Clinical application of a GPU-accelerated monte carlo dose verification for cyberknife M6 with Iris collimator.

PURPOSE: To apply an independent GPU-accelerated Monte Carlo (MC) dose verification for CyberKnife M6 with Iris collimator and evaluate the dose calculation accuracy of RayTracing (TPS-RT) algorithm and Monte Carlo (TPS-MC) algorithm in the Precision treatment planning system (TPS). METHODS: GPU-accelerated MC algorithm (ArcherQA-CK) was integrated into a commercial dose verification system, ArcherQA, to implement the patient-specific quality assurance in the CyberKnife M6 system. 30 clinical cases (10 cases in head, and 10 cases in chest, and 10 cases in abdomen) were collected in this study. For each case, three different dose calculation methods (TPS-MC, TPS-RT and ArcherQA-CK) were implemented based on the same treatment plan and compared with each other. For evaluation, the 3D global gamma analysis and dose parameters of the target volume and organs at risk (OARs) were analyzed comparatively. RESULTS: For gamma pass rates at the criterion of 2%/2 mm, the results were over 98.0% for TPS-MC vs.TPS-RT, TPS-MC vs. ArcherQA-CK and TPS-RT vs. ArcherQA-CK in head cases, 84.9% for TPS-MC vs.TPS-RT, 98.0% for TPS-MC vs. ArcherQA-CK and 83.3% for TPS-RT vs. ArcherQA-CK in chest cases, 98.2% for TPS-MC vs.TPS-RT, 99.4% for TPS-MC vs. ArcherQA-CK and 94.5% for TPS-RT vs. ArcherQA-CK in abdomen cases. For dose parameters of planning target volume (PTV) in chest cases, the deviations of TPS-RT vs. TPS-MC and ArcherQA-CK vs. TPS-MC had significant difference (P < 0.01), and the deviations of TPS-RT vs. TPS-MC and TPS-RT vs. ArcherQA-CK were similar (P > 0.05). ArcherQA-CK had less calculation time compared with TPS-MC (1.66 min vs. 65.11 min). CONCLUSIONS: Our proposed MC dose engine (ArcherQA-CK) has a high degree of consistency with the Precision TPS-MC algorithm, which can quickly identify the calculation errors of TPS-RT algorithm for some chest cases. ArcherQA-CK can provide accurate patient-specific quality assurance in clinical practice.

Experimental and Monte Carlo based dosimetric investigation of a novel 3 mm radiosurgery 3 MV beam using the microSilicon detector.

BACKGROUND: The ZAP-X system is a novel gyroscopic radiosurgical system based on a 3 MV linear accelerator and collimator cones with a diameter between 4 and 25 mm. Advances in imaging modalities to detect small and early-stage pathologies allow for an early and less invasive treatment, where a smaller collimator matching the anatomical target could provide better sparing of surrounding healthy tissue. PURPOSE: A novel 3 mm collimator cone for the ZAP-X was developed. This study aims to investigate the usability of a commercial diode detector (microSilicon) for the dosimetric characterization of this small collimator cone; and to investigate the underlying small field perturbation effects. METHODS: Profile measurements in five depths as well as PDD and output ratio measurements were performed with a microSilicon detector and radiochromic EBT3 films. In addition, comprehensive Monte Carlo simulations were performed to validate the measurement observations and to quantify the perturbation effects of the microSilicon detector in these extremely small field conditions. RESULTS: It is shown that the microSilicon detector enables an accurate dosimetric characterization of the 3 mm beam. The profile parameters, such as the FWHM and 20%-80% penumbra width, agree within 0.1 to 0.2 mm between film and detector measurements. The output ratios agree within the measurement uncertainty between microSilicon detector and films, whereas the comparisons of the PDD results show good agreement with the Monte Carlo simulations. The analysis of the perturbation factors of the microSilicon detector reveals a small field correction factor of approximately 3% for the 3 mm circular beam and a correction factor smaller than 1.5% for field diameters above 3 mm. CONCLUSIONS: It could be shown that the microSilicon detector is well-suitable for the characterization of the new 3 mm circular beam of the ZAP-X system.

Evaluation of radiation detectors for the determination of field output factors in Leksell Gamma Knife dosimetry using 3D printed phantom inserts.

