CPT code 77300 designates dosimetry services used in radiation therapy planning — the quantitative calculation of radiation dose (measured in grays, Gy) required to treat malignant tumors. Accurate dosimetry is central to effective radiation oncology because it balances tumor control against risk to healthy tissue and guides subsequent adjustments to therapy. Nationally, dosimetry underpins treatment quality, safety, and billing for radiation oncology services. Key payers covered in this overview include Aetna, Blue Cross Blue Shield, Cigna, UnitedHealthcare, and Medicare. Readers will find a focused explanation of what 77300 covers clinically, typical sites of service, and why dosimetry matters in treatment planning. The publication summarizes common payer engagement and claims contexts, outlines typical use cases for 77300 in radiation oncology workflows, and provides benchmarks and policy-relevant considerations affecting coverage and billing practices. Content addresses clinical context, coding definition, and areas where payers commonly evaluate documentation for medical necessity. Data not available in the input is noted where applicable.