QM in XRT for brachytherapy QA

What are the common materials for interstitial applicators?

-Large bore needles -Nylon afterloading catheter -Metal buttons -Plastic buttons

What are the 7 photon emitting radioisotope sources and their half-lives for brachytherapy?

1) 226 Radium - 1622 years 2) 137 Cesium - 30.23 years 3) 131 Cesium - 9.7 days 4) 192 Iridium - 74 days 5) 198 Gold - 2.7 days 6) 125 Iodine - 60 days 7) 103 Palladium - 17 days

What are the 8 most commonly used isotopes and their half-lives?

1) 226 Radium - 1622 yrs 2) 60 Cobalt - 5.27 yrs 3) 137 Cesium - 30 yrs 4) 192 Iridium - 73.83 days 5) 125 Iodine - 59.4 days 6) 103 Palladium - 16.99 days 7) 198 Gold - 2.7 days 8) 222 Radon - 3.82 days

What are the 3 beta emitting radioisotope sources and their half-lives for brachytherapy?

1) 90 Strontium - 28 years 2) 90 Yttrium - 64.2 hours (2.67 days) 3) 32 Phosphorus - 14.3 days

What are the 4 disadvantages of HDR?

1) Afterloaders are expensive 2) There is an increased maintenance cost 3) May need more room shielding 4) Needs more staffing

What are the 2 ways of using this technique?

1) Applicators or catheters are placed in the patient, and treatment is delivered after the plan is devised and sources are readied 2) Sources are placed manually into applicators or catheters by physician, and after treatment is given the sources and applicators are removed

What are the 6 things 32 phosphorus is used for?

1) As a liquid in a balloon 2) As wire in an intravascular brachytherapy delivery system 3) Infused by catheter into the abdominal cavity or the linings around the lungs 4) To treat fluid accumulation in cavities which can occur from some cancers that start in the ovary or lungs 5) It can also be injected directly into certain tumors 6) For limited depth of penetration

What are the 3 three things that caused a comeback for brachytherapy?

1) Discovery of man-made radioisotopes and afterloading techniques 2) Newer imaging modalities and more sophisticated RTP systems 3) The use of brachytherapy for non-malignant diseases (vascular restenosis)

What are the 5 advantages for brachytherapy?

1) High concentration of dose distribution around the source 2) Rapid fall off of dose around the source (inverse square) 3) Accurate location of tumor 4) Good immobilization of treatment area 5) Eliminates any set up inaccuracies

What are the 7 reasons that make HDR more convenient than LDR?

1) Less time to treat (5-10 min) so patient stay is less 2) Less space is required to house the unit and don't have to have special hospital room for overnight stays 3) Less expensive due to patient being an outpatient 4) Similar outcomes than LDR 5) Can be given on a fractionated outpatient basis 6) Less radiation dose to medical personnel 7) Treatment techniques are more consistent

What are the 3 disadvantages for brachytherapy?

1) Placement of the source usually requires surgery 2) It requires a skilled radiation oncologist to place sources 3) Handling of radioactive sources

What and where is the source(s) for temporary implants?

192 Iridium is used in areas where there is no body cavity or orifice like the breast and chest wall

What are the 2 sources most commonly used for HDR and why?

192 iridium or 60 cobalt because of the their high specific activity and ability to produce a gamma ray with sufficient penetration

What is the neutron emitting radioisotope source and half-life for brachytherapy treatment?

252 californium with a half-life of 2.6 years

What is 137 cesium's HVL and what does it emit?

5.5 mm Pb and emits 0.662 MeV photons

What are the properties of 192 iridium?

95% decays by beta emission, its average energy is 0.38 MeV, and its HVL is 2.5 mm Pb

What is the decay formula?

An = Ao e- ^ (0.693/t ½)t

What is the SI (systeme internationale) units of activity for brachytherapy?

Bq = one disintegration per second

What are the 3 newer imaging modalities that allow for increased accuracy and superior optimized dose distribution?

CT, MRI, and US

What is the traditional units of activity for brachytherapy?

