Robustness of Radiotherapy Plans to Geometric Uncertainties in Irradiating Patients with High-Density Prostheses

The concept of introducing additional target margins has proven effective in photon radiotherapy and, therefore, is a widely accepted method for ensuring the required dose distribution during planning. However, due to the specific interactions of photon radiation with matter in cases of significant tissue heterogeneity, radiotherapy planning necessitates assessing the robustness of the plan or developing a plan resilient to existing dose delivery uncertainties. This study tested the robustness of radiotherapy plans to geometric uncertainties using two irradiation technologies: CRT (conformal radiation therapy) and IMRT (intensity-modulated radiation therapy). A total of 15 patient plans with metallic prostheses were analyzed. The patient’s position relative to the isocenter of the irradiation beams was geometrically shifted to simulate potential patient setup errors. Data on actual displacements obtained during pretreatment visualization—approximately 25 000 treatment fractions for patients with various tumor localizations—were analyzed. According to the results of the study, the probability of not achieving the required dose distribution for the clinical target volume is no more than \(0.04\pm 0.03\%\) when using the CRT technique and no more than \(7\pm 4\%\) when using IMRT. Thus, the CRT plans demonstrated greater robustness with respect to the target compared to IMRT plans. When IMRT techniques are required for treating patients with prostheses, increased attention must be paid to the patient’s setup and plan robustness verification.