Outpatient therapeutic nuclear oncology

Harmonization of practice of release of patients after radiopharmaceutical therapy

The implementation of novel therapeutic radiopharmaceuticals requires developing, updating, and harmonizing requirements for radiation safety in radiopharmaceutical therapy (RPT). Public exposure from patients with administered radiopharmaceuticals and biological radioactive waste management have been identified as the main problems in RPT. The aim of our study was to compare different approaches to the development of patient release criteria after RPT with different radiopharmaceuticals, considering radiation exposure of members of the public in transport, biological elimination of radionuclides from a patient's body, and the generation of biological waste. The study was performed for the following radiopharmaceuticals:177Lu-PSMA-617,177Lu-DOTATATE, Na131I,131I-mIBG, and153Sm-oxabifor. Two base approaches to patient release criteria were considered. The first approach is based on the radioactive decay of radionuclides and is divided into two groups: considering one radiopharmaceutical administration and considering several radiopharmaceutical administrations per course. The second approach is based on the radioactive decay of radionuclides and biological elimination of radiopharmaceuticals from the patient's body (effective half-life) and is divided into groups based on 1 and 5 mSv dose constraints per course. The ffective dose rates from patients and sewage tanks to passengers and staff on public transport were estimated for various scenarios of patients traveling after RPT. The results demonstrated that the radiation safety of members of the public in transport should be considered when establishing the release criteria of patients after RPT. Based on the results, it is recommended to follow the approach based on the radioactive decay of radionuclides and dose constraints to members of the public in contact with patients of 1 mSv per radiopharmaceutical administration, and keep patients in the nuclear medicine department after radiopharmaceutical administration for at least 4-6 h. The patient release criteria defined according to this approach comply with patient release criteria used in different countries, and allow the radiation safety of the public to be maintained.

Radiation levels outside a patient undergoing177Lu-PSMA radioligand therapy

Understanding the spatial distribution of radiation levels outside of a patient undergoing177Lu radioligand therapy is not only helpful for conducting correct tests for patient release, but also useful for estimation of its potential exposure to healthcare workers, caregivers, family members, and the general public. In this study, by mimicking the177Lu-labeled prostate-specific membrane antigen radioligand therapy for prostate cancers in an adult male, the spatial distribution of radiation levels outside of the phantom was simulated based on the Monte Carlo software of Particle and Heavy Ion Transport System, and verified by a series of measurements. Moreover, the normalized dose rates were further formulized on the three transverse planes representing the heights of pelvis, abdomen and chest. The results showed that the distributions of radiation levels were quite complex. Multi-directional and multi-height measurements are needed to ensure the external dose rate to meet the release criteria. In general, the radiation level was higher at the horizontal plane where the source was located, and the levels in front and behind of the body were higher than those of the left and right sides at the same height. The ratio of simulated dose rates to measured ones ranged from 0.82 to 1.19 within 1 m away from the body surface in all directions. Based on the established functions, the relative root mean square deviation between the calculated and simulated values were 0.21, 0.25 and 0.23 within a radius of 1 m on the pelvis, abdomen and chest transverse planes, respectively. It is expected that the results of this study would be helpful for guiding the test of extracorporeal radiation to determine the patient's release, and of benefit to estimate the radiation exposure to others.

Simple model for estimation of absorbed dose by organs and tumors after PRRT from a single SPECT/CT study

Background

Following each cycle of peptide receptor radionuclide therapy (PRRT), absorbed doses by tumors and normal organs are typically calculated from three quantitative single-photon emission computed tomography (SPECT)/computed tomography (CT) studies acquired at t₁ = 24 h, t₂ = 96 h, t₃ = 168 h after the first cycle of treatment and from a single study at t₁ after the subsequent cycles. In the present study, we have assessed the feasibility of a single SPECT/CT study after each PRRT cycle using a trained multiple linear regression (MLR) model for absorbed dose calculation and have evaluated its impact on patient management. Quantitative [¹⁷⁷Lu]-DOTA-TATE SPECT/CT data after PRRT of seventy-two consecutive metastatic neuroendocrine tumors patients were retrospectively evaluated. A set of 40 consecutive studies was used to train the MLR model. The two independent variables of the model included the time of imaging after administration of the treatment and the radiopharmaceutical activity concentration in a given  organ/tumor. The dependent variable was the dose absorbed by the organ/tumor obtained with the standard protocol. For bone marrow dosimetry, the independent variables included the time of imaging, and the blood and remainder of the body activity concentration. The model was evaluated in 32 consecutive patients. Absorbed doses were assessed for kidneys, bone marrow, liver, spleen and tumor sites.

