Application Of Intensity-modulated Radiotherapy Research Articles

Selectively Irradiation of the Supraclavicular Area in Nasopharyngeal Carcinoma Treated with Intensity Modulated Radiotherapy

The application of intensity-modulated radiotherapy (IMRT) has significantly improved the locoregional control and overall survival of patients with nasopharyngeal carcinoma (NPC), but how to deescalate the intensity of treatment to further reduce the side effects while ensuring the efficacy is the main concern of clinicians. Decreasing radiation volume is one of the hot research topics. Whole-neck irradiation is recommended for patients with cervical lymph node involvement, which includes levels IVb and Vc. Since the implementation of IMRT in our clinic, patients with only upper cervical lymph node invasion have not been irradiated in the levels IVb and Vc, and the regional control rate is comparable to that of other centers. This study intends to retrospectively analyze the feasibility of omitting levels IVb and Vc in patients with only upper cervical lymph node invasion, and provide a basis for the revision of international guideline for the delineation of the clinical target volume (CTV). Patients with histologically confirmed NPC who completed IMRT successfully at our attending group between January 2014 to March 2018 were candidates for this study. Other eligibility criteria for analysis were as follows: (1) The first patient without distant metastasis; (2) Only patients with upper cervical lymph node invasion (only N1, N2, because the maximum diameter of the upper neck 6cm diagnosed as N3 patients were not included) (AJCC staging system, 8th edition); (3) Having complete baseline imaging data; (4) Over 3 months of follow-up; (5) Patients without previous history of malignant tumor and secondary cancer. According to the delineation of CTV in our protocol for patients with stage N1 and N2, levels IVb and Vc are not irradiated (i.e., retaining the original supraclavicular area). The main endpoints of the study were regional recurrence-free survival (RRFS) and recurrence rates in levels IVb and Vc. In all, 363 patients with NPC and median follow-up of 61.9 months (range, 3.67-93.3) met the study inclusion criteria and comprise the dataset for the analysis. The overall survival, survival without local recurrence, survival without regional recurrence, and survival without distant metastasis at 3 and 5 years were 94.6% and 91.1%, 97.7% and 96.5%, 98.6% and 98.0%, 93.5% and 91.1%. At the final follow-up, 11 cases showed regional recurrence, and only one case (0.28%) showed recurrence in regions IVb and Vc, which were field recurrences, while the rest were intra-field recurrences. Omitting levels Ⅳb and Ⅴc IMRT should be safe and feasible for patients who only had involvement of upper neck LNs. Further well-designed multicenter prospective trials should be conducted to confirm our results and further optimize the recommendation of the International Guideline.

Evaluation of the effect of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc radiotherapy (VMAT) techniques on survival response in cell lines with a new radiobiological modeling.

The optimal radiobiological model, which assesses the biological effects of novel radiotherapy techniques that concurrently modify multiple physical factors, has not yet been defined. This study aimed to investigate the impact of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) on cellular response in head and neck cancer and melanoma models. Clonogenic analysis, DNA double-strand break analysis, apoptosis, and cell cycle analysis were performed on cancer stem cell models, cancer models, and normal tissue cell models to assess radiation sensitivity. The segmented radiation approach used in IMRT applications enhanced radiosensitivity and cytotoxicity in the cancer models, while changes in dose rate had varying effects on cytotoxicity depending on the tumor cell type. VMAT increased cellular resistance, favoring treatment outcomes. The biological processes were influenced differently by dose rate, IMRT, and VMAT depending on the tumor cell type. The selection of the most appropriate technique is crucial in representing new radiotherapy approaches. The obtained data can serve as a model to address clinical questions in daily practice. The integration of non-standard outcomes with standard applications should be considered in clinical settings.

