Placement of an absorbable rectal hydrogel spacer in patients undergoing low-dose-rate brachytherapy with palladium-103.
PURPOSE
Rates of rectal toxicity after low-dose-rate (LDR) brachytherapy for prostate cancer are dependent on rectal dose, which is associated with rectal distance from prostate and implanted seeds. Placement of a hydrogel spacer between the prostate and rectum has proven to reduce the volume of the rectum exposed to higher radiation dose levels in the setting of external beam radiotherapy. We present our findings with placing a rectal hydrogel spacer in patients following LDR brachytherapy, and we further assess the impact of this placement on dosimetry and acute rectal toxicity.


METHODS AND MATERIALS
Between January 2016 and April 2017, 74 patients had placement of a hydrogel spacer, immediately following a Pd-103 seed-implant procedure. Brachytherapy was delivered as follows: as a monotherapy to 26 (35%) patients; as part of planned combination therapy with external beam radiotherapy to 40 (54%) patients; or as a salvage monotherapy to eight (11%) patients. Postoperative MRI was used to assess separation achieved with rectal spacer. Acute toxicity was assessed retrospectively using Radiation Oncology Therapy Group radiation toxicity grading system. Rectal dosimetry was compared with a consecutive cohort of 136 patients treated with seed implantation at our institution without a spacer, using a 2-tailed paired Student's t test (p < 0.05 for statistical significance).


RESULTS
On average, 11.2-mm (SD 3.3) separation was achieved between the prostate and the rectum. The resultant mean rectal volume receiving 100% of prescribed dose (V100%), dose to 1 cc of rectum (D1cc), and dose to 2 cc of rectum (D2cc) were 0 (SD 0.05 cc), 25.3% (SD 12.7), and 20.5% (SD 9.9), respectively. All rectal dosimetric parameters improved significantly for the cohort with spacer placement as compared with the nonspacer cohort. Mean prostate volume, prostate V100 and dose to 90% of gland (D90) were 29.3 cc (SD 12.4), 94.0% (SD 3.81), and 112.4% (SD 12.0), respectively. Urethral D20, D5cc, and D1cc were 122.0% (SD 17.27), 133.8% (SD 22.8), and 144.0% (SD 25.4), respectively. After completing all treatments, at the time of first the followup, 7 patients reported acute rectal toxicity-6 experiencing Grade 1 rectal discomfort and 1 (with preexisting hemorrhoids) experiencing Grade 1 bleeding.


CONCLUSIONS
Injection of rectal spacer is feasible in the post-LDR brachytherapy setting and reduces dose to the rectum with minimal toxicity. Prostate and urethral dosimetries do not appear to be affected by the placement of a spacer. Further studies with long-term followup are warranted to assess the impact on reduction of late rectal toxicity.
['Taggar|Amandeep S|AS|', 'Charas|Tomer|T|', "Cohen|Gil'ad N|GN|", 'Boonyawan|Keeratikarn|K|', 'Kollmeier|Marisa|M|', 'McBride|Sean|S|', 'Mathur|Nitin|N|', 'Damato|Antonio L|AL|', 'Zelefsky|Michael J|MJ|']
D000368:Aged D001918:Brachytherapy D015331:Cohort Studies D006801:Humans D020100:Hydrogels D008279:Magnetic Resonance Imaging D008297:Male D009929:Organ Size D058958:Organs at Risk D010165:Palladium D011467:Prostate D011471:Prostatic Neoplasms D011829:Radiation Dosage D011832:Radiation Injuries D011868:Radioisotopes D011879:Radiotherapy Dosage D012002:Rectal Diseases D012007:Rectum D012189:Retrospective Studies D016879:Salvage Therapy D014521:Urethra
Low-dose-rate brachytherapy Prostate cancer Rectal spacer