IAEA methodology for on-site end-to-end IMRT/VMAT audits : an international pilot study

The IAEA has developed and tested an on-site, end-to-end IMRT/VMAT dosimetry audit methodology for head and neck cases using an anthropomorphic phantom. The audit methodology is described, and the results of the international pilot testing are presented. The audit utilizes a specially designed, commercially available anthropomorphic phantom capable of accommodating a small volume ion chamber (IC) in four locations (three in planning target volumes (PTVs) and one in an organ at risk (OAR)) and a Gafchromic film in a coronal plane for the absorbed dose to water and two-dimensional dose distribution measurements, respectively. The audit consists of a pre-visit and on-site phases. The pre-visit phase is carried out remotely and includes a treatment planning task and a set of computational exercises. The on-site phase aims at comparing the treatment planning system (TPS) calculations with measurements in the anthropomorphic phantom following an end-to-end approach. Two main aspects were tested in the pilot study: feasibility of the planning constraints and the accuracy of IC and film results in comparison with TPS calculations. Treatment plan quality was scored from 0 to 100. Results: Forty-two treatment plans were submitted by 14 institutions from 10 countries, with 79% of them having a plan quality score over 90. Seventeen sets of IC measurement results were collected, and the average measured to calculated dose ratio was 0.988 ± 0.016 for PTVs and 1.020 ± 0.029 for OAR. For 13 film measurement results, the average gamma passing rate was 94.1% using criteria of 3%/3 mm, 20% threshold and global gamma. The audit methodology was proved to be feasible and ready to be adopted by national dosimetry audit networks for local implementation

Le système de tomothérapie hélicoïdale pour la radiothérapie modulée en intensité et guidée par l'image: développements récents et applications cliniques.

The advent of 3D conformal radiotherapy and intensity modulated radiation therapy (IMRT) make possible the dose optimization to complex target volumes close to sane organs at risk. IMRT's introduction of numerous small radiation fields inherently increases delivery inaccuracies. As a consequence, the use of IMRT without precise localization of the tumor and sensitive structures, at both the planning and delivery stages, and the absence of continuous verification represent the most significant challenges to the implementation of IMRT in routine clinical use. Intensity modulated (or not) conformal radiotherapy delivery requires better precision in the definition of treatment volume, frequently if necessary. Helical tomotherapy has been designed to use CT imaging technology to plan, deliver, and verify that the delivery has been carried out as planned. The image-guided and intensity modulations processes of helical tomotherapy that enable this goal are described

Clinical and theoretical quasi-IMAT study of prostate cancer to show high plan quality with a single arc

Purpose: Commonly IMAT treatment plans for clinical use can only be generated by forward planning. We present a quasi-IMAT technique, simulated by step-and-shoot treatment. The purpose of this study is to investigate, if the plan quality can be improved by increasing the number of beams, keeping the number of segments constant. Materials and Methods: Quasi-IMAT plans with 18 and 36 equidistant beams were generated and the total number of segments was reduced to 36. In a second step the number of segments was increased to 72, in order to investigate if the quality of the plans as determined by DVHs of PTV and OAR improves with the number of segments. A conventional six-field IMRT plan was used as a reference. The beam setups were applied to the Carpet Phantom and to five prostate cancer patients. The plans were optimized with Oncentra Masterplan (version 3.0, DSS) for 15 MV photons and a MLC with 1 cm leaf width at isocenter. After optimization plans were normalized to the average of the PTV. For evaluation, DVHs for the plans with 18 and 36 beams were compared to the reference six-field IMRT plan. Results: In the phantom case with the very concave PTV the percentage of the volume of the OAR that receives more than 70 % of the prescribed dose were 60.7%, 31.0% and 21.7% (for the 6, 18 and 36 beams plans with 36 segments). For the prostate cases, adequate dose coverage and dose homogeneity where acomplished inside the PTV. The average percentage of dose received by 50% of the rectum volume was reduced from 45% to 41,7% (6 and 36 fields with 36 segments). Only a slight improvement in OAR sparing was observed by increasing the number of segments. In all cases the dose received by the OARs was reduced by increasing the number of beams. This effect is more pronounced in the phantom, because the target is more concave. Simultaneously the coverage and dose homogeneity of the target is unaffected. Conclusions: The advantage of quasi-IMAT technique is that it can be realized with a standard IMRT treatment planning system and a standard linac equipment. No special arc sequencing (Shepard et al., 2007) and dynamic leaf control is necessary. The plan quality is high even with a single gantry arc. Acknowledgement: This work was supported by Elekt

Critères de qualité en radiothérapie des cancers de la tête et du cou sous l'égide de l'Intergroupe ORL Quality criteria in radiotherapy for head and neck cancers under the aegis of Head and Neck Intergroup.

The aim of radiotherapy is to deliver enough radiation to the tumor in order to achieve maximum tumour control in the irradiated volume with as few serious complications as possible with an irradiation dose as low as possible to normal tissue. The quality of radiotherapy is essential for optimal treatment and quality control is to reduce the bias in clinical trials avoiding possible major deviations. The assurance and quality control programs have been developed in large european (EORTC, GORTEC) and american cooperative groups (RTOG) of radiation oncology since the 1980s. We insist here on the importance of quality assurance in radiotherapy and the current status in this domain and the criteria for quality control especially for current clinical trials within GORTEC are discussed here

Monte Carlo simulation of the Tomotherapy treatment unit in the static mode using MC HAMMER, a Monte Carlo tool dedicated to Tomotherapy

Helical tomotherapy (HT) is designed to deliver highly modulated IMRT treatments. The concept of HT provides new challenges in MC simulation, because simultaneous movement of the gantry, the couch and the multi-leaf collimator (MLC) must be simulated accurately. However, before accounting for gantry, couch movement and multileaf collimator configurations, high accuracy must be achieved while simulating open static fields (1 times 40, 2.5 times 40 and 5 times 40 cm 2). This is performed using MC HAMMER, which is a graphical user interface allowing MC simulation using PENELOPE for various configurations of HT. Since the geometry of the different elements and materials involved in the beam generation are precisely known and defined, the only parameters that need to be tuned on are therefore electron source spot size and electron energy. Beyond the build up region, good agreement (2%/1 mm) is achieved for all the field sizes between measurements (ion chamber) and simulations with an electron source energy set to 5.5 MeV. The electron source spot size is modelled as a gaussian distribution with full width half maximum equal to 1.4 mm. This value was chosen to match measured and calculated penumbras in the longitudinal direction