Treating Thyroid Cancer using I-131 Maximum Tolerable Dose Method

Transcription

1 Treating Thyroid Cancer using I-131 Maximum Tolerable Dose Method Christopher Martel, M.Sc., CHP Lisa Thornhill,, NRRPT, RT(NM) Boston University Medical Center

2 Thyroid Carcinoma New cases and deaths in the U.S., 2007 New Cases 33,550 Deaths - 1,530 Risk factors that increase chances 1) White female, over 40 y.o. 2) Genetic (for medullary thyroid carcinoma) 3) Not enough iodine in the diet 4) Radiation and/or radioactive fallout National Cancer Institute,

3 Thyroid Cancer Incidence Rates

4 Thyroid Cancer Incidence Rates National Cancer Institute,

5 Methods of Treatment Depending on type and stage of the cancer: 1) surgery 2) radioactive iodine 3) hormone therapy 4) external radiation 5) chemotherapy Maxon,HR J Nuclear Med, 1992; 33:

6 Radioactive Iodine Therapy 1. post surgery for thyroid removal 2. related to tumor s future capacity to concentrate iodine 3. positive relationship between total I-131 I uptake per tumor mass and outcome but not proven for maximal doses ** doses < 35 Gy to tumor likely will not respond to I-131 therapy need 300 Gy to thyroid remnant, 120 Gy to metastatic foci

7 Radioiodine Uptake Ranges Radioiodine is used to determine thyroid uptake. Isotopes used include I-123 and I-131. I Normal uptake 15-25% Hypo <10% Hyper - >30%

8 Images of Thyroid Cancer Surgical Tumor Removal WB PET Scan with FDG WB Nuclear Med Scan with Tl-201

9 Iodine Kinetics (simplified) 3 T 3 K 13 = 0.56 K 32 = I - K 21 = K 12 = thyroid K 01 = 2 K 14 = 0.1 K 42 = urine 4 T 4 feces K 04 = 0.018

10 Estimated % of Administered I - 1 hour 6 hours 24 hours Excreted Other Liver (1.4) Thyroid (1.5) Intestine Blood Stomach ECEV Excreted Other Liver Thyroid Intestine Blood Stomach ECEV Excreted Other Liver Thyroid Intestine 1.6 Blood 1.6 Stomach 1.4 ECEV MIRD Dose Estimate Report No. 5 (Maximum thyroid uptake of 15%)

11 I-131 Review physical half-life life of days Beta emitter max energy 610 KeV; avg energy 193 KeV tissue range of 0.8 mm Gamma emitter principal energy 365 KeV (81%) 94% of radiation dose is from the beta emissions

12 Half life: Iodine-131 Decay Data 8.06 days Energy Emissions No. (Mev) Yield gamma % % % % % % beta % % %

13 SNM: Dose Selection General Guidelines for Thyroid Cancer patients For postoperative ablation of thyroid bed remnants depending on the amount of functioning tissue present ( mci) For treatment of presumed thyroid cancer in the neck or mediastinal lymph nodes ( mci) For treatment of distant metastases (> 200 mci) ) *Candidate for MTD*

14 Maximal Dose Therapy Considered When Patients with life-threatening disease Patients with progressive disease but little response to previous treatments Patients with bone mets Patients with nodal disease Goal is to treat but not to cure disease

15 Why Perform Maximal Dose Therapy? Standard treatment using empiric guidelines is only a best guess and not truly tailored for each patient Better outcome if treated with one rather than multiple I-131 treatments

16 Common Side Effects from >200 mci Dose I-131 I Therapy 60-70% radiation sickness 10-15% 15% sialoadenitis 10% leukopenia for up to one year 70% transient azoospermia Cystitis, radiation thyroiditis,, gastritis, transient loss of taste

17 Absorbed Dose Calculations Uses Modification to the MIRD System Practical Determination of Patient-Specific Marrow Dose Using Radioactivity Concentration in Blood and Body Shen, Denardo Sgouros,, et. al UC Davis/Memorial Sloan-Kettering Cancer Institute Journal of Nuclear Medicine, Vol 40, No. 12 December 1999

18 Critical Factors in Calculating Patient Dose Dose to red marrow Red marrow self dose Total body to red marrow dose Dose to lungs Whole body retention at 48 hours

19 Limiting Factors for Maximal I-131 I Dose Therapy Whole Body Retention at 48 hours 80 mci if lung metastases are present 120 mci if lung mets not present Requires: WB counting using dual head Gamma Camera 200 cgy (200 Rads) ) absorbed dose to the red BM Requires: WB counting blood sampling mathematical modeling

