Engineering dosimetric excellence in total body irradiation: Tomotherapy-driven protocols for precision and reproducibility.

PROBLEM: The clinical feasibility, dosimetric reproducibility, and in vivo accuracy of a tomotherapy-based total-body irradiation (TBI) protocol in a large cohort of patients undergoing hematopoietic stem cell transplantation (HSCT) is evaluated.

METHODS

Patients (128 patients with hematological malignancies undergoing TBI with helical tomotherapy) were simulated in dual orientations (head-first and feet-first supine) to accommodate extended anatomical lengths. Plans were generated as separate upper and lower components with structured gradient overlap zones and then composited for delivery. Quality assurance included an ArcCHECK 3D diode array for patient-specific gamma analysis (3%/3 mm criteria), point-dose verification, and in vivo dosimetry. The gamma pass rates, regional dose deviations, and Pearson correlation coefficients were analyzed. Statistical evaluation was performed using the Shapiro-Wilk test, Levene's test, and ANOVA.

RESULTS

All treatment plans met the institutional constraints for planning target volume (PTV) coverage and organs at risk sparing. The mean D95% of the PTV consistently exceeded 95% of the prescribed dose, ensuring robust target coverage. This reflects excellent conformity with the planned dose distribution. Region-wise gamma pass rates exceeded 97% in all areas except junctions, where rates were slightly lower owing to dose gradients. The point-dose agreement showed tight clustering within the ±3% range, with the pelvis exhibiting the most significant positive shift. The in vivo optically stimulated luminescence dosimeter dose remained within the clinically acceptable range of 0.8-1.2 Gy. A strong interregional correlation (r > 0.90) was observed, confirming reproducibility. ANOVA identified statistically significant but clinically acceptable regional dose variations (p = 0.030).

CONCLUSION

Tomotherapy-based TBI demonstrated high dosimetric precision, reproducibility, and workflow efficiency. This protocol offers a clinically reliable approach for modern TBI delivery in transplant conditioning.