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The use of compensators in order to achieve desired dose distribution had a long history and is well-established technique in radiation therapy planning. There are several different methods of calculation for compensator’ s shape discussed in literature. An alternative method is presented. The method is based on Cunningham's modification of Clarkson's method to calculate scattered radiation in beams with inhomogeneous cross-sectional dose distribution. The algorithm is rather general and could be applied to different required dose distributions in various clinical situations, different photon beams, and various compensating materials. The algorithm is feasible, quickly computable and versatile. The method is verified using film dosimetry in several practical situations manufacturing compensators out of steel granules and low melting alloy. Additional measurements were made using electronic portal imaging developed in our hospital. The results are compared with effective attenuation method.

The use of compensators in order to achieve desired dose distribution had a long history and is well-established technique in radiation therapy planning. Although the use of linear accelerators with multileaf collimators diminished need for compensators it is reported [1] that the use of compensators still offers some advantages, especially regarding spatial distribution. The production of compensators, either for simply tissue compensation or as an alternative way to accomplish intensity-modulated radiotherapy (IMRT), remains common practice [2-5]. There are several different methods of calculation for compensator’ s shape. An alternative method is suggested. The method is based on Cunningham's modification of Clarkson's method [6] to calculate scattered radiation in beams with inhomogeneous cross-sectional dose distribution. It is well known that the total dose distribution of radiotherapy beams is consisted of the contributions of the primary beam attenuated by the tissue layer and the scattered radiation which is generated by the primary radiation in single and multiple photon scatter events. Since the scattered component could be represented as a function of primary, the central point of the method is numerical estimation of the primary distribution required achieving desired total distribution. Now using calculated primary distribution the shape of the modulator could be determined. In this way the contribution of the scattered component is validate in more accurate way than using effective attenuation coefficients which was common practice. The method is verified in various clinical situations and compared with standard method. The accuracy was better at least 2%, depending on geometry. Namely, more complex geometry results in higher gain in accuracy of our method comparing to the standard method. References [1] S.X.Chang, T.J.Cullip, K.M.Deschesne, E.P.Miller and J.G.Rosenman, Compensators: An alternative IMRT delivery technique J.Appl.Clin.Med.Phys. 2004, 5, 15-36. [2] J. Meyer, J.A. Mills, O.C.L.Haas, K.J. Parvin and K.J.Burnham, Some limitations in the practical delivery of intensity modulated radiation therapy, Br.J.Radiol. 2000, 73, 854-863. [3] S.X.Chang, T.J.Cullip, K.M.Deschesne, Intensity modulation delivery techniques: ‘ Step&shot’ MLC autosequence versus the use of a modulator Med.Phys. 2000, 27, 948-959. [4] V.N.Hansen, P.M.Evans, G.S.Shentall, S.J.Helyer, J.R.Yarnold and W. Swindel W, Dosimetric evaluation of compensation in radiotherapy of the breast: MLC intensity modulation and physical compensators Radiother.Oncol. 1997, 42, 249-256. [5] D.M.Dimitriadis and B.G.Fallone, Compensators for intensity-modulated beams, Med.Dosim. 2002, 27, 215-220. [6] J.R. Cunningham, Scatter-Air Ratios, Phys.Med.Biol. 1971, 17, 42-51.

137CS brachytherapy sources are practical for the intracavitary application due to their relatively long lifetime (T In = 30 y). On the other hand, due to the relatively low energy (0.66 MeV) of the emitted photons, they are suitable for an efficient radiation protection. The dose distribution around the sources is usually calculated by a specific program. However this program requires the knowledge of the position of sources within the applicator as well as the distribution of activity along them. The only way to leam these data is to make an X-ray picture of applicators and sources superimposed to the autoradiography of every source. It is difficult to achieve satisfactory radiographs with high dose rate sources with standard X-ray film material because autoradiography covers the structure of the radigraphic shadow .The problem can be overcome either by applying a high intensity X-ray or gamma beam (originating from a raditherapeutic machine), or by using photographic material of very low sensitivity, for example photographic paper .Combining both possibilities one can obtain satisfactory images.

20 godina ginekološke brahiterapije u Klinici za tumore u Zagrebu

The both recently published protocols for clinical dosimetry IAEA (TRS 398) [1] and AAPM (TG-51) [2] contain improvements for the purpose of more accurate and safe dosimetry of electron beams. The most important novelty is the definition of the reference depthdref as dref = 0.6 R5o -0.1 (1) where R50 is the depth of fifty percent absorbed dose. This value is also used as quality index for electron beams. The authors compare two planparallel ionisation chambers under the new protocols. The Marcus chamber, an old type, and the Roos, a new well-guarded type chamber, are furnished with calibration factors in terms of absorbed dose in water in 60CO beam. The chambers and their cross-sections are shown in Figures 1 and 2. The measurements were performed in a W ellhofer water phantom using a PTW Unidos electrometer. The absorbed dose in water in both protocols can be calculated by equationM is corrected dosimeter reading and kQ -conversion factor.

The Estimation of the Entrance and Exit Dose in Diagnostic Radiology Using X-ray Spectra.

The Use of Transparency Graphics Scanner as a Field Densitometer for Irradiated Films

Paper describes the dosimetry characteristics of the total skin electron therapy (TSET) as omplemented at the University hospital Osijek radiotherapy department. Patients are treated in the standing position, using six dual angled fields at a "source to skin" distance of 3.5m. Acceptable beam uniformity and depth dose distribution were achieved while maintaining a low level of x-ray contamination. Tge measurements showed that special care must be taken with ionisation chamber measurements under TSET conditions to avoid incorrect readings due to a "polarity effect". This technique enable implementation of the TSET in a treatment room of standard dimensions.

