Testicular uptake and radiation dose in patients receiving Zevalin and Pretarget CC49Fusion protein.
OBJECTIVE
Radiation dose to the testes from radionuclide therapies is of concern. This study evaluated image-quantification methods for testicular uptake in a phantom and in patients.


METHODS
A 50-mL vial and a large water tank were used to simulate testes and the body, respectively. Activity concentration in the vial and water tank was prepared to generate testes-to-background concentrations of 1.3 and 1.1. Five male lymphoma patients who received a Zevalin (Biogen Idec, Cambridge, MA) regimen and 6 male colorectal cancer patients who received a Pretarget (Neo Rx, Seattle, WA) CC49Fusion protein were evaluated. Testicular activity was quantified using two methods: (1) geometric-mean, background-corrected testicular region of interest (ROI) counts as a fraction of body counts without explicit attenuation correction (Zevalin Kit); (2) background-corrected anterior testicular ROI counts with attenuation correction using known depth in the phantom and CT depth in patients.


RESULTS
In the phantom study, Method 1 underestimated 49% and 39%, at image contrast of 1.3 and 1.1, respectively. Quantification was improved using Method 2 (7% for a 1.3 contrast, -17% for a 1.1 contrast). Method 2 was used in patients because background-corrected posterior ROI counts were statistically unreliable due to poor image contrast. In patients receiving Zevalin, the median peak percent injected dose (%ID)/testis was 0.10 (range, 0.08-0.18) with a median biologic half-time (T(bio1/2)) of 156 (range, 91-4200) hours. The median dose was 2.4 (range, 1.5-3.6) Gy/GBq, compared to the originally reported mean dose of 9.1 (range, 5.4-11.4) Gy/GBq (Zevalin package insert). In patients receiving the Pretarget CC49Fusion protein, the median peak %ID/testis was 0.22 (range, 0.05-0.29) with a median T(bio1/2) of 44 (range, 37-64) hours. The median dose was 0.84 (range, 0.3-1.2) Gy/GBq.


CONCLUSIONS
This study found that testicular doses from Zevalin were much lower than that originally reported in the package insert. The median testicular dose from Pretarget CC49Fusion protein was less than half that of the median testicular dose from Zevalin.
Shen
Sui
S
Department of Radiation Oncology, University of Alabama, Birmingham, AL 35249, USA. sshen@uabmc.edu
Meredith
Ruby
R
Duan
Jun
J
Forero
Andres
A
Breitz
Hazel
H
Khazaeli
M B
MB
Brezovich
Ivan
I
LoBuglio
Albert
A
D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics*; D000912:Antibodies, Neoplasm / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000493:pharmacokinetics*; D015179:Colorectal Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008223:Lymphoma / Q000532:radiotherapy*; D008297:Male; D019047:Phantoms, Imaging; D016499:Radioimmunotherapy / Q000379:methods; D011868:Radioisotopes / Q000493:pharmacokinetics*; D011874:Radiometry / Q000379:methods; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000493:pharmacokinetics*; D013737:Testis / Q000187:drug effects / Q000528:radiation effects*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D014915:Whole-Body Counting / Q000379:methods
D000911:Antibodies, Monoclonal; D000912:Antibodies, Neoplasm; D000970:Antineoplastic Agents; C091202:B72.3 antibody; D011868:Radioisotopes; D011993:Recombinant Fusion Proteins; C422802:ibritumomab tiuxetan