During this period, dosimetry-driven optimization guided external radiotherapy design, supported by advances in depth-dose mapping across energies and field geometries. Detector technology and metrology for dosimetry and spectroscopy advanced, including scintillation detectors, counting-efficiency data, and spectrometry, which in turn improved clinical measurement capabilities. Energy-selective X-ray measurement and monochromatization enabled more precise imaging and analysis, complemented by calibration and microradiography infrastructure and strengthened by safety-focused dosimetry reliability. Influential Works: Key breakthroughs include radiophotoluminescence dosimetry, enabling direct patient dose measurement and quality assurance for imaging. Early investigations into radiation-induced cataracts provided quantitative evidence of lens risk, informing safety limits for ophthalmic imaging. Additional cross-period innovations—dichromatic absorption radiography and dipping sections in fluid emulsion for radioautography—opened new imaging contrasts and higher-resolution tissue mapping.