A novel conformal arc technique for postoperative whole pelvic radiotherapy for endometrial cancer

Conventional whole pelvic radiotherapy (WPRT) with 3-dimensional conformal radiotherapy (3D-CRT) exposes most of the contents of the true pelvis to the prescribed dose. Intensity-modulated radiation therapy (IMRT) provides more conformal dose distribution and better sparing of critical structures for WPRT. However, IMRT is more complicated in planning and delivery, requiring more expensive equipment and time-consuming quality assurance. We explore and evaluate a novel conformal arc radiotherapeutic technique for postoperative WPRT for endometrial cancer in this study.

This technique involves 2-axis conformal arc therapy (2A-CAT) with 180-degree rotation around 2 isocenters each in 2 separate dose-shaping structures. Dosimetric comparison with 3D-CRT and IMRT for 10 endometrial cancer patients undergoing postoperative WPRT was performed to evaluate this new 2A-CAT technique.

The mean conformity indices were 0.83, 0.61, and 0.88 for 2A-CAT, 3D-CRT, and IMRT, respectively. The mean homogeneity indices were 1.15, 1.08, and 1.10. The mean doses to bowel, rectum, bladder, and pelvic bone marrow were, respectively, 1.19, 3.39, 4.65, and 1.64 Gy lower with 2A-CAT than with 3D-CRT (P < 0.05), whereas a little higher than with IMRT. The mean dose to normal tissue was 1.87 Gy higher with 2A-CAT than with IMRT (P = 0.00).

In postoperative WPRT for endometrial cancer, 2A-CAT significantly improves the dose conformity and sparing of bowel, rectum, and bladder compared with 3D-CRT. Despite dose uniformity and conformity being still inferior to those of IMRT, its simplicity and extensive availability combined with further improvement warrant it as a potential shortcut alternative to IMRT.