Phase II Randomized Trial of 2 Versus 5 Fraction Prostate Stereotactic Ablative Radiotherapy for Intermediate Risk Prostate Cancer

Prostate cancer is a common cancer, and a significant cause of cancer death in men. There are many potentially curative treatment options for prostate cancers that have not spread. A relatively recent option is called prostate stereotactic ablative radiotherapy (SABR). SABR is a form of external beam radiotherapy, where patients receive a small number (5-7) of treatments (also called fractions) of radiation delivered in a highly accurate and precise fashion. Standard prostate SABR is generally given in 5 fractions and has been shown to be at least as effective as conventional external beam radiotherapy. Disease control with SABR appears excellent, and it compares favorably to surgery in terms of side effects and quality of life. In theory, reducing the number of fractions from 5 to 2 may improve disease control and reduce side effects, in addition to providing added convenience for patients. Small studies suggest prostate SABR in 2 fractions may be highly effective and well tolerated. However, there is little available data comparing 2 and 5 fraction SABR head to head to tell us which is superior. Two fraction SABR involves delivery of 2 large dose fractions of radiotherapy which could result in significant side effects if proper precautions are not taken. The use of continuous tracking of the prostate gland position during treatment delivery reduces the risk of missing the prostate or overdosing organs near by. Such tracking has been shown to reduce bladder side effects. Also, the use of a rectal spacer placed between the prostate and rectum has been shown to reduce bowel side effects. Also, advanced artificial intelligence (AI)-directed computer applications could potentially improve the targeting of radiation during each treatment. The ADAPT-2 study is a randomized phase II trial comparing standard 5-fraction SABR with an experimental 2-fraction approach in men with intermediate risk prostate cancer. All treatment, whether 5 or 2-fractions, will use continuous prostate tracking (also called triggered imaging) and a rectal spacer (called Space OAR Hydrogel) to minimize side effects. The trial will also evaluate the potential of a new AI-guided dose guidance application to see if it can improve current methods of targeting SABR each day. This aspect of the study will be offline; that is, the AI application will not be used to actually target treatment for the trial patients. Rather, daily targeting of SABR will use standard conventional means, and the AI application will be studied in a simulated fashion to determine it is useful and can be incorporated into workflow. The main goal of the ADAPT-25 study is to compare the long-term side effects and quality of life between 5- and 2-fraction prostate SABR. Secondary goals will be to compare the long-term disease control between 5-and 2-fraction prostate SABR, and to evaluate whether a novel AI-directed dose guidance application can be used to better target SABR by reducing doses to neighboring organs, and whether it can be easily fit into prostate SABR workflow.