scholarly journals Analysis of Dose Load on a Pregnant patient in Radiotherapy of Oropharal Cancer

2021 ◽  
Vol 4 (1) ◽  
pp. 65-73
Author(s):  
E. O. Sannikova ◽  
I. M. Lebedenko ◽  
S. S. Khromov ◽  
G. E. Gorlachev
Keyword(s):  
Radiation Therapy ◽  
Photon Energy ◽  
Absorbed Dose ◽  
Pregnant Patient ◽  
Planning System ◽  
Dose Load ◽  
Tissue Equivalent ◽  
Phantom Measurements ◽  
Irradiation Field ◽  
Tissue Equivalent Phantom

Purpose: The assessment of the dose load on a pregnant patient during irradiation of the oropharyngeal tumor at different distances from the border of the irradiated field, including at the level corresponding to the position of the fetus, based on phantom measurements.Material and methods: To calculate the exposure plan, the ECLIPSE planning system with the AAA algorithm was used. Irradiation was performed on a LinacClinaciX (Varian, USA) with a nominal photon energy of 6 MeV. The tissue equivalent phantom Alderson–Rando was used to assess the dose load on the fetus.Results and conclusions: It was shown that the total absorbed dose at the level and below the diaphragm (the level of the fetus) at a distance of more than 40 cm from the border of the irradiation field for the entire course of radiation therapy turned out to be significantly less than the permissible limits indicated in the literature and amounted from 41.71 to 14.03 mGy. 

scholarly journals A Probability Approach to the Study on Uncertainty Effects on Gamma Index Evaluations in Radiation Therapy

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
Francisco Cutanda Henríquez ◽  
Silvia Vargas Castrillón
Keyword(s):  
Radiation Therapy ◽  
Uncertainty Propagation ◽  
Absorbed Dose ◽  
Planning System ◽  
External Beam Radiation ◽  
Treatment Planning System ◽  
Mathematical Methods ◽  
Beam Radiation ◽  
Treatment Unit ◽  
Gamma Index

Two datasets of points of known spatial positions and an associated absorbed dose value are often compared for quality assurance purposes in External Beam Radiation Therapy (EBRT). Some problems usually arise regarding the pass fail criterion to accept both datasets as close enough for practical purposes. Instances of this kind of comparisons are fluence or dose checks for intensity modulated radiation therapy, modelling of a treatment unit in a treatment planning system, and so forth. The gamma index is a figure of merit that can be obtained from both datasets; it is widely used, as well as other indices, as part of a comparison procedure. However, it is recognized that false negatives may take place (there are acceptable cases where a certain number of points do not pass the test) due in part to computation and experimental uncertainty. This work utilizes mathematical methods to analyse comparisons, so that uncertainty can be taken into account. Therefore, false rejections due to uncertainty do not take place and there is no need to expand tolerances to take uncertainty into account. The methods provided are based on the rules of uncertainty propagation and help obtain rigorous pass/fail criteria, based on experimental information.

scholarly journals Implementation of compensator-based intensity modulated radiotherapy with a conventional telecobalt machine using missing tissue approach

2018 ◽  
Vol 24 (4) ◽  
pp. 171-179
Author(s):  
Samuel N. A. Tagoe ◽  
Samuel Y. Mensah ◽  
John J. Fletcher
Keyword(s):  
Treatment Planning ◽  
Specific Treatment ◽  
Intensity Modulated Radiotherapy ◽  
Planning System ◽  
Treatment Planning System ◽  
Dose Distributions ◽  
Intensity Modulated ◽  
Limit Value ◽  
Tissue Equivalent ◽  
Tissue Equivalent Phantom

Abstract Objectives: The present study aimed to generate intensity-modulated beams with compensators for a conventional telecobalt machine, based on dose distributions generated with a treatment planning system (TPS) performing forward planning, and cannot directly simulate a compensator. Materials and Methods: The following materials were selected for compensator construction: Brass, Copper and Perspex (PMMA). Boluses with varying thicknesses across the surface of a tissue-equivalent phantom were used to achieve beam intensity modulations during treatment planning with the TPS. Beam data measured for specific treatment parameters in a full scatter water phantom with a 0.125 cc cylindrical ionization chamber, with a particular compensator material in the path of beams from the telecobalt machine, and that without the compensator but the heights of water above the detector adjusted to get the same detector readings as before, were used to develop and propose a semi-empirical equation for converting a bolus thickness to compensator material thickness, such that any point within the phantom would receive the planned dose. Once the dimensions of a compensator had been determined, the compensator was constructed using the cubic pile method. The treatment plans generated with the TPS were replicated on the telecobalt machine with a bolus within each beam represented with its corresponding compensator mounted on the accessory holder of the telecobalt machine. Results: Dose distributions measured in the tissue-equivalent phantom with calibrated Gafchromic EBT2 films for compensators constructed based on the proposed approach, were comparable to those of the TPS with deviation less than or equal to ± 3% (mean of 2.29 ± 0.61%) of the measured doses, with resultant confidence limit value of 3.21. Conclusion: The use of the proposed approach for clinical application is recommended, and could facilitate the generation of intensity-modulated beams with limited resources using the missing tissue approach rendering encouraging results.

scholarly journals Measurement with electret ion chambers of absorbed dose outside the treated volume, during external-photon radiation therapy

2021 ◽  
pp. 15-15
Author(s):  
Alexandros Clouvas ◽  
Anna Makridou ◽  
Michalis Chatzimarkou
Keyword(s):  
Radiation Therapy ◽  
Treatment Planning ◽  
Absorbed Dose ◽  
Planning System ◽  
Photon Radiation ◽  
Treatment Planning System ◽  
Low Doses ◽  
Prescription Dose ◽  
Ion Chambers ◽  
Leakage Radiation

The capabilities of electret ion chambers to measure non-target absorbed dose for distances greater than 20 cm from the irradiated volume during radiotherapy treatment was investigated for the first time. During radiotherapy, nontarget doses can be classified as one of three approximate dose levels: high doses, intermediate doses and low doses. Low doses (<5 % of the prescription dose) are not generally considered during treatment planning, due to the fact that is difficult to measure, characterize, or model them in the planning system. In this work were performed measurements with electret ion chambers of absorbed dose outside the treated volume (<5 % of the prescription dose), during external photon radiation therapy in an Elekta Infinity Linear Accelerator of ?Theagenio? Cancer Hospital of Thessaloniki, Greece. The absorbed dose values for distances greater than 20 cm from the irradiated volume varied from 0.3 to 17 mGy which corresponds to 0.01% up to 0.6% of the prescription dose (2660 mGy). Near the irradiation volume the absorbed dose values were greater than the upper detection limit of the electret ion chambers (threshold 40 mGy). The results are compared with the calculated ones by the Monaco Treatment Planning System (Elekta Monaco 5.11.03). In the non-target radiation region where Monaco Treatment Planning System calculates rather precisely (within uncertainties of less than 10%) the absorbed dose, measured and calculated doses are the same within experimental uncertainties. On the contrary, when leakage radiation becomes the dominant source of out-of-field dose the differences are up to 31%.

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