High-Accuracy In-Vivo Dosimetry Using Film Cut-Outs In Total Skin Electron Therapy
Abstract
Purpose
Precise, accessible, and patient-conformal in-vivo dosimetry remains a central requirement for assurance of safe radiotherapy delivery, particularly in high-dose-rate Total Skin Electron Therapy (HDR-TSET), where large treatment fields and complex patient geometry challenge traditional verification methods. Existing dosimetry systems such as TLDs and OSLDs often impose high financial and workflow burdens, limiting routine adoption and creating barriers for new or resource-constrained clinics. This work introduces and evaluates small (~12 mm) EBT-3 Film Cut-Out (FCO) dosimeters as a practical alternative for point-dose and profile-mapping applications in TSET.
Methods
FCO dosimeters were fabricated by cutting square segments from standard EBT-3 film using a Cricut® machine. Commissioning measurements included absolute dose comparison against calibrated ion-chamber measurements and beam-profile analysis at 6 MeV and 9 MeV. Clinical feasibility was assessed through in-vivo placement on an anthropomorphic phantom to evaluate conformality, workflow integration, and practical usability. Material cost per FCO was calculated and compared with commercially available OSLDs.
Results
Despite their small size, FCOs preserved the sensitivity and accuracy of full-size radiochromic film. Absolute dose measurements agreed with parallel-plate ion-chamber data within 2.5% in a water-phantom setup behind the scatter plate. Profile measurements exhibited a 4.3% uncertainty (2σ) relative to ion-chamber data in the TSET field. In comparison, standard OSLDs showed variations up to 10% in the same geometry. FCOs easily conformed to highly curved anatomy while maintaining full film-based dosimetric fidelity. Fabrication was simple and low-cost, with material cost of approximately $0.30 per FCO compared with $15 per OSLD (no longer available).
Conclusion
FCO dosimeters combine the dosimetric rigor of film with unprecedented practicality, offering a highly accurate, sensitive, and low-cost solution for routine HDR-TSET in-vivo dose verification. These findings suggest that FCOs can expand access to high-quality dosimetry and support broader clinical adoption of routine in-vivo dosimetry measurements.