FAQs about Radiation Therapy for Prostate Cancer
Below you will find answers to frequently asked questions about radiation therapy at the Smilow Center.
How is radiation therapy delivered to the prostate for prostate cancer treatment?
Radiation may be delivered to the prostate by an external source of ionizing radiation (external beam radiotherapy) or by inserting radioactive seeds directly into the prostate gland (brachytherapy).
What are the advantages and disadvantages of brachytherapy (seed implantation) versus external beam radiation?
There are advantages and disadvantages to both internal radiation therapy (brachytherapy) and external beam radiation therapy. The recommendation by Smilow Center radiation oncologists will depend both on the patient’s concerns about the duration and side effects of treatment, as well as the stage and aggressiveness of the cancer.
Some studies have shown that brachytherapy is superior at preserving erectile function, although these studies have not been conclusive. In addition, brachytherapy may not be appropriate for men with severe lower urinary tract symptoms such as frequency and urgency, since the symptoms may be aggravated, and acute urinary retention may develop.
How does external beam radiation therapy work for prostate cancer treatment?
In external beam radiation therapy, X-rays are generated by a machine and focused on the prostate. Treatment usually takes place daily for several weeks, for a total of 40–45 treatment sessions.
Over the past 5 to 10 years, the computer software controlling the beam delivery has advanced, allowing more precise focusing of the radiation beam and less damage to surrounding structures. The better precision of the beam results in fewer radiation-induced side effects.
The primary external radiation therapy technique used at NYU is a daily intensity-modulated radiation therapy with image guidance via cone-beam CT scan (IMRT/IGRT).
In intensity-modulated radiation therapy (IMRT), radiation is delivered from many different angles by a machine rotating around the patient. The intensity of the radiation is altered depending on its path, helping to minimize damage to surrounding healthy tissues.
In image-guided radiation therapy (IGRT), each daily radiation treatment session is preceded by a CT scan to determine the exact location of the prostate and adjacent structures. A CT scan is a series of X-ray ‘slices’ of the body that, when reconstructed by a computer, produces a three-dimensional view of the internal organs. The IGRT takes into account that the prostate configuration nay be altered by the radiation treatment.
MRI is also being studied at NYU Langone as a method of imaging prior to and after radiation delivery to assess response to treatment.
What is seed implantation for prostate cancer treatment, and when should it be used?
The technique of seed implantation (brachytherapy) for localized prostate cancer involves implanting radioactive pellets in the prostate. These pellets slowly release a high dose of radiation directly into the prostate.
Because the type of radiation used in brachytherapy does not travel far, it destroys the cancer but minimizes damage to the surrounding healthy tissues.
Smilow radiation oncologists and urologic oncologists working in collaboration regularly perform permanent seed implants. This procedure can be completed in one day. Medical research has demonstrated the effectiveness of this treatment for low-risk disease over the course of 10–12 years.
Brachytherapy may be used as a single mode of treatment in patients with low-risk prostate cancer (Gleason score <6, PSA <10, and only a small nodule of prostate cancer on digital rectal exam) or in combination with external beam radiation therapy for patients with intermediate-risk disease (Gleason score of 7, or PSA of 10–20).
Brachytherapy may not be appropriate for men with a large prostate (more than 50–60 grams) or for men who have significant lower urinary tract symptoms such as urinary urgency or frequency. In addition, brachytherapy should not be used alone for cancers with adverse clinical or pathologic features.
What is the CyberKnife and how is it used to treat prostate cancer?
The CyberKnife is a frameless robotic radiosurgery system. It produces radiation using a small linear particle accelerator and has a robotic arm that allows the energy to be directed at any part of the body from any direction. By increasing the accuracy of the delivery of radiation, there is a potential for dose escalation, resulting in an increase in effectiveness.
The CyberKnife system has been approved by the US Food and Drug Administration to treat any solid tumor, including tumors of the prostate. Studies of the CyberKnife have not shown any general survival benefit over conventional treatment methods. Studies to date have been limited in scope, and more extensive research will be needed to show any effects on survival.
Is proton beam radiation effective in treating prostate cancer?
Proton beam therapy is a type of external beam radiotherapy that works by aiming energetic ionizing particles (in this case, protons accelerated with a particle accelerator) onto the target tumor. Because protons are relatively large, they do not spread or “scatter” significantly in tissue. Therefore, the beam stays focused on the tumor, with less radiation delivered to surrounding structures. It is possible to focus the proton beam at the precise depth in the tissue where the tumor is situated.
Proton therapy has been used for numerous tumors throughout the body, including the prostate. Some studies in prostate cancer show a reduction in long-term rectal and genitiourinary side effects when compared with conventional X-ray therapy. However, other studies show that the difference is small and limited to a small subset of cases where the prostate is particularly close to certain anatomical structures (Slater JD et al. Int. J. Radiat. Oncol. Biol. Phys. 59: 348-352 (2004); Zietman AL et al. JAMA 294(10):1233-1239 (2005)).
Is hormonal therapy typically administered in conjunction with radiation therapy?
There is an abundance of clinical information demonstrating that preoperative (neoadjuvant) and postoperative (adjuvant) hormonal therapy improves survival outcomes for men with high-risk, clinically localized prostate cancer. For this reason, hormonal therapy is almost always offered in conjunction with radiotherapy for men with high-risk disease. The duration of hormonal therapy remains controversial.
Because of the side efforts and unproven benefit, hormonal therapy is not offered in conjunction with radiotherapy for low-risk disease.
In treating prostate cancer, what are the typical side effects of radiation therapy?
