ESTRO 36 _______________________________________________________________________________________________ angle, MLC position, and MU were 0.16° ± 0.01° (range, 0.12°-0.17°),0.08° ± 0.00° (range, 0.0.7°-0.08°),0.08 ± 0.02 mm (range, 0.04-0.11mm), and 0.37 ± 0.05 MU (range, 0.30-0.44MU), respectively.In the delivered dose reconstruction, the means ± SDs of the dose difference of the all dose-volumetric indices were 0.5% ± 0.8% (range, 0.0%-4.2%)and 0.2% ± 0.2% (range, 0.0%-0.7%)for the brain and prostate tumors, respectively. ConclusionWe have established patient-specific QA procedure for the DWA using ArcCHECK and log files.Our results have shown that DWA with Vero4DRT delivered the accurate dose distribution.

Purpose: Accurate clinical dosimetry of electron beams produced by linear accelerators dedicated to intraoperative radiation therapy (IORT) is challenging due to the very high dose-per-pulse (0.3–10 cGy per pulse) as compared to conventional accelerators (<0.01 cGy per pulse). The aim of this work is to characterize electron beams produced by a dedicated mobile accelerator for IORT by using the microDiamond 60019 PTW Freiburg dosimeter.

Introduction: In the past years, there has been a growing interest in IOERT using dedicated electron linacs, as LIAC and NOVAC (SIT, Italy). These, when compared to traditional external beam radiotherapy accelerators, are characterized by smaller field sizes and SSD as well as higher dose per pulse and degraded energy spectrum, thus making the application of international protocols questionable. For instance the standard two voltage analysis (TVA) for determining the correction factor associated with ion recombination in ionization chambers leads to significant errors. This paper investigates systematically the procedures and results obtained by using and integrating the international protocols (IAEA TRS 398, AAPM TG51 and DIN 6800-2) with the TVA corrected for the high dose per pulse range.

Introduction: The image guided intra-operative radiotherapy (IGIORT) is a new methodology based on the planning optimization using intra-operative target images acquired after surgery. The dedicated treatment planning system (TPS) CSRAD+ has been developed in order to plan intra-operative radiotherapy treatments for patients with malignant diseases as clinically appropriate, using a dedicated mobile accelerator and an imaging device. The CSRAD+ performs IORT dose distribution calculation relying on pre-treatment and intra-operative DICOM_RT images. The aim of this work is to validate the dosimetric output and the performances of CSRAD+ before its introduction in clinical practice.

Introduction: In this study, the IORT dedicated Treatment planning system (CSRAD+), already validated on simple geometries, has been used to perform calculation on sarcoma cancer patients and to compare the measured and the calculated dose distribution in a clinical configuration In sarcoma IORT treatments, the air gap between target and applicator and the extended dimensions are critical parameters that must be fully taken into account.

Figure 1 kQ of modelled NE2561 chamber with beams with the flattening filter (closed shapes), beams with the flattening filter removed (open shapes) and beams with thin replacement filter (red shapes).(a) shows the results for Elekta beams and (b) shows the results for Varian beams.The dashed grey line shows the average of kQ from TRS-398 and Muir et al. Conclusion:The average difference between linac outputs measured with TRS-398 and TG-51 protocols was less than 0.2 % for 6 MV FFF and 10 MV FFF.Modelling suggests a 2-3 mm metal plate used in place of the flattening filter offers sufficient filtration for the FFF beam to produce a similar kQ to WFF beams.

Introduction: IORT breast carcinoma treatment clinical practice has evidenced the need of real time monitoring the dose delivery on the target. The commercially available in vivo dosimetry technologies allow either a real time measurement in one point (MOSFET type detectors) or a non real time measurement over a surface (radio chromic films). A cooperation between ASMN Reggio Emilia, INFN and SIT has led to the conceptual design of a new device capable of satisfying the above mentioned needs. Such device has been patented (Italian Patent # TO2014A000943). The new dosimeter consists in four leaf shaped plastic scintillators positioned between the two parts of the radiation protection disc. Such device can measure in real time the dose in the four sectors, providing both the integral dose and a measurement of the field symmetry on the target.

