CyberKnife® M6™: Peripheral dose evaluation for brain treatments.

PURPOSE: This study evaluates the peripheral dose (PD) delivered to healthy tissues for brain stereotactic radiotherapy treatments (SRT) performed with a CyberKnife M6™ Robotic Radiosurgery System and proposes a model to estimate PD before treatment. METHOD: PD was measured with thermoluminescent dosimeters. Measurements were performed to evaluate the influence of distance, collimator type (fixed or Iris™) and aperture size on PD for typical brain treatment plans simulated on an anthropomorphic phantom. A model to estimate PD was defined by fitting functions to these measurements. In vivo measurements were subsequently performed on 30 patients and compared to the model-predicted PD. RESULTS: PD (in cGy) was about 0.06% of MU at 15cm for a 20mm fixed collimator and 0.04% of MU for the same aperture with Iris™ collimator. In vivo measurements showed an average thyroid dose of 55mGy (σ=18.8mGy). Computed dose for thyroid, breast, umbilicus and gonads showed on average a relative difference of 3.4% with the in vivo dose (σ=12.4%). CONCLUSION: PD at the thyroid with Iris™ was about a third lower than with a fixed collimator in case of brain SRT. Despite uncertainties (use of anthropomorphic PD to estimate patient specific PD, surface PD to estimate OAR PD) the model allows PD to be estimated without in vivo measurements. This method could be used to optimise PD with different planning strategies.

[Which IMRT? From "step and shoot" to VMAT: physicist point of view]. / Quelle RCMI? Du step and shoot au VMAT: point de vue du physicien.

Intensity-modulated radiation therapy (IMRT) is essential to have a dose distribution matching with the planning target volume (PTV) in case of concave-shape target. Today IMRT delivery techniques with linear accelerator can be divided into two classes: techniques with fixed gantry, called "step and shoot" (S&S) and "sliding window" (SW), and rotational techniques, called intensity modulated arc therapy (IMAT) and volumetric modulated arc therapy (VMAT). We discuss about constraints for IMRT implementation from dosimetric planning to treatment delivery. We compare S&S and VMAT performances concerning dose distribution quality, efficiency and delivery time. We describe quality controls that must be implemented and the methods for analysis and follow-up performances. VMAT tends to yield similar dose distribution to MRT with fixed gantry. VMAT also decreases monitor units as well as treatment delivery time to less than 5 minutes. However, VMAT is an IMRT technique more difficult to master than S&S technique because there are more variable parameters.

[High dose for prostate irradiation with image guided radiotherapy: contribution of intensity modulation arctherapy]. / Haute dose dans la prostate par radiothérapie guidée par l'image: apport de l'arcthérapie avec modulation d'intensité du faisceau.

PURPOSE: To compare two Intensity Modulated Radiation Therapy (IMRT) techniques for prostate cancer: the Volumetric Modulated Arc Therapy (VMAT) and the "Step and Shoot" technique (S&S). MATERIALS AND METHODS: VMAT and S&S plans (RX 18MV) were created and compared (Wilcoxon test) for 10 patients. The dosimetric goal of both treatments was to deliver 46 Gy to the seminal vesicles and 80 Gy to the prostate, while respecting the dose constrains in the organs at risk of toxicity. For one patient, the two techniques were compared for dose painting and escalation in target volumes defined on MRI and registered thanks to intraprostatic fiducials. RESULTS: VMAT, compared to S&S, offered: an increase of the PTV2s (prostate) volume receiving 77 to 80 Gy and a decrease of V(82) and V(83); a decrease of V(4) to V(6), V(16) to V(23), and V(69) to V(73) for the rectal wall; a decrease of V(25) for the bladder wall; a decrease of V(21) to V(43) for the femoral heads; a decrease of V(26) to V(44) and V(72) to V(80) but an increase of V(1) to V(21) and V(49) to V(60) for the healthy tissues. The Conformal Index "COIN" was better with VMAT than S&S (0.60 to 0.66). The delivered MU were significantly reduced with VMAT (8% mean) as well as the delivery time (4 min to 1.5 min). VMAT allowed delivering theorically 90Gy in the peripheral zone and 100 Gy in the tumor. CONCLUSION: In case of prostate irradiation, VMAT shows improvement compared with S&S. In particular, organs at risk are better spared, the delivery time is shortened and the number of delivered UM is decreased.

