Volumetric decrease of pancreas after abdominal irradiation, it is time to consider pancreas as an organ at risk for radiotherapy planning

Paediatric Anatomical Models in Radiotherapy Applications

Anatomical models have key applications in radiotherapy, notably to help understand the relationship between radiation dose and risk of developing side effects. This review analyses whether age-specific computational phantoms, developed from healthy subjects and paediatric cancer patient data, are adequate to model a paediatric population. The phantoms used in the study were International Commission on Radiological Protection (ICRP), 4D extended cardiac torso (XCAT) and Radiotherapy Paediatric Atlas (RT-PAL), which were also compared to literature data. Organ volume data for 19 organs was collected for all phantoms and literature. ICRP was treated as the reference for comparison, and percentage difference (P.D) for the other phantoms were calculated relative to ICRP. Overall comparisons were made for each age category (1, 5, 10, 15) and each organ. Statistical analysis was performed using Microsoft Excel (version 16.59). The smallest P.D to ICRP was for Literature (-17.4%), closely followed by XCAT (26.6%). The largest was for RT-PAL (88.1%). The rectum had the largest average P.D (1,049.2%) and the large bowel had the smallest (2.0%). The P.D was 122.6% at age 1 but this decreased to 43.5% by age 15. Linear regression analysis showed a correlation between organ volume and age to be the strongest for ICRP (R2 = 0.943) and weakest for XCAT (R2 = 0.676). The phantoms are similar enough to ICRP for potential use in modelling paediatric populations. ICRP and XCAT could be used to model a healthy population, whereas RT-PAL could be used for a population undergoing/after radiotherapy.

Preclinical Evaluation of Gastrin-Releasing Peptide Receptor Antagonists Labeled with 161Tb and 177Lu: A Comparative Study

To elucidate potential benefits of the Auger-electron-emitting radionuclide 161Tb, we compared the preclinical performance of the gastrin-releasing peptide receptor antagonists RM2 (DOTA-Pip5-d-Phe6-Gln7-Trp8-Ala9-Val10-Gly11-His12-Sta13-Leu14-NH2) and AMTG (α-Me-Trp8-RM2), each labeled with both 177Lu and 161Tb. Methods: 161Tb/177Lu labeling (90°C, 5 min) and cell-based experiments (PC-3 cells) were performed. In vivo stability (30 min after injection) and biodistribution studies (1-72 h after injection) were performed on PC-3 tumor-bearing CB17-SCID mice. Results: Gastrin-releasing peptide receptor affinity was high for all compounds (half-maximal inhibitory concentration [nM]: [161Tb]Tb-RM2, 2.46 ± 0.16; [161Tb]Tb-AMTG, 2.16 ± 0.09; [177Lu]Lu-RM2, 3.45 ± 0.18; [177Lu]Lu-AMTG, 3.04 ± 0.08), and 75%-84% of cell-associated activity was receptor-bound. In vivo, both AMTG analogs displayed distinctly higher stability (30 min after injection) and noticeably higher tumor retention than their RM2 counterparts. Conclusion: On the basis of preclinical results, [161Tb]Tb-/[177Lu]Lu-AMTG might reveal a higher therapeutic efficacy than [161Tb]Tb-/[177Lu]Lu-RM2, particularly [161Tb]Tb-AMTG because of additional Auger-electron emissions at the cell membrane level.

The impact of apelin-13 on cisplatin-induced endocrine pancreas damage in rats: an in vivo study

