Comparison between the HyperArc™ technique and the CyberKnife® technique for stereotactic treatment of brain metastases.

PURPOSE: The purpose of this study was to compare the planimetric capacities between HyperArc™-based stereotactic radiosurgery and robotic radiosurgery system-based planning using CyberKnife® M6 for single and multiple cranial metastases. MATERIALS AND METHODS: We evaluated 51 treatment plans for cranial metastases, including 30 patients with a single lesion and 21 patients with multiple lesions, treated with the CyberKnife® M6. These treatment plans were optimized using the HyperArc™ (HA) system with the TrueBeam. The comparison of the quality of the treatment plans between the two treatment techniques (CyberKnife and HyperArc) was performed using the Eclipse treatment planning system. Dosimetric parameters were compared for target volumes and organs at risk. RESULTS: Coverage of the target volumes was equivalent between the two techniques, whereas median Paddick conformity index and median gradient index for all target volumes were 0.9 and 3.4, respectively for HyperArc plans, and 0.8 and 4.5 for CyberKnife plans (P<0.001). The median dose of gross tumor volume (GTV) for HyperArc and CyberKnife plans were 28.4 and 28.8, respectively. Total brain V18Gy and V12Gy-GTVs were 11cm3 and 20.2cm3 for HyperArc plans versus 18cm3 and 34.1cm3 for CyberKnife plans (P<0.001). CONCLUSION: The HyperArc provided better brain sparing, with a significant reduction in V12Gy and V18Gy, associated with a lower gradient index, whereas the CyberKnife gave a higher median GTV dose. The HyperArc technique seems to be more appropriate for multiple cranial metastases and for large single metastatic lesions.

An empirical model for calculation of the collimator contamination dose in therapeutic proton beams.

Collimators are used as lateral beam shaping devices in proton therapy with passive scattering beam lines. The dose contamination due to collimator scattering can be as high as 10% of the maximum dose and influences calculation of the output factor or monitor units (MU). To date, commercial treatment planning systems generally use a zero-thickness collimator approximation ignoring edge scattering in the aperture collimator and few analytical models have been proposed to take scattering effects into account, mainly limited to the inner collimator face component. The aim of this study was to characterize and model aperture contamination by means of a fast and accurate analytical model. The entrance face collimator scatter distribution was modeled as a 3D secondary dose source. Predicted dose contaminations were compared to measurements and Monte Carlo simulations. Measurements were performed on two different proton beam lines (a fixed horizontal beam line and a gantry beam line) with divergent apertures and for several field sizes and energies. Discrepancies between analytical algorithm dose prediction and measurements were decreased from 10% to 2% using the proposed model. Gamma-index (2%/1 mm) was respected for more than 90% of pixels. The proposed analytical algorithm increases the accuracy of analytical dose calculations with reasonable computation times.

[Dosimetric comparaison between VMAT and tomotherapy with para-aortic irradiation for cervix carcinoma]. / Comparaison entre arcthérapie volumétrique modulée et tomothérapie pour le cancer du col utérin, avec irradiation lomboaortique.

PURPOSE: Intensity-modulated radiotherapy (IMRT) has proven its dosimetric superiority over conformational radiotherapy for cervix cancers in terms of digestive toxicity. Volumetric modulated arctherapy (VMAT) has shown its dosimetric interest when compared to IMRT with static beams. The purpose of our study was to compare conformational radiotherapy, VMAT and tomotherapy for cervical cancers with para-aortic lymph nodes irradiation. PATIENTS AND METHODS: The dosimetric data from ten patients were compared between the three techniques, with collection of the dose received by the planning target volume, kidneys, bowel, rectum, bladder, bone marrow and spinal cord, as well as the complete dose. RESULTS: There was a significant difference in favour of VMAT and tomotherapy when compared with conformational radiotherapy for the organs at risk: intestines (V(20 Gy), V(30 Gy) and V(45 Gy)), rectum (V(30 Gy) and V(45 Gy)), bladder (V(30 Gy) and V(45 Gy)) and kidneys (V(12 Gy), Daverage, V(20 Gy)). Volumes receiving 20, 30 and 45 Gy were significantly higher in conformational radiotherapy than in VMAT and tomotherapy. There was a significant difference in favour of tomotherapy when compared with VMAT for V(12 Gy) in kidneys and V(45 Gy) in the bladder. CONCLUSION: This study confirms the interest of VMAT and tomotherapy for pelvic and para-aortic lymph nodes irradiation of cervix cancer when compared with conformational radiotherapy. There was little difference between VMAT and tomotherapy, except for kidney sparing, which was better with tomotherapy and thus may be interesting for patients receiving nephrotoxic chemotherapy.

[Head and neck adaptive radiotherapy: A tool for the detection of patients requiring adaptive radiotherapy]. / Radiothérapie adaptative des cancers ORL : un outil permettant d'identifier les patients nécessitant une adaptation de leur traitement.

PURPOSE: The purpose of this work was to implement a simple dosimetric alert tool in a retrospective study for six patients suffering from head and neck cancer to detect when a patient might require an adaptive radiotherapy. MATERIALS AND METHODS: The dosimetric tool generates a 3D cartography of two dosimetric complementary information: a dose variation tolerance map and a dose differential map. The tolerance map is calculated on the initial scanner (CTinit) using the planned dose distribution. It shows for each voxel of each delineated volume the availability for local dose variations during the course of radiotherapy without exceeding the dose threshold. The differential dose map is generated on the tomographic image CBCT (CBCTtreatment). It shows dose variations between the planned and the actual delivered dose distribution for each voxel. By comparing both maps, when a voxel presents a value superior to the corresponding dose variation tolerance, an alert is generated and the anatomical areas concerned are visually indicated to the physician. RESULTS: The application of the dosimetric tool on six patients with head and neck cancers reveals the ability of the tool to detect cases requiring a new treatment plan. Two patients whose the tumour shrinkage produced an increase of the delivered dose to the spinal cord beyond 45 Gy have been detected. CONCLUSION: The development of the dosimetric tool allows the automatic detection, with no delineation needs, of patients suffering from head and neck cancers requiring an adaptive strategy.

[Development of external quality control protocol for CyberKnife beams dosimetry: preliminary tests multicentre]. / Développement d'une procédure de contrôle de qualité externe des faisceaux du CyberKnife: étude préliminaire multicentrique.

PURPOSE: To develop an external quality control procedure for CyberKnife(®) beams. This work conducted in Nancy, has included a test protocol initially drawn by the medical physicist of Nancy and Lille in collaboration with Equal-Estro Laboratory. MATERIALS AND METHODS: A head and neck anthropomorphic phantom and a water-equivalent homogeneous cubic plastic test-object, so-called "MiniCube", have been used. Powder and solid thermoluminescent dosimeters as well as radiochromic films have been used to perform absolute and relative dose studies, respectively. The comparison between doses calculated by Multiplan treatment planning system and measured doses have been studied in absolute dose. The dose distributions measured with films and treatment planning system calculations have been compared via the gamma function, configured with different tolerance criteria. RESULTS: This work allowed, via solid thermoluminescent dosimeter measurements, verifying the beam reliability with a reproducibility of 1.7 %. The absolute dose measured in the phantom irradiated by the seven participating centres has shown an error inferior to the standard tolerance limits (± 5 %), for most of participating centres. The relative dose measurements performed at Nancy and by the Equal-Estro laboratory allowed defining the most adequate parameters for gamma index (5 %/2mm--with at least 95 % of pixels satisfying acceptability criteria: γ<1). These parameters should be independent of the film analysis software. CONCLUSION: This work allowed defining a dosimetric external quality control for CyberKnife(®) systems, based on a reproducible irradiation plan through measurements performed with thermoluminescent dosimeters and radiochromic films. This protocol should be validated by a new series of measurement and taking into account the lessons of this work.