Vienna, Austria

ESTRO 2023

Session Item

Poster (Digital)
Sparing Neurovascular bundle with hyaluronic acid rectal spacer: a prospective study.
Sara Simoes, Portugal


Sparing Neurovascular bundle with hyaluronic acid rectal spacer: a prospective study.

Sara Simoes1, Sofia Ramos2, Marina Amorim2, Osvaldo Carvalhosa2, Catarina Silva2, Diana Oliveira3, Maria Rodrigues3, João Gagean3, Cármen Calçada3, Carlos Fardilha3, Paulo Costa3

1Hospital de Braga, Radiation Oncology, Braga, Portugal; 2Hospital de Braga , Radiation Oncology, Braga, Portugal; 3Júlio Teixeira SA - Instituto CUF , Radiation Oncology, Porto, Portugal

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Purpose or Objective

To characterize the effect of a prostate-rectum spacer on dose to neurovascular bundle (NVB) during external beam radiation therapy (EBRT). Dose to rectum was also evaluated.

Material and Methods

In February 2022, ten consecutive patients with histologically confirmed prostate adenocarcinoma, were enrolled into a prospective study at our institution, with the following inclusion criteria: age >= 18 years, clinical stage of T1c-2, Karnofsky Performance Status > 70, with any NCCN risk group. Initially, the patients underwent a baseline CT scan. Then, they were injected with perirectal hyaluronic acid (HA) spacer and rescanned with CT and MRI. 3D-CRT plans were created on both scans (pre-spacer and post-spacer) for dosimetric comparison of NVB. The dose prescribed to prostate was 76Gy in 38 fractions. The comparison of dosimetric parameters was performed using the Paired-sample T Test and Wilcoxon Test, using the IBM SPSS Statistics version 26 software.


The population included males with a mean age of 72 (±2.56) years, presenting with a mean PSA 8.51 (±7.56) ng/mL. All patients underwent androgen deprivation therapy (ADT). The mean prostate volume (PV) was 34.3 cc (21-66, ±13.36).

Neurovascular bundle dosimetry

Non - hyaluronic acid spacer plans

Hyaluronic acid spacer plans

P value

Mean dose (Gy, DP)

71.59 ±2.44

68.37 ±4.17


Maximum dose (Gy, DP)

79.45 ±0.51

78.75 ±0.73


V60Gy (%)

88.21 ±9.30

82.73 ±15.14


V70Gy (%)

71.06 ±11.13

57.38 ±14.33


Rectum dosimetry

Non - hyaluronic acid spacer plans

Hyaluronic acid spacer plans

P value

V60Gy (%)

25.73 ± 6.60

13.62 ± 4.51


V70Gy (%)

11.10 ± 5.43

2.67 ± 1.82


V75Gy (%)

5.09 ±3.82

0.20 ±0.23


The PV does not correlate significantly with the mean dose (p=0.361), maximum (p=0.071), V60 (p=0.669) and V70 (p=0.064) to NVB after placing the HA.

In all, 40% of patients (4/10) developed acute Grade 1 GI toxicities. No patients had acute Grade ≥2 GI toxicities. None of the patients reported any rectal bleeding. There were no reports of any adverse events including rectal perforation, or infection after HA injection. 8 patients (80%) had erectile disfunction (ED) at baseline. During the follow-up (3 months after treatment) all patients had ED (EPIC).


Injection of HA was able to achieve a reduction of irradiated NVB dose volumes irrespective of PV. It reduced the V70 Gy, mean and maximum doses in the NVB, which potentially might decrease sexual impairment. However, it was not possible to associate the use of the spacer with sexual toxicity, since all patients were under ADT. Injection of HA also significantly reduced rectum V60, V70 and V75. In a future analysis we will evaluate ED using EPIC after resuming ADT and correlate it with dose to NVB. The presenting study proves that injection of HA reduces significantly the dose to NVB with 3DRT, however we believe differences will be greater when using IMRT or SBRT, and we look forward to present it in a future work.