Leaf Movement Research Articles

Clinical examples of 3D dose distribution reconstruction, based on the actual MLC leaves movement, for dynamic treatment techniques

AimTo present practical examples of our new algorithm for reconstruction of 3D dose distribution, based on the actual MLC leaf movement. BackgroundDynaLog and RTplan files were used by DDcon software to prepare a new RTplan file for dose distribution reconstruction. Materials and methodsFour different clinically relevant scenarios were used to assess the feasibility of the proposed new approach: (1) Reconstruction of whole treatment sessions for prostate cancer; (2) Reconstruction of IMRT verification treatment plan; (3) Dose reconstruction in breast cancer; (4) Reconstruction of interrupted arc and complementary plan for an interrupted VMAT treatment session of prostate cancer. The applied reconstruction method was validated by comparing reconstructed and measured fluence maps. For all statistical analysis, the U Mann–Whitney test was used. ResultsIn the first two and the fourth cases, there were no statistically significant differences between the planned and reconstructed dose distribution (p=0.910, p=0.975, p=0.893, respectively). In the third case the differences were statistically significant (p=0.015). Treatment plan had to be reconstructed. ConclusionDeveloped dose distribution reconstruction algorithm presents a very useful QA tool. It provides means for 3D dose distribution verification in patient volume and allows to evaluate the influence of actual MLC leaf motion on the dose distribution.

Environmental stimuli and physiological responses: The current view on electrical signalling

Electrical signals have been studied in numerous species so far. It appears that two main types of such signals occur in plants, rapid action potentials (APs) and slower variation potentials (VPs). While APs are generally evoked by non-invasive stimuli and follow the all-or-nothing principle as in neurons, VPs are mostly triggered by wounding and do not follow the all-or-nothing law. They are correlated to the stimulus strength and last longer than APs. The transmission of both, APs and VPs, occurs via the phloem over long distances and via plasmodesmata over short distances from cell to cell. Regarding physiological functions of electrical signals, numerous examples exist. They regulate rapid leaf movements in order to catch insects and for instance, affect nutrient uptake, gene expression and phloem transport. Recently, it was shown that apart from hydraulic signals, electric signals also play a significant role in root-to-shoot communication of drought-stressed plants. Re-irrigation of plants after soil drying initiates rapid hydraulic as well as electric signalling which affects the gas exchange of leaves. In addition, evidence was found for a link between electrical signals and photosynthesis as well as respiration. Wound-induced VPs cause a transient suppression in photosynthetic activity and an increase in respiratory CO2 release. The results led us to conclude that different stimulation types trigger characteristic electrical signals each with specific influence on physiological processes.

Evidence for the regulation of leaf movement by photosystem II activity

Some light-demanding plants fold leaves under high light and open leaves under low light. Since paraheliotropism leaf movement under high light could be induced by environmental stresses that aggravate photoinhibition of photosystem II (PSII), we hypothesize that the leaf movement is regulated by PSII activity. To test this hypothesis, we examined photosynthetic gas exchange and chlorophyll fluorescence, diurnal changes in leaf angle, and maximum quantum yield of PSII (Fv/Fm) in a leaf-foldable canopy liana, Bauhinia tenuiflora, grown in an open field. The rate of CO2 assimilation, electron transport rate, and non-photochemical quenching was saturated under light of 1000μmolphotonsm−2s−1. After exposure to high light of 1000μmolphotonsm−2s−1 and 2000μmolphotonsm−2s−1 for 8h, Fv/Fm decreased to 54% and 19%, respectively. The repair of photodamaged PSII was strongly suppressed when illuminated at high light. After high light treatment, the recovery of PSII activity under low light functions efficiently. During the daytime, the minimum values of Fv/Fm and leaf angle were 0.75° and 9°, respectively. In the early morning, high Fv/Fm was accompanied by large leaf angle. At noon, when Fv/Fm was lower than 0.8, B. tenuiflora strongly folded its leaves. In the afternoon, when Fv/Fm was higher than 0.8, leaf angle gradually increased. After treatment with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU, an inhibitor of PSII), Fv/Fm and leaf angle decreased significantly. Based on these results, the leaf movement in B. tenuiflora can be regulated by PSII photoinhibition, suggesting that PSII photoinhibition plays a potential role in the regulation of leaf movement under environmental stresses.

