Selective Internal Radiation Therapy With Yttrium-90 Glass Microspheres: Biases and Uncertainties in Absorbed Dose Calculations Between Clinical Dosimetry Models.
To quantify differences that exist between dosimetry models used for90Y selective internal radiation therapy (SIRT).



Retrospectively, 37 tumors were delineated on 19 post-therapy quantitative90Y single photon emission computed tomography/computed tomography scans. Using matched volumes of interest (VOIs), absorbed doses were reported using 3 dosimetry models: glass microsphere package insert standard model (SM), partition model (PM), and Monte Carlo (MC). Univariate linear regressions were performed to predict mean MC from SM and PM. Analysis was performed for 2 subsets: cases with a single tumor delineated (best case for PM), and cases with multiple tumors delineated (typical clinical scenario). Variability in PM from the ad hoc placement of a single spherical VOI to estimate the entire normal liver activity concentration for tumor (T) to nontumoral liver (NL) ratios (TNR) was investigated. We interpreted the slope of the resulting regression as bias and the 95% prediction interval (95%PI) as uncertainty. MCNLsinglerepresents MC absorbed doses to the NL for the single tumor patient subset; other combinations of calculations follow a similar naming convention.



SM was unable to predict MCTsingleor MCTmultiple(p>.12, 95%PI >±177 Gy). However, SMsinglewas able to predict (p<.012) MCNLsingle, albeit with large uncertainties; SMsingleand SMmultipleyielded biases of 0.62 and 0.71, and 95%PI of ±40 and ± 32 Gy, respectively. PMTsingleand PMTmultiplepredicted (p<2E-6) MCTsingleand MCTmultiplewith biases of 0.52 and 0.54, and 95%PI of ±38 and ± 111 Gy, respectively. The TNR variability in PMTsingleincreased the 95%PI for predicting MCTsingle(bias = 0.46 and 95%PI = ±103 Gy). The TNR variability in PMTmultiplemodified the bias when predicting MCTmultiple(bias = 0.32 and 95%PI = ±110 Gy).



The SM is unable to predict mean MC tumor absorbed dose. The PM is statistically correlated with mean MC, but the resulting uncertainties in predicted MC are large. Large differences observed between dosimetry models for90Y SIRT warrant caution when interpreting published SIRT absorbed doses. To reduce uncertainty, we suggest the entire NL VOI be used for TNR estimates when using PM.
Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas.
Justin K
JK
Mikell
Department of Interventional Radiology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
Armeen
A
Mahvash
Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas.
Wendy
W
Siman
The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas; Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
Veera
V
Baladandayuthapani
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; Department of Radiation Oncology, Christiana Care, Newark, Delaware; Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, Pennsylvania.
Firas
F
Mourtada
Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas. Electronic address: skappadath@mdanderson.org.
S Cheenu
SC
Kappadath
D005898:Glass; D006801:Humans; D016014:Linear Models; D008099:Liver / Q000000981:diagnostic imaging / Q000528:radiation effects*; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008863:Microspheres; D015233:Models, Statistical; D009010:Monte Carlo Method; D009378:Neoplasms, Multiple Primary / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D019275:Radiopharmaceuticals; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D013668:Technetium Tc 99m Aggregated Albumin; D015899:Tomography, Emission-Computed, Single-Photon; D035501:Uncertainty; D015021:Yttrium Radioisotopes / Q000627:therapeutic use*
D019275:Radiopharmaceuticals; D013668:Technetium Tc 99m Aggregated Albumin; D015021:Yttrium Radioisotopes