DOSAGE AND ADMINISTRATION
Recommended Dose
The BEXXAR therapeutic regimen consists of four components administered in two discrete steps: the dosimetric step, followed 7-14 days later by a therapeutic step.
Note: The safety of the BEXXAR therapeutic regimen was established only in the setting of patients receiving thyroid blocking agents and premedication to ameliorate/prevent infusion reactions (see Concomitant Medications).
Dosimetric step
- Tositumomab 450 mg intravenously in 50 ml 0.9% Sodium Chloride over 60 minutes. Reduce the rate of infusion by 50% for mild to moderate infusional toxicity; interrupt infusion for severe infusional toxicity. After complete resolution of severe infusional toxicity, infusion may be resumed with a 50% reduction in the rate of infusion.
- Iodine I 131 Tositumomab (containing 5.0 mCi Iodine-131 and 35 mg Tositumomab) intravenously in 30 ml 0.9% Sodium Chloride over 20 minutes. Reduce the rate of infusion by 50% for mild to moderate infusional toxicity; interrupt infusion for severe infusional toxicity. After complete resolution of severe infusional toxicity, infusion may be resumed with a 50% reduction in the rate of infusion.
Therapeutic step
Note: Do not administer the therapeutic step if biodistribution is altered (see Assessment of Biodistribution of Iodine I 131 Tositumomab).
- Tositumomab 450 mg intravenously in 50 ml 0.9% Sodium Chloride over 60 minutes. Reduce the rate of infusion by 50% for mild to moderate infusional toxicity; interrupt infusion for severe infusional toxicity. After complete resolution of severe infusional toxicity, infusion may be resumed with a 50% reduction in the rate of infusion.
- Iodine I 131 Tositumomab (see CALCULATION OF IODINE-131 ACTIVITY FOR THE THERAPEUTIC DOSE). Reduce the rate of infusion by 50% for mild to moderate infusional toxicity; interrupt infusion for severe infusional toxicity. After complete resolution of severe infusional toxicity, infusion may be resumed with a 50% reduction in the rate of infusion.
- Withdraw and dispose of 32 mL of saline from a 50 mL bag of sterile 0.9% Sodium Chloride for Injection, USP.
- Withdraw the entire contents from each of the two 225 mg vials (a total of 450 mg Tositumomab in 32 mL) and transfer to the infusion bag containing 18 mL of 0.9% Sodium Chloride for Injection, USP to yield a final volume of 50 mL.
- Gently mix the solution by inverting/rotating the bag. DO NOT SHAKE.
- The diluted Tositumomab may be stored for up to 24 hours when stored refrigerated at 2°C−8°C (36°F−46°F) and for up to 8 hours at room temperature.
Note: Tositumomab solution may contain particulates that are generally white in nature. The product should appear clear to opalescent, colorless to slightly yellow.
Preparation of Iodine I 131 Tositumomab Dosimetric Dose
Required materials not supplied:
A. Lead shielding for preparation vial and syringe pump
B. One 30 mL syringe with 18-gauge needle to withdraw the calculated volume of Iodine I 131 Tositumomab from the Iodine I 131 Tositumomab vial. One 60 mL syringe with 18-gauge needle to withdraw the volume from the preparation vial for administration
C. One 20 mL syringe with attached needle, filled with 0.9% Sodium Chloride for Injection, USP
D. One 3 mL syringe with attached needle to withdraw Tositumomab from 35 mg vial
E. One sterile, 30 or 50 mL preparation vial
F. Two lead pots, both kept at room temperature. One pot is used to thaw the labeled antibody and the second pot is used to hold the preparation vial
Method:
- Allow approximately 60 minutes for thawing (at ambient temperature) of the Iodine I 131 Tositumomab dosimetric vial with appropriate lead shielding.
- Based on the activity concentration of the vial (see actual product specification sheet for the vial supplied in the dosimetric package), calculate the volume required for an Iodine I 131 Tositumomab activity of 5.0 mCi.
- Withdraw the calculated volume from the Iodine I 131 Tositumomab vial.
- Transfer this volume to the shielded preparation vial.
