Research ArticleClinical Investigation

Lesion Dosimetry for [177Lu]Lu-PSMA-617 Radiopharmaceutical Therapy Combined with Stereotactic Body Radiotherapy in Patients with Oligometastatic Castration-Sensitive Prostate Cancer

Milan Grkovski, Joseph A. O’Donoghue, Brandon S. Imber, George Andl, Cheng Tu, Daniel Lafontaine, Jazmin Schwartz, Maria Thor, Michael J. Zelefsky, John L. Humm and Lisa Bodei
Journal of Nuclear Medicine November 2023, 64 (11) 1779-1787; DOI: https://doi.org/10.2967/jnumed.123.265763

Article Figures & Data

Figures

  • Figure
  • FIGURE 1.
    FIGURE 1.

    Top: Maximum-intensity projections for 3 PSMA PET/CT scans of 72-y-old patient initially treated with radical retropubic prostatectomy in 1998 (patient 4). Oligorecurrent lymph nodes in lower retrocaval (blue arrow), right posterior common iliac (red arrow), and superior presacral (orange arrow) regions. Bottom: Axial CT slices, centered on lower retrocaval lymph node.

  • FIGURE 2.
    FIGURE 2.

    Top: Maximum-intensity projections for 3 [177Lu]Lu-PSMA-617 SPECT/CT scans of patient 4. Oligorecurrent lymph nodes in lower retrocaval (blue arrow), right posterior common iliac (red arrow), and superior presacral (orange arrow) regions. Bottom: Axial CT slices, centered on lower retrocaval lymph node.

  • FIGURE 3.
    FIGURE 3.

    Axial views of voxelwise dose maps of patient 4, focused on lower retrocaval lymph node. From left to right: BED (assuming α/β ratio of 3 [BEDα/β = 3]) from first cycle of [177Lu]Lu-PSMA-617 RPT only, from SBRT, and from combined therapy. If second RPT cycle delivers 90% of AD from first cycle, total mean and maximum lesion BEDα/β = 3 would be 219 and 258 Gy, respectively, corresponding to prescription of 40.1 Gy (mean) and 43.9 Gy (maximum) in 3 fractions or EQD2α/β = 3 of 131 Gy (mean) and 155 Gy (maximum). Two cycles of [177Lu]Lu-PSMA-617 RPT were estimated to contribute 52% and 61% to combined mean and maximum BEDα/β = 3, respectively.

  • FIGURE 4.
    FIGURE 4.

    Correlations between imaging and dosimetry-based metrics: SPECT SUVmax vs. baseline PSMA PET SUVmax (A), ADRPT vs. baseline PSMA PET SUVmax (B), and ADRPT vs. SPECT SUVmax (C).

  • FIGURE 5.
    FIGURE 5.

    Relationship between lesion BED and PSMA PET–assessed response to [177Lu]Lu-PSMA-617 RPT before SBRT (i.e., interim) (A) and after SBRT (i.e., post) (B).

Tables

  • TABLE 1.

    Summary of Patient Characteristics and Imaging Results

    PatientAge (y)Gleason scoreStageLocationPSMA PET[177Lu]Lu-PSMA-617Lesion volume (cm3)
    SUVmax*TLRmax*
    BaselineInterimPostBaselineInterimPostSUVmaxTLRmaxPET-derivedGTV
    1 [1]754 + 5N1Left transverse process of T7 vertebra16.85.52.53.81.20.411.414.20.81.4
    1 [2]Right femoral neck27.29.62.56.22.00.4NANA0.84.0
    2 [3]783 + 4cT2aRight internal iliac node12.16.24.12.21.91.08.47.80.70.6
    3 [4]605 + 4pT3bN1Left transverse process of C6 vertebra12.79.33.32.32.10.75.87.50.81.3
    4 [5]724 + 3pT3aN0Lower retrocaval lymph node23.74.22.43.20.80.411.710.50.41.7
    4 [6]Right posterior common iliac lymph node18.85.93.82.61.10.615.414.00.91.9
    4 [7]Superior presacral lymph node26.37.29.43.61.31.415.013.60.82.1
    5 [8]774 + 3pT4N0Right posterior middle lobe perifissural nodule2.71.91.90.70.50.43.32.21.72.4
    6 [9]514 + 4pT3aN0Right obturator lymph node5.78.23.40.81.40.73.32.70.815.0†
    Median74 (14)16.8 (11.6)6.2 (2.7)3.3 (1.3)2.6 (1.4)1.3 (0.8)0.6 (0.3)9.9 (7.3)9.1 (7.4)0.8 (0.0)1.9 (1.0)

    • ↵* Partial-volume correction not applied.

    • ↵† Patient 6 had small pelvic lymph nodes that were in vicinity of PSMA-avid node. Clinical judgment was made to cover nonavid nearby nodes.

    • NA = not available; TLRmax = maximum tumor-to-liver ratio; GTV = gross tumor volume.

    • Numbers in brackets are number of lesions; numbers in parentheses are IQR.

  • TABLE 2.

    Summary of Dosimetry Results

    PatientMean ADRPT (Gy/GBq)*Mean AD delivered by SBRT (Gy)†Mean total from RPT (Gy)‡Mean BED from SBRT (Gy)†Mean total BED (Gy)§Maximum total BED (Gy)§
    1 [1]3.727.753113160185
    1 [2]NA27.9NA114NANA
    2 [3]5.028.173116186217
    3 [4]2.928.841121158171
    4 [5]7.728.4114118219258
    4 [6]5.127.975114187209
    4 [7]3.728.254116158179
    5 [8]1.128.316117124138
    6 [9]2.126.731106131141
    Median3.7 (2.4)28.1 (0.4)58 (37)116 (3)159 (35)182 (48)

    • ↵* As calculated from first-cycle serial SPECT/CT imaging.

    • ↵† Mean within gross tumor volume.

    • ↵‡ Total dose from both cycles, assuming second cycle contributes 90% of dose from first cycle. Mean within VOI is as defined on PSMA PET/CT.

    • ↵§ Mean BED from RPT and SBRT within VOI as defined on PSMA PET/CT. Mean BED from RPT and SBRT within gross tumor volume was approximately 5% lower.

    • NA = not available.

    • Numbers in brackets are number of lesions; numbers in parentheses are IQR. Lesion 2 was not within SPECT field of view, assuming α/β ratio of 3 Gy.

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