A case study comparing VMAT treatment techniques to reduce dose to femoral heads for postmenopausal women during pelvic radiotherapy

Abstract

Volumetric modulated arc therapy (VMAT) is a common radiation treatment technique that delivers radiation to the planning target volume (PTV) while sparing the organs at risk (OAR). One limitation of VMAT on Varian linear accelerators is the limited distance the multileaf collimators (MLCs) can travel across the x-axis of the treatment field. The researchers in this case study sought to evaluate whether a split-field technique offers improved sparing of OAR, particularly dose to the femoral heads, in postmenopausal women undergoing treatment for the endometrium and pelvic lymph nodes. In the following retrospective study, 3 patients with endometrial cancer were selected. Two plans were generated for each patient, 1 split-field and 1 full-field. The full-field plan covered the full width of the PTV in both arcs. The split-field plan was created by reducing the X1 jaw to 2.0 cm on the clockwise arc, and the X2 jaw was reduced to 2.0 cm on the counterclockwise arc. PTV coverage along with OAR doses, was evaluated for all plans. All 3 patients showed lower doses to the femoral heads in the split-field plan. Doses to the rectum, bladder, and small bowel were also lower in the split-field plan. Differences in the dose were sometimes very small between the 2 techniques. Overall, the split-field technique demonstrated improved dose reduction over the full-field technique, but more research with a larger sample size is required to confirm the split-field technique.