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Set-Up Errors, Organ Motion, Tumour Regression and its Implications on Internal Target Volume-Planning Target Volume
U Mahantshetty1, P Naga2, A Nachankar3
1Department of Radiation Oncology & Medical Physics, Tata Memorial Hospital, Homi Bhabha National Institute, Mumbai, India; Department of Radiation Oncology & Medical Physics, Homi Bhabha Cancer Hospital and Research Centre, Visakhapatnam, India.
Clinical Oncology (Royal College of Radiologists (Great Britain))
|November 5, 2021
Summary
This study on cervical cancer radiotherapy found that anisotropic margins are needed for both internal target volume (ITV) and planning target volume (PTV) to account for organ movement. This ensures accurate radiation delivery to the target area.
Area of Science:
- Radiation Oncology
- Medical Imaging
- Gynecologic Oncology
Background:
- Uterocervical motion and organ filling present complexities in conformal radiotherapy for cervical cancer.
- Accurate margin definition is crucial for effective radiation delivery and minimizing dose to healthy tissues.
Purpose of the Study:
- To investigate set-up margins (clinical target volume [CTV] to planning target volume [PTV]) for pelvic nodal CTV.
- To determine internal margins (CTV to internal target volume [ITV]) for uterocervical movements during cervical cancer radiotherapy.
Main Methods:
- Prospective, observational study involving daily kilovoltage cone-beam computed tomography (CBCT) scans in 67 patients.
- Bony anatomy and vessel-based rigid co-registration to calculate CTV to PTV margins.
- Soft-tissue matching at the mid-cervical region and uterine fundus to calculate CTV to ITV margins.
Main Results:
- Pelvic nodal CTV to PTV margins were within 10 mm, with a slight increase anteriorly (10.3 mm).
- Internal margins for the cervix (CTV-ITV) were <10 mm.
- Uterine fundus exhibited anisotropic internal margins (CTV-ITV), ranging from 10 mm (anterior-posterior, lateral) to 12-20 mm (superior-inferior).
Conclusions:
- Anisotropic margins are recommended for both CTV to ITV and CTV to PTV expansions in cervical cancer radiotherapy.
- These findings support tailored margin strategies to accommodate specific organ motion patterns.
