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When trying to treat the target volume for IVBT at the region of angioplasty, why is the dose distribution so highly conformal and significantly reduces radiation to surrounding tissue? Pg. 491
The reason is due to the severity of the inverse square falloff of the radiation at short distances, which in result produces highly conformal dose distribution, in result delivering a high dose to the arterial wall while sparing surrounding normal vessels or mycocardium.
What are the specific requirements that AAPM has for the depth of dose prescription for intracoronary irradiation and for peripheral arteries? Pg. 491
The depth of dose prescription for intracoronary irradiation is recommended by AAPM to be 2 mm from the center of the source and for the peripheral arteries 2 mm beyond the average lumen radius.
Intravascular brachytherapy techniques may be classified into two categories: temporary implants (sealed sources or liquid-filled balloons) and permanent implants (radioactive stents). Each method has its advantages and limitations but which is the most commonly used and why? Pg. 491
The catheter-based sealed source is the most commonly used method of treatment. It is the preferred method because of its better control of dose delivery.
What are the three typical dosimetric requirements for a temporary intravascular implant? Pg. 491
- 1.) to deliver a target dose of 15 to 20 Gy to a 2- to 3-cm length of the arterial wall involved at a radial distance of about 2 mm from the source center.
- 2.) to minimize the dose to tissues outside the region of angioplasty.
- 3.) to take as little time as possible for completion of the procedure, that is, provide target dose rates on the order of 5 Gy/min or greater.
What type of radionuclides come fit the typical three typical dosimetric requirements for a temporary intravascular implant? Pg. 491
Those three typical dosimetric requirements suggest the suitability of high-energy beta sources such as Strontium-90, Yttrium-90, and P-32 or high-activity gamma sources such as Ir-192. The latter could be an HDR afterloading unit with the source dimensions small enough to allow intravascular brachytherapy.
The radionuclides used to meet the typical three dosimetric requirements for a temporary intravascular implant has its advantages/disadvantages. What are they for beta and gamma ray sources? Pg. 491
The beta sources have several advantages over gamma sources:
- 1.) higher specific activity.
- 2.) higher dose rate.
- 3.) longer half-life.
- 4.) greater radiation safety for the patient as well as personnel.
The major disadvantage of beta sources however is:
1.) the extremely rapid radial dose falloff within the target region.
The advantage with gamma ray (Ir-192) sources are:
1.) provides relatively more uniform target dose, governed primarily by the inverse square law falloff with distance.
The disadvantage with gamma ray (Ir-192) sources are:
- 1.) requires high activity to yield a reasonbly high dose rate (> or = to 5 Gy/min).
- 2.) due to the necessary high dose rate, shielding becomes even more important but it is expensive to implement.
List five IVBT treatment radiation systems.
- 1.) Cordis CHECKMATE.
- 2.) Guidant GALILEO.
- 3.) Novoste Beta-Cath.
- 4.) Beta-Emitting Liquid-filled Balloon.
- 5.) Radioactive Stents.
What are the three main components of the Cordis CHECKMATE IVBT radiation system? Also, what source does it mainly use? Pg. 492
- 1.) a nylon ribbon containing an array of Ir-192 seeds.
- 2.) a delivery catheter.
- 3.) a ribbon delivery device.
What type of radioactive source does the Guidant GALILEO system use? And what are the major advantage/disadvantage of this system? Pg. 494
The Guidant GALILEO System uses a beta-source, P-32, for intravascular brachytherapy.
The major advantages of the system are the centering capability of the delivery catheter, automation of the afterloader, and availability of the treatment-planning system.
The major disadvantage is the rapid dose falloff radially, which is a characteristic of all the beta sources.
What type of radioactive source does the Novoste Beta-Cath system use and what type of device is it? What are its two main systemic components? Pg. 494
The Novoste Beta-Cath System uses beta sources of Sr-90/Y-90. It is a manual afterloader device with a catheter-based delivery system. The system consists of two main components:
- 1.) a transfer device for housing and hydraulic delivery of a radiation source train.
- 2.) a deliver catheter to transport the source train.
What are the advantages/disadvatanges of the Novoste Beta-Cath system? Pg. 494
Major advantages of the Novoste system is its use of the Sr-90/Y-90 source, which is one of the highest-energy beta emitters with a long half-life (28 years). Other advantages include high dose rate (treatment time approximately 5 minutes), patient and personnel safety, and simplicity of the handheld transfer device. The major disadvantage is the lack of a catheter-centering device, which could result in extreme dosimetric hot and cold spots within the target volume.
Out of the five different radiation delivery systems used for IVBT, which of them use catheters? Pg. 494
- 1.) Cordis CHECKMATE.
- 2.) Guidant GALILEO.
- 3.) Novoste Beta-Cath.
Which system inflates the balloon dilation catheter with beta emitting radioactive liquid instead of using catheter-based wire and seeds? Pg. 494
The Beta-Emitting Liquid-filled Balloon.
What are the advantages of using a liquid filled balloon (Beta-Emitting Liquid-filled Balloon system)? Pg. 494
The advantages of a liquid-filled balloon are inherent source centering and dose uiformity to the vessel wall. Several beta-emitting isotopes such as P-32, Y-90, and Re-188, which can be obtained in a liquid radiopharmaceutical preparation, may be used in this technique.
What are the major disadvantages of using beta-emitting liquid-filled balloons? Pg. 494
- 1.) higher ratio of surface/adventitial dose compared to the catheter based gamma-source systems.
- 2.) the possibility, although remote, of balloon rupture and consequently leakage of radioisotope within the patient.
What reference distance for dose calculations of IVBTs does the AAPM recommend? Pg. 496
As discussed in Chp. 15, the reference distance r_o in conventional brachytherapy is 1 cm. For intravascular brachytherapy, the AAPM recommends r_o = 2 mm.
What best measures the dose distribution around intravascular brachytherapy sources and why? Pg. 497
Dose distribution around intravascular brachytherapy sources is best measured by film dosimetry. Because of the high dose rate and steep dose gradients near the source, the film must have very thin emulsion, slow speed, and high resolution. Radiochromic films meet these rquirements and are the detectors of choice for measuring dose distribution around brachytherapy sources in a contact geometry.
Read pages bottom-497 to 499 before exam.