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This study investigates dosimetric influence and gradient-analysis of leaf-width of various Multi-leaf-collimators (MLC) from Truebeam and Halcyon linear accelerators. The leaf-width effects of Millennium120 and HD120MLC from Truebeam and SX1 and SX2 from Halcyon were studied using virtual phantom in Eclipse16.1.2 TPS. Target structures consist of bore and wave cylinders of equally spaced projected Planning target volume (PTV) of diameters ranging from 1-to-5 cm and 20 cm length. Treatment plans for all PTVs, and four different MLCs configurations from both machines were created utilizing 6MVFFF beam to deliver dose of 50Gy/25# using IMRT and VMAT. Plans were evaluated using plan quality indices including dose conformity, homogeneity, gradient radius, and Monitor-unit (MU). Also, dose gradients were analyzed by estimating distinct integral volume V D% and paired-t-tests were performed to evaluate statistical differences. All the plan satisfied the minimum criteria of D 95 % ≥prescription dose and V 107 % ≤2cc. Mean conformity and homogeneity indices for SX1MLC(CI = 0.680,HI = 0.022) were found significantly higher and lower than SX2(CI = 0.746,HI = 0.016), Millennium120 (CI = 0.739,HI = 0.012), and HD120MLC(CI = 0.745,HI = 0.017), respectively. However, CI and HI for SX2, Millennium120, and HD120MLC found comparable. Gradient radius enclosing 50 % of isodose observed maximum and minimum for SX1 and HD120MLC, respectively. Plan MUs for Truebeam MLCs were found approximately 25 % higher than Halcyon MLCs. Dose distribution generated using SX2 and Millennium120 found comparable, however p ≤ 0.05 ascertained substantial differences among SX1, Millennium120, and HD120MLC. MLC leaf-width influences intensity-modulation and significantly alters dosimetric outcome depending on the magnitude of the leaf-width. HD120MLC does not show much significant advantages over SX2 and Millennium120 except gradient control. Halcyon SX1MLC produces least effective plan compared to all other MLC types. However, SX2 and Millennium120 can produce plans of comparable quality except plan MUs difference. [ABSTRACT FROM AUTHOR]

• The equations that use the product between L and W are the most suitable for predicting LA. • The linear and power models are the most suitable for estimating the leaf area of sweet potato cultivars;. • The proposed non-destructive method presents high accuracy for four sweet potato cultivars. Many researchers consider the leaf area the most critical parameter for plant growth and physiology studies. Using allometric equations is considered an effective and non-destructive method for estimating the leaf area of plants. The objectives of this study were to construct allometric equations to predict the leaf area of sweet potato cultivars as a function of leaf dimensions and to verify the effectiveness of the allometric equations constructed for each cultivar individually and for the grouped data. Two hundred fifty leaves of the sweet potato cultivars Beauregard, BRS Amélia, BRS Cuia, and Coquinho were collected, and then the length and width of each leaf were measured. Subsequently, the product between leaf length and width and the actual leaf area was calculated. Linear, linear without intercept, power, and exponential regression models were used to construct allometric equations to predict leaf area. The best equations were chosen according to the highest coefficients of determination and correlation, Willmott agreement index, and lowest Akaike information criterion and root mean square error. The equations obtained with the linear models without intercept and power using the length and width of the leaves were the most indicated for predicting the leaf area of sweet potato cultivars. [ABSTRACT FROM AUTHOR]

