Search

Purpose For determining small‐field profile and output factor during stereotactic radiotherapy quality assurance (QA) procedures, we propose a novel system based on the scintillating fiber (SciFi) detector with output image acquisition and processing to allow real‐time monitoring of profile and output factor. Materials and methods The employed detector is a SciFi detector made of tissue‐equivalent scintillating plastic fibers arranged in 6‐layer fiber ribbons with a fiber pitch of 275 μm in each layer. The scintillating signal at the detector output is acquired by a sCMOS (scientific complementary metal–oxide–semiconductor) camera and represents the projected field profile along the fibers axis. An iterative reconstruction method of the field from its projected profile based on a priori knowledge of some features of the radiation field defined by the stereotactic cones is suggested. The detector with implemented data processing has been tested in clinical conditions, for determining beam profiles and output factors, using cone collimators of different sizes from 4 to 15 mm diameter. The detector under test was placed at 1.4 cm depth and 98.6 cm source to surface distance (SSD) in a water‐equivalent phantom and irradiated by a 6 MV photon beam. Results The reconstructed field profiles obtained from the detector are coherent with data from EBT3 radiochromic films, with differences within ±0.32 mm for both the FWHM and the penumbra region. For real‐time determination of the field output factor, the measured data are also in good agreement with data independently determined by the French Institute for Radiological Protection and Nuclear Safety (IRSN) based on radiochromic films and thermoluminescent 1 × 1 mm2 micro‐cubes dosimeters (TLD). The differences are within ±1.6% for all the tested cone sizes. Conclusions We propose and have tested a SciFi plastic scintillating detector with an optimized signal processing method to characterize small fields defined by cone collimators. It allows the determination of key field parameters such as full width at half maximum (FWHM) and field output factors. The results are consistent with those independently measured using TLD and radiochromic films. As the SciFi detector does not require a correction factor, it is in line with the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) TRS‐483 recommendations, and can be suitable for online QA of small radiation fields used in photon beam radiotherapy, and is compatible with MRI‐LINAC.

Introduction Extravasation of radiopharmaceuticals used for therapy purpose, such as Lu-177 ( E β Max = 498 keV, E γ = 113 keV (6%) and 208 keV (10%), T = 6.6 days) can lead to severe tissue damage [1] . In September 2017, an extravasation occurred in the arm of a patient during a 7.4 GBq perfusion of lutathera ® (AAA). Methods Four whole body (WB) acquisitions were performed at 2 h, 5 h, 20 h and 26 h after the beginning of the perfusion (H0). Three SPECT/CT were performed following the WB acquisitions at 5 h, 20 h and 26 h. Images were acquired with a Symbia T2® camera (Siemens Healthcare) with a MELP collimator, a main window around 208 keV, 20 cm/min for the WB acquisition and 2x30 projections of 30s for the SPECT acquisition. A local quantification procedure developed for renal dosimetry and based on a calibration factor was used, with the following parameters: FLASH 3D®, 10 iterations, 10 subsets, CT-based attenuation correction, scatter correction and 4 mm FWHM Gaussian filtering. Effective period was determined on the geometric mean of whole body images. Given the complexity of subcutaneous tissue contouring, 3 volumes (V1 = 180, V2 = 400 et V3 = 1000 mL) were defined on SPECT images using a 3D threshold. Cumulated activities and associated doses (D1, D2, D3) were calculated in the 3 volumes using a conversion factor ξ = 0.0024 mGy.g/(MBq.s), from the website RADAR [2] . Results Estimated effective periods were 11 h in the whole body and 3 h in the arm. As SPECT images at H0 + 2 h were not available, activity at H0 + 2 h was evaluated using estimated activity from SPECT images at H0 + 5 h and a ratio of the number of counts in a ROI around the arm on geometric mean of WB images at H0 + 2 h and at H0 + 5 h. Cumulated activities were evaluated using a mono exponential fit on activities calculated on SPECT images. Estimated doses in V1, V2 and V3 were D1 = 7.8 Gy, D2 = 5.4 Gy and D3 = 2.8 Gy. Conclusions Estimated doses values are in the range of deterministic effects. However, the patient did not show any clinical sign of the irradiation. Elimination of the product was quick in the arm (Teff = 3 h) and was promoted by specific interventions (warming, repeated massages around the injection site).