- Assay the dose to ensure that the appropriate activity (mCi) has been prepared.
a. If the assayed dose is 5.0 mCi (±10%) proceed with step 6.
b. If the assayed dose does not contain 5.0 mCi (±10%) recalculate the activity concentration of the Iodine I 131 Tositumomab at this time, based on the volume and the activity in the preparation vial. Recalculate the volume required for an Iodine I 131 Tositumomab activity of 5.0 mCi. Using the same 30 mL syringe, add or subtract the appropriate volume from the Iodine I 131 Tositumomab vial so that the preparation vial contains the volume required for an Iodine I 131 Tositumomab activity of 5.0 mCi (±10%). Re-assay the preparation vial and proceed with step 6.
- Calculate the amount of Tositumomab contained in the solution of Iodine I 131 Tositumomab in the shielded preparation vial, based on the volume and protein concentration (see actual product specification sheet supplied in the dosimetric package).
- If the shielded preparation vial contains less than 35 mg, calculate the amount of additional Tositumomab needed to yield a total of 35 mg protein. Calculate the volume needed from the 35 mg vial of Tositumomab, based on the protein concentration. Withdraw the calculated volume of Tositumomab from the 35 mg vial of Tositumomab, and transfer this volume to the shielded preparation vial. The preparation vial should now contain a total of 35 mg of Tositumomab.
- Using the 20 mL syringe containing 0.9% Sodium Chloride for Injection, USP, add a sufficient quantity to the shielded preparation vial to yield a final volume of 30 mL. Gently mix the solutions.
- Withdraw the entire contents from the preparation vial into a 60 mL syringe using a large bore needle (18-gauge).
- Assay and record the activity.
Administration of the Dosimetric Step
Required materials not supplied: For questions about required materials call the BEXXAR Service Center at 1-877-423-9927.
- IV Filter set (0.22 micron filter), 15 inch with injection site (port) and luer lock
- One Primary IV infusion set
- One 100 mL bag of sterile 0.9% Sodium Chloride for Injection, USP
- Two Secondary IV infusion sets
- One IV Extension set, 30 inch luer lock
- One 3-way stopcock
- One 50 mL bag of sterile 0.9% Sodium Chloride for Injection, USP
- One Infusion pump for Tositumomab infusion
- One Syringe Pump for Iodine I 131 Tositumomab infusion
- Lead shielding for use in the administration of the dosimetric dose
Tositumomab Infusion:
(See Figure 1 in the “Workbook for Dosimetry Methodology and Administration Set-Up” for diagrammatic illustration of the configuration of the infusion set components.)
- Attach a primary IV infusion set (Item B) to the 0.22 micron in-line filter set (Item A) and the 100 mL bag of sterile 0.9% Sodium Chloride for Injection, USP (Item C).
- After priming the primary IV infusion set (Item B) and IV filter set (Item A), connect the infusion bag containing 450 mg Tositumomab (50 mL) via a secondary IV infusion set (Item D) to the primary IV infusion set (Item B) at a port distal to the 0.22 micron in-line filter. Infuse Tositumomab over 60 minutes.
- After completion of the Tositumomab infusion, disconnect the secondary IV infusion set (Item D) and flush the primary IV infusion set (Item B) and the in-line IV filter set (Item A) with sterile 0.9% Sodium Chloride for Injection, USP. Discard the Tositumomab bag and secondary IV infusion set.
Iodine I 131 Tositumomab Dosimetric Infusion:
(See Figure 2 in the “Workbook for Dosimetry Methodology and Administration Set-Up” for diagrammatic illustration of the configuration of the infusion set components.)
- Appropriate shielding should be used in the administration of the dosimetric dose.
- The dosimetric dose is delivered in a 60 mL syringe.
- Connect the extension set (Item E) to the 3-way stopcock (Item F).
- Connect the 50 mL bag of sterile 0.9% Sodium Chloride for Injection, USP (Item G) to a secondary IV infusion set (Item D) and connect the infusion set to the 3-way stopcock (Item F). Prime the secondary IV infusion set (Item D) and the extension set (Item E). Connect the extension set (Item E) to a port in the primary IV infusion set (Item B), distal to the filter.
