BERKELEY, CA (UroToday.com) - The application of a spacer to increase the distance between the prostate and the anterior rectal wall is an innovative technique helping to effectively protect the rectal wall. Studies applying a hydrogel spacer have shown that the rectal wall volume inside the 70Gy isodose can be decreased by > 50%. As rectal toxicity is known to be associated with both total dose to a specific volume and the volume inside a specific isodose, a considerable reduction of toxicity can be expected. A consistent protection of the rectal wall throughout a fractionated treatment is essential for a successful outcome.
The aim of this study was to analyze changes throughout the treatment by comparing planning CT scans (CT1) with CT scans performed in the last week of treatment (CT2). Spacer dimensions, spacer displacements, prostate displacements, and changes of the distance between the prostate and anterior rectal wall were determined (patient group defined as “G1”). Additionally, a group of conventionally treated patients (G2) was used as a reference for the displacements and distances without a spacer (CT scans performed at the same intervals).
Hydrogel was identified in all levels (base, middle, apex) before treatment and in the last treatment week for patients with prostate volumes up to 69cm3. No spacer was seen at the level of the base only for the patients with larger prostates of at least 70cm3 (p < 0.01 in chi-square test). Mean volume of the hydrogel increased slightly (17%; p < 0.01) in 4 of 15 patients > 2 cm3. The average displacement of the hydrogel centre of mass was 0.6mm (87% ≤ 2.2mm), -0.6mm (100% ≤ 2.2mm) and 1.4mm (87% ≤ 4.3mm) 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 1.6cm/1.5cm, 1.2cm/1.3cm and 1.0cm/1.1cm at the level of the base, middle and apex (G1). Differences between the respective distances in CT1 and CT2 have not been found to differ significantly. Prostate position variations were similar comparing G1 and G2, but significant systematic posterior displacements were only found in G2 (> 6.5mm in 27% vs. 0% in G2 vs. G1; p=0.03).
In summary, 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.
Written by:
Michael Pinkawa, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
Department of Radiation Oncology, RWTH Aachen University, Germany
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