[Quantification of the volumetric benefit of image-guided radiotherapy (IGRT) in prostate cancer: margins and presence probability map]. / Bénéfice volumétrique de la radiothérapie guidée par l'image dans les cancers prostatiques : marges et cartographies de probabilité de présence.

PURPOSE: To quantify the prostate and seminal vesicles (SV) anatomic variations in order to choose appropriate margins including intrapelvic anatomic variations. To quantify volumetric benefit of image-guided radiotherapy (IGRT). PATIENTS AND METHODS: Twenty patients, receiving a total dose of 70 Gy in the prostate, had a planning CT scan and eight weekly CT scans during treatment. Prostate and SV were manually contoured. Each weekly CT scan was registered to the planning CT scan according to three modalities: radiopaque skin marks, pelvis bone or prostate. For each patient, prostate and SV displacements were quantified. 3D maps of prostate and SV presence probability were established. Volumes including minimal presence probabilities were compared between the three modalities of registration. RESULTS: For the prostate intrapelvic displacements, systematic and random variations and maximal displacements for the entire population were: 5mm, 2.7 mm and 16.5mm in anteroposterior axis; 2.7 mm, 2.4mm and 11.4mm in superoinferior axis and 0.5mm, 0.8mm and 3.3mm laterally. Margins according to van Herk recipe (to cover the prostate for 90% of the patients with the 95% isodose) were: 8mm, 8.3mm and 1.9 mm, respectively. The 100% prostate presence probability volumes correspond to 37%, 50% and 61% according to the registration modality. For the SV, these volumes correspond to 8%, 14% and 18% of the SV volume. CONCLUSIONS: Without IGRT, 5mm prostate posterior margins are insufficient and should be at least 8mm, to account for intrapelvic anatomic variations. Prostate registration almost doubles the 100% presence probability volume compared to skin registration. Deformation of SV will require either to increase dramatically margins (simple) or new planning (not realistic).

[Preliminary results of the assessment of intensity modulated radiotherapy (IMRT) for prostatic and head and neck tumors (STIC 2001)]. / Résultats préliminaires de l'évaluation de la radiothérapie conformationnelle avec modulation d'intensité (RCMI) pour le traitement des cancers prostatiques et ORL (STIC 2001).

INTRODUCTION: Between May 2002 and May 2004, eight French comprehensive cancer centres did a prospective nonrandomized study including 200 patients, 100 with cancer of the prostate and 100 with head and neck cancers. Half of each patient group was treated by IMRT and the others by RTC 3D. This clinical study was associated with an economic study and a physics study. We report here the first results. PATIENTS AND METHODS: For the clinical study, the analysis of the data of the first 88 patients irradiated for a prostatic cancer shows that 39 received RTC and 49 IMRT with a mean dose of 78 Gy at the ICRU point at 2 Gy per fraction. For H&N tumours, the preliminary analysis was done on the 87 first patients with a mean follow-up of 11.5 months (2 to 25 months) and a median of 8.4 months for the IMRT groups and 13.2 months for the RTC group. The economic study was done on the first 157 patients included during the first 18 months: 71 treated by RTC (35 for H&N and 36 for prostate) and 86 treated by IMRT (38 for H&N and 48 for prostate). The assessment of the direct costs was realized by a micro-costing technique. The physical study compared dose distributions for both techniques and has created quality control recommendations. RESULTS: Clinical studies of the acute reactions do not show any difference between groups, but we want to point out the short follow-up and the relatively high dose delivered to cancers of the prostate. The physics study demonstrates that IMRT is technically feasible in good clinical conditions with high quality assurance, a good reproducibility and precision. Dosimetric data show that IMRT could certainly spare organs at risk more than RTC for H&N tumours. The direct costs of "routine" treatments for H&N tumours were 4922 euros for IMRT versus 1899 euros for RTC and for the prostatic cancers 4911 euros for IMRT versus 2357 for RTC.

[Dosimetry of small-size photon beams]. / Dosimétrie des faisceaux de photons de faibles dimensions.

