Brachytherapy Flashcards
‘Brachy’ means what?
Short or nearby in Greek
What is brachytherapy?
Radioactive sources are placed into, or in contact with disease.
Delivers high dose to tissues surrounding implanted source.
Advantages over XBRT?
- delivers high dose of radiation to specific volume with rapid dose fall-off to adjacent tissues
- may improve local control of disease
- can target area at high risk for reoccurrence
- reduces toxicity to nearby structures
- can be used for sites that have been previously irradiated
Implantation techniques include…
- Approach to disease
- Dose rate
- Type of implant
Approach to disease:
Interstitial Brachy
“Inter-tissue”
Surgically implanting small radioactive sources directly into target tissue via needles, wires, catheters, or seeds
Ex: Seeds for Prostate cancer
Approach to disease:
Intracavitary brachy
-Places into body cavity via applicator
-Most common application is Tandem, and ovoid implant for cervical cancer
-TEMPORARY
Ex: Cervical Cancer
Approach to disease:
Surface brachy
Placed on/near the tumor using surface black or custom mold
Ex: Melanoma
Approach to disease:
Transluminal brachy
- inserted into a body lumen
- uncommon, but has been used to treat esophageal cancer
Dose rate:
LDR
Low Dose Rate (LDR)
Delivers dose rate of 0.4 - 2 Gy/hour
Treatment times of 24-144 hours
Inpatient procedure
Dose Rate:
HDR
High Dose Rate (HDR)
> 0.2 Gy/min (12 Gy/hour)
Outpatient procedure
Iridium-192
Typical for HDR 0.397 MeV Half life of 73.8 days Seeds HDR IS & IC
Iodine-125
Typical for LDR 0.028 MeV Half life of 59.6 days Seeds LDR IS
Radium-226
Modeled after 0.83 MeV Half life of 1626 years Tubes and needles LDR IC & IS
HDR
Mostly use Iridium-192
Procedure room must be shielded
—> walls and ceiling 4-5 cm of lead or 43-50 cm of concrete
Treatment delivers in few minutes
Iridium replaced every 3-4 months
What is Remote Afterloader?
Use during HDR
Automatically moves radioactive source from storage safe to specific dwell point within implant
Advantages of HDR
+ dose delivered quickly
+ reliable source positioning
+ no exposure to staff
+ although large $ upfront, less expensive over time
Common procedures:
Endometrial Brachy
Usually undergone TAHBSO and upper part of vagina is at high risk of reoccurrence.
HDR brachy delivered to increase dose to upper vagina using vaginal cylinder and IRIDUM-192 sources
Cervical Brachy (general)
Cervix requires high dose of radiation to cure
If delivered by XBRT, tolerance of bladder and rectum would be FAR exceeded (bladder= 65 Gy, rectum= 60Gy, cervix= 100 Gy)
LDR or HDR usually after XBRT
LDR Cervical Brachy
CESIUM-137
Insert tandem and ovoid implant, pack with guaze to stabilize
X-ray for proper alignment
Implant placed and remains for ~2 days while source decays and delivers dose
Fletcher-suit applicator
HDR Cervical Brachy
IRIDIUM-192 Patient under anesthesia, implant placed and attach remote afterloader. Physics programs to move source from shielded storage into implant. Once source has moved to all dwell points, dose delivered, source is retracted. Done multiple times (~5 times) Outpatient basis Tandem and ring applicator
Considerations for Cervical Brachy
- special care with needle implants (avoiding the bladder)
- cysto and rectal exam
- implant is then gauzed Ant/Post to stabilize in place
- long term side effects include Vaginal Stenosis (narrowing and shortening of vaginal canal)
Prostate Brachytherapy (criteria)
- T1-T3 tumors (VERY SMALL)
- No pubic arch interference
- Volume study shows prostate is appropriate size (<60 g)
- PSA < 10 (low risk disease)
- No previous TURP
Prostate Brachytherapy
- May be used definitively or as a boost to XBRT
- Most common source use is IODINE - 125 (LDR)
- Some institutions use PALLADIUM - 103 (LDR)
- Done under general or epidural anesthesia, needles loaded with sees and inserted through template using transrectal ultrasound guidance, seeds are dropped into gland
- # of needles and seeds depends on prostate size (70-100)
Prostate Brachytherapy:
Acute side effects
- Procedural trauma
- Seed migration to lungs
- Urethral irritation
- Urinary issues (frequency, urgency, nocturia, dysuria, retention, incontinence, weakened stream)
- Bowel changes (softer, frequency, abdominal cramping, diarrhea, bloating, urgency, incontinence, bleeding)
Prostate Brachytherapy:
Chronic side effects
- Chronic inflammatory changes to the prostate gland
- Urinary symptoms may persist ~ 2 years post-op
- Erectile dysfunction (occurs in as many as 61% post-seed implant)
- Proctitis 1-2 years post-op
Prostate Brachytherapy:
Safety issues
- No danger to the general public (sources are low energy and absorbed by surrounding tissues)
- Patients should use condoms during sexual relations to avoid seeds being expelled in ejaculation
- Minimize exposure to small children and pregnant women (based on half-life of source used)
Breast Brachytherapy
- Uses IRIDIUM - 192
- May use catheters (LDR) or Mammosite balloon (HDR)
Criteria:
- > 50 years
- Small tumor (greater or equal to 2 cm)
- Negative margins in all direction (at least 2 mm)
- No nodal involvement
Head and Neck Brachytherapy
Intracavitary — Nasal cancers
Interstitial catheters — Tongue, neck cancers
Intraluminal — Trachea, esophageal cancers
Ocular Brachytherapy
- Gold plaque with radioactive seeds is placed on surface of the eye (during surgery)
- Uses IODINE - 125 or PALLADIUM -103
- May prevent enucleation (removal of entire eye)
Lung Brachytherapy
- Vicryl mesh with IODINE -125 seeds placed on the pleural surface
- Endobronchial catheters can be placed during fiberoptic bronchoscopy under conscious sedation
Soft tissue sarcomas Brachytherapy
Interstitial catheters may be used
UNSEALED sources:
Bone metastases
- STRONTIUM - 89 chemical avidly concentrated by areas of high osteoblastic activity
- SAMARIUM -153
Considerations for this procedure:
- body fluids are reactive
- myelosuppression is common side effect
- bone pain can flare up to 72 hours after administration
UNSEALED sources:
Thyroid cancer
- IODINE - 131 pill that thyroid glad absorbs an will accumulate in thyroid cells, where radiation can destroy
Consideration for procedure:
- body fluids are radioactive
- limit time in public places for a few days
- documentation if traveling
General brachy risks
- acute and late toxicity
Any invasive brachytherapy procedures carry risk of:
- perforation
- infection
- bleeding
LDR complications associated with bedrest and catherization:
- thrombophlebitis
- pulmonary embolus
- urinary sepsis
General Radiation safety
- TIME, DISTANCE, SHIELDING
- No more than 30min/24 hours in close proximity to patient while implant is in
- Stay > 6 ft from patient while implant is in
- Lead shielding or screens
For patients:
- minimize contact with small children and pregnant women util source has sufficiently decayed
- flush toiled twice
- no sexual contact until source has sufficiently decayed
- wash hands thoroughly
- wash linens separately