The Leksell Gamma Knife® Perfexion™ and Icon™ have a unique geometry, containing 192 60Co sources with collimation for field sizes of 4 mm, 8 mm, and 16 mm. 4 mm and 8 mm collimated fields lack lateral charged particle equilibrium, so accurate field output factors are essential. This study performs field output factor measurements for the microDiamond, microSilicon, and RAZOR™ Nano detectors. 3D printed inserts for the spherical Solid Water® Phantom were fabricated for microDiamond detector, the microSilicon unshielded diode and the RAZOR™ Nano micro-ionisation chamber. Detectors were moved iteratively to identify the peak detector signal for each collimator, representing the effective point of measurement of the chamber. In addition, field output correction factors were calculated for each detector relative to vendor supplied Monte Carlo simulated field output factors and field output factors measured with a W2 scintillator. All field output factors where within 1.1 % for the 4 mm collimator and within 2.3 % for the 8 mm collimator. The 3D printed phantom inserts were suitable for routine measurements if the user identifies the effective point of measurement, and ensures a reproducible setup by marking the rotational alignment of the cylindrical print. Measurements with the microDiamond and microSilicon can be performed faster compared to the RAZOR™ Nano due to differences in the signal to noise ratio. All detectors are suitable for field output factor measurements for the Leksell Gamma Knife® Perfexion™ and Icon™.

Output factor measurements with multiple detectors in CyberKnife® Robotic Radiosurgery System.

AIM: The aim of this study was to measure and compare the output factor (OF) of a CyberKnife Robotic Radiosurgery System with eight different small field detectors and validate with Technical Report Series (TRS) report 483. BACKGROUND: Accurate dosimetry of CyberKnife system is limited due to the challenges in small field dosimetry. OF is a vital dosimetric parameter used in the photon beam modeling and any error would affect the dose calculation accuracy. MATERIALS AND METHODS: In this study, the OF was measured with eight different small-field detectors for the 12 IRIS collimators at 800 mm SAD setup at 15 mm depth. The detectors used were PTW 31016 PinPoint 3D, IBA PFD shielded diode, IBA EFD unshielded diode, IBA SFD unshielded diode (stereotactic), PTW 60008 shielded diode, PTW 60012 unshielded diode, PTW 60018 unshielded diode (stereotactic), and PTW 60019 CVD diamond detector. OF was obtained after correcting for field output correction factors from IAEA TRS No. 483. RESULTS: The field OFs in CyberKnife are derived from the measured data by applying the correction factors from Table 23 in TRS 483 for the eight small field detectors. These field OFs matched within 2% of peer-reviewed published values. The range and standard deviation showed a decreasing trend with collimator diameter. CONCLUSION: The field OF obtained after applying the appropriate correction factor from TRS 483 matched well with the peer-reviewed published OFs. The inter-detector variation showed a decreasing trend with increasing collimator field size. This study gives physicists confidence in measuring field OFs while using small field detectors mentioned in this work.

Performance assessment of two motion management systems for frameless stereotactic radiosurgery.

BACKGROUND/PURPOSE: Frameless stereotactic radiosurgery (SRS) requires dedicated systems to monitor patient motion in order to avoid inaccurate radiation delivery due to involuntary shifts. The purpose of this study is to assess the accuracy and sensitivity of two distinct motion monitoring systems used for frameless SRS. METHODS: A surface image-guided system known as optical surface monitoring system (OSMS), and a fiducial marker-based system known as high definition motion management (HDMM) as part of the latest Gamma Knife Icon® were compared. A 3D printer-based cranial motion phantom was developed to evaluate the accuracy and sensitivity of these two systems in terms of: (1) the capability to recognize predefined shifts up to 3 cm, and (2) the capability to recognize predefined speeds up to 3 cm/s. The performance of OSMS, in terms of different reference surfaces, was also evaluated. RESULTS: Translational motion could be accurately detected by both systems, with an accuracy of 0.3 mm for displacement up to 1 cm, and 0.5 mm for larger displacements. The reference surface selection had an impact on OSMS performance, with flat surface resulting in less accuracy. HDMM was in general more sensitive when compared with OSMS in capturing the motion, due to its faster frame rate, but a delay in response was observed with faster speeds. Both systems were less sensitive in detection of superior-inferior motion when compared to lateral or vertical displacement directions. CONCLUSION: Translational motion can be accurately and sensitively detected by OSMS and HDMM real-time monitoring systems. However, performance variations were observed along different motion directions, as well as amongst the selection of reference images. Caution is needed when using real-time monitoring systems for frameless SRS treatment.