Apelin-13 is a peptide hormone that regulates pancreatic endocrine functions, and its benefits on the endocrine pancreas are of interest. This study aims to investigate the potential protective effects of apelin-13 in cisplatin-induced endocrine pancreatic damage. Twenty-four rats were divided into four groups: control, apelin-13, cisplatin, and cisplatin + apelin-13. Caspase-3, TUNEL, and Ki-67 immunohistochemical staining were used as markers of apoptosis and mitosis. NF-κB/p65 and TNFα were used to show inflammation. β-cells and α-cells were also evaluated with insulin and glucagon staining in the microscopic examination. Pancreatic tissue was subjected to biochemical analyses of glutathione (GSH) and malondialdehyde (MDA). Apelin-13 ameliorated cisplatin-induced damage in the islets of Langerhans. The immunopositivity of apelin-13 on β-cells and α-cells was found to be increased compared to the cisplatin group (p = 0.001, p = 0.001). Mitosis and apoptosis were significantly higher in the cisplatin group (p = 0.001). Apelin-13 reduced TNFα, NF-κB/p65 positivity, and apoptosis caused by cisplatin (p = 0.001, p = 0.001, p = 0.001). While cisplatin caused a significant increase in MDA levels (p = 0.001), apelin caused a significant decrease in MDA levels (p = 0.001). The results demonstrated a significant decrease in pancreatic tissue GSH levels following cisplatin treatment (p = 0.001). Nevertheless, apelin-13 significantly enhanced cisplatin-induced GSH reduction (p = 0.001). On the other hand, the serum glucose level, which was measured as 18.7 ± 2.5 mmol/L in the cisplatin group, decreased to 13.8 ± 0.7 mmol/L in the cisplatin + apelin-13 group (p = 0.001). The study shows that apelin-13 ameliorated cisplatin-induced endocrine pancreas damage by reducing oxidative stress and preventing apoptosis.

The potential antioxidant effect of N-acetylcysteine on X-ray ionizing radiation-induced pancreas islet cell toxicity

PURPOSE

Previous research has highlighted the impact of X-ray irradiation-induced organ damage, on cancer patients after radiation therapy. The ionizing radiation-induced oxidative stress causes injury to the pancreatic islet cells of Langerhans. We used histopathological, immunohistochemical, and biochemical analyses to examine α- and β-cells in the islets of Langerhans in rats undergoing whole-body x-ray ionizing radiation, a group of which was treated with NAC.

MATERIAL AND METHODS

Twenty-four male rats were randomly divided into 3 groups, one control, and two experimental groups. Group I (Control) was administered only saline solution (0.09% NaCl) by oral gavage for 7 days. Group II (IR) was administrated whole body single dose 6 Gray ionizing radiation (IR) and saline solution (0.09% NaCl) by oral gavage for 7 days. Group III (IR + NAC) was administered 300 mg/kg NAC (N-acetylcysteine) by oral gavage for 7 days, 5 days before, and 2 days after 6 Gray IR application.

RESULTS

In the X-ray irradiation group, we observed diffuse necrotic endocrine cells in the islets of Langerhans. In addition, we found that Caspase-3, malondialdehyde (MDA) levels increased, and insulin, glucagon, and glutathione (GSH) levels decreased in the IR group compared to the control group. In contrast, we observed a decrease in Caspase-3, and MDA levels in necrotic endocrine cells, and an increase in insulin, glucagon, and GSH levels in the IR + NAC group compared to the IR group.

CONCLUSION

This study provides evidence for the beneficial effects of N-acetyl cysteine on islets of Langerhans cells with X-ray ionizing-radiation-induced damage in a rat model.

Diagnosis and management of pancreatic insufficiency in patients with gastrectomy due to cancer or gastric ulcers: a virtual roundtable expert discussion

INTRODUCTION

Pancreatic exocrine insufficiency (PEI) is common after gastric resection for cancer or ulcers but is under-recognized and undertreated. Although pancreatic enzyme replacement therapy (PERT) is the mainstay of PEI management, robust evidence supporting its use after gastric surgery is limited.

AREAS COVERED

In the absence of guideline recommendations specific for patients with pancreatic insufficiency after gastrectomy, a panel of experts from different geographical regions convened in a virtual meeting to discuss their approach to patient management.

EXPERT OPINION

Pancreatic insufficiency after gastrointestinal surgery is not a simple post-surgical complication as several factors contribute to its development. Although the pancreas is unimpaired after gastrectomy, it cannot function normally in the altered environment. Pancreatic insufficiency can be challenging to diagnose in gastrectomy patients due to nonspecific symptoms and the absence of a simple diagnostic test. Fecal elastase appears to be the default test, although it is not sufficiently sensitive nor reliable for diagnosing or monitoring PEI. Patients with maldigestion symptoms after gastrectomy are treated pragmatically: those with clinical suspicion of pancreatic insufficiency receive a trial of PERT and are monitored for symptom improvement. There is a clear need for high-quality evidence from clinical trials to guide the management of this patient population.

