From Imaging to Therapy: A Simulation-Based Radiobiological and Dosimetric Feasibility Study of Kilovoltage X-Ray VMAT for Skin Field Treatment
Abstract
Purpose
To investigate the dosimetric and radiobiological advantages of repurposing a standard kilovoltage (kV) X-ray source for the treatment of nonmelanoma skin cancer. This study assessed the kV X-ray beam character and plan quality indices compared with other radiotherapy (RT) modalities.
Methods
A diagnostic CT scanner source was re-engineered for therapeutic delivery. The advantages of kV X-ray was evaluated through depth-dose curve analysis and relative biological effect assessments, comparing it against traditional electron and MV X-ray. Dosimetric performance was evaluated on phantom and patient datasets by comparing kV-VMAT against other RT techniques (Electron+bolus, MV-VMAT, MV-VMAT+bolus) for superficial treatments using the Conformity Index (CI) and Heterogeneity Index (HI). Doses to Organs at Risk (OARs) were quantified to evaluate the normal tissue sparing efficacy of the different RT techniques.
Results
Radiobiologically, simulations indicated that 120 kVp X-rays possess a higher therapeutic potential at superficial depths. At a depth of 2 cm, the DNA DSB-based RBE (compared with 6 MV X-ray) for 120 kVp X-rays was 1.12, surpassing the RBE of 0.98 calculated for 6 MeV electrons. For phantoms with convex PTV, 120 kVp kV-VMAT consistently achieved improved average CI (0.62) and average HI (1.10) across all PTV thickness relative to MV-VMAT plans (average CI:0.56, average HI:1.20) and Electron+bolus (average CI: 0.55, average HI:1.15). In patient study, dosimetric analysis indicated that the kV-VMAT technique yielded a superior HI ((1.088 (kV-VMAT) vs 1.228 (Electron+bolus), 1.269 (MV-VMAT), 1.278 (MV-VMAT+bolus)) and enhanced sparing of healthy tissues indicated by improved OAR mean dose (3.85 Gy (kV-VMAT) vs. 17.23 Gy (Electron+bolus), 4.23 Gy (6 MV MV-VMAT), 4.23 Gy (6 MV MV-VMAT+ bolus)). These findings underscore the potential of kV-VMAT for superficial skin field carcinomas treatment.
Conclusion
This study validates the dosimetric and radiobiological advantages of kV-VMAT for treating non-melanoma skin cancer in both phantom and patient cohorts.