Evaluating Potential Dosimetric Advantage of Integrating Highly Conformal Target Delineation with VMAT Compared to Conventional Flank Irradiation for Wilms Tumors

Abstract

Objectives

Conventionally flank irradiation for Wilms tumor typically utilized anteroposterior (AP-PA) photon beams. However, recent publications prioritize precise flank target volume delineation following SIOP Renal Tumor Study Group (RTSG) consensus protocol taking postoperative organ shifts and intrafractional motion into consideration. This study aims to evaluate the dosimetric advantage of Volumetric Modulated Arc Therapy (VMAT) versus conventional AP/PA technique for Wilms tumor.

Method

Patients with stage II and III High-risk Wilms tumors referred for postoperative radiotherapy were included. Dosimetric analysis was conducted retrospectively on eight cases. For each patient, separate target volumes were delineated for highly conformal and conventional treatment plans, employing VMAT for highly conformal and AP/PA for conventional volumes. All cases were planned preceding mandatory peer review. A dose of 2520cGy/14fraction was prescribed as per SIOP High-Risk Wilms tumor protocol. Planning target volume (PTV) in cm3, mean doses to the liver, small bowel, contralateral kidney, and spleen were calculated and subsequently compared.

Results

Five (n=10) right-sided and three(n=6) left-sided flank volumes were included. In the study, highly conformal volumes planned via VMAT demonstrated a reduction in PTV compared to conventional volumes, 629.04 cm³ vs. 798.8 cm³ respectively. Mean dose reduction favoring highly conformal target volumes was observed for mean of all OARs, including liver (942.5 cGy conformal vs. 1264 cGy conventional), contralateral kidney (258.6 cGy conformal vs. 294.2 cGy conventional), small bowel (1114.7 cGy conformal vs. 1411.7 cGy conventional), and spleen (1401cGy conformal vs. 1990cGy conventional). VMAT provided greater dose sparing to normal structures as compared to AP/PA techniques.

Conclusion

Compared to conventional AP/PA photon beams, flank irradiation, employing highly conformal flank target volumes with VMAT resulted in reduced doses to the OARs, while still maintaining acceptable organ doses in the AP/PA plan highlighting the value of peer review in ensuring radiation quality, and dosimetric benefits.