Results

There was no difference in management decisions, whether PRRT can be safely continued or not because unsafe absorbed dose to risk organs between the standard and the MLR model-based protocol using a single SPECT/CT study performed at t₃ = 168 h after the first cycle and at t₁ = 24 h after the subsequent cycles. Cumulative absorbed doses were obtained with mean relative differences of − 0.5% ± 5.4%, 1.6% ± 15.1%, − 6.2% ± 7.3%, − 5.5% ± 5.8% and 2.9% ± 12.7% for kidneys, bone marrow, liver, spleen and tumors, respectively (Pearson’s r correlation coefficient 0.99, 0.91, 0.99, 0.99 and 0.97, respectively).

Conclusion

Dosimetry calculations using a MLR model with a single SPECT/CT study are in good agreement with the standard protocol, while avoiding the use of dosimetry software and enabling improved patient comfort and reduced scanner and staff time.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00409-z.

Integrating Early Rapid Post-Peptide Receptor Radionuclide Therapy Quality Assurance Scan into the Outpatient Setting

Objective

To understand value of early rapid, quality-assurance (QA), post-therapy whole-body scan (Tx-WBS) in patients receiving peptide receptor radionuclide therapy (PRRT) in outpatient setting.

Methods

Sixteen patients with metastatic neuroendocrine tumors received PRRT and underwent Tx-WBS after each cycle. Early imaging (3 hour post-injection) was favored. Planar-images obtained on dual-headed gamma camera (speed 30 cm/min) were visually assessed and qualitatively compared with pre-therapy diagnostic scans. Retention% and lesion/spleen (L/S) ratios were calculated.

Results

Fifty three Tx-WBS were analyzed. No cutaneous contamination, extravasation or unexpected tracer distribution was observed. 46/53 (87%) Tx-WBS in 14/16 (88%) patients demonstrated uptake in metastatic lesions. No significant correlation was seen between L/S ratios and response on follow-up imaging. Qualitative assessment of follow-up images during four-cycles of PRRT provided preliminary estimate of disease course in 11/16 patients; with unexpected findings in 2.

Conclusion

In daily practice, especially in outpatient setting, an early QA post-PRRT scan proved effective for validating successful treatment and allowing preliminary disease monitoring, at no additional cost.

Predictive power of the post-treatment scans after the initial or first two courses of [177Lu]-DOTA-TATE

BACKGROUND

The aim of this study was to evaluate the predictive power of the absorbed dose to kidneys after the first course of treatment with [¹⁷⁷Lu]-DOTA-TATE for neuroendocrine tumors (NETs) on the cumulative kidney absorbed dose after 3 or 4 cycles of treatment. Post-treatment scans (PTS) are acquired after each cycle of peptide receptor radionuclide therapy (PRRT) with [¹⁷⁷Lu]-DOTA-TATE for personalized radiation dosimetry in order to ensure a cumulative absorbed dose to kidneys under a safety threshold of 25 Gy. One hundred eighty-seven patients who completed treatment with [¹⁷⁷Lu]-DOTA-TATE and underwent PTS for dosimetry calculation were included in this retrospective study. The correlation between the cumulative absorbed dose to kidneys after the completion of treatment and the absorbed dose after the first cycle(s) was studied. Multilinear regression analysis was done to predict the cumulative absorbed dose to the kidneys of the subsequent cycles, and an algorithm for the follow up of kidney absorbed dose is proposed.

RESULTS

Patients whose absorbed dose to kidneys after the first cycle of treatment is below 5.6 Gy can receive four cycles of treatment with a cumulative dose less than 25 Gy (p < 0.1). For the other patients, the cumulative absorbed dose after 3 or 4 cycles of treatment can be predicted after the second cycle of treatment to allow for an early decision regarding the number of cycles that may be given.

