A portable primary-standard level graphite calorimeter for absolute dosimetry in clinical pencil beam scanning proton beams.

Objective. To report the use of a portable primary standard level graphite calorimeter for direct dose determination in clinical pencil beam scanning proton beams, which forms part of the recommendations of the proposed Institute of Physics and Engineering in Medicine (IPEM) Code of Practice (CoP) for proton therapy dosimetry.Approach. The primary standard proton calorimeter (PSPC) was developed at the National Physical Laboratory (NPL) and measurements were performed at four clinical proton therapy facilities that use pencil beam scanning for beam delivery. Correction factors for the presence of impurities and vacuum gaps were calculated and applied, as well as dose conversion factors to obtain dose to water. Measurements were performed in the middle of 10 × 10 × 10 cm3homogeneous dose volumes, centred at 10.0, 15.0 and 25.0 g·cm-2depth in water. The absorbed dose to water determined with the calorimeter was compared to the dose obtained using PTW Roos-type ionisation chambers calibrated in terms of absorbed dose to water in60Co applying the recommendations in the IAEA TRS-398 CoP.Main results.The relative dose difference between the two protocols varied between 0.4% and 2.1% depending on the facility. The reported overall uncertainty in the determination of absorbed dose to water using the calorimeter is 0.9% (k= 1), which corresponds to a significant reduction of uncertainty in comparison with the TRS-398 CoP (currently with an uncertainty equal or larger than 2.0% (k= 1) for proton beams).Significance. The establishment of a purpose-built primary standard and associated CoP will considerably reduce the uncertainty of the absorbed dose to water determination and ensure improved accuracy and consistency in the dose delivered to patients treated with proton therapy and bring proton reference dosimetry uncertainty in line with megavoltage photon radiotherapy.

Dosimetric comparison of four high performance techniques for irradiation of breast cancer patients.

PURPOSE: The use of IMRT for the treatment of breast cancer has been growing considerably in our institution since 2009. Alternatively, helical tomotherapy (HT) using a field width of 2.5 and 5cm (HT_FW_5), volumetric-modulated arc therapy (VMAT), or proton therapy with pencil-beam scanning (PT-PBS) have also been used to reduce treatment duration or optimize organ-at-risk (OAR) sparing. The purpose of this study was to compare the 4 treatment modalities available at our site. PATIENTS AND METHODS: We studied 10 patients treated for breast cancer with lymph node involvement. The prescribed dose was 51.8Gy to the breast with a simultaneous integrated boost up to 63Gy, and 50.4Gy to lymph nodes in 28 fractions. The CTV was delineated according to ESTRO Guidelines. Dosimetric planning in routine clinical practice was performed using HT_FW_2.5. The approved clinical plan was compared to the 3 other plans. Dosimetric goals for PTV coverage were D95%≥95% and D2%≤107% of the prescribed dose. Mean and maximum doses to OAR were recorded. RESULTS: HT_FW_5 and VMAT plans ensure equivalent or even better PTV coverage compared to the initial clinically approved plan but at the cost of poorer OAR sparing. PT_PBS plans showed that an excellent PTV coverage can be maintained with significantly lower doses to OAR. CONCLUSION: HT_FW_5 and VMAT plans allow a significant reduction of treatment duration and can be a good alternative to HT_FW_2.5 for specific populations. HT_FW_2.5 could be chosen for patients at higher risk of side effects. In addition, PT_PBS should be considered in the near future as it has been shown to have a major potential benefit to lower the risk of side effects with the same level of PTV coverage.

Experimental characterisation of a proton kernel model for pencil beam scanning techniques.

The aim of this work is to perform Monte Carlo simulations of a proton pencil beam scanning machine, characterise the low-dose envelope of scanned proton beams and assess the differences between various approximations for nozzle geometry. Measurements and Monte Carlo simulations were carried out in order to describe the dose distribution of a proton pencil beam in water for energies between 100 and 220 MeV. Dose distributions were simulated by using a Geant4 Monte Carlo platform (TOPAS), and were measured in water using a two-dimensional ion chamber array detector. The beam source in air was adjusted for each configuration. Double Gaussian parameterisation was proposed for definition of the beam source model in order to improve simulations starting at the nozzle exit. Absolute dose distributions and field size factors were measured and compared with simulations. The influence of the high-density components present in the treatment nozzle was also investigated by analysis of proton phase spaces at the nozzle exit. An excellent agreement was observed between experimental dose distributions and simulations for energies higher than 160 MeV. However, minor differences were observed between 100 and 160 MeV, suggesting poorer modelling of the beam when the full treatment head was not taken into account. We found that the first ionisation chamber was the main cause of the tail component observed for low proton beam energies. In this work, various parameterisations of proton sources were proposed, thereby allowing reproduction of the low-dose envelope of proton beams and excellent agreement with measured data.

