Three-dimensional versus four-dimensional dose calculation for breast intensity-modulated radiation therapy
Joo-Hyun Chung1, Minsoo Chun1,2,3, Jung-In Kim1,2,3
1Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea.
The British Journal of Radiology
|March 19, 2020
Summary
Respiratory motion significantly distorts radiation dose distribution in breast IMRT, increasing doses to the heart, lungs, and particularly internal mammary lymph nodes (IMN). Optimization is crucial for IMN during dose calculation.
Area of Science:
- Radiation Oncology
- Medical Physics
- Oncology
Background:
- Breast cancer treatment often involves intensity-modulated radiation therapy (IMRT).
- Respiratory motion during IMRT can introduce intra- and interfractional variations in radiation dose delivery.
- Accurate dose calculation considering motion is essential for effective treatment and minimizing side effects.
Purpose of the Study:
- To analyze the impact of intra- and interfractional motion on dose distribution during breast IMRT.
- To quantify the discrepancies in dose calculation caused by respiratory motion using four-dimensional computed tomography (4DCT).
Main Methods:
- 20 left breast cancer patients underwent 3DCT and 4DCT scans.
- IMRT plans were created based on 3DCT, with dose distributions recalculated for 10 respiratory phases using 4DCT data.
- Interfractional variations were simulated by randomizing starting respiratory phases for 16 fractionations.
Main Results:
- 4D-calculated doses showed significant distortions in conformity and homogeneity compared to 3D plans.
- Mean doses to the heart (0.34 Gy) and ipsilateral lung (0.59 Gy) were significantly higher in 4D-calculated doses.
- The mean internal mammary lymph node (IMN) dose was significantly increased (1.42 Gy) in the 4D-calculated plan.
Conclusions:
- Respiratory motion and the interplay effect with IMRT significantly alter dose distribution, especially for IMN.
- Current dose calculation methods may not fully account for motion-induced discrepancies.
- Optimization of IMN dose calculation is recommended for free-breathing left breast IMRT to improve treatment accuracy.