CONCLUSIONS

The follow up of kidney absorbed dose after PRRT can be simplified with the algorithm presented in this study, reducing by one-third the number of post-treatment scans and reducing hospitalization time for more than half of the treatment cycles.

Blood clearance and occupational exposure for 177Lu-DOTATATE compared to 177Lu-PSMA radionuclide therapy

The main target of this work is to examine blood clearance and external exposure for ¹⁷⁷Lu-DOTATATE compared with new emerging ¹⁷⁷Lu-PSMA therapy. Blood clearance and radiation exposure of 31 patients treated with 5.5 ± 1.1 GBq ¹⁷⁷Lu-DOTATATE were compared to those of 23 patients treated with 7.4 GBq ¹⁷⁷Lu-PSMA. Dose rates were measured at several distances and time points up to 120 h after treatment. Blood samples were collected conjunctively after infusion. Caregiver's cumulative dose was measured by means of an OSL (optically stimulated luminescence) dosimeter for 4-5 days and medical staff's dose was also estimated using electronic personal dosimeters. Finger dose was determined via ring TLD (Thermoluminescence Dosimeter) for radiopharmacists and nurses. Dose rates due to ¹⁷⁷Lu-DOTATATE at a distance of 1 m, 4 h and 6 h after infusion, were 3.0 ± 2.8 and 2 ± 1.9 µSv/(h GBq), respectively, while those due to ¹⁷⁷Lu-PSMA were 3.1 ± 0.8 and 2.2 ± 0.9 µSv/(h GBq). Total effective dose of 17 caregivers was 100-200 µSv for ¹⁷⁷Lu-DOTATATE therapy. Mean effective doses to nurses and radiopharmacists were 5 and 4 µSv per patient, respectively, while those for physicists and physicians were 2 µSv per patient. For ¹⁷⁷Lu-DOTATATE, effective half-life in blood and early elimination phase were 0.31 ± 0.13 and 4.5 ± 1 h, while they were found as 0.4 ± 0.1 and 5 ± 1 h, respectively, for ¹⁷⁷Lu-PSMA. The first micturition time following ¹⁷⁷Lu-DOTATATE infusion was noted after 36 ± 14 min, while the second and third voiding times were after 74 ± 9 and 128 ± 41 min, respectively. It is concluded that blood clearance and radiation exposure for ¹⁷⁷Lu-DOTATATE are very similar to those for ¹⁷⁷Lu-PSMA, and both treatment modalities are reasonably reliable for outpatient treatment, since the mean dose rate [2.1 µSv/(h GBq)] decreased below the dose rate that allows release of the patient from the hospital (20 µSv/h) after 6 h at 1 m distance.

Synthesis, Characterization, and In Vitro Evaluation of New (99m)Tc/Re(V)-Cyclized Octreotide Analogues: An Experimental and Computational Approach

Radiolabeled proteolytic degradation-resistant somatostatin analogues have been of long-standing interest as cancer imaging and radiotherapy agents for targeting somatostatin receptor-positive tumors. Our interest in developing (186)Re- and (188)Re-based therapeutic radiopharmaceuticals led to investigation of a new Re(V)-cyclized octreotide analogue, Re(V)-cyclized, thiolated-DPhe(1)-Cys(2)-Tyr(3)-DTrp(4)-Lys(5)-Thr(6)-Cys(7)-Thr(OH)(8) (Re-SDPhe-TATE) using both experimental and quantum chemical methods. The metal is directly coordinated to SDPhe-TATE through cyclization of the peptide around the [ReO](3+) core. Upon complexation, four isomers were observed; the isolated/semi-isolated isomers exhibited different somatostatin receptor (sstr) binding affinities, 0.13 to 1.5 μM, in rat pancreatic tumor cells. Two-dimensional NMR experiments and electronic structure calculations were employed to elucidate the structural differences among the different isomers. According to NMR studies, the metal is coordinated to three thiolates and the backbone amide of Cys(2) in isomers 1 and 4, whereas the metal is coordinated to three thiolates and the backbone amide of Tyr(3) in isomer 2. Quantum chemical methods clarified the stereochemistry of Re-SDPhe-TATE and the possible peptide arrangements around the [ReO](3+) core. The re-cyclization reaction was translated to the (99m)Tc radiotracer level with four isomers observed on complexation with comparable HPLC retention times as the Re-SDPhe-TATE isomers. About 85% total (99m)Tc labeling yield was achieved by ligand exchange from (99m)Tc-glucoheptonate at 60 °C for an hour. About 100% and 51% of (99m)Tc(V)-cyclized SDPhe-TATE remained intact in phosphate buffered saline and 1 mM cysteine solution under physiological conditions at 6 h, respectively.

