Many approaches have been tried for reducing the rectal toxicity of radiotherapy (Radiat Oncol 2013; 8:96; Int J Radiat Oncol Biol Phys 2012; 82:1918-22; Radiat Oncol 2014; 9:96). This article discusses a newer therapy that involves the injection of a temporary hydrogel in the plane between the prostate and rectum.
Even in an era of unclear screening policy, prostate cancer is a highly prevalent malignancy treated with myriad therapeutic options (CA Cancer J Clin 2015; 65:5-29). Surgical therapy and radiotherapy are the best studied, most frequently used options for men with clinically localized prostate cancer.
The most common approach for delivering radiotherapy to the prostate is external beam radiation, either via a conventionally fractionated (intensity-modulated radiation therapy, 3-D conformal radiotherapy) or hypofractionated (stereotactic body radiation therapy) approach. In general, greater doses of external beam radiotherapies are associated with better disease control and a higher proportion of patients with undetectable PSA levels (Int J Radiat Oncol Biol Phys 2008; 70:67-74). Unfortunately, greater doses of prostate radiation are also associated with increased local toxicity to adjacent organs, and the dose-limiting regional toxicity of these radiotherapies has generally been rectal toxicity.
Many approaches have been tried for reducing the rectal toxicity of radiotherapy (Radiat Oncol 2013; 8:96; Int J Radiat Oncol Biol Phys 2012; 82:1918-22; Radiat Oncol 2014; 9:96). This article discusses a newer therapy that involves the injection of a temporary hydrogel in the plane between the prostate and rectum (Int J Radiat Oncol Biol Phys 2015; 92:971-7)(figure 1). This product, which received FDA clearance in April 2015 and is marketed under the name SpaceOAR (Augmenix, Inc.), has been shown in prospective, randomized trials to decrease rates of rectal toxicity.
With increasing scrutiny of the sequelae of prostate cancer therapies, placement of a pretreatment spacer may become increasingly prevalent. Since many radiation oncologists utilize fiducials or gold seeds for optimal radiation delivery, the spacer can be placed at the same time, avoiding another invasive procedure.
Placement of the SpaceOAR rectal spacer is indicated for the reduction of rectal toxicity in men with prostate cancer undergoing radiotherapy. Full instructions for use of the product are included with each kit. Spacer placement can be performed under local or general anesthetic. The transperineal route is required to provide appropriate spacer distribution and to reduce risk of introducing infection. Initial procedures can be performed under anesthesia to overcome the learning curve, but outpatient procedures with local anesthetic are feasible.
The procedure itself is usually coupled with the placement of gold localizing seeds, which obviates the need for a secondary invasive procedure. The steps themselves are straightforward and utilize a skill set possessed by urologists who have experience with transrectal ultrasound and prostate biopsy.
The initial step is verification of available equipment, including SpaceOAR, gold seeds (if planned), and confirmation of the operation of the transrectal ultrasound probe in both the transverse and longitudinal planes. The use of a bed-mounted brachytherapy-type ultrasound stabilization unit is required to perform the procedure. After perineal prep and a universal time-out protocol, placement of gold fiducial markers is completed with transrectal ultrasound guidance and freehand transperineally placed needles.
After fiducial placement, the spacer kit is then prepared. The goal is to have 5 cc of the gel and 5 cc of the developer in equal syringes prior to assembly. The gel itself comes in a lyophilized container and is reconstituted with a prefilled diluent syringe so that a 5-cc aliquot can be retrieved. These are color coded with a blue diluent syringe that mates with the cap of the blue gel vial, which can then be mixed and retrieved into the syringe. We recommend having a very small amount of air remaining in the syringe to prevent inadvertent leakage and premature mixture of the gel, which will quickly harden within the delivery device.
Once the gel and developer are ready, the syringes are fastened to the Y connector via their Luer-lock tips. Two plastic stabilizing pieces (one for the body of the syringes and one for the plunger of the syringes) are attached by pressing them in place (figure 2). The assembly can then be set aside until use, with the tip propped up to avoid inadvertent mixing.
The spacer injection portion of the procedure first requires identification of perirectal fat, which is bright (hyperechoic) on ultrasound (figure 3). Under ultrasound guidance, an 18-gauge needle is localized to this layer and a small amount (5 cc) of injectable saline used to confirm and hydrodissect this potential space. By ultrasound, the space appears similar to a local anesthetic block for the prostate and will display wispy septations as it develops. It is important to confirm a location near the base of the prostate just distal to the border of the seminal vesicles and in midline. This should be done on longitudinal and transverse images.
After confirming the 18-gauge needle is in the correct position, the Y connector is then attached to the needle while holding it steady within the patient and the gel applied by a quick, steady emptying of the syringes under live ultrasound guidance. This should be done in approximately 8 seconds. At completion, a dark (hypoechoic) region is visible where the spacer is placed (figure 4). Unless additional procedures are expected, the procedure is then terminated.
A full review of the literature is beyond the scope of this article, but a few salient points with respect to safety and efficacy warrant mention. Placement of a hydrogel spacer has been studied at multiple institutions (Int J Radiat Oncol Biol Phys 2015; 92:971-7; Int J Radiat Oncol Biol Phys 2013; 87:81-7; Brachytherapy 2014; 13:442-9; Urology Practice 2016; 3:141–6) and has a favorable safety profile with published literature on over 300 men having received therapy without a major spacer-related adverse event. Placement of the device is considered “easy or very easy” by over 90% of providers and uses a skill set most urologists already possess.
While longer follow-up is needed, the largest prospective cohort treated with spacer prior to radiotherapy appears to have approximately 70% fewer long-term rectal complications than those patients treated with standard therapy (Int J Radiat Oncol Biol Phys 2015; 92:971-7).
In an era of scrutiny of the very concept of local treatment for prostate cancer, functional outcomes for those patients receiving treatment are under intense review. Any practitioner involved with caring for high-grade, radiation-induced rectal complications is acutely aware of the challenges in managing these patients and the value of avoiding these events (Am J Surg 2008; 195:616-20). They bear both a high cost of care and a high cost of patient suffering. While the placement of a rectal spacer before radiotherapy incurs additional cost, this is partially or fully offset by decreased care costs for rectal complications (article in press).
Rectal spacers are generally placed at the time of fiducial seed placement and so add minimal additional morbidity to the patient and confer a reasonable amount of additional labor burden on the provider. Practically speaking, patients have been amenable to the concept, and the majority in our clinic have wished to pursue placement of a spacer prior to radiation when the risks and benefits are discussed.
Placement of a hydrogel rectal spacer before radiotherapy draws on the pre-existing skill set of urologists and in multiple published studies confers a benefit in reduced rectal toxicity from radiation for prostate cancer. With FDA approval of the device, we suspect more providers will offer their patients placement of a spacer prior to radiotherapy in the coming years.
|Section Editor Christopher M. Gonzalez, MD, MBA||Dr. Gonzalez|
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