Time-Driven Activity-Based Costing Comparison of Stereotactic Radiosurgery to Multiple Brain Lesions Using Single-Isocenter Versus Multiple-Isocenter Technique.

PURPOSE: Stereotactic radiosurgery (SRS) historically has been used to treat multiple brain lesions using a multiple-isocenter technique-frequently associated with significant complexity in treatment planning and long treatment times. Recently, given innovations in planning algorithms, patients with multiple brain lesions may now be treated with a single-isocenter technique using fewer total arcs and less time spent during image guidance (though with stricter image guided radiation therapy tolerances). This study used time-driven activity-based costing to determine the difference in cost to a provider for delivering SRS to multiple brain lesions using single-isocenter versus multiple-isocenter techniques. METHODS AND MATERIALS: Process maps, consisting of discrete steps, were created for each phase of the SRS care cycle and were based on interviews with department personnel. Actual treatment times (including image guidance) were extracted from treatment record and verify software. Additional sources of data to determine costs included salary/benefit data of personnel and average list price/maintenance costs for equipment. RESULTS: Data were collected for 22 patients who underwent single-isocenter SRS (mean lesions treated, 5.2; mean treatment time, 30.2 minutes) and 51 patients who underwent multiple-isocenter SRS (mean lesions treated, 4.4; mean treatment time, 75.2 minutes). Treatment time for multiple-isocenter SRS varied substantially with increasing number of lesions (11.8 minutes/lesion; P < .001), but to a much lesser degree in single-isocenter SRS (1.8 minutes/lesion; P = .029). The resulting cost savings from single-isocenter SRS based on number of lesions treated ranged from $296 to $3878 for 2 to 10 lesions treated. The 2-mm planning treatment volume margin used with single-isocenter SRS resulted in a mean 43% increase of total volume treated compared with a 1-mm planning treatment volume expansion. CONCLUSIONS: In a comparison of time-driven activity-based costing assessment of single-isocenter versus multiple-isocenter SRS for multiple brain lesions, single-isocenter SRS appears to save time and resources for as few as 2 lesions, with incremental benefits for additional lesions treated.

Characterization of a microSilicon diode detector for small-field photon beam dosimetry.

This study characterized a new unshielded diode detector, the microSilicon (model 60023), for small-field photon beam dosimetry by evaluating the photon beams generated by a TrueBeam STx and a CyberKnife. Temperature dependence was evaluated by irradiating photons and increasing the water temperature from 11.5 to 31.3°C. For Diode E, microSilicon, microDiamond and EDGE detectors, dose linearity, dose rate dependence, energy dependence, percent-depth-dose (PDD), beam profiles and detector output factor (OFdet) were evaluated. The OFdet of the microSilicon detector was compared to the field output factors of the other detectors. The microSilicon exhibited small temperature dependence within 0.4%, although the Diode E showed a linear variation with a ratio of 0.26%/°C. The Diode E and EDGE detectors showed positive correlations between the detector reading and dose rate, whereas the microSilicon showed a stable response within 0.11%. The Diode E and microSilicon demonstrated negative correlations with the beam energy. The OFdet of microSilicon was the smallest among all the detectors. The maximum differences between the OFdet of microSilicon and the field output factors of microDiamond were 2.3 and 1.6% for 5 × 5 mm2 TrueBeam and 5 mm φ CyberKnife beams, respectively. The PDD data exhibited small variations in the dose fall-off region. The microSilicon and microDiamond detectors yielded similar penumbra widths, whereas the other detectors showed steeper penumbra profiles. The microSilicon demonstrated favorable characteristics including small temperature and dose rate dependence as well as the small spatial resolution and output factors suitable for small field dosimetry.

Assessment of an Elekta Versa HD linear accelerator for stereotactic radiosurgery with circular cone collimators.