Solid-state dosimetry employs highly sensitive semiconductors such as Gallium Nitride (GaN) and Silicon (Si), but they have a common drawback of over response compared to tissues for low-energy scattered photons, which induces inacceptable errors for radiotherapy application. To tackle this issue, we propose a compensation method consisting in using two different materials of dosimetric interest with different atomic numbers. Their responses are denoted as SC1 and SC2. The response ratio SC1/water as a function of the ratio SC1/SC2 exhibits a monotonic curve that can serve as reference to compensate the over-response of SC1. To validate this method, we have studied the dosimetric response of GaN (0.1 mm3) and Si crystals (2.5 mm3) by simulations, using a validated model based on the general cavity theory in a homogeneous water phantom. The dosimetric response of GaN and Si calculated using the model has errors within 2.5% compared to measured data. The local fluence spectra have been obtained by convolution of pencil beam kernel built by Monte Carlo simulations for different clinical irradiation conditions with field size (from 5×5 cm2up to 20×20 cm2) at depth in the phantom (from 2 cm to 25 cm). The obtained results confirm a monotone relationship between GaN/water dose ratio and GaN/Si dose ratio. The reference curve is independent of irradiation conditions (field size, dosimeter position...), and allows determination of compensation value by identification.

Purpose Gold markers are frequently used for a better daily repositioning of the prostate before irradiation. The purpose of this work was to analyze if the combination of an androgen deprivation with the external irradiation could modify the position of the gold markers in the prostate. Patients and methods Ten patients have been treated for a prostate cancer, using three implanted gold markers. The variations of the intermarker distances in the prostate were measured and collected on daily OBI® kilovoltage images acquired at 0° and 90°. Five patients had a 6-month androgen deprivation started before the external irradiation (H group) and five did not (NH group). Results A total number of 1062 distances were calculated. No distance variation greater than 3.7 mm was seen between two markers, in any of the two groups. The median standard deviations of the daily intermarker distance differences were 0.7 mm (range 0.3–1.2 mm) for the H group and 0.6 mm (range 0.2–1.2 mm) for the NH group. The intermarker distances variations were noted as greater than –2 mm, between –2 mm and 2 mm and greater than 2 mm in 16.4, 83.4 and 0.2% for the H group and 1.3, 98.5 and 0.2% for the NH group, respectively. Conclusion The distance variations remained less than 4 mm in both groups and for all the measurements. In the NH group, the variation of the distance between two markers remained below 2 mm in 98.5%. In the H group, the presence of a reduction of distance above 2 mm in 16.4% of measurements could indicate the shrinkage of the prostate volume.

International audience

High dose rate brachytherapy (HDR-BT) is widely used to treat gynecologic, anal, prostate, head, neck, and breast cancers. These treatments are typically administered in large dose per fraction (5 Gy) and with high-gradient-dose-distributions, with serious consequences in case of a treatment delivery error (e.g., on dwell position and dwell time). Thus, quality assurance (QA) or quality control (QC) should be systematically and independently implemented. This paper describes the design and testing of a phantom and an instrumented gynecological applicator for pretreatment QA and in vivo QC, respectively.The authors have designed a HDR-BT phantom equipped with four GaN-based dosimeters. The authors have also instrumented a commercial multichannel HDR-BT gynecological applicator by rigid incorporation of four GaN-based dosimeters in four channels. Specific methods based on the four GaN dosimeter responses are proposed for accurate determination of dwell time and dwell position inside phantom or applicator. The phantom and the applicator have been tested for HDR-BT QA in routine over two different periods: 29 and 15 days, respectively. Measurements in dwell position and time are compared to the treatment plan. A modified position-time gamma index is used to monitor the quality of treatment delivery.The HDR-BT phantom and the instrumented applicator have been used to determine more than 900 dwell positions over the different testing periods. The errors between the planned and measured dwell positions are 0.11 ± 0.70 mm (1σ) and 0.01 ± 0.42 mm (1σ), with the phantom and the applicator, respectively. The dwell time errors for these positions do not exhibit significant bias, with a standard deviation of less than 100 ms for both systems. The modified position-time gamma index sets a threshold, determining whether the treatment run passes or fails. The error detectability of their systems has been evaluated through tests on intentionally introduced error protocols. With a detection threshold of 0.7 mm, the error detection rate on dwell position is 22% at 0.5 mm, 96% at 1 mm, and 100% at and beyond 1.5 mm. On dwell time with a dwell time threshold of 0.1 s, it is 90% at 0.2 s and 100% at and beyond 0.3 s.The proposed HDR-BT phantom and instrumented applicator have been tested and their main characteristics have been evaluated. These systems perform unsupervised measurements and analysis without prior treatment plan information. They allow independent verification of dwell position and time with accuracy of measurements comparable with other similar systems reported in the literature.