Ci = 3.7 x 10 disintegration per second (measured from 1 gram of radium)

Interstitial brachytherapy is used in the treatment of what tumors?

H&N, breast, prostate, and soft tissue sarcomas

What and where are the sources for permanent implants?

Iodine-125, palladium-103, and gold-198 in the pelvis, abdomen, or lung

What are the two treatment techniques for brachytherapy?

Low dose rate and High dose rate

Brachytherapy is defined as

Radiotherapy in which the source of radiation is placed close to the surface of the body or within a body cavity

What are the energies for 226 radium?

Range from 0.184 to 4.78 MeV with an average energy of 0.83 MeV - Alpha 4.78 MeV (94.5%), 4.61 MeV(5.55%) - Gamma 0.186 (3.5%)

What are preloaded needles?

Same as mick applicator but slightly more accurate

How does seed implants for permanent brachytherapy work?

Small radioactive sources are placed directly in the targeted tissue where they are left to deliver a dose to the tumor over a period of several weeks or months until complete decay (usually for prostate)

How is activity defined in brachytherapy?

The intensity of a radioactive source, strength of a source, or the rate of decay or change in the number of atoms in a certain material over a given amount of time.

What led to the decline in brachytherapy towards the middle of the century?

The use of high voltage teletherapy for deep seated tumors and the problems associated with exposure from the radionuclide's

What is the VariSource HDR unit?

a device that enables doctors to place radioactive sources directly into a tumor for irradiation "from the inside out"

What is the mick applicator?

a device that has a magazine of radioactive seeds and is used for permanent seed implants

What is a volume study?

a simple procedure which requires placing the ultrasound probe into the rectum and taking a series of pictures

How is 90 strontium produced?

as a by-product of the fission of uranium and plutonium in nuclear reactors and in nuclear weapons

Why is the volume study important?

because it is the first step in a prostate implant where an ultrasound is studied to help determine whether seed implantation is technically appropriate and to help plan the implant

Why is 192 Ir prefered over other sources?

because of its to small diameter of 1mm - a larger diameter limits the application of HDR to intracavitary pelvis and intraluminal esophagus

Why does brachytherapy use the inverse square law?

because the sources are placed in the target area

What is LDR brachytherapy?

brachytherapy that is delivered in a conventional low dose rate regimen that lasts several days and requires a hospital stay with a dose rate of under 2 Gy/hr

How does 103 palladium decay?

by electron capture to excited states of Rhodium-103 followed by characteristic x-ray emission

How is the free hand technique with a sealed end used?

catheters are sewn in place with chromic catgut sutures 1-2 cm apart in multiple or single planes during surgery and buttons are placed on the catheters by the skin surface (the number of catheters are determined by tumor size)

What is another name for 32 phosphorus?

chromic phosphate

What are the types of templates?

either Syed-Neblett or Universal Martinez brands and each has a number of variations depending on the cancer being treated

When is the free hand technique with a sealed end used?

for tumors in the thoracic or abdominal cavities when the tumor is only accessible from one side.

When is the through and through technique used?

for tumors of the skin, breast, or neck when both sides of the tumor are accessible

What 2 ways can interstitial brachytherapy be applied?

free hand or with a template

How and when was radioactivity discovered?

in 1896 Henri Becquerel found that uranium produced a black spot on photographic plates that had not been exposed to sunlight.

How and when was radium discovered?

in 1898 the Curie's extracted Polonium from Uranium ore and later that year extracted Radium

What began the start brachytherapy treatment?

in 1901 when they suggested to insert a small radium tube into a tumor

How is interstitial brachytherapy used?

in treatment of the breast, neck, prostate or soft tissue, as the sole form of radiotherapy, or it may be combined with external radiation

What is the disadvantage of 192 Ir?

it has a half life of 74 days so the source has to be replaced every 3 to 4 months

Which decay series is 226 radium a part of?

it is a radioactive decay product in the uranium-238 decay series and is the precursor of radon-222

What are the 2 facts we know about 137 cesium?

it is the most common radioactive form of cesium and the biological half-life of cesium isotopes is short so they get excreted in urine fairly quickly

What is 192 iridium?

