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Intensity modulated radiotherapy using Monte Carlo for routine postmastectomy radiotherapy

100%
Sayed Omer H. B. E.
Polish Journal of Medical Physics And Engineering
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2012
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vol. 18
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issue 2
49-58
EN
Radiotherapy given after mastectomy (PMRT) will reduce the risk of local recurrence by about two-thirds. Clinical and dosimetric trials were carried out using various techniques to optimize the treatments by maximizing the dose to the tumour and minimizing it to the healthy tissues at proximity. Different conventional techniques which have been studied suffer from important dose inhomogeneities due to the complex anatomy of the chest, which reduces the benefits from such treatments. Moreover, due to the heterogeneity of breast cancer, the response to therapy and a systematic approach to treatment cannot be derived and treatment regimens must be determined on a patient-by-patient basis. This is only possible if accurate and fast treatment planning systems are available. Intensity Modulated Radiotherapy (IMRT) allows delivering higher doses to the target volume and limits the doses to the surrounding tissues. The objective of this study is to test the feasibility of applying a Monte Carlo-based treatment planning system, Hyperion accurately in routine Intensity Modulated Radiotherapy (IMRT) postmastectomy. In order to use a treatment planning system for routine work it should prove to provide optimized dose delivery in a suitable time. Treatment planning for IMRT application to PMRT was performed using Hyperion. Constraints were set to deliver the prescribed dose to the target and minimize the dose to the organs at risk. Dose Volume Histograms (DVH) were used to evaluate the set up plans. Time taken to optimize the plan was measured. The target coverage was within the accepted values. Approximately 90% of the breast and 80% of the PTV received 45 Gy or above. The volume of the lung that received 40Gy was less than 10% and the volume that received 20Gy (V20) was less than 25%. The volume of the heart receiving 30 Gy (V30) or above was negligible. This indicates low NTCP of these organs. The time taken for optimization, showed it possible to apply Monte Carlo-based treatment-planning systems for patient-to-patient PMRT.
2
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Entropy as a quality descriptor for the dose distribution - theory and practice for the patient target volume

100%
Moravek Z., Bogner L.
Polish Journal of Medical Physics And Engineering
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2008
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vol. 14
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issue 3
135-149
EN
The most common and established way to evaluate the quality of a radiotherapy plan is to use the dose-volume histogram (DVH). The evaluation of the DVH, however, is a subjective procedure. This may not be crucial as long as the two plans are significantly different. In the case of several plans obtained with different planning or optimisation strategies the differences are often subtle and therefore a more objective comparison method is desirable. A commonly used approach is based on evaluation of the conformity index, however we show how it can fail for plans of similar quality.Therefore we propose a new method based on the similarity of DVH to statistical distributions, which can be characterised uniquely by their entropy. The concept is defined separately for target volumes, where it is derived from the Fermi-like distribution, and for organs at risk, where the traditional approach is also considered in its derivation. The artificial illustratory and clinical examples show the properties of the entropy as the quality descriptor and compare it to the conformity index. The examples are focused to the patient target volumes, where the advantage of the concept is more evident.
3
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Quality assurance and dosimetric analysis of intensity modulation radiotherapy using compensators for head and neck cancers

88%
Tyagi A., Nangia S., Chufal K., Mishra M., Ghosh D., Supe S., Singh M.
Polish Journal of Medical Physics And Engineering
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2009
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vol. 15
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issue 4
193-208
EN
In this study we describe our experience in implementing compensator based intensity modulated radiotherapy (cIMRT) for head and neck cancer with regard to pre treatment quality assurance (QA), dosimetric parameters and other technical detail.This study represents the analysis of initial 48 patients who underwent cIMRT for head and neck cancers. All patients were treated with pre treatment QA in terms of point dose with ion chamber and spatial dose comparison with film dosimetry.In our study for all 48 patients, compensators revealed a deviation in central axis dose of 2% ± 1.8% in terms of cumulative calculated versus measured dose. Target coverage for high dose volume (70 Gy) was adequate in terms of volume receiving 93% and 95% of the prescription dose, which was 98.5% and 97.5% respectively. Parotid and other critical organs were spared adequately. Contralateral parotid (CLP) was spared. V30 Gy and V35 Gy was 55.9% and 36.8% for CLP and average dose was 31.7 Gy. Median variation in cumulative measured dose versus cumulative calculated dose was 1.8% (SD + 1.8) and mean variation was 2.5% (95%CI 1.5, 2.6). Range was 0 to 7%.cIMRT is practically feasible. Our QA tests revealed high degree of concordance between cumulative measured doses versus cumulative calculated doses. All dosimetric parameters were within acceptable limits. The manufacturing of compensator is cumbersome but it is a one time job followed by easy treatment delivery and simple QA procedure, high monitor unit (MU) efficiency and less treatment time. cIMRT is easy to implement and now can be applied to larger number of patients with different type of tumor.
4
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Assesing multileaf collimator effect on the build-up region using Monte Carlo method

88%
Moreno M., Teixeira N., Jesus A., Mora G.
Polish Journal of Medical Physics And Engineering
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2008
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vol. 14
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issue 3
163-182
EN
Previous Monte Carlo studies have investigated the multileaf collimator (MLC) contribution to the build-up region for fields in which the MLC leaves were fully blocking the openings defined by the collimation jaws. In the present work, we investigate the same effect but for symmetric and asymmetric MLC defined field sizes (2×2, 4×4, 10×10 and 3×7 cm2). A Varian 2100C/D accelerator with 120-leaf MLC is accurately modeled for a 6MV photon beam using the BEAMnrc/EGSnrc code.Our results indicate that particles scattered from accelerator head and MLC are responsible for the increase of about 7% on the surface dose when comparing 2×2 and 10×10 cm2 fields. We found that the MLC contribution to the total build-up dose is about 2% for the 2×2 cm2 field and less than 1% for the largest fields.
5
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IMRT versus 3D-CRT for thyroid cancer

88%
Gizynska M., Zawadzka A.
Polish Journal of Medical Physics And Engineering
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2008
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vol. 14
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issue 3
151-162
EN
A 3D-CRT involving a 4-field (5-field, 6-field, etc.) technique (photon and electron beams) and an alternative IMRT 7-field technique with 6 MV photon fields for thyroid cancer were compared. The IMRT allows reduction in the dose to the spinal cord of about 12 Gy and permits better coverage of the target volume with smaller standard deviation (average 4.65% for 3D-CRT as compared with 1.81% for IMRT). The time needed to prepare therapy (TPS, dosimetry, preparing boluses and electron aperture) and the session time are about the same for both techniques.
6
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IMRT implementation and patient specific dose verification with film and ion chamber array detectors

75%
Saminathan S., Manickam R., Chandraraj V., Supe S., Keshava S.
Polish Journal of Medical Physics And Engineering
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2009
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vol. 15
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issue 2
87-102
EN
Implementation of Intensity Modulation Radiotherapy (IMRT) and patient dose verification was carried out with film and I'mariXX using linear accelerator with 120-leaf Millennium dynamic multileaf collimator (dMLC). The basic mechanical and electrical commissioning and quality assurance tests of linear accelerator were carried out. The leaf position accuracy and leaf position repeatability checks were performed for static MLC positions. Picket fence test and garden fence test were performed to check the stability of the dMLC and the reproducibility of the gap between leaves. The radiation checks were performed to verify the position accuracy of MLCs in the collimator system. The dMLC dosimetric checks like output stability, average leaf transmission and dosimetric leaf separation were also investigated. The variation of output with gravitation at different gantry angles was found to be within 0.9%. The measured average leaf transmission for 6 MV was 1.6% and 1.8% for 18 MV beam. The dosimetric leaf separation was found to be 2.2 mm and 2.3 mm for 6 MV and 18 MV beams. In order to check the consistency of the stability and the precision of the dMLC, it is necessary to carryout regular weekly and monthly checks. The dynalog files analysis for Garden fence, leaf gap width and step wedge test patterns carried out weekly were in good agreement. Pretreatment verification was performed for 50 patients with ion chamber and I'matiXX device. The variations of calculated absolute dose for all treatment fields with the ion chamber measurement were within the acceptable criterion. Treatment Planning System (TPS) calculated dose distribution pattern was comparable with the I'matriXX measured dose distribution pattern. Out of 50 patients for which the comparison was made, 36 patients were agreed with the gamma pixel match of > 95% and 14 patients were with the gamma pixel match of 90-95% with the criteria of 3% delta dose (DD) and 3 mm distance-to-agreement (DTA). Commissioning and quality assurance of dMLC for IMRT application requires considerable time and effort. Many dosimetric characteristics need to be assessed carefully failing which the delivered dose will be significantly different from the planned dose. In addition to the issues discussed above we feel that individual MU check is necessary before the treatment is delivered.
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