Radioprotective effects of α2-adrenergic receptor agonist dexmedetomidine on X-ray irradiation-induced pancreatic islet cell damage

Comprehensive epidemiological analyses conducted in the last 30 years have revealed a link between radiation and DM. We aimed to determine the effects of dexmedetomidine pretreatment on radiation-induced pancreatic islet cell damage. Twenty-four rats were divided into three groups: group 1 (control group), group 2 (only X-ray irradiation group), and group 3 (X-ray irradiation + dexmedetomidine). We observed necrotic cells with vacuoles accompanying loss of cytoplasm in the islets of Langerhans, extensive edematous areas, and vascular congestions in group 2. In group 3, we observed a decrease in necrotic cells in the islets of Langerhans, and edematous areas and vascular congestion was also reduced. We determined a decrease in β-cells, α-cells, and D-cells in the islets of Langerhans in group 2 compared to the control group. In group 3, β-cells, α-cells, and D-cells were elevated compared to group 2. Ionizing radiation may induce DM. Dexmedetomidine appears to exert a radioprotective effect.

Recent Advances in Pancreatic Ductal Adenocarcinoma: Strategies to Optimise the Perioperative Nutritional Status in Pancreatoduodenectomy Patients

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy for which the mainstay of treatment is surgical resection, followed by adjuvant chemotherapy. Patients with PDAC are disproportionately affected by malnutrition, which increases the rate of perioperative morbidity and mortality, as well as reducing the chance of completing adjuvant chemotherapy. This review presents the current evidence for pre-, intra-, and post-operative strategies to improve the nutritional status of PDAC patients. Such preoperative strategies include accurate assessment of nutritional status, diagnosis and appropriate treatment of pancreatic exocrine insufficiency, and prehabilitation. Postoperative interventions include accurate monitoring of nutritional intake and proactive use of supplementary feeding methods, as required. There is early evidence to suggest that perioperative supplementation with immunonutrition and probiotics may be beneficial, but further study and understanding of the underlying mechanism of action are required.

Can the Realization of an External Wirsungostomy be an Option for High-Risk Pancreatic Anastomosis After Pancreaticoduodenectomy?

BACKGROUND

Clinically relevant postoperative pancreatic fistula (POPF) occurs in 15-20% of patients after pancreaticoduodenectomy (PD) and reintervention in the setting of Grade C POPF remains associated with a mortality rate of up to 25%. In patients at high risk of POPF, PD with external wirsungostomy (EW) could be a safe alternative that avoids pancreatico-enteric anastomosis while preserving the remnant pancreas.

METHODS

Of the 155 consecutive patients who underwent PD from November 2015 to December 2020, 10 patients were managed using an EW, all with a fistula risk score (FRS) ≥ 7 and BMI ≥30 kg/m², and/or major associated abdominal surgery. The pancreatic duct was cannulated with a polyethylene tube to allow good external drainage of the pancreatic fluid. We retrospectively analyzed postoperative complications and endocrine and exocrine insufficiencies.

RESULTS

The median alternative FRS was 36.9% [22.1-45.2]. There was no postoperative death. The 90-day overall severe complication (grade  ≥3) rate was 30% (n = 3 patients), no patient required reoperation, and 2 hospital readmissions occurred. 3 patients experienced Grade B POPF (30%), managed using image-guided drainage for 2 patients. The external pancreatic drain was removed after a median drainage time of 75 days [63-80]. Two patients presented with late symptoms (> 6 months) warranting interventional management (pancreaticojejunostomy and transgastric drainage). Six patients experienced significant weight loss (> 2 kg) 3 months after surgery. One year after surgery, 4 patients still complained of diarrhea and were treated with transit-delaying drugs. One patient presented new-onset diabetes one year after surgery, and 1 of the 4 patients with preexisting diabetes experienced worsening disease.