Case Report of Advanced Juvenile Nasopharyngeal Angiofibroma with Cavernous Sinus Involvement: Advantages of Advanced Radiotherapy Thechnique Volumetric Modulated Arc Therapy

Objectives: In very advance unresectable stages Juvenile nasopharyngeal angiofibroma (JNA)radiotherapy is treatment of choice. Usually JNA is in close proximity to different organ at risk, which necessitates accurate and precise radiation delivery. Series reported the application of IMRT (Intensity Modulated Radiotherapy) with good sparing of organ at risk, but the literature search found no report on VMAT (Volumetric Modulated Arc Therapy) treatment in case of JNA. Clinical case: The present publication report for first time a patient irradiated with VMAT and IGRT (Image guided radiotherapy) for JNA. The stage of the tumor based on CT and MRI was IIIB according to Radkovsi with cavernous sinus invasion. Moderate total radiation dose 36 Gy in 1.8 Gy per fraction was delivered. No early and late toxicity was recorded. The patient is followed up every six months and persistent residual tumor on MRI was seen, but no bleeding onphysical exam. At one year follow up this is accepted as good local control. Conclusion: VMAT and IGRT could be safely applied with reduction of the radiation dose at organ of risk. VMAT is promising in the treatment of juvenile angiofibroma with advantages over conventional radiotherapy, but as this is case report of only one patient, further experience with VMAT is needed in JNA

Research progress on the combined application of brachytherapy and IMRT for the treatment of cervical cancer

Brachytherapy is a key part of radical radiotherapy for cervical cancer. Along with the persistent development of radiotherapy techniques, the combined application of brachytherapy and intensity-modulated radiotherapy (IMRT) has been proposed by scholars for cervical cancer patients presenting with large residual tumors accompanied by parametrial infiltration after IMRT. In this article, recent research progress on IMRT combined with brachytherapy applied in the treatment of cervical cancer was reviewed. Key words: Cervical neoplasm/brachytherapy; Cervical neoplasm/intensity-modulated radiotherapy; Research progress

Application of intensity-modulated radiotherapy in unresectable poorly differentiated thyroid carcinoma.

Poorly differentiated thyroid carcinoma (PDTC) is a rare and aggressive malignancy with high rates of invasion and distant metastasis. This study was to explore the ability of intensity-modulated radiotherapy (IMRT) combined with chemotherapy to manage unresectable PDTC. Between February 2011 and April 2012, 5 patients with unresectable PDTC were treated by IMRT at our institution and were included in this analysis. The median radiotherapy dose to the gross tumor volume (GTV) was 66 Gy/33 fractions/6.4 weeks. All patients received chemotherapy, and one patient with tumor compression symptoms had a tracheotomy before treatment. The mean survival time of the 5 patients was 41.6 months. The direct causes of death were distant metastases (40%) and progression of the locoregional disease (20%). In conclusion, IMRT combined with chemotherapy for unresectable PDTC might be beneficial to improve locoregional control. Further new therapies are needed to control metastases.

Sinus mucosa status in patients with nasopharyngeal carcinoma treated with intensity-modulated radiotherapy: A 5-year follow-up.

Sinus mucosa abnormalities on image studies, which is the major diagnostic measure for sinusitis, were investigated in patients with nasopharyngeal carcinoma (NPC) after intensity-modulated radiotherapy (IMRT). A retrospective review of the MRIs for patients with NPC was conducted. Sinus mucosa abnormalities were staged by the Lund-Mackay system. A total of 94 patients were enrolled in this study. The rate and severity of sinus abnormalities were highest on the third postradiotherapy month (p < .005, t test). There was no significant increase in the incidence of abnormalities on the fifth postradiotherapy year (t test). The anterior ethmoid and maxillary sinuses were the most affected sinuses before and after radiotherapy (p < .005, chi-square test). Our data showed that the anterior ethmoid and maxillary sinuses were the most vulnerable sinuses for therapeutic toxicity after IMRT in patients with NPC. In the long run, however, the application of IMRT does not significantly increase the incidence of sinus toxicities.

Late toxicities after intensity-modulated radiotherapy for nasopharyngeal carcinoma: patient and treatment-related risk factors

Background:The objective of this study is to analyse the factors affecting late toxicity for nasopharyngeal carcinoma (NPC) patients treated with intensity-modulated radiotherapy (IMRT).Methods:Seven hundred and eighty-nine consecutive NPC patients treated with IMRT at our centre from January 2003 to February 2008 were retrospectively analysed. Radiotherapy-related complications were categorised using the RTOG Late Radiation Morbidity Scoring Criteria and the Common Terminology Criteria for Adverse Events (Version 3.0). Two hundred and thirty-three patients were treated with IMRT alone (group 1) and 556 patients underwent cisplatin-based chemotherapy (group 2).Results:Median follow-up was 65 months (range, 4–106 months). The 5-year major late toxicity rate was significantly greater in group 2 than group 1 (63.2% vs 42.0%, P<0.001). Multivariate analyses showed that N category, T category and chemotherapy were significant factors. The maximal dose (Dmax) to the temporal lobe was a significant factor affecting temporal lobe injury (TLI), with a hazard ratio of 1.26 (95% confidence interval (CI), 1.18–1.35; P<0.001) per 1-Gy increase. The 5-year TLI rate increased from 0.8% for 284 lobes with Dmax <65.77 Gy to 27.1% for 176 lobes with greater doses (P<0.001). Logistic regression showed that the hazard ratio attributed to the parotid gland mean dose was 1.36 (95% CI, 1.21–1.53; P<0.001) per 1-Gy increase. Chemotherapy was not a significant factor (P=0.211).Conclusion:With the application of IMRT, the incidence of radiation-related complications has been reduced except for TLI. The significant factors affecting the risk of TLI included T category, chemotherapy and Dmax.

Image-Guided Adaptive Radiotherapy – Delivering Personalized Radiation Medicine to Improve Treatment Quality and Patients’ Outcome

The application of Intensity-Modulated Radiotherapy and Image-Guided Radiotherapy as a standard of practice at our institution has facilitated the development of expertise among radiation therapists in image registration of multi-modality imaging, generation of high quality radiation distribution and image assessment/interpretation for position verification & target localization. With this wealth of expertise, Image-Guided Adaptive Radiotherapy (IG-ART), a process of adapting the treatment to the anatomical changes, for example, tumor shrinkage or interfraction motion, of an individual patient during the course of radiotherapy, is to be implemented at our institution for the purpose of providing personalized cancer care to improve treatment quality and patients’ outcome.

Application of the measurement-based Monte Carlo method in nasopharyngeal cancer patients for intensity modulated radiation therapy

This study aims to utilize a measurement-based Monte Carlo (MBMC) method to evaluate the accuracy of dose distributions calculated using the Eclipse radiotherapy treatment planning system (TPS) based on the anisotropic analytical algorithm. Dose distributions were calculated for the nasopharyngeal carcinoma (NPC) patients treated with the intensity modulated radiotherapy (IMRT). Ten NPC IMRT plans were evaluated by comparing their dose distributions with those obtained from the in-house MBMC programs for the same CT images and beam geometry. To reconstruct the fluence distribution of the IMRT field, an efficiency map was obtained by dividing the energy fluence of the intensity modulated field by that of the open field, both acquired from an aS1000 electronic portal imaging device. The integrated image of the non-gated mode was used to acquire the full dose distribution delivered during the IMRT treatment. This efficiency map redistributed the particle weightings of the open field phase-space file for IMRT applications. Dose differences were observed in the tumor and air cavity boundary. The mean difference between MBMC and TPS in terms of the planning target volume coverage was 0.6% (range: 0.0–2.3%). The mean difference for the conformity index was 0.01 (range: 0.0–0.01). In conclusion, the MBMC method serves as an independent IMRT dose verification tool in a clinical setting.