BACKGROUND: Versa HD linear accelerators (linacs) are used for stereotactic radiosurgery treatment. However, the mechanical accuracy of such systems remains a concern. OBJECTIVE: The purpose of this study was to evaluate the accuracy of an Elekta Versa HD linac. METHODS: We performed measurements with a ball bearing phantom to calculate the rotational isocenter radii of the linac's gantry, collimator, and table, and determine the relative locations of those isocenters. We evaluated the accuracy of the cone-beam computed tomography (CBCT) guidance with a film-embedding head phantom and circular cone-collimated radiation beams. We also performed dosimetric simulations to study the effects of the linac mechanical uncertainties on non-coplanar cone arc delivery. RESULTS: The mechanical uncertainty of the linac gantry rotation was 0.78 mm in radius, whereas that of the collimator and the table was <0.1 mm and 0.33 mm, respectively. The axes of rotation of the collimator and the table were coinciding with and 0.13 mm away from the gantry isocenter, respectively. Experiments with test plans demonstrated the limited dosimetric consequences on the circular arc delivery given the aforementioned mechanical uncertainties. End-to-end measurements determined that the uncertainty of the CBCT guidance was≤1 mm in each direction with respect to the reference CT image. CONCLUSIONS: In arc delivery, the mechanical uncertainties associated with the gantry and the table do not require remarkable increases in geometric margins. If large enough, the residual setup errors following CBCT guidance will dominate the overall dosimetric consequence. Therefore, the Versa HD linac is a valid system for stereotactic radiosurgery using non-coplanar arc delivery.

A Monte Carlo study of neutron contamination in presence of circular cones during stereotactic radiotherapy with 18 MV photon beams.

High-energy photons are being used to treat different kinds of cancer, but it may increase the rate of secondary cancers due to the neutron contamination as well as over exposing of patients and medical staffs in radiation therapy Takam, Bezak, Marcu, and Yeoh, 2011, Radiation Research, 176, 508-520. Due to some difficulties in experimental measurements of neutron contamination, Monte Carlo method is an efficient tool to investigate dose parameters and characteristics in new techniques. The 18-MV photon beam of linac and circular cones have been simulated by MCNP5 code. Various parameters of photon and neutron including mean energy, flux, KERMA, the number of particles crossing a surface at a distance of 100 cm (SSD = 100 cm) as well as the change in photon and neutron spectrum as well as in intensity through the transmission in the circular collimators have been investigated. The results of this study show that the use of a circular collimator decreases neutron dose in the central axis, which is an advantage, but neutron contamination inducing small neutron dose is distributed all over the space. On the surface of phantom, photon dose rate is approximately equal to 3.41E7 (mGy/mA.min) for different collimators, but the neutron dose rate is 1.64E2 (mGy/ mA.min), 2.03E2 (mGy/ mA.min) and 2.52E2 (mGy/mA.min) for diameters of 12, 20 and 40 mm, respectively and it decreases by decreasing the diameter of the collimator. The neutron dose rate decreases from 9.68E7 and 9.74E7 (mGy/min.mA) for open field size 33 cm2 and 55 cm2 to 1.64E2 (mGy/min.mA), 2.02E2 (mGy/min.mA) and 2.52E2 (mGy/min.mA) for collimator diameter of 12 mm, 20 mm and 40 mm. It can be concluded that the use of circular collimators has an advantage of reducing neutron dose in the central axis. It should be mentioned that the off-axis neutron dose surrounding the collimator can be eliminated using an external neutron shield without perturbing the treatment field.

Estimation of dosimetric discrepancy due to use of Onyx™ embolic system in Stereotactic Radiosurgery/Radiotherapy (SRS/SRT) planning.

