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