Elsevier

Radiotherapy and Oncology

Volume 106, Issue 2, February 2013, Pages 220-224
Radiotherapy and Oncology

Rectal spacing in prostate RT
Spacer stability and prostate position variability during radiotherapy for prostate cancer applying a hydrogel to protect the rectal wall

https://doi.org/10.1016/j.radonc.2012.11.010Get rights and content

Abstract

Background and purpose

The aim was to evaluate the spacer dimensions and prostate position variability during the course of radiotherapy for prostate cancer.

Materials and methods

CT scans were performed in a group of 15 patients (G1) after the 10 ml injection of a hydrogel spacer (SpaceOAR™) and 30 patients without a spacer (G2) before the beginning of treatment (CT1) and in the last treatment week, 10–12 weeks following spacer implantation (CT2). Spacer dimensions and displacements were determined and prostate displacements compared.

Results

Mean volume of the hydrogel increased slightly (17%; p < 0.01), in 4 of 15 patients >2 cm3. The average displacement of the hydrogel center of mass was 0.6 mm (87%  2.2 mm), −0.6 mm (100%  2.2 mm) and 1.4 mm (87%  4.3 mm) in the x-, y- and z-axes (not significant). The average distance between prostate and anterior rectal wall before/at the end of radiotherapy was 1.6 cm/1.5 cm, 1.2 cm/1.3 cm and 1.0 cm/1.1 cm at the level of the base, middle and apex (G1). Prostate position variations were similar comparing G1 and G2, but significant systematic posterior displacements were only found in G2.

Conclusions

A stable distance between the prostate and anterior rectal wall results during the radiotherapy course after injection of the spacer before treatment planning. Larger posterior prostate displacements could be reduced.

Section snippets

Hydrogel implant

The injection of a spacer gel (SpaceOAR™ System, Augmenix Inc., Waltham, MA) was performed in 18 patients with prostate cancer (PSA < 20 ng/ml, Gleason score < 3 + 4) in our department after local ethics committee approval. These patients have been included in a multi-institutional phase II clinical trial (study sponsor: Augmenix Inc.). All patients have signed informed consent before being included in this study.

The SpaceOAR™ System is a polyethylene glycol gel (PEG) that polymerizes in seconds,

Results

Prostate, rectum and bladder volumes in both subgroups at the specific intervals are presented in Table 1. Mean bladder and rectum volumes decreased in both groups (G1: 49 cm3 and 9 cm3; G2: 69 cm3 and 13 cm3, statistically significant only in G2). Comparing the subgroups G1 and G2, the only significant difference resulted for the bladder volume in the last treatment week. It was significantly smaller in the G2 subgroup (p < 0.01). No significant differences were found comparing the percentages of

Discussion

The application of a hydrogel spacer has been shown to be a very effective technique to reduce the dose to the rectal wall, potentially allowing a safe dose escalation to the prostate or hypofractionated treatments without detrimental bowel effects for the patient. Effects on dose distribution have been demonstrated recently in a cadaver study [20] and a clinical study evaluating three-dimensional conformal and IMRT techniques before and after spacer injection [21].

This study demonstrates a

Conclusions

A stable distance between the prostate and anterior rectal wall results during the radiotherapy course after injection of the hydrogel spacer before treatment planning. Prostate position variations are comparable to patients who are treated conventionally without a spacer, but larger posterior prostate displacements could be reduced.

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