Authors: Tae Kyu Lee, PhD^∗, Magdalyn D. Cunningham, BS, Tamara Eng, BS, Angela Kempen, BS, Adam Ries, BS

Department of Radiation Oncology, Allina Health Cancer Institute, St. Paul, MN, USA

Low-dose radiotherapy (LDRT) is increasingly used for degenerative and inflammatory joint conditions, yet technical guidance for planning shallow-depth periarticular targets remains limited. This study reports our institutional experience with CT-based planning for LDRT to the hands and knees, including immobilization, bolus configuration, beam selection, and quantitative analysis of V100, V95, Dmax, and Dmin for both GTV and PTV. Over a 6-month period, CT simulation and planning workflows were standardized for patients receiving LDRT. For hands, bolus was applied beneath the hand during simulation and again in the TPS; immobilization used individualized or combined masks. Knee simulations used a standard knee sponge. Plans used 6 MV AP–PA or mixed 6 MV (AP) and 10 MV (PA). A total of 56 knees and 30 hands were analyzed. Knee plans achieved strong target coverage (median PTV V95 ≈ 96%) with low hotspot volumes (median Dmax ≈ 107%). Hand plans demonstrated similarly robust coverage (median V95 ≈ 99%), with reproducible hotspot control across all cases. Dmin variability reflected expected dose behavior in shallow-depth regions influenced by anatomic curvature and residual MV buildup. LDRT to hands and knees can be effectively planned using standard 3DCRT techniques with consistent immobilization, bolus placement, and beam energy selection. The workflow produced reproducible dose distributions with V95 > 95% and Dmax < 110%, supporting the technical feasibility and clinical practicality of this approach.

As of January 1, 2022, ARRT requires CE Credits for Directed Journal Readings to be based on the word count for each article. So, the number of CE Credits for each DJR article will vary for ARRT.