Session Item

Low dose rate (LDR) prostate brachytherapy (LDR-PB) is an effective treatment for early prostate cancer. Used either as monotherapy in low to intermediate risk patients, or in combination with androgen deprivation therapy (ADT) and external beam radiotherapy (EBRT) in patients with more advanced disease. Acute and especially late GI toxicity due to adverse dosimetry of the anterior rectal wall can impact patients’ quality of life.

The purpose of this study is to assess whether the use of rectal spacing gel can reduce rectal dose, and therefore reduce the risk of rectal toxicity.

A detailed analysis of patients treated with I¹²⁵ LDR-PB was conducted using our prospective patient database. All patients included had a same day, post-implantation CT scan prior to catheter removal with rectal dosimetric analysis, as per local protocol.  SpaceOAR hydrogel (SpOAR), a polyethylene glycol based gel, was injected transperineally posterior to Denonvilliers’ fascia under ultrasound guidance. In patients treated with LDR-PB as part of a trimodal approach (ADT+EBRT+ then LDR-PB), SpOAR was inserted at the time of fiducial marker insertion under LA. Patients treated with LDR-PB alone, or LDR-PB in combination with ADT, had SpOAR inserted immediately following LDR-PB seed implantation.

Consecutive patients treated with SpOAR were compared with control patients without SpOAR, who were matched for age, clinical stage, Gleason score,  iPSA and prostate volume; identified from our database and matched using GenMatch.

The rectal dosimetry assessed was maximum dose received by 0.1cc of the rectum (D0.1cc Gy) and maximum dose received by 2cc of the rectum (D2cc Gy).

Patients were divided into three treatment groups for analysis: LDR-PB monotherapy; LDR-PB+ADT; and trimodal treatment. Using unpaired t-test analysis, with significance set at p<0.05, rectal dosimetry was compared in patients with and without SpOAR.

67 patients with SpOAR were identified, with 201 controls matched for age, stage, Gleason score, PSA and prostate volume (Figure 1). 29 patients had BXT alone, 19 ADT + BXT and 19 trimodal therapy.

Figure 1. Baseline characteristics of patients. 

Patients receiving LDR-PB alone or LDR-PB+ADT were treated to a dose prescription of 145Gy, patients receiving trimodal treatment were treated to 110Gy.

Rectal dosimetric analysis demonstrated significant reduction in rectal doses in patients with SpOAR across all treatment groups (p<0.05) (Figure 2).

Figure 2. Rectal dosimetry in patients with SpOAR and without.

Use of rectal spacing gels in patients treated with LDR-PB results in a significant reduction in rectal dose. Longer-term follow-up is underway to assess whether this correlates with improved quality of life outcomes.