Clinical in-vivo dosimetry for total skin electron therapy using gafchromic™ EBT4 film.

BACKGROUND: Total skin electron therapy (TSET) is a standard treatment for cutaneous T-cell lymphoma. Due to the complex patient positioning and irregular body contours, robust in-vivo dosimetry (IVD) is essential to verify dose uniformity. While thermoluminescent dosimeters (TLDs) are traditional standard, their utility is hindered by labor-intensive, manual processing. PURPOSES: This study evaluates the clinical implementation of a Gafchromic™ EBT4 film-based IVD system integrated with a bespoke, open-source analysis platform for automated batch-processing. To address the inherent orientation dependence and loss of film orientation frequently encountered when preparing small-format IVD films with a manual paper cutter, we developed an orthogonal dual-scan protocol. By averaging pixel values from two perpendicular scans for both calibration and clinical measurement, this protocol effectively mitigates orientation-dependent uncertainties and ensures dosimetric robustness. METHODS: The film-based IVD system was clinically assessed in five TSET treatments and compared to six treatments utilizing TLD-based IVD. Dosimetric accuracy was evaluated by comparing normalized fractional doses to the prescription. Statistical analysis was performed using the Mann-Whitney U test with the Benjamini-Hochberg procedure to control the false discovery rate across 20 anatomical sites. Workflow efficiency was quantified by the total time required for data readout and analysis per patient. RESULTS: The EBT4 film-based IVD demonstrated dosimetric accuracy comparable to the TLDs, with mean fractional doses of 102.7% ± 9.6% and 100.4% ± 9.7%, respectively (p = 0.25). Clinical implementation of the film-based approach significantly enhanced efficiency, reducing the total processing time from approximately 50 min to 15 min per treatment. CONCLUSIONS: The proposed EBT4 film-based IVD system, supported by open-source software and an orthogonal dual-scan protocol, offers a robust, cost-effective, and time-efficient alternative to traditional TLDs. This approach streamlines the clinical workflow without compromising dosimetric accuracy, making it a viable solution for TSET and broader radiotherapy IVD applications.