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The Durham Regional Cancer Centre (DRCC) has used hydrogel tissue spacers for prostate patients undergoing stereotactic body radiation therapy (SBRT) since 2018. The hydrogel is inserted between the prostate and the rectum, increasing the space between these two organs. Radiation dose fall-off in the hydrogel as opposed to the rectum results in lower rectal dose without compromising prostate dose. In this review, we evaluated and quantified the impact that the presence of hydrogel had on these patients. Symptom burden, quality of life and outcome were reviewed. In addition, the rectal dose constraints that would have been achieved without hydrogel spacer were assessed.
25 prostate were treated at DRCC with our SBRT protocol and hydrogel spacer between June 2018 and June 2020. The protocol consists of 3625cGy delivered in 5 fractions, with a planning target volume (PTV) margin of 0.45 cm. The dose distributions for these patients were assessed via 3 rectum dose constraints as per the protocol. The same treatment plan was used to assess the simulated rectum dose constraints in the absence of hydrogel. The non-hydrogel dose values were compared to the protocol constraints and pass rates determined. The volume of rectum spared by the use of hydrogel was quantified.
The patients’ medical charts were reviewed to extract clinician reported late rectal toxicity scores (CTCAE V4) and patient reported bowel symptom scores (EPIC system) for patients with follow up visits at least 3 months after treatment.
Our dosimetric analysis quantifies the impact of hydrogel on the rectum. For all 25 patients, when hydrogel was used, the three rectum dose criteria were met with the exception of one patient who had a minor violation of protocol at one dose point. Without the use of hydrogel, the opposite result was found. All patients failed at least one rectal constraint, with the exception of one patient. The volume of rectum at each dose criterion was reduced with the use of hydrogel.
Follow up data was available for 12 patients. For all patients with followup data, there was no late rectal toxicity: The CTCAE score was 0. Patient reported bowel symptoms also indicate good patient tolerance for this treatment. Three patients reported any symptom, and only one patient reported a score above 1 for one symptom (frequency score of 3). Only 4 of the 12 patients with followup appointments chose to complete the EPIC scoring tool. This is attributed to a lack of concern or issues on the part of the patients.
We conclude that the use of hydrogel tissue spacers allows for the safe delivery of hypofractionated SBRT courses of radiation therapy to the prostate, as based on dose distributions, clinician reported late rectal toxicity and patient reported symptoms. It is interesting to note that the use of SBRT treatment protocols with hydrogel for prostate cancer has dramatically increased by a factor of 2.5 since the onset of the COVID-19 pandemic. This has allowed us to minimize hospital visits while delivering safe and effective treatments.