Background and purpose During the irradiation of the prostate cancer, it is crucial to take into account the possible displacements in defining the planning target volume. The objective of this study was to specifically analyze the respiratory-induced prostate motion using a four-dimensional CT scan (4DCT). Materials and methods Ten patients have been treated for prostate cancer in the supine position and with three implanted gold markers; they underwent a 4DCT using a GE LightSpeed16® CT scan (slice thickness 2.5 mm). This acquisition was divided into 10 phases over the respiratory cycle using the Advantage4D software. For each phase, digitally-reconstructed radiographs (DRRs) were created at 0° and 90° with the view of the markers. The coordinates of each marker center were generated from the scan isocenter. The motion amplitude was: visually analyzed on the dynamic 4DCT sequences and then more precisely calculated by comparing the marker coordinates on the 10 scans. Results There was not any difficulty in defining the coordinates of the markers on each series. No prostate motion was observed on a simple visual analysis of the dynamic 4DCT sequences. After a more specific analysis, using the coordinates of the fiducials on the 10 phases, the prostate motion remained below 1 mm in all directions, except for the cranio-caudal, where it was undetectable (thereby below the slice thickness of 2.5 mm). Conclusions To our knowledge, this is the first study that evaluates the respiratory-induced prostate motion, using a 4DCT scan. Even if important prostate displacement can occur during the prostate treatment, because of the bladder or rectum filling, in the present study no respiratory-induced prostate motion was observed.

Purpose Investigate whether the use of non coplanar fields and intensity modulated radiation therapy (IMRT) reduces the dose to the heart, in irradiation of middle and lower lung tumors. Materials and methods Four plans are compared on 10 CT scans: (1) a reference plan, corresponding to coplanar plan of 3D conformal radiotherapy (3DCRT); (2) a 3DCRTnoncopl plan, differing from reference plan by the change of one field in non coplanar fields; (3) an IMRTcopl plan optimized on the same coplanar plan as reference plan; and (4) an IMRTnoncopl plan optimized on the same non coplanar beams as 3DCRTnoncopl plan. The equivalent uniform dose (EUD) for PTV was 74 Gy in 37 fractions. Results In all plans, the 95% isodose surface covers at least 99% of the PTV with very similar conformity index values. A significant reduction in EUD, V30, V40 and V50 is observed for heart when either non coplanar fields or IMRT is used. IMRT also reduces the lung NTCP, V5, V13, V20 and V30 values and esophagus NTCP. Conclusion Both the use of non coplanar fields and IMRT dramatically reduces the dose received by the heart. The largest benefit is seen when the two techniques are combined.

