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Phase I/II Study Of A 5-fraction Hypofractionated Accelerated Radiotherapy Treatment For Low-risk Localised Prostate Cancer

December 21, 2019

UroToday - We are in a renaissance in the management of prostate cancer due to two main factors: advancements in technology and research. Standard management options include active surveillance, brachytherapy, external beam radiotherapy, or surgery and each approach is being influenced by research and technology.

In this paper, we report the initial results of image-guided intensity modulated radiotherapy (IGRT) that takes advantage of a weakness that's been discovered in prostate cancer. This allows patients to achieve the same or better cure rates with less side effects and fewer visits. In addition, it allows healthcare systems adopting this approach to treat far more patients at less cost per patient.

Like many tumours, prostate cancer is more likely to be killed using higher doses of radiation. This has now been confirmed in multiple properly designed clinical trials. The challenge was to limit the volume of normal tissues around the tumour target that received these higher doses as the greater the volume and dose received by these normal tissues, the greater the chance of irreparable long-term damage. However, unlike almost all tumours of the body, prostate cancer is more easily killed using large doses of radiation (as opposed to many smaller doses).

We combined these two research paradigms with IGRT to deliver the equivalent of 10 weeks of radiotherapy (5 treatments per week for a total of 52 treatments) in 5 treatments, one treatment per week over one month (total dose 35 Gray).

Even though we used 3.5 - 4 times the normal daily dose, we saw no significant (grade 3 or higher) side effects involving the bladder, bowel or tiredness in the first 30 patients (the subject of this paper). Since then we have treated 84 total patients on this protocol and only one (1%) has required a temporary urinary catheter during treatment.

While the follow-up is immature to make conclusions about PSA control rates long-term, thus far, the patients' PSAs are falling as expected and none have recurred. More follow-up will be required to determine the long-term efficacy of this program.

There are other groups that have implemented similar programs and published their work. One from Seattle used a stereotactic body radiotherapy (SBRT) machine to deliver 33.5 Gray in 5 fractions. Their 4-year PSA control rate was documented at 90% with no late grade 3 or higher toxicities. One advantage of our approach is that we used standard linear accelerators which are more widely available and cheaper than the SBRT machines and allow more comfortable patient setup.

Further study will be needed to resolve whether this approach is as effective as a standard external beam protocol. The challenge, however, is that both treatments are evolving so quickly that by the time mature data from these trials are available, the technology of 2006 - 2008 will be of historical interest only.

D. Andrew Loblaw, BSc, MD, MSc, FRCPC, CIP as part of Beyond the Abstract on UroToday

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