Radiation Therapy for Prostate Cancer


CHAPTER 45 Radiation Therapy for Prostate Cancer







Gregory J. Kubicek, MD and
Ashraf Youssef, MD, MBA


image List the most important clinical prognostic factors predicting disease-free survival for prostate cancer?


T stage, biopsy Gleason score, pretreatment PSA.


image Describe the most important clinical prognostic factors predicting disease-free survival for prostate cancer?


T stage, biopsy Gleason score, and pretreatment PSA have been the most extensively studied 3 factors. They provide reproducible outcomes among prostate cancer patients treated with radiation therapy alone. Several investigators (D’Amico) have used a combination of these factors to stratify disease-free survival according to low, intermediate, and high-risk groups. Such a strategy is helpful in providing prognostic information for patients and in stratifying patients for prospective trials.


image What other clinical prognostic factors can help predict prostate cancer survival?


PSA doubling time, percent of biopsy cores positive for disease, patient age, comorbidities, and obesity. Race is an unclear prognostic factor with some studies showing a worse clinical outcome for African Americans.


image Which of these factors is the single, strongest predictor of death from prostate cancer?


The Gleason score is the clinical prognostic factor that has consistently been shown to best predict death from prostate cancer. While pretreatment PSA has been shown to correlate with biochemical recurrence, no investigation has yet been able to demonstrate that pretreatment PSA reliably predicts prostate cancer death rate.


image How would this affect treatment recommendations for radiation therapy?


In recommending radiation therapy for prostate cancer, more weight should be given to the Gleason score over any other factor. Dose escalation studies have shown more benefit for high-risk and high-grade cancers than for low- or intermediate-risk groups. Also, several prospective randomized trials have shown that patients with high Gleason score tumors have a survival benefit from the use of long duration adjuvant hormonal therapy.


image A 65-year-old male has Gleason 6 prostate cancer involving 2 of 12 cores, PSA 7.5. What is the ideal treatment for this patient?


The patient has multiple options including active surveillance. There are no data to support one form of treatment (surgery, external beam radiation, and brachytherapy) over another one for this patient. Treatment decisions should be based on patient preference, quality of life, performance status, comorbidities, etc, with an understanding of differences in logistics for the different treatments and side effect profile.


image What are the different forms of treatment for nonmetastatic prostate cancer?


Accepted options for prostate cancer exist including active surveillance, surgery (radical prostatectomy), and several forms of radiation (see the next question). Several other forms of treatment include cryotherapy and high intensity focused ultrasound (HIFU), these treatments are not considered standard at this time and are not recognized by NCCN.


image What are the different forms of radiation in the treatment of prostate cancer?


Accepted forms of radiation include external beam radiation (most commonly intensity modulated radiation therapy [IMRT]) and brachytherapy (low dose and high dose rate). Other types of radiation include proton beam therapy and stereotactic radiosurgery (ie, cyberKnife). These treatments are not considered standard at this time.


image What is the difference between 3D and IMRT?


These are 2 types of radiation used for external beam radiation. The difference is in how the radiation energy is delivered. With IMRT multiple small radiation beams (called beamlets) are used from different angles with different radiation intensities. In effect, IMRT allows the radiation to bend and curve around normal structures.


image Is there an advantage of IMRT over 3D?


Yes, IMRT has been shown to reduce side effects and toxicity when compared to 3D. Because it is more conformal it also allows for radiation doses to be more safely increased. 3D conformal techniques allow a dose 75 to 76 Gy, and IMRT doses can be in excess of 80 Gy with essentially equivalent side effects.


image What is IGRT?


IGRT stands for image guided radiation therapy. IGRT uses various techniques in order to ensure that patient set-up and positioning are correct and that the radiation is being delivered with a high degree of precision. IGRT can take several forms, including daily imaging using cone beam CT scan (CBCT), rectal ultrasound, or placement of fiducial markers into the prostate. IGRT is considered a standard treatment option when using external beam radiation.


image What are the typical side effects of external beam radiation?


During radiation side effects are fairly minimal, the majority of patients can continue to work full time during the entire course of treatment. After radiation long-term side effects can include toxicity to bowel and bladder and erectile dysfunction (ED). Bladder toxicity includes urinary urgency and frequency, this will typically resolves after 1 year. Bowel toxicity includes rectal urgency, frequency and pain, fecal incontinence, or hematochezia can occur; unlike bladder toxicity, bowel toxicity may not resolve. The incidence of grade 2 or great toxicity is less than 10%.


image What is the incidence of potency after external beam radiation therapy for prostate cancer?


Depending on patient age, comorbid conditions, and the use of other medications, potent patients undergoing external beam radiation therapy for prostate cancer have a 50% to 75% chance of remaining potent after treatment.


image What is the mechanism by which radiation therapy causes ED?


Radiation therapy causes ED primarily through arteriogenic and vascular means as opposed to radical prostatectomy, which affects the nerves.


image What is the difference between external beam radiation therapy and brachytherapy?


External beam radiation consists of 8 weeks of daily (M to F) treatment. Brachytherapy (low dose rate) consists of a single procedure in which multiple radioactive seeds are inserted into the prostate. The 2 can be done together but not simultaneously.


image What is the cyberKnife?

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Jan 3, 2017 | Posted by in UROLOGY | Comments Off on Radiation Therapy for Prostate Cancer
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