Most of us who have gone through image-guided external beam radiotherapy have had TRUS-guided transrectal placement of gold fiducial markers or radio transponders placed in out prostates. Some who have had salvage radiation have had them placed in the prostate bed. Fiducial placement carries a risk of infection, a risk that may be growing because of increased resistance to fluoroquinolone antibiotics. The procedure is similar to a transrectal biopsy, and carries many of the same risks.
Loh et al. reported the results of an Australian study among 359 patients who had fiducials placed between 2012 and 2013. All patients had received standard prophylactic fluoroquinolone antibiotics. The men were all sent a brief questionnaire within 2 years of the procedure. Responses were confirmed based on patient records. They got a very good response rate (79%) with the following findings:
- · 27% experienced increased urinary frequency and dysuria
- · 11.6% experienced chills and fever
- · 7.7% received subsequent antibiotics for urinary tract infection
- · 2.8% were admitted to the hospital for sepsis
A similar study by Berglund et al. of Calypso radio transponder placement in 50 men reported that 10% had subsequent infections, with 6% going on antibiotic therapy. One patient suffered an epidural abscess that required open debridement and lumbar fusion. One patient suffered a prostate abscess with MRSA.
This rate of infection is higher than what is reported by physicians, which is 1.3% or less, but is consistent with current infection rates reported after transrectal biopsies. Liss et al. reported biopsy-related resistant infections of 8% among men who received only fluoroquinolone prophylaxis and 6% were hospitalized. Almost all of them were found to have fluoroquinolone-resistant infections. Rectal culture of all the men in the study revealed fluoroquinolone-resistant bacteria, predominantly E. coli, in 1 in 5 men. The rate of infection has been steadily increasing. Resistant E. coli infections can cause potentially fatal septic shock and intractable chronic prostatitis.
Loh et al. go so far as to recommend that radiation oncologists forgo the use of fiducials for IMRT (but not for SBRT). They point to a dosimetry study that showed that the difference in prostate localization without fiducials was almost always less than 5 mm. However, it also showed differences could be as high as 1 cm. It is the extremes of motion that fiducial image guidance controls for so well, and it is those extremes that accounts for most of the toxicity.
There are less radical measures that can be taken:
- · Careful screening of patients for previous fluoroquinolone use, major surgeries with antibiotics, hospital workers and their families, diabetes and other comorbidities that may increase risk of infection. Men with a number of previous biopsies, as may happen with Active Surveillance, are especially susceptible.
- · Rectal swab culture for resistant bacteria, and selection of more specific antibiotics based on it.
- · Use of a different class of prophylactic antibiotic, like aminoglycosides, Flagyl, clindamycin, Bactrim, amoxicillin or carbapenems.
- · Applying povidone-iodine to clean the rectum (as in this study).
- · Transperineal fiducial placement carries insignificant risk of infection, but may require a spinal block or local anesthesia.
Patients should raise this concern with their doctors prior to fiducial placement. As someone who got a UTI from fiducial placement, I wish, in hindsight, that I had.