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

Abstract

The 'tongue-and-groove problem' in step-and-shoot delivery of intensity modulated radiotherapy is investigated. A 'tongue-and-groove' index (TGI) is introduced to quantify the 'tongue-and-groove' effect in step-and-shoot delivery. Four different types of leaf sequencing methods are compared. The sliding window method and the reducing level method use the same number of field segments to deliver the same intensity map, but the TGI is much less for the reducing level method. The leaf synchronization method of Van Santvoort and Heijmen fails in step-and-shoot delivery, but a new method inspired by the method of Van Santvoort and Heijmen is shown to eliminate 'tongue-and-groove' underdosage completely.

Mathematical optimization in intensity modulated radiation therapy

“…The process is repeated for the residual intensity matrix. Kamath et al (2004b) prove that the algorithm of Que et al (2004) generates segmentations free of tongue-and-groove effects and interdigitation. However, they also show that this algorithm generates solutions with high decomposition time and cardinality and therefore it is not suitable for clinical use.…”

“…The algorithms, then, search afresh from x w for new violations until none exists. Que et al (2004) also propose an algorithm to eliminate tongue-and-groove effects. They use the sliding window method of Bortfeld et al (1994b) to generate a tentative segment.…”

Mathematical optimization in intensity modulated radiation therapy

“…The process is repeated for the residual intensity matrix. Kamath et al (2004b) prove that the algorithm of Que et al (2004) generates segmentations free of T&G effects and interdigitation. However, they also show that this algorithm generates solutions with high decomposition time and cardinality and therefore it is not suitable for clinical use.…”

“…The algorithms, then, search afresh from x w for new violations until none exists. Que et al (2004) also propose an algorithm to eliminate T&G effects. They use the sliding window method of Bortfeld et al (1994b) to generate a tentative segment.…”

Determination of depth and field size dependence of multileaf collimator transmission in intensity‐modulated radiation therapy beams

“…Although (i) is effectively included in the notion of the spatially averaged MLC transmission T (equation 2), (ii) may cause an overall underdosage of the target that can be numerically estimated only if the tongue, or groove, or both, of the MLC transmissions are directly included in the fluence calculations. This negative dose bias may be significant when fluence delivery is complex (20) . Furthermore, even though use of non‐coplanar IMRT fields or variation in the collimator angle can blur the effects of both (i) and (ii), it cannot alter the total dose deposited within the target because of (ii).…”