A two isocenter IMRT technique with a controlled junction dose for long volume targets.

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Intensity-modulated radiation therapy (IMRT) is limited by conventional linear accelerator field sizes for large targets.
• Treating long volume targets with IMRT requires overcoming these field size restrictions.

Purpose of the Study:

• To develop and evaluate a two-isocenter IMRT technique for treating long volume targets.
• To overcome field size limitations of conventional IMRT delivery.

Main Methods:

• A two-isocenter IMRT technique was developed, creating an extended dose gradient (4-6 cm) at the junction.
• Inverse planning and IMRT segments were manipulated for dose uniformity within the junction.
• Techniques included abutting conventional fields with IMRT ('Static + IMRT') and IMRT fields ('IMRT + IMRT').
• Five long volume sarcoma cases were planned using Pinnacle software on Elekta Synergy and Varian 2100EX linacs.

Main Results:

• The technique demonstrated well-controlled junction target uniformity and tolerance to setup uncertainties.
• Junction target dose heterogeneity was maintained within +/-5%.
• A 3 mm setup error resulted in less than 5% change in junction target dose.
• Dose sparing to organs at risk (OARs) was preserved.
• Treatment planning results were confirmed by film measurements.

Conclusions:

• The two-isocenter IMRT technique effectively treats long volume targets by managing junction dose heterogeneity.
• This method overcomes IMRT field size limitations while maintaining target conformity and OAR sparing.
• The technique shows promise for clinical application in treating extensive targets with radiation therapy.