The typical short-term side effects associated with radiation therapy include fatigue and urinary and rectal symptoms. Urinary symptoms may include frequency, urgency, urge incontinence, nocturia and diminished urinary stream. Rectal symptoms may include diarrhea, fecal incontinence, rectal bleeding and rectal urgency. In most cases, the urinary and rectal symptoms are transient. In addition, erectile dysfunction often develops months or years after radiation therapy.
Long-term complications are rare and include rectal or urinary fistulas, urinary strictures, hemorrhagic cystitis and proctitis (chronic bleeding from the rectum and bladder) and dysfunctional bladder or rectum due to scarring. There is increasing evidence than men undergoing pelvic radiation are at significantly greater risk of developing bladder and colon cancer.
Are any medications prescribed to alleviate the acute lower urinary tract symptoms after prostate cancer treatment?
Medications prescribed for men with lower urinary tract symptoms due to other conditions like BPH and overactive bladder are often administered to men who develop these bothersome symptoms during and after radiation therapy. These medications include alpha-blockers or anticholinergic agents. These drugs are not offered as preventative measures but rather if symptoms become bothersome.
When does the PSA level reach its nadir (lowest) level after radiation therapy?
The PSA level often takes up to two years after the completion of radiation therapy to reach a nadir level. Androgen deprivation therapy offered before and after radiation therapy will lower the PSA level. Therefore, the effect of radiation therapy cannot be determined while there are any ongoing, residual effects on PSA due to androgen deprivation therapy.
How do you know if the prostate cancer is “cured” after radiation therapy?
Just as after radical prostatectomy, the PSA is the best measure of disease control after radiation therapy. The PSA typically is undetectable after radical prostatectomy, since the entire prostate is removed. Low levels of PSA are often detectable after radiation therapy because it is not feasible to totally eradicate the prostate with radiation without destroying adjacent structures. Therefore, a measureable PSA after radiation therapy does not necessarily indicate residual prostate cancer.
Recurrence after radiation therapy is typically defined as a PSA level 2.5 ng/dl above the nadir (lowest) PSA level measured after treatment. It should be noted that a biochemical recurrence after radical prostatectomy and biochemical recurrence after radiation have very different clinical connotations: a biochemical recurrence after radical prostatectomy simply implies the presence of some residual disease, whereas a biochemical recurrence after radiation therapy portends a poor prognosis.
What are the options for treating a recurrence of prostate cancer after radiation therapy?
As with surgery, the challenge in cases of biochemical recurrence after radiation therapy is to determine the site of recurrence.
If the recurrence is localized to the prostate, there are several options for eradicating the disease:
- Salvage radical prostatectomy
- Cryotherapy (destroying the prostate by freezing the gland under ultrasound guidance)
- High-intensity focused ultrasound (HIFU)
Smilow Center surgeons offer all of these options. Salvage radical prostatectomy is a very challenging technical procedure because of the prostate is embedded in a fibrous scar produced by radiation. Even in the hands of the most experienced prostate cancer surgeons, complications such as incontinence and strictures are common after salvage radical prostatectomy. Therefore, minimally invasive ablative therapies are gaining increasing acceptance for the treatment of recurrent prostate cancer after failed radiation therapy. Smilow Center surgeons are among the most experienced in the country at performing salvage cryotherapy. NYU is currently one of eight centers in the US investigating HIFU, a promising new technology for ablating the prostate in after failed radiation therapy.
In the past, most men opted for hormonal therapy because of the complications associated with salvage radical prostatectomy. It is imperative to obtain a prostate biopsy before embarking on any attempt to cure localized disease to ensure that recurrence is localized to the prostate. In addition to biopsy, imaging studies are routinely performed to determine if there is evidence of systemic metastasis, which would obviate attempts at achieving local disease control.
In terms of side effects, how does surgery compare to radiation in treating prostate cancer?
A recent study published in the New England Journal of Medicine examined quality of life outcomes after radical prostatectomy and radiation therapy for localized prostate cancer. (Sanda MG et al. N. Engl. J. Med. 358:1250-1261 (2008)). In this study, long-term urinary incontinence was very rare after both treatment options. Urinary and rectal symptoms were worse after radiation therapy. Erectile function was slightly better after radiation therapy. The outcomes from this study were captured 2 years after treatment. It should be noted that surgeons at the Smilow Center have reported that potency continues to improve between 2 to 4 years after radical prostatectomy (Glickman L, Godoy G, Lepor H. J. Urol. 181(2):731-5 (2009)). In contrast, there is evidence that potency deteriorates beyond 2 years after radiation therapy (Penson DF et al. J Urol. 173(5):1701-5 (2005)). In addition, the above comparison study excluded men who underwent radiation and received neoadjuvant and/or adjuvant androgen deprivation therapy. Virtually all of these men would experience both erectile dysfunction and loss of libido.
How do surgery and radiation compare for curing prostate cancer?
There have been no recent long-term, randomized studies comparing survival after radical prostatectomy and radiation therapy. A randomized Veterans Administration study in the 1980s demonstrated a survival advantage of surgery over radiation therapy. This study is not relevant today because of advances in radiation therapy technology and a stage shift in the disease due to increased PSA screening. Several retrospective studies have examined survival after radical prostatectomy and radiation therapy after correcting for factors such as disease severity and medical comorbidities. The study from Henry Ford Hospital reported a survival advantage for surgery over radiation for low-, intermediate- and high-risk localized disease (Tewari A et al. J. Urol. 177(3):911-5 (2007)). A recent study from Memorial Sloan Kettering Cancer Center examining differences in survival between surgery and radiation therapy for high-risk disease (Gleason score >8 or PSA >20 or stage cT2c/cT3) found a significant survival advantage for radical prostatectomy.