3302 - Comparison of Perirectal Spacer Placement Quality during the Learning Curve for 3 FDA Approved Products

J. D. Tward; Department of Radiation Oncology, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT

Purpose/Objective(s): Perirectal spacers have proven to improve QOL and reduce the toxicity of radiation therapy for prostate cancer patients. The FDA has approved three absorbable products in this category, a PEG-based gel, a Hyaluronic-based gel (HA) , and a Vicryl balloon. We aimed to compare the separation heights, spacer quality, and symmetry scores for these products during the initial learning curve for each product. Materials/

Methods: Patients were enrolled in an IRB-approved prospective registry and the first ten patients ever implanted with each product by a single physician experienced with brachytherapy were identified. The Rectal Spacing Quality Score (SQS) and the prostate spacer symmetry score (SSS) were evaluated using established methods.^1,2 A validated AI contouring tool was used to derive the prostate and rectal contours and prevent bias. The spacer heights were measured from the posterior edge of the prostate gland to the anterior edge of the rectum. For SQS, the spacing height was measured at the rectal midline and 1 cm to the right and left in 3 axial planes (base-6mm. midgland, apex +6mm), while for SSS, the spacing symmetry was measured at the prostate midline and 1 cm right and left, at the midgland, and 1 cm superior and inferior.

Results: The median age of men receiving PEG, HA, and balloon was 73, 68, and 68 years, respectively (p=0.03). There were no significant differences in prostate volume between the three groups (mean=36.7cc, p=0.24). Mean spacer volumes were significantly different: PEG=9.2cc, HA=6.7cc, Balloon=13.5cc, p<0.001. The space achieved at base-6mm was statistically equivalent (p=0.89) for all, however the balloon achieved significantly greater space at the midgland and apex+6mm locations (p=0.002, p=0.003, respectively), Table 1. There were no significant differences in SQS or SSS scores (p=0.13, p=0.33, respectively). There were no acute grade = 2 toxicities noted in any of the procedures, and all procedures took <30 min from initial needle entry to completion.

Conclusion: The balloon achieved superior volume, separation near the midgland, and apex, and a higher proportion of best SQS scores compared to the PEG or HA spacer. Physicians accustomed to brachytherapy procedures can implant all three products in less than 30 minutes with minimal discomfort and toxicity, as demonstrated during the learning curve phase. Abstract 3302 – Table 1

1. Fischer-Valuck, et al: Pract Radiat Oncol 7:195-202, 2017
2. Grossman CE, , et al: Adv Radiat Oncol 8:101070, 2023

	Distance from Post. Prost to Ant. Rectum						Spacer Quality Score2				Spacer Symmetry Score1
	Base-6mm		Midgland		Apex+6mm		0=worst, 1=acceptable, 2=best				1=best to 5=worst
	mm						%				%
	mean	min-max	mean	min-max	mean	min-max	0	1	2	Mean	1	2	3	4	5	Mean
PEG	22	20-24	11	9-13	8	6-11	10	60	30	1.2	90	0	10	0	0	1.2
HA	21	18-25	11	9-14	8	7-10	0	60	40	1.4	60	30	20	0	0	1.5
Balloon	23	20-26	17	15-20	14	13-16	0	10	90	1.8	60	30	0	10	0	1.6