Phase I Study of Targeting Dominant Intraprostatic Lesion Using Functional MR Spectroscopy and High Dose Rate Brachytherapy

Trial Information

Phase I Study of Targeting Dominant Intraprostatic Lesion Using Functional MR Spectroscopy and High Dose Rate Brachytherapy

1.1 The goal of radiotherapy is to deliver a high dose of radiation to the target volume
while minimizing the dose to the surrounding normal tissue. Using CT based
three-dimensional treatment planning system and multiple field technique, the three
dimensional conformal radiotherapy (CRT) has become the standard of care for external beam
radiotherapy for prostate cancer. Multiple institutional studies and prospective randomized
trials have been done documenting the safety and efficacy of this modality. Brachytherapy
is an alternative method of delivering conformal radiotherapy for treatment of prostate
cancer. The technique of HDR prostate brachytherapy has been in clinical practice since the
1980's [1-13]. Kovacs et al reported one of the earliest experiences using HDR brachytherapy
boost at University of Kiel.[10, 11, 13] Patients treated were mostly T2b-T3, G3. They
used a combination of split course external beam radiotherapy and two 15 Gy HDR treatments.
They reported 18% positive biopsy rate 18 months post treatment. The result was updated at
10 years and 78 percent of 171 patients remained free of disease at median follow-up of 55
months. Mate et al at Swedish Medical Center reported their experience with HDR
brachytherapy [9]. They used a more moderated hypofractionated schema with four treatments
of 3-4 Gy fractions of HDR treatments combined with 45-50 Gy of external beam radiotherapy.
They recommended routine cystoscopy at the end of the implant procedure to ensure the
catheters are placed at the proper depth and to avoid injuring the urethra. Pretreatment
patient characteristics were stage T1b to T3c, mean initial PSA was 12.9 and Gleason grade
ranges 3 to 9. They reported 84% 5-year biochemical disease free survival. Martinez et al
at the William Beaumont Hospital reported the only on-going prospective dose escalation
trial using HDR brachytherapy as a boost. There have been multiple updates of their
results.[5-7, 12] They have continued to dose escalate using increasingly larger fractions
of HDR treatment range from 5.5-6.5 Gy x 3 to 8.25-11.5 Gy x 2 combined with 46 Gy of
external beam radiotherapy. As of their most recent update, they have shown acceptable
toxicity level using 9.5 Gy x 2 treatments. Patients with PSA ≥ 10, T ≥ T2b, and Gleason
score ≥ 7 were selected for the trial. Despite a high frequency of poor prognostic factors,
the actuarial biochemical control rate was 89% at 2 years and 63% at 5 years. The 5-year
actuarial rates of local failure and distant metastasis were 16% and 14%, respectively.
Borghede et al. at Goteborg University in Sweden reported their experience using 50 Gy of
external beam radiotherapy combined with 2 fractions of 10 Gy HDR boost.[1, 2] They used
ultrasound to target tumor nodules within the prostate and gave an additional 5 Gy boost
during each HDR treatment. Patients included in the study were T1-3, and grade 1-3. They
report a 4% positive biopsy rate at 18-months post treatment. This is a remarkably low
positive biopsy rate considering no hormonal therapy was used in the study. The results
from these clinical trials and others have shown the technique of HDR brachytherapy for
prostate cancer is feasible with minimal morbidity. Other institutional trials have
suggested HDR boost may be more efficacious compared to external beam radiotherapy alone or
external beam radiotherapy with short term hormonal therapy. Results of these studies need
to be confirmed in large multi-institutional trials.