[Prevention of radio-induced cancers]. / Prévention des cancers radio-induits.

The article deals with the prevention of cancers only directly related to therapeutic radiation which are distinguished from "secondary cancer". The consideration of the risk of radiation-induced cancers after radiation therapy, although it is fortunately rare events, has become indispensable today. With a review of the literature, are detailed the various involved parameters. The age of the irradiated patient is one of the main parameters. The impact of the dose is also discussed based on the model used, and based on clinical data. Other parameters defining a radiation treatment are discussed one after the other: field with the example of Hodgkin's disease, the type of radiation and the participation of secondary neutrons, spreading and splitting. All these parameters are discussed according to each organ whose sensitivity is different. The article concludes with a list of recommendations to reduce the risk of radio-induced cancers. Even with the advent of conformal radiotherapy, intensity modulation, the modulated volume arctherapy, and the development of specific machinery for the extra-cranial stereotactic, the radiation therapist must consider this risk and use of reasonable and justified control imaging. Although they constitute a small percentage of cancers that occur secondarily after a first malignant tumor, radiation-induced cancers, can not and must not be concealed or ignored and justify regular monitoring over the long term, precisely adapted on the described parameters.

Dosimetric characteristics of four PTW microDiamond detectors in high-energy proton beams.

Small diamond detectors are useful for the dosimetry of high-energy proton beams. However, linear energy transfer (LET) dependence has been observed in the literature with such solid state detectors. A novel synthetic diamond detector has recently become commercially available from the manufacturer PTW-Freiburg (PTW microDiamond type 60019). This study was designed to thoroughly characterize four microDiamond detectors in clinical proton beams, in order to investigate their response and their reproducibility in high LET regions. Very good dosimetric characteristics were observed for two of them, with good stability of their response (deviation less than 0.4% after a pre-irradiation dose of approximately 12 Gy), good repeatability (coefficient of variation of 0.06%) and a sensitivity of approximately 0.85 nC Gy(-1). A negligible dose rate dependence was also observed for these two microDiamonds with a deviation of the sensitivity less than 0.7% with respect to the one measured at the reference dose rate of 2.17 Gy min(-1), in the investigated dose rate range from 1.01 Gy min(-1) to 5.52 Gy min(-1). Lateral dose profile measurements showed the high spatial resolution of the microDiamond oriented with its stem perpendicular to the beam axis and with its small sensitive thickness of about 1 µm in the scanning profile direction. Finally, no significant LET dependence was found with these two diamond dosimeters in comparison to a reference ionization chamber (model IBA PPC05). These good results were in accordance to the literature. However, this study showed also a non reproducibility between the devices in terms of stability, sensitivity and LET dependence, since the two other microDiamonds characterized in this work showed different dosimetric characteristics making them not suitable for proton beam dosimetry with a maximum difference of the peak-to-plateau ratio of 6.7% relative to the reference ionization chamber in a clinical 138 MeV proton beam.

Analytical linear energy transfer model including secondary particles: calculations along the central axis of the proton pencil beam.

