2/13/12. Brachytherapy: What, Where, Why, How, Kent A. Gifford, Ph.D. What is it? Where? Brachy- Treatment sites

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1 Brachytherapy: What, Where, Why, How, When Kent A. Gifford, Ph.D. What is it? Brachy- Greek word for near or short distance Notice no mention of internal Can involve sources placed in or on patient Can even be external and not touching patient Treatment sites Bladder Breast Brain Bronchi Cervix Eye H & N Prostate Skin Where? 1

2 Why? Placing sources close to tumor yields high dose while keeping OAR dose low - Inverse square fall off Integral dose typically lower then EBRT Normal tissue sparing Interstitial How? Breast H & N Gyn How? Bob Kuske, MD 2

3 How? Intracavitary Breast Cervical How? How? Intralumen IVBT Endobronchial 3

4 How? How? Surface Eye Skin How? 4

5 How? How? Brachytherapy Treatments Low Dose Rate vs. High Dose Rate Definitive vs. Boost prostate implant cervical implant 5

6 Dose Rate The rate at which the radiation delivers a therapeutic dose to the tumor is the dose rate. Low Dose Rate (LDR) The rate is slow - it takes hours, even days to deliver the prescribed dose. Pulsed Dose Rate (PDR) Delivered so as to mimic LDR, typically one pulse per hour. High Dose Rate (HDR) The dose rate is high - the treatment takes only minutes to deliver the dose. Delivery Applicators Radioactive sources are usually placed in applicators. Applicator function is to maintain source position in diseased area. They are specific for each area and should not be used where they were not planned to be placed. Fletcher-Suit-Delclos Applicator System 6

7 Orthogonal Films - T&O Applicators Needles for Temporary Interstitial MammoSite 7

8 Inflated balloon Catheter MammoSite Vaginal Dome Cylinder 8

9 Endobronchial catheter Tracheal or adjustable catheter Rotterdam Nasopharyngeal Applicator 9

10 HAM Applicator Afterloading Technique Preloaded Originally sources were pre-loaded into or made into the applicator, such as radium needles. Increased radiation safety issues Manual afterloading Sources are manually loaded once the applicator was in place. Dummy sources - non radioactive source replicas, used for filming and dosimetry Remote Afterloading Sources are loaded into the applicator by a machine once all personnel have left the room. Technology developed in the last three decades of the 20th century. 10

11 Equipment Special equipment is needed to perform brachytherapy procedures Shielded work area Leaded storage safe Leaded transport pigs Area Monitors GM Survey Meters Handling instruments - forceps Special applicators to place radioactive material in the applicator or tumor volume. Special calibration equipment 11

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13 Remote Afterloading Unit Remote Afterloading Units - these machines have become popular in the last years. LDR, PDR, HDR Units are available. Remote control mechanisms use computer control to introduce the radioactive sources. Low Dose Rate Afterloading Units are rare in the US. Manually loaded sources are still the most popular. High Dose Rate Afterloading Units are required if HDR treatments are to be preformed due to high activity of source. LDR Remote Afterloader HDR Remote Afterloader 13

14 Remote Afterloading Units Advantage: Minimal radiation exposure to personnel - sources retract Reduced inventory of sources Multiple sites can be treated Safety features inherent in the treatment unit Outpatient treatment with HDR Disadvantages: Room availability Maintenance Cost 14

15 Physics/Dosimetry Duties RAM License type of radioactive material, amount, manufacturer, inventory, radiation safety features, training, shielding for storage, etc.. Preparation Applicator Equipment Simulation Dosimetry Sources Order/Activate Receive - wipe test (see your RSO) Prepare - assay, load, store (inventory) Procedures Temporary Implants Low Dose Rate/High Dose Rate Attend procedure supply applicators - Tandem and Ovoid, dome/ cylinders, catheters and needles equipment - Geiger Mueller Survey Meter, forceps, shields, or shield containers Simulation Dosimetry/Planning Assist with loading radioactive material Survey - exposure rate Assist with removal of radioactive material Return sources to inventory Ham Applicator 15

16 Ham Applicator w/shield Ham Applicator Connected Procedures Permanent Implant Low Dose Rate Attend clinical application of radioactive sources equipment - Mick Applicator, Gold Grain Applicator, needles Geiger Mueller Survey Meter, NaI detector, leaded containers (lead pig), shielding Assist with radioactive material placement using fluoroscopy, CT or ultrasound or by naked eye Survey patient Radiation Safety Surveys/Paperwork 16

17 Implant Dosimetry Predictive in nature? Based on prior measurements and understanding of radiation interaction Designed to demonstrate dose distribution to the physician according to their prescription Assists in evaluation Determine source arrangement Treatment Planning Hand Calculations prior to the advent of computers manual systems of planning were developed these systems consisted of tables and rules for implantation still done today to verify doses (although a spread sheet is helpful) Computer Planning Fast Accurate Flexible Easily reproduced 2D - Single transverse plane presented 3D - three dimensional plans show the distribution of radiation around the entire implant. 17

18 CT Planning CT for treatment planning this modality has only recently become important in brachytherapy planning. Prostate implant post-planning real-time dosimetry planning for prostate implants can be used to assist the physician in determining if if applicator is placed properly and what source configuration or dose to allow (limiting structures) 18

19 Old 2D AP Plan Films with all Sources and Ref. Pts. Identified New 2D Plan 19

20 Real-Time Imaging Post-Implant Dosimetry Seed Identification- 5 mm CT scan example 20

21 3-D Dose Clouds but no volumetric target/critical structure dosimetry 21

22 3-D Image Reconstruction 3D Image Set formed from the imported CT Slices Organs of Interest Body Bone Bladder Foley Balloon Bladder Rectum Sigmoid Uterus Applicators Tandem Ovoids Packing (optional) Contouring Streaking Artifacts Ovoids Contoured Applicators Rt. Ovoid Lt. Ovoid Tandem 22

23 3D Sagittal View Uterus Rectum Foley Balloon Applicators Dose Profile Lines Final reconstructed T&O w/ Isodose 23

24 DVHs Duplicating 2-D Planning w/ CT Planning (3D) Base of Tongue Example 24

25 Catheters and Active Lengths Midcut Final 3D/ LAT View 25

26 Initial Planning Images 3D View of Implant Midcut 26

27 2D Endobronchial Treatment 3D Endobronchial Treatment 27

28 CT of Mammosite Balloon Catheter Radiation Safety Special radiation precautions are required when patients are implanted with radioactive material. All Temporary Implant patients are hospitalized and radiation levels are monitored to assure safe levels for personnel attending the patient. The three principle safety rules for dealing with Brachytherapy Patients are: Time Distance Shielding 28