The content in this “Frequently Asked Question” section is for informative purposes only. DxTx Medical is not engaged in rendering medical advice or recommendations. Please refer to the respective Instructions for Use or Operators Manuals for detailed information about use, indications, and contraindications of these products. There is no substitute for your professional judgement when deciding a course of action to treat your patients.
View common questions about radiation therapy with an Endorectal Balloon.
According to PI-RADS 2.1 “When integrated with external (surface) phased array coils, endorectal coils (ERCs) increase SNR in the prostate at any magnetic field strength. This may be particularly valuable for high spatial resolution imaging used in cancer staging and for signal deprived sequences, such as DWI and high temporal resolution DCE.”
In addition, “ERCs can also be advantageous for larger patients where the SNR in the prostate may be compromised using only external phased array RF coils.”
Generally speaking, mpMRI with ERC can be used in prostate cancer detection, localization and staging for treatment planning.
“With some 1.5T MRI systems, especially older ones, use of an ERC is considered indispensable for achieving the type of high-resolution diagnostic quality imaging needed for staging prostate cancer.” (PI-RADS 2.1)
According to Lee, the use of an ERC can increase quantitative and qualitative image quality in T2 weighted imaging and diffusion weighted imaging at any field strength when compared to no-ERC. An ERC can
When compared to non-ERC, use of an ERC can increase
Accepted guidelines do not currently support substitution of mpMRI for core biopsy in all cases. However, due to relatively high sensitivity and PPV, mpMRI can serve to provide road-mapping for targeted biopsy, therefore helping to avoid less specific random biopsies. mpMRI is particularly well suited to provide diagnostic images of peripheral and transition zones as well as potential extra capsular extensions.
Although further research is necessary, one single center, single arm prospective trial indicates “that 1-year confirmatory biopsy may be omitted with minimal risk to patients in AS protocols where magnetic resonance-targeted + saturation template biopsy was performed at baseline.” (Doan, 2022)
Endorectal coil imaging significantly reduces motion artifacts. However, the inflated balloon can produce geometric distortions of the prostate. There is a risk of other artifacts such as aliasing, ghosting, or blurring as well as susceptibility artifact when the coil is inflated with air, all of which can be avoided or reduced with careful planning and use of the eCoil system.
Your patients may initially hesitate when hearing about imaging with an endorectal coil. This hesitation may be more likely based in the feeling of embarrassment rather than the fear of a painful experience. Imaging with the eCoil has shown to be well tolerated by patients, at most causing moderate discomfort. When you explain the advantages of eCoil imaging, i.e., the potential to allow more accurate diagnosis, your patients will most likely embrace the procedure.
The use of topical analgesic gel may be indicated for patients with sensitivities other than those contraindicated for ERC use.
The use of the endorectal coil does not add time to the actual imaging procedure. In comparison, imaging with body coil or pelvic phased array coil alone may require longer sequences in order to achieve equal SNR and image quality especially in DWI and other sequences with inherently low SNR.
The endorectal coil contributes relatively little time to the overall procedure as part of general patient preparation and positioning (in the order of a few minutes).
The ERC is a single patient, single use disposable device that adds minimal expense to the overall imaging procedure expense. The coil is not separately reimbursed.
The ERB is inserted into the rectum of the patient, inflated, and securely positioned using the insertion depth markers and the migration stopper on the shaft. The inflated balloon restrains the movement of the prostate and displaces predominantly the lateral and posterior walls of the rectum and any rectal content. The passive venting feature allows rectal gas to escape further reducing the potential of involuntary prostate motion.
Radiation therapy technology has made fantastic strides in improving lesion targeting. Unfortunately, the prostate remains a “moving target” based on ventilatory movement and bladder motion, bowel peristalsis, and presence of rectal gas. The ERB stabilizes the prostate and surrounding anatomic structures and the passive venting feature continuous removes rectal gas thus significantly reducing intra-fraction motion of the prostate. These features allow for narrow PTV margins compared to non-ERB.
The ERB creates a reproducible rectal volume, removing large parts of the rectum and anus out of the intermediate to high radiation zones. Studies have shown that longer balloons with larger fill capacity (>60ml) have an enhanced rectal sparing effect compared to smaller balloons. Although the balloon can be filled with various media including air, distilled water, saline, or CT Barium, filling it with air for X-Ray based radiation therapy may confer additional rectal wall dose reduction at the air tissue interface. It is hypothesized that in small areas of high dose exposure, rectal mucosal regeneration is faster when they are surrounded by areas of low dose exposure.
Insertion, inflation, and positioning of the ERB adds minimal time to the overall procedure, typically less than 3 minutes. Daily prostate positioning verification has become common place and should certainly include balloon positioning.
Tight CTV to PTV margins and dose escalation demand rigorous tracking and realignment practices during radiation therapy which can increase the workload of the radiotherapist. The prostate stabilizing effect of the ERB has the potential to reduce the need for table corrections and repositioning, in turn causing fewer treatment interruptions and decreasing the radiotherapist’s burden of work.
The ERB can significantly reduce intra-fraction motion of the prostate. Despite consistent balloon fill volume and insertion depth, inter-fraction motion is not significantly affected by the balloon but can be impacted by bladder filling, as well as stool and gas in the rectum. Therefore, patient bowel and bladder preparation are important. Additional positioning techniques such as implanted fiducial markers or online imaging provide further opportunity to reduce PTV margins for dose escalation.
The prostate stabilizing and rectal sparing effect of ERB has been shown to provide similar benefits with various radiation therapy technologies starting with early 3D-RT systems, through IMRT and IGRT, SBRT, and proton therapy. Typically, the balloon is filled with air for X-Ray based radiation therapy and water for proton therapy. In general, the balloon can be filled with air, distilled water, saline, and CT Barium.
Besides therapeutic success clinicians are rightfully concerned with patient comfort during treatment. ERBs have been in use for more than 30 years and during this time have been shown to be well tolerated by patients. Retrospective analyses of patient records demonstrate that 97-99% of patient’s tolerate daily balloon insertion throughout their entire treatment period (Bastasch 2006 and Ronson 2006).
Patients will likely feel some pressure in their rectum and bladder when the balloon is inserted and inflated. Typically, this feeling will subside within minutes. For some patients it may be necessary to limit the balloon inflation volume or use topical analgesic such as lidocaine jelly unless contraindications prevent ERB use entirely.
Similar to ERBs, hydrogel spacers are effective in reducing the radiation dose to the rectum by increasing the distance between the prostate and the rectal wall during radiation treatment of patients with localized prostate cancer. The final results of a phase III clinical trial indicate that the spacer does not significantly improve short term rectal toxicities and urinary incontinence versus control. However, the device appears to indicate that the functional performance translates into clinical benefits of reducing long term toxicity effects of prostate radiation therapy and returning bowel and urinary QoL to pretreatment levels versus control.
Injection of the hydrogel into the perirectal space requires a separate outpatient procedure typically performed by the urologist incurring significant cost. The procedure is performed multiple days before the start of radiation therapy to allow any swelling or inflammation to subside. Due to their placement in the perirectal space, hydrogels may not be ideal for patients with posterior extra capsular extensions since the gel could infiltrate tumor cells. This danger does not exist for endorectal balloons because they are isolated within the rectum. Spacer gels are made of bioresorbable material that may lose shape over the period of radiation treatment.