Drought stress poses a severe threat to grain yield in rice. Our previous report demonstrated the role of OsJAZ9 in potassium homeostasis by modulating Jasmonic Acid (JA) signalling. While both potassium (K) and JA are known to have an important role in drought stress response, JA's repressor, i.e., JAZs' role in drought stress, remains elusive. Here we report that OsJAZ9 plays a critical role in rice water-deficit stress tolerance via influencing JA and ABA signalling. Overexpression of OsJAZ9 led to the enhanced ABA and JA levels. Our data further revealed that exogenous JA application antagonises the ABA-mediated inhibition of seed germination. Further, OsJAZ9 overexpression reduces leaf width and stomata density, leading to lower leaf transpiration rates than WT. This reduced transpiration and higher K content as osmoticum improved the water-deficit stress tolerance in OsJAZ9 overexpression lines. On the contrary, OsJAZ9 RNAi lines displayed enhanced sensitivity towards water-deficit stress. Our data provide new insights on the role of JA signalling repressors in rice response to water-deficit stress. • OsJAZ9 overexpressing plants having higher JA and ABA, show reduced stomata density and narrow leaves. • OsJAZ9 regulates ABA biosynthesis by modulating ABA biosynthesis-related genes through jasmonic acid in rice. • ABA along with JA regulates stomata development and leaf width to control transpirational loss of water. • Reduced transpirational loss of water in OsJAZ9 overexpression lines leads to water deficit tolerance. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the feasibility of noncoplanar volumetric modulated arc stereotactic radiotherapy (VMAT-SRT) using a 5-mm multileaf collimator (MLC) for multiple brain metastases. We identified 34 multiple-target cases (3 to 19 targets in each case) with a total of 257 of targets and constructed noncoplanar VMAT-SRT plans using 5-mm and 2.5-mm MLCs with 4-arc. The prescribed dose was 36 Gy/6 fr. Plans were evaluated using the Paddick conformity indices (PCI), Paddick gradient index (PGI), and normal brain dose (NBD, equal to the mean brain dose minus gross tumor volume). There were no significant differences in PCI (median [range]: 5 mm, 0.88 [0.78 to 0.94]; 2.5 mm, 0.89 [0.78 to 0.94]; p = 0.691), PGI (median [range]: 5 mm, 3.96 [2.21 to 6.63]; 2.5 mm, 3.96 [2.24 to 6.45]; p = 0.358), or NBD (median [range]: 5 mm, 7.5 Gy [2.5 to 12.4]; 2.5 mm, 7.5 Gy [2.5 to 12.5]; p = 0.675). The performance of the 5-mm MLC was not inferior to the 2.5-mm MLC in applications of noncoplanar VMAT-SRT for multiple brain metastases with regards to dose conformity, gradient, and NBD. This study provides the necessary background for generalizing noncoplanar VMAT-SRT approaches in treating multiple brain lesions. [ABSTRACT FROM AUTHOR]

Receptor-like kinases (RLKs) are important for plant growth, development and defense responses. The S-receptor protein kinases (SRKs), which represent an RLK subfamily, control the self- incompatibility among Brassica species. However, little information is available regarding SRK functions in rice. We identified a gene OsSRK1 encoding an atypical SRK. The transcript of OsSRK1 was induced by abscisic acid (ABA), salt and polyethylene glycol. OsSRK1 localized to the plasma membrane and cytoplasm. Leaf width was increased in OsSRK1 -overexpression (OsSRK1 -OX) transgenic rice plants, likely because of an increase in cell number per leaf. Furthermore, the expression levels of OsCYCA3-1 and OsCYCD2-1, which encode positive regulators of cell division, were up-regulated in leaf primordium of OsSRK1 -OX rice plants relative to those in wild type. Meanwhile, the expression level of OsKRP1 , which encodes cell cycle inhibitor, was down-regulated in the OsSRK1 -OX plants. Therefore, it is deduced that OsSRK1 regulates leaf width by promoting cell division in the leaf primordium. Additionally, Os SRK1 -OX plants exhibited enhanced ABA sensitivity and salt tolerance compared with wild type. These results suggest that OsSRK1 plays important roles in leaf development and salt responses in rice. [ABSTRACT FROM AUTHOR]

Area (LA) estimation, based on individual leaf dimensions [length (L) and width (W)], was addressed in olive tree. Ten cultivars exposed to two watering regimes (irrigated versus rainfed) under field conditions were examined. Petiole length, leaf L, W, perimeter, base and apex angles, four shape indicators, together with LA were digitally assessed in fully-expanded leaves (480 leaves per treatment; 9.600 leaves in total). Large cultivar differences mainly in leaf size and secondarily in leaf shape were apparent. All parameters were affected by water deficit, but to a cultivar dependent extent. Leaf size was generally reduced by lack of irrigation in most cultivars. LA was estimated with higher accuracy by employing L alone, as compared to W alone, in eight cultivars. LA estimation was always improved by considering both L and W simultaneously, as compared to a single dimension. By studying each cultivar individually, LA estimation was within accepted limits (0.71 ≤ R 2 ≤ 0.92) in nine cultivars, whereas in the tenth one a moderate R 2 (0.63) was obtained. The accuracy of this estimation was not improved by pooling the data of all cultivars. Watering did not significantly affect the relation between estimated and measured LA. The obtained data indicate that a universal LA estimation model for olive tree carries the pitfall of moderate accuracy, owing only to cultivar differences, since environmental effects were trivial. [ABSTRACT FROM AUTHOR]