Monitor units are not predictive of neutron dose for high-energy IMRT

BackgroundDue to the substantial increase in beam-on time of high energy intensity-modulated radiotherapy (>10 MV) techniques to deliver the same target dose compared to conventional treatment techniques, an increased dose of scatter radiation, including neutrons, is delivered to the patient. As a consequence, an increase in second malignancies may be expected in the future with the application of intensity-modulated radiotherapy. It is commonly assumed that the neutron dose equivalent scales with the number of monitor units.MethodsMeasurements of neutron dose equivalent were performed for an open and an intensity-modulated field at four positions: inside and outside of the treatment field at 0.2 cm and 15 cm depth, respectively.ResultsIt was shown that the neutron dose equivalent, which a patient receives during an intensity-modulated radiotherapy treatment, does not scale with the ratio of applied monitor units relative to an open field irradiation. Outside the treatment volume at larger depth 35% less neutron dose equivalent is delivered than expected.ConclusionsThe predicted increase of second cancer induction rates from intensity-modulated treatment techniques can be overestimated when the neutron dose is simply scaled with monitor units.

SU-E-T-208: The Secondary Malignancy Risk Estimation Due to the Neutron Contamination in 3D-CRT and IMRT Treatment Techniques by Using Bubble Detectors.

In this study, the neutron measurements were performed in free in air and RW3 solid water phantom to estimate the secondary malignancy risk for three dimensional conformal radiotherapy (3D-CRT) and intensity modulated radiotherapy (IMRT) techniques in prostate cancer treatment. Neutron dose were measured in 18 MV Elekta Synergy Platform and Varian Clinac linear accelerators by using bubble detector for personal neutron dosimetry (BD-PND). To determine the neutron equivalent dose in different depths and different distance from the edge of treatment field RW3 solid water phantom was used and organs location was defined in Alderson Rando phantom with respect to target (prostate) position in the treatment field. By using these data, we determined the neutron equivalent dose and effective dose for the standard prostate cancer patient treated with 3D-CRT and IMRT with 18 MV photon energy. The total dose was 70 Gy in 3D-CRT and 76 Gy in IMRT treatment in the current study. For both of these treatment techniques, we estimated the risk of secondary malignancies due to the neutron contamination by using the International Commission on Radiological Protection (ICRP) report 103. The equivalent dose and effective dose due the neutron contamination were considerably high in 18 MV IMRT technique. The secondary malignancy risk estimation for 3D-CRT and IMRT were found to be 0.44% and 1.15% for Elekta Synergy Platform linear accelerator, 0.92% and 2.38% for the Varian Clinac DHX High Performance linear accelerator, respectively. Therefore, one should take care of the secondary malignancy risk in case of using 18 MV in IMRT applications.

Application of IMRT Combined with Cone-beam Computed Tomography in Treatment of Intracranial Tumor

Objective To evaluate the interfractional three-dimensional(3D) setup error and propose optimum margin of planning target volume(PTV) in radiotherapy for intracranial tumor at risk of using intensity modulated radiotherapy(IMRT) guided with cone-beam computed tomography(CBCT).MethodsThirty-six patients received radiotherapy of IMRT imaging-guided with megavolt MVision CBCT scans equipped in ONCOR Linear Accelerator.The initial five fractional CBCT volume-imaging and data obtained by CBCT scans after initial setup and after re-positioning were dimensionally matched with planned CT images.Results The interfractional setup errors on X,Y and Z axes were(2.22±1.37) mm,(2.62±1.50) mm and(2.77±1.34) mm,respectively,for 36 intracranial tumors.Comparing with the pre-correction position,the post-correction setup errors decreased significantly on all three axes(P0.05),whereas there were no statistically significant difference in five fractional setup errors(P0.05).While without correction of CBCT setup errors,PTV margin in three dimension were Lat(cm)-X:2.94 mm,Long(cm)-Y:3.31mm,Vert(cm)-Z:3.52 mm.While with correction of CBCT setup errors,PTV margin in three dimension were,Lat(cm)-X: 1.00 mm,Long(cm)-Y: 1.19 mm,Vert(cm)-Z: 1.68 mm.Conclusion The set-up margins were 4 mm in all directions.Measurement and correction of interfractional setup errors and PTV margins before fractional radiotherapy using megavolt MVision CBCT could help to improve the precision of IMRT radiotherapy for intracranial tumors.

Application of IMAT versus fixed-gantry IMRT in cervical esophageal cancer : A comparison in dosimetry and implementation

Objective To compare and analyze the characteristics of intensity-modulated arc therapy (IMAT) versus fixed-gantry intensity-modulated radiotherapy (IMRT) in the treatment of cervical esophageal cancer.Methods Ten patients treated in our radiotherapy center were selected for this study.Based on the identical CT and planning target volume (PTV), two IMAT plans were generated with Eclipse ver8.6 planning system.IMAT1 consisting of a single 359.8° rotation, and IMAT2 consisting of two coplanar 359.8° rotations.PTV were prescribed to 60 Gy in 30 fractions.Planning objectives for PTV,corresponding with the IMRT plans, were V98 larger than 97% and V110 no more than 15%.The maximum dose of spinal-cord was constrained below 45 Gy.One-way ANOVA were applied to dose-volume values for PTV and OAR from DVH.Results There were no significant differences between IMRT and IMAT in PTV D98, V98, CI or total-lung V5, V10, V30, V40, V50 and mean lung dose (all P > 0.05).However, the differences were significant in terms of D2, V110 and HI of PTV, V20 of the total-lung (all P<0.05).On the MU,IMRT = 1174.8 MU,IMAT1 =709.7 MU,and IMAT2 =803.8 MU (F =39.25,P =0.000).On the treatment time,IMRT= 14.9 min,IMAT1 = 1.9 min, and IMAT2 =2.66 min (F=45.14,P=0.000).Conclusions IMAT is equal to IMRT in dosimetric evaluation.Due to much less MU and delivery time,IMAT is an ideal technique in treating patients by reducing the uncomfortable influences which could effect the treatment.However, IMAT1 is slightly inferior to IMAT2. Key words: Esophageal neoplasms/radiotherapy; Radiotherapy, intensity-modulated ; Radiotherapy, intensity-modulated arc; Dosimetry

UK Guidelines for the Safe Delivery of Intensity-modulated Radiotherapy

This paper outlines the guidelines for the development of intensity-modulated radiotherapy (IMRT) in the UK. The guidelines are designed to cover the complete implementation of IMRT, with guidelines in the following categories: commissioning, quality, clinical, audit, and training and education. These guidelines have been compiled by the Radiotherapy Development Board of the Royal College of Radiologists and will support the safe application of IMRT in the UK.

Dosimetric comparison between intensity-modulated radiotherapy and conformal radiotherapy for upper thoracic esophageal carcinoma

Treatment planning for radiotherapy of upper thoracic esophageal carcinoma is challenging due to the anatomical features. The difficulty may be resolved by intensity-modulated radiotherapy (IMRT). This study was to compare the dosimetric advantages of IMRT to that of conformal radiotherapy (CRT) for upper thoracic esophageal carcinoma, and to explore the clinical application of IMRT. Eleven patients with upper thoracic esophageal carcinoma were enrolled. In addition to the actually used CRT plan, a five-field IMRT plan was generated for each case. The parameters of dose volume histogram for targets and organs at risk were compared between two techniques. For the planning target volume (PTV) of tumor and para-tumor tissues, the mean dose, maximal dose, doses covering 99% and 95% volume were similar in IMRT and CRT plans (P>0.05). However, IMRT plan had a higher conformity index than CRT plan (0.68+/-0.04 vs. 0.46+/-0.11, P<0.01). For the PTV of supraclavicular region, IMRT plan showed a better dose heterogeneity index than CRT plan (1.17+/-0.05 vs. 1.33+/-0.15, P=0.01). IMRT plan had lower maximal dose to the planning risk volume of the spinal cord (44.4 Gy vs. 52.5 Gy, P<0.05) and lower lung volume received dose of 10 Gy or higher [(32+/-6)% vs. (35+/-9)%, P<0.05] than CRT plan. For the upper thoracic esophageal carcinoma, IMRT has more conformal distribution of dose and better spinal cord sparing than CRT, and can reduce the volume of lung that received dose of 10 Gy or higher.

