Workup/Staging

Question 1

What is the purpose of the preimplant volume study in prostate cancer pts being treated with LDR BT?

Answer 1

A volume study is done prior to implant to assess prostate volume and architecture (presence of median lobe size, assessment for pubic arch interference) and to develop a preliminary seed distribution plan for ordering seeds.

Question 2

What is pubic arch interference, and how can it be avoided?

Answer 2

Pubic arch interference is when the needle paths are obstructed by the pubic arch. It occurs more frequently in pts with large glands and affects the ant and lat needles. To evaluate for interference, TRUS can be used to compare the largest prostate cross-section with the narrowest portion of the pubic arch. Other than hormonal downsizing, the use of an extended lithotomy position (Trendelenburg) may also alleviate pubic arch interference.

Question 3

What sources are typically used in LDR prostate BT?

Answer 3

I-125 and Pd-103 are the sources typically used in LDR BT. Cesium-131 (Cs-131) has also been utilized more recently.

Question 4

What are the half-lives of the 3 most common sources used in LDR BT?

Answer 4

Half-lives of the 3 most common sources:

I-125 (60 days)
Pd-103 (17 days)
Cs-131 (9.7 days)