CONCLUSION

EW after PD might be a solution to reduce post-operative mortality following PD in high-risk patients.

Dose-Volume Constraints fOr oRganS At risk In Radiotherapy (CORSAIR): An "All-in-One" Multicenter-Multidisciplinary Practical Summary

BACKGROUND

The safe use of radiotherapy (RT) requires compliance with dose/volume constraints (DVCs) for organs at risk (OaRs). However, the available recommendations are sometimes conflicting and scattered across a number of different documents. Therefore, the aim of this work is to provide, in a single document, practical indications on DVCs for OaRs in external beam RT available in the literature.

MATERIAL AND METHODS

A multidisciplinary team collected bibliographic information on the anatomical definition of OaRs, on the imaging methods needed for their definition, and on DVCs in general and in specific settings (curative RT of Hodgkin's lymphomas, postoperative RT of breast tumors, curative RT of pediatric cancers, stereotactic ablative RT of ventricular arrythmia). The information provided in terms of DVCs was graded based on levels of evidence.

RESULTS

Over 650 papers/documents/websites were examined. The search results, together with the levels of evidence, are presented in tabular form.

CONCLUSIONS

A working tool, based on collected guidelines on DVCs in different settings, is provided to help in daily clinical practice of RT departments. This could be a first step for further optimizations.

Response Evaluation Following Radiation Therapy With 18F-FDG PET/CT: Common Variants of Radiation-Induced Changes and Potential Pitfalls

Radiation therapy (RT) is one of the cornerstones in cancer treatment and approximately half of all patients will receive some form of RT during the course of their cancer management. Response evaluation after RT and follow-up imaging with ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) can be complicated by RT-induced acute, chronic or consequential effects. There is a general consensus that ¹⁸F-FDG PET/CT for response evaluation should be delayed for 12 weeks after completing RT to minimize the risk of false-positive findings. Radiation-induced late side effects in normal tissue can take years to develop and eventually cause symptoms that on imaging can potentially mimic recurrent disease. Imaging findings in radiation induced injuries depend on the normal tissue included in the irradiated volume and the radiation therapy regime including the total dose delivered, dose per fraction and treatment schedule. The intent for radiation therapy should be taken in consideration when evaluating the response on imaging, that is palliative vs curative or neoadjuvant vs adjuvant RT. Imaging findings can further be distorted by altered anatomy and sequelae following surgery within the radiation field. An awareness of common PET/CT-induced changes/injuries is essential when interpreting ¹⁸F-FDG PET/CT as well as obtaining a complete medical history, as patients are occasionally scanned for an unrelated cause to previously RT treated malignancy. In addition, secondary malignancies due to carcinogenic effects of radiation exposure in long-term cancer survivors should not be overlooked. ¹⁸F-FDG PET/CT can be very useful in response evaluation and follow-up in patients treated with RT, however, variants and pitfalls are common and it is important to remember that radiation-induced injury is often a diagnosis of exclusion.

Incidence of Diabetes in the Atomic Bomb Survivors: 1969-2015

CONTEXT

Recent epidemiological studies have shown increased risk of diabetes among childhood cancer survivors who received high therapeutic doses of radiation, particularly to the total body or to the abdomen. However, the effect of low-to-moderate dose radiation (<4 Gy) on the risk of diabetes is still unknown.

OBJECTIVES

To investigate the radiation effect on diabetes incidence among atomic bomb (A-bomb) survivors, and whether the dose response is modified by other factors including city, sex, and age at time of bombing (ATB).

METHODS

9131 participants without diabetes at baseline were observed through biennial clinical exams from 1969 to 2015. A Cox proportional hazards model was used to estimate hazard ratios (HR) to evaluate the dose response for diabetes incidence.

