Feasibility of In Vivo Dosimetry in Contact Radiotherapy Using Germanium‐Doped Silica Optical Fibers

Contact radiotherapy is an effective technique for treating superficial skin tumors, delivering highly localized doses while sparing healthy tissues. However, anatomical complexity in regions such as the nasolabial fold, eyelids, and auricular structures hinders applicator positioning and causes dosimetric uncertainties. This article evaluates germanium‐doped silica optical fibers (Ge‐doped OFs) as innovative radioluminescent in vivo dosimeters for real‐time dose monitoring. Four fibers with different germanium content (0.1%–9.5%) are fabricated using modified chemical vapor deposition and tested under 50–95 kV X‐rays on polymethyl methacrylate and anthropomorphic phantoms. The 9.5% Ge‐doped OF exhibits the highest sensitivity, excellent dose linearity ( R 2 = 0.9992), repeatability (0.4%), and reproducibility (2.6%). Its response closely follows that of a 0.02 cc ionization chamber across all field sizes and energies, with deviations <3%. On anthropomorphic phantoms, dose deviations of 1.8% and 6.8% in simple and complex configurations are shown, respectively. The latter value is reduced to 1.3% after correction using the inverse square law of distance. These findings support the use of Ge‐doped radioluminescent OFs as compact, high‐resolution detectors for precise in vivo dosimetry in contact radiotherapy.