Highlights • Drought tolerance in Andropogon gerardii ecotypes relates to surface area. • Morphology in A. gerardii ecotypes is mostly controlled by genetics. • Drought-adapted A. gerardii plants had fewer and smaller leaves. • There is little effect of environment on morphology in A. gerardii. Abstract Big bluestem ( Andropogon gerardii Vitman) is a dominant tallgrass species that has a wide range in North America with numerous genetically-distinct ecotypes, each adapted to conditions in their native habitat. In an evolutionary context, it was hypothesized that drought adaptation in A. gerardii would relate to plant surface area, where drought-adapted ecotypes were expected to be short with narrow leaves, thin stems, and few leaves per tiller. In the context of individual plants acclimating to reduced rainfall, rainout shelters were hypothesized to cause morphological reductions in surface area of individual plants. Morphological measurements were taken from four genetically-distinct ecotypes of A. gerardii across a precipitation gradient ranging from 500 to 900 mm rain per year at three common garden sites in Colby, Hays, and Manhattan, Kansas, USA. Evolutionary responses to drier soils in A. gerardii resulted in reduction of evaporative surface area from leaves, as drought-adapted plants had fewer and smaller leaves. The most mesic ecotype of A. gerardii had the highest maximum leaf width, stem diameter, and leaf count across sites. There were few effects of environment on morphology in A. gerardii with reduced rainfall, however, indicating genetics plays a more prominent role than environment to influence morphology. We conclude that increased drought tolerance is related to an evolutionary reduction in evaporative surface area. [ABSTRACT FROM AUTHOR]

Purpose To investigate the changes in quality of the volumetric modulated arc therapy (VMAT) plans with couch-shift between arcs by half of a multi-leaf collimator (MLC) leaf width. Methods A total of 22 patients with head-and-neck cancer were retrospectively selected. Since the smallest MLC leaf width was 5 mm in this study, the couch was shifted by 2.5 mm in the longitudinal-direction between arcs to increase the resolution of fluence map. A total of three types of VMAT plans were generated for each patient; the three types of plans were a two-full-arc plan without couch-shift ( NS plan ), a two-half-arc-pair plan with couch-shift ( HAS plan ), and a two-full-arc pair plan with couch-shift ( FAS plan ). Changes in the dose-volumetric parameters were investigated. Results The FAS plan showed the best plan quality for the target volumes and organs at risk compared to the NS and HAS plans . However, the magnitudes of differences among the three types of plans were minimal, and every plan was clinically acceptable. The average integral doses of the NS , HAS , and FAS plans were 160,549 ± 37,600 Gy-cc, 147,828 ± 33,343 Gy-cc, and 156,030 ± 36,263 Gy-cc, respectively. The average monitor unit of the NS , HAS , and FAS plans were 717 ± 120 MU, 648 ± 100 MU, and 763 ± 158 MU, respectively. Conclusions The HAS plan was better than the others in terms of normal tissue sparing and plan efficiency. By shifting the couch by half of the MLC leaf width in the longitudinal direction between arcs, the VMAT plan quality could be improved. [ABSTRACT FROM AUTHOR]

Based on a linear mixed-effect model, we propose here a non-destructive, rapid and reliable way for estimating leaf area, leaf mass and specific leaf area (SLA) at leaf scale for broadleaf species. For the construction of the model, the product of leaf length by width (LW) was the optimum variable to predict the leaf area of five deciduous broadleaf species in northeast China. In contrast, for species with leaf thickness (T) lower than 0.10 mm, the surface metric of a leaf (e.g., LW or width) was more suitable for predicting leaf mass; and for species with leaf thickness larger than 0.10 mm, the volume metric of a leaf (e.g., the product of length, width and thickness together, LWT) was a better predictor. The linear mixed-effect model was reasonable and accurate in predicting the leaf area and leaf mass of leaves in different seasons and positions within the canopy. The mean MAE% (mean absolute error percent) values were 6.9% (with a scope of 4.1–13.0%) for leaf area and 13.8% (9.9–20.7%) for leaf mass for the five broadleaf species. Furthermore, these models can also be used to effectively estimate SLA at leaf scale, with a mean MAE% value of 11.9% (8.2–14.1%) for the five broadleaf species. We also propose that for the SLA estimation of the five broadleaf species examined, the optimum number of sample leaves necessary for good accuracy and reasonable error was 40–60. The use of the provided method would enable researchers or managers to rapidly and effectively detect the seasonal dynamic of leaf traits (e.g., leaf area, leaf mass or SLA) of the same sample leaves in the future. [ABSTRACT FROM AUTHOR]