In proton therapy, the relative biological effectiveness (RBE) depends on various types of parameters such as linear energy transfer (LET). An analytical model for LET calculation exists (Wilkens' model), but secondary particles are not included in this model. In the present study, we propose a correction factor, L sec, for Wilkens' model in order to take into account the LET contributions of certain secondary particles. This study includes secondary protons and deuterons, since the effects of these two types of particles can be described by the same RBE-LET relationship. L sec was evaluated by Monte Carlo (MC) simulations using the GATE/GEANT4 platform and was defined by the ratio of the LET d distributions of all protons and deuterons and only primary protons. This method was applied to the innovative Pencil Beam Scanning (PBS) delivery systems and L sec was evaluated along the beam axis. This correction factor indicates the high contribution of secondary particles in the entrance region, with L sec values higher than 1.6 for a 220 MeV clinical pencil beam. MC simulations showed the impact of pencil beam parameters, such as mean initial energy, spot size, and depth in water, on L sec. The variation of L sec with these different parameters was integrated in a polynomial function of the L sec factor in order to obtain a model universally applicable to all PBS delivery systems. The validity of this correction factor applied to Wilkens' model was verified along the beam axis of various pencil beams in comparison with MC simulations. A good agreement was obtained between the corrected analytical model and the MC calculations, with mean-LET deviations along the beam axis less than 0.05 keV µm(-1). These results demonstrate the efficacy of our new correction of the existing LET model in order to take into account secondary protons and deuterons along the pencil beam axis.

Use of gEUD for predicting ear and pituitary gland damage following proton and photon radiation therapy.

OBJECTIVE: To determine the relationship between the dose to the inner ear or pituitary gland and radiation-induced late effects of skull base radiation therapy. METHODS: 140 patients treated between 2000 and 2008 were considered for this study. Hearing loss and endocrine dysfunction were retrospectively reviewed on pre- and post-radiation therapy audiometry or endocrine assessments. Two normal tissue complication probability (NTCP) models were considered (Lyman-Kutcher-Burman and log-logistic) whose parameters were fitted to patient data using receiver operating characteristics and maximum likelihood analysis. The method provided an estimation of the parameters of a generalized equivalent uniform dose (gEUD)-based NTCP after conversion of dose-volume histograms to equivalent doses. RESULTS: All 140 patients had a minimum follow up of 26 months. 26% and 44% of patients experienced mild hearing loss and endocrine dysfunction, respectively. The fitted values for TD50 and γ50 ranged from 53.6 to 60.7 Gy and from 1.9 to 2.9 for the inner ear and were equal to 60.6 Gy and 4.9 for the pituitary gland, respectively. All models were ranked equal according to Akaike's information criterion. CONCLUSION: Mean dose and gEUD may be used as predictive factors for late ear and pituitary gland late complications after skull base proton and photon radiation therapy. ADVANCES IN KNOWLEDGE: In this study, we have reported mean dose effects and dose-response relationship of small organs at risk (partial volumes of the inner ear and pituitary gland), which could be useful to define optimal dose constraints resulting in an improved therapeutic ratio.

Polyethylene glycol-fused allografts produce rapid behavioral recovery after ablation of sciatic nerve segments.

Restoration of neuronal functions by outgrowths regenerating at ∼1 mm/day from the proximal stumps of severed peripheral nerves takes many weeks or months, if it occurs at all, especially after ablation of nerve segments. Distal segments of severed axons typically degenerate in 1-3 days. This study shows that Wallerian degeneration can be prevented or retarded, and lost behavioral function can be restored, following ablation of 0.5-1-cm segments of rat sciatic nerves in host animals. This is achieved by using 0.8-1.1-cm microsutured donor allografts treated with bioengineered solutions varying in ionic and polyethylene glycol (PEG) concentrations (modified PEG-fusion procedure), being careful not to stretch any portion of donor or host sciatic nerves. The data show that PEG fusion permanently restores axonal continuity within minutes, as initially assessed by action potential conduction and intracellular diffusion of dye. Behavioral functions mediated by the sciatic nerve are largely restored within 2-4 weeks, as measured by the sciatic functional index. Increased restoration of sciatic behavioral functions after ablating 0.5-1-cm segments is associated with greater numbers of viable myelinated axons within and distal to PEG-fused allografts. Many such viable myelinated axons are almost certainly spared from Wallerian degeneration by PEG fusion. PEG fusion of donor allografts may produce a paradigm shift in the treatment of peripheral nerve injuries.

[Evaluation and implementation of in vivo transit dosimetry with an electronic portal imaging device]. / Évaluation et mise en œuvre de la dosimétrie in vivo de transmission par imageurs portals.

