Dose distribution verifications of IMRT for NPC

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Intensity-modulated radiation therapy (IMRT) is a complex radiotherapy technique requiring rigorous dose verification.
• Nasopharyngeal carcinoma (NPC) treatment with IMRT necessitates precise dose delivery and accurate verification methods.
• Establishing reliable evaluation criteria for patient-specific IMRT verification is crucial for clinical implementation.

Purpose of the Study:

• To explore a dose distribution verification procedure for IMRT in NPC.
• To establish evaluation criteria for IMRT dose verification.
• To assess the effectiveness of gamma passing rate and Normalized Agreement Test (NAT) index in quality assurance.

Main Methods:

• Performed 35 two-dimensional (2D) patient-specific IMRT verifications.
• Utilized gamma passing rate and NAT index to assess dose distribution agreement.
• Evaluated three criteria: 2%/2 mm, 3%/3 mm, and 5%/3 mm.

Main Results:

• All cases passed verification with the three criteria, except one NAT index exceeding the limit.
• Different tolerance levels yielded similar clinical results but varied gamma passing rates and NAT indices.
• Gamma passing rate and NAT index were found to be complementary metrics for IMRT verification.

Conclusions:

• An IMRT plan is considered acceptable if gamma passing rate >95% and NAT index <5 using the 5%/3 mm criteria.
• The study recommends using both gamma passing rate and NAT index for comprehensive IMRT patient-specific quality assurance (QA).
• These findings contribute to refining IMRT verification protocols for NPC treatment.