Non destructive estimation of leaf area is necessary for taking successive observations on the same leaf. Usually, a common method for developing leaf area estimation models was to execute regression analysis by taking leaf area as dependant variable and leaf parameters as independent variables. However, the regression analysis applicable only when there is a relation between dependent and independent variables. Therefore, the objective of this work was to develop an artificial neural network (ANN) model including leaf length and leaf width as inputs and to make comparison with regression models. Leaf area (LA) of Durain ( Durio zibethinus ) was estimated by ANN and regression models. Among the linear regression models (LRM), the equation LA = 0.888 (L*W) − 4.961 ( R 2 = 0.91, MSE = 5.17) was found to be the best fitting for durian. In ANN modelling best fitting results were obtained with two input nodes (leaf length and leaf width), one hidden layer, and one output layer (leaf area) as 2-1-1. Based on the values of root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE) and coefficient determination ( R 2 ), ANN model was found to be more accurate both in terms of training ( R 2 = 0.96, RMSE = 3.77, MAE = 2.41 and MAPE = 7.77) and testing phases ( R 2 = 0.94, RMSE = 4.81, MAE = 2.91 and MAPE = 0.05) than the best fitting regression model. Hence ANN method may be used as an alternative or supportive model in the estimation of leaf area of durian. [ABSTRACT FROM AUTHOR]

Artificial neural network (ANN) is applied for many subjects in agricultural science such as: crop yield and evapotranspiration prediction, soil parameters estimation, water demand forecasting, hydrological forecasting. Leaf area is one of parameters that is used to assess the plant vegetative growth. In this study, leaf areas of 61 plant species with different leaf shapes were estimated by ANNs and the effect of input data and pre-processing methods on ANNs performance was assessed. Results showed that the ANNs could provide good estimation of leaf area. ANNs input variable combination affected the ANNs performance to estimate the leaf area. With increase in number of hidden layers the epochs decreased and accuracy of the leaf area prediction and running speed increased. Results of test data set showed that MinMax pre-processing method resulted in more accurate prediction in comparison with the no pre-processed method and Norm STD method. The most conclusive result of this study is the application of ANNs for all of plant species, whereas, in application of other methods: specific equation should be prepared for each plant. [ABSTRACT FROM AUTHOR]

To study the effect of multileaf collimator (MLC) leaf widths (standard MLC [sMLC] width of 10mm and micro-MLC [mMLC] width of 4mm) on intensity-modulated radiotherapy (IMRT) for cervical cancer. Between January 2010 and August 2010, a retrospective analysis was conducted on 12 patients with cervical cancer. The treatment plans for all patients were generated with the same machine setup parameters and optimization methods in a treatment planning system (TPS) based on 2 commercial Elekta MLC devices. The dose distribution for the planning tumor volume (PTV), the dose sparing for organs at risk (OARs), the monitor units (MUs), and the number of IMRT segments were evaluated. For the delivery efficiency, the MUs were significantly higher in the sMLC-IMRT plan than in the mMLC-IMRT plan (802 ± 56.9 vs 702 ± 56.7; p < 0.05). The number of segments in the plans were 58.75 ± 1.8 and 59 ± 1.04 (p > 0.05). For the planning quality, the conformity index (CI) between the 2 paired IMRT plans with the mMLC and the sMLC did not differ significantly (average: 0.817 ± 0.024 vs 0.810 ± 0.028; p > 0.05). The differences of the homogeneity index (HI) between the 2 paired plans were statistically significant (average: 1.122 ± 0.010 vs 1.132 ± 0.014; p < 0.01). For OARs, the rectum, bladder, small intestine, and bony pelvis were evaluated in terms of V10, V20, V30, and V40, percentage of contoured OAR volumes receiving 10, 20, 30, and 40Gy, respectively, and the mean dose (Dmean) received. The IMRT plans with the mMLC protected the OARs better than the plans with the sMLC. There were significant differences (p < 0.05) in evaluated parameters between the 2 paired IMRT plans, except for V30 and V40 of the rectum and V10, V20, V40, and Dmean of the bladder. IMRT plans with the mMLC showed advantages over the plans with the sMLC in dose homogeneity for targets, dose sparing of OARs, and fewer MUs in cervical cancer. [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the current used allometric models and proposed a reliable and accurate model using non-destructive measurements of leaf length (L) and/or width (W) for estimating the leaf area of the Jatropha plant (Jatropha curcas L.). For model construction, a total of 1200 leaves were randomly selected from different levels of the tree canopies and encompassed the full spectrum of measurable leaf sizes (0.19–367 cm2). Power models better fit the Jatropha leaf area (LA) compared to linear models; however, when the LW was used, the intercept was removed from the linear model to precisely estimate LA. To validate these models, two independent data sets of 300 leaves were used. We demonstrate that the currently used models are biased and underestimate the area of Jatropha leaves. We developed an unbiased, single power model (Y = xβ1) based on two leaf dimensions [LA = (LW)0.9660] with high precision and accuracy as well as a random dispersion pattern of the residuals. The model may be simplified by using only one leaf dimension (Y = xβ1), LA = L1.9644 or LA = W1.8929. However, when either W or L alone was used as the single leaf dimension, the power model predicted the LA with good accuracy at the expense heteroscedastic residual dispersion behavior. [Copyright &y& Elsevier]