PURPOSE: In vivo dosimetry is now widely recommended to avoid major treatment error. Transit dosimetry using portal imagers allows fast and accurate in vivo dose verifications. Several teams have published clinical studies but no recommendation has been proposed to define tolerance levels and validation criteria. This study proposes a simple methodology to assess the overall standard deviation of transit dosimetry and was applied to our transit dosimetry method. MATERIAL AND METHODS: In a first step, the uncertainties due to the dose reconstruction method are evaluated. Their estimation is based on a set of geometries, representative of clinical situations for which 45 points of measurement have been defined. In a second step, we studied the variations of our method in clinical situations. During the treatment session of the patient, the dose was reconstructed and the differences between reconstructed dose and prescribed dose were used to define a realistic tolerance level, adapted to the clinical routine. Then, a methodology is proposed to determine if the transit dosimetry method, with the defined tolerance level allows detecting significant treatment errors (>5% of the prescribed dose). RESULTS -  CONCLUSION: Applying this methodology we concluded that a tolerance level of 6.5% (k=2) can be associated with our method. With this value, it is demonstrated that in many cases differences of 5% (or less) on the prescribed dose can be detected. This study demonstrates clearly that in vivo transit dosimetry is not able to detect all the treatment errors but remains an ultimate and efficient tool in many situations.

Calibration of CT Hounsfield units for proton therapy treatment planning: use of kilovoltage and megavoltage images and comparison of parameterized methods.

Proton beam range is of major concern, in particular, when images used for dose computations are artifacted (for example in patients with surgically treated bone tumors). We investigated several conditions and methods for determination of computed tomography Hounsfield unit (CT-HU) calibration curves, using two different conversion schemes. A stoichiometric methodology was used on either kilovoltage (kV) or megavoltage (MV) CT images and the accuracy of the calibration methods was evaluated. We then studied the effects of metal artifacts on proton dose distributions using metallic implants in rigid phantom mimicking clinical conditions. MV-CT images were used to evaluate relative proton stopping power in certain high density implants, and a methodology is proposed for accurate delineation and dose calculation, using a combined set of kV- and MV-CT images. Our results show good agreement between measurements and dose calculations or relative proton stopping power determination (<5%). The results also show that range uncertainty increases when only kV-CT images are used or when no correction is made on artifacted images. However, differences between treatment plans calculated on corrected kV-CT data and MV-CT data remained insignificant in the investigated patient case, even with streak artifacts and volume effects that reduce the accuracy of manual corrections.

Potential benefits of using cardiac gated images to reduce the dose to the left anterior descending coronary during radiotherapy of left breast and internal mammary nodes.

PURPOSE: To assess the benefits of using cardiac gated images for treatment planning of breast and internal mammary nodes. PATIENTS AND METHODS: Inspiration breath hold computed tomography (CT) series acquired at prospectively gated diastolic phase were used for planning. Three different techniques were compared. Technique A used tangents and an internal mammary nodes field covering the three first inter-rib spaces; technique B used an extended internal mammary nodes including part of the medial breast in junction with tangential fields; the 3(rd) technique used helical tomotherapy. For each technique, two treatment plans were performed: one plan (plan-01) where mean dose and V(25) to the heart were considered for plan evaluation and a second plan (plan-02) where the irradiation of the left anterior descending artery was minimized. RESULTS: V(25) to the heart was found to be less than 5% for all six plans. Mean doses to the heart were within 4.8 to 7.2 Gy. By attempting to lower the dose to the left anterior descending artery, heart D(mean) was decreased by 20-30% for the two techniques A and B while being unchanged for tomotherapy. Regarding target coverage, there was no marked difference between plans where only heart dose was considered (plans-01) and plans where the left anterior descending artery dose was minimized (plans-02). When the left anterior descending artery dose was part of plan evaluation, D(mean) to the left anterior descending artery could be decreased by 24, 19 and 9% for techniques A, B and tomotherapy respectively. The three techniques exposed segments of the left coronary to different levels of dose. CONCLUSION: This study showed that evaluation of the dose to the left anterior descending artery coronary may change the treatment strategy. Cardiac gated images without IV contrast permitted a good visualization of the coronaries in order to optimize the dose on these structures. In addition to heart V(25,) the dose to the coronaries should be included in prospective studies on radiotherapy related heart toxicity in association with all additional risk factors.