Objectifs Le traitement a l’aide d’iode 131 est une arme therapeutique de choix pour les patients souffrant de cancer thyroidien. Dans l’unite de therapie du centre de medecine nucleaire du GHE des Hospices Civils de Lyon, le personnel soignant subit une exposition externe a proximite des patients. La contamination interne est egalement presente, des radiotoxicologies des urines sont ponctuellement positives pour une partie du personnel. L’analyse des risques de contamination par le personnel dans le secteur de therapie par radionucleides repose sur des donnees publiees (Ibis et al. JNM 1992;33:2110). L’objectif de cette etude est de reevaluer et completer ces donnees publiees pour constituer une base de donnees locale et actualisee de valeurs de contamination atmospherique et surfacique. Materiels et methodes L’etude porte sur 12 patients ayant recu 3,7 GBq : 6 patients hospitalises 3 jours ayant recu une stimulation par TSHr et 6 patients hospitalises 5 jours en sevrage d’hormone thyroidienne. Les mesures sont realisees a 4, 24 et 48 heures apres la prise d’iode. Des frottis cutanes sur les mains et le front des patients sont realises. Des prelevements salivaires sont effectues grâce a un dispositif dedie (Salivette © ). La contamination atmospherique dans les chambres est mesuree par des prelevements sur filtre a charbon actif. La contamination des sols est evaluee en fin de sejour en mesurant les bandeaux de lavage. On realise egalement des mesures de debit de dose. Les prelevements sont mesures soit par un activimetre « puit » soit par un spectrometre gamma germanium. Resultats Le debit de dose moyen a 1 m est de 133 μSv/h a t = 4 h. Il est inferieur a 14 μSv/h a t = 48 h. La contamination de l’air est en moyenne de 184 Bq/m 3 a t = 4 h et 25 Bq/m 3 a t = 48 h. Dans la salive, la concentration moyenne est de 8 MBq/g de salive a t = 4 h et 0,6 MBq/g a t = 48 h. Au niveau de la peau, les activites sont plus importantes sur les mains que sur le front. On mesure en moyenne aux mains 81 Bq/cm 2 a t = 4 h et 22 Bq/cm 2 a t = 48 h. Au niveau du sol de la chambre, on mesure une activite surfacique moyenne de 0,5 Bq/cm 2 en fin de sejour. Hormis pour la salive, les mesures sont proches dans les deux groupes. Il y a de grandes variabilites d’un patient a l’autre qui peuvent s’expliquer par des differences physiologiques d’excretion mais aussi par l’application inegale des consignes d’hygiene. Conclusions L’etude confirme des niveaux importants d’iode dans la salive. Les contaminations atmospheriques mesurees, dont l’impact dosimetrique reste tres faible par rapport a l’exposition externe du au patient, peuvent expliquer les faibles et ponctuelles contaminations internes du personnel. Limiter les entrees dans la chambre pendant les premieres 24 h et faire appliquer strictement les consignes.

Introduction The stereotactic irradiation is a new approach for low-risk prostate cancer. The aim of the present study was to evaluate a schema of stereotactic irradiation of the prostate with an integrated-boost into the tumor. Material and methods The prostate and the tumor were delineated by a radiologist on CT/MRI fusion. A 9-coplanar fields IMRT plan was optimized with three different dose levels: 1) 5 × 6.5 Gy to the PTV1 (plan 1), 2) 5 × 8 Gy to the PTV1 (plan 2) and 3) 5 × 6.5 Gy on the PTV1 with 5 × 8 Gy on the PTV2 (plan 3). The maximum dose (MaxD), mean dose (MD) and doses received by 2% (D2), 5% (D5), 10% (D10) and 25% (D25) of the rectum and bladder walls were used to compare the 3 IMRT plans. Results A dose escalation to entire prostate from 6.5 Gy to 8 Gy increased the rectum MD, MaxD, D2, D5, D10 and D25 by 3.75 Gy, 8.42 Gy, 7.88 Gy, 7.36 Gy, 6.67 Gy and 5.54 Gy. Similar results were observed for the bladder with 1.72 Gy, 8.28 Gy, 7.01 Gy, 5.69 Gy, 4.36 Gy and 2.42 Gy for the same dosimetric parameters. An integrated SBRT boost only to PTV2 reduced by about 50% the dose difference for rectum and bladder compared to a homogenous prostate dose escalation. Thereby, the MD, D2, D5, D10 and D25 for rectum were increased by 1.51 Gy, 4.24 Gy, 3.08 Gy, 2.84 Gy and 2.37 Gy in plan 3 compared to plan 1. Conclusions The present planning study of an integrated SBRT boost limits the doses received by the rectum and bladder if compared to a whole prostate dose escalation for SBRT approach.