Proteomic Analysis of the Pulvinus, a Heliotropic Tissue, in Glycine max

Certain plant species respond to light, dark, and other environmental factors by leaf movement. Leguminous plants both track and avoid the sun through turgor changes of the pulvinus tissue at the base of leaves. Mechanisms leading to pulvinar turgor flux, particularly knowledge of the proteins involved, are not well-known. In this study we used two-dimensional gel electrophoresis and liquid chromatography-tandom mass spectrometry to separate and identify the proteins located in the soybean pulvinus. A total of 183 spots were separated and 195 proteins from 165 spots were identified and functionally analyzed using single enrichment analysis for gene ontology terms. The most significant terms were related to proton transport. Comparison with guard cell proteomes revealed similar significant processes but a greater number of pulvinus proteins are required for comparable analysis. To our knowledge, this is a novel report on the analysis of proteins found in soybean pulvinus. These findings provide a better understanding of the proteins required for turgor change in the pulvinus.

SU‐E‐T‐430: Modeling MLC Leaf End in 2D for Sliding Window IMRT and Arc Therapy

Purpose:To develop a 2D geometric model for MLC accounting for leaf end dose leakage for dynamic IMRT and Rapidarc therapy.Methods:Leaf‐end dose leakage is one of the problems for MLC dose calculation and modeling. Dosimetric leaf gap used to model the MLC and to count for leakage in dose calculation, but may not be accurate for smaller leaf gaps. We propose another geometric modeling method to compensate for the MLC round‐shape leaf ends dose leakage, and improve the accuracy of dose calculation and dose verification. A triangular function is used to geometrically model the MLC leaf end leakage in the leaf motion direction, and a step function is used in the perpendicular direction. Dose measurements with different leaf gap, different window width, and different window height were conducted, and the results were used to fit the analytical model to get the model parameters.Results:Analytical models have been obtained for stop‐and‐shoot and dynamic modes for MLC motion. Parameters a=0.4, lw' =5.0 mm for 6X and a=0.54, lw' =4.1 mm for 15x were obtained from the fitting process. The proposed MLC leaf end model improves the dose profile at the two ends of the sliding window opening. This improvement is especially significant for smaller sliding window openings, which are commonly used for highly modulated IMRT plans and arc therapy plans.Conclusion:This work models the MLC round leaf end shape and movement pattern for IMRT dose calculation. The theory, as well as the results in this work provides a useful tool for photon beam IMRT dose calculation and verification.

Development of an Agrobacterium-Mediated Stable Transformation Method for the Sensitive Plant Mimosa pudica

The sensitive plant Mimosa pudica has long attracted the interest of researchers due to its spectacular leaf movements in response to touch or other external stimuli. Although various aspects of this seismonastic movement have been elucidated by histological, physiological, biochemical, and behavioral approaches, the lack of reverse genetic tools has hampered the investigation of molecular mechanisms involved in these processes. To overcome this obstacle, we developed an efficient genetic transformation method for M. pudica mediated by Agrobacterium tumefaciens (Agrobacterium). We found that the cotyledonary node explant is suitable for Agrobacterium-mediated transformation because of its high frequency of shoot formation, which was most efficiently induced on medium containing 0.5 µg/ml of a synthetic cytokinin, 6-benzylaminopurine (BAP). Transformation efficiency of cotyledonary node cells was improved from almost 0 to 30.8 positive signals arising from the intron-sGFP reporter gene by using Agrobacterium carrying a super-binary vector pSB111 and stabilizing the pH of the co-cultivation medium with 2-(N-morpholino)ethanesulfonic acid (MES) buffer. Furthermore, treatment of the explants with the detergent Silwet L-77 prior to co-cultivation led to a two-fold increase in the number of transformed shoot buds. Rooting of the regenerated shoots was efficiently induced by cultivation on irrigated vermiculite. The entire procedure for generating transgenic plants achieved a transformation frequency of 18.8%, which is comparable to frequencies obtained for other recalcitrant legumes, such as soybean (Glycine max) and pea (Pisum sativum). The transgene was stably integrated into the host genome and was inherited across generations, without affecting the seismonastic or nyctinastic movements of the plants. This transformation method thus provides an effective genetic tool for studying genes involved in M. pudica movements.

