AbstractID: 4584 Title: Advanced mixed beam therapy using MERT and IMRT
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 photon
radiotherapy (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 Carlo dose calculations, optimization methods and beam
delivery systems using prototype electron MLCs or existing photon MLCs have been
investigated. Smaller SSDs (60–70cm) are recommended when existing photon MLCs
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.