A high performance standard radiotherapy treatment unit could be used to perform stereotactic radiosurgery. The dosimetric aspects of stereotactic irradiation with small size photon beams (energies from 5 to 25 MV produced by electron linear accelerator or gamma-rays produced by cobalt-60 treatment unit) are analyzed. The diameter of circular beams used are 5 to 40 millimeters wide at the isocenter of the treatment unit. The dosimetry of small x-ray fields is complicated by two factors: the relationship between detector size and field size dimensions, and the lack of lateral electron equilibrium. The large dose gradients outside the beam's central axis require dosimetry techniques with higher spatial resolution. To determine the best dosimetry system for measurements at the beam's small focal point, particularly for measurement of the field size dependent on output factors, several different detectors were investigated: ionization chamber, silicon diode, diamond detector, thermoluminescent dosimeter, and film. Ionization chamber, which presents a sensitive volume smaller than 0.02 cm3, is the most commonly recommended detector for field diameter above 8 mm. Current representative examples of dosimetric measurements for different x-ray energies, including percent depth dose, tissue maximum ratios, beam profiles (off axis ratios), and output factors, are presented and discussed. As well, the dosimetric characteristics of small photon beams are detailed.

[Exchange of medical imaging and data information in radiotherapy: needs, methods and current limits]. / L'échange de données médicotechniques en radiothérapie: les besoins, les méthodes et les limites actuelles.

Extension of the image network within radiotherapy departments provides the technical infrastructure which is made necessary by the rapid evolution of techniques in the field of diagnosis and treatment in radiotherapy. The system is aimed at managing the whole set of data (textual data and images) that are needed for planning and control of treatments. The radiotherapy network addresses two objectives: managing both the information necessary for treatment planning (target volumes definition, planning dosimetry) and the control of all parameters involved during the patient's treatment under the treatment unit. The major challenge is to improve the quality of treatment. Multimodal imaging is a major advance as it allows the use of new dosimetry and simulation techniques. The need for standards to exchange medical imaging information is now recognized by all the institutions and a majority of users and manufacturers. It is widely accepted that the lack of standard has been one of the fundamental obstacles in the deployment of operational "Picture Archiving Communication Systems". The International Standard Organisation Open System Interconnection model is the standard reference mode used to describe network protocols. The network is based on the Ethernet and TCP/IP protocol that provides the means to interconnect imaging devices and workstations dedicated to specific image processing or machines used in radiotherapy. The network uses Ethernet cabled on twisted-pair (10 BaseT) or optical fibres in a star-shaped physical layout. Dicom V3.0 supports fundamental network interactions: transfer of images (computerized tomography magnetic resonance imaging query and retrieve of images), printing on network attached cameras, support of HIS/RIS related interfacing and image management. The supplement to the Dicom standard, Dicom RT, specifies five data objects known in Dicom as Information Object Definition for relevant radiotherapy. Dicom RT objects can provide a mean for standardized transfer of most of the information wich circulates in a radiotherapy department. A wide range of device types are represented, (treatment planning systems, portal imaging devices, linear accelerators, recording and verifying systems, conventional and virtual simulators). There will be additions and perhaps new developments in dataflow management, more complete integration with HIS/RIS system and printing, but the lion's share of the work has now been done. A project to integrate some security features into the Dicom protocol has begun.

Measurement of irradiation doses secondary to bedside radiographs in a medical intensive care unit.

The authors prospectively studied the radiation doses to radio-sensitive organs secondary to bedside radiographs in intensive care patients and in a control phantom. Dosimeters were taped on different organs during each bedside X-ray. The mean radiation doses, expressed in 10(-5) Gy (m-rad), for an "average patient" who was hospitalized 9 days and had 6 chest X-rays were respectively: 292 to the sternal bone marrow; 239 to the thyroid gland; 3 to the testes; 1 to the ovaries; 605 to the eye for 2 maxillary sinus X-rays. No diffused irradiation was measured during a 2-month period in the intensive care unit nor on dosimeters worn by four nurses.

[Dosimetric study of radiographs produced in the neonatal intensive care unit in newborn infants from 1 to 30 days of age]. / Etude dosimétrique des radiographies réalisées en réanimation néo-natale chez les nouveau-nés de un à trente jours.

This work is part of general program of the diagnostic radiation dosage monitoring in the C.H.U. of Brest. The aim of these measurements is to precise the doses delivered to the sensitive organs in infants from one to thirty days of age in the intensive care pediatric Department. We present in this paper the technology used and the results of these controls. We complete this experimental work with a statistical study of the number of radiographies made in the intensive care pediatric Department on 623 children. We insist on the use of leaded protection in the radiodiagnostic practice, as often as it is possible.