Wpływ energii wiązek fotonowych na rozkład dawek dla planów IMRT i VMAT

Abstract

Purpose. Estimation of the difference between photon X-6MV and X-20MV beams for IMRT and VMAT plan's, in respect to dose-volume results and irradiation time (MU). Materials and methods. For each of 74 selected patients four plans, two IMRT with X-6MV & X-20MV beams and two VMAT: X-6MV & X-20MV arcs, were performed. Patients were divided into two groups according to tumor localization: head & neck (H&N) and pelvis. Those localizations were chosen to highlight potential differences regarding the depth of target volume. Each plan was optimized using the same plan objectives and constraints. Plans were compared according to dose-volume results for target and Organs at Risk (OaR's) with Radiation Planning Index (RPI), and beam on time regarding the monitor units (MUs). Results. The mean RPI factor for both technique (IMRT/VMAT) and energies (X-6MV/X-20MV) were similar for H&N region in the range of 0.2310-0.2934 and for the pelvis region the range was 0.3683-0.4007. The difference were not statistically significant (p > 0.05), showing the photon between 6-20 MV, doesn't influence the dose-volume results, for both localization: H&N and pelvis. The mean monitor units in IMRT plans varied from 765 MU to 1116 MU, as in VMAT plans it was from 325 MU to 492 MU. Generally, the number of MU on IMRT technique is greater than MU's in VMAT (difference statistically significant), regardless of the beam energy (X-6MV, X-20MV) and localization (H&N, pelvis). Both techniques; IMRT and VMAT plans with higher photon energy, showed shorter irradiation time (expressed in MU). But, only for pelvic region on VMAT technique, is statistically significant (p = 0.0467). Conclusions. On average, photons beam, between 6-20 MV don't induce significant dose-volume difference. However, higher energy used for planning regions other than head & neck, minimizes the number of MUs and significantly reduces the time of irradiation. Furthermore, reduction of beam on time can be achieved by using VMAT plan rather than IMRT plan. Wpływ energii wiązek fotonowych na rozkład dawek dla planów IMRT i VMATCel. Ocena różnic w planach IMRT i VMAT pomiędzy wiązkami X-6MV i X-20MV w odniesieniu do uzyskanych rozkła-dów dawek oraz czasu napromieniania (MU). Materiały i metody. Na potrzeby porównania wybrano 74 pacjentów, następnie dla każdego obliczono 4 plany: dwa w technice IMRT z wiązkami X-6MV i X-20MV oraz dwa w technice VMAT z łukami X-6MV i X-20MV, uzyskując rozkłady dawek. Pacjentów podzielono na dwie grupy zgodnie z obszarem napromienienia: rejon głowy/szyi oraz rejon miednicy. Lokalizacje zostały wybrane w celu uwidocznienia ewentualnych różnic wynikających z różnych głębokości na których zdefiniowano obszar tarczowy. Każdy plan był optymalizowany z wykorzystaniem z tych samych wytycznych i ograniczeń związanych z obszarami anatomicznymi. Plany zostały następnie porównane pod względem dawek dla obszarów tarczowych i organów krytycznych z użyciem współczynnika RPI (Radiation Planning Index). Następnie porównano czas napromieniania w ujęciu liczby jednostek ...

Effects of flattening filter (FF) and flattening filter-free (FFF) beams on small-field and large-field dose distribution using the VMAT treatment plan

“…Large irradiation fields are used for bigger volumes and greater depths. Thus, it seems we can use higher radiation energies 20,21 for e.g. gynecology.…”

Comparison of EPID portal dosimetry verification and RadCalc dose verification for VMAT treatment plans

“…Such a plan allows for irradiation of the EPID matrix without the patient before the first therapeutic session. Modern EPID devices are matrices of semiconductor detectors that record the radiation generated by the accelerator, measured in a plane perpendicular to the beam axis of this radiation (measurement of the so-called fluence maps) [1][2][3][4][5][6][7]. The signal is collected and saved from all detectors from the active measurement area.…”

“…The assessment is based on the gamma index, which verifies compliance with the measurement in the specified range of dose and location. [1][2][3][4][5][6][7][8][9] The gamma index calculates the difference between the dose calculated and measured at the same point (dose difference [DD]) and the distance (distance to agreement [DTA]) between points with the same dose. By determining the acceptable difference (DD) in the dose and the distance (DTA), we define the sphere within which the points located meet the compliance criterion: TPS calculations -measurement; then the value of the coefficient is less than 1 [1][2][3][4][5][6][7].…”

“…[1][2][3][4][5][6][7][8][9] The gamma index calculates the difference between the dose calculated and measured at the same point (dose difference [DD]) and the distance (distance to agreement [DTA]) between points with the same dose. By determining the acceptable difference (DD) in the dose and the distance (DTA), we define the sphere within which the points located meet the compliance criterion: TPS calculations -measurement; then the value of the coefficient is less than 1 [1][2][3][4][5][6][7]. The advantage of this method is that it does not require any phantom, and the assessment of treatment plans is quick.…”