Automation Highlights from the Literature

Automation Highlights from the Literature

Effect of iron deficiency stress on leaves movements and electrical potentials in mimosa (Mimosa pudica L.)

The aim of the studies was to trace the motorical and electrical activity of the mimosa (<em>Mimosa pudica</em> L.) grown under conditions of iron deficiency. The speed of leaf folding was measured (motorical activity) and the action potential induced with thermic and light stimuli and turgorin (electrical activity was recorded). It was found that the iron deficiency caused acidification of medium and the maximum of the process coincided with the period when the young leaves were turning green. Chlorotic mimosa leaves, not detached from the plant, showed an increased motorical activity. Motorical and electrical activity of the leaves were inhibited by an inhibitor of the plasmalemma redox systems - quinacrine, and stimulated by blue light. Leaf movement factor - turgorin - caused a hypersensitivity of chlorotic plants. It follows from the studies that the observed effects resulted from the adaptation of mimosa to the iron stress. The adaptation was a result of formation of new plasmalemma redox systems (turbo-reductase), responsible for maintaining high energy levels in the cells.

Shade avoidance: phytochrome signalling and other aboveground neighbour detection cues

Plants compete with neighbouring vegetation for limited resources. In competition for light, plants adjust their architecture to bring the leaves higher in the vegetation where more light is available than in the lower strata. These architectural responses include accelerated elongation of the hypocotyl, internodes and petioles, upward leaf movement (hyponasty), and reduced shoot branching and are collectively referred to as the shade avoidance syndrome. This review discusses various cues that plants use to detect the presence and proximity of neighbouring competitors and respond to with the shade avoidance syndrome. These cues include light quality and quantity signals, mechanical stimulation, and plant-emitted volatile chemicals. We will outline current knowledge about each of these signals individually and discuss their possible interactions. In conclusion, we will make a case for a whole-plant, ecophysiology approach to identify the relative importance of the various neighbour detection cues and their possible interactions in determining plant performance during competition.

NAC transcription factor speedy hyponastic growth regulates flooding-induced leaf movement in Arabidopsis.

In rosette plants, root flooding (waterlogging) triggers rapid upward (hyponastic) leaf movement representing an important architectural stress response that critically determines plant performance in natural habitats. The directional growth is based on localized longitudinal cell expansion at the lower (abaxial) side of the leaf petiole and involves the volatile phytohormone ethylene (ET). We report the existence of a transcriptional core unit underlying directional petiole growth in Arabidopsis thaliana, governed by the NAC transcription factor speedy hyponastic growth (SHYG). Overexpression of SHYG in transgenic Arabidopsis thaliana enhances waterlogging-triggered hyponastic leaf movement and cell expansion in abaxial cells of the basal petiole region, while both responses are largely diminished in shyg knockout mutants. Expression of several expansin and xyloglucan endotransglycosylase/hydrolase genes encoding cell wall-loosening proteins was enhanced in SHYG overexpressors but lowered in shyg. We identified ACC oxidase5 (ACO5), encoding a key enzyme of ET biosynthesis, as a direct transcriptional output gene of SHYG and found a significantly reduced leaf movement in response to root flooding in aco5 T-DNA insertion mutants. Expression of SHYG in shoot tissue is triggered by root flooding and treatment with ET, constituting an intrinsic ET-SHYG-ACO5 activator loop for rapid petiole cell expansion upon waterlogging.

