Vulvar Cancer: Dosimetric Comparison of Advanced 3D Conformal Radiation Therapy Technique with Anteroposterior and Posteroanterior Irradiation Techniques

Introduction: The commonly used technique of radiation therapy for vulvar cancer consists of anteroposterior (AP) and posteroanterior (PA) fields. This is the first study that reports the dosimetric comparison between the AP-PA techniques and the new 3D advanced conformal technique (3D-ACT) based on the multiplicity of treatment fields in patients with squamous cell cancer of the vulva in the postoperative setting. Material and Methods: This comparative planning study was conducted on15 patients with vulvar carcinoma treated with adjuvant radiation therapy at the National Institute of Oncology in Rabat, Morocco. Three treatment plans were performed, corresponding to three techniques, namely photons with source-skin distance inguinal supplement, modified segmental boost technique and 3D advanced conformal technique. For each plan, the dose-volume histogram was used to generate planning target volumes (total and inguinal PTV) and organs at risk (bladder, rectum, bowel and femoral heads) parameters. Results: The 95% isodose volume was significantly reduced with the advanced conformal technique (P<0.0001) without compromising the total PTV coverage (P= 0.94). This technique resulted in the best conformity and homogeneity index. The 3D-ACT decreased significantly the PTVs Dmax and Dmean (P<0.0001), and offered better homogeneity for inguinal PTV (i.e., 1.07±0.01, P<0.0001).The 3D-ACT decreased the rectum absorbed dose, V40 (volume receiving ≥40Gy), V45, and Dmaxto50.21±27.21, 22.81±10.22, and 46.56±1.11, respectively. With regard to femoral heads, the 3D-ACT decreased the Dmax and V45 in comparison to the other two techniques. Conclusion: The 3D-ACT seems to be an alternative to the AP-PA irradiation techniques in postoperative setting when IMRT is unavailable.