Protection of the Rectum during Prostate Radiation

Prostate cancer is the most common malignancy in men, with an estimated 191,900 new diagnoses and 33,330 deaths in 2019.[1] Treatment modalities range from radical prostatectomy to radiation therapy to close observation and are standardized by national guidelines.[2]

Radiation therapy for prostate cancer can take the form of placement of brachytherapy seeds into the prostate or external beam radiation therapy. Scatter radiation from these techniques, however, provides a significant risk to adjacent organs. As radiation therapy technology and administration techniques have improved, a significant limiting factor to dose administration is the risk of rectal toxicity from scatter radiation.[3] Depending on the dose delivered and sensitivity of the organ, in this case the rectum, there may be long-lasting radiation injury.

As radiation dose is reduced by the square of the distance, separating the prostate from the rectum is a very effective means of decreasing radiation exposure. The inverse holds true as well, as some studies have suggested dose modulation in patients with decreased prostate to rectum distances.[4] By definition, this makes the rectum an “organ at risk.”

Increasing the distance between the prostate and rectum serves as a protective mechanism for the rectum and may allow for increased and more effective dose to the prostate. Hydrodissection with saline to increase this space, while technically feasible, proves ineffective as saline quickly dissipates and is resorbed. However, placement of a hydrogel into the peri-rectal fat with ultrasound guidance can create up to 1.5 cm of separation between the prostate and rectum. This hydrogel remains in place for approximately 3 months. Use of rectal spacer material has been established to be safe and effective in limiting rectal toxicity.[5] [6] [7] Herein, we review the technique and considerations for placement of a hydrogel between the prostate and rectum in patients undergoing radiation therapy for prostate cancer.

• References

• 1 Siegel RL, Miller KD, Jemal A. Cancer statistics, 2020. CA Cancer J Clin 2020; 70 (01) 7-30
• 2 National Comprehensive Cancer Network. Prostate Cancer (Version 4.) 2019 . Secondary Prostate Cancer (Version 4.2019). Available at: https://www.nccn.org/professionals/physician_gls/pdf/prostate_blocks.pdf . Accessed May 25, 2020
• 3 Budäus L, Bolla M, Bossi A. , et al. Functional outcomes and complications following radiation therapy for prostate cancer: a critical analysis of the literature. Eur Urol 2012; 61 (01) 112-127
• 4 Kang MH, Yu YD, Shin HS, Oh JJ, Park DS. Difference in the rate of rectal complications following prostate brachytherapy based on the prostate-rectum distance and the prostate longitudinal length among early prostate cancer patients. Korean J Urol 2015; 56 (09) 637-643
• 5 Mariados N, Sylvester J, Shah D. , et al. Hydrogel spacer prospective multicenter randomized controlled pivotal trial: dosimetric and clinical effects of perirectal spacer application in men undergoing prostate image guided intensity modulated radiation therapy. Int J Radiat Oncol Biol Phys 2015; 92 (05) 971-977
• 6 Mahal BA, Ziehr DR, Hyatt AS. , et al. Use of a rectal spacer with low-dose-rate brachytherapy for treatment of prostate cancer in previously irradiated patients: Initial experience and short-term results. Brachytherapy 2014; 13 (05) 442-449
• 7 Karsh LI, Gross ET, Pieczonka CM. , et al. Absorbable hydrogel spacer use in prostate radiotherapy: a comprehensive review of phase 3 clinical trial published data. Urology 2018; 115: 39-44
• 8 Aminsharifi A, Kotamarti S, Silver D, Schulman A. Major complications and adverse events related to the injection of the SpaceOAR Hydrogel System Before radiotherapy for prostate cancer: review of the manufacturer and user facility device experience database. J Endourol 2019; 33 (10) 868-871
• 9 2019 SpaceOAR® Coding and Payment Quick Reference Guide. Secondary 2019 SpaceOAR® Coding and Payment Quick Reference Guide 2019 . Available at: https://2ygv9l350b7a2gm5pl1ftyu1-wpengine.netdna-ssl.com/assets/SpaceOAR-Hydrogel-2019-Billing-and-Coding-Guide-Rev-J.pdf . Accessed May 25, 2020