KEY POINTS
- This single-center retrospective cohort included 4,699 patients treated for non-malignant musculoskeletal disorders between 1994 and 2011, encompassing 5,614 treatment series. Mean age at treatment was 64 years, and Kaplan–Meier estimates suggested an expected post-treatment survival of approximately 21 years.
- The historical low-dose radiotherapy regimen was typically 6 × 1 Gy to 6 Gy using 200-kV orthovoltage irradiation, delivered two to three times weekly. Reirradiation of the same site occurred in 679 patients (14.4%), while smaller subsets underwent third or fourth courses.
- Only 3 solid malignancies were identified within previously irradiated fields, corresponding to 0.064% of the cohort. The authors note that the observed in-field solid cancers were predominantly basal-cell carcinomas in sun-exposed regions, where ultraviolet exposure represents an important competing carcinogenic factor.
- Hematologic malignancies were evaluated according to whether the treated field contained hematopoietic red bone marrow. In total, 60 hematologic malignancies (1.28%) were recorded: 34/1,793 (1.90%) after treatment of marrow-containing regions versus 26/2,906 (0.89%) after treatment of regions without active marrow.
- At 12.5 years, hematologic malignancy-free survival was 97.7% after irradiation near active marrow versus 99.0% after irradiation of non-marrow regions, an absolute difference of 1.3 percentage points (p=0.002). Differences were most evident for shoulder and trunk/pelvic treatment locations.
- Exposure patterns varied substantially: the most frequently treated sites were shoulder (29.5%), foot (25.3%) and knee (25.0%). Shoulder, hip and axial-skeleton fields were classified as containing active red marrow, whereas foot, knee, elbow and hand fields were not.
- Causal inference is limited by retrospective hospital-based event ascertainment, low absolute event counts, incomplete capture of cancers diagnosed outside the institution and major potential confounding from age, obesity, lifestyle and cancer-screening behaviour. The study also evaluated an older 6-Gy orthovoltage regimen, whereas contemporary benign-disease schedules may use lower total doses.
CLINICAL TAKEAWAY
For older adults receiving low-dose RT to peripheral musculoskeletal sites, this large cohort provides reassuring long-term evidence that in-field solid malignancies are exceedingly uncommon. The marrow-associated hematologic signal deserves caution for central or marrow-rich treatment sites, but the observational design cannot establish that radiation caused the excess.
SOURCE
International Journal of Radiation Oncology, Biology, Physics