Brachytherapy

///Brachytherapy
Brachytherapy 2017-10-19T10:44:53+00:00

Current techniques with permanent prostate brachytherapy are associated with excellent biochemical control for patients with localized prostate cancer. Data is now available for this treatment modality that offers 10-year results that are compatible to external beam irradiation or radical prostatectomy. Nonetheless, treatment protocols and techniques vary between centers that perform prostate brachytherapy and there is little conformity of treatment protocols. Controversy exists regarding the selection of patients for monotherapy or combined external beam irradiation and brachytherapy. The role of neoadjuvant androgen deprivation also remains unanswered in patients with localized prostate cancer. In addition, post-implant dosimetry may in fact be more significant for predicting outcome than the addition of adjuvant therapies and should be a requirement when performing prostate brachytherapy. Data now appears to support specific CT-based criteria to evaluate implant quality and delivered dose to the prostate. Unfortunately, prostate edema and poor imaging techniques are limiting factors for evaluating implant dosimetry. Treatment planning techniques that utilize new treatment planning computers may assist in improving the implant procedure and dosimetry and are now available.
Modern transperineal brachytherapy techniques using ultrasound guidance with either iodine-125 or palladium-103 offer good alternatives for management of localized prostate cancer in appropriately selected patients. This modality allows delivery of a higher localized radiation dose than that achievable by external beam radiation alone; and it is an effective alternative to surgery for those patients who, for various reasons either may be unable to undergo surgery or who elect brachytherapy as an alternative therapy. The non-surgical, outpatient basis of permanent, ultrasound-guided transperineal prostate brachytherapy has high patient appeal and offers minimal morbidity in appropriately selected patients. Brachytherapy is convenient and cost effective, and it generally results in minimal impairment of the patient’s lifestyle. However, it requires a motivated patient; one who understands the disturbing symptoms that can potentially occur.
It is believed that permanent prostate brachytherapy with advanced biplane-transrectal ultrasonography (TRUS), perineal guidance systems, treatment planning computers and post-implant CT-scanning has enhanced our ability to perform an adequate implant with associated biochemical control rates that are as good as radical prostatectomy or high-dose external beam radiation.
Patients who have been treated for benign prostatic hypertrophy with a transurethral resection of the prostate (TURP) pose potential problems when treated with permanent prostate brachytherapy. A fresh TURP defect may lead to excessive morbidity and inadequate seed geometry 17. In general, a preimplant ultrasound is required for these patients to assess the TURP defect relative to the planned seed locations. Further, it has been reported that patients with a previous TURP may experience prolonged post-implant dysuria and are at risk of urethral necrosis 18. Current protocols for permanent prostate brachytherapy which place seeds peripherally in the prostate gland, may not cause the high rates of urethral necrosis originally reported 19.

After a patient has been assessed and is deemed eligible for an implant, an initial assessment of the prostate volume is required. The purpose of this is to establish a preplan 20. If using an intraoperative technique, the preimplant volume assessment allows one to determine the total isotope activity required. It has been reported that patients with large volume glands that exceed 60 cc are difficult to implant and when using the preloaded needle technique it is advised that a pubic arch study be performed to determine if interference will limit the needle path. Pubic arch interference is not as much an issue with the intraoperative technique, as patient positioning is not as critical, allowing the brachytherapist to extend the patients hips into exaggerated lithotomy position, rotating the pelvic floor away from the anterior part of the prostate gland. Using this approach, Stone et. al. have reported their experience implanting patients with prostates larger than 60 cc with excellent post-implant dosimetry 21. While prostate volume reductions of 35% or more have been reported with LHRH agonist therapy over a 3-4 month duration, these patients have a higher incidence of post-implant urinary morbidity 22. In a recent study reported by Crook et. al. examining the incidence of acute retention following an implant failed to identify any relief for patients that had their prostate volumes reduced with hormones, and in fact those patients had higher rates of retention 23. Therefore, while a large prostate volume may not be an absolute contraindication for permanent prostate brachytherapy, the issues of pubic arch interference and increased post-implant symptoms require one to consider all the ramifications when developing an implant plan.

Other relative contraindications for permanent prostate brachytherapy include patients with high American Urological Association (AUA) urinary scores assessing benign prostatic hypertrophy symptoms 24, 25. In this setting, pre-implant treatment with an alpha-blocking medication may decrease the risk of post-implant retention and urinary symptoms. Nonetheless, a patient with a high AUA score coupled with an enlarged prostate gland should be evaluated very carefully for permanent prostate brachytherapy and be advised of the increased risk of post-operative urinary morbidity.