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Clinical summary

Expanding the Utilization of Rectal Spacer Hydrogel for Larger Prostate Glands (>80cc): Feasibility and Dosimetric Outcomes

By: Fagundes M, Rodrigues MA, Olszewski S, et al.

33 patients with localized prostate cancer with glands exceeding 80cc were treated at a single institution using intensity-modulated radiotherapy (IMRT, n=15) and proton therapy (n=18) from 2017 to 2019. 16 patients received conventional fractionation and 17 received hypofractionation. Previous prospective multi-institutional studies only included prostates <80cc.1 The mean separation was 9.9 mm (range, 6.6 – 19.4 mm) for glands measuring >80 to 100 cm3 and 8.8 mm (range, 4.7 – 12.3 mm) for glands >100 cm3. Patients were assessed weekly using common terminology criteria for adverse events (CTCAE).

Dosimetric outcomes

Conventional fractionation (78 Gy/39 fractions)
  Pts rV75 rV70 rV60 rV50
All 16 0.84% (0-2.7) 2.25% (0-4.7) 5.61% (1.7-9.5) 10.5% (2.39-15.2)
P + SV 4 0.75% (0.06-1.77) 2% (0.75-4.4) 5.47% (2.5-9.5) 10.1% (6.4-15.2)
P + SV + Lns 12 0.87% (0-2.7%) 2.3% (0-4.7) 5.66% (1.7-8.9) 10.7% (2.3-14.9)
P + SV (IMRT) 2 0.58% (0.06-1.1) 1.61% (0.93-2.3) 4.95% (4.5-5.4) 9.45% (9.4-9.5)
P + SV (PT) 2 0.93% (0.09-1.77) 2.57% (0.75-4.4) 6% (2.5-9.5) 10.8% (6.4-15.2)
Moderate hypofractionation (70 Gy/28 fractions)
  Pts rV65 rV63 rV60 rV50
All P + SV 17 1.67% (0-5.8) 2.3% (0.1-6.7) 3.4% (0.4-9.6) 8.6% (3.3-15.7)
P + SV (IMRT) 9 1.16% (0-4.6) 1.65% (0.1-5.8) 2.5% (0.3-7.8) 6.9% (2.46-15)
P + SV (PT) 8 2.24% (0.7-5.8) 3.1% (1.3-6.7) 4.48% (2.4-9.6) 10.5% (4.9-15.7)

Abbreviations: IMRT = intensity modulated radiation therapy; (P + SV) = prostate plus seminal vesicles; (P + SV + Lns) = prostate plus seminal vesicles plus lymph nodes; PT = proton therapy; Pts = patients.

Conventional fractionation (78 Gy/39 fractions)

All patients (n=16)

Mean value and range, rV75=0.84% (range, 0-2.7), rV70=2.25% (range, 0-4.7), rV60=5.61% (range, 1.7 -9.5), rV50=10.5%(range, 2.39-15.2) bar chart.

Mean value and range, rV75 = 0.84% (range, 0 – 2.7), rV70 = 2.25% (range, 0 – 4.7), rV60 = 5.61% (range, 1.7 – 9.5), rV50 = 10.5% (range, 2.39 – 15.2)

Moderate hypofractionation (70 Gy/28 fractions)

All P + SV (n=17)

Mean value and range, rV65=1.67%(range 0-5.8), rV63=2.3%(range, 0.1-6.7),rV60=3.4%(range=0.4-9.6), rV50=8.6%(range, 3.3-15.7) bar chart.

Mean value and range, rV65 = 1.67% (range, 0 – 5.8), rV63 = 2.3% (range, 0.1 – 6.7), rV60 = 3.4% (range, 0.4 – 9.6), rV50 = 8.6% (range, 3.3 – 15.7)

“Hydrogel placement is feasible in large glands >80cc, even when including a subgroup of patients with prostates >100cc (100.1–186.6 cc) with very favorable dosimetric outcomes which are in line with benchmark published results with smaller glands.”

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Limitations of this report include:

  • Study was retrospective in nature
  • The SpaceOAR Hydrogel pivotal study did not evaluate glands >80cc so the results may not be comparable
  • This study was not designed or powered to make definitive claims about the benefits of a spacer
  • These results may not be achieved with other large gland protocols
  • The pivotal study done for SpaceOAR Hydrogel utilized fractionation schedules of 79.2Gy over 44 fractions

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Reference

  1. 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(5):971–977.

78Gy over 39 fractions was not the method used in the SpaceOAR™ Hydrogel single-blind Phase III trial performed to evaluate dosimetric and clinical effects of SpaceOAR Hydrogel. IG-IMRT delivered at 79.2 Gy in 1.8-Gy fractions was the method used.

Results from case studies are not necessarily predictive of results in other cases. Results in other cases may vary.

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