[Radiotherapy for breast cancer and pacemaker]. / Radiothérapie pour un cancer du sein et stimulateur cardiaque.

PURPOSE: Patients with permanent cardiac pacemakers occasionally require radiotherapy. Therapeutic irradiation may cause pacemakers to malfunction due to the effects of ionizing radiation or electromagnetic interference. We studied the breast cancer patients who needed breast and/or chest wall and lymph node irradiation to assess the feasibility and tolerance in this population of patients. PATIENTS AND METHODS: From November 2008 to December 2009, more than 900 patients received radiotherapy for their breast cancer in our department using megavoltage linear accelerator (X 4-6 MV and electrons). Among them, seven patients were with permanent pacemaker. All patients have been treated to the breast and chest wall and/or lymph nodes. Total dose to breast and/or chest wall was 50 Gy/25 fractions and 46 Gy/23 fractions to lymph nodes. Patients who underwent conserving surgery followed by breast irradiation were boosted when indicated to tumour bed with 16 Gy/8 fractions. All patients were monitored everyday in presence of radiation oncologist to follow the function of their pacemaker. All pacemakers were controlled before and after radiotherapy by the patients' cardiologist. RESULTS: Seven patients were referred in our department for postoperative breast cancer radiotherapy. Among them, only one patient was declined for radiotherapy and underwent mastectomy without radiotherapy. In four cases the pacemaker was repositioned before the beginning of radiotherapy. Six patients, aged between 48 and 84 years underwent irradiation for their breast cancer. Four patients were treated with conserving surgery followed by breast radiotherapy and two with mastectomy followed by chest wall and internal mammary chain, supra- and infra-clavicular lymph node irradiation. The dose to the pacemaker generator was kept below 2 Gy. There was no pacemaker dysfunction observed during the radiotherapy. CONCLUSION: The multidisciplinary work with position change of the pacemaker before radiotherapy and everyday monitoring permitted the safe treatment of our patients. Updated guidelines are definitely needed with more details about acceptable doses at the different parts of the pacemaker.

[Protontherapy: basis, indications and new technologies]. / La protonthérapie : bases, indications et nouvelles technologies.

With over 70,000 patients treated worldwide, protontherapy has an evolution on their clinical applications and technological developments. The ballistic advantage of the Bragg peak gives the possibility of getting a high conformation of the dose distribution to the target volume. Protontherapy has accumulated a considerable experience in the management of selected rare malignancies such as uveal melanomas and base of the skull chordomas and chondrosarcomas. The growing interest for exploring new and more common conditions, such as prostate, lung, liver, ENT, breast carcinomas, as well as the implementation of large pediatric programs advocated by many experts has been challenged up to now by the limited access to operational proton facilities, and by the relatively slow pace of technical developments in terms of ion production, beam shaping and modelling, on-line verification etc. One challenge today is to deliver dynamic techniques with intensity modulation in clinical facilities as a standard treatment. We concentrate in this paper on the evolution of clinical indications as well as the potentialities of new technological concepts on ion production, such as dielectric walls and laser-plasma interactions. While these concepts could sooner or later translate into prototypes of highly compact equipments that would make easier the implantation of cost-effective hospital-based facilities, the feasibility of their clinical use must still be proved.

Technique alternatives for breast radiation oncology: Conventional radiation therapy to tomotherapy.

Breast conserving radiotherapy uses tangential fields and compensating wedges. This conventional approach can be improved by a field-in-field technique using the linac multi-leaf collimator (MLC). A simplified field-in-field technique that planners can easily achieve and which improves dose uniformity in the breast volume is presented here. Field junction problems are more easily solved by the use of a virtual simulation. A unique isocenter can be set at the junction between the supra-clavicular field and the breast tangential fields. However, careful quality assurance of the treatment planning system must be performed. Tomotherapy has promising clinical advantages: the ability of a tomographic image to correct for random set-up errors, a continuous cranio-caudal delivery which suppresses junction problems, the conformality of the dose distribution throughout the complex volumes formed by the lymph nodes and the breasts. Tomotherapy is a valuable recourse for complex irradiations like bilateral breast or mammary plus axillary irradiation while a field-in-field associated with a unique isocenter technique can be used for majority of the patients.

