DEPARTMENT OF ACCELERATOR PHYSICS AND TECHNOLOGY 177

been built in the Department of Accelerator Physics The advantage of the above SW accelerating and Technology of the SINS. structure is the connection of the high value of the The geometry of the gun has been optimized with shunt impedance characteristic for the SW structures, the aid of the programme E-Gun of Hermansfeldt. with the large value of group velocity responsible for the energy propagation and deciding on the stability of Accelerating structure is the most important the electromagnetic field distribution in the structure. element of the accelerating system, defining the quality of the beam. On the basis of a long term RF power supply system in ATENA project is experience, we propose to use a modified version of based on klystron. At the level of beam power we deal the accelerating structure working successfully in our with in such a linac, it is necessary to use the klystron medical accelerators 4 and 10 MeV, in industrial with average RF power of the order of several tens accelerators 4, 6 and 10 MeV, in the PILOT kilowatts. Such a system in conjunction with AFC accelerator, and also in the special structure working loop offers very good stability of accelerator as an injector to the superconducting accelerator LISA operation, broad band of output power regulation and in Frascati. It is the Standing Wave (SW) biperiodic long life duration of the klystron. structure of the TT/2 type. The structure is composed of the interchanging strings of two types resonators: l) Institute of Nuclear Chemistry and Technology bigger accelerating and smaller coupling cells. The structure is of the nl2 type since the phase difference between neighbour cavities is n/2. PL0001594 10.4 Dosimetric Characteristics of Circular 6-MV X-Ray Beams for Stereotactic Radiotherapy with a Linear Accelerator by A.Wysocka, J.Rostkowska0, M.Kania0, W.Bulski0, J.Fijuth0

Stereotactic radiosurgery (SRS) is a method of common point (the isocentre) and remain stable treatment of small intracranial lesions, using external during all rotation. Verification of alignment for beams of radiation. In this technique a high dose of Clinac 2300CD accelerator has been performed with radiation is delivered to the stereotactically localized Winston-Lutz test. lesion, while minimaly irradiating adjacent normal Accurate dosimetry of small-field photon beams brain tissue. Radiosurgery can be performed either used in stereotactic radiosurgery (SRS) and with gamma beams from multi-mini cobalt sources radiotherapy (SRT) is difficult because of the presence and heavy charged particle beams from cyclotrons, or of lateral electronic disequilibrium and steep dose with narrow photon beams from isocentric linear gradients. The detectors used for measurements of electron accelerators absorbed dose distribution must be small in respect to Once a central point of the tumour is located at the the size of radiation field and must have a sufficient isocentre of the accelerator a whole treatment is spatial resolution. Therefore a PTW-MP3 water- performed by combining rotation of an accelerator scanning system was used with a 0.015 cm3 PTW ion with a sequential number of patient couch positions. chamber and a PTW diamond detector. The three The quality of the radiosurgical treatments following characteristics of the small fields required depends on two fundamental parameters: by the treatment planning system BrainSCAN were measured for each stereotactic collimator, for - mechanical tolerances due to gantry and couch diameters ranging from 0.75 to 3.50 cm at the rotations, and isocentre: - the dose distribution and the actual dose delivered - tissue maximum ratio (TMR), by a therapy unit with narrow photon beams. - off axis ratios (OAR) and These two mechanical and dosimetric characteristics of the therapy unit have been - relative output factors (ROF). investigated by the authors [1]. The 6 MeV X-ray Tissue Maximum Ratio (TMR) is defined as: beam from Clinac 2300CD (Varian,USA) was formed using additional cylindrical BrainLAB's collimators. TMR(c ,d) = D{c,0,d)/D(ct0,dmm) Nominal field diameters at the isocentre range where d is depth in the phantom, dmm is reference between 0.75 cm and 3.50 cm in steps of 0.25 cm. The depth, c is collimator diameter. The dmax was treated at rectangular collimator of the linac was set to a field of a constant depth of 1.5 cm within the limits of 5x5 cm2 at isocentre. experimental accuracy. Radiosurgical technique involves rotation of the Off Axis Ratio (OAR) defined as: accelerator gantry and the treatment coach. Therefore, OAR(c, r ,d) = D(c r, d) /D(c, 0, d) the three principal mechanical axes of the gantry, the turntable and the collimator should intersect at a 178 Annual Report 1999

is the ratio of the dose measured at a radial with ionization chamber with sensitive volume distance r relative to the dose at the central axis for a 0.015cm3. Relative output factor (ROF) for the collimator diameter c. circular collimator is the function of the primary jaws Relative Output factor ROF is defined by: field size setting. We suggest that measurements of 2 TMR, OAR and ROF for all circular stereotactic ROF(c) = D(c, 0, d max)/D( 10x10 cm , 0, dcal) collimators should be made with a fixed primary jaws 2 and is the ratio of the dose at a depth dmaK on the field size setting: 5x5cm . central axis for a collimator diameter c relative to the The mechanical and dosimetric characteristics of dose measured at the same point in a standard radiotherapy unit (Clinac 2 300 CD with BrainLAB's lOxlOcm" calibration field. collimators) are found to be suitable for stereotactic TMR and OAR measurements were performed at radiosurgery and radiotherapy. Source Surface (of phantom) Distance SSD equal 92.5cm and depth in the phantom d equal 7.5cm. [1] A.Wysocka, J.Rostkowska, M.Kania, W.Bulski, Since most cranial tumours are within a range of J.Fijuth, "Dosimetry of Small Circular 6-MV X- 7.5cm, the OAR at depth 7.5cm was entered in the Ray Beams for Stereotactic Radiotherapy with a treatment planning system for dose calculation. ROF Linear Accelerator" Proc.XXVI Mazurian Lakes values were measured at SSD=98.5cm and School of Physics 1-11 Sept. 1999, Krzyze,Poland d=dmax=] .5cm. The diamond detector was found to be more ]) Maria Sklodowska-Curie Memorial Cancer appropriate choice for beam profile measurements Centre and Institute of Oncology, ul.Roentgena 5, than the ionization chambers and yields more accurate 02-781 Warszawa, Poland results. Collimator output factors can be measured

LO 10.5 Room Temperature Model of Superconducting Accelerating 1300 MHz CD LO "Superstructure" of TESLA Collider 0 o by E.Plawski, J.Sekutowicz , J.Olszewski, W.P^cito o o The superconducting RF accelerating resonators In 1999 the production of 8 copper resonators was are basis of future TESLA 2x250 GeV electron- successfully finished giving the necessary positron collider[l]. In TTF (TESLA Test Facility) the reproducibility of frequency spectrum. The fabrication 9-cell superconducting RF resonators (in number of resonator shown in Fig. 1 was preceded by exceeding 30) elaborated since 1992 are under theoretical evaluation of frequencies, couplings and extensive testsfl]. The new approach is also under the wakefield dependence on shape and dimensions of study to find the solution less expensive in building of cells. The technological details (ie. the due to deep- accelerator and with even higher reliability in draw wall thickness homogeneity, the after-deep-draw operation. This approach known under the name of flow of shapes, the shrinkage due to electron beam "superstructure" was signalled in 1997 [2] and the welding and so on) were arrived at experimentally by "room temperature", 1:1 models of such the series of sample measurements. The measured superstructures were made in 1998-1999. The frequency spectrum of one complete resonator is progress and planning in realisation of this copper shown in Fig. 2. model was already given in Annual Report[3].

CENTER 1 293.888 868 KHz 36.838 aaa KM

Fig. 1 .Seven-cell single resonator of superstructure Fig. 2 The resonant modes in TM01 passband of 7-cell resonator