Brachytherapy for Prostate Cancer

Charles H. Matthews and Danny Y. Song

Background

What are the 2 most common types of prostate brachytherapy (brachy)?

Most common types of prostate brachy:

LDR using permanently implanted iodine-125 (I-125) or palladium-103 (Pd-103) radioisotopes.
HDR using temporarily implanted iridium-192 (Ir-192).

Which prostate cancer pts are good candidates for LDR brachy monotherapy?

According to the American Brachytherapy Society (ABS) guidelines, pts with the following values are good candidates for LDR brachy monotherapy:

T1–T2a
Gleason score <7
PSA <10

(Nag S et al., IJROBP 1999)

Name 8 relative contraindications to prostate LDR brachy as monotherapy or as a boost.

Relative contraindications to prostate LDR brachy as monotherapy or as a boost:

Prostate size >60 cc
Severe pre-existing urinary outlet obstruction Sx (International Prostate Symptom Score [IPSS] >15)
Large median lobe
Previous pelvic RT
Multiple previous pelvic surgeries
Severe diabetes
Prior transurethral resection of the prostate gland (TURP)
Involved seminal vesicles

(Nag S et al., IJROBP 1999)

Why is the presence of seminal vesicle involvement a contraindication to prostate brachy monotherapy?

Seminal vesicle involvement is a contraindication to brachy monotherapy b/c seminal vesicles are technically challenging to implant with acceptable dose coverage, and involvement is associated with higher risk of regional spread as well as metastatic involvement of Dz, rendering LC potentially less effective.

Why is a prostate size >60 cc a contraindication to prostate brachy?

Large prostate volumes >60 cc are considered a relative contraindication to brachy b/c they have been associated with a higher rate of postimplant urinary retention and prolonged obstructive urinary Sx. Implantation is also more technically difficult. (Nag S et al., IJROBP 1999)

Is neoadjuvant hormonal therapy (NHT) effective at shrinking prostate size and decreasing the risk of retention?

Prostate volume may be reduced by 25%–40% after 3 mos of androgen deprivation therapy (ADT). It is controversial whether this decreases the risk of urinary retention. A large retrospective series demonstrated that in pts with IPSS scores ≥15, urinary retention occurred in 25% of those not taking NHT vs. 5% in those taking NHT (p = 0.039) (Stone RG et al., J Urol 2009).

Why is the presence of pre-existing urinary Sx a contraindication to brachy?

Obstructive and irritative urinary Sx are common after brachy, and pre-existing Sx increase the risks and severity of these side effects.

What are the advantages of prostate brachy over EBRT?

Advantages of prostate brachy over EBRT:

Decreased integral dose to the pt, particularly to the rectum and bladder, which allows for dose escalation
Simplified targeting of RT (i.e., no issues with setup variation, prostate motion, etc.)
Shorter Tx course

What is the purpose of ADT prior to brachy?

The purpose of ADT prior to brachy is to downsize large glands prior to implant, thereby potentially:

Decreasing urinary Sx post implant
Decreasing operative time and # of seeds required
Decreasing rectal dose due to smaller gland size
Decreasing chance of pubic arch interference

Note: Several large retrospective studies have failed to show that androgen suppression improves cancer control outcomes in combination with LDR brachy.