An investigation on the power energy injection in a resonator by electron stream is reported in this paper, by documenting the power transfer from an electron beam to a resonant cavity, coupled to an external circuitry. The proposed system has been employed to measure the radiation dose deposed by a medical electron linear accelerator. A prototype has been fabricated and tested through VNA cold measurements and dose deposition measurements. A microcon- troller system has been employed to obtain a digital output, the Monitor Units. The linearity of the Monitor Units for di®erent values of accumulated dose, have allowed to employ this system for the real time dose measurements.

PURPOSE:To characterize a synthetic diamond dosimeter (PTW Freiburg microDiamond 60019) in high dose-per-pulse electron beams produced by an Intra Operative Radiation Therapy (IORT) dedicated accelerator.METHODS:The dosimetric properties of the microDiamond were assessed under 6, 8 and 9 MeV electron beams by a NOVAC11 mobile accelerator (Sordina IORT Technologies S.p.A.). The characterization was carried out with dose-per-pulse ranging from 26 to 105 mGy per pulse. The microDiamond performance was compared with an Advanced Markus ionization chamber and a PTW silicon diode E in terms of dose linearity, percentage depth dose (PDD) curves, beam profiles and output factors.RESULTS:A good linearity of the microDiamond response was verified in the dose range from 0.2 Gy to 28 Gy. A sensitivity of 1.29 nC/Gy was measured under IORT electron beams, resulting within 1% with respect to the one obtained in reference condition under (60)Co gamma irradiation. PDD measurements were found in agreement with the ones by the reference dosimeters, with differences in R50 values below 0.3 mm. Profile measurements evidenced a high spatial resolution of the microDiamond, slightly worse than the one of the silicon diode. The penumbra widths measured by the microDiamond resulted approximately 0.5 mm larger than the ones by the Silicon diode. Output factors measured by the microDiamond were found within 2% with those obtained by the Advanced Markus down to 3 cm diameter field sizes.CONCLUSIONS:The microDiamond dosimeter was demonstrated to be suitable for precise dosimetry in IORT applications under high dose-per-pulse conditions.

Dose measurements of a Medical Linear Accelerator (LINAC’s) performed through a passive resonant cavity are shown in this paper. The cavity is coupled through a magnetic loop with a coaxial transmission line loaded on a microwave envelope detector. Output signal has been documented while receiving electron currents ranging from several values. This paper shows the complete equivalency, in terms of global performance, of the current revelation performed by exploiting the cavitybeam interaction principle with the classical technology, based on ionization chambers, without need of high voltage. The most important point is that the resonant cavity system, by measuring the beam current, gives a direct measurement of a physical observable quantity directly related with the dose deposed by the beam.

This paper proposes a particular Dielectric Window (DW) for Standing Wave (SW) Linear Accelerators (LINAC’s). This study investigates the in-frequency return loss behaviour of the LINAC, in order to improve matching and transmitting conditions while maintaining the optimum coupling between LINAC and High Power Microwave (HPMW) source. Device design considers the DW input interface as an Input Matching Network (IMN) at the LINAC Normal Mode (NM) working frequency. Thus, design formulas are provided and Computer Aided Design (CAD) techniques are proposed. A prototype has been made and tested by performing cold S-parameter and Percentage Depth Dose (PDD) measurements of a LINAC with the proposed DW and with a traditional DW. The proposed device offers more energy transport attitude over the traditional DW, as shown by a return loss increase of 167 % and an output electron energy increase of 5.5% while maintaining the same LINAC input power settings. This solution can offer a decrease of power line size, weight and cost. An after brazing global improvement of the accelerator figures of merit is also possible, as this study have demonstrated...

Background: Accurate clinical dosimetry of electron beams produced by special linear accelerators dedicated to intraoperative radiation therapy (IORT) is challenging due to the presence of very high dose per pulse (1-10 cGy per pulse) with respect to conventional accelerators (<0.1 cGy per pulse). This high dose rate can affect the dose determination by means of dosimeters currently used for absolute and relative dosimetry (e.g. ionization chambers). In addition, due to the high dose gradients of electron beams, small volume dosimeters are needed. Recently, the PTW microDiamond type 60019 has been proven to be a suitable device for a very wide radiation quality range such as photons, electrons and protons both for small and large irradiation fields.