In this randomized study, 470 men with intermediate or high risk clinically-localized prostate cancer who were undergoing IGRT were randomized to undergo either daily or weekly control imaging in order to guide treatment. 77% of these patients had cone beam CT imaging to plan treatment. The primary outcome for this study was to evaluate the safety and efficacy of daily control imaging, and to detect a minimum of a 12% difference in 5-year disease free survival between the groups. Their hypothesis was that more frequent control imaging would lead to more accurate treatment and, thus, improved cancer-specific outcomes. Secondary outcomes included toxicity, clinical recurrence, overall survival, and development of a second malignancy. The median follow-up was 4.1 years.
They found that in men who underwent daily control imaging had a decreased incidence of development of acute rectal bleeding (6% versus 11%, p = 0.014). Men in the daily imaging group also experienced lower rates of biochemical recurrence (HR 0.45, p = 0.007). Clinical recurrence rates were additionally lower in the daily imaging group (HR 0.50, p = 0.057). Overall survival was similar between the two groups.
Conversely, when they evaluated the risk of a patient developing a secondary malignancy after the trial, the men in the daily imaging group were found to have an increased risk of a second cancer as compared to the weekly imaging group. Dr. de Crevoisier explained that this finding may be related to the increased frequency of imaging, which leads to a higher whole-body exposure to radiation. Only 18% of the secondary malignancies that occurred were located within the pelvis, near the field.
He concluded that as compared to weekly imaging, by improving targeting, daily control imaging in prostate cancer IGRT significantly decreases the risks of cancer recurrence and rectal toxicity, however it is associated with an increased risk of development of a secondary malignancy. They are plan to re-evaluate their data with longer follow-up to better assess the rate of radiation-associated secondary malignancies.
Presented by: Renaud de Crevoisier, MD, PhD
Written by: Brian Kadow, MD, Fox Chase Cancer Center, Philadelphia, PA, at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA