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Published on: February 6, 2019
Inter- and intrafraction uncertainty in prostate bed image-guided radiotherapy
Kitty Huang1, David A Palma, Danielle Scott
1Department of Radiation Oncology, London Health Sciences Centre, London, Canada.
Summary
Prostate bed motion (PBM) is a major source of error in radiotherapy after prostatectomy. Image-guided radiotherapy (IGRT) can reduce planning target volume (PTV) margins by 1-2 mm, optimizing treatment.
Area of Science:
- Radiation Oncology
- Medical Physics
- Oncology
Background:
- Post-prostatectomy radiotherapy requires precise targeting of the prostate bed.
- Image-guided radiotherapy (IGRT) aims to improve accuracy in radiation delivery.
- Understanding prostate bed motion (PBM) is crucial for determining appropriate planning target volume (PTV) margins.
Purpose of the Study:
- To quantify inter- and intrafraction setup errors and PBM in patients undergoing post-prostatectomy IGRT.
- To propose evidence-based 3D clinical target volume to planning target volume (CTV-PTV) margins for both IGRT and non-IGRT scenarios.
Main Methods:
- Prospective study involving 14 patients receiving adjuvant or salvage radiotherapy.
- Linac-based kilovoltage cone-beam CT (kV-CBCT) used for image guidance.
- Offline analysis of daily kV-CBCT scans to assess inter- and intrafraction motion.
Main Results:
- Interfraction PBM measured at 2.1 mm; intrafraction PBM at 0.4 mm.
- Maximum motion predominantly in the anterior-posterior direction.
- Recommended margins: 3-5 mm with IGRT, 4-7 mm without IGRT to cover 95% of CTV in 90% of patients.
Conclusions:
- PBM is a significant contributor to intrafraction error, impacting PTV margins.
- CBCT-guided IGRT can potentially reduce CTV-PTV margins by 1-2 mm.
- Proposed margins for IGRT and non-IGRT scenarios, with recommendations for larger margins in cases of higher uncertainty.
