2/13/12

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

Where?

•  Treatment sites – Bladder – Breast – Brain – Bronchi – Cervix – Eye – H & N – Prostate – Skin

2/13/12

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

How?

•  Interstitial

– Breast

– H & N

– Gyn

How?

Bob Kuske, MD

2/13/12

3

How?

•  Intracavitary – Breast

– Cervical

How?

How?

•  Intralumen –  IVBT

– Endobronchial

2/13/12

4

How?

How?

•  Surface

– Eye

– Skin

How?

2/13/12

5

How?

How?

Brachytherapy Treatments

•  Low Dose Rate vs. High Dose Rate

•  Definitive vs. Boost

–  prostate implant

–  cervical implant

2/13/12

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

2/13/12

7

Orthogonal Films - T&O Applicators

Needles for Temporary Interstitial

MammoSite

2/13/12

8

Inflated balloon Catheter

MammoSite

Vaginal Dome Cylinder

2/13/12

9

Endobronchial catheter

Tracheal or adjustable catheter

Rotterdam Nasopharyngeal Applicator

2/13/12

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.

2/13/12

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

2/13/12

12

2/13/12

13

Remote Afterloading Unit

•  Remote Afterloading Units - these machines have become popular in the last 10 -15 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

2/13/12

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

2/13/12

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

2/13/12

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

2/13/12

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.

2/13/12

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)

2/13/12

19

Old 2D AP Plan

Films with all Sources and Ref. Pts. Identified

New 2D Plan

2/13/12

20

Real-Time Imaging

Post-Implant Dosimetry •  Seed Identification- 5 mm CT scan example

2/13/12

21

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

2/13/12

22

3-D Image Reconstruction

•  3D Image Set formed from the imported CT Slices

Contouring •  Organs of

Interest –  Body –  Bone –  Bladder

•  Foley Balloon •  Bladder

–  Rectum –  Sigmoid –  Uterus

•  Applicators –  Tandem –  Ovoids –  Packing

(optional)

Ovoids

Streaking Artifacts

Contoured Applicators

Tandem

Lt. Ovoid Rt. Ovoid

2/13/12

23

3D Sagittal View

Applicators

Rectum Uterus

Foley Balloon

Dose Profile Lines

Final reconstructed T&O w/Isodose

2/13/12

24

DVHs

Duplicating 2-D Planning w/ CT Planning (3D)

Base of Tongue Example

2/13/12

25

Catheters and Active Lengths

Midcut

Final 3D/ LAT View

2/13/12

26

Initial Planning Images

3D View of Implant

Midcut

2/13/12

27

2D Endobronchial Treatment

3D Endobronchial Treatment

2/13/12

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