Prostate brachytherapy seed migration to the right renal artery due to right‐to‐left shunting across a patent foramen ovale

The seeds used in brachytherapy for prostate cancer may migrate through the surrounding venous plexus to other sites in the body, most commonly to the pulmonary vasculature.


Background
Seed migration is a common event that occurs after 125I LDB for prostate cancer.Seed migration to the pulmonary vasculature has most frequently been reported.][3][4][5][6][7] The prostate is surrounded by a well-developed venous plexus, and the seed is implanted near or within the vein. 1 Thus, seed migration is thought to be caused by the seeds entering the vessel and circulating through the blood. 8We report a rare case in which a right-to-left shunt due to a PFO caused seed migration to the right renal artery after LDB for prostate cancer.
Seventy-six seeds were placed without complications, one of which migrated into the patient's pelvis.The next day, a follow-up pelvic radiograph indicated that seed had migrated to the right side of the middle abdomen (Fig. 1).CT revealed that the seed had migrated to the right kidney (Fig. 2).Although the exact location of the seed was difficult to determine, we suspected that it was in the urinary tract or renal vasculature.As adverse events due to the seed migration were considered unlikely, we monitored the patient without intervention.One year after LDB, contrast-enhanced CT revealed that the seed had remained in the same area (Fig. 2).The patient had not had an inflammatory response or subjective symptoms.No seed was observed in the ureter upon ureteroscopy.We suspected the presence of a right-to-left shunt causing the seed to migrate into an artery via the systemic circulation.TEE confirmed a right-to-left cardiac shunt due to a PFO (Fig. 3).These results suggested that the seed had migrated into the right renal artery.Three years after treatment, no recurrence of prostate cancer and no adverse events due to seed migration or due to the PFO occurred.

Discussion
LDB is an effective treatment for localized prostate cancer. 9,10The radioactive seeds used in LDB are cylindrical, 4.5-mm long, and 800 lm in diameter. 5They are placed at the periphery of the prostate, the most common area for prostate cancer.The surrounding blood vessels are large enough to accommodate hematogenous migration of the seeds to other sites. 1 In one study, one or more seeds were identified upon chest radiography in 55% of patients who underwent prostate brachytherapy. 3 Therefore, patients undergoing brachytherapy must undergo radiography.Even so, migration to the lungs may be missed in 10-15% of cases when chest radiographs alone are used to confirm migration. 11CT is reportedly very useful in detecting migrated seeds in the chest but may cause overexposure, as additional CT is needed if the seed causes an adverse event. 126][7] Although the probability of adverse events due to seed migration is very low, the seed migration site should be carefully monitored for such events.Previous reports of seed migration to the lungs, pelvis, heart, mediastinum, kidney, inguinal canal, liver, urinary tract, and sacrum after brachytherapy have been published.Most cases are asymptomatic.However, various adverse events caused by seed migration have been reported.Nguyen et al. 6 reported cases of back pain and asymptomatic gross hematuria due to seed migration into the renal artery.In addition, Chen et al. 13 reported a case of stone formation due to seed migration into the bladder after brachytherapy.As determining whether the seed migrated to the renal vasculature or urinary tract is challenging when using only contrast-enhanced CT, we performed ureteroscopy in this case for confirmation.We considered the possibility of excision if the seed had migrated into the urinary tract.
Migration of a single seed does not affect the dose covering 90% of the prostate volume (D90), but migration of two or more seeds reportedly decreases the D90 (Gy) value and the percentage of the prostate receiving 100% of the prescribed dose compared with no seed migration. 8However, the differences in radiation dose owing to migrated seeds are reportedly very small and have little impact on treatment outcomes. 12eed migration into the coronary arteries or the systemic circulation may be caused by a right-to-left atrial or  ventricular shunt. 14In this case, as the seed had migrated into the right renal artery, we assumed that the seed had migrated through the systemic circulation without passing through the pulmonary circulation, and thus a right-to-left shunt due to a PFO was suspected and confirmed.A PFO is a valve in the interatrial septum that allows the shunting of blood or thrombotic material between the atria.Options for the diagnosis of a PFO include transthoracic echocardiography, TEE, and transcranial Doppler ultrasonography.In a pooled analysis of autopsy studies, the mean prevalence of PFOs was 26% (range: 17-35%), with no pathologic association in the vast majority of cases. 15Most people with a PFO remain asymptomatic and do not require treatment.However, PFOs can cause a paradoxical thromboembolism to form in the veins and move into the systemic circulation.In a recent study of 61 patients, a PFO was discovered in 45% of those with cryptogenic stroke. 16Treatment options for secondary stroke prevention in the presence of a PFO include antiplatelet therapy, anticoagulation therapy, and percutaneous device closure. 17Rare cases of seed migration to the coronary artery, right ventricle, and right renal artery have been reported [5][6][7] ; however, to our knowledge, this is the first report demonstrating that a right-to-left shunt due to a PFO might have caused seed migration to the right renal artery, which strongly supports the hypothesis of previous report. 6If the seed migrates into an artery of the circulatory system, a pulmonary arteriovenous malformation or right-to-left cardiac shunt should be suspected.PFO closure is recommended for secondary prevention of cryptogenic stroke. 18,19This patient did not undergo PFO closure as he had no history of cerebral infarction.However, considering that the seeds entered his systemic circulation, he has to be carefully monitored for the occurrence of paradoxical cerebral embolism through the PFO in the future.Diagnosis of cryptogenic stroke can be difficult in clinical practice, and an awareness of the history of arterial embolism through a PFO is important as it may promote the early and appropriate diagnosis of the disease.
In conclusion, arteriovenous malformations and a right-toleft shunt should be suspected if a brachytherapy seed has migrated to an artery of the systemic circulatory system.

Fig. 1
Fig. 1 Pelvic radiograph revealing that a seed (yellow arrow) had migrated to the right side of the patient's middle abdomen.

Fig. 2
Fig. 2 CT (a) immediately after and (b) 1 year after LDB, revealing that the seed had migrated to the right kidney.