Clinical implementation of coverage probability planning for nodal boosting in locally advanced cervical cancer

To implement coverage probability (CovP) for dose planning of simultaneous integrated boost (SIB) of pathologic lymph nodes in locally advanced cervical cancer (LACC).

CovP constraints for SIB of the pathological nodal target (PTV-N) with a central dose peak and a relaxed coverage at the perimeter were generated for use with the treatment planning system Eclipse: PTV-N D98 >90%, CTV-N D98 >100% and CTV-N D50 >101.5% of prescribed dose. Dose of EBRT was 45Gy/25 fx with a SIB of 55-57.5Gy depending on expected dose from brachytherapy (BT). Twenty-five previously treated patients with 47 boosted nodes were analysed. Nodes were contoured on cone beam CT (CBCT) and the accumulated dose in GTV-N_CBCT and volume of body, pelvic bones and bowel receiving >50Gy (V50) were determined.

Nearly all nodes (89%) were visible on CBCT and showed considerable concentric regression during EBRT. Total EBRT and BT D98 was >57 Gy_EQD2 in 98% of the visible nodes. Compared to treatment plans aiming for full PTV-N coverage, CovP significantly reduced V50 of body, bones and bowel (p<0.001) CONCLUSION: CovP is clinically feasible for SIB of pathological nodes and significantly decreases collateral SIB dose to nearby OAR.