Objectif de l’etude L’objectif principal de cette etude de phase II etait d’evaluer la toxicite rectale tardive (de grade 2 ou plus) a 3 ans d’une radiotherapie hypofractionnee de la prostate apres injection d’acide hyaluronique. Materiel et methode Entre 2010 et 2012, 36 patients atteints d’un cancer de prostate ont recu une radiotherapie conformationnelle avec modulation d’intensite (RCMI) guidee par l’image de 20 fractions de 3,1 Gy apres injection transperineale de 10 cm3 d’acide hyaluronique entre la prostate et le rectum. Trois grains d’or ont ete implantes dans la prostate pour une fusion scanographie/IRM et un repositionnement journalier. La toxicite tardive a ete definie comme survenant au moins 3 mois apres la fin du traitement. Elle a ete evaluee tous les 3 mois jusqu’a 3 ans de suivi en utilisant la Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. Les caracteristiques tumorales etaient : concentration mediane d’antigene specifique de la prostate ([PSA]) egale a 7,32 ng/mL ; stade T1 dans 50 % des cas et T2 dans 50 % ; score de Gleason de 6 egal dans 61 % des cas et 7 dans 39 %. Un patient a ete retire de l’etude avant de debuter sa radiotherapie hypofractionnee et n’a pas ete compte dans les analyses. Trois patients ont quitte l’etude (1 a 3 mois et 2 apres 30 mois), leurs donnees ont ete conservees. Resultats L’injection d’acide hyaluronique a ete tres bien toleree, sans douleur ni inconfort pendant le suivi. Aucune toxicite tardive de grade 3–4 n’a ete observee. Des cas de toxicite digestive de grade 2 sont survenus : trois rectorragies et une diarrhee. Aucune ne persistait a 3 ans de suivi. Le taux de toxicite urinaire tardive de grade 2 etait de 41 % (dysuries et pollakiuries). A 36 mois, quatre patients gardaient une toxicite urinaire de grade 2. Le taux de recidive biochimique (nadir + 2 ng/mL) etait de 6 %. Conclusion Apres une injection d’acide hyaluronique, l’irradiation hypofractionnee de quatre semaines a ete tres bien toleree, sans toxicite rectale de grade 3 et avec un taux de rectorragies de grade 2 de moins de 10 %, ne persistant pas a 3 ans de suivi. La toxicite urinaire tardive etait la plus frequente, mais le taux diminuait a 3 ans.

Objectif de l’etude La preservation sexuelle est une question importante dans le traitement des cancers localises de la prostate. Une technique d’irradiation visant a preserver la fonction erectile a ete mise au point et est evaluee. Materiel et methode Entre 2010 et 2014, 13 patients sans dysfonction erectile initiale ont ete pris en charge par RCMI guidee par l’image a des doses entre 74 et 78 Gy pour un cancer de la prostate localise de risque faible a intermediaire. Trois grains d’or ont ete implantes pour une fusion scanographie/IRM et le repositionnement journalier. Une optimisation de dose a ete realisee sur les deux arteres pudendales, le bulbe penien et le corps caverneux (plus une marge de 5 mm) afin d’obtenir les doses les plus basses possible. La fonction erectile a ete evaluee avec le questionnaire index of erectile function (IIEF5) avant la radiotherapie, a 6, 12 et 24 mois. L’absence de dysfonction erectile a ete definie par un IIEF5 ≥ 20/25, une dysfonction erectile legere par un score entre 17–19 et une dysfonction erectile importante par un score Resultats La moyenne d’âge etait de 69,2 ans. A la date d’analyse, aucun patient n’a ete atteint de recidive biochimique. Le score IIEF5 moyen etait de 23,4 [20–25] avant le traitement, 19,5 [5–25] a 6 mois, 18,8 [5–25] a 1 an et 20,3 [6–25] a 2 ans. A 2 ans, huit patients (61,5 %) n’avaient pas de dysfonction erectile et deux (13,3 %) une dysfonction erectile legere. Seulement trois patients souffraient d’une dysfonction erectile importante, dont deux ont pu recouvrir une bonne fonction sous sidenafil (scores de 22 et 24). Conclusion Les premiers resultats avec cette technique d’optimisation visant a preserver la fonction sexuelle sont encourageants. Malgre une moyenne d’âge de 70 ans, 75 % des patients n’avaient pas de dysfonction erectile importante a 2 ans. Ce taux augmentait a 92 % apres traitement medical.

