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Meeting ReportEducational Exhibits - Radiopharmaceutical Sciences
Thanh-Tai Duong, Danny De Sarno, Hatim Fakir, Shahin Ghaseminejed, Martin Martinov, Glenn Bauman and Ting Yim Lee
Journal of Nuclear Medicine June 2024, 65 (supplement 2) 242528;
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Abstract
242528
Introduction: Localized prostate cancer is commonly managed using different radiotherapy modalities, including external beam radiotherapy (EBRT), low-dose-rate (LDR) and high-dose-rate (HDR) brachytherapy (BT). Recently, Targeted Radionuclide Therapy (TRT) utilizing radiolabeled targeted molecules was successful in the treatment of advanced prostate cancer demonstrating improved overall and progression free survival (PFS). Also, the FLAME trial indicated that incorporating a focal boost within EBRT can significantly improve the PFS outcomes for patients with localized prostate cancer. However, the potential interchangeability of this integrated focal boost, specifically targeted at the dominant intraprostatic lesion (DIL), with TRT remains uncertain. This study investigated variations in tumor and normal tissue doses when comparing the efficacy of EBRT/Boost versus EBRT/TRT. By investigating these differences, we hope to gain insights into the potential of TRT as a substitute for the proven focal boost technique in EBRT, thereby contributing to the evolving landscape of prostate cancer treatment.
Methods: A total of six prostate cancer patients from the IGPC-02 database () were selected. Two simulated plans were compared for the treatment of the DIL. Both consisted of a common Volumetric Modulated Arc Therapy (VMAT) EBRT plan delivering 35 Gy in 5 fractions to the prostate planning target volume (PTV) (a) plus a boost of 45.5 Gy to the PTVDIL as identified with 18F-DCFPyL PET in 5 fractions or (b) simulated TRT with 7.4, 3.7 or 1.85 GBq 177Lu-PSMA-617. For TRT, we derived time-integrated activity (TIA) by predicting it from dynamic 18F-DCFPyL PET/CT images through Logan graphical analysis. Subsequently, absolute doses were calculated using egs_mird (), a Monte Carlo program developed in-house based on EGSnrc. The therapeutic effect of both boost and TRT plans was compared using biological effective doses (BEDs) calculated with the linear quadratic model as well as accounting for the effects of DNA repair and clonal repopulation (Figure 1-a).
Results: Figure 1(b) compares the BEDs for the different simulated treatment plans. EBRT plus TRT with 1.85 GBq 177Lu-PSMA-617 TRT gave comparable prostate PTV and PTVDIL BEDs as EBRT/Boost. The mean PTV BED between the two treatment plans were not significantly different (p>0.05) while the mean PTVDIL was slightly higher with the EBRT plus TRT plan (1.3 Gy; P<0.05). However, the bone marrow (femur) dose was 24.81% higher (p>0.05) with the EBRT plus TRT plan. In addition, Figure 2 presents the BED dose distribution (a) and biological effective dose-volume histogram (BEDVH) of the combined EBRT plus 1.85 GBq TRT and EBRT/Boost for a representative patient (IGPC-02 #26). PTV and PTVDIL BEDs for EBRT plus 7.40 GBq TRT were significantly higher than EBRT/Boost (p<0.05, Figure 1(b))
Conclusions: For the treatment of DIL in patients with localized prostate cancer EBRT/Boost can be replaced with EBRT/TRT at one quarter of the radiopharmaceutical dose as conventionally used in TRT alone. However, boosted EBRT with the tested fractionation schedule delivered less normal tissue (femur bone marrow) dose than the EBRT plus TRT treatment. The higher bone marrow dose was primarily due to the insufficient differential uptake of 177Lu-PSMA-617 between tumor and blood marrow. Therefore, before implementing the combined EBRT and TRT approach, a personalized dose calculation based on a diagnostic PET PMSA scan may be necessary to minimize the potential adverse effects on normal tissues. Future work will investigate different fractionation schemes of EBRT with TRT and brachytherapy with TRT.
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Journal of Nuclear Medicine
Vol. 65, Issue supplement 2
June 1, 2024
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