Stereotactic Body Radiotherapy for Prostate Cancer
Overview of Contents
- Brief Overview of Prostate Cancer Diagnosis
- What is Stereotactic Body Radiotherapy (SBRT)?
- How Does SBRT Compare with Longer Course of Radiation?
- Why Choose SBRT for Prostate Cancer?
- Can I get SBRT for High-Risk Prostate Cancer?
- How is SBRT Delivered? What Technology is Used?
- Is MRI-guidance superior to CT-guidance?
- Does UCLA Offer SpaceOARTM?
- Do You Have Any Educational Materials for Prostate SBRT?
- Request an Appointment
Men who are diagnosed with prostate cancer are placed into "risk groups" based on a variety of features, including:
-Their initial prostate specific antigen (PSA) laboratory values
-What the doctor has felt on a digital rectal examination
-The Gleason score given to their prostate cancer on review of the biopsy samples
-The number of cores that are positive and the number of cores that are negative on the biopsy samples
More information about the general basics of prostate cancer diagnosis can be found at the following patient-friendly websites
Traditionally, prostate cancer radiotherapy (RT) has been delivered over the course of multiple treatment sessions with a low dose per treatment session. In order to deliver the total dose needed to eradicate prostate cancer, up to 45 treatments were needed, which translates to nine weeks of daily treatments (Monday through Friday). It has since become appreciated that prostate cancer appears to be uniquely sensitive to a higher dose per treatment session, such that prostate cancer could be eradicated in a much shorter amount of time with significantly fewer treatments. Various ways of doing this have been explored. Among them, stereotactic body radiotherapy (SBRT), also known as stereotactic ablative radiotherapy, is a radiation therapy technique that allows the prostate radiotherapy course to be condensed to just five treatment sessions. With SBRT, advanced treatment delivery technologies and radiation planning parameters are used to deliver higher doses per day in a safe and effective manner.
As of 2020, SBRT is considered a standard of care option for any patient with low through very-high risk prostate cancer who is considering radiation therapy. The first patient to be treated with modern prostate SBRT was treated in December 2000. Since then, a large amount of data and evidence have amassed demonstrating the safety and efficacy of SBRT. UCLA investigators have played a leading role in accumulating and publishing these data. To date, the best data available to support SBRT for prostate cancer are:
(a) A study led by Dr. Amar Kishan that compiled the outcomes of 2142 men treated with SBRT between 2000-2012, showing low rates of toxicity and high efficacy with a median follow-up of nearly 7 years. The article can be found here: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2723641
(b) The HYPO-RT-PC randomized trial, which directly compared conventional radiation (39 treatments) against a high-dose-per-day treatment across seven sessions in 1200 Swedish men. Importantly, this trial used older radiation planning techniques and did not deliver modern SBRT. Regardless, the efficacy and long-term side effects were equivalent in both arms of the trial. The article can be found here: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(19)31131-6/fulltext
(c) The PACE-B randomized trial, which directly compared modern, longer course radiation (20 to 39 treatments) against modern SBRT in 874 men in the United Kingdom. No differences in short term side effects were found. The article can be found here: https://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(19)30569-8/fulltext
All of these trials included men with low and intermediate risk prostate cancer. As a result of these data, the National Comprehensive Cancer Network now supports SBRT as a standard option in these patients. Many of the ongoing studies evaluating SBRT, such as the national NRG GU-005 trials, are actually designed to show that SBRT is in fact superior to a longer course of radiation (no longer directly questioning the efficacy or safety of the treatment).
Your radiation oncologist at UCLA will review all of the treatment options with you, comparing the pros and cons of each in great detail. Often, there will be several equally good options, and together with your doctors you will be guided through the decision making process in order to arrive at a treatment that is the most appropriate for you and you feel most comfortable with.
All patients are eligible for prostate SBRT. UCLA has clinical protocols specifically designed for low/intermediate risk patients as well as high risk patients.
There are many good reasons to consider and choose SBRT over the other potential options, including:
- It is entirely non-invasive (unlike brachytherapy it does not involve the insertion of needles, risks of bleeding, risk of infection, general anesthesia, hospital stays, or wearing a catheter).
- It is a very short treatment course (unlike conventional external beam radiotherapy treatments, which can take up to 9 weeks). SBRT is a total of 5 treatment sessions, with each session taking between 15-60 minutes depending on the technology used.
- The cancer control rates of SBRT are equivalent to those of brachytherapy, conventional external beam radiotherapy, or surgery.
- Sparing of radiation exposure to the rectum and bladder is equal to or better than with brachytherapy, particularly with advanced radiation techniques.
Yes, as of 2020, SBRT is considered a standard of care option for patients with high-risk and very-high risk prostate cancer. Dr. Kishan led the largest study of SBRT for high-risk prostate cancer, which was published in early 2021 and pooled data from seven trials from across the world (https://pubmed.ncbi.nlm.nih.gov/33493615/). This study showed extremely favorable outcomes for SBRT for high- and very-high risk prostate cancer in a group of 344 patients.
SBRT consists of a much shorter course of radiotherapy than the conventional approaches, with only five treatment sessions. This is accomplished by delivering a higher dose per day, which requires significant precision and accuracy with expertise from the treating radiation oncologist as well as a team of medical physicists, medical dosimetrists, and radiation therapists. Modern and advanced linear accelerator technology is also required. Overall, SBRT planning and treatment delivery requires six visits to the department (one planning visit and five treatment visits).
Because the prostate can move due to filling up and emptying of the bladder and rectum, pinpoint accuracy is required for SBRT. There are two ways to achieve this level of accuracy:
(a) CT-guidance: In order to make sure that the prostate is accurately targeted and tracked, we place 3 implanted markers (called fiducials) into the prostate. All of our treatment devices are equipped with onboard X-ray imagers or cone-beam CT technology that allow us to triangulate these markers (and thus accurately hone in on the prostate). Also, prior to each treatment session, a cone-beam CT is obtained in order to make sure the anatomy is stable for treatment. This generally means having a full bladder and an empty rectum. We do provide detailed instructions on preparation for treatment to each patient.
(b) MRI-guidance: Our new, MRI-guided radiation delivery platform (the MRIdian device) allows direct, MRI-guided SBRT. In this process, implanted markers are no longer needed. We simply obtain an MRI image for planning purposes, and then obtain an MRI image before each radiation treatment. During radiation, an MRI will be obtained at least four times per second to “track” the prostate in real-time. If the prostate moves outside a pre-specified boundary, the radiation beam will automatically turn off. This added layer of precision allows greater precision and accuracy.
Dr. Kishan recently ran the MIRAGE randomized trial, which was designed to directly answer the question of whether MRI-guided SBRT is superior to CT-guided SBRT with respect to side effects. The early results show a significant benefit, with a significant reduction in bladder and bowel side effects with MRI-guidance (https://ascopubs.org/doi/abs/10.1200/JCO.2022.40.6_suppl.255?af=R). Therefore, we are now recommending MRI-guidance. In certain cases (having a pacemaker, having extreme claustrophobia), MRI-guidance may not be possible and CT-guidance will be used.
SpaceOARTM is a product that can be placed between the rectum and the prostate, leading to decreased radiation dose to the rectum. UCLA does offer SpaceOARTM treatment, though not everyone is a good candidate for SpaceOARTM.
(a) A patient-directed webinar on prostate SBRT given by Dr. Amar Kishan:
(b) A lay-media press release on the UCLA led study, first reported in October 2018
(c) A physician-directed commentary on SBRT for prostate cancer