TU-D-224A-06: Advanced Mixed Beam Therapy Using MERT and IMRT

Abstract

Purpose: To review and highlight the current status of the investigation and implementation of advanced mixed beam radiation therapy (MBRT) using energy‐ and intensity‐modulated electron radiotherapy (MERT) and intensity‐modulated photonradiotherapy(IMRT).Methods and Material: Disease sites such as post‐mastectomy chest wall, breast and head and neck etc. are better suited for MERT or MBRT. Feasibility studies on this topic have been performed. Monte Carlodose calculations, optimization methods and beam delivery systems using prototype electron MLCs or existing photonMLCs have been investigated. Smaller SSDs (60–70cm) are recommended when existing photonMLCs are used for beam delivery on Simens or Varian accelerators. Surface dose and beam properties are studied using the Monte Carlo method and compared with measurements. Treatment plans for head and neck and breast are generated with advanced MBRT using IMRT and MERT. MBRT beam delivery accuracy and efficiency are evaluated with phantom measurements. Results: Results show that the Monte Carlo method can provide accurate (2% or 2mm) dose distributions for MBRT. MBRT plans show advantageous dose distributions because IMRT provides superior lateral dose conformity while MERT added extra conformity in the depth direction. The combination of IMRT and MERT provides excellent dose conformity for treatments involving shallow target volumes such as breast and head and neck. Our results of MBRT for 78 breast patients showed that the acute skin complications were significantly reduced in a hypofractionated breast trial. Conclusion: MBRT can provide much improved target dose conformity and uniformity, adequate skin coverage/avoidance and significant reduction in the dose to the adjacent normal organs and critical structures for shallow tumor treatment. Preliminary results have shown great potential of this technique for treating breast, chest wall and head and neck cancers.