man-made radioactive element formed by non-radioactive iridium metal in a nuclear reactor

How is 103 palladium produced?

produced in a nuclear reactor or in a cyclotron by proton bombardment, maybe from 102 palladium, and is man-made

How does seed implants for temporary brachytherapy work?

radioactive sources are placed in or next to a target volume for a limited amount of time before they are removed from a patient

What is 125 iodine used for in brachytherapy?

seeds are encapsulated in 0.05 mm of titanium used as temporary or permanent implants, as tracer in thyroid studies and as therapy in hyperthyroidism when liquid, and used in bioassays

How is remote afterloading done?

sources are inserted and removed from the applicator through some type of source transportation device

How is afterloading done manually?

sources are manually inserted and removed from the applicators

What did these early experiences reveal?

that radiation caused cancers to shrink

What are the 4 brachytherapy tumor sites where a source can be placed near or in the tumor accessible via needles or catheters?

the breast, head and neck, prostate, and skin

What is HDR brachytherapy?

the delivering brachytherapy on an outpatient basis where the actual treatment delivery lasts about 5 to 10 minutes and the dose rate is more than 12 Gy/hr

How is interstitial brachytherapy defined?

the implantation of radioactive sources (usually in the form of rigid needles or tubes) directly into a tumor or tumor bed

What is the concept of the inverse square law?

the intensity of radiation reduced by the square of the distance from the source

What is the afterloading technique for brachytherapy?

the source is placed in the applicator after the applicator is placed in or on the patient and can be done manually or remotely

What is the preloading technique for brachytherapy?

the source is placed in the applicator before the applicator is placed in or on the patient

What is the Intraluminal brachytherapy treatment technique?

the technique where sources are placed inside body tubes like the esophagus bronchus, and trachea

What is the intracavitary brachytherapy treatment technique?

the technique where the sources are placed inside a body cavity through an applicator (ei cervical treatment)

Brachytherapy refers to

the therapeutic use of encapsulated radionuclide's within or close to a tumor

How is half-life defined in brachytherapy?

the time period in which the activity decays to one half its original value

What are the 4 brachytherapy tumor sites where a source can be placed near or in the tumor of body cavities?

the uterus, vagina, esophagus, and bronchus

How are templates placed?

they are sewn to the perineum in the operating room under general anesthesia sewn to the perineum and remain in place until treatments are completed (typically 3 to 5 days)

what is unique about the isotopes used for permanent implants?

they have shorter half=lives

What is the rule for visitors of patients receiving LDR brachytherapy?

they should only remain in the patient's room for 20 minutes per visit per day

How is temporary brachytherapy usually administered?

through the afterloading technique

what is the goal of brachytherapy?

to conform the radiation dose to the size and shape of the target, and limit side effects by sparing the surrounding healthy anatomy

Why would metal buttons be used?

to prevent the catheter from slipping

What are 2 reasons for using plastic buttons?

to separate the skin from the metal button and to prevent electron scatter (from the metal button) to reach the skin

When is the loop technique used?

to treat tumors of the oral cavity particularly the base of the tongue

How is 182 iridium used in brachytherapy?

used as an LDR temporary implant or as an HDR source, used especially in the head & neck and breast, produced in wire form, introduced through a catheter to the target area, and after being left in place for the time required to deliver the desired dose the implant wire is removed

When is the intravascular brachytherapy treatment technique used?

used to be used to reduce the rate of restenosis after angioplasty and stent placement but is now limited and reserved for select recurrent cases

How was 252 californium used in brachytherapy treatments?

used to determine the health bones by the radiation it gives off when it is injected into the body (deposits it in the bone) and also used to treat ovarian and cervical cancers

What is the Interstitial brachytherapy treatment technique?

when radioactive sources are placed directly into the tumor or tumor bed (permanent or temporary)

What is the topical or surface brachytherapy treatment technique?

when sources are placed on top of the area to be treated

How is the template used for interstitial brachytherapy?

when the accuracy of seed placements is extremely important like for prostate, vagina, and rectum cancers, it is typically used for permanent seed implants with a rigid stainless steel needle rather than flexible catheter

What is the main difference between temporary and permanent brachy?

while temporary implants can be after-loaded permanent implants can not and must be hot loaded

What is the process of permanent interstitial brachytherapy?