(Note: You must use the same primary infusion set (Item B) and IV filter set (Item A) with pre-wetted filter that was used for the Tositumomab infusion. A change in filter can result in loss of up to 7% of the Iodine I 131 Tositumomab dose.)
- Attach the syringe filled with the Iodine I 131 Tositumomab to the 3-way stopcock (Item F)
- Set syringe pump to deliver the entire 5.0 mCi (35 mg) dose of Iodine I 131 Tositumomab over 20 minutes.
- After completion of the infusion of Iodine I 131 Tositumomab, close the stopcock (Item F) to the syringe. Flush the extension set (Item E) and the secondary IV infusion set (Item D) with 0.9% Sodium Chloride for Injection, USP from the 50 mL bag (Item G).
- After the flush, disconnect the extension set (Item E), 3-way stopcock (Item F) and syringe. Disconnect the primary IV infusion set (Item B) and in-line filter set (Item A). Determine the combined residual activity of the syringe and infusion set components (stopcock, extension set, primary infusion set and in-line filter set) by assaying these items in a suitable radioactivity calibration system immediately following completion of administration of all components of the dosimetric step. Calculate and record the dose delivered to the patient by subtracting the residual activity in the syringe and the infusion set components from the activity of Iodine I 131 Tositumomab in the syringe prior to infusion.
- Discard all materials used to deliver the Iodine I 131 Tositumomab (e.g., syringes, vials, in-line filter set, extension set and infusion sets) in accordance with local, state, and federal regulations governing radioactive and biohazardous waste.
Determination of Dose for the Therapeutic Step (see Calculation of Iodine-131 Activity for Therapeutic Dose): The method for determining and calculating the patient-specific dose of Iodine-131 activity (mCi) to be administered in the therapeutic step is described below. The derived values obtained in steps 3 and 4 and calculation of the therapeutic dose as described in step 6 may be determined manually [see “Workbook for Dosimetry Methodology and Administration Set-Up” ] or calculated automatically using the GlaxoSmithKline proprietary software program [BEXXAR Patient Management Templates]. To receive training and to obtain the “BEXXAR Patient Management Templates” call the BEXXAR Service Center at 1-877-423-9927. For assistance with either manual or automated calculations call the BEXXAR Service Center at 1-877-423-9927.
- Following infusion of the Iodine I 131 Tositumomab dosimetric dose, obtain total body gamma camera counts and whole body images at the following timepoints:
a. Within one hour of infusion and prior to urination
b. 2-4 days after infusion of the dosimetric dose, following urination
c. 6-7 days after infusion of the dosimetric dose, following urination
- Assess biodistribution. If biodistribution is altered, the therapeutic step should not be administered.
- Determine total body residence time (see Graph 1, “Determination of Residence Time”, in the “Workbook for Dosimetry Methodology and Administration Set-Up”).
- Determine activity hours (see Table 2, “Determination of Activity Hours”, in the “Workbook for Dosimetry Methodology and Administration Set-Up”), according to gender. Use actual patient mass (in kg) or maximum effective mass (in kg) whichever is lower (see Table 1, “Determination of Maximum Effective Mass”, in the “Workbook for Dosimetry Methodology and Administration Set-Up”).
- Determine whether the desired total body dose should be reduced (to 65 cGy) due to a platelet count of 100,000 to <150,000 cells/mm3.
- Based on the total body residence time and activity hours, calculate the Iodine-131 activity (mCi) to be administered to deliver the therapeutic dose of 65 or 75 cGy.
The following equation is used to calculate the activity of Iodine-131 required for delivery of the desired total body dose of radiation.
Preparation for the Therapeutic Step
Tositumomab Dose
Required materials not supplied:
- One 50 mL syringe with attached 18-gauge needle (to withdraw 450 mg of Tositumomab from two vials each containing 225 mg Tositumomab)
- One 50 mL bag of sterile 0.9% Sodium Chloride for Injection, USP
- One 50 mL syringe for drawing up 32 mL of saline for disposal from the 50 mL bag of sterile 0.9% Sodium Chloride for Injection, USP
Method:
- Withdraw and dispose of 32 mL of saline from a 50 mL bag of sterile 0.9% Sodium Chloride for Injection, USP.