International audience

Objectifs Un rapport α/β de moins de 3 Gy pour les cancers de la prostate encouragerait des schemas de radiotherapie hypofractionnee. Cependant, leurs developpements ne pourront se faire que si la toxicite rectale est parfaitement maitrisee. Une injection d’acide hyaluronique a ete associee a une irradiation hypofractionnee pour proteger le rectum. La tolerance de l’injection ainsi que la toxicite aigue sont rapportees. Patients et methodes De 2010 a 2012, 36 patients atteints d’un cancer de prostate de risque faible a intermediaire ont ete inclus dans une etude de phase II multicentrique. Une injection transperineale de 10 cm 3 d’acide hyaluronique (NASHA Spacer gel, Q-Med AB, Uppsala, Suede) a ete realisee entre le rectum et la prostate. Une technique de radiotherapie conformationnelle avec modulation d’intensite (RCMI) guidee par l’image a ete utilisee pour delivrer 62 Gy en 20 fractions de 3,1 Gy (dose biologique equivalente, BED = 84 Gy ; α/β = 1,5 Gy) et 4 semaines. La toxicite aigue a ete evaluee selon la Common Terminology Criteria for Adverse Events v4.0. La tolerance de l’injection d’acide hyaluronique l’a ete par une echelle visuelle analogique (EVA). Resultat L’injection d’acide hyaluronique a induit une douleur moyennes de 4,6/10 ± 2,3 sur l’echelle EVA. Aucune douleur ne persistait au cours du suivi. Un patient a ete atteint dans les suites de l’injection d’un hematome en arriere de la vessie, traite par chirurgie. Vingt patients ont souffert d’ une toxicite urinaire de grade 2 (dysurie et/ou pollakiurie). Aucune toxicite urinaire de grade 3 ou 4 n’a ete observee. Seulement un patient a souffert d’une toxicite rectale de grade 2 (syndrome rectal). A 3 mois de suivi, il persistait chez quatre patients une toxicite urinaire de grade 2. Aucune toxicite rectale de grade 2 n’a ete notee. Conclusion L’injection d’acide hyaluronique est faisable et bien toleree. L’hematome observe souligne l’importance de bien selectionner des patients sans aucun trouble de la coagulation. Cette injection assure une parfaite tolerance rectale d’un schema hypofractionne en quatre semaines avec des doses par fraction de plus de 3 Gy.

Introduction Delta4 device is designed for three-dimensional dose verification and shows excellent reproducibility, linearity and doserate independence. The purpose of this work was to verify the sensitivity of the Delta4 (ScandiDos) for small MLC and gantry errors in intensity modulated radiotherapy (IMRT). Materials and methods Ten IMRT plans (5 prostate and 5 head and neck) were used. Systematic MLC errors of (–0.2), (–0.5), (–0.7), (–1), (–2), (–3), (–5) and (–10) mm, were introduced for one leaf. Gantry errors of 0.2°, 0.5°, 0.7°, 1°, 2°, 2.5°, 3°, 4° and 5° were introduced for the same plans. The Delta4 system was used to acquire and analyze the data. All the measurements were acquired consecutively for each patient. To eliminate the repeatability errors, standard deviations (SD) of the maximum gamma (Gmax) were calculated for 10 successively beams with no offsets. Gmax values were noted for both global gamma (normalization dose) and local gamma (local detector dose) with pass/fail criteria of 2%/2 mm. Gmax was evaluated for each modified field when compared to the measured field with no introduced error (0 mm or 0°). Because we had a single leaf with a small offset we evaluated only the Gmax and not the mean gamma or the percentage of area gamma Results For local gamma evaluation (LGE), the maximum SD for Gmax was of 0.06. For global gamma evaluation (GGE), the maximum SD was of 0.02. The MLC and gantry offsets had a noticeable impact on the plan evaluation. For all the ten plans modifications in Gmax were observed starting with 0.2 mm (from 0.2 to 4.75 for LGE and from 0.13 to 2.45 for GGE) for MLC plans and with 0.2° for the gantry errors (from 0.54 to 9.23 for LGE and from 0.37 to 4.71 for GGE). Conclusion The Delta4 system seems to be a very sensitive instrument for the quality assurance of IMRT plans. In our study it detected submilimetric and subdegree errors for MLC and gantry, respectively. In clinical use these small errors may not be detected and could be hidden by the residual error between planned and delivered dose.

