Dosimetric Study of Synchronous Integrated Boost Intensity-Modulated Radiation Therapy for Metastatic Lymph Nodes In Rectal Cancer
Abstract
Purpose
This study designed SIB-IMRT plans based on pathologically confirmed positive LNs and compared them with conventional IMRT plans to evaluate the feasibility and dosimetric advantages of SIB-IMRT for rectal cancer patients with metastatic LNs.
Methods
A retrospective study was conducted on 30 patients with confirmed LN metastasis. Based on fused MRI/CT images, target volumes (GTVn, PGTVn, PTV45, PTV50) and organs at risk (OARs: bladder, small intestine, femoral heads) were delineated. Two treatment plans were designed for each patient: 1) Conventional IMRT: A uniform dose of 50 Gy in 25 fractions to the combined PTV. 2) SIB-IMRT: Delivering simultaneous but different doses: 52.5 Gy to metastatic nodes (PGTVn), 50 Gy to the primary tumor area (PTV50), and 45 Gy to the elective nodal area (PTV45), all in 25 fractions. Dosimetric parameters for PTV (Dmax, Dmean, D98%, Conformity Index CI, Homogeneity Index HI, Tumor Control Probability TCP) and OARs were compared.
Results
PTV Coverage: Both plans met coverage requirements. SIB-IMRT achieved a significantly higher TCP (median 95.37% vs. 91.84%, p<0.05) and a higher Dmax (median 55.65 Gy vs. 53.95 Gy, p=0.002) compared to IMRT, while Dmean, D98%, CI, and HI were not significantly different. OARs Sparing: SIB-IMRT demonstrated better organ sparing: Small Intestine: Significantly reduced Dmax, Dmean, and V50 (p<0.05). Bladder: Significantly reduced V30 and V40 (p<0.05). Femoral Heads: Significantly reduced Dmax and V20 for both left and right sides (p<0.05).
Conclusion
IMRT is a common technique for rectal cancer radiotherapy, SIB-IMRT can increase the TCP for the target volume, suggesting it may be an effective treatment strategy for rectal cancer metastatic lymph nodes.