- Withdraw the entire contents from each of the two 225 mg vials (a total of 450 mg Tositumomab in 32 mL) and transfer to the infusion bag containing 18 mL of 0.9% Sodium Chloride for Injection, USP to yield a final volume of 50 mL.
- Gently mix the solutions by inverting/rotating the bag. DO NOT SHAKE.
- The diluted Tositumomab may be stored for up to 24 hours when stored refrigerated at 2°C−8°C (36°F−46°F) and for up to 8 hours at room temperature.
Note: Tositumomab solution may contain particulates that are generally white in nature. The product should appear clear to opalescent, colorless to slightly yellow.
Preparation of Iodine I 131 Tositumomab Therapeutic Dose
Required materials not supplied:
A. Lead shielding for preparation vial and syringe pump
B. One or two 30 mL syringes with 18-gauge needles to withdraw the calculated volume of Iodine I 131 Tositumomab from the Iodine I 131 Tositumomab vial(s). One or two 60 mL syringes with 18-gauge needles to withdraw the volume from the preparation vial for administration
C. One 20 mL syringe with attached needle filled with 0.9% Sodium Chloride for Injection, USP
D. One 3 mL sterile syringe with attached needle to draw up Tositumomab from the 35 mg vial
E. One sterile, 30 or 50 mL preparation vial
F. Two lead pots both kept at room temperature. One pot is used to thaw the labeled antibody, and the second pot is used to hold the preparation vial
Method:
- Allow approximately 60 minutes for thawing (at ambient temperature) of the Iodine I 131 Tositumomab therapeutic vial with appropriate lead shielding.
- Calculate the dose of Iodine I 131 Tositumomab required (see CALCULATION OF IODINE-131 ACTIVITY FOR THERAPEUTIC DOSE).
- Based on the activity concentration of the vial (see actual product specification sheet for each vial supplied in the therapeutic package), calculate the volume required for the Iodine I 131 Tositumomab activity required for the therapeutic dose.
- Using one or more 30 mL syringes with an 18-gauge needle, withdraw the calculated volume from the Iodine I 131 Tositumomab vial.
- Transfer this volume to the shielded preparation vial.
- Assay the dose to ensure that the appropriate activity (mCi) has been prepared.
a. If the assayed dose is the calculated dose (±10%) needed for the therapeutic step, proceed with step 7.
b. If the assayed dose does not contain the desired dose (±10%), re-calculate the activity concentration of the Iodine I 131 Tositumomab at this time, based on the volume and the activity in the preparation vial. Re-calculate the volume required for an Iodine I 131 Tositumomab activity for the therapeutic dose. Using the same 30 mL syringe, add or subtract the appropriate volume from the Iodine I 131 Tositumomab vial so that the preparation vial contains the volume required for the Iodine I 131 Tositumomab activity required for the therapeutic dose. Re-assay the preparation vial. Proceed to step 7.
- Calculate the amount of Tositumomab protein contained in the solution of Iodine I 131 Tositumomab in the shielded preparation vial, based on the volume and protein concentration (see product specification sheet).
- If the shielded preparation vial contains less than 35 mg, calculate the amount of additional Tositumomab needed to yield a total of 35 mg protein. Calculate the volume needed from the 35 mg vial of Tositumomab, based on the protein concentration. Withdraw the calculated volume of Tositumomab from the 35 mg vial of Tositumomab, and transfer this volume to the shielded preparation vial. The preparation vial should now contain a total of 35 mg of Tositumomab.
Note: If the dose of Iodine I 131 Tositumomab requires the use of 2 vials of Iodine I 131 Tositumomab or the entire contents of a single vial of Iodine I 131 Tositumomab, there may be no need to add protein from the 35 mg vial of Tositumomab.
- Using the 20 mL syringe containing 0.9% Sodium Chloride for Injection, USP, add a sufficient volume (if needed) to the shielded preparation vial to yield a final volume of 30 mL. Gently mix the solution.
