HDR Brachytherapy as Monotherapy for Low and Intermediate Risk Prostate Cancer

INTRODUCTION:

Several modalities of radiotherapy treatments are available for low and intermediate risk of prostate cancer, all avec similar results on biochemical control and toxicities. Among them, the brachytherapy consist in the implantation of radioactive sources directly in the prostate. Due to the fast dose shot/application of brachytherapy, the irradiation dose is less damaging to neighbor organs. This specific brachytherapy behavior can enhance the control over cancer while reducing toxicities.

Brachytherapy treatment can be delivered by high-dose-rate (HDR) while, at this time, catheters are implanted in the prostate and retrieved right after treatment (10-15 minutes). HDR brachytherapy dose is more coherent than LDR brachytherapy, because it is not under the risk of loss or migration of its source, neither the variations of prostate size due to swelling or shrinkage after the implantation. A more precise and reproducible dose coverage is accomplished with better preserving of the urethra, bladder, and rectum.

Several authors are investigating HDR brachytherapy and comparing doses and the number of fractions of the different treatment plans.

Morton et al. researched the use of one single fraction of 15 Gray HDR with External Beam Radiation Therapy (EBRT) for the treatment of intermediate risk. The investigators found a progression free survival rate higher than 95% at 5 years follow-up, making this the more used treatment plan at this time.

Since investigators already have good control rates with LDR brachytherapy for low and intermediate risk cancers with lower toxicity rates, investigators began to question the need of adjunct external radiotherapy. Besides those rates, HDR brachytherapy has other advantages such as: Medical staff is not subjected to radiation, no radiation source is left on the patient's body, treatment time is decreased from several months to few minutes, and the dose distribution is better used because of the capacity to precisely control the source position during treatment.

HDR brachytherapy is usually given is small fraction number, but the optimal fraction number for HDR monotherapy is unknown. Most researchers prescribe 4 to 6 fractions, with a 6 hours interval between fractions. Catheters are left in place and treatment lasts from two to several days, unavoidably needing patient's hospitalisation. Another possible inconvenience is the possible catheters displacement between fractions, leading to verifications and corrections before each fraction is delivered. Trying to reduce the number of fractions and give enough dose is being studied in several institutions. The dose is not only related to the efficacy of the treatment, but also to the toxicities related to it.

The purpose of this study is to evaluate High-dose rate (HDR) brachytherapy (1 vs 2 fractions on single implant) as monotherapy for the treatment of low risk and intermediate risk prostate cancer. One fraction HDR brachytherapy will be delivered in one 19.5 Gy dose, while the two fractions will be delivered in two fractions of 14.5 Gy (total dose of 29Gy), both on single implant procedure. This evaluation will be carried under a single institution as a phase II randomized clinical trial (RTC) design.

Hypothesis:

The HDR brachytherapy as monotherapy given in one or two fractions (one fraction of 19.5 Gy or two fractions of 14.5Gy) is well tolerated and effective for the treatment of low and intermediate risk prostate cancers.

Objectives:

Primary Objective:

The aim of this study is to evaluate acute (early) toxicities (genitourinary and gastrointestinal) of HDR brachytherapy (1 vs 2 fractions on single implant) as monotherapy for low and intermediate risk prostate cancer.

Secondary Objectives:

• Measure overall survival and progression free survival rate
• Evaluate the evolution of the International Prostate Symptom Score (IPSS) and its time to return to baseline.
• Evaluate late genitourinary and gastrointestinal toxicities changes measured by RTOG and CTCAE v4 score
• Evaluate biochemical failure
• Evaluate erectile dysfunction rates
• Investigate associations between dosimetric parameters and toxicity
• Investigate associations between iUrethra parameters and toxicity
• Assess changes in the quality of life of patients - EORTC QLQ-C30

METHODS:

Patient's selection and randomization:

Inclusion and exclusion criteria are described elsewhere. Once patients fullfil all selection criteria they will be randomized between one of the 2 arms of the study (1 or 2 fractions) by sealed envelope system.

Treatment:

Patients will undergo preoperative standard care conditions. The procedure will be taken under regional anesthesia with sterile conditions; Foley urinary catheter will be inserted and will aid the urethra delimitation. The bladder will be emptied and the catheter will be clamped. Transrectal ultrasound (TRUS) will guide the placement of the transperineal catheters. The number of temporary interstitial catheters will be based on the size and shape of the prostate (at least 16 catheters will be implanted).

Optimization of treatment plan will be done with Oncentra (Elekta) based on MRI imaging done post-implant. The following contours will be delimited: the prostate, the urinary catheter (urethra), the urethra as seen on the MRI (iUrethra), the rectum and the bladder. Catheters will be rebuilt on the planning system. The dose calculations will be done by reverse planning. After treatment, catheters will be removed and the patient will be transferred to the recovery room. Patient will be sent home after recovery with urinary catheter. Urinary catheter will be retrieved the day after.

Patients receiving two fractions will undergo CT scan before the second fraction, if the catheters have to be repositioned, appropriate adjustments will be made to optimize the dose distribution and correct any changes in dosimetry of the implant.

Patient's evaluation:

After the end of treatment, patients will be seen at 1, 3 and 6 weeks, 3 months, 6 months, 12 months and then every 6 months until year 5. PSA, IPSS, IIEF5 and EORTC QLQ-C30 will be fulfilled during follow-up appointments.

Procedures for biochemical recurrence will be at the discretion of the attending physician.

New biopsies will not be performed if local recurrence is suspected and that the metastatic work-up (abdominopelvic CT scan, bone scintigraphy) is positive. Nevertheless, in cases of suspicion of local or remote recccurence investigation will take place.

Statistics:

The assumption is that for each arm the probability of a standard deviation difference will be higher than 0.5 of the urinary toxicities at one year compared to the baseline will be lower than or equal to our current standards.

Sample size:

To detect this difference, the test of proportions was used with the NCSS / PASS software. The sample size was estimated at 180 patients (90 per arm) calculated with 99% power and a 0.05 significance level (one-tail test). Considering 10% ineligibility, the required sample size is 200 patients (100 per arm).

Statistical analysis:

Statistical analysis will be performed at SAS 9.3 software package. Anova repeated measures (Mixed Models) and regression logistic regression models (GEE: Generalized Estimation Equations) will be used.

These multivariate models will allow us to determine the potential associations between our dependent variables while controlling as much for socio-demographic factors and especially for potentially confounding clinical variables.