Using Rectal Hydrogel Spacer for Salvage SABR in Prostate Cancer

Feasibility of Integrating Rectal Hydrogel Spacer for Salvage Treatment Using Stereotactic Ablative Body Radiotherapy for Locally Recurrent Prostate Cancer

There are several single institutional series that have reported their experience with salvage radiotherapy options that include EBRT, LDR and HDR brachytherapy. Gastrointestinal (GI) toxicity with salvage radiotherapy range between14-58%, respectively for patients undergoing re-irradiation. There is a concern for an increased risk of fistula development in these patients who receive second course of radiation. Hypofractionation using SABR has been utilized in the re-irradiation setting for prostate cancer with good tumor control and toxicity outcomes. In order to decrease the rectal toxicity, dose to the rectum should be kept as low as possible. Several techniques can be used to achieve this: tighter dosimetric dose painting, better patient or organ immobilization or use of a biodegradable gel. The Investigators ropose a phase I study to assess placement of a hydrogel spacer between the prostate and rectum, in an effort to decrease toxicity and improve patient's bowel quality of life.

Primary treatment of prostate cancer includes surgery or radiotherapy. Although significant improvements have been made in patient selection and treatment planning, local recurrence remains a common problem.

In the case of local recurrence after radiation, salvage options may include prostatectomy, salvage external beam radiotherapy (EBRT) or brachytherapy with low-dose (LDR) or high-dose rate (HDR) implantation, cryotherapy and high intensity focused ultrasound.

There are several single institutional series that have reported their experience with salvage radiotherapy options that include EBRT, LDR and HDR brachytherapy (2-7). Rates of grade 2 or higher genitourinary (GU) and gastrointestinal (GI) toxicity with salvage radiotherapy range between 36-50% and 14-58%, respectively for patients undergoing re-irradiation. GI Toxicity, however, is dependent on total rectal dose. This is especially important among patients who are being considered for re-irradiation. There is a concern for an increased risk of fistula development in these patients who receive second course of radiation although with salvage brachytherapy that risk was only 2% and seen only in patients who had a surgical intervention after salvage brachytherapy.

Hypofractionated regimens have become increasingly common in treatment of prostate cancer, especially with advancement of immobilization and imaging techniques that allow smaller margins and daily verification. Hypofractionation using SABR (Stereotatic Ablative Body Therapy) has been utilized in the re-irradiation setting for prostate cancer with good tumor control and toxicity outcomes. In order to decrease the rectal toxicity, dose to the rectum should be kept as low as possible. Several techniques can be used to achieve this: tighter dosimetric objectives, dose painting, better patient or organ immobilization or use of a biodegradable gel. The latter has been used to increase the distance between the prostate and the rectum for patients who are undergoing prostate radiotherapy. Placement of a hydrogel spacer between the prostate and the rectum has been proven in a randomized controlled trial to reduce rectal dose resulting in decreased acute and long-term rectal toxicity and improvement in bowel-related quality of life. SpaceOAR is an FDA and Health Canada approved, commercially available rectal spacer that, when placed between the prostate and the rectum, has demonstrated to greatly reduce rectal dose and toxicity for patients undergoing external beam radiation and LDR brachytherapy.

Inclusion Criteria:

• Histologically and radiologically confirmed locally recurrent prostate adenocarcinoma
• Willing to give informed consent to participate in this clinical trial
• Able and willing to complete EPIC and EQ-5D questionnaires

Exclusion Criteria:

• Contraindication to prostate MRI
• Anticoagulation medication (if unsafe to discontinue)
• Diagnosis of bleeding diathesis
• Poor baseline urinary function defined as International Prostate Symptom Score (IPSS) >20
• Evidence of castrate resistance (defined as PSA > 3 ng/ml while testosterone is < 0.7nmol/l). Patients could have been on combined androgen blockade but are excluded if this was started due to PSA progression.
• Definitive extrapelvic nodal or distant metastatic disease on staging investigations.
• Prior ultra-hypofractionated radiotherapy ( SBRT of 5Gy/fraction or higher)