Prostate motion during radiotherapy of prostate cancer patients with and without application of a hydrogel spacer: a comparative study

Background and purpose: The use of a tissue expander (hydrogel) for sparing of the rectum from increased irradiation during prostate radiotherapy is becoming popular. The goal of this study is to investigate the effect of a tissue expander (hydrogel) on the intrafraction prostate motion during radiotherapy. Methods and material: Real time prostate motion was analysed for 26 patients and 742 fractions; 12 patients with and 14 patients without hydrogel (SpaceOAR T). The intra-fraction motion was quantified and compared between the two groups. Results: The average (+/- standard deviation) of the mean motion during the treatment for patients with and without hydrogel was 1.5 (+/- 0.8 mm) and 1.1 (+/- 0.9 mm) respectively (p < 0.05). The average time of motion >3 mm for patients with and without hydrogel was 7.7 % (+/- 1.1 %) and 4.5 % (+/- 0.9 %) respectively (p > 0.05). The hydrogel age, fraction number and treatment time were found to have no effect (R-2 < 0.05) on the prostate motion. Conclusions: Differences in intrafraction motion in patients with hydrogel and without hydrogel were within measurement uncertainty (< 1 mm). This result confirms that the addition of a spacer does not negate the need for intrafraction motion management if clinically indicated.