A new strategy for craniospinal axis localization and adaptive dosimetric evaluation using cone beam CT

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Radiation Therapy

Background:

• Craniospinal irradiation (CSI) presents computational complexities and challenges in localizing the entire craniospinal axis (CSA).
• Adaptive treatment plan evaluation has been historically overlooked in CSI protocols.
• Extended longitudinal field-of-view cone-beam CT (CBCT_eLFOV) offers a potential solution for comprehensive imaging in CSI.

Purpose of the Study:

• To demonstrate a novel strategy for CSI utilizing CBCT_eLFOV for precise CSA localization and adaptive plan evaluation.
• To validate the accuracy and reliability of the CBCT_eLFOV technique for complex radiotherapy.
• To assess the potential for under-dosing in adaptive CSI plans.

Main Methods:

• Acquisition and fusion of multi-scan CBCT images using custom MatLab™ software.
• Validation of CBCT_eLFOV using Catphan phantoms and an anthropomorphic phantom for end-to-end workflow simulation.
• Application of the developed protocol to two patient cases for adaptive plan evaluation.

Main Results:

• Fused CBCT_eLFOV images showed excellent agreement with planning CT (pCT).
• Custom software effectively managed spatial misalignments, with a mean displacement of 0.8 ± 0.3 cm in phantom studies.
• Adaptive plan evaluation indicated a potential for under-dosing the craniospinal target.

Conclusions:

• The developed protocol enables precise localization of the entire CSA for adequate dose delivery in CSI.
• This method can be adapted for other complex treatments like total-marrow and total-lymphoid irradiation.
• The findings highlight the importance of adaptive plan evaluation in CSI to ensure treatment efficacy.