[French national evaluation for helicoidal tomotherapy: description of indications, dose constraints and set-up margins]. / Evaluation nationale de la tomothérapie hélicoïdale: description des indications, des contraintes de dose et des seuils de repositionnement.

After a request for proposal initiated by National Institute against cancer (INCa) in 2005, three French centers in France started tomotherapy in the first semester of 2007. A national policy of evaluation was performed to study the feasibility of this innovative technique and to compare the interest of helicoidal tomotherapy with other modalities of conformal therapy. Common protocols have been designed to facilitate this evaluation. Description of dose, IMRT levels and constraints are achieved according to each selected indication as: sarcoma, head and neck tumors, lung cancer, mesothelioma, bone metastases, anal carcinoma and craniospinal irradiation.

[Helical tomotherapy: general methodology for clinical and dosimetric evaluation (national French project)]. / Questions d'actualité: schéma général d'élaboration des protocoles de tomothérapie hélicoïdale pour chaque localisation.

The methodology and choice of criteria and indexes used for a common evaluation of helical tomotherapy by 3 French centres are described. After a selection of clinical indications and definition of the general purpose are successively described the criteria and index selected for: 1) description of volumes and adaptation for on board imaging; 2) dose prescription and constraints related to IMRT; 3) intercomparaison of volumes and doses and potential dosimetric gain with this new equipment.

[Results of treating uveal melanoma with proton beam radiation: 10-year follow-up]. / Résultats du traitement du mélanome malin de l'uvée par faisceau de protons: 10 ans de recul.

PURPOSE: We analyzed the long-term results of uveal melanoma treatment with proton beam irradiation in a series of patients with a follow-up of at least 10 years. PATIENTS AND METHODS: The patients were treated with proton beam radiation between September 1991 and December 1992. They had an initial examination including visual acuity, funduscopy, A and B scan ultrasonography of the eye, fundus photographs and fluorescein angiography. General examination included chest radiography and B scan ultrasonography of the liver. All tumors received a total dose of 60 cobalt-Gray equivalents (applied in four daily fractions) at the Orsay proton therapy center. RESULTS: A total of 167 patients were treated with a median follow-up of 116 months. Their median age was 59 years. Thirteen tumors were anterior to the equator, 76 overlapped the equator and 78 were posterior to the equator. An initial retinal detachment was present in 41 cases. The optic disk was invaded in 10 cases. The median tumor diameter was 12 mm and the median tumor thickness was 5.8 mm. The mean initial acuity was 20/50. The survival rate was 62.93% at 10 years; 72.9% of deaths resulted from metastasis. Statistically significant risk factors for death identified in the multivariate analysis were tumor diameter greater than 12 mm (p=0.0004) and age over 60 years (p=0.0001). The metastasis rate at 10 years was 31%. The liver was affected in 97.8% of these patients. Risk factors for metastasis were the anterior site of the tumor, its volume greater than 0.4 cc and the presence of retinal detachment at diagnosis. The secondary enucleation rate at 10 years was 13.23%, mainly attributable to secondary neovascular glaucoma. The local recurrence rate was 6%. The visual acuity rate in 42.1% of patients was better than 20/100 at 10 years. Visual loss was mainly due to postradiation maculopathy and neuropathy. CONCLUSION: Our study confirms the long-term results found in the literature on proton beam radiation. This therapy allows good tumor control, an excellent eye retention rate, and good final visual acuity for approximately half of the patients.

[Chordomas of the base of the skull and upper cervical spine. 100 patients irradiated by a 3D conformal technique combining photon and proton beams]. / Les chordomes de la base du crâne et du rachis cervical haut. A propos d'une série de 100 patients irradiés selon une technique conformationnelle 3D par une association de faisceaux de photons et de protons.

