The physical basis of IMRT and inverse planning

Abstract

Intensity-modulated radiation therapy (IMRT) can sculpt the high-dose volume around the site of disease with hitherto unachievable precision. Conformal avoidance of normal tissues goes hand in hand with this. Inhomogeneous dose painting is possible. The technique has become a clinical reality and is likely to be the dominant approach this decade for improving the clinical practice of photon therapy. This Series will explore all aspects of the "IMRT chain". Only 15 years ago just a handful of physicists were working on this subject. IMRT has developed so rapidly that its recent past is also its ancient history. This article will review the history of IMRT with just a glance at precursors. The physical basis of IMRT is then described including an attempt to introduce the concepts of convex and concave dose distributions, ill-conditioning, inverse-problem degeneracy, cost functions and complex solutions all with a minimum of technical jargon or mathematics. The many techniques for inverse planning are described and the review concludes with a look forward to the future of image-guided IMRT (IG-IMRT).

Agility MLC transmission optimization in the Monaco treatment planning system

“…Traditional forward based treatment planning has been supplemented by inverse planning, which uses dose optimization techniques including intensity modulated radiotherapy (IMRT)1 and volumetric modulated arc therapy (VMAT),2, 3 to satisfy user specified criteria. To achieve the appropriate target coverage and respect the dose constraint criteria for organs at risk, both IMRT and VMAT use many irregularly shaped fields defined by multileaf collimators (MLCs).…”

Effect of smoothing on treatment plan efficiency in IMRT: eclipse Helios™ dose optimisation

“…A recommendation for good IMRT practice is to minimise the complexity of the plan. 10 A fall in the total number of MUs per plan was also evident for both sets of patients, being more pronounced for the prostate patients. Again, this corroborates the findings of Nicolini et al but is based on a much larger number of treatment plans.…”

Evaluation of targeted image-guided radiation therapy treatment planning system by use of american association of physicists in medicine task group-119 test cases

“…[1] Introduction of IMRT creates the possibility of generating dramatically improved dose distributions that could be tailored to fit complex shapes. The IMRT is a promising treatment technique having advantage of delivering highly conformal dose distribution to the target volume and sparing of organs at risk.…”