The Effect of Time of Day on the Activity of Postemergence Soybean Herbicides

The effect of time of day (TOD) on the activity of six common POST herbicides was investigated in field trials from 2007 to 2009 at two locations in southwestern Ontario. Percentage weed control was assessed following application of bentazon, chlorimuron-ethyl, fomesafen, glyphosate, imazethapyr, or quizalofop-p-ethyl applied at 3-h intervals from 6:00 A.M. to midnight, when weeds averaged 15 cm tall. The effect of time of day varied with weed species, but weed control was generally reduced when herbicides were applied at 6:00 A.M., 9:00 P.M., and midnight. Herbicide activity on velvetleaf was most frequently reduced, especially for chlorimuron-ethyl, glyphosate, and imazethapyr. Control of common ragweed with glyphosate and imazethapyr was also affected by the timing of application, and pigweed species only showed an effect with glyphosate. Variation in temperature, relative humidity, and dew presence/absence at different times of the day, as well as morphological/physiological characteristics such as weed size at time of application and diurnal leaf movement in response to light intensity, may account for the variation in weed control at different times of the day. Significant soybean yield loss was not observed in this study, but may occur if herbicide efficacy is severely reduced by application at inappropriate times of day. These results provide valuable information for growers, and suggest that POST herbicides are most effective when applied midday, rather than in the early morning or late evening.

Assessing Water Stress of Desert Tamarugo Trees Using in situ Data and Very High Spatial Resolution Remote Sensing

The hyper-arid Atacama Desert is one of the most extreme environments for life and only few species have evolved to survive its aridness. One such species is the tree Prosopis tamarugo Phil. Because Tamarugo completely depends on groundwater, it is being threatened by the high water demand from the Chilean mining industry and the human consumption. In this paper, we identified the most important biophysical variables to assess the water status of Tamarugo trees and tested the potential of WorldView2 satellite images to retrieve these variables. We propose green canopy fraction (GCF) and green drip line leaf area index (DLLAIgreen) as best variables and a value of 0.25 GCF as a critical threshold for Tamarugo survival. Using the WorldView2 spectral bands and an object-based image analysis, we showed that the NDVI and the Red-edge Chlorophyll Index (CIRed-edge) have good potential to retrieve GCF and DLLAIgreen. The NDVI performed best for DLLAIgreen (RMSE = 0.4) while the CIRed-edge was best for GCF (RMSE = 0.1). However, both indices were affected by Tamarugo leaf movements (leaves avoid facing direct solar radiation at the hottest time of the day). Thus, monitoring systems based on these indices should consider the time of the day and the season of the year at which the satellite images are acquired.

Dynamic behavioral strategies during sonar signal emission in roundleaf bats

For echolocating bats which emit biosonar pulses nasally, their nostrils are surrounded by fleshy appendages that diffract the outgoing ultrasonic waves. The posterior leaf, as a prominent part of the noseleaf, was mentioned in previous preliminary observations to move during flight in some species of bats, yet the detailed motion patterns and thus the possible functional role of the posterior leaf movement in biosonar systems remain unclear. In the current work, the motion of the posterior leaf of living pratt's roundleaf bats has been investigated quantitatively. Temporal characterizations of the noseleaf movement and the ultrasonic pulse emission were performed by virtue of synchronized laser vibrometry and sound recording. The results showed that the posterior leaf tilted forwards and restored to original position within tens of milliseconds. Noseleaf motions were temporally correlated with the emitted ultrasonic pulses. The surfaces of the posterior leaf were moving in the anterior direction in most of the pulse duration. The bats were able to switch the motions on or off. From the comparison with the previously reported noseleaf dynamics in horseshoe bat, we find similar ratio sizes and displacements of the noseleaves compared to the used wavelengths, implying that similar behavioral strategies are utilized by species of bats and it may be applied to different components of the signal emitting apparatus. It suggests that the dynamic sensing principles may widely play a role in the biosonar systems and the investigation on time-variant mechanisms is of capital importance to understand the biosonar sensing strategies used by echolocating bats.

