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The HYACINCT trial will investigate the role of dose-adapted hypofractionated pelvic RT in cisplatin-intolerant locally advanced cervical cancer patients (ClinicalTrials.gov Identifier: NCT05210270). This dummy run evaluated the feasibility of the protocol treatment planning objectives using IMRT and VMAT.

The HYACINCT protocol defines a set of guidelines for image acquisition, target and organ delineation and treatment planning objectives (Table 1).

Fifteen dummy cases were prepared, five each for three levels of dose requirements: 40Gy without boost, and with boost to 45Gy and to 48Gy. IMRT and VMAT plans were prepared for each case, evaluated and assigned penalty and compliance scores according to planning objectives, and subjected to quality control.  

IMRT and VMAT plans were created by the same physicist for each case using the Eclipse® v. 16.1 (Varian Medical Systems) treatment planning system (TPS) for a Varian VitalBeam® linear accelerator, using 6-MV photons. For the IMRT plan, a single isocenter and seven evenly-spaced coplanar beams were employed. Sliding-window multi-collimator leaf motion was used. For the VMAT plan, the isocenter was placed at the same location similar to that of the IMRT plan. Two full-rotation arcs and collimator angles 45° and/or 315° were used.

IMRT and VMAT plans were compared in terms of treatment plan quality (target coverage, penalty and compliance scores), and treatment delivery. Tumor extent (T-stage, T-score), nodal status, and PTV volumes (in cc) were examined as potential determinants of penalty and compliance scores.

IMRT was able to meet the planning objectives for all but one case; and VMAT, for all cases. All plans passed the quality control check. IMRT and VMAT were equivalent in terms of target coverage and penalty and compliance scores, but the latter was associated with better treatment delivery (Table 2).

On univariate analysis, no significant determinant was identified for the compliance score for the IMRT and VMAT plans. The T-score was found to be a borderline statistically significant determinant for the penalty score for the IMRT plans (ß = 0.903, 95% CI = -0.24 to 2.05, p = 0.079); none for the VMAT plans. On multivariate analysis, T-score was confirmed to be a significant determinant for penalty score for the IMRT plans (ß = 1.11, 95% CI = 0.15 to 2.07, p = 0.028).

The HYACINCT radiotherapy protocol is feasible with either IMRT or VMAT. VMAT may be beneficial in more extensive cases, as measured by the T-score.