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Factors Affecting Prostate Displacement During Volumetric Modulated Arc Therapy in Prone Position After
Takayuki Sakurai1, Shigeyuki Takamatsu1, Satoshi Shibata1
1Department of Radiology, Graduate School of Medicine, Kanazawa University, Kanazawa, Ishikawa, Japan.
Advances in Radiation Oncology
|December 4, 2023
Summary
Prostate displacement during radiation therapy is influenced by bladder and rectal anatomy, and changes in prostate volume. Understanding these factors is crucial for accurate treatment targeting and improved outcomes in prostate cancer patients.
Area of Science:
- Radiation Oncology
- Medical Physics
- Prostate Cancer Treatment
Background:
- Accurate radiation targeting in prostate cancer is challenging due to prostate displacement.
- Registration based on bony structures may not precisely align with the prostate's actual position.
- Identifying factors influencing prostate displacement is crucial for optimizing treatment delivery.
Purpose of the Study:
- To investigate factors influencing prostate displacement during volumetric modulated arc therapy (VMAT) after high-dose-rate brachytherapy (HDR-BT).
- To analyze trends in prostate displacement across multiple radiation fractions.
- To correlate displacement with clinical and anatomical factors for improved treatment accuracy.
Main Methods:
- Seventy prostate cancer patients receiving VMAT after HDR-BT were analyzed.
- Prostate displacement was measured using cone-beam computed tomography (CBCT).
- Systematic error (SE) and random error (RE) were assessed in three directions (RL, CC, AP).
- Prostate volume change (PVC) and anatomical factors (bladder, rectum) were evaluated.
Main Results:
- Mean SE was minimal in RL (-0.01 mm) and AP (-0.47 mm) but significant in CC (-2.34 mm).
- SE in CC and AP directions correlated with bladder volume and PVC.
- RE in CC direction was linked to smoking, while AP RE was associated with PVC.
- A gradual caudal and posterior prostate displacement was observed throughout treatment.
Conclusions:
- Anatomical features of the bladder, rectum, and prostate volume changes significantly predict systematic errors.
- Smoking status and prostate volume changes are key predictors of random errors.
- Prostate volume changes exceeding 140% necessitate adjustments in internal margins for precise targeting.