More often the embolic materials in the brain create artefacts in the planning CT images that could lead to a dose variation in planned and delivered dose. The aim of the study was to evaluate the dosimetric effect of artefacts generated by the Onyx™ embolization material during Stereotactic Radiosurgery/Radiotherapy (SRS/SRT) planning. An in-house made novel Polymethyl Methacrylate (PMMA) head phantom (specially designed for SRS/SRT plans) was used for this purpose. For the evaluation process, we have created concentric ring structures around the central Onyx materials on both the CT sets (with and without Onyx material). The verification plans were generated using different algorithms namely Analytical Anisotropic Algorithm (AAA), Acuros XB and Monaco based Monte Carlo on both CT sets. Mean integral dose over the region of interest were calculated in both CT sets. The dosimetric results shows, due to the presence of Onyx material, relative variation in mean integral dose to the proximal structure (Ring 1) were -4.02%, -2.98%, and -2.49% for Monte Carlo, Acuros XB, and AAA respectively. Observed variations are attributed to the presence of artefacts due to Onyx material. Artefacts influence the accuracy of dose calculation during the planning. All the calculation algorithms are not equally capable to account such variations. Special cares are to be taken while choosing the calculation algorithms as it impacts the results of treatment outcome.

Evaluation of the IAEA-TRS 483 protocol for the dosimetry of small fields (square and stereotactic cones) using multiple detectors.

The IAEA TRS 483 protocol1 for the dosimetry of small static fields in radiotherapy was used to calculate output factors for the Elekta Synergy linac at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Small field output factors for both square and circular fields were measured using nine different detectors. The "corrected" output factors (ratio of detector readings multiplied by the appropriate correction factor from the protocol) showed better consistency compared to the "uncorrected" output factors (ratio of detector readings only), with the relative standard deviation decreasing by approximately 1% after the application of the relevant correction factors. Comparisons relative to an arbitrarily chosen PTW 60019 microDiamond detector showed a reduction of maximal variation for the corrected values of approximately 3%. A full uncertainty budget was prepared to analyze the consistency of the output factors. Agreement within uncertainties between all detectors and field sizes was found, except for the 15 mm circular field. The results of this study show that the application of IAEA TRS 4831 when measuring small fields will improve the consistency of small field measurements when using multiple detectors contained within the protocol.

Small field dosimetry correction factors for circular and MLC shaped fields with the CyberKnife M6 System: evaluation of the PTW 60023 microSilicon detector.

The PTW 60023 microSilicon is a new unshielded diode detector for small-field photon dosimetry. It provides improved water equivalence and a slightly larger sensitive region diameter in comparison to previous diode detectors in this range. In this study we evaluated the correction factors relevant to commissioning a CyberKnife System with this detector by Monte Carlo simulation and verified this data by multi-detector measurement comparison. The correction factors required for output factor determination were substantially closer to unity at small field sizes than for previous diode versions (e.g. [Formula: see text] = 0.981 at 5 mm field size which compares with corrections of 5%-6% with other stereotactic diodes). Because of these differences we recommend that corrections to small field output factor measurements generated specifically for the microSilicon detector rather than generic data taken from other diode types should be used with this new detector. For depth-dose measurements the microSilicon is consistent with a microDiamond detector to <1% (global), except at depths <10 mm where the diode gives a significantly lower measurement, by 6%-8% at the surface. For profile measurements, the microSilicon requires negligible corrections except in the low dose region outside the beam, where it underestimates off-axis-ratio (OAR) for small fields and overestimates for large fields. Where this effect is most noticeable at the largest field size and depth (115 mm × 100 mm and 300 mm depth) the microSilicon overestimates OAR by 2.3% (global) in the profile tail. This is consistent with other unshielded diodes.

Benchmarking Monte-Carlo dose calculation for MLC CyberKnife treatments.

BACKGROUND: Vendor-independent Monte Carlo (MC) dose calculation (IDC) for patient-specific quality assurance of multi-leaf collimator (MLC) based CyberKnife treatments is used to benchmark and validate the commercial MC dose calculation engine for MLC based treatments built into the CyberKnife treatment planning system (Precision MC). METHODS: The benchmark included dose profiles in water in 15 mm depth and depth dose curves of rectangular MLC shaped fields ranging from 7.6 mm × 7.7 mm to 115.0 mm × 100.1 mm, which were compared between IDC, Precision MC and measurements in terms of dose difference and distance to agreement. Dose distributions of three phantom cases and seven clinical lung cases were calculated using both IDC and Precision MC. The lung PTVs ranged from 14 cm3 to 93 cm3. Quantitative comparison of these dose distributions was performed using dose-volume parameters and 3D gamma analysis with 2% global dose difference and 1 mm distance criteria and a global 10% dose threshold. Time to calculate dose distributions was recorded and efficiency was assessed. RESULTS: Absolute dose profiles in 15 mm depth in water showed agreement between Precision MC and IDC within 3.1% or 1 mm. Depth dose curves agreed within 2.3% / 1 mm. For the phantom and clinical lung cases, mean PTV doses differed from - 1.0 to + 2.3% between IDC and Precision MC and gamma passing rates were > =98.1% for all multiple beam treatment plans. For the lung cases, lung V20 agreed within ±1.5%. Calculation times ranged from 2.2 min (for 39 cm3 PTV at 1.0 × 1.0 × 2.5 mm3 native CT resolution) to 8.1 min (93 cm3 at 1.1 × 1.1 × 1.0 mm3), at 2% uncertainty for Precision MC for the 7 examined lung cases and 4-6 h for IDC, which, however, is not optimized for efficiency but used as a gold standard for accuracy. CONCLUSIONS: Both accuracy and efficiency of Precision MC in the context of MLC based planning for the CyberKnife M6 system were benchmarked against MC based IDC framework. Precision MC is used in clinical practice at our institute.

