'Tongue-and-groove' effect in intensity modulated radiotherapy with static multileaf collimator fields

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Step-and-shoot intensity modulated radiotherapy (IMRT) delivery can cause the 'tongue-and-groove' effect, leading to underdosage.
• Quantifying this effect is crucial for ensuring accurate radiation doses.

Purpose of the Study:

• To investigate the 'tongue-and-groove' problem in step-and-shoot IMRT.
• To introduce and evaluate a quantitative index (TGI) for this effect.
• To compare different leaf sequencing methods for minimizing underdosage.

Main Methods:

• Developed a 'tongue-and-groove' index (TGI) to quantify the effect.
• Compared four leaf sequencing methods: sliding window, reducing level, Van Santvoort and Heijmen's method, and a novel inspired method.
• Evaluated methods based on TGI values and their ability to deliver intensity maps.

Main Results:

• The reducing level method showed a significantly lower TGI compared to the sliding window method.
• Van Santvoort and Heijmen's leaf synchronization method was unsuitable for step-and-shoot delivery.
• A new method, inspired by Van Santvoort and Heijmen, completely eliminated 'tongue-and-groove' underdosage.

Conclusions:

• The 'tongue-and-groove' effect is a significant concern in step-and-shoot IMRT.
• Leaf sequencing strategies critically impact dose accuracy.
• The novel leaf sequencing method offers a promising solution for eliminating underdosage in IMRT.