OBJECTIVE: To define prognostic factors for local control and survival in 100 consecutive patients treated by fractionated photon and proton radiation for chordoma of the skull base and upper cervical spine. PATIENTS AND METHODS: Between December 1995 and August 2002, 100 patients (median age: 53 years, range: 8-85, M/F sex-ratio: 3/2), were treated by a combination of high-energy photons and protons. The proton component was delivered by the 201 MeV proton beam of the Centre de Protonthérapie d'Orsay (CPO). The median total dose delivered to the gross tumour volume was 67 Cobalt Gray Equivalent (CGE) (range: 60-71). A complete surgery, incomplete surgery or a biopsy was performed before the radiotherapy in 16, 75 and 9 cases, respectively. RESULTS: With a median follow-up of 31 months (range: 1-87), 25 tumours failed locally. The 2 and 4-year local control rates were 86.3% (+/-3.9%) and 53.8% (+/-7.5%), respectively. According to multivariate analysis, less than 95% of the tumour volume encompassed by the 95% isodose line (P=0.048; RR: 3.4 IC95% [1.01-11.8]) and a minimal dose less than 56 CGE (p=0.042; RR: 2.3 IC95% [1.03-5.2]) were independent prognostic factors of local control. Ten patients died. The 2 and 5-year overall survival rates were 94.3% (+/-2.5%) and 80.5% (+/-7.2%). According to multivariate analysis, a controlled tumour (P=0.005; RR: 21 IC95% [2.2-200]) was the lonely independent favourable prognostic factor for overall survival. CONCLUSION: In chordomas of the skull base and upper cervical spine treated by surgical resection followed by high-dose photon and proton irradiation, local control is mainly dependent on the quality of radiation, especially dose-uniformity within the gross tumour volume. Special attention must be paid to minimise underdosed areas due to the close proximity of critical structures and possibly escalate dose-constraints to tumour targets in future studies, in view of the low toxicity observed to date.

The sliding slit test for dynamic IMRT: a useful tool for adjustment of MLC related parameters.

For treatments with dynamic intensity modulated radiotherapy (IMRT), the adjustment of multileaf collimator (MLC) parameters affecting both the optimization algorithm and dose distributions is crucial. The main parameters characterizing the MLC are the transmission (T) and the dosimetric leaf separation (DLS). The aim of this study is twofold: a methodology based on the 'sliding slit' test is proposed to determine (T, DLS) combinations inducing the best conformity between calculations and measurements. Secondly, the effects of the MLC adjustment on measured dose and on optimization are presented for different configurations as the chair test and for the patient dosimetric quality control (DQC). Tests were performed with a Varian 23EX linac operated at 20 MV and equipped with a 120 leaf Millenium dynamic collimator. The treatment planning system was CadPlan/Helios (version 6.3.6). Results demonstrated that the sliding width (SW) strongly depends on the (T, DLS) combinations, and the measured dose is a linear function of the SW. Different (T, DLS) combinations induced a good agreement between calculations and measurements. The influence of the MLC calibration was found to be particularly important on the 'sliding slit' test (11.8% for a gap change of 0.8 mm) but not so much on the chair test and on the DQC. To detect small variations in leaf adjustment and to ensure consistency between calculation and actual dose delivered to patients, a daily check called IMRT MU check is proposed.

125I plaque brachytherapy for anterior uveal melanomas.

PURPOSE: To describe the results of 125I plaque brachytherapy of uveal melanomas anterior to the equator in terms of local control and the associated complications while trying to identify their risk factors (patients' demographic data, ocular, and tumour characteristics). METHODS: Retrospective analysis of a series of patients treated by 125I between 1990 and 2000 in a single institution. The main outcome measures are evaluation of local tumour control and complications associated with 125I plaque brachytherapy of these melanomas. RESULTS: During the study period, 136 patients were treated for an anterior tumour. The median follow-up was 62 months. The overall 5-year survival rate was 88.3%, the 5-year metastasis rate was 4% and the local recurrence rate was 1.5%. The mean final visual acuity was 20/40. The ocular complications most frequently observed at 5 years were cataract (50.3%), maculopathy (18.3%), intraocular inflammation (19.3%), and glaucoma (10.6%). Optic neuropathy, retinal detachment, keratitis, and intravitreous haemorrhage were also described. Risk factors for worse survival were age greater than 65 years and initial tumour thickness greater than 4 mm. Risk factors for the development of cataract were age more than 65 years old, male gender, and tumour diameter of more than 10 mm. Risk factors for intraocular inflammation were tumour thickness of more than 4 mm and invasion of the ciliary body. CONCLUSIONS: The use of 125I plaque brachytherapy to treat melanomas situated anterior to the equator allows good local and systemic control with a low rate of macular and optic disc complications. The most frequent complication was cataract formation.