Does radiation therapy need more than two photon energies from Linac?

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Modern linear accelerators (Linacs) offer multiple photon energies for radiation therapy.
• Energy selection is crucial and depends on tumor characteristics and patient anatomy.

Purpose of the Study:

• To investigate the necessity of using more than two photon energies on a Linac.
• To determine if two photon energies can adequately cover the spectrum of clinical needs.

Main Methods:

• Photon energy synthesis principle demonstrated using linear combinations of low and high energies.
• Validation across various scenarios: different Linacs, beam types (open/wedge), and published data.
• 3D dose distributions compared using Gamma analysis in water phantom and clinical cases.
• Experimental measurements for Intensity-Modulated Radiation Therapy (IMRT) plans.

Main Results:

• Photon energy synthesis achieved with root mean square error (RMSE) within 1.1% for open/wedge fields.
• Excellent agreement with published data (BJR) with an average RMSE of 0.11%.
• 3D Gamma analysis showed good agreement in phantom and clinical cases, with a minimum passing rate of 95.7% at 1%/1mm for IMRT plans.

Conclusions:

• A Linac with two photon energies can produce dosimetrically equivalent plans for any intermediate energy via synthesis.
• This supports the conclusion that more than two photon energies per Linac are unnecessary.
• Implementing this can significantly reduce radiation therapy equipment costs.