs) paradigm are detailed. The diverse approaches in current practice are addressed, and this broad variability represents a major weakness that erodes our specialty's trust-based relationship with patients and referring physicians. The currently developing inter-specialty collaboration should be hailed as a positive change. It promises to clarify the target-based terminology for RAIT. It defines RAIT of post total thyroidectomy (PTT), presumably benign thyroid as 'remnant ablation' (RA). 'Adjuvant treatment' (AT) referrers to RAIT of suspected microscopic DTC that is inherently occult on diagnostic imaging. RAIT directed at DTC lesion(s) overtly seen on diagnostic imaging is termed 'treatment of known disease' (TKD). It was recently recognized that a 'recurrent' DTC is actually occult residual DTC in the majority of cases. Thyroglobulin with remnant uptake concord (TRUC) method (aka Tulchinsky method) was developed to validate that a benign remnant in the post-thyroidectomy neck bed, as quantified by the RAI uptake, is concordant with a measured thyroglobulin (Tg) level at the time of the initial post-thyroidectomy evaluation. It allows recognition of occult residual DTC contribution to post-thyroidectomy Tg. Case examples demonstrate the application of the TRUC method for a logical selection of a specific RAIT category, using imaging-guided identification and management of RAI-avid versus RAI-nonavid residual DTC, i.e. the radiotheragnostics paradigm.

Advanced differentiated thyroid cancer: when to stop radioiodine?

Radioiodine (RAI) is a pivotal important treatment for patients with metastatic differentiated thyroid cancer (DTC). In order to determine when a patient will no longer respond to RAI, multiple classifications have been described to categorize a patient as RAI refractory (RAI-R). Current classifications, although very useful, are problematic and controversial and cannot be merely applied in the context of individualized patient management. In addition, classifications on how to define RAI-R disease are continuously evolving as more studies are published and managing physicians better understand the limitations and confounding factors of present classifications. Accordingly, each patient should be individually managed with a good understanding of the limitations of the various classifications, assessing the many other factors that affect the patient's specific clinical situation and delivering appropriate individualized patient care.

Bone-Marrow Suppression in Elderly Patients Following Empiric Radioiodine Therapy: Real-Life Data

Background: Elderly patients with differentiated thyroid cancer (DTC) tend to have more advanced disease at presentation, for which high activities of radioiodine (RAI) are often recommended. However, the 2015 American Thyroid Association guidelines recommend that empirically administered activities of RAI >150 mCi should be avoided in patients >70 years of age, based on calculated bone-marrow exposure according to two dosimetry-based studies. This study aimed to evaluate the effect of RAI treatment on bone-marrow function in elderly DTC patients. Methods: DTC patients ≥70 years of age who received RAI treatment and on whom a complete blood count was performed before and after treatment were included. Blood counts within one year before RAI and one year following treatment were compared in order to assess for marrow suppression. The impact of demographic, clinical, and laboratory variables on complete blood count were assessed. Results: One hundred fifty-three treatments in 122 patients met inclusion criteria, with a mean patient age of 76 ± 4.3 years, and 75% were women. High-risk features at presentation included T4 disease in 17%, lymph node metastases in 34%, and distant metastases in 14%. Mean RAI activity was 136.8 ± 48 mCi (82% ≥ 100 mCi, 66% ≥ 150 mCi). Of 153 RAI treatments analyzed, 114 (74%) were first treatments, 28 (18%) second treatments, seven (5%) third treatments, and four (3%) fourth treatments. At 0-3 months after RAI treatment, there was a statistically significant decrease in platelets (238 ± 66 vs. 216 ± 69 × 10⁹/L, 10% decrease; p < 0.001), white blood cells (WBC; 6.9 ± 2 vs. 6.1 ± 1.9 × 10⁹/L, 13% decrease; p < 0.001), and hemoglobin (Hb) in women (12.8 ± 1.1 vs. 12.4 ± 1.1 g/dL, 3% decrease; p = 0.01). Mean platelets, WBC, Hb in women, and lymphocytes remained decreased (but within the reference range) one year after treatment. Subgroup analysis demonstrated platelet suppression only with activities ≥100 mCi, and WBC and Hb suppression only with activities ≥150 mCi, with mean values within the reference ranges. There were no clinically significant cytopenia events during follow-up. Conclusions: Empiric RAI treatment in elderly patients causes mild bone-marrow suppression, with little clinical significance. Activities of 150-200 mCi can be safely used when indicated.