RESULTS

During the study period, 1417 incident diabetes cases were identified. The overall crude incidence rate was 7.01/103 person-years. Radiation dose was significantly associated with diabetes incidence, with effect modification by city and age ATB. In Hiroshima, at ages 10 and 30 ATB, the HRs at 1 Gy of pancreatic radiation dose were 1.47 (95% CI, 1.31-1.66) and 1.13 (95% CI, 0.97-1.31), respectively. However, no significant radiation dose response was observed at these ages in Nagasaki. The HR for radiation dose was higher among those who were younger ATB and decreased 1% for each additional year of age.

CONCLUSIONS

Among A-bomb survivors, a radiation association was suggested for incidence of diabetes. Results were inconsistent by city and age ATB, which could indicate potential confounding of the radiation association with diabetes.

Organs at risk radiation dose constraints

Dose constraints are essential for performing dosimetry, especially for intensity modulation and for radiotherapy under stereotaxic conditions. We present the update of the recommendations of the French society of oncological radiotherapy for the use of these doses in classical current practice but also for reirradiation.

Deterioration of pancreatic exocrine function in carbon ion radiotherapy for pancreatic cancer

Background and purpose

In radiotherapy (RT) for pancreatic cancer, the pancreas is considered an important organ at risk. However, there are insufficient reports on pancreatic function deterioration after X-ray RT as organ at risk, and there are no reports on those after carbon ion (C-ion) RT. Here, we evaluated pancreatic exocrine insufficiency (PEI) after C-ion RT using dose-volume histogram (DVH) analysis.

Materials and methods

Data were retrospectively collected from patients who had undergone C-ion RT for pancreatic cancer between July 2013 and June 2019. The prescribed C-ion doses were 55.2 Gy (relative biological effectiveness) in 12 fractions. Serum pancreatic amylase and lipase values were measured before and after C-ion RT. In DVH analysis, we assessed V_5Gy-50Gy and V_{<5 Gy-50Gy} of pancreatic volume and analyzed whether these DVH parameters involved PEI.

Results

Thirty-three patients were included in the analysis. The median follow-up duration after the initiation of C-ion RT in these patients was 15.8 months (range, 4.3-64.8). During and after treatment, 57.6% of patients developed PEI within 13.6 months, defined as pancreatic amylase and lipase deficiencies. In DVH analysis, V_<5Gy was the most effective factor for the PEI, and the cutoff value for developing PEI in V_<5Gy was 4.57 cm³.

Conclusion

We showed that pancreatic exocrine function declined after C-ion RT for pancreatic cancer and that PEI was initiated early in the course of C-ion RT. Additionally, a low dose of DVH parameters, such as V_<5Gy, was a prognostic factor of PEI.

Delineation of organs at risk

The delineation of organs at risk is the basis of radiotherapy oncologists' work. Indeed, the knowledge of this delineation enables to better identify the target volumes and to optimize dose distribution, involving the prognosis of the patients but also their future. The learning of this delineation must continue throughout the clinician's career. Some contour changes have appeared with better imaging, some volumes are now required due to development of knowledge of side effects. In addition, the increasing survival time of patients requires to be more systematic and precise in the delineations, both to avoid complications until now exceptional but also because re-irradiations are becoming more and more frequent. We present the update of the recommendations of the French Society for Radiation Oncology (SFRO) on new findings or adaptations to volumes at risk.

MDCT evaluation of pancreatic contour variations in head, neck, body and tail: surgical and radiological significance

OBJECTIVE

The purpose of the study was to investigate the incidence of pancreatic contour variations on multidetector CT (MDCT) for abdominal examinations.

METHODS

A retrospective analysis of 700 MDCT scans was performed in patients who underwent triple phase CT abdomen between October 2018 and January 2021. After excluding 176 patients, finally total of 524 patients were included in the study. For simplification, we classified the pancreatic contour variations as classified by Ross et al. and Omeri et al. Pancreatic head-neck variations was classified into Type I-anterior, Type II-posterior and Type III-horizontal variety. Pancreatic body-tail variation was divided into Type Ia-anterior projection; Ib-posterior projection and Type IIa-globular, IIb-lobulated, IIc-tapered, and IId-bifid pancreatic tail.

