Rectal perforation following SpaceOAR placement combined with permanent prostate brachytherapy

Introduction We report a case of rectal perforation following SpaceOAR placement utilized with iodine‐125 low‐dose‐rate brachytherapy for prostate cancer. Case presentation A 65‐year‐old patient with localized prostate cancer underwent SpaceOAR placement following LDR‐BT. No significant issues occurred with the SpaceOAR procedure, and no abnormalities were found on the next day's T2‐weighted magnetic resonance imaging. Two weeks later, a colonoscopy was performed due to mucus stools revealing rectal perforation attributed to SpaceOAR. By maintaining Macrogol 4000 and a low residue diet, the perforation healed within 6 months. Conclusion Rectal ulcers and perforations are the most common severe adverse events from SpaceOAR placement. Effective management strategies are crucial since complications can't be entirely avoided, even with skilled surgeons.


Introduction
The SOAR system (Boston Scientific, Marlborough, MA, USA) significantly reduces ≧G2 rectal AEs when used with IMRT. 1 It is also reported that 98.7% of physicians found the procedure easy despite their initial experience. 1 Our previous report of SOAR with LDR-BT also found that 94% of cases were successfully placed. 2 While the procedure is safe and beneficial for rectal sparing, some cases required surgery due to procedure-related AEs, and some intended RT could not be performed. 3,4We report an early-onset rectal perforation case after SOAR combined with LDR-BT.

Case presentation
A 65-year-old male with an initial prostate-specific antigen of 6.80 ng/mL, Gleason score of 4 + 3, and cT2aN0M0 underwent LDR-BT.The patient had no history of bowel disease.A physician with experience in 560 cases performed the SOAR placement following LDR-BT.The procedure was done without particular issues (Fig. 1a,b).The T2-MRI performed the following day also showed no abnormalities such as RWI (Fig. 1c,d).At a scheduled visit after 2 weeks, the patient reported mucus stools starting on the fourth postoperative day, with no fever or bloody stools.Due to early-onset gastrointestinal symptoms, T2-MRI was done.SOAR infiltration toward the prostate side was seen at the apex, with a slight suspicion of RWI (Fig. 2a), prompting CS.CS revealed extensive ulceration on the anterior wall of the rectum without surrounding vascular inflammation (Fig. 2a), leading to a diagnosis of SOAR-induced ulceration.Multiple physicians reviewed the procedure video; however, there were no clear abnormal findings.A conservative approach was chosen, involving the administration of Macrogol 4000 and a low-residue diet, with monthly follow-up visits and MRI monitoring.Although symptoms worsened most in the first month, limited to mucus stools, there were no signs of inflammation like fever or pain, and blood tests remained normal.No unscheduled visits occurred due to symptom exacerbation.By the second month, SOAR absorption began, with air images suggestive of fistula on T2-MRI (Fig. 2b).By the third month, seeds were visible beyond the rectal wall on CS (Fig. 2c), indicating complete recto-prostatic fistula formation.Although hyperbaric oxygen therapy was recommended, the patient declined due to commuting from a distant location.Mucus stools were reduced in the fourth month.By the fifth month, there was marked improvement in the perforation site on MRI and CS (Fig. 2e).By the sixth month, the mucosal surface had almost fully recovered (Fig. 2f).

Discussion
Despite its simplicity and safety, various SOAR-related AEs have been reported.According to reports using The Manufacturer and User Facility Device Experience database, 3,4 device-related AEs of ≥G2 appear most frequently associated with ulcers or perforations resulting from RWI. RWI cannot be entirely avoided solely through the operator's skill and proficiency.This is because the technique itself involves needle insertion beyond the rectal hump and into the Denonvilliers' thin layer, sometimes under unclear ultrasound imaging.
To the best of our knowledge, there have been seven case reports of rectal ulcers or perforations attributed to SOAR, including ours, up to the present (Table 1).It is anticipated that there will be many more unreported cases.We did not include cases where the onset occurred with symptoms such as abscess formation, and ulcers or perforations developed secondarily.The majority did not happen during the initial experience. 5,6,10The reason is unknown, but our experience was also seen in the 561st case during 617 SOAR procedures.In five reports, early T2-MRI was performed after SOAR procedure to assess the placement.Among these, RWI was suspected in two reports, 9,10 although no findings were detected in the others.In our case as well, no abnormalities were detected on the T2-MRI.We routinely perform T2-MRI the day after SOAR.In two cases, we suspected RWI and performed CS the next day.CS showed no perforation, and the rectal mucosa was normal.Thus, both cases planned LDR-BT plus IMRT, boosted IMRT performed as scheduled, with no significant rectal AEs.RWI without rectal mucosal abnormalities likely allows the safe continuation of planned RTs.Therefore, postoperative MRI is valuable for investigating the presence of RWI, 11,12 and if RWI is detected, performing CS to evaluate the rectal mucosal surface may provide valuable information for safely conducting planned RT.However, early postoperative T2-MRI often does not reveal findings leading to fistula or ulcer formation.Detecting early signs of bowel symptoms, which are less likely with SOAR placement, is important.CS should be performed to check for ulcers or fistulas, and RT should be delayed until healing if these are present.
Furthermore, the problem is that RWI, which can cause perforation or ulcers, is often undetectable during surgery.One factor is the slight mixing of bubbles during gel injection, making the ultrasound image unclear.The case reports listed in Table 1 also indicate a lack of awareness of RWI during the procedure, although some reports mention minor

Fig. 1
Fig. 1 Ultrasound imaging during procedure (a, b) shows no abnormalities.T2-MRI images from the following day (c, d) indicate successful gel placement.

Table 1
8eports of rectal ulcer/perforation following SOAR placement Teh et al.6experienced coagulation during the two-component injection process, indicating the possibility of multiple needle punctures.Similarly, Imai et al.8reported multiple needle punctures.It is most likely that the rectal hump, which is the narrowest part of the puncture route at the apex, is unconsciously being punctured by the needle.A pinhole might form, allowing SOAR to flow into the intestinal wall under pressure.Additionally, the mass effect from SOAR retention may cause localized ischemia, leading to larger perforations.Although our video check showed no abnormalities, the lowest needle often punctures the rectal hump during prior LDR-BT, potentially allowing SOAR infiltration through these tiny holes.ConclusionWhile rare, perforations and ulcers from SOAR can occur.Without infection, deep ulcers can heal conservatively.Early detection and proper management are crucial to prevent additional surgeries or abandonment of RT.