- Withdraw the entire volume from the preparation vial into a one or more sterile 60 mL syringes using a large bore needle (18-gauge).
- Assay and record the activity.
Administration of the Therapeutic Step
Note: Restrictions on patient contact with others and release from the hospital must follow all applicable federal, state, and institutional regulations.
Required materials not supplied: For questions about required materials call the BEXXAR Service Center at 1-877-423-9927.
- One IV Filter set (0.22 micron, filter), 15 inch with injection site (port) and luer lock
- One Primary IV infusion set
- One 100 mL bag of sterile 0.9% Sodium Chloride for Injection, USP
- Two Secondary IV infusion sets
- One IV extension set, 30 inch luer lock
- One 3-way stopcock
- One 50 mL bag of sterile 0.9% Sodium Chloride for Injection, USP
- One Infusion pump for Tositumomab infusion
- One Syringe Pump for Iodine I 131 Tositumomab infusion
- Lead shielding for use in the administration of the therapeutic dose
Tositumomab Infusion:
(See Figure 1 in the “Workbook for Dosimetry Methodology and Administration Set-Up” for diagrammatic illustration of the configuration of the infusion set components.)
- Attach a primary IV infusion set (Item B) to the 0.22 micron in-line filter set (Item A) and a 100 mL bag of sterile 0.9% Sodium Chloride for Injection, USP (Item C).
- After priming the primary IV infusion set (Item B) and filter set (Item A), connect the infusion bag containing 450 mg Tositumomab (50 mL) via a secondary IV infusion set (Item D) to the primary IV infusion set (Item B) at a port distal to the 0.22 micron in-line filter. Infuse Tositumomab over 60 minutes.
- After completion of the Tositumomab infusion, disconnect the secondary IV infusion set (Item D) and flush the primary IV infusion set (Item B) and the IV filter set (Item A) with sterile 0.9% Sodium Chloride for Injection, USP. Discard the Tositumomab bag and secondary IV infusion set.
Iodine I 131 Tositumomab Therapeutic Infusion:
(See Figure 2 in the “Workbook for Dosimetry Methodology and Administration Set-Up” for diagrammatic illustration of the configuration of the infusion set components.)
- Appropriate shielding should be used in the administration of the therapeutic dose.
- The therapeutic dose is delivered in one or more 60 mL syringes.
- Connect the extension set (Item E) to the 3-way stopcock (Item F).
- Connect the 50 mL bag of sterile 0.9% Sodium Chloride for Injection, USP (Item G) to a secondary IV infusion set (Item D) and connect the infusion set to the 3-way stopcock (Item F). Prime the secondary IV infusion set (Item D) and the extension set (Item E). Connect the extension set (Item E) to a port in the primary IV infusion set (Item B), distal to the filter.
(Note: You must use the same primary infusion set (Item B) and IV filter set (Item A) with pre-wetted filter that was used for the Tositumomab infusion. A change in filter can result in loss of up to 7% of the Iodine I 131 Tositumomab dose.)
- Attach the syringe filled with the Iodine I 131 Tositumomab to the 3-way stopcock (Item F).
- Set syringe pump to deliver the entire therapeutic dose of Iodine I 131 Tositumomab over 20 minutes. (Note: If more than one syringe is required, remove the syringe and repeat steps 5 and 6.)
- After completion of the infusion of Iodine I 131 Tositumomab, close the stopcock (Item F) to the syringe. Flush the secondary IV infusion set (Item D) and the extension set (Item E) with 0.9% Sodium Chloride from the 50 mL bag of sterile, 0.9% Sodium Chloride for Injection, USP (Item G).
- After the flush, disconnect the extension set (Item E), 3-way stopcock (Item F) and syringe. Disconnect the primary IV infusion set (Item B) and in-line filter set (Item A). Determine the combined residual activity of the syringe(s) and infusion set components (stopcock, extension set, primary infusion set and in-line filter set) by assaying these items in a suitable radioactivity calibration system immediately following completion of administration of all components of the therapeutic step. Calculate and record the dose delivered to the patient by subtracting the residual activity in the syringe and infusion set components from the activity of Iodine I 131 Tositumomab in the syringe prior to infusion.
