High dose rate brachytherapy in patients with high IPSS, large glands, or with prior TURP

Abstract

Prostate cancer is the most common cancer diagnosed among men in the United States, with an estimated 230 110 new cases and 29 900 deaths in 2004.1 In the prostatespecific antigen (PSA) era, the majority of men are diagnosed at an early stage, and treatment options include surgery, external beam radiotherapy (EBRT), and interstitial brachytherapy. Because of the risks of impotence and incontinence associated with radical prostatectomy, many men opt for a non-surgical approach. During the past decade prostate brachytherapy has been increasingly used as monotherapy or in combination with EBRT.2-5 Exponential growth has been forecasted so that while only 4% of men diagnosed with prostate cancer in 1996 were treated with brachytherapy, it is estimated that approximately half of those diagnosed in 2006 will be implanted.6 A 1999 medicare utilization review demonstrated that brachytherapy may supplant prostatectomy as the treatment of choice for localized prostate cancer.7 The majority of prostate interstitial brachytherapy is performed with permanent seed implants with or without supplemental external beam radiotherapy. Ten year PSA-free survival rates of 80-90% have been achieved with acceptable rates of morbidity.2-5The development of the high dose rate (HDR) iridium192 (192Ir) remote afterloader and its success in treating gynecologic, pulmonary, and head and neck cancers prompted interest in treating prostate cancer with temporary HDR interstitial brachytherapy. The initial experience with multifractionated HDR brachytherapy in conjunction with EBRT noted excellent tolerance with superior conformality and minimal morbidity (Table 36.1).8-14 Mate et al delivered four HDR treatments with a minimum peripheral dose ranging from 3 Gy to 4 Gy.8 Dwell times in the periurethral needles were reduced limiting the maximum urethral dose to 120% while achieving 6-7 Gy per fraction to the posterolateral prostate. Approximately 10% of patients developed late genitourinary toxicity. However, as the implant technique evolved and steel needles were replaced with plastic catheters the incidence of urethral strictures became uncommon. Galalae et al combined irradiation of the prostate and pelvic lymphatics with HDR implants interdigitated after 20 Gy and 40 Gy external beam dose.9 The clinical target volume (CTV) was divided so that 15 Gy was delivered to CTV1, defined as the peripheral zone and 9 Gy to CTV2, which included the entire prostate gland. At a median follow-up of 8 years, the disease-free survival was 83% with an acceptable toxicity profile. Of patients, 12% developed significant late genitourinary toxicity consisting of incontinence, urethral stricture, or bladder sphincter sclerosis. These patients had undergone a transurethral resection of the prostate (TURP) with a median interval to radiotherapy of less than 5months. In contrast, none of 10 patients who had undergone TURP with a median interval to radiotherapy greater than 6 months experienced incontinence. Martinez et al treated high risk prostate cancer patients with 46 Gy pelvic EBRT and increasing doses of HDR brachytherapy using from 5.5 Gy to 11.5 Gy per fraction.10 An improved cause-specific survival was noted in patients treated with higher biological effective doses (>93 Gy).