Practical dose delivery verification of craniospinal IMRT.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Intensity-modulated radiation therapy (IMRT) for craniospinal irradiation (CSI) offers improved organ-at-risk (OAR) sparing.
• The complexity of multi-isocenter CSI necessitates robust pre-treatment dose verification methods.
• Accurate dose delivery verification is crucial for patient safety and treatment efficacy in CSI.

Purpose of the Study:

• To propose and evaluate dosimetry techniques for commissioning and patient-specific verification of craniospinal IMRT.
• To compare the accuracy and clinical applicability of ionization chambers, MapCHECK, and ArcCHECK for CSI dose verification.
• To establish acceptable criteria for dose difference and gamma index in the verification of craniospinal IMRT.

Main Methods:

• Retrospective planning of 10 conventional CSI patients using a 3-isocenter IMRT technique.
• Dose verification using ionization chambers in junction regions, MapCHECK in overlap regions, and ArcCHECK for all beams.
• Defined clinical acceptability criteria: ±3% dose difference for ionization chambers, and ≥95% of points with a γ-index < 1 for 3%/3 mm for MapCHECK and ArcCHECK.

Main Results:

• Median planned to measured dose differences were within ±3% for ionization chambers.
• Median percentage of points passing the γ-index < 1 (3%/3 mm) criterion was 98.0% for MapCHECK and 99.7% for ArcCHECK.
• All tested methods demonstrated clinically acceptable agreement between planned and measured doses.

Conclusions:

• Ionization chambers, MapCHECK, and ArcCHECK are suitable for verifying craniospinal IMRT dose delivery.
• These methods can be employed for both commissioning the treatment technique and for patient-specific pre-treatment verification.
• The combined use of these techniques provides comprehensive quality assurance for craniospinal IMRT.