RESULTS

The most common type of variation in the head was Type II (n = 112, 21.3%) followed by Type III (n = 37, 7%) and Type I (n = 21, 4%). The most common type of variation in the body of pancreas was Type Ia (n = 33, 6.2%) followed by Type Ib (n = 13, 2.4%). In the tail region of pancreas, the most common variation was Type IIb (n = 21, 4%) followed by Type IIa (n = 19, 3.6%).

CONCLUSION

Pancreatic contour variations are not very uncommon in daily practice. Knowledge of these variations is important for surgeons, radiologists and avoids misjudgement of normal pancreatic tissue as tumor or lymph node especially on unenhanced or single phase MDCT.

Curative role of mesenchymal stromal cells in chronic pancreatitis: Modulation of MAPK and TGF-β1/SMAD factors

BACKGROUND AND OBJECTIVE

Living organisms respond to physical, chemical, and biological threats with a potent inflammatory response which alters organ cell signaling and leads to dysfunction. We evaluated the therapeutic effect of bone marrow-based mesenchymal stromal cell (BM-MSC) transplanted in rats to preserve tissue integrity and to restore homeostasis and function in the pancreatitis experimental pattern.

METHODS

This study involved 40 adult male Wister rats. Repeated L-arginine injections caused chronic pancreatitis (CP), leading to the development of pancreatic damage and shifting the intracellular signaling pathways. Rats were then infused with BM-MSC labeled with PKH26 fluorescent linker dye for 12 weeks.

RESULTS

Cell-surface indicators of BM-MSCs such as CD 90 and CD29 were expressed with the lack of CD34 expression. BM-MSC treatment considerably improved the alterations induced in a series of inflammatory markers, including IL-18, TNF-α, CRP, PGE2, and MCP-1. Furthermore, improvement was found in digestive enzymes and lipid profile with amelioration in myeloperoxidase activity. BM-MSC treatment also regulated the (TGF-/p-38MPAK/SMAD2/3) signaling factors that enhances repair of damaged pancreatic tissue, confirmed by reversed alteration of histopathological examination.

CONCLUSION

our results further bring to light the promise of cell transplant therapy for chronic pancreatitis.

Icariin Promote Stem Cells Regeneration and Repair Acinar Cells in L-arginine / Radiation -Inducing Chronic Pancreatitis in Rats

Objective:

Chronic Pancreatitis (CP) is a multifactorial disease. It was characterized by severe inflammation and acinar cell destruction. Thus, the present study was initiated to evaluating the ability of bone marrow-based mesenchymal stem cell (MSCs) combined with Icariin to restore and regenerate acinar cells in the pancreas of rats suffering chronic pancreatitis.

Methods:

Chronic pancreatitis was induced in rats via both L-arginine plus radiation, repeated L-arginine injection (2.5g/Kg body-weight, 1, 4,7,10,13,16,19 days), then, on day 21, rats were exposed to a single dose of gamma-radiation (6 Gy), which exacerbate injury of pancreatic acinar cells. One day after irradiation, rats were treated with either MSCs (1 × 10⁷ /rat, once, tail vein injection) labeled PKH26 fluorescent linker dye and/or Icariin (100 mg/Kg, daily, orally) for 8 weeks.

Results:

Icariin promotes MSCs proliferation boosting its productivity in vitro. MSCs, and/or icariin treatments has regulated molecular factors TGF-β/PDGF and promoted the regeneration of pancreatic tissues by releasing PDX-1 and MafA involved in the recruitment of stem/progenitor cell in the tissue, and confirmed by histopathological examination. Moreover, a significant decrease in IL-8 and TNF-α cytokines with significant amelioration of myeloperoxidase activity were noted. As well as, reduction in MCP-1 and collagen type-1 levels along with Hedgehog signaling down-regulating expression in such cells, Patched-1, Smoothened, and GLi-1.

Conclusion:

The potent bioactive therapeutic Icariin combined with MSCs induces a significantly greater improvement, compared to each therapy alone.

