ESTRO 2024 - Abstract Book

S1027

Clinical - Gynaecology

ESTRO 2024

evidence comparing advanced volume based techniques to simple fields arrangements in the palliative setting. The time-limiting factor is often the need to contour target volume and normal structures. When optimising for a volumetric arc therapy (VMAT) plan, it is feasible to use a normal tissue objective (NTO) tool which sharpens the dose gradient beyond the target volume without accounting for avoidance of organs at risk (OAR) (5). This provides a practical and time-saving solution to speed up the planning pathway. The aims of this study were to evaluate the pattern of palliative treatments currently used, and to undertake a dosimetric comparison of VMAT plan versus conventional fields for patients with gynaecological cancer treated with palliative treatment in the pelvis. The potential time-saving approach with NTO-optimisation was assessed, and dose escalation to the planning target volume (PTV) was also examined.

Material/Methods:

The radiotherapy techniques for palliative treatment of gynaecological cancer were assessed for all patients treated in one department from Jan 2017-March 2020. The radiotherapy CT planning scans from twenty patients who received palliative radiotherapy for gynaecological cancer were used for the dosimetric study; 10 with localised disease and 10 with more widespread disease. For each case, the gross tumour volume (GTV) and OARs including the rectum, bladder and bowel were contoured. A 1cm isotropic margin was added to generate a PTV. For each patient, 4 separate plans were generated using Eclipse v16.0. These were planned using;

2 Parallel opposed fields (POP) Standard VMAT plan (VMAT)

•

•

• Simplified VMAT plan optimised using NTO tool (VMAT_NTO) • VMAT plan with dose escalation to the PTV (SBRT-like). This is achieved by normalising the plan to cover 95% of the PTV with the prescription dose without setting a maximum dose limit for the PTV.

For each data set, dosimetric parameters pertaining to the PTV and OARs, conformity index (CI) and homogeneity index were compared to the standard VMAT plan. The prescribed dose was 30Gy in 10 fractions.

Results:

In total, 177 patients with gynaecological malignancy were treated with palliative radiotherapy, of which 68 had treatment to the pelvis, excluding bone metastases. Of these 68 patients, the majority (69%) were treated with a simple POP technique, while only 25% had VMAT.