Abstract
BackgroundThis study’s aim was to develop our dosimetric methodology using a commercial workstation for the routine evaluation of the organs at risk during peptide receptor radionuclide therapy (PRRT) with 177Lu.MethodsFirst, planar and SPECT sensitivity factors were determined on phantoms. The reconstruction parameters were optimized by SPECT/CT image acquisition using a NEMA IEC phantom containing a 500 ml bottle of 177Lu, to simulate a kidney. The recovery coefficients were determined on various phantoms. For the red marrow, this was calculated using a NEMA IEC phantom that contained a centrally placed bottle of 80 ml of 177Lu (to model the L2-L4 red marrow) flanked by two 200 ml bottles with 177Lu to simulate the kidneys.Then, SPECT/CT images were acquired at 4, 24, 72, and 192 h after injection in 12 patients with neuroendocrine tumors who underwent PRRT with 177Lu-DOTATATE. SPECT data were reconstructed using the iterative ordered subset expectation maximization (OSEM) method, with six iterations and ten subsets, attenuation, scatter, recovery resolution corrections, and a Gaussian post-filter of 0.11 cm. The liver, spleen, kidneys, and red marrow dose per administered activity (AD/A admin) values were calculated with the Medical Internal Radiation Dose (MIRD) formalism and the residence times (Dosimetry toolkit® application) using standard and CT imaging-based organ masses (OLINDA/EXM® V1.0 software).ResultsSensitivity factors of 6.11 ± 0.01 and 5.67 ± 0.08 counts/s/MBq were obtained with planar and SPECT/CT acquisitions, respectively. A recovery coefficient of 0.78 was obtained for the modeled L2–L4 red marrow. The mean AD/A admin values were 0.43 ± 0.13 mGy/MBq [0.27–0.91] for kidneys, 0.54 ± 0.58 mGy/MBq [0.12–2.26] for liver, 0.61 ± 0.13 mGy/MBq [0.42–0.89] for spleen, and 0.04 ± 0.02 mGy/MBq [0.01–0.09] for red marrow. The AD/A admin values varied when calculated using the personalized and standard organ mass, particularly for kidneys (p = 1 × 10−7), spleen (p = 0.0069), and red marrow (p = 0.0027). Intra-patient differences were observed especially in organs close to or including tumor cells or metastases.ConclusionsThe obtained AD/A admin values were in agreement with the literature data. This study shows the technical feasibility of patient dosimetry in clinical practice and the need to obtain patient-specific information.
Highlights
This study’s aim was to develop our dosimetric methodology using a commercial workstation for the routine evaluation of the organs at risk during peptide receptor radionuclide therapy (PRRT) with 177Lu
No clear cumulative absorbed dose cut-off has been identified in PRRT with 177Lu to predict the risk of organ failure, which is probably multifactorial [4, 8], 23 Gy for kidneys and 2 Gy for bone marrow are sometimes proposed, these values are based on studies with fractionated external beam radiotherapy (EBRT) that has different physical and radiobiological mechanisms
A SPECT/CT sensitivity factor of 5.67 ± 0.08 counts/s/ MBq was obtained with these optimized reconstruction parameters
Summary
This study’s aim was to develop our dosimetric methodology using a commercial workstation for the routine evaluation of the organs at risk during peptide receptor radionuclide therapy (PRRT) with 177Lu. In recent years, new radiopharmaceuticals, such as radiopeptides, have been developed for targeted radiotherapy. Peptide receptor radionuclide therapy (PRRT) is a promising treatment for patients with neuroendocrine tumors (NET). It has been shown that 177Lu-DOTATATE uptake in kidneys and tumors greatly varies among patients [7], and bone marrow and kidneys are considered as dose-limiting organs. No clear cumulative absorbed dose cut-off has been identified in PRRT with 177Lu to predict the risk of organ failure, which is probably multifactorial [4, 8], 23 Gy for kidneys and 2 Gy for bone marrow are sometimes proposed, these values are based on studies with fractionated external beam radiotherapy (EBRT) that has different physical and radiobiological mechanisms. Based on fractionated EBRT, a 5% risk of renal dysfunction at 5 years has been described for a mean absorbed dose of 18–23 Gy and 0.5–1.25 Gy/fraction [9, 10]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call