A new Monte Carlo model of a Cyberknife® system for the precise determination of out-of-field doses.

In a previous work, a PENELOPE Monte Carlo model of a Cyberknife system equipped with fixed collimator was developed and validated for in-field dose evaluation. The aim of this work is to extend it to evaluate peripheral doses and to determine the precision of the treatment planning system (TPS) Multiplan in evaluating the off-axis doses. The Cyberknife® head model was completed with surrounding components based on manufacturer drawings. The contribution of the different head parts on the out-of-field dose was studied. To model the attenuation and the modification of particle energy caused by components not modelled, the photon transport was modified in one of the added components. The model was iteratively adjusted to fit dose profiles measured with EBT3 films and an ionization chamber for several collimator sizes. Finally, dose profiles were calculated using the two Multiplan TPS algorithms and were compared to our simulations. The contributions to out-of-field dose were identified as scattered radiation from the phantom and head leakage and scatter originating at the secondary collimator level. Particle transport in the additional pieces was modified to model this radiation. The maximum differences between simulated and measured doses are of 20.4%. Regarding the detector responses away from axis, EBT3 films and the Farmer chamber give similar response (less than 20% difference). The TPS Monte Carlo algorithm underestimates the doses away from axis more importantly for the smaller field sizes (up to 98%). Besides, RayTracing simplifies peripheral dose to a constant value with no inclusion of particle transport. A Monte Carlo model of a Cyberknife system for the determination of out-of-field doses up to 14 cm off-axis was successfully developed and validated for different depths and field sizes in comparison with measurements. This study also confirms that TPS algorithms do not model peripheral dose properly.

Cost-effectiveness of Linac-based single-isocenter non-coplanar technique (HyperArcTM) for brain metastases radiosurgery.

In the last few years, the major change has occurred in the expansion of indications for radiosurgery (SRS) to include patients with more than four brain metastases (BM). To address the expanding indications for SRS in the treatment of multiple BMs, HyperArcTM (Varian Medical System, Palo Alto, CA, U.S.) was recently introduced in order to automate and simplify sophisticated treatments such as SRS/FSRT for multiple lesions (up to 20 BM). In this editorial some consideration about HyperArc cost-effectiveness were discussed in terms of reduction of treatment delivery time (multiple intracranial targets can be treated in a few minutes), the reduction of overall treatment time (treatment course of SRS of multiple BMs in a single session, rather than having to irradiate lesion per lesion during separate sessions on different days); reduction of costs for health systems. In summary HyperArc™ system is a promising, safe and accurate solution for SRS/SFRT to treat multiple BMs in a single or few sessions. This has the potential to impact direct and indirect costs of SRS/SFRT delivery.