Abstract: Mathematical models based on dynamic growth process of greenhouse melon leaves were built. Two experiments, involving different years, organic fertilizer rates and cultivar types in melon, were carried out for data acquisition. In each experiment, time-course observations of leaf morphological properties (leaf length and leaf width) on different leaf positions of melon were obtained. The results showed that the logistic mathematical models were suitable to simulate the dynamic elongation of leaf length and leaf width with the dynamic changes of (accumulated thermal units), logarithmic equation and quadratic curve equation fit the dynamic changes of the final leaf length and the maximum leaf width with different leaf positions well, and the leaf area dynamic changes were simulated by binary regression equation. In addition, the effects of nitrogen conditions on leaf growth were quantified by the effectiveness values of nitrogen concentration in leaves. The model was validated with independent field experiment data, and the results showed that the mean RMSE (root mean square error) of leaf length, leaf width and leaf area under different was 0.54 cm, 1.19 cm, 0.44 cm2, respectively. [Copyright &y& Elsevier]

Abstract: We compared the impacts of multileaf collimator (MLC) widths (standard MLC width of 10 mm [SMLC] and micro-MLC width of 4 mm [MMLC]) on intensity-modulated radiotherapy (IMRT) planning for nasopharyngeal carcinoma (NPC). Ten patients with NPC were recruited in this study. In each patient''s case, plans were generated with the same machine setup parameter and optimizing methods in a treatment planning system according to 2 commercial Elekta MLC devices. All of the parameters were collected from dose-volume histograms of paired plans and evaluated. The average conformity index (CI) and homogeneous index (HI) for the planning gross target volume in IMRT plans with MMLC were 0.790 ± 0.036 and 1.062 ± 0.011, respectively. Data in plans with SMLC were 0.754 ± 0.038 and 1.070 ± 0.010, respectively. The differences were statistically significant (p < 0.05). Compared with CI and HI for planning target volume in paired plans, data with MMLC obviously were better than those with SMLC (CI: 0.858 ± 0.026 vs. 0.850 ± 0.021, p < 0.05; and HI: 1.185 ± 0.011 vs. 1.195 ± 0.011, p < 0.05). However, there was no statistical significance between evaluated parameters (Dmean, Dmax, D5, gEUD, or NTCP) for organs at risk (OARs) in the 2 paired IMRT plans. According to these two kinds of Elekta MLC devices, IMRT plans with the MMLC have significant advantages in dose coverage for the targets, with more efficiency in treatment for NPC but fail to improve dose sparing of the OARs. [Copyright &y& Elsevier]