Introduction For the stereotactic irradiation it is highly recommended to use a great number of fields to improve the conformity of the dose to the target and to reduce the entrance dose to the patient. The purpose of this study was to evaluate the impact of the number of fields on a SBRT delivery for prostate cancer (5 × 6.5 Gy) with a simultaneous integrated boost (SIB) into the tumor (5 × 8Gy). Materials and Methods The SBRT-IMRT simulations were made for nine patients with three different non-coplanar-beam conformations: 7-fields (Plan1), 9-fields (Plan2) and 11-fields (Plan3). For all three plans there were used the same optimization values and a number of 300 iterations. The comparison between plans was made using three conformity indexes (CI): RTOG, Lomax and SALT, the gradient index (dose fall-off) and the homogeneity index, as well as the dose-volume histogram (DVH) values for rectum and bladder. The gradient index was calculated only for the PTVprostate and the homogeneity index only for the PTVtumor, as a consequence of the influence of the SIB dose gradient. Results With similar coverage of the prescription isodose the dose conformity was comparable between the three plans. For example, for the PTVprostate, the CIRTOG was 1.28 [1.17–1.4], 1.26 [1.17– 1.38] and 1.27 [1.16–1.39] for Plan 1, 2 and 3, respectively. For the PTVtumor, the CIRTOG was 1.57 [1.33–1.81], 1.52 [1.33–1.7] and 1.51 [1.28–1.7] for the same plans. The average gradient index was 3.8 [3.5–4.4], 3.7 [3.6–4] and 3.8 [3.5–4.1] for Plans 1, 2 and 3, respectively. The average doses received by 2 cc, 5 cc and 10 cc of the rectum-wall were 33.7 Gy, 25.8 Gy and 16.7 Gy for Plan1, 33.2 Gy, 24.7 Gy and 15.8 Gy for Plan2 and 33.1 Gy, 24.5 Gy and 15.1 Gy for Plan3. Similarly, the average doses received by the bladder-wall were 28.9 Gy, 21.5 Gy and 13.9 Gy for Plan1, 28.8 Gy, 21.3 Gy and 13.6 Gy for Plan2 and 28.7 Gy, 21.1 Gy and 13.5 Gy for Plan3. Conclusion There wasn't established any impact of the number of beams on the dosimetric parameters, conformity, gradient, or homogeneity indexes of the present prostate SBRT schema with a SIB.

Introduction The Delta4 system (ScandiDos) is dedicated for quality assurance (QA) of treatment delivery and is an independent-unit from the accelerator. The purpose of this work was to evaluate the impact of the irradiation geometry on the QA for prostate SBRT using the Delta4 device. Materials and methods The prostate and the tumor were delineated by a radiologist on CT/MRI registrations of 5 patients. As part of a protocol, a 9-coplanar fields IMRT plan was optimized following a schema of prostate SBRT (5 × 6.5 Gy) with a simultaneous integrated boost into the tumor (5 × 8Gy). All the beams were verified four times consecutively using Delta4, with the gantry at: (a) 0° (Plan B0), (b) 90° (B90), (c) 315° (B315) and (d) at their original angulations (242°, 270°, 297°, 328°, 0°, 38°, 76°, 101°, 127°), named BFbyF (field-by-field). The plans B90, B315 and BFbyF were compared with B0 using two evaluation indexes (global gamma index (GGI) and local gamma index (LGI)) as differences of: percentage of detectors with gamma Results For GGI, the average differences ± SD in ‘‘%G Conclusion Usually the IMRT plan verification is made using all beams with gantry at 0_. However, it is important to verify the irradiation plans in the exact situation as at the time of treatment. We have showed here that there is an important difference in the evaluation of a stereotactic IMRT plan as it depends of the irradiation condition. These differences could be explained by the impact of the MLC weight and the couch attenuation. Therefore, it can be recommended that the IMRT verification is made with a detector independent from the accelerator and in the exact configuration of the irradiation as at the time of the treatment (gantry angle and couch position).

