Radiotherapy is a type of cancer treatment using high-energy ionising radiation to kill cancer cells. For prostate cancer, radiotherapy has long been established as one of the standard treatments. Radiotherapy works as well as surgery in curing early stage prostate cancer, yet is associated with less erectile dysfunction and urinary incontinence.

Traditional radiotherapy requires daily treatments for a total of 37-39 sessions and the entire treatment course often lasts up to two months. Over the past decades, advances in radiotherapy technology and incorporation of X-ray and computer tomography (CT) imaging during treatment (image-guided radiation therapy [IGRT]) have allowed radiotherapy to be given at the level of precision within millimeters.

Stereotactic Body Radiation Therapy (SBRT) was first developed to treat small brain lesions not amenable for surgery, and quickly expanded to treat other types of cancer. SBRT can deliver much larger radiation doses for each treatment and complete the entire radiotherapy course in as short as five sessions.

Prostate SBRT was first studied by a group of radiation oncologists from the University of California, Los Angeles (UCLA) in 2000. In a recently updated publication of more than 2,000 patients treated across several centers in US, after a median follow-up of seven years, no patients died from prostate cancer while only 6% had recurrence and 0.6% had developed distant metastases.

Two large randomised studies from Scandinavia and Canada also confirmed that long-term side effects of SBRT were similar to conventional fractionated radiotherapy.

The SBRT Process

Although SBRT significantly reduces total duration of radiotherapy from two months to less than two weeks, it requires a more complex and longer preparation for the treatment. An additional magnetic resonance imaging (MRI) scan has to be performed in the treatment position to accurately identify the prostate and other normal structures.

Prior to treatment delivery, a cone beam computed tomogram (CBCT) is acquired by the linear accelerator machine. The attending radiation oncologist will verify the treatment position prior to actual radiation delivery. The entire process can last up to 20 minutes but the actual radiation beam-on time only takes less than two minutes to complete.   

This short delivery time is made possible by the use of a novel technology called flattening-filter-free (FFF) delivery, which increases the speed of delivery up to four times as compared to the standard treatment; which greatly reduces the uncertainty of patient motion during treatment. An example of the trend and magnitude of the required treatment planning margins to account for such prostate motion during treatment is illustrated in Figure 1.

Common side effects

During SBRT, common side effects encountered by patients are: mild tiredness, urinary frequency and a burning sensation on passing urine. These side effects sometimes can continue after treatment but eventually will improve after a few weeks. After SBRT, radiation oncologists will follow-up with patients in the clinic every three to six months with a PSA blood test.

REFERENCE 1. Eric Pei Ping Pang, Kellie Knight, Sung Yong Park, Weixiang Lian, Zubin Master, Marilyn Baird, Jason Wei Xiang Chan, Michael Lian Chek Wang, Terence Wee Kiat Tan, Melvin L. K. Chua, Eu Tiong Chua, Wen Shen Looi, Wen Long Nei, Jeffrey Kit Loong Tuan. Duration-dependent margins for prostate radiotherapy—a practical motion mitigation strategy. Strahlenther Onkol ; In press. DOI: 10.1007/s00066-019-01558-y

Dr Jeffrey Tuan is a Senior Consultant and Research Director in the Division of Radiation Oncology at the National Cancer Centre Singapore (NCCS). Dr Tuan received his medical degree from the National University Singapore School of Medicine in 2000. He received his specialist training in the Division of Radiation Oncology at the NCCS and the Royal Marsden Hospital in London, UK.

Acknowledgments: Li Youquan, Ashley Ong and Eric Pang for help in preparing the article.