Chapter 23: Prostate Implants
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What are the three radiation therapy treatment options that can be used to treat carcinomas in the prostate? Pg. 481
Treatment options for carcinoma of the prostate include radical prostatectomy (e.g., nerve-sparing surgical procedure), external photon beam irradiation, and brachytherapy implantation.
- 1.) radical prostatectomy.
- 2.) external photon beam irradiation.
- 3.) brachytherapy implantation.
How is the selection of one of the three procedures made for prostate cancer patients? Pg. 481
The selection of a particular procedure or a combination of procedures depends on established prognostic factors such as stage, grade, and pre-treatment prostate-specific antigen (PSA) concentration.
Surgery is indicated if the tumor is confined to the prostate gland with no extension through the capsule or into the seminal vesicles. Implants are used for early-stage cancers, either alone or in conjunction with external beam radiation therapy. Patients with extensive tumors (TNM stage T3 and T4) are not good candidates for implantation.
What are the two types of seed implants and which one is currently gaining popularity? Pg. 481
The two types of seed implants that are used for prostate gland carcinomas are temporary implant and permanent implant.
The temporary implants involve radioisotopes of relatively long half-life and sufficient dose rate to deliver the prescribed target dose in 3 to 4 days. The sources are removed at the end of that period.
In the permanent implant the radioisotope either has a short half-life (e.g. Au-198 , 2.7days(?)) or emits photons of low enough energy that the radiation from the patient poses no significant hazard to persons in the surrounding environment. The sources are left in the patient forever and the prescribed dose is delivered during complete decay of the sources.
Of these two types of seed implants, the permanent implants are gaining more popularity and will be discussed in greater detail.
For early stage prostate cancer, what are two possible radioisotopes that can be used for permanent implants? Pg. 481
Permanent implants with I-125 or Pd-103 are used in the treatment of early-stage prostate cancer as the sole modality or in combination with external beam radiation therapy.
What facilitates the challenge of inserting I-125 or Pd-103 permanent implant seeds into the prostate gland? Pg. 481
The modern technique of implantation consists of a transperineal approach in which the seeds are inserted into the prostate gland with the guidance of transrectal ultrasonography and perineal template.
For prostate cancer patients, what type of imaging modality is used to study the prostate gland volume and also use the image to determine the location of the implantation target? Pg. 482
How are the target outlines from the ultrasound images used for prostate gland treatment planning (treatment system made specifically for prostate gland cancer)? Pg. 483
A treatment planning system specifically designed for prostate gland implants allows the target outlines from the volume study to be digitized into the computer.
What is the prescribed minimum peripheral dose dealt with when treatment planning? Pg. 483
Seed strength can be adjusted to deliver a prescribed minimum peripheral dose (MPD), which is the isodose surface just covering the prostate target volume.
What is one significant problem with permanent implant seeds? Pg. 483
One significant problem is how the size of the prostate gland shrinks following a certain amount/time of exposure to the radiation. Due to that, there is most times a disagreement between the planned dose distributions and the dose distribution of what actually happens. It is challenging in predicting exactly how much, and where there will be a size reduction of the prostate gland.
What is the main reason for the use of temporary implants? Pg. 486
Temporary prostate gland implants have almost exclusively used Ir-192. The treatment is given mainly as a boost to external beam therapy.
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