Clinical Study
Quantitative Dosimetry for Yttrium-90 Radionuclide Therapy: Tumor Dose Predicts Fluorodeoxyglucose Positron Emission Tomography Response in Hepatic Metastatic Melanoma

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Abstract

Purpose

To assess a new method for generating patient-specific volumetric dose calculations and analyze the relationship between tumor dose and positron emission tomography (PET) response after radioembolization of hepatic melanoma metastases.

Methods and Materials

Yttrium-90 (90Y) bremsstrahlung single photon emission computed tomography (SPECT)/computed tomography (CT) acquired after 90Y radioembolization was convolved with published 90Y Monte Carlo estimated dose deposition kernels to create a three-dimensional dose distribution. Dose-volume histograms were calculated for tumor volumes manually defined from magnetic resonance imaging or PET/CT imaging. Tumor response was assessed by absolute reduction in maximum standardized uptake value (SUVmax) and total lesion glycolysis (TLG).

Results

Seven patients with 30 tumors treated with 90Y for hepatic metastatic melanoma with available 90Y SPECT/CT and PET/CT before and after treatment were identified for analysis. The median (range) for minimum, mean, and maximum dose per tumor volume was 16.9 Gy (5.7–43.5 Gy), 28.6 Gy (13.8–65.6 Gy) and 36.6 Gy (20–124 Gy), respectively. Response was assessed by fluorodeoxyglucose PET/CT at a median time after treatment of 2.8 months (range, 1.2–7.9 months). Mean tumor dose (P = .03) and the percentage of tumor volume receiving ≥ 50 Gy (P < .01) significantly predicted for decrease in tumor SUVmax, whereas maximum tumor dose predicted for decrease in tumor TLG (P < .01).

Conclusions

Volumetric dose calculations showed a statistically significant association with metabolic tumor response. The significant dose-response relationship points to the clinical utility of patient-specific absorbed dose calculations for radionuclide therapy.

Section snippets

Patients

This is a correlative study to a single institutional prospective observational study comprising patients treated with 90Y radioembolization, which was approved by the local institutional review board and compliant with the Health Insurance Portability and Accountability Act. We identified 14 consecutive patients with metastatic melanoma treated with 90Y radioembolization for hepatic metastases between April 2009 and October 2010. Seven patients were excluded because no FDG-PET/CT imaging

Tumor Dosimetry

The dose-volume statistics for tumor (n = 30) and normal liver (n = 7) are presented in Table 1. The mean ratio of absorbed dose to cumulated activity per voxel was 1.28 (range, 1.17–1.34; SD, < 0.01). On univariate analysis, injected activity was significantly associated with minimum and mean tumor dose (P = .003 and P = .028, respectively); however, this association did not remain significant on multivariable analysis (P = .463 and P = .656, respectively). A statistically significant

Discussion

In this analysis evaluating quantitative tumor dosimetry calculated from the 90Y SPECT/CT performed after radioembolization of hepatic metastatic melanoma, a statistically significant correlation was demonstrated between mean and maximum tumor doses and tumor PET response. A dose-response relationship was found, with greater tumor volume receiving doses > 50 Gy predicting for improved FGD-PET response.

The dose-response relationship presented here is consistent with previous reports

References (21)

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T.F. is entitled to royalties derived from Velocity Medical Solution’s sale of products and serves as a scientific advisor to Velocity Medical Solutions and owns equity in the company. The terms of this agreement have been reviewed and approved by Emory University in accordance with its conflict of interest policies. E.S. is entitled to royalties derived from Velocity Medical Solution’s sale of products. The terms of this agreement have been reviewed and approved by Emory University in accordance with its conflict of interest policies. None of the other authors have identified a conflict of interest.

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