- Discard all materials used to deliver the Iodine I 131 Tositumomab (e.g., syringes, vials, in-line filter set, extension set and infusion sets) in accordance with local, state, and federal regulations governing radioactive and biohazardous waste.
DOSIMETRY
The following sections describe the procedures for image acquisition for collection of dosimetry data, interpretation of biodistribution images, calculation of residence time, and calculation of activity hours. Please read all sections carefully.
IMAGE ACQUISITION AND INTERPRETATION
Gamma Camera and Dose Calibrator Procedures
Manufacturer-specific quality control procedures should be followed for the gamma camera/computer system, the collimator, and the dose calibrator. Less than 20% variance between maximum and minimum pixel count values in the useful field of view is acceptable on Iodine-131 intrinsic flood fields and variability <10% is preferable. Iodine-131-specific camera uniformity corrections are strongly recommended, rather than applying lower energy correction to the Iodine-131 window. Camera extrinsic uniformity should be assessed at least monthly using 99mTc or 57Co as a source with imaging at the appropriate window.
Additional (non-routine) quality control procedures are required. To assure the accuracy and precision of the patient total body counts, the gamma camera must undergo validation and daily quality control on each day it is used to collect patient images.
Use the same setup and region of interest (ROI) for calibration, determination of background, and whole body patient studies.
Gamma Camera Set-Up
The same camera, collimator, scanning speed, energy window, and setup must be used for all studies. The gamma camera must be capable of whole body imaging and have a large or extra large field of view with a digital interface. It must be equipped with a parallel-hole collimator rated to at least 364 keV by the manufacturer with a septal penetration for Iodine-131 of <7%.
The camera and computer must be set up for scanning as follows:
- Parallel hole collimator rated to at least 364 keV with a septal penetration for Iodine-131 of <7%
- Symmetric window (20-25%) centered on the 364 keV photo peak of Iodine-131 (314-414 keV)
- Matrix: appropriate whole body matrix
- Scanning speed: 10-30 cm/minute
Counts from Calibrated Source for Quality Control
Camera sensitivity for Iodine-131 must be determined each day. Determination of the gamma camera’s sensitivity is obtained by scanning a calibrated activity of Iodine-131 (e.g., 200−250 μCi in at least 20 mL of saline within a sealed pharmaceutical vial). The radioactivity of the Iodine-131 source is first determined using a NIST-traceable-calibrated clinical dose calibrator at the Iodine-131 setting.
Background Counts
The background count is obtained from a scan with no radioactive source. This should be obtained following the count of the calibrated source and just prior to obtaining the patient count.
If abnormally high background counts are measured, the source should be identified and, if possible, removed. If abnormally low background counts are measured, the camera energy window setting and collimator should be verified before repeating the background counts.
The counts per μCi are obtained by dividing the background-corrected source count by the calibrated activity for that day. For a specific camera and collimator, the counts per μCi should be relatively constant. When values vary more than 10% from the established ratio, the reason for the discrepancy should be ascertained and corrected and the source count repeated.
Patient Total Body Counts
The source and background counts are obtained first and the camera sensitivity (i.e., constant counting efficiency) is established prior to obtaining the patient count. The same rectangular region of interest (ROI) must be used for the whole body counts, the quality control counts of the radioactive source, and the background counts.
Acquire anterior and posterior whole body images for gamma camera counts. For any particular patient, the same gamma camera must be used for all scans. To obtain proper counts, extremities must be included in the images, and arms should not cross over the body. The scans should be centered on the midline of the patient. Record the time of the start of the radiolabeled dosimetric infusion and the time of the start of each count acquisition.
Gamma camera counts will be obtained at the three imaging timepoints:
- Count 1: Within an hour of end of the infusion of the Iodine I 131 Tositumomab dosimetric dose prior to patient voiding.
- Count 2: Two to 4 days after administration of the Iodine I 131 Tositumomab dosimetric dose and immediately following patient voiding.
- Count 3: Six to 7 days after the administration of the Iodine I 131 Tositumomab dosimetric dose and immediately following patient voiding.