An introduction to the clinical practice of theranostics in oncology

"Those who cannot remember the past are condemned to repeat it." George Santayana 1905 "If men could learn from history, what lessons it might teach us! But passion and party blind our eyes, and the light which experience gives is a lantern on the stern, which shines only on the waves behind us!" Samuel Taylor Coleridge 1835 The medical speciality of theranostic nuclear oncology has taken three-quarters of a century to move the stern light cast retrospectively by single-centre clinical reports, to the forepeak in the bow of our theranostic craft, where prospective randomised controlled multicentre clinical trials now illuminate the way forward. This recent reorientation of nuclear medicine clinical research practice to align with that of standard medical and radiation oncology protocols, reflects the paradigm shift toward individualised molecular oncology and precision medicine. Theranostics is the epitome of personalised medicine. The specific tumour biomarker is quantitatively imaged on positron emission tomography (PET)/CT or single photon emission computed tomography (SPECT)/CT. If it is clearly demonstrated that a tumoricidal radiation absorbed dose can be delivered, the theranostic beta or alpha-emitting radionuclide pair, coupled to the same targeted molecule, is then administered, to control advanced metastatic cancer in that individual patient. This prior selection of patients who may benefit from theranostic treatment is in direct contrast to the evolving oncological indirect treatments using immune-check point inhibitors, where there is an urgent need to define biomarkers which can reliably predict response, and thus avoid the high cost and toxicity of these agents in patients who are unlikely to benefit. The immune and molecular treatment approaches of oncology are a recent phenomenon and the efficacy and safety of immune-check point blockade and chimeric antigen receptor T-cell therapies are currently under evaluation in multicentre randomised controlled trials. Such objective evaluation is compromised by the inadequacy of conventional response evaluation criteria in solid tumour (RECIST) CT/MR anatomical/functional imaging to define tumour response, in both immune-oncology and theranostic nuclear oncology. This introduction to the clinical practice of theranostics explores ways in which nuclear physicians can learn from the lessons of history, and join with their medical, surgical and radiation oncology colleagues to establish a symbiotic collaboration to realise the potential of personalised molecular medicine to control advanced cancer and actually enhance quality of life whilst prolonging survival.

Radioiodine Refractory Differentiated Thyroid Cancer: Time to Update the Classifications

BACKGROUND

The management of aggressive and progressing metastatic differentiated thyroid cancer (DTC) is very difficult, and the determination as to when such patients are refractory to ¹³¹I therapy (e.g., radioiodine refractory) is problematic and controversial.

OBJECTIVE

The objective of this review is to discuss (i) the present major classifications of radioiodine refractory disease in DTC, (ii) factors that should be considered before designating a patient's DTC as radioiodine refractory, (iii) potential approaches and caveats to help manage and minimize a patient's exclusion from an ¹³¹I therapy that may have potential benefit in patients with aggressive and progressing metastatic DTC, (iv) next steps for revision of the classifications of radioiodine refractory DTC, and (v) areas for future research.

SUMMARY

To date, the classifications of radioiodine refractory DTC, although very useful, are not sacrosanct especially in the context of individualized patient management, and merely because a patient meets one or more of the various classifications, one should not consider by definition, fiat, or de facto that that a patient's DTC is radioiodine refractory. Rather, each patient should be individually managed with a good understanding of the limitations of the various classifications and potential approaches to help manage that patient. With awareness of the suggestions and caveats discussed herein and with assessment of the many other factors that affect the patient's specific clinical situation, the managing physician can deliver appropriate individualized patient care. A multi-organizational committee should be established as a standing committee to supervise and assist in the update of the classifications of radioiodine refractory DTC, including discussions of their limitations.

CONCLUSION

Classifications to help determine radioiodine refractory disease will continue to evolve as (i) more studies are published, (ii) managing physicians better understand the limitations and confounding factors of present classifications, and (iii) new agents either increase or reestablish ¹³¹I uptake.