Investigation of Simple IMRT Delivery Techniques for Non-Small Cell Lung Cancer Patients with Respiratory Motion Using 4DCT

Techniques for generating simplified IMRT treatment plans for treating non-small cell lung cancer (NSCLC) patients with respiratory motion were investigated. To estimate and account for respiratory motion, 4-dimensional computed tomography (4DCT) datasets from 5 patients were used to design 5-field 6-MV ungated step-and-shoot intensity modulated radiotherapy (IMRT) plans delivering a dose of 66 Gy to the planning target volume (PTV). For each patient, 2 plans were generated using the mean intensity and the maximum intensity of 10 CT datasets from different breathing phases. The plans also utilized different margins around the clinical target volume/internal target volume (CTV/ITV) to account for tumor motion. To reduce the treatment time and ensure accurate dose delivery to moving targets, the number of intensity levels was minimized while maintaining dose coverage to PTV and minimizing dose to organs at risk (OARs). Dose-volume histograms (DVHs), dosimetric metrics, and outcome probabilities were evaluated for all plans. Plans using the averaged CT image dataset were inferior, requiring larger margins around the PTV, with a maximum of 1.5 cm, to ensure coverage of the tumor, and therefore increased the dose to OARs located in proximity of the tumor. The plans based on superimposed CT image datasets achieved full coverage of the tumor, while allowing tight margins around the PTV and minimizing the dose to OARs. A small number of intensity-levels (3 to 5), resulting in IMRT plans with a total of 13 to 30 segments, were sufficient for homogeneous PTV coverage, without affecting the sparing of OARs. In conclusion, a technique involving treatment planning with the superimposed CT scans of all respiratory phases, and the application of IMRT with only a small number of segments was feasible despite significant tumor motion; however, greater patient numbers are needed to support the statistical significance of the results presented in this work.

Clinical application of intensity-modulated radiotherapy for head and neck cancer

Intensity-modulated radiotherapy (IMRT) is a modern treatment technique that allows one to shape the dose to the target volume and to reduce the dose delivered to healthy tissue. Over the last decade, IMRT has been implemented for head and neck cancer treatment, with the aim of reducing the dose delivered to the parotid glands and improving the dose coverage of complex target volumes located close to critical structures. The potential benefits of IMRT in terms of salivary function preservation and better local control have contributed to the rapid diffusion of this new technology. However, it should not be overlooked that IMRT is a novel treatment technique and that its clinical application represents a paradigm shift in the practice of radiation oncology. The purpose of this article is to review the clinical experience with IMRT for head and neck cancer treatment and to discuss some important issues related to its implementation.

The clinical implementation of respiratory-gated intensity-modulated radiotherapy

The clinical use of respiratory-gated radiotherapy and the application of intensity-modulated radiotherapy (IMRT) are 2 relatively new innovations to the treatment of lung cancer. Respiratory gating can reduce the deleterious effects of intrafraction motion, and IMRT can concurrently increase tumor dose homogeneity and reduce dose to critical structures including the lungs, spinal cord, esophagus, and heart. The aim of this work is to describe the clinical implementation of respiratory-gated IMRT for the treatment of non-small cell lung cancer. Documented clinical procedures were developed to include a tumor motion study, gated CT imaging, IMRT treatment planning, and gated IMRT delivery. Treatment planning procedures for respiratory-gated IMRT including beam arrangements and dose-volume constraints were developed. Quality assurance procedures were designed to quantify both the dosimetric and positional accuracy of respiratory-gated IMRT, including film dosimetry dose measurements and Monte Carlo dose calculations for verification and validation of individual patient treatments. Respiratory-gated IMRT is accepted by both treatment staff and patients. The dosimetric and positional quality assurance test results indicate that respiratory-gated IMRT can be delivered accurately. If carefully implemented, respiratory-gated IMRT is a practical alternative to conventional thoracic radiotherapy. For mobile tumors, respiratory-gated radiotherapy is used as the standard of care at our institution. Due to the increased workload, the choice of IMRT is taken on a case-by-case basis, with approximately half of the non-small cell lung cancer patients receiving respiratory-gated IMRT. We are currently evaluating whether superior tumor coverage and limited normal tissue dosing will lead to improvements in local control and survival in non-small cell lung cancer.