Assessment of Biodistribution of Iodine I 131 Tositumomab
The biodistribution of Iodine I 131 Tositumomab should be assessed by determination of total body residence time and by visual examination of whole body camera images from the first image taken at the time of Count 1 (within an hour of the end of the infusion) and from the second image taken at the time of Count 2 (at 2 to 4 days after administration). To resolve ambiguities, an evaluation of the third image at the time of Count 3 (6 to 7 days after administration) may be necessary. If either of these methods indicates that the biodistribution is altered, the Iodine I 131 Tositumomab therapeutic dose should not be administered.
Expected Biodistribution
- On the first imaging timepoint: Most of the activity is in the blood pool (heart and major blood vessels) and the uptake in normal liver and spleen is less than in the heart.
- On the second and third imaging timepoints: The activity in the blood pool decreases significantly and there is decreased accumulation of activity in normal liver and spleen. Images may show uptake by thyroid, kidney, and urinary bladder and minimal uptake in the lungs. Tumor uptake in soft tissues and in normal organs is seen as areas of increased intensity.
Results Indicating Altered Biodistribution
- On the first imaging timepoint: If the blood pool is not visualized or if there is diffuse, intense tracer uptake in the liver and/or spleen or uptake suggestive of urinary obstruction the biodistribution is altered. Diffuse lung uptake greater than that of blood pool on the first day represents altered biodistribution.
- On the second and third imaging timepoints: Uptake suggestive of urinary obstruction and diffuse lung uptake greater than that of the blood pool represent altered biodistribution.
- Total body residence times of less than 50 hours and more than 150 hours.
CALCULATION OF IODINE-131 ACTIVITY FOR THE THERAPEUTIC DOSE
There are two options for calculation of the Iodine-131 activity for the therapeutic dose. The derived values and calculation of the therapeutic dose may be determined manually [see “Workbook for Dosimetry Methodology and Administration Set-Up” ] or calculated automatically using the GlaxoSmithKline proprietary software program [BEXXAR Patient Management Templates]. The following describes in greater detail the stepwise method for manual determination of the Iodine-131 activity for the therapeutic dose.
Residence Time (hr)
For each timepoint, calculate the background corrected total body count at each timepoint (defined as the geometric mean). The following equation is used:
In this equation, CA = the anterior counts, CBA = the anterior background counts, CP = the posterior counts, and CBP = the posterior background counts.
Once the geometric mean of the counts has been calculated for each of the 3 timepoints, the % injected activity remaining for each timepoint is calculated by dividing the geometric mean of the counts from that timepoint by the geometric mean of the counts from Day 0 and multiplying by 100.
The residence time (h) is then determined by plotting the time from the start of
infusion and the % injected activity values for the 3 imaging timepoints on
Graph 1 (see Worksheet “Determination of Residence Time” in the “Workbook for Dosimetry Methodology and Administration Set-Up” supplied with Dosimetric Dose Packaging). A best-fit line is then drawn from 100% (the pre-plotted Day 0 value) through the other 2 plotted points (if the line does not intersect the two points, one point must lie above the best-fit line and one point must lie below the best-fit line). The residence time (h) is read from the x-axis of the graph at the point where the fitted line intersects with the horizontal 37% injected activity line.
Activity Hours (mCi hr)
In order to determine the activity hours (mCi hr), look up the patient’s maximum effective mass derived from the patient’s sex and height (see Worksheet “Determination of Maximum Effective Mass” in the “Workbook for Dosimetry Methodology and Administration Set-Up” supplied with Dosimetric Dose Packaging). If the patient’s actual weight is less than the maximum effective mass, the actual weight should be used in the activity hours table (see Worksheet “Determination of Activity Hours” in the “Workbook for Dosimetry Methodology and Administration Set-Up” supplied with Dosimetric Dose Packaging). If the patient’s actual weight is greater than the maximum effective mass, the mass from the worksheet for “Determination of Maximum Effective Mass” should be used.
Calculation of Iodine-131 Activity for the Therapeutic Dose
The following equation is used to calculate the activity of Iodine-131 required for delivery of the desired total body dose of radiation.
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