Session Item

Hyaluronic acid (HA) is one of the four commercialized implantable rectum spacers available on the market, besides hydrogel, saline filled balloon, and human collagen. These implantable rectum spacers are used to decrease rectal radiation dose in prostate cancer radiotherapy to avoid rectal complications after prostate cancer radiotherapy. However implantation of such devices are not risk-free: if such spacers are accidentally implanted in the rectal wall, might result in a chronic wound. Then it can take 3 to 9 months for such spacers to resolve. Furthermore, such a complication results in a significant treatment delay, since an immediate start of radiotherapy could increase the risk of fistula development. So, the feasibility to resolve such a spacer is of great interest in the community. To determine a dose response relationship of disintegration between a hyaluronic acid (HA) used in prostate cancer radiotherapy and hyaluronidase (HAS).

Five in-vitro prostate cancer models (SIM^TM) are applicated with 3 milliliter (ml) HA (Figure 1For dissolution varying doses of HAS were used: 6 ml, 3 ml, 1.5 ml, and 0 ml. One ml contains 150 International Units (IU). Each HAS was added with saline till the complementary amount of 6 ml. One phantom was solely implanted with a HA 3 ml acting as a control. Length, width and height were measured on different time points: 1^st day 4 times, 2^nd day 3 times, third day 2 times, and then once daily during one week, with a final measurement 2 weeks after implantation.

The fastest dissolution was observed with the highest concentration of HAS, starting already at the first time point 2 hours after implantation, with volume decrease of 50% on the second day, and less than 1 ml residue (33%) on day 4. The 2 other concentrations of HAS also showed a volume decrease, with less than 2 ml (66%) on day 4. All the applied quantities of HAS are observed with a residue of less than 1 ml after 7 days. After 14 days the control phantom and the saline filled one remains on steady state volume (3 ml).

A dose response was observed by HAS injection: highest volumes of HAS dissolute most swiftly. A ratio of HA:HAS of 1:2 has already a decrease of half of volume on the second day. This is of special interest while using the HA in clinical practice when wrongly positioned, and dissolution is urgently needed.