Re-treatment of a lung tumour using a simple intensity-modulated radiotherapy approach

We present a lung tumour case where, although the proximal spinal cord had already reached its dose tolerance, re-treatment was indicated. Minimization of the cord dose was defined as the main constraint for this case, however additional dose to the heart was considered. A simple (4 field) intensity-modulated radiotherapy (IMRT) treatment which proved superior to the standard conformal plan was developed using the Computerized Medical Systems (CMS) XiO treatment planning system. The IMRT plan was found to be superior to the conventional conformal plan regarding tumour coverage. It provided 100% saturation of the planning target volume (PTV) by the 95% isodose cloud, whereas the latter only provided 77% coverage. A step and shoot delivery using 10 intensity levels was developed and subsequently delivered for this patient. We considered it to be a routine application of IMRT and an important example of how it can offer benefit in individual and appropriate cases where conventional treatment is inadequate.

Impact of IMRT and leaf width on stereotactic body radiotherapy of liver and lung lesions

The present study explored the impact of intensity-modulated radiotherapy (IMRT) on stereotactic body RT (SBRT) of liver and lung lesions. Additionally, because target dose conformity can be affected by the leaf width of a multileaf collimator (MLC), especially for small targets and stereotactic applications, the use of a micro-MLC on "uniform intensity" conformal and intensity-modulated SBRT was evaluated. The present study included 10 patients treated previously with SBRT in our institution (seven lung and three liver lesions). All patients were treated with 3 x 12 Gy prescribed to the 65% isodose level. The actual MLC-based conformal treatment plan served as the standard for additional comparison. In total, seven alternative treatment plans were made for each patient: a standard (actual) plan and an IMRT plan, both calculated with Helax TMS (Nucletron) using a pencil beam model; and a recalculated standard and a recalculated IMRT plan on Helax TMS using a point dose kernel approach. These four treatment plans were based on a standard MLC with 1-cm leaf width. Additionally, the following micro-MLC (central leaf width 3 mm)-based treatment plans were calculated with the BrainSCAN (BrainLAB) system: standard, IMRT, and dynamic arc treatments. For each treatment plan, various target parameters (conformity, coverage, mean, maximal, and minimal target dose, equivalent uniform doses, and dose-volume histogram), as well as organs at risk parameters (3 Gy and 6 Gy volume, mean dose, dose-volume histogram) were evaluated. Finally, treatment efficiency was estimated from monitor units and the number of segments for IMRT solutions. For both treatment planning systems, no significant difference could be observed in terms of target conformity between the standard and IMRT dose distributions. All dose distributions obtained with the micro-MLC showed significantly better conformity values compared with the standard and IMRT plans using a regular MLC. Dynamic arc plans were characterized by the steepest dose gradient and thus the smallest V(6 Gy) values, which were on average 7% smaller than the standard plans and 20% lower than the IMRT plans. Although the Helax TMS IMRT plans show about 18% more monitor units than the standard plan, BrainSCAN IMRT plans require approximately twice the number of monitor units relative to the standard plan. All treatment plans optimized with a pencil beam model but recalculated with a superposition method showed significant qualitative, as well as quantitative, differences, especially with respect to conformity and the dose to organs at risk. Standard conformal treatment techniques for SBRT could not be improved with inversely planned IMRT approaches. Dose calculation algorithms applied in optimization modules for IMRT applications in the thoracic region need to be based on the most accurate dose calculation algorithms, especially when using higher energy photon beams.