Quantifying public radiation exposure related to lutetium-177 octreotate therapy for the development of a safe outpatient treatment protocol

OBJECTIVES

Radionuclide therapies, including treatment of neuroendocrine tumors with lutetium-177 (Lu-177) octreotate, often involve hospital admission to minimize radiation exposure to the public. Overnight admission due to Lu-177 octreotate therapy incurs additional cost for the hospital and is an inconvenience for the patient. This study endeavors to characterize the potential radiation risk to caregivers and the public should Lu-177 octreotate therapies be performed on an outpatient basis.

MATERIALS AND METHODS

Dose rate measurements of radiation emanating from 10 patients were taken 30 min, 4, and 20 h after initiation of Lu-177 octreotate therapy. Instadose radiation dose measurement monitors were also placed around the patients' rooms to assess the potential cumulative radiation exposure during the initial 30 min-4 h after treatment (simulating the hospital-based component of the outpatient model) as well as 4-20 h after treatment (simulating the discharged outpatient portion).

RESULTS

The mean recorded dose rate at 30 min, 4, and 20 h after therapy was 20.4, 14.0, and 6.6 μSv/h, respectively. The majority of the cumulative dose readings were below the minimum recordable threshold of 0.03 mSv, with a maximum dose recorded of 0.18 mSv.

CONCLUSION

Given the low dose rate and cumulative levels of radiation measured, the results support that an outpatient Lu-177 octreotate treatment protocol would not jeopardize public safety. Nevertheless, the concept of ALARA still requires that detailed radiation safety protocols be developed for Lu-177 octreotate outpatients to minimize radiation exposure to family members, caregivers, and the general public.

The study of external dose rate and retained body activity of patients receiving 131I therapy for differentiated thyroid carcinoma

Radiation safety is an integral part of targeted radionuclide therapy. The aim of this work was to study the external dose rate and retained body activity as functions of time in differentiated thyroid carcinoma patients receiving ¹³¹I therapy. Seventy patients were stratified into two groups: the ablation group (A) and the follow-up group (FU). The patients’ external dose rate was measured, and simultaneously, their retained body radiation activity was monitored at various time points. The equations of the external dose rate and the retained body activity, described as a function of hours post administration, were fitted. Additionally, the release time for patients was calculated. The reduction in activity in the group receiving a second or subsequent treatment was more rapid than the group receiving only the initial treatment. Most important, an expeditious method was established to indirectly evaluate the retained body activity of patients by measuring the external dose rate with a portable radiation survey meter. By this method, the calculated external dose rate limits are 19.2, 8.85, 5.08 and 2.32 μSv·h⁻¹ at 1, 1.5, 2 and 3 m, respectively, according to a patient’s released threshold level of retained body activity <400 MBq. This study is beneficial for radiation safety decision-making.

Hematological toxicity of combined 177Lu-octreotate radiopeptide chemotherapy of gastroenteropancreatic neuroendocrine tumors in long-term follow-up

BACKGROUND

The combination of radiopeptide therapy [peptide receptor radionuclide therapy (PRRT)] with radiosensitizing chemotherapy of gastroenteropancreatic neuroendocrine tumors (GEP NETs) may improve efficacy, but has the potential to increase myelotoxicity. In a prospective clinical study of GEP NET patients treated with (177)Lu-octreotate PRRT in combination with capecitabine and temozolomide, as a prelude to a planned Australasian Gastro-Intestinal Trials Group (AGITG) international randomized controlled trial, we characterized the incidence and degree of hematological toxicity.

