Simulation of dose to surrounding normal structures in tangential breast radiotherapy due to setup error
Ramachandran Prabhakar1, Goura K Rath, Pramod K Julka
1Department of Radiotherapy & Oncology, Institute Rotary Cancer Hospital, All India Institute of Medical Sciences, New Delhi, India. prabhakar_smr@hotmail.com
Summary
Radiotherapy setup errors significantly impact treatment outcomes. Minimizing isocenter shifts to below 3 mm is crucial for reducing complications and ensuring effective tumor control, especially with tangential fields.
Area of Science:
- Radiation oncology
- Medical physics
- Radiotherapy planning
Background:
- Setup error is a critical factor influencing radiotherapy outcomes.
- Understanding its dosimetric impact on target volumes and organs at risk is essential for safe and effective treatment.
Purpose of the Study:
- To evaluate the dosimetric effects of simulated setup errors on the planning target volume (PTV) and critical structures in breast cancer radiotherapy.
- To determine acceptable tolerance limits for isocenter shifts.
Main Methods:
- Twelve breast cancer patients (8 right-sided, 4 left-sided) underwent tangential field radiotherapy planning.
- Simulated isocenter shifts of 3 mm and 10 mm in X, Y, and Z directions were applied to 3D-CT datasets.
- Dose-volume histograms (DVHs) were analyzed for PTV, ipsilateral lung (IL), contralateral lung (CLL), contralateral breast (CLB), heart, and liver.
Main Results:
- Posterior and lateral isocenter shifts significantly affected the dose to the heart, lungs, and contralateral breast.
- A setup error of 3 mm was identified as a critical threshold.
Conclusions:
- Isocenter verification is vital for tangential fields in radiotherapy.
- Strictly limiting setup error to below 3 mm can minimize complications to normal tissues and maintain tumor control probability.
