Clinical knowledge-based inverse treatment planning

Abstract

Clinical IMRT treatment plans are currently made using dose-based optimization algorithms, which do not consider the nonlinear dose-volume effects for tumours and normal structures. The choice of structure specific importance factors represents an additional degree of freedom of the system and makes rigorous optimization intractable. The purpose of this work is to circumvent the two problems by developing a biologically more sensible yet clinically practical inverse planning framework. To implement this, the dose-volume status of a structure was characterized by using the effective volume in the voxel domain. A new objective function was constructed with the incorporation of the volumetric information of the system so that the figure of merit of a given IMRT plan depends not only on the dose deviation from the desired distribution but also the dose-volume status of the involved organs. The conventional importance factor of an organ was written into a product of two components: (i) a generic importance that parametrizes the relative importance of the organs in the ideal situation when the goals for all the organs are met; (ii) a dose-dependent factor that quantifies our level of clinical/dosimetric satisfaction for a given plan. The generic importance can be determined a priori, and in most circumstances, does not need adjustment, whereas the second one, which is responsible for the intractable behaviour of the trade-off seen in conventional inverse planning, was determined automatically. An inverse planning module based on the proposed formalism was implemented and applied to a prostate case and a head-neck case. A comparison with the conventional inverse planning technique indicated that, for the same target dose coverage, the critical structure sparing was substantially improved for both cases. The incorporation of clinical knowledge allows us to obtain better IMRT plans and makes it possible to auto-select the importance factors, greatly facilitating the inverse planning process. The new formalism proposed also reveals the relationship between different inverse planning schemes and gives important insight into the problem of therapeutic plan optimization. In particular, we show that the EUD-based optimization is a special case of the general inverse planning formalism described in this paper.

Simultaneous beam sampling and aperture shape optimization for SPORT

“…Noteworthy, a significant improvement in plan quality was observed for the head and neck case. We would like to mention that a manual adjustment process was employed for the selection of the weighting factors in the optimization of the quadratic objective function, but this can be alleviated by incorporating the knowledge either from prior clinical experience 25,43,44 or from the data of previously treated patients. 45 In this case, all we need is an automated procedure to adjust the parameters in order to replicate prior clinical data.…”

Search for IMRT inverse plans with piecewise constant fluence maps using compressed sensing techniques

“…This is inherently an underdetermined problem and thus has no unique solution. 24 Indeed, in inverse planning, a clinically satisfactory dose distribution for a given case can generally be achieved using different sets of fluence maps. In other words, there are many fluence maps that can yield a sensible IMRT treatment plan.…”

Formulating adaptive radiation therapy (ART) treatment planning into a closed-loop control framework

“…Better predictive schemes for future patient geometry should improve the PCA algorithm greatly. Our use of a weighted quadratic objective function for plan optimization (specifically the selection of beamlet weights) is probably suboptimal (Yang and Xing 2004a, 2004b, Wu et al 2002, Thieke et al 2003, Bedford and Webb 2006, Popple et al 2005, Oelfke and Bortfeld 1999, Choi and Deasy 2002. However, all the algorithms discussed in this paper would work with other objective functions.…”