U liječenju limfoma, kao osnovni terapijski modaliteti, upotrebljavaju se radioterapija i/ili kemoterapija. Liječenje ovisi o vrsti limfoma, stupnju proširenosti bolesti i općem stanju bolesnika. Radioterapija se primjenjuje s kurativnom ili palijativnom namjerom i to kao jedini način liječenja ili u kombinaciji s drugim metodama liječenja. U bolesnika oboljelih od Hodgkinova limfoma (HL) zračenje se provodi kao jedina terapija u stadijima bolesti I i IIA bez nepovoljnih činitelja rizika. Takodjer, u fazi kliničkog testiranja je liječenje ranih stadija HL (I i IIA) i samo s kemoterapijom ili združeno s radioterapijom. Kada se zračenje primjenjuje kao primarna radikalna metoda liječenja (stadiji I i IIA), ciljni volumen zračenja, osim regije/a s klinički zahvaćenim limfnim čvorovima, obuhvaća i klinički nezahvaćene limfne čvorove susjednih regije, a sa ciljem njihovog profilaktičkog ozračenja. Primjeri takvih proširenih polja zračenja su npr. “plašt polje” i polje “obrnuti ipsilon”. Kod primjena radioterapije u kombinaciji s kemoterapijom, ciljni volumen ovisi kako o stadiju bolesti tako i o broju kemoterapijskih ciklusa, odnosno o tome da li je uloga radioterapije samo kontrola klinički zahvaćenih regija ili i regija s mogućom subkliničkom bolešću. U liječenju bolesnika oboljelih od ne-Hodgkinovih limfoma (NHL) najčešća je kemoterapija. Radioterapija se s kurativnom namjerom kao jedini modalitet liječenja primjenjuje u bolesnika koji po histopatološkom razvrstavanju imaju NHL indolentnog tipa i stadija bolesti su I ili II u kontinuitetu. Ciljni volumen zračenja obuhvaća klinički zahvaćenu regiju tijela; u ciljni volumen mogu se još pridati i susjedne klinički nezahvaćene regije. U viših stadija bolesti ili kod drugih, agresivnijih NHL primjenjuje se kemoterapija sama ili nadopunjena sa zračenjem.

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Two approaches for aproximation of collimator scatter correction factors of rectangular fields can be found in recent publications. One is based on empirical equations or some more sophisticated physical methods using certain parameters which have to be adjusted for a specific machine. The other is based on idea of decomposition of collimator scatter correction factor of two variables - into the product of two functions of one variable. In this work four models, based on decomposition are compared. The measurements were carried out using nominal 6MV and 15 MV photon beams of a Siemens Mevatron MD2 and Varian Clinac 1800 accelerators. It was shown that better approximation can be achieved with a suitable choice of basic measurements and normalisation data.

Ispitivanje i odabir atenuacijskih filtara u filmskim dozimetrima za osobnu zaštitu

Usporedba mjerene i izračunate doze pod zaštitnim blokovima u radioterapiji fotonskim snopovima

Kalibracija elektronskih snopova Markusovom komorom u fantomu od bijelog polistirena

Radiation Treatment Plan Represented by Iso-ERD Curves

We reply to the Comment of von Neumann-Cosel et al., [Phys. Rev. C 44, 554 (1991)]. Some of our results were quoted incorrectly in the Comment ; the correct values are listed in Table I. We extend the analysis of the Comment by also discussing our most recent result for 115In. An experimental investigation of Monte Carlo predictions made in the Comment shows that the intensity of additional environmental Compton scattering is seriously overestimated.

A 60Co source has been used to photoactivate the 396 keV isomeric level (T1/2∼48.6 min) of 111Cd. Our results confirm the existence of nonresonant contributions.

Radioterapijsko planiranje računalom

Primjena stereo-radiografije u radioterapiji

Use of computers in radiation treatment planning, Pixel by pixel planning based on simulator-supplied CT scan

A 60Co source has been used to photoactivate the 392 keV (T1/2~99.5 min) isomeric level of 113In and the 388 keV (T1/2~2.8 h) isomeric level of 87Sr. As observed in investigations of 115In and 111Cd, nonresonant processes were found to make significant contributions to the excitation of isomeric levels.

Digitalizacija radioterapijskog snopa

Use of computers in radiation treatment planning, Tissue inhomogeities and application of Bathos correction.

Dozimetrijska greška uzrokovana rekombinacijom u ionizacijskoj komori

Digitalizacija radioterapijskog snopa i njegova rekonstrukcija

Primjena Theradosova linearnog skenera LSC-1 u sprezi s računalom

Raspršeno zračenje Mantel-field terapija

A 60Co source has been used to study the photoactivation of the 336 keV (T1/2=4.3 h) isomeric level of 115In in the indium-lead alloys. We have investigated the contribution to the nonresonant excitation from photon-atom interactions, involving Compton scattering, photoelectric effect and pair production. Our results show very clearly that the nonresonant excitations of the isomeric level are due to direct interactions between the photons and 115In atoms.

During a short-lasting high radioactivity gynaecological treatment the position of the sources does not change significantly. A fast and accurate technique was developed allowing for the determination of source positions. It is based on the use of a radiotherapy simulator. The simulator was declined by 200 to the right, and the X-ray projection of the sources was copied with blue colour on a PVC foil firmly attached to the intensifier display. This was repeated with the simulator declined by 200 to the left and with red. From the paralax shift the threedimensional position of sources was evaluated, and dose distribution was then calculated using a computer program.

Upotreba radioterapijskog simulatora kao CT skenera.