Activity Trackers During Breast Cancer Radiation Therapy

Do Activity Trackers Reveal the Real Impact of Radiation Therapy on Breast Cancer Patients?

A wearable-based study quantifying steps, distance, calories, and sleep before, during, and after radiation therapy challenges assumptions about treatment-related fatigue.

Fatigue is one of the most commonly reported side effects of radiation therapy (RT) for breast cancer, but until recently, its actual impact on daily activity and sleep had rarely been measured objectively. Assessing Changes in the Activity Levels of Breast Cancer Patients During Radiation Therapy (Champ et al., Clinical Breast Cancer, 2018) used consumer activity trackers to quantify exactly that, in 10 women undergoing RT after lumpectomy.

Key Takeaways

Activity levels, steps, distance walked, and calories burned were continuously tracked before, during, and after RT using wearable devices, rather than relying on patient-reported fatigue.
Median daily step count was 5,047 steps (range 2,741–15,508), with a median distance of 1.6 miles/day.
During RT, patients showed a small but statistically significant decrease in steps (–54/day), distance (–0.02 miles/day), and calories burned (–3/day), changes the authors describe as not clinically meaningful.
Sleep duration did not change significantly across treatment, averaging 6.8 hours per night (range 5.5–8.3).
Overall conclusion: RT has only a minimal, non-clinically relevant effect on objectively measured activity and sleep in women treated for early-stage breast cancer.

Why It Matters

Patient-reported fatigue during RT doesn’t always translate into measurable declines in real-world activity or sleep. This distinction matters for how clinicians counsel patients, how “fatigue” is defined and measured in trials, and how wearable-derived digital biomarkers can supplement, or challenge, subjective symptom reporting in oncology.