Background Flashcards
What are the 2 most common types of prostate brachytherapy (BT)?
Most common types of prostate BT:
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 BT monotherapy?
According to the American Brachytherapy Society (ABS) guidelines, low-risk pts (cT1–2a, GS ≤6, PSA <10) are good candidates for LDR BT monotherapy (Davis et al., Brachytherapy 2012). BT also an option for some intermediate-risk pts with more favorable Dz (PSA 10–20 or small-volume GS 7, preferably with primary GS 3).
Why is the presence of seminal vesicle involvement a relative contraindication to prostate BT monotherapy?
Seminal vesicle involvement is a relative contraindication to BT 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 mets, rendering LC potentially less effective.
List the relative contraindications to prostate LDR BT.
Relative contraindications to prostate LDR BT: (Davis BJ et al., Brachytherapy 2012)
- Severe pre-existing urinary outlet obstruction Sx (IPSS >20)
- Previous pelvic RT
- Transurethral resection defects
- Large median lobes
- Prostate gland >60 cc
- Inflammatory bowel Dz
Other relative contraindications: very small prostates (<20 cc) or active acute prostatitis.
Why is a prostate size >60 cc a relative contraindication to LDR prostate BT?
Large prostate volumes >60 cc are considered a relative contraindication to BT b/c they have been associated with a higher rate of post-implant urinary retention and prolonged obstructive urinary Sx. Implantation is also more technically difficult (Davis BJ et al., Brachytherapy 2012). Size is less of a restriction for HDR BT, and experienced LDR brachytherapists can implant >60 cc prostates.
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 ADT. After 6 mos, there is no further volume reduction. 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 2010)
Why is the presence of significant pre-existing urinary Sx a contraindication to BT?
Obstructive and irritative urinary Sx are common after BT, and pre-existing Sx increase the risks and severity of these side effects.
What are the advantages of prostate BT over EBRT?
Advantages of prostate BT 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
- Potential radiobiologic advantage from hypofractionation with HDR BT given the low alpha/beta of prostate cancer
What is the purpose of ADT prior to BT?
The main purpose of ADT prior to BT is to downsize large glands prior to implant, thereby potentially:
- Decreasing urinary Sx post implant
- Decreasing operative time and # of seeds/catheters required
- Decreasing rectal dose d/t smaller gland size
- Decreasing risk of pubic arch interference
Is there an oncologic benefit to adding ADT to BT monotherapy?
Systematic review by Keyes et al. (Brachytherapy 2017) suggested no benefit to adding ADT for low-risk and favorable intermediate-risk pts. Unfavorable intermediate-risk and high-risk pts and those with suboptimal dosimetry may have up to 15% improvement in biochemical recurrence-free survival (bRFS) with 3–12 mos of ADT, although impact on cancer-specific survival is uncertain.
Is there a role for prophylactic alpha-blockers?
Prophylactic use of alpha-blockers does not significantly affect retention rates but does result in significantly faster return of urinary Sx to baseline. (Merrick et al., IJROBP 2002)