Radioterapia corporal estereotáxica en neoplasias de pulmón / Stereotaxic body radiation therapy in lung neoplasms

CONTEXTO CLÍNICO: El cáncer de pulmón (CP) es el tumor más frecuentemente diagnosticado a nivel mundial. En la Argentina cada año mueren aproximadamente 10.000 personas por CP. . El CP afecta sobre todo a personas entre 60 y 65 años, es la primer causa de mortalidad por cáncer en varones y la tercera en mujeres. Si se diferencia por sexo la mortalidad por este cáncer se encuentra en primer lugar para varones y en tercer lugar para las mujeres. El CP de Células No Pequeñas (CPCNP), representa el 85 a 90% de todos los tipos de CP. La sobrevida de los pacientes está estrechamente relacionada al estadio de la enfermedad al momento del diagnóstico. Desafortunadamente, el 85% de los pacientes es diagnosticado en estadios avanzado, siendo la sobrevida en este escenario de 4 a 6 meses sin tratamiento. La radioterapia (RT) puede considerarse parte del tratamiento en cada uno de los estadios. En estadios tempranos, la lobectomía con disección ganglionar mediastinal es considerada el tratamiento estándar. En pacientes con comorbilidades que aumenten el riesgo quirúrgico, la RT puede ser una opción terapéutica. La RT podría considerarse en los pacientes en estadio temprano que no sean candidatos quirúrgicos. En estadios avanzados con oligometástasis, la radioterapia se plantea como parte del tratamiento local definitivo. TECNOLOGÍA: La RT consiste en la administración de radiaciones ionizantes capaces de eliminar las células neoplásicas al dañar de manera irreversible la molécula de ADN.7 Antes de iniciar el tratamiento se realiza una planificación para delimitar la localización exacta del área a tratar (volumen objetivo) y calcular la dosis que se desea administrar. OBJETIVO: El objetivo del presente informe es evaluar la evidencia disponible acerca de la eficacia, seguridad y aspectos relacionados a las políticas de cobertura del uso de la radioterapia corporal estereotáxica en cáncer de pulmón. MÉTODOS: Se realizó una búsqueda en las principales bases de datos bibliográficas, en buscadores genéricos de internet, y financiadores de salud. Se priorizó la inclusión de revisiones sistemáticas (RS), ensayos clínicos controlados aleatorizados (ECAs), evaluaciones de tecnologías sanitarias (ETS), evaluaciones económicas, guías de práctica clínica (GPC) y políticas de cobertura de diferentes sistemas de salud. RESULTADOS: Se incluyeron 7 RS, un análisis conjunto de dos ECAs, 5 GPC, una ETS y 8 informes de políticas de cobertura de SBRT para neoplasias pulmonares. CONCLUSIONES: Evidencia de moderada calidad sugiere que la radioterapia corporal estereotáxica mejora la sobrevida global en pacientes con cáncer de pulmón de células no pequeñas en estadio temprano inoperables en comparación con otras modalidades de radioterapia. Evidencia de moderada calidad sugiere que la radioterapia corporal estereotáxica no presenta beneficios en sobrevida global en los pacientes con cáncer de pulmón en estadío temprano operables en comparación con la cirugía. Evidencia de muy baja calidad no permite arribar a conclusiones sobre la utilidad de la radioterapia corporal estereotáxica en pacientes con metástasis pulmonares en comparación con la cirugía u otras modalidades de radioterapia. Todas las guías de práctica clínica relevadas recomiendan el tratamiento con radioterapia corporal estereotáxica en pacientes con cáncer de pulmón en estadío temprano inoperables. Financiadores públicos de Latinoamérica no mencionan la cobertura de la radioterapia corporal estereotáxica en pacientes con cáncer de pulmón. Financiadores estatales y privados de Estados Unidos prestan cobertura en pacientes seleccionados con cáncer de pulmón inoperables.

Independent dose validation system for Gamma Knife radiosurgery, using a DICOM-RT interface and Geant4.

Leksell GammaPlan was specifically designed for Gamma Knife (GK) radiosurgery planning, but it has limited accuracy for estimating the dose distribution in inhomogeneous areas, such as the embolization of arteriovenous malformations. We aimed to develop an independent patient dose validation system based on a patient-specific model, constructed using a DICOM-RT interface and the Geant4 toolkit. Leksell Gamma Knife Perfexion was designed in Geant4.10.00 and includes a DICOM-RT interface. Output factors for each collimator in a sector and dose distributions in a spherical water phantom calculated using a Monte Carlo (MC) algorithm were compared with the output factors calculated by the tissue maximum ratio (TMR) 10 algorithm and dose distributions measured using film, respectively. Studies using two types of water phantom and two patient simulation cases were evaluated by comparing the dose distributions calculated by the MC, the TMR and the convolution algorithms. The water phantom studies showed that if the beam size is small and the target is located in heterogeneous media, the dose difference could be up to 11%. In the two patient simulations, the TMR algorithm overestimated the dose by about 4% of the maximum dose if a complex and large bony structure was located on the beam path, whereas the convolution algorithm showed similar results to those of the MC algorithm. This study demonstrated that the in-house system could accurately verify the patient dose based on full MC simulation and so would be useful for patient cases where the dose differences are suspected.

