DOSE RELATIONSHIP DURING RADIOABLATION OF THYROID RESIDUAL IN PATIENTS WITH THYROID DIFFERENTIATED CANCER

Area of Science:

• Nuclear Medicine
• Oncology
• Radiotherapy

Background:

• Differentiated thyroid cancer (DTC) management often involves radioiodine therapy (RIT) to ablate residual thyroid tissue (RTT).
• Understanding the relationship between radiation dose delivered to RTT and treatment outcomes is crucial for optimizing RIT protocols.

Purpose of the Study:

• To investigate the correlation between focal adsorbed doses (FAD) in RTT and the efficacy of radioablation (RA) in DTC patients undergoing RIT.
• To identify optimal FAD levels for effective RA and explore factors influencing treatment response.

Main Methods:

• Analysis of FAD in RTT from 221 DTC patients treated with RIT.
• Scintigraphic imaging using gamma-camera and SPECT.
• FAD determination based on Medical Internal Radiation Dose (MIRD) Committee recommendations.

Main Results:

• Mean FAD in RTT was (125.9 ± 8.6) Gy, with significant variability (1.8-1373.4 Gy).
• Complete RA of 78% of RTT was achieved in 77.4% of patients after the first RIT course.
• RA efficacy increased with FAD, reaching a plateau around 350-400 Gy, with diminishing returns at higher doses.
• Regression analysis showed efficacy at 40 Gy was 72.8%, increasing to 95.7% at 500 Gy.

Conclusions:

• FAD in RTT varies widely due to post-surgical anatomical/functional changes and radioresistance.
• RA efficacy is non-linearly related to FAD, with an upper dose threshold around 350-400 Gy.
• Approximately 6% of RTT exhibits high radioresistance, potentially impacting treatment success.