Introduction The aim of this work was to evaluate two delivery techniques for prostate irradiation: RapidArc (Varian) and HybridArc (Brainlab). Materials and methods HybridArc (HA) is a recent treatment technique which may combine optimized dynamic conformal arc (DCA) therapy with fixed port IMRT. RapidArc (RA) generates IMRT-quality dose distributions in one or two optimized arcs around the patient, being capable to deliver continuously modulated dose to the entire tumor volume while sparing healthy tissue. Seven patients were treated with RA with a total prescribed dose of 76 Gy. The dose to the PTV1 (prostate + seminal vesicles) was of 46 Gy and the dose to the PTV2 (prostate) was of 30 Gy. Two arcs were created for RA (130–230° and inversely) and one aperture-arc was optimized for HA with a gantry start-stop from 240–120° combined with 5-IMRT beams equally distributed over the arc. The weighting of the HA arcs were adjusted to 60%-DCA and 40%-IMRT. The PTV had to be covered by the 95% isodoseline in both plans. The two plans were compared using the conformal index (CI) for healthy tissue and the dose-volume histogram parameters. For the rectum, the volume that receives 60 Gy (V60), 74 Gy (V74) and the maximum dose (Dmax) were noted. Similarly, the values for the bladder (V60 and Dmax) and the femoral heads (Dmax) were reported. Results The average [range] V95% for PTV1 was 99.6%[97.5–100%] and 99.7%[98.2–100%] and for PTV2 was 98.2%[95–99.9%] and 99.7[99.3–100%], for RA and HA, respectively. The CI average and range values for PTV1 were 0.9[0.8–1] and 0.8[0.8–.0.9] and for PTV2 were 0.9[0.9–1] and 0.8[0.8–0.9] for RA and HA, respectively. For the rectum, the average V74Gy were 3.5%[1.6–7.5%] and 6.9%[1.5–13.7%] for RA and HA, respectively. For the bladder, the average V60Gy were 21.2%[9–38%] and 24.2%[10.9–38.9%] for the same plans. Conclusions In our experience, RapidArc and HybridArc produced similar plans for PTV coverage. There was a significant difference between the two plans for rectum V74Gy (p = 0.02) and bladder V60Gy (p = 0.001) in favour of RA. Additionally, 5 hypophysis cases will be presented at the time of the meeting.

202 Background: Several studies are in favor of an α/β ratio of less than 3Gy for prostate (P) cancer, encouraging HFR. However, the development of such radiation patterns can only be done if the risk of rectal toxicity is well controlled. The objective of the present study was to evaluate the contribution of an injection of HA between the rectum and the P to reduce the risk of rectal toxicity in a HFR approach. Methods: A phase II study of HFR at 62Gy in 20 fractions (BED = 84Gy; α / β = 1.5Gy) is currently conducted. A transperineal injection of 10cc of HA (NASHA Spacer gel, Q-Med AB, Uppsala, Sweden) is systematically performed, between the rectum and the P, under local anesthesia and under ultrasound guidance. A dosimetric CT scan is performed before (CT1) and after injection (CT2). Patients are treated with a 7 beams IMRT plan, optimized on the CT2. For the first 10 patients included in the study, the same treatment plan was optimized on CT1. The rectum was empty on the 2 CTs and defined from 2cm above the seminal vesicles to 2 cm below the P. The rectal wall was defined by an internal expansion of 5 mm. The volumes of rectum irradiated, with and without HA, were compared on the following dosimetric parameters: maximum dose (D max), dose to 2.5cc (D2.5), 5cc (D5) and 10cc (D10) of rectal wall and volume of rectum receiving 90% (V90), 80% (V80) and 70% (V70) of the prescribed dose of 62Gy. To limit a potential impact of variation of rectal volume between the two CT, all results are given in cc and not in % of volume. Results: The mean P volume was 52.4cc (30cc - 93.8cc) on the CT1 and 52cc (32.5 - 92.7) on the CT2. The injection of HA reduced the mean D max value to the rectal wall of 4.5Gy (57.5Gy vs 62 Gy). The mean values of V90, V80, and V70 are reduced by 69% (1.9cc vs 6.1cc), 46% (4.5cc vs 8.4cc) and 32% (7.4cc vs 10.9cc). Same way, the average values of D2.5, D5 and D10 are reduced by 6.2 Gy (54.6Gy vs 60.8Gy) 9.3Gy (49.0Gy vs 58.3Gy) and 7.8Gy (39.7Gy vs 47.5Gy). Conclusions: In this study, the injection of HA limited the doses to the rectal wall. These results suggest that late toxicities could be significantly reduced. A phase II study is underway to assess the rate of late rectal toxicities when a HFR at 62Gy in 20 fractions is combined with an injection of HA.

respectively in 50%, 33.3%,10%,and 6%ofall the measurements (10 pts x 3 distances). The average reductions ofdistance between thetwomarkersM1M2,M2M3,andM1M3were1.26mm(0.2-3.3mm),1.26mm(0-3.1mm)and1.25mm(0.4-3mm),respectively. Conclusions: The constant reduction of the distances between the 3 markers is more likely in favor of a reduction of the prostate volume during irradiation than a migration of the makers. This reduction of distances remained very low and should not affect the accuracy of the prostate repositioning.