3345 - Separation Effect of Biodegradable Balloon Spacer on Rectal Dose from Apex to Base in Prostate Cancer SBRT
Presenter(s)
E. M. Soffen1, J. Steele2, and V. C. Ng3; 1Princeton Radiation Oncology, Astera Cancer Care, Jamesburg, NJ, 2Astera Cancer Care/Princeton Radiation Oncology Center, 9 Centre Drive Monroe, NJ, 3Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY
Purpose/Objective(s): Biodegradable balloon spacers minimize rectal dose during prostate cancer radiation therapy. The potential benefit in reducing rectal toxicity during SBRT may be even more relevant as the higher daily dose has a greater effect on late toxicity in normal tissues. Therefore, the degree and extent of achieved prostate-rectum separation may prove to be relevant. This study measures spacer-induced separation at the distal apex, midgland and base, categorizing into three groups based on separation degree. The effects on rectal dose-volume are presented, while the correlation with acute and late gastrointestinal (GI) and genitourinary (GU) toxicities is forthcoming.
Materials/Methods: Twenty consecutive patients with low or intermediate-risk prostate cancer were treated with definitive SBRT (36.25 Gy in 5 fractions), employing a biodegradable balloon spacer. Post-implant CT/MRI scans were used for contouring and radiation treatment planning. Prostate-rectum spacing measurements were taken at the most inferior apical slice, midgland, and the most superior base contour. The spacing measurements were taken as the distance between the posterior prostate and the anterior rectal wall at midline. These measurements were categorized into three groups: <10 mm, 10–14 mm, and =14 mm.
Results: At the apex, dose differences between separation groups were most evident at lower dose levels (18.25 Gy to 25.38 Gy), with the =14 mm group showing the lowest doses and the <10 mm group exhibiting the highest. Midgland, differences were more pronounced at higher doses (29 Gy to 36.25 Gy), where greater separation was associated with lower doses, while the <10 mm group had the highest rectal doses. In the base region, the relationship between separation and dose in the three groups was less evident (Table 1).
Conclusion: Strategic spacer placement is important with prostate SBRT, specifically with greater than 14mm separation from the base to apex. Proper implantation, particularly towards the apex, may reduce gastrointestinal toxicity by ensuring optimal protection of the anterior rectal wall along the entire length of the gland. Ongoing analysis will evaluate the relationship between apical spacing and acute and late GI and GU toxicities.
Abstract 3345 - Table 1| Rectal Dose Volume, cc (SE) | |||||||||
| Apical | Midgland | Base | |||||||
| Dose Level | <10 mm | 10-14 mm | =14 mm | <10 mm | 10-14 mm | =14 mm | <10 mm | 10-14 mm | =14 mm |
| 18.25Gy | 10.0 (2.7)% | 5.3 (2.9)% | 3.1 (0.6)% | 6.3 (5.6)% | 5.8 (1.1)% | 6.0 (1.7)% | 9.3 (4.6)% | 5.2 (1.2)% | 4.8 (1.0)% |
| 21.75Gy | 7.6 (2.3)% | 2.6 (1.2)% | 1.7 (0.3)% | 5.5 (5.0)5 | 3.5 (0.8)% | 3.8 (1.3)% | 6.1 (3.6)% | 3.1 (0.8)% | 3.2 (0.9)% |
| 25.38Gy | 4.9 (1.3)% | 2.1 (0.7)% | 0.9 (0.2)% | 4.0 (3.8)% | 2.1 (0.6)% | 2.3 (0.8)% | 3.1 (2.0)% | 1.9 (0.5)% | 2.1 (0.7)% |
| 29.0Gy | 1.4 (0.7)% | 0.7 (0.4)% | 0.7 (0.3)% | 2.8 (2.6)% | 1.7 (0.4)% | 0.8 (0.2)% | 0.6 (0.3) % | 1.1 (0.3)% | 1.1 (0.4)% |
| 32.63Gy | 0.7 (0.4)% | 0.2 (0.05)% | 0.2 (0.1)% | 1.7 (1.6)% | 0.4 (0.2) | 0.1 (0.09) % | 0.04 (0.02)% | 0.4 (0.1)% | 0.5 (0.2)% |
| 36.25Gy | 0.2 (0.1)% | 0.1 (0.03)% | 0.1 (0.09)% | 0.5 (0.5)% | 0.2 (0.2)% | 0.05 (0.03)% | 0.01 (0.004)% | 0.03 (0.01)% | 0.2 (0.1)% |