20 General Principles for Calculating Absorbed Dose Give amount of radioactivity which will reside in a particular organo Must determine total # nuclear transformations that occur within that organ 1) activity (transition rate or decay rate) Physical characteristics 2) time that nuclide is resident in that organ Biologic characteristics Cumulated Activity (mci( mci-hrs) = Activity (mci( mci) ) in organ x time = (mci( mci-hrs) Divide the Cumulated Activity in the organ / Total given Activity y to body = total # nuclear transitions in organ per unit activity This is also known as the Residence Time in the organ of interest

21 Phantom Models in OLINDA-EXM 70 kg adult (reference male) 57 kg (reference female) 57 kg 15 year old 32 kg 10 year old 19 kg 5 year old 9.2 kg 1 year old 3.4 kg newborn

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23 Biodistribution of I-131 For most radiopharmaceuticals, the activity in a given organ does not remain constant throughout the period of interest radioactive (physical) decay ongoing biologic processes of uptake and removal of metabolites

24 Problems with Biodistribution Patients have very different rates of metabolism, especially older or sicker patients Patients with Thyroid Cancer have had their thyroids removed Each lesion will have its own uptake and biological removal rate

25 Performing Maximal Dose I-131 I Therapy Administer tracer dose of I-131 I 131 (~2-3 mci) Obtain blood samples at specific time intervals Obtain whole body images (gamma camera) at specific time intervals

26 I-131 Dosimetry Chronological Steps 1. Patient is booked for the procedure HP needs name, medical record number, DOB, weight and recent hematocrit 2. Work must begin on a Monday, dosimetry done Monday- Friday 3. Patient gets dosed with the I-131 treatment the following Monday 4. Patient must stay in the hospital post treatment, usually up to five days

27 Day One BACKGROUND IV inserted Blood draw Whole Body Count Administer Iodine NO VOID Blood draw Whole Body Count VOID Blood draw Whole Body Count VOID Blood draw Whole Body Count HOURS

28 Days 2 through 5 Day 2 (24 hr) Blood draw and whole body count Day 3 (48 hr) Blood draw and whole body count Day 4 (72 hr) Blood draw and whole body count Day 5 (96 hr) Blood draw and whole body count Dosimetry calculations Review with MD Order dose

29 Room Preparation for I-131 Radiotherapy Patient on 7W Room 7W-26

30 Patient #1 43 yo female with Papillary Thyroid Cancer 01/28/2005 I-123 I uptake focal nodal disease, four distinct areas within neck region; total neck uptake 0.26 % 02/04/2005 I-131 I Therapy Dose 196 mci 02/11/2005 WB scan, 7 days post I-131 I therapy 09/20/2005 I-131 I WB dosimetry (five days) 09/27/2005 I-131 I Therapy Dose 450 mci 10/07/2005 WB scan, 7 days post I-131 I therapy

31 90 minutes post ingestion intake

32 3 hours post ingestion intake

33 5 hours post ingestion intake

34 24 hours post ingestion intake

35 48 hours post ingestion intake

36 I-131 WB scan 09/22/ hours post ingestion intake

37 96 hours post ingestion intake

38 Patient #2 60 yo female with metastatic papillary thyroid cancer to the lungs 06/06/2006 I-131 WB dosimetry (five days) Intense uptake in the thyroid bed; patchy uptake in both mid lung bases 06/28/2006 WB scan, 15 days post I-131 therapy Findings similar to previous dosimetry scans; In addition, iodine avid focus in right mid neck

39 Two hours post tracer dose

40 Four hours post tracer dose

41 24 hours post tracer dose

42 48 hours post tracer dose

43 72 hours post tracer dose

44 Dosimetry Results Blood Activity per Gram vs Time Post Administration Blood Activity (uci/gm) Exponential fit to all data Exponential y = e fit to all x R 2 = data Exponential fit to last 3 data points Exponential fit to y = 0.278e last 3 data x points R 2 = Time (hours)

45 Whole Body Activity versus Time Post Administration Exponential fit to all data Exponential fit to all data Activity (mci) y = e x R 2 = Exponential fit to last three data points Exponential fit to last three data points y = e x R 2 = Time (Hours)

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48 Administered 352 mci

49 THYROID ANTERIOR COUNTS AVG CNTS/PIXEL TIME

50 LEFT LUNG POSTERIOR VIEW COUNTS AVG CNTS/PIXEL TIME (HOURS)

51 RIGHT LUNG POSTERIOR VIEW COUNTS AVG CNTS/PIXEL TIME (HOURS)

52 8 days post therapy dose

53 15 days post therapy dose

54 As of October 17, 2007 Both patients are doing very well No recurrence of cancerous cells

55 Acknowledgments Stephanie Lee, M.D., Ph.D. Dept. Endocrine / Diabetes Boston University Medical Center Richard H. Behrman, Ph.D. Head Medical Physicist, Diagnostic Radiology Boston University Medical Center