In 2021 it is estimated that there will be 248,530 new cases of prostate cancer.
Treatment options for prostate cancer are broad and based primarily on the risk category
of prostate cancer as well as the life expectancy of the patient. For patients with
intermediate and high-risk prostate cancer, there are a multitude of treatment options
including radical prostatectomy, external beam radiation, brachytherapy, a combination of
external beam and brachytherapy, and with strong consideration of androgen deprivation
therapy (ADT) for patients receiving radiation who have higher risk disease. Furthermore,
external beam radiotherapy can be delivered in a variety of dose / fractionation
schedules, such as conventionally fractionated courses over 8-9 weeks, moderately
hypofractionationed courses over 4-6 weeks, and stereotactic body radiation therapy
(SBRT) over just 5 treatments. Since the prostate location is variable and dependent on
rectal and bladder filling, on any given treatment day the prostate may shift > 1cm
relative to bony anatomy. A current state of the art image guided radiotherapy (IGRT)
includes the use of cone beam CT (CBCT) for alignment of the prostate based on internal
3D anatomy. Since this technology lacks soft tissue contrast, the implantation of at
least three non-colinear fiducial markers in the prostate is commonly utilized to help
with daily IGRT to reproducibly align the prostate for radiotherapy. The use of three
fiducials ensures that alignment of the three points at the time of CBCT accurately
triangulates the location of the prostate gland in three-dimensional space.
Another major advance prostate radiotherapy is the use of rectal hydrogel spacer to
displace the anterior rectal wall posteriorly away from the high doses of radiation
prescribed to the prostate. A phase III trial of hydrogel rectal spacer during prostate
radiotherapy found decreased toxicity and improved bowel quality of life at 3 years for
patients receiving the spacer. Subsequently, the device (SpaceOAR®) was FDA approved in
April 2015. The first generation of spaceOAR® is only discernable on MRI, which most
commonly necessitates a prostate MRI after placement to assist with radiotherapy
planning. The second generation of SpaceOAR®, deemed SpaceOAR Vue ®, is an iodinated
version of the hydrogel that is visible on CT scan and thus obviates the need for a
post-procedural MRI scan for radiotherapy treatment planning. In July 2019 the SpaceOAR
Vue® device received 510(k) clearance indicating that it is substantially equivalent to
predicate devices and can thus be marketed for use in the United States. SpaceOAR Vue® is
now offered to patients with prostate cancer undergoing radiotherapy to decrease rectal
toxicity.
The placement of fiducial markers and rectal hydrogel spacers are relatively well
tolerated, though they are both still invasive procedures that carry a small, but
tangible amount of risk due to transperineal or transrectal needle placement.
Approximately 1/3 of patients will have at least one new symptom after fiducial marker
placement, most commonly increased urinary frequency, hematuria, rectal bleeding,
dysuria, hematospermia, pain, obstruction, or fever. Most of these side effects are grade
2, though 0.5-1.5% of patients have been shown to have a grade 3 complication from
fiducial marker placement. With placement of rectal hydrogel, mild transient procedural
adverse events such as perineal discomfort was noted in 10% of patients receiving
spaceOAR. The investigator proposes that SpaceOAR Vue® may be used not only as a
radiopaque rectal spacer, but also as a three-dimensional fiducial marker. This would
obviate the need for fiducial marker placement resulting in improved patient experience,
less procedural invasiveness, and decreased procedural toxicity.