The analysis of absorbed dose by pancreas during gastric cancer radiotherapy

INTRODUCTION

The toxicity of radiotherapy is a very important issue in the everyday work of radiation oncologist. The tolerance to certain doses of radiotherapy in organs at risk determines the safety of radiotherapy. Despite the increasing number of publications concerning the injury of the pancreas after radiotherapy, this organ does not have common directives. We decided to reanalyse our previously published data in terms of the dose of radiation absorbed by the pancreas to determine a dose-effect relationship with the use of radiation-induced hypoamylasaemia and hypolipasaemia.

MATERIALS AND METHODS

We reanalysed a group of 127 gastric cancer patients after preoperative or postoperative chemoradiotherapy who were treated with a total dose of 45 Gy administered in 25 fractions. To identify the absorbed doses, the pancreas was contoured based on the CT scans used for radiotherapy planning and divided into anatomical parts: the head, the body and the tail.

RESULTS

We found that 80% of the whole pancreatic volume absorbed at least 44.5 Gy. The body, tail and head absorbed 100%, 90% and 70% of the abovementioned dose, respectively. The mean dose absorbed by the whole pancreas ranged from 32 to 48 Gy, with a mean of 44 Gy. A total dose of 45 Gy administered to gastric cancer patients can lead to subclinical insufficiency of the pancreas (hypolipasaemia and hypoamylasaemia). This dose is not able to cause symptomatic damage to the pancreas.

First-in-human dosimetry of gastrin-releasing peptide receptor antagonist [177Lu]Lu-RM2: a radiopharmaceutical for the treatment of metastatic castration-resistant prostate cancer

PURPOSE

Besides PSMA, prostate cancer cells also express gastrin-releasing peptide receptor (GRPr) which is therefore a promising target for theranostic approaches. The high affinity GRPr antagonist RM2 can be labeled with beta-emitting radiometals for therapeutic purposes. The aim of this study was to calculate absorbed doses for critical organs and tumor lesions for [¹⁷⁷Lu]Lu-RM2 therapy administered in a group of metastatic castration-resistant prostate cancer (mCRPC) patients who had insufficient PSMA expression or showed lower PSMA accumulation after previous cycles of [¹⁷⁷Lu]Lu-PSMA-617 therapy.

METHODS

Thirty-five patients suffering from mCRPC without further treatment options for approved therapies were examined with [⁶⁸Ga]Ga-RM2-PET/CT. Out of these, 4 patients (mean age 68 years) were treated with [¹⁷⁷Lu]Lu-RM2; two of these also received a 2nd therapy cycle. Mean activity was 4.5 ± 0.9 GBq. For dosimetry, patients underwent planar WB-scintigraphy and SPECT/CT imaging of the upper and lower abdomen at approximately 1, 24, 48, and 72 h p.i. along with blood sampling. Absorbed doses for kidneys, pancreas, liver, spleen, gallbladder wall, and tumor lesions were derived based on quantitative SPECT/CT according to RADAR dosimetry scheme; individual organ masses were extracted from CT. Absorbed dose to bone marrow was calculated based on serial whole-body images and blood sampling according to the EANM guideline.

RESULTS

Therapy was well tolerated by all patients and no side effects were observed. An increased uptake in tumor lesions and the pancreas was seen within the first 1 h. Mean absorbed organ doses were 1.08 ± 0.44 Gy/GBq in the pancreas, 0.35 ± 0.14 Gy/GBq in the kidneys, 0.05 ± 0.02 Gy/GBq in the liver, 0.07 ± 0.02 Gy/GBq in the gallbladder wall, 0.10 ± 0.06 Gy/GBq in the spleen, and 0.02 ± 0.01 Gy/GBq for the red bone marrow. The mean dose for tumor lesions was 6.20 ± 3.00 Gy/GBq.

CONCLUSIONS

Application of GRPr antagonist [¹⁷⁷Lu]Lu-RM2 is suitable for targeted radiotherapy of mCRPC as it shows high tumor uptake and rapid clearance from normal organs. Absorbed doses in tumor lesions are therapeutically relevant. The critical organ receiving the highest absorbed dose was the pancreas. Results suggest that the activity administered for each cycle could be increased to maximize the absorbed dose of tumors and metastases.