Texture analysis on the fluence map to evaluate the degree of modulation for volumetric modulated arc therapy

Abstract

The contrast (d = 1) and variance (d = 1) calculated from fluence maps of VMAT plans showed considerable correlations with the plan deliverability, indicating their potential use as indicators for assessing the degree of modulation of VMAT plans. Both contrast and variance consistently showed better performance than the conventional modulation indices for VMAT.

Textural feature calculated from segmental fluences as a modulation index for VMAT

“…Park et al suggested a modulation index for VMAT (MIt) by quantifying variations in MLC speeds and accelerations weighted by variations in accelerations of gantry rotation and dose-rate simultaneously [14]. We also suggested textural features of the fluences generated by summations of all the delivered MUs with various shapes defined with MLCs at each control point (CP) as modulation indices for VMAT [17].…”

“…Intensity modulated radiation therapy modulates photon beam intensities by modulating multi-leaf collimator (MLC) positions, while VMAT modulates photon intensities by modulating MLC positions, gantry rotation speed and dose-rate, simultaneously [1,4,7]. Although modulation of photon beam intensity is essential for both IMRT and VMAT, excessive modulation results in differences between calculated dose, which is the dose intended to be delivered to the patient, and the dose which is actually delivered to the patient [8][9][10][11][12][13][14][15][16][17][18][19]. Excessive modulation increases uncertainties in the mechanical operation of linac components, as well as increases the use of small or irregular MLC apertures of which dose calculation with commercial treatment planning system (TPS) is currently inaccurate as compared to that of large or regular MLC apertures [14,16,17].…”

“…Besides the gamma-index method and log file analysis, several modulation indices have been suggested as alternative QA methods for both IMRT and VMAT [8,9,[11][12][13][14][15][16][17][18][19]. One of the benefits of using a modulation index is the reduction in the use of clinical resources, as the index could be calculated at the planning stage.…”

“…Although modulation of photon beam intensity is essential for both IMRT and VMAT, excessive modulation results in differences between calculated dose, which is the dose intended to be delivered to the patient, and the dose which is actually delivered to the patient [8][9][10][11][12][13][14][15][16][17][18][19]. Excessive modulation increases uncertainties in the mechanical operation of linac components, as well as increases the use of small or irregular MLC apertures of which dose calculation with commercial treatment planning system (TPS) is currently inaccurate as compared to that of large or regular MLC apertures [14,16,17]. Therefore, pre-treatment quality assurance (QA) for each patient being treated with IMRT or VMAT is routinely performed in the clinic to detect clinically unacceptable discrepancies in dose distributions between calculation and delivery due to excessive modulation [20][21][22][23][24][25][26][27].…”

Gamma Evaluation with Portal Dosimetry for Volumetric Modulated Arc Therapy and Intensity-Modulated Radiation Therapy

“…4,5) Moreover, calculations of the small or irregular fields which are frequently used for both IMRT and VMAT are not accurate even with the state-of-theart dose calculation algorithms. 7,8) Therefore, there is potential for both IMRT and VMAT to cause differences between the calculated dose distribution and the actually delivered dose distribution to a patient. 3) This can result in unintended treatment which is detrimental to patients, which should be avoided.…”