Antiphase light and temperature cycles affect PHYTOCHROME B-controlled ethylene sensitivity and biosynthesis, limiting leaf movement and growth of Arabidopsis.

In the natural environment, days are generally warmer than the night, resulting in a positive day/night temperature difference (+DIF). Plants have adapted to these conditions, and when exposed to antiphase light and temperature cycles (cold photoperiod/warm night [-DIF]), most species exhibit reduced elongation growth. To study the physiological mechanism of how light and temperature cycles affect plant growth, we used infrared imaging to dissect growth dynamics under +DIF and -DIF in the model plant Arabidopsis (Arabidopsis thaliana). We found that -DIF altered leaf growth patterns, decreasing the amplitude and delaying the phase of leaf movement. Ethylene application restored leaf growth in -DIF conditions, and constitutive ethylene signaling mutants maintain robust leaf movement amplitudes under -DIF, indicating that ethylene signaling becomes limiting under these conditions. In response to -DIF, the phase of ethylene emission advanced 2 h, but total ethylene emission was not reduced. However, expression analysis on members of the 1-aminocyclopropane-1-carboxylic acid (ACC) synthase ethylene biosynthesis gene family showed that ACS2 activity is specifically suppressed in the petiole region under -DIF conditions. Indeed, petioles of plants under -DIF had reduced ACC content, and application of ACC to the petiole restored leaf growth patterns. Moreover, acs2 mutants displayed reduced leaf movement under +DIF, similar to wild-type plants under -DIF. In addition, we demonstrate that the photoreceptor PHYTOCHROME B restricts ethylene biosynthesis and constrains the -DIF-induced phase shift in rhythmic growth. Our findings provide a mechanistic insight into how fluctuating temperature cycles regulate plant growth.

Is expression of aquaporins (plasma membrane intrinsic protein 2s, PIP2s) associated with thermonasty (leaf-curling) in Rhododendron?

It is postulated that leaf thermonasty (leaf curling) in rhododendrons under sub-freezing temperatures is caused by water redistribution due to extracellular freezing. We hypothesize that aquaporins (AQPs), the transmembrane water-channels, may be involved in regulating water redistribution and thus leaf curling. Our experimental system includes two Rhododendron species with contrasting leaf curling behavior whereby it was observed in R. catawbiense but not in R. ponticum. We compared leaf movements and the expression of two AQPs, i.e. R. catawbiense/ponticum plasma-membrane intrinsic protein 2 (Rc/RpPIP2;1 and Rc/RpPIP2;2), in the two species under freezing–rewarming and dehydration–rehydration cycles. To determine the relationship between extracellular freezing and leaf-curling, we monitored leaf-curling in R. catawbiense with or without controlled ice-nucleation. Our data indicate that extracellular freezing may be required for leaf curling. Moreover, in both species, PIP2s were up-regulated at temperatures that fell in ice-nucleation temperature range. Such up-regulation could be associated with the bulk-water efflux caused by extracellular freezing. When leaves were frozen beyond the ice-nucleation temperature range, PIP2s were continuously down-regulated in R. catawbiense along with the progressive leaf curling, as also observed for RcPIP2;2 in dehydrated leaves; as leaves uncurled during re-warming/rehydration, RcPIP2 expression was restored. On the other hand, R. ponticum, a non-curling species, exhibited substantial up-regulation of RpPIP2s during freezing/dehydration. Taken together, our data suggest that RcPIP2 down-regulation was associated with leaf curling. Moreover, the contrasting PIP2 expression patterns combined with leaf behavior of R. catawbiense and R. ponticum under these two cycles may reflect different strategies employed by these two species to tolerate/resist cellular dehydration.

