A practical methodology for patient release after tositumomab and (131)I-tositumomab therapy.
A methodology was developed determining patient releasability after radioimmunotherapy with tositumomab and (131)I-tositumomab for the treatment of non-Hodgkin's lymphoma.


METHODS
Dosimetry data were obtained and analyzed after 157 administrations of (131)I-tositumomab to 139 patients with relapsed or refractory non-Hodgkin's lymphoma. Tositumomab and (131)I-tositumomab therapy included dosimetric (low activity) and therapeutic (high activity) administrations. For each patient, the total-body residence time was calculated after the dosimetric administration from total-body counts obtained over 6 or 7 d and was then used to determine the appropriate therapeutic activity to deliver a specific total-body radiation dose. Patient dose rates at 1 m were measured immediately after the therapeutic infusion. Patient-specific calculations based on the measured total-body residence time and dose rate for (131)I-tositumomab were derived to determine the patient's maximum releasable dose rate at 1 m, estimated radiation dose to maximally exposed individuals, and the amount of time necessary to avoid close contact with others.


RESULTS
The mean administered activity (+/-SD), determined by dosimetry studies for each patient before therapy, was 3,108 +/- 1,073 MBq (84 +/- 29 mCi) (range, 1,221 +/- 5,957 MBq [33--161 mCi]). Immediately after treatment, the mean measured dose rate (+/- SD) at 1 m was 0.109 +/- 0.032 mSv/h (10.9 +/- 3.2 mrem/h; range, 0.04--0.24 mSv/h [4--24 mrem/h]). The measured dose rates were 60% (range, 37%--90%; P < 0.0001) of the theoretic dose rates from a point source in air predicted using the dose equivalent rate per unit activity of (131)I (5.95 x 10(-5) mSv/MBq h [0.22 mrem/mCi h] at 1 m). The mean estimated radiation dose to the maximally exposed individual was 3.06 mSv (306 mrem) (range, 1.95--4.96 mSv [195--496 mrem]). On the basis of current regulatory patient-release criteria, all (131)I-tositumomab--treated patients were determined to be releasable by comparing the dose rate at 1 m with a predetermined maximum releasable dose rate. Detailed instructions were provided to limit family members' exposure.


CONCLUSIONS
A methodology has been developed for the release of patients administered radioactive materials based on the new Nuclear Regulatory Commission regulations. This approach uses a patient-specific dose calculation based on the measured total-body residence time and dose rate. This analysis shows the feasibility of outpatient radioimmunotherapy with tositumomab and (131)I-tositumomab.
Siegel
Jeffry A
JA
Nuclear Physics Enterprises, Cherry Hill, New Jersey 08003, USA. siegelja@aol.com
Kroll
Stewart
S
Regan
Denise
D
Kaminski
Mark S
MS
Wahl
Richard L
RL
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000553:Ambulatory Care; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000627:therapeutic use*; D018951:Antigens, CD20 / Q000276:immunology; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D017028:Caregivers; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000627:therapeutic use*; D008228:Lymphoma, Non-Hodgkin / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D010351:Patient Discharge / Q000331:legislation & jurisprudence; D011829:Radiation Dosage; D011835:Radiation Protection / Q000331:legislation & jurisprudence; D016499:Radioimmunotherapy; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D014481:United States
D000911:Antibodies, Monoclonal; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D007457:Iodine Radioisotopes; C119496:tositumomab I-131