MATERIALS AND METHODS

Well-differentiated progressive metastatic GEP NETs in 65 patients were treated with 4 cycles of 7.8 GBq (177)Lu-octreotate, 1,650 mg/m(2) capecitabine (n = 28) and 1,500 mg/m(2) capecitabine with 200 mg/m(2) temozolomide (n = 37), and monitored for hematological toxicity over a 5-year period.

RESULTS

Short-term, self-limited hematological toxicity grade 3/4 comprised anemia in 1 patient (3.5%) in the 28 patient-cohort of patients treated with (177)Lu-octreotate and capecitabine. One of these patients (3.5%) later developed significant anemia and one developed thrombocytopenia (3.5%) over a median follow-up of 60 months (SD 20). The incidence of short-term grade 3/4 reversible myelosuppression in 37 patients after (177)Lu-octreotate/capecitabine/temozolomide was zero. Long- term follow-up for a median of 36 months (SD 11) showed significant thrombocytopenia in 2.7% and neutropenia in 2.7% of the patients and anemia in 10.8% of the patients (n = 4). The 3-year median hemoglobin and platelet and neutrophil counts trended downwards, but remained within normal ranges. Two patients in this cohort developed myelodysplastic syndrome.

CONCLUSION

The modest reversible hematological toxicity of PRRT of GEP NETs is not significantly increased by the addition of radiosensitizing chemotherapy with capecitabine and temozolomide in combination with (177)Lu-octreotate, which has the potential to enhance the efficacy of radiopeptide therapy.

Phase I-II study of radiopeptide 177Lu-octreotate in combination with capecitabine and temozolomide in advanced low-grade neuroendocrine tumors

Abstract We conducted a phase I-II clinical trial to assess the safety and efficacy of combining lutetium-177 ((177)Lu)-octreotate with capecitabine and temozolomide in treating advanced low-grade neuroendocrine tumors (NETs). All 35 patients received fixed activities of 7.8 GBq (177)Lu-octreotate each 8 weeks, with 14 days of capecitabine 1500 mg/m(2) for 4 cycles. In phase I, successive cohorts of patients received escalating doses of temozolomide in groupings of 100, 150, and 200 mg/m(2) in the last 5 days of each capecitabine cycle. In phase II, patients were treated with 200 mg/m(2) temozolomide. Treatment was well tolerated in all dosage groups. No dose-limiting grade 2, 3, or 4 toxicities were seen in cohorts 1 (100 mg/m(2)) or 2 (150 mg/m(2)). Twenty-eight patients completed treatment at the 200 mg/m(2) temozolomide level. Adverse events were mild to moderate. The commonest toxicities were transient nausea grade 2 (18%), grade 3 (3%), thrombocytopenia grade 2 (24%), and neutropenia grade 3 (6%). There were no grade 4 events. Thirty-four patients were evaluable for tumor response. Overall, complete response (CR) was achieved in 15% (95% CI 3-27); partial response (PR), in 38% (95% CI 22-55); stable disease (SD), in 38% (95% CI 22-55); and 3 patients failed to respond to treatment. Median progression free survival (PFS) was 31 months (95% CI 21-33), and median overall survival (OS) has not been reached with 90% surviving at 24 months follow-up (range 21-30). Overall objective response rate (ORR) in patients with gastroenteropancreatic NETs showed CR 16% (95% CI 3-28), PR 41% (95% CI 24-58), SD 37% (95% CI 21-54), and PD 6% (95% CI 0-15). Response rates were higher in patients with gastropancreatic NETs than in those with bowel primaries (enteric-NETs); CR 18% versus 13%, PR 64% versus 13%, SD 12% versus 67%. (177)Lu-octreotate, in combination with capecitabine and temozolomide, is well tolerated in patients with advanced low-grade NETs, and shows substantial tumor control rates.