A fast circadian clock at high temperatures is a conserved feature across Arabidopsis accessions and likely to be important for vegetative yield

The circadian clock is an endogenous 24 h oscillator regulating many critical biological processes in plants. One of the key characteristics of the circadian clock is that it is buffered against temperature, maintaining an approximately 24 h rhythm over a broad physiological temperature range. Here, we tested temperature-buffering capacity of the circadian clock across a number of Arabidopsis accessions using several circadian clock reporters: leaf movement, CCA1 : LUC and LHY : LUC. We found that leaf movement was the best temperature buffered circadian output. On the other hand, when temperature increases, circadian rhythms of CCA1 and LHY transcription shorten considerably across all accessions, indicating that the clock driving expression of CCA1 and LHY is not perfectly buffered. This feature might be crucial to plants growing in a constantly changing environment, and here, we provide insight into the importance of period shortening to plant growth performance and the benefits of a flexible clock.

Morphing structures and signal transduction in Mimosa pudica L. induced by localized thermal stress

Leaf movements in Mimosa pudica, are in response to thermal stress, touch, and light or darkness, appear to be regulated by electrical, hydrodynamical, and chemical signal transduction. The pulvinus of the M. pudica shows elastic properties. We have found that the movements of the petiole, or pinnules, are accompanied by a change of the pulvinus morphing structures. After brief flaming of a pinna, the volume of the lower part of the pulvinus decreases and the volume of the upper part increases due to the redistribution of electrolytes between these parts of the pulvinus; as a result of these changes the petiole falls. During the relaxation of the petiole, the process goes in the opposite direction. Ion and water channel blockers, uncouplers as well as anesthetic agents diethyl ether or chloroform decrease the speed of alert wave propagation along the plant. Brief flaming of a pinna induces bidirectional propagation of electrical signal in pulvini. Transduction of electrical signals along a pulvinus induces generation of an action potential in perpendicular direction between extensor and flexor sides of a pulvinus. Inhibition of signal transduction and mechanical responses in M. pudica by volatile anesthetic agents chloroform or by blockers of voltage gated ion channels shows that the generation and propagation of electrical signals is a primary effect responsible for turgor change and propagation of an excitation. There is an electrical coupling in a pulvinus similar to the electrical synapse in the animal nerves.

MO‐D‐108‐01: Cloud‐Based Monte Carlo Patient‐Specific Quality Assurance (QA) Method for Volumetric‐Modulated Arc Therapy (VMAT): Clinical and Educational Impacts

Purpose: Patient‐specific QA for VMAT is labor‐intensive,especially in cases which tend to be associated with severe heterogeneities or small aperture beams. We developed a robust cloud‐based Monte Carlo method as an independent QA tool or backup for commercial dosimeters. It is also educationally innovative because it helps physicists to comprehend the underlying physics of complex VMAT procedures. Methods: The workflow of the cloud‐based voxel Monte Carlo method(cVMC++) developed here is the following: (1) After a VMAT plan is approved by the physician, a dose verification plan is created and delivered to the phantom using the Varian Trilogy™ or TrueBeam™ system. (2) Actual delivery parameters (i.e., dose fraction, gantry angle, and MLC leaf position) are extracted from dynamic log or trajectory files. (3) Based on the delivery parameters, a new phase space is constructed for each control point. The 3D dose distribution in the phantom containing the detector array (e.g., Delta 4 from ScandiDos) are then recomputed using cVMC++. (4) Comparison and Gamma index analyses are then conducted to evaluate the agreement between measured, recomputed, and planned dose distributions. To enhance the educational function, we are developing visualization and animation modules to display the intermediate processes such as leaf movement, dose distribution and DVH accumulation with each control point. The software has been wrapped as a web‐based service so that it can readily be used by physicists via a browser. To test the robustness of this system, we examined several representative VMAT treatments. Results: For all cases, agreement between measured, recomputed and planned doses was examined with the gamma criterion of >90% of the points satisfying <3% of relative dose difference and <3 mm of distance to agreement. Conclusion: The proposed method offers a robust patient specific QA tool for VMAT treatments and provides a valuable educational tool for physicists. NIH (1R01 CA133474) and Department of Radiation Oncology of Stanford University Seed Grant

