High dose Stereotactic Body Radiotherapy (SBRT)
by Dr. C.H. Weaver M.D. updated 3/2021
High dose stereotactic body radiotherapy (SBRT) for men newly diagnosed prostate cancer appears to result in shorter treatment times, less severe toxicity and excellent cancer control rates. (1-6)
Although prostate tumors generally respond well to radiation therapy, the possibility of radiation exposure to healthy tissue in the genitourinary and gastrointestinal systems can be of concern. SBRT is an advanced technique that precisely targets high doses of radiation to the tumor in a small number fractions, simultaneously avoiding surrounding tissue and reducing toxicity to non-cancerous cells.
Men with early stage prostate cancer can currently be treated with surgical prostatectomy, brachytherapy or external beam radiation therapy (EBRT). SBRT, a form of EBRT condenses the radiation treatment for prostate cancer into as few as four to five sessions (compared with 20-45 sessions previously). The technique has become the standard of care for many non-surgical lung cancer patients, as it limits exposure to the heart and surrounding lungs. When treating tumors in the prostate, SBRT avoids the adjacent bladder, sex organs and rectum.
Stereotactic body radiotherapy (SBRT) is a specific form of EBRT in which advanced radiotherapy techniques are used to deliver very large doses of radiation over shorter time periods. Stereotactic radiation can be administered over four to five days instead 45 days and has been in use for several years at select institutions.
Low-Intermediate Risk Early Stage Prostate Cancer
The initial report on SBRT and published in JAMA analyzed 2,142 men with low or intermediate risk prostate cancer treated at multiple institutions with SBRT between 2000 and 2012 that had been followed for an average of ~ 7 years from initiation of treatment.
The recurrence rate for men with low risk disease was reported to be 4.5%, and 10.2% for intermediate-risk disease. Although the study did not directly compare SBRT to traditional EBRT these recurrence rates are essentially identical. The study provides us with longer term data regarding the safety and clinical effectiveness of SBRT which represents a more convenient and lower cost alternative for men with low to intermediated risk early stage prostate cancer. (1)
Another institution studying the use of SBRT as the primary treatment for prostate cancer confirms SBRT as front-line therapy for men with prostate cancer. A total of 309 men with newly diagnosed prostate cancer were enrolled in a trial at 21 community, regional and academic hospitals across the U.S. Eligible patients had either low-risk disease (T1-T2a, Gleason 6, PSA < 10) or intermediate-risk disease (T1c-T2b with either Gleason 7 and PSA < 10, or Gleason 6 and PSA 10-20).
- At five years following SBRT, 97% of patients were free from prostate cancer progression. In low-risk patients, the cancer control rates was superior to historical controls.
- 97.3% of low-risk patients survived 5 years without cancer recurrence.
- Five-year relapse free survival was 91.3% for intermediate-risk individuals.
- Fewer than two percent of all patients experienced serious side effects in the five years following SBRT. (1)
Comparative trials have since confirmed that SBRT is at least equivalent to traditional longer course radiation therapy. As a result of these data, the National Comprehensive Cancer Network now supports SBRT as a standard option in these patients. (3,4)
High-risk Early Stage Prostate Cancer
An analysis of data from a consortium of seven institutional phase 2 studies and registries was published in International Journal of Radiation Oncology, Biology, Physics in February 2021.
Analysis of 344 men (median age, 72.3 years) with high-risk prostate cancer treated with SBRT reported a 4-year cure rate of 82% with the 5-day regimen of high dose SBRT. Overall, 72% of men did receive ADT (median duration, 9 months) and 19% received elective nodal radiotherapy. Eighteen percent of men experienced grade 2 or worse genitourinary toxicities and 5% experienced grade 2 or worse gastrointestinal toxicities.
The 4-year PSA free recurrence rate is similar to the 5-year rates among men in the ASCENDE-RT trial of brachytherapy boost (85.5%) or dose-escalated conventionally fractionated radiotherapy alone (83.6%) along with 12 months of ADT, despite that some men in the current trial received no or shorter courses of ADT. (2)
How is SBRT Delivered?
SBRT is accomplished by delivering a higher radiation dose per day from an advanced linear accelerator, which requires significant precision and accuracy from a team of experts consisting of a radiation oncologist, medical dosimetrists, and radiation therapists. Modern and advanced linear accelerator technology is also required. Combined SBRT planning and treatment delivery requires six visits.
In order to make sure that the prostate is accurately targeted and tracked doctors place 3 implanted markers (called fiducials) into the prostate which can be tracked as the prostate moves. This is often referred to as image-guided radiotherapy (IGRT).
A custom radiation plan is created for each patient using a scan obtained after the implanted markers are placed with a special high-resolution CT called a CT simulation scan. After the simulation scan is performed a customized radiation plan is designed and the radiation is delivered in 5 short sessions.
Patients should discuss the pros and cons of high dose SBRT with their treating physicians. Additional ongoing large. randomized trials, such as the PACE-C randomized clinical trial in the United Kingdom are ongoing and will be critical to confirm SBRT as standard treatment.
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Other Research Supporting Short Course Intensive Therapy
Duke researchers have also reported that shorter, intensive radiation can be recommended for low-grade prostate cancer at the 2016 annual Genitourinary Cancers Symposium in men with low-grade prostate cancer. The trial included 1,115 men with low-risk, early-stage prostate cancer who were treated with either conventional radiation therapy (41 fractions over 8.2 weeks) or hypofractionated radiation therapy (28 fractions over 5.6 weeks). Patients were treated between 2006 and 2009, and were followed for an average of nearly 6 years.
- The estimated 7-year cancer-free survival rates are 75.6% among men treated with conventional radiation, and 81.8% among those treated with hypofractionated radiation.
- Other outcomes, such as overall survival, time to biochemical relapse (elevation of PSA levels), and severe side effects were also similar between the two treatment groups.
The researchers concluded that among men with low-risk prostate cancer, a shorter course of radiation therapy utilizing a hypofractionated radiation schedule, provides similar outcomes compared to a longer course of conventional radiation therapy. (7)
- The American Society of Radiation Oncology (ASTRO). (2016.) SBRT offers prostate cancer patients high cancer control and low toxicity in fewer treatments. Can be retrieved from: here
- Study Finds Shorter Radiation Regimen Safe Effective for Advanced Prostate Cancer
- [Ultra-hypofractionated versus conventionally fractionated radiotherapy for prostate cancer: 5-year outcomes of the HYPO-RT-PC randomised, non-inferiority, phase 3 trial](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(19%2931131-6/fulltext)
- [Intensity-modulated fractionated radiotherapy versus stereotactic body radiotherapy for prostate cancer (PACE-B): acute toxicity findings from an international, randomised, open-label, phase 3, non-inferiority trial](https://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(19%2930569-8/fulltext)
- Long-term Outcomes of Stereotactic Body Radiotherapy for Low-Risk and Intermediate-Risk Prostate Cancer
- Abstract no: OC-0599, “Ultrahypofractionation for prostate cancer: outcome from the Scandinavian phase 3 HYPORT-PC trial”, Late-breaking abstracts and practice changing trials at 17:05 hrs (CEST) on Monday, 23 April, room 117. The research was funded by the Swedish Research Council and the Swedish Cancer Society.
- Lee W, Dignam J, Amin M, et al. NRG Oncology RTOG 0415: A randomized phase III non-inferiority study comparing two fractionation schedules in patients with low-risk prostate cancer. Proceedings from the 2016 annual genitourinary cancers symposium.
- Duke Medicine. (2016.) Shorter, Intensive Radiation Can Be Recommended in Early Prostate Cancer. [Press release.] Retrieved from here