•A gun-type applicator with a long hollow insertion needle is used to insert sources •The needle is pushed through the skin into the deep tumor using CT guidance •The sources are inserted into the tumor •The needle is withdrawn 5 to 10 mm •The next source is inserted •Steps are repeated until the desired length and number of sources are applied

How is the decay formula calculated?

•Ao is the original known activity •An is the current activity •t ½ is the half life •t is the length of time passed since the time of known activity •e = the base of natural logarithms

What do we know about 90 strontium?

•Emits a beta particle as it decays to 90 yttrium •90 Strontium behaves chemically like calcium because it also tends to concentrate in the bones and teeth •Differs from 89 Strontium which is used for metastatic bone lesions (half life of 50.57 days)

What is the process of temporary interstitial brachytherapy?

•Hollow stainless steel needles pushed through the tissues to accommodate catheters •Tubes are 1 cm apart using several planes depending on tumor size •Catheters are placed in the tubes before they are removed •When tubes are removed the catheters are left in place for dummy sources (non-radioactive seeds that can be visualized by x-rays) •Sources are a guide for placement of radioactive seeds used for treatment planning purposes •When plan is complete dummy sources are removed so radioactive sources can be placed in their spot

What is 252 californium and its decay scheme properties?

•It is a man-made isotope that is produced in nuclear reactors •Alpha decay (97%) •Fission (3%) •Average neutron energy of 2.15 MeV •Average photon energy of 0.8 MeV

How is 198 gold used in brchy therapy?

•Not commonly used in US as a brachytherapy source •Small seeds or gold "grains" •Suitable for permanent implants (prostate) •Can be used for HDR procedures

How is 198 gold produced and what are its properties

•Produced by neutron activation in a reactor •Near monoenergetic photon emission •0.412 MeV •HVL of 2.5 mm Pb

How is 125 iodine produced and what are its properties?

•Produced in a nuclear reactor by electron capture to an excited state of Te-125 followed by characteristic x-ray emission •Has an average energy of 0.028 MeV •HVL of 0.025 mm Pb

What sources are used for the preloading technique?

•Radium-226 needles •Cesium-137 needles •Iodine-125 eye plaques •Strontium-90 eye applicators

How is the through and through technique used?

•The large bore needle is inserted through the skin into the tumor and exits through the skin on the opposite side •The catheter is then passed through the needle and the needle removed •The process is repeated until the tumor is adequately covered •Both ends of the catheter are stabilized with metal and plastic buttons

How is the loop technique used?

•Two large bore needles are inserted through the neck into the oral cavity on opposite sides of the tumor •A single catheter is threaded through one needle and redirected down the second catheter •The needles are removed leaving the catheter lopped around the tumor (catheters are typically spaced 1-1.5 cm apart) •Both ends of the catheter are stabilized with metal and plastic buttons •The ends of the catheter are cut off with at least 4 cm extending beyond the metal button

How is 90 yttrium used?

•in the treatment of metastatic liver cancer and as an integral constituent of the insoluble glass microspheres in TheraSphere®

What do we know about 131 cesium?

•is is an extremely new isotope first introduced at ASTRO in 2005 •it has photon energies of 4-34 keV and an average energy of 30 keV •It was used in brachytherapy for prostate cancer in 2004

What are the properties of 90 yttrium?

•it is a pure beta emitter •it decays to stable zirconium 90 •its average energy is 0.9367 MeV •its maximum energy is 2.27 MeV

What is 32 phosphorus and its properties?

•one of the most commonly used radioactive substance used in biomedical research •decays to S-32 (stable) by beta emission •maximum energy of 1.7 MeV •average beta energy of 0.69 MeV

How is the mick applicator used?

•the needle is inserted into the prostate •when positioning is correct a plunge releases a single seed into the prostate •external ruler allows the needle to be retracted •allow some distance before a second seed is deposited •applicator allows practitioner to make quick adjustments to seed loading to achieve the best treatment plan