SU‐E‐T‐380: Modeling MLC Leaf End in 2D for Sliding Window IMRT and Arc Therapy

Purpose: To develop a 2D geometric model for MLC accounting for leaf end dose leakage for IMRT and arc therapy. Methods: Leaf‐end dose leakage is one of the problems for MLC dose calculation and modeling. Dosimetric leaf gap used to model the MLC and to count for leakage in dose calculation, but may not be accurate for smaller leaf gaps. We propose another geometric modeling method to compensate for the MLC round‐shape leaf ends dose leakage, and improve the accuracy of dose calculation and dose verification. A triangular function is used to geometrically model the MLC leaf end leakage in the leaf motion direction, and a step function is used in the perpendicular direction. Dose measurements with different leaf gap, different window width, and different window height were conducted, and the results were used to fit the analytical model to get the model parameters. Results: Analytical models have been obtained for stop‐and‐shoot and dynamic modes for MLC motion. Parameters a=0.4, lw=5.0 mm for 6X and a=0.54, lw=4.1 mm for 15x were obtained from the fitting process. The proposed MLC leaf end model improves the dose profile at the two ends of the sliding window opening. This improvement is especially significant for smaller sliding window openings, which are commonly used for highly modulated IMRT plans and arc therapy plans. Conclusion: This work models the MLC round leaf end shape and movement pattern for IMRT dose calculation. The theory, as well as the results in this work provides a useful tool for photon beam IMRT dose calculation and verification.

TH-C-137-07: Population-Based IMRT Beam Aperture Shape Inference Using Retrospective Treatment Plan and Patient Data

Purpose: Existing IMRT aperture selection process is not only highly computationally expensive, but also lacks mechanism that would utilize historical data on high‐quality apertures. The purpose of our aperture classification model, apClass, is to alleviate both aforementioned issues by employing advanced machine‐learning algorithms to “learn” the high‐quality aperture patterns and, subsequently, “correlate” the identified aperture patterns to anatomic features specific to each and every patient. Methods: We have evaluated our ap Class model on ten advanced head‐and‐neck cancer patients. For each of the patients, key anatomic features and aperture shapes were retrieved from the existing physician‐approved clinical treatment plans. A greedy heuristic procedure was then used to generate a library of small area aperture envelopes. Those generated aperture envelopes represent the key tenet of our model: we recognize that patients with similar anatomic features are likely to benefit from “somewhat” similar aperture shapes. Our notion of “aperture envelope”, therefore, refers to a continuous range of mlc leaf movements which those similar aperture shapes might share. Once the library of aperture envelopes was constructed, we have implemented advanced multi‐target classification that seeks to identify similarities between anatomy of each individual patient (organ/tumor volumes and organ/tumor distances) and types of high‐quality aperture envelopes that can be used for IMRT planning. Results: Our case study of ten head‐and‐neck cancer patients indicated strong similarities between aperture patterns used in the clinical treatment plans. We were able to generate 189 aperture envelopes from over 2600 apertures used in the original clinical treatment plans and our multi‐target classification tests indicated near 80% mean 5‐fold validation accuracies for the top 25% generated aperture envelopes. Conclusion: We have presented an innovative aperture classification model with promising potential for efficient utilization of historical clinical treatment plans for new patient IMRT planning.