Radioterapia corporal estereotáxica en cáncer de próstata / Stereotaxic body radiation therapy in cancer of prostate

CONTEXTO CLÍNICO: El cáncer de próstata (CP) es una enfermedad prevalente a nivel mundial, constituyendo en Argentina la segunda causa de muerte por cáncer en hombres, con una incidencia estimada de 44 nuevos casos cada 100.000 habitantes.1,2 El riesgo de presentar esta patología aumenta con la edad, más del 60% de todos los casos de CP son diagnosticados en mayores de 65 años y casi la totalidad de los mismos luego de los 50 años. El diagnóstico de esta neoplasia requiere de la sospecha clínica por síntomas compatibles, determinaciones séricas del antígeno prostático específico (PSA, su sigla del inglés Prostate Specific Antigen), estudios de imágenes y estudios invasivos como la biopsia. TECNOLOGÍA: La RT consiste en la administración de radiaciones ionizantes capaces de eliminar las células neoplásicas al dañar de manera irreversible la molécula de ADN. Antes de iniciar el tratamiento se realiza una planificación para delimitar la localización exacta del área a tratar (volumen objetivo) y calcular la dosis que se desea administrar. OBJETIVO: El objetivo del presente informe es evaluar la evidencia disponible acerca de la eficacia, seguridad y aspectos relacionados a las políticas de cobertura del uso de radioterapia corporal estereotáxica en cáncer de próstata. MÉTODOS: Se realizó una búsqueda en las principales bases de datos bibliográficas, en buscadores genéricos de internet, y financiadores de salud. Se priorizó la inclusión de revisiones sistemáticas (RS), ensayos clínicos controlados aleatorizados (ECAs), evaluaciones de tecnologías sanitarias (ETS), evaluaciones económicas, guías de práctica clínica (GPC) y políticas de cobertura de diferentes sistemas de salud. RESULTADOS: Se incluyeron dos ECAs en fase de reclutamiento, dos RS, cinco GPC, dos informes de ETS, y 12 informes de políticas de cobertura acerca del uso de SBRT en cáncer de próstata. CONCLUSIONES: No se identificó evidencia comparativa acerca del uso de radioterapia corporal estereotáxica versus observación controlada o cirugía radical en pacientes con cáncer de próstata candidatos a estos tratamientos. Evidencia de muy baja calidad no permite inferir conclusiones acerca de la efectividad y/o seguridad del uso de SBRT en comparación con otras técnicas de radioterapia en pacientes con cáncer de próstata localizado. La mayoría de las GPC y/o documentos de consenso relevados que mencionan el uso de SBRT no la recomiendan en cáncer de próstata, con excepción de una guía estadounidense que sí la recomienda como una alternativa más en el tratamiento de estos pacientes. Los financiadores públicos de Latinoamérica relevados no mencionan o no prestan cobertura para SBRT en cáncer de próstata. Entre los países de altos ingresos, mientras que los financiadores públicos y privados de Estados Unidos contemplan la cobertura de SBRT en cáncer de próstata, Inglaterra y Francia no prestan cobertura.

Radioterapia corporal estereotáxica en tumores hepáticos / Stereotaxic body radiation therapy in tumors liver

CONTEXTO CLÍNICO: Los tumores hepáticos pueden ser primarios o secundarios, siendo estos últimos los tumores malignos más frecuentes y principalmente secundarios a cáncer colorrectal. Según datos de GLOBOCAN 2012, en Argentina es el segundo tumor más frecuente y la segunda causa de muerte por cáncer. Otros tumores que producen metástasis hepáticas incluyen, cáncer de mama (sobrevida global promedio a 10 meses), el melanoma (2,4 meses), y tumores neuroendocrinos (5 a 57 meses). