Dynamic-arc respiratory-gated stereotactic radiotherapy — technique presentation

Main advancements in radiation treatment in recent years have included the introduction of dynamic techniques and 4D radiotherapy. The treatment of movable tumors relies on two important techniques: gating and tracking. The limitation of the former is the relatively short duration of the respiratory phase during which the radiation can be delivered and the need to teach the patient to breathe in accordance with the correct pattern. At the same time, certain clinical situations require the use of dynamic techniques. Intensity modulated radiotherapy (IMRT), combined with gantry rotation, forms the basis for the VMAT technique. The procedure usually takes a shorter time to complete than other dynamic techniques, which considerably improves patient comfort. The recently introduced True BeamTM accelerator employs all the latest innovations in terms of dose-rate modeling and respiratory gating

Influence of optional measurement parameters in the Eclipse treatment planning system on the quality of the dosimetric model of the biomedical accelerator using the Acuros XB algorithm

Background: To properly configure a treatment planning system, a measurement data set is needed, which consists of the values required for its configuration. The aim is to obtain a dosimetric model of the beam that is as compatible as possible with the measured values. The set of required data can be supplemented with optional values. The aim of the study was to assess the influence of optional measurement data on the compliance of the calculations with the measurements. Materials and methods: Dosimetric measurements, model configuration and dose distribution calculations were performed for the photon radiation beams generated by the VMS TrueBeam® linear accelerator. Beams were configured on an Eclipse™ v. 15.6 system using the Acuros v. 15.6 algorithm. The measured and calculated data were entered into the Alfard™ software for comparison with the calculated dose distributions. In the last stage, the absolute dose values at the designated points were also compared. The obtained data were statistically analysed with Statistica™ v. 13.3. Results: The work showed that the differences in the shape of the beam profile, depth dose and the dose value in points were not related to the use of optional data. Differences in dose distributions are within the tolerance. It cannot be determined under which conditions the use of optional data has a more favourable effect on the reflection of the actual dose values. Conclusions: The use of optional data in modelling photon radiation beams does not significantly improve the compliance of the calculated and measured dose values

Using beam profile inflection point in process of treatment planning system verification

BACKGROUND: The comparison between profiles during the commissioning of the treatment planning system is an essential procedure. It is impossible to designate a field size for off-axis, wedged, and FFF beams directly by using the definition of the on-axis symmetric field size. This work proposes the use of different characteristic points as indicators of the field size for commissioning and QA purposes. This work aimed to search for the beam profile's characteristic points and use them for the TPS commissioning purposes. MATERIAL AND METHODS: The proposal is to use profile inflection points as the beam profile characteristic points. The usage of dedicated software allowed for comparing distances between inflection points and between points of 50% intensity. For the off-axis, wedged, and FFF fields, comparisons were made to the nominal field sizes. RESULTS: Distances between inflection points proved to be different by less than 1 mm from nominal field sizes for all kinds of investigated beams. CONCLUSIONS: Inflection points are convenient for comparing the off-axis, wedged, and FFF field sizes because of their independence from profile normalization. With finite accuracy, the inflection points could be used for the above kind of beam sizes designation

Optimal values of the Electron Monte Carlo dose engine parameters

Background: The aim of this study was to indicate the most favorable — in terms of to the time of calculation and the uncertainty of determining the dose distribution — values of the parameters for the Electron Monte Carlo (eMC) algorithm in the Eclipse treatment planning system. Materials and methods: Using the eMC algorithm and the variability of the values of its individual parameters, calculations of the electron dose distribution in the full-scattering virtual water phantom were performed, obtaining percentage depth doses, beam profiles, absolute dose values in points and calculation times. The reference data included water tank measurements such as relative dose distributions and absolute point doses. Results: For 63 sets of calculation data created from selected values of the parameters for the eMC algorithm, calculation times were analyzed and the absolute calculated and measured doses were compared. Performing a statistical analysis made it possible to determine whether the differences in the values of deviations between the actual dose and the calculated dose in individual regions of the percentage depth dose curve and the beam profile are statistically significant between the analyzed sets of parameters. Conclusions: Taking into account obtained results from the analysis of the discrepancy between the distribution of the calculated and measured dose, the correspondence of the absolute value of the calculated and measured dose and the duration of the calculation of the dose distribution, the optimal set of parameters was indicated for the eMC algorithm which allows obtaining the dose distribution and the number of monitor units in an acceptable time

Radioterapia stereotaktyczna łukami dynamicznymi z zastosowaniem bramkowania oddechowego — prezentacja techniki

   Główne postępy radioterapii w ostatnich latach związane są z wprowadzeniem technik dynamicznych oraz radiote­rapii 4D. Radioterapia ruchomych guzów realizowana jest poprzez dwie techniki: bramkowanie (gating) i śledzenie ruchów (tracking). Ograniczeniem techniki bramkowania jest stosunkowo mały czas fazy oddechowej, w którym można podać dawkę promieniowania, oraz konieczność nauczenia pacjenta właściwego toru oddechowego. Jednocześnie istnieją sytuacje kliniczne, w których niezbędne staje się użycie technik dynamicznych. Modulacja intensywności mocy dawki (IMRT) w połączeniu z obrotem głowicy stały się podstawą techniki VMAT. Realizacja takiego leczenia zwykle trwa krócej niż w przypadku pozostałych technik dynamicznych, co poza innymi aspektami również wpływa na komfort leczenia pacjenta. Wprowadzony niedawno do użytkowania przyspieszacz True BeamTM wykorzystuje wszystkie innowacje dotyczące modelowania intensywności mocy dawki oraz bramkowania oddechowego

EPID-a useful interfraction QC tool

Biomedical accelerators used in radiotherapy are equipped with detector arrays which are commonly used to obtain the image of patient position during the treatment session. These devices use both kilovolt and megavolt x-ray beams. The advantage of EPID (Electronic Portal Imaging Device) megavolt panels is the correlation of the measured signal with the calibrated dose. The EPID gives a possibility to verify delivered dose. The aim of the study is to answer the question whether EPID can be useful as a tool for interfraction QC (quality control) of dose and geometry repeatability. The EPID system has been calibrated according to the manufacturer's recommendations to obtain a signal and dose values correlation. Initially, the uncertainty of the EPID matrix measurement was estimated. According to that, the detecting sensitivity of two parameters was checked: discrepancies between the planned and measured dose and field geometry variance. Moreover, the linearity of measured signal-dose function was evaluated. In the second part of the work, an analysis of several dose distributions was performed. In this study, the analysis of clinical cases was limited to stereotactic dynamic radiotherapy. Fluence maps were obtained as a result of the dose distribution measurements with the EPID during treatment sessions. The compatibility of fluence maps was analyzed using the gamma index. The fluence map acquired during the first fraction was the reference one. The obtained results show that EPID system can be used for interfraction control of dose and geometry repeatability

EPID in vivo dosimetry in RapidArc technique

AbstractAimThe aim of the study was to estimate the dose at the reference point applying an aSi-EPID device in the course of patient treatment.Materials and methodsThe method assumes direct proportionality between EPID signal and dose delivered to the patient reference point during the treatment session. The procedure consists of treatment plan calculation for the actual patient in the arc technique. The plan was realized with an elliptic water-equivalent phantom. An ionization chamber inside the phantom measured the dose delivered to the reference point. Simultaneously, the EPID matrix measured the CU distribution. EPID signal was also registered during patient irradiation with the same treatment plan. The formula for in vivo dose calculation was based on the CU(g) function, EPID signal registered during therapy and the relation between the dose and EPID signal level measured for the phantom. In vivo dose was compared with dose planned with the treatment planning system.Irradiation was performed with a Clinac accelerator by Varian Medical Systems in the RapidArc technique. The Clinac was equipped with an EPID matrix (electronic portal image device) of aSi-1000. Treatment plans were calculated with the Eclipse/Helios system. The phantom was a Scanditronix/Wellhöfer Slab phantom, and the ionization chamber was a 0.6ccm PTW chamber.ResultsIn vivo dose calculations were performed for five patients. Planned dose at the reference point was 2Gy for each treatment plan. Mean in vivo dose was in the range of 1.96–2.09.ConclusionsOur method was shown to be appropriate for in vivo dose evaluation in the RapidArc technique