Dosimetry for linac with multileaf collimator

Our work shows measurments of depth dose function and beam profiles dependance on field's contour and size shaped by the multileaf collimator.All measurements were done for linear accelerator Clinac 2300 – Varian. Such obtained values were compared with analogical ones for square fields. Dose distributions across the beam for multileaf collimator and for individual blocks were analized.Work load needed for clinical dosimetry of multileaf collimator was estimated.Proposols for measurment protocol in clinical dosimetry is shown

Dose specification in External Beam Radiotherapy for CyberKnife and VMAT techniques applied to a case of prostate cancer

Recent technological development in radiotherapy allows to introduce new irradiation techniques implemented on the conventional accelerators and on the machines such as CyberKnife (CK). These significantly changes the philosophy of planning and execution of radiotherapy. One of the fundamental concepts in radiotherapy is to define the therapeutic dose. It can be defined in the point, at the selected isodose, as an average value, or combined with the volume. We present the case of prostate cancer patient irradiated using CK machine and classic accelerator (VMAT). The differences in dose distribution and its value are shown. The analysis indicates that the average dose in Planning Treatment Volume (PTV) is a useful parameter during comparison of the dose distributions realized on machines of different type

Radiobiological rationale for stereotactic hypofractionated radiosurgery Part II. Normal tissue tolerance — dose constraints

The response of normal tissues/organs to SHRS is more complex than to conventional radiotherapy. Tolerance doses TD5/5 and TD50/5, proposed by Rubin and Casarett, cannot be simply used for SHRS. Instead of LQED2, the BED is advised. The term risk dose (RD) corresponds better than TD to the risk of late morphological and functional disorders (OAR). BED doses show a rapid gradient with increasing distance of the OAR from the tumour GTV. Other risk factors include the dose-volume relationship, OAR organization (serial or parallel) and the ratio of the FSU to the target call. Vasculoendothelial cell damage initiates series of processes resulting in clinical and functional late effect. Using available data and studies, RDmin and RDmax for doses are listed as physical and BED doses for various OAR and dose-volume constraints. The RD values and constraints are rough estimates, since the available SHRS data are sparse and fragmentary, which should be interpreted cautiously and need further clinical validation

Radiobiological rationale for stereotactic hypofractionated radiosurgery Part II. Normal tissue tolerance — dose constraints

The response of normal tissues/organs to SHRS is more complex than to conventional radiotherapy. Tolerance doses TD5/5 and TD50/5, proposed by Rubin and Casarett, cannot be simply used for SHRS. Instead of LQED2, the BED is advised. The term risk dose (RD) corresponds better than TD to the risk of late morphological and functional disorders (OAR). BED doses show a rapid gradient with increasing distance of the OAR from the tumour GTV. Other risk factors include the dose-volume relationship, OAR organization (serial or parallel) and the ratio of the FSU to the target call. Vasculoendothelial cell damage initiates series of processes resulting in clinical and functional late effect. Using available data and studies, RDmin and RDmax for doses are listed as physical and BED doses for various OAR and dose-volume constraints. The RD values and constraints are rough estimates, since the available SHRS data are sparse and fragmentary, which should be interpreted cautiously and need further clinical validation

Radiobiological rationale for Stereotactic Hypofractionated Radiosurgery (SHRS) Part I. LQED2 or BED formalism

In conventional radiotherapy, 5R’s mechanisms influence tumour cell kill, but in SHRS they do not sufficiently explain the biology of large doses. Indirect cell death is also induced by endothelial damage, stem cell death and antitumour immunity are also activated by a single dose ≥ 12–15 Gy. These three processes defined as extra 3R’s are characterizers in details. Despite some controversies, LQED formalism seems not quite adequate for SHRS. Experimental and a few clinical studies suggest BED formalism as much more useful. Both formalisms are compared and discussed. Clinical reports show a monotonical increase in Tumour Cure Probability (TCP) with higher BED doses. The advantage of SHRS results in significant shortening overall treatment time and in delivery of the BED doses higher than 100 Gy, producing an increase in the TCP, likely unachievable by conventional dose fractionation

Radiobiological rationale for stereotactic hypofractionated radiosurgery Part I. LQED2 or BED formalism

In conventional radiotherapy, 5R’s mechanisms influence tumour cell kill, but in SHRS they do not sufficiently explain the biology of large doses. Indirect cell death is also induced by endothelial damage, stem cell death and antitumour immunity are also activated by a single dose ≥ 12–15 Gy. These three processes defined as extra 3R’s are characterizers in details. Despite some controversies, LQED formalism seems not quite adequate for SHRS. Experimental and a few clinical studies suggest BED formalism as much more useful. Both formalisms are compared and discussed. Clinical reports show a monotonical increase in Tumour Cure Probability (TCP) with higher BED doses. The advantage of SHRS results in significant shortening overall treatment time and in delivery of the BED doses higher than 100 Gy, producing an increase in the TCP, likely unachievable by conventional dose fractionation