Abstract: We studied the effect of MLC (multileaf collimator) leaf width and PTV (planning target volume) margin on treatment planning of intensity modulated stereotactic radiosurgery (IMSRS) or radiotherapy (IMSRT). Twelve patients previously treated with IMSRS/IMSRT were retrospectively planned with 5- and 3-mm MLC leaf widths and 3- and 2-mm PTV margins using the already contoured clinical target volume and critical structures. The same beam arrangement, planning parameters, and optimization method were used in each of the 4 plans for a given patient. Each plan was normalized so that the prescription dose covered at least 99% of the PTV. Plan indices — D mean (mean dose), conformity index (CI), V70 (volume receiving ≥ 70% of the prescription dose), and V50 (volume receiving ≥ 50% of the prescription dose) — were calculated from the dose-volume histograms (DVHs) of the PTV, normal tissue, and organs at risk (OARs). Hypothesis testing was performed on the mean ratios of plan indices to determine the statistical significance of the relative differences. The PTV was well covered for all plans, as no significant differences were observed for D95, V95, Dmax, Dmin, and Dmean of the PTV. The irradiated volume was ∼23% smaller when 2-mm instead of 3-mm PTV margin was used, but it was only reduced by ∼6% when the MLC leaf width was reduced from 5 mm to 3 mm. For normal tissue and brainstem, V70, V50, and Dmean were reduced more effectively by a decrease in MLC width, while Dmean of optic nerve and chiasm were more sensitive to a change in PTV margin. The DVH statistics for the PTV and normal structures from the treatment plan with 5-mm MLC and 2-mm PTV margin were equal to those with 3-mm MLC and 3-mm PTV margin. PTV margin reduction is more effective in sparing the normal tissue and OARs than a reduction in MLC leaf width. For IMSRS, where highly accurate setup and small PTV margins are routinely employed, the use of 5-mm MLC is therefore less desirable. [Copyright &y& Elsevier]

Abstract: Non-destructive and mathematical approaches of modeling can be very convenient and useful for plant growth estimation. To predict individual leaf area, fresh weight, and dry weight of a cucumber (Cucumis sativus L.), models were developed using leaf length, leaf width, SPAD value, and different combinations of these variables. Eight regression equations, commonly used for developing growth models, were compared for accuracy and adaptability. The three nonlinear models developed were as follows: individual leaf area (LA)=−210.61+13.358W +0.5356LW (R 2 =0.980***), fresh weight (FW)=−2.72+0.0135LW +0.00022LWS (R 2 =0.956***), and dry weight (DW)=0.25−0.00102LS +0.000077LWS (R 2 =0.956***), where L is the leaf length, W the leaf width, S the SPAD value, and LWS = L × W × S. For validation of the model, estimated values for individual leaf area, fresh weight, and dry weight showed strong agreement with the measured values, respectively. Leaf dry weight, especially, was estimated with a higher degree of accuracy through the use of a SPAD value, as well as leaf length and width. Therefore, it is concluded that models presented herein may be useful for the estimation of the individual leaf area, fresh weight, and dry weight of a cucumber with a high degree of accuracy. [Copyright &y& Elsevier]

Abstract: Purpose: A planning study to analyze the impact of different leaf widths on the achievable dose distributions with intensity modulated radiation therapy (IMRT). Methods: Five patients (3 intra- and 2 extra-cranial) with projected planning target volume (PTV) sizes smaller than 10cm by 10cm were re-planned with four different multileaf collimators (MLC). Two internal collimators with an isocentric leaf width of 4 and 10mm and two add-on collimators with an isocentric leaf width of 2.75 and 4mm were evaluated. The inverse treatment planning system KonRad (Siemens Medical Solutions) was used to create IMRT ‘step & shoot’ plans. For each patient the same arrangement of beams and the same parameters for the optimization were used for all MLCs. The beamlet size for all treatment plans was chosen to coincide with the leaf width of the respective MLC. To evaluate the treatment plans 3D dose distributions and dose volume histograms were analyzed. As indicators for the quality of the PTV dose distribution the minimum dose, maximum dose and the standard deviation were used. For the organs at risk (OAR) the equivalent uniform dose (EUD) was calculated. To measure the dose coverage of the PTV the volume (V 90) that received doses higher than 90% of the prescribed dose was calculated where for the conformity the dose conformity index given by Baltas et al. was determined. Results: The MLC with the smallest leaf width yields the best mean value of all five patients for the PTV coverage and for the conformity. For the MLCs with the same leaf width, the add-on MLC leads to superior treatment plans than the internal MLC. This is due to the sharper penumbra of the add-on MLC. The number of IMRT field segments to deliver increased by approximately a factor of two if 2.75mm MLC leafs are used instead of the standard 10mm leafs. In case of the para-spinal patients the EUD value for the spinal cord is only reduced slightly by using MLCs with leaf widths smaller than 5mm. For the intra-cranial the EUD value for some organs improved with reduced leaf widths while for some organs the 10mm MLC leafs give comparable values. Conclusion: As expected the MLC with the smallest leaf width always yields the best PTV coverage. Reducing the leaf width from 4 to 2.75mm results in a slight enhancement of the PTV coverage. With the selected organ parameters no significant improvement for most OAR was found. The disadvantage of the reduction of the leaf width is the increasing number of segments due to the more complex fluence patterns and therefore an increased delivery time. [Copyright &y& Elsevier]