Dosimetry audit for a multi-centre IMRT head and neck trial

Area of Science:

• Radiation Oncology
• Medical Physics
• Clinical Trials

Background:

• The PARSPORT trial compared Intensity-Modulated Radiotherapy (IMRT) with conventional radiotherapy (CRT) for head and neck cancer.
• Multi-centre trials require robust quality assurance for radiotherapy plan delivery.

Purpose of the Study:

• To verify radiotherapy plan delivery in participating centres for the PARSPORT trial.
• To determine appropriate dosimetry tolerances for head and neck IMRT trials.
• To develop an IMRT credentialing program for multi-centre trials.

Main Methods:

• Rigorous quality assurance and site visits for dosimetry audits were conducted.
• Audits included treatment planning system tests, fluence verification films, and dose point measurements.
• Gamma analysis was used to assess dose distribution accuracy.

Main Results:

• Mean dose point measurements for the primary planning target volume (PTV) were within 0.7% of planned values for both IMRT and CRT arms.
• Ninety-four percent of IMRT individual field fluence films met the 3%/3mm gamma criterion.
• Seventy-five percent of IMRT combined field fluence films met the 4%/3mm gamma criterion.

Conclusions:

• A 3% tolerance for PTV point doses is suggested for multi-centre head and neck IMRT trials.
• Proposed tolerances for dose distributions are 3%/3mm for individual fields and 4%/3mm for combined fields.
• These proposed tolerances can guide quality assurance in future IMRT trials.