Thyroid remnant ablation using 1,110 MBq of I-131 after total thyroidectomy: regulatory considerations on release of patients after unsealed radioiodine therapy

OBJECTIVES

This study was undertaken to measure the radiation exposure level of caregivers following outpatient NaI (I-131) 1,110 MBq therapy for remnant thyroid ablation after total thyroidectomy in patients with differentiated thyroid cancer, and to evaluate the influence of activities of daily living on radiation exposure level, with the goal of proposing an optimum method of I-131 therapy.

METHODS

The study included 37 patients with differentiated thyroid cancer, who had undergone total thyroidectomy and received outpatient based remnant thyroid ablation using NaI (I-131) 1,110 MBq, who were satisfying the following requirements: (1) patients who have no evidence of distant metastases, (2) whose living environments were appropriate for outpatient I-131 (1,110 MBq) therapy, and (3) patients who gave written informed consent. The dose rate at a distance of 1 m from the body surface of the patient at the moment of release was measured using survey meters of the GM type or ionization chamber type. The dose level for the caregiver was measured with a personal dosimeter in all cases.

RESULTS

The dose rate at a distance of 1 m from the patient's body surface 1 h after I-131 administration was in the range of 29-115 μSv/h (mean 63.8 μSv/h). The 7-day cumulative effective dose of caregivers was 0.11 ± 0.08 mSv, on an average, in 34 dosimeters. In 31 of 34 dosimeters, cumulative effective dose of caregivers was below 0.2 mSv. Dose levels exceeding 0.2 mSv were recorded in 3 cases (0.21, 0.35 and 0.43 mSv in one case each). These results suggest that the exposure level of family members (caregiver and others) was minimal and is lower than the radiation levels affecting human environments.

CONCLUSION

Outpatient-based remnant thyroid ablation with I-131 (1,110 MBq) performed after total thyroidectomy in patients with differentiated thyroid cancer is safe if applied in accordance with the appropriate supervision and guidance by experts with certain qualifications.

A retrospective study on the transition of radiation dose rate and iodine distribution in patients with I-131-treated well-differentiated thyroid cancer to improve bed control shorten isolation periods

OBJECTIVE

To evaluate for how long patients should be isolated after I-131 treatment for thyroid cancer according to the guidelines issued by the Japanese Ministry of Welfare.

METHODS

We reviewed 92 therapies performed in 76 patients who were administered I-131 at our hospital from July 2007 to September 2009. Fifty-six patients were given 2220 or 2960 MBq I-131 at the first therapy, and 29 patients underwent 36 repeated therapies using 2960, 3700, 5550 or 7400 MBq I-131. We surveyed radioactivity for a 1 cm dose equivalent rate at 1 m intervals at 30 and 48 h after administration of I-131, obtained planar scintigrams at 48 h, and surveyed radioactivity repeatedly until it fell to under 30 μSv/h.

RESULTS

The radioactivity was under 30 μSv/h at 30 h in 51 out of 92 cases (55%). Among the remaining 41 (45%) cases, 27 (29%) and 32 (35%) cases showed decreased radioactivity under 30 μSv/h at 48 and 72 h, respectively, and it remained higher than 30 μSv/h at 72 h in another 9 cases (10%). In 5 (38%) of the 13 cases with bone metastasis, the radioactivity remained over 30 μSv/h after 72 h, and scintigrams showed strong accumulation in bone metastases. Among the 27 cases demonstrating below 30 μSv/h at 48 h, 26 showed radioactivity being below 50 μSv/h at 30 h, while it was above 50 μSv/h at 30 h in all 14 cases which demonstrated above 30 μSv/h at 48 h. We compared the radioactivity levels of 27 cases under 30 μSv/h at 48 h and 14 cases over 30 μSv/h at 48 h using a cutoff value of under 50 μSv/h at 30 h to release patient at 48 h, the positive predictive value and negative predictive value were 100 and 93%, respectively, and radioactivity was found to differ significantly (P < 0.001).

CONCLUSIONS

To predict external radiation levels at 48 h, it is helpful to consider external radiation levels at 30 h after treatment. Consideration of intracellular uptake in thyroid cancer, especially in cases of bone metastases, digestive tract function, and renal function, is important for predicting isolated period.