Real time brachytherapy for prostate cancer – A new challenge for medical physicists

BackgroundThe paper present the “real time” brachytherapy for planning prostate cancer. The differences between treatment planning for “traditional” and “real time” brachytherapy, from the point of view of the medical physicist, are taken into account and each step of treatment planning is presented.AimThe aim of the paper was to present the difference between in “conventional” and “real time” planning treatment from the point of view of medical physicist.Materials/MethodsTwo significant aspects of treatment planning in “real time” brachytherapy are underlined. The first is connected with the place of work of the medical physicist (operating room), and the second one regarding the time (patient is under spinal anesthesia).Results/ConclusionsTreatment planning and patient treatment, based on Ultrasound examinations, allows us to minimize topographical errors during the application of brachytherapy

Quality Assurance of TPS: comparison of dose calculation for stereotactic patients in Eclipse and iPlan RT Dose

BackgroundQuality assurance (QA) in the radiation therapy planning process is essential to ensure accurate dose delivery to the patient and to minimize the possibility of accidental exposure. In recent years, several reports have been developed addressing issues related to the commissioning and quality assurance (QA) of RTPSs.AimTo evaluate the differences between dose distributions obtained with different dose calculation algorithms implemented in TPSs for stereotactic irradiation.Materials and MethodsBrainLab's iPlan v. 3.0.2 RT Dose calculates by pencil beam algorithm, while Eclipse v.7.5.18 (Varian Medical Systems) calculates by different types of pencil beam/AAA algorithms (selectable).ResultsThe largest difference was found in the lung patient, where a difference of 10.3% in the number of monitor units and 8.3% in dose to the isocentre occurred (with calculation by AAA algorithm of Eclipse in relation to iPlan PB algorithm). The average difference in all other cases (AAA compared to iPlan) was 2.2% for MUs and 1.5% for dose to the isocentre. The average difference in all other cases (PB compared to iPlan) was 1.9% for MUs and 3.2% for dose to the isocentre. When data were transferred from iPlan through DICOM RT to Eclipse, for all patients an isocentre shift was observed.ConclusionThe dose distribution calculated by three different photon calculation algorithms results in clinically significant dose differences in isodose distribution, especially in the area of high inhomogeneities

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

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 beamon 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&Nregion 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 inVMAT plans it was from 325 MU to 492 MU. Generally, the number of MU on IMRT technique is greater than MU’s inVMAT (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 (expressedin 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.Cel. Ocena różnic w planach IMRT i VMAT pomiędzy wiązkami X-6MV i X-20MV w odniesieniu do uzyskanych rozkładów 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 monitorowych MU.Wyniki. Średnie współczynniki RPI dla obydwóch technik (IMRT/VMAT) i energii wiązek/łuków (X-6MV/X-20MV) były porównywalne i zawierały się w przedziale 0,2310–0,2934 dla rejonu głowy i szyi oraz 0,3683–0,4007 dla rejonu miednicy. Różnice nie były statystycznie istotne (p > 0,05), wykazując brak wpływu wyboru energii wiązek/łuków na uzyskane rozkłady dawek dla obydwu obszarów napromieniania: głowy/szyi oraz miednicy. Średnia liczba jednostek monitorowych zawierała się w przedziale 765 MU do 1116 MU dla planów w technice IMRT oraz 325 MU do 492 MU dla planów w technice VMAT. Liczba jednostek monitorowych w planach wykorzystujących technikę IMRT była zawsze większa od liczby jednostek w planach z techniką VMAT (potwierdzona istotnością statystyczną), niezależnie od stosowanej energii wiązek/łuków oraz napromienianego regionu głowa/szyja/miednica. Wykorzystanie wiązek/łuków o wyższej energii podczas planowania z wykorzystaniem każdej techniki (IMRT i VMAT) skutkowało zmniejszeniem czasu napromieniania (rozpatrywanego w oparciu o jednostki monitorowe), jednak tylko w przypadku techniki VMAT i obszaru miednicy jest to poparte istotnością statystyczną (p = 0,0467).Wnioski. Zasadniczo wybór energii wiązek z przedziału 6–20 MV nie wprowadza znaczących różnic w uzyskiwanych rozkładach dawek, jednakże wykorzystanie wyższej energii w obszarach napromieniania innych niż głowa/szyja zmniejsza liczbę jednostek monitorowych i znacząco skraca czas napromieniania. Ponadto dalsze skrócenie czasu napromieniania jest możliwe z zastosowaniem techniki VMAT zamiast IMRT