Dosimetric and Radiobiological Impact of Patient Setup Errors in Intensity-modulated Radiotherapy for Esophageal...

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Patient setup accuracy is crucial for effective intensity-modulated radiotherapy (IMRT).
• Esophageal cancer treatment with IMRT requires precise dose delivery to maximize tumor control and minimize toxicity.
• Understanding the impact of setup errors is essential for optimizing treatment planning and delivery.

Purpose of the Study:

• To evaluate the impact of patient setup errors on dosimetry and radiobiological outcomes in IMRT for esophageal cancer.
• To compare the effects of setup errors between thermoplastic mask (TM) and vacuum bag (VB) immobilization techniques.
• To analyze the correlation between real setup errors (RSE) and predicted treatment outcomes (TCP/NTCP).

Main Methods:

• Retrospective analysis of 56 esophageal cancer patients undergoing IMRT.
• Utilized cone-beam CT data to generate simulated setup errors (SSE) based on real setup errors (RSE).
• Simulated treatment fractions by shifting the isocenter and recalculated doses; compared simulated plan sums (SPS) with original treatment plans (OTPs) for dosimetric and radiobiological indices.

Main Results:

• Setup errors reduced PTV dose homogeneity and conformity, decreasing PTV TCP in both TM and VB groups.
• VB group showed larger reductions in PTV homogeneity, conformity, and TCP compared to the TM group.
• Mean RSE correlated negatively with PTV TCP and positively with NTCP of lung and spinal cord, indicating potential for increased complications.

Conclusions:

• Patient setup errors can compromise IMRT efficacy for esophageal cancer by reducing dose conformity and potentially lowering TCP.
• Increased NTCP for organs at risk, particularly with isocenter shifts towards them, highlights the clinical significance of setup errors.
• Vacuum bag immobilization may be more susceptible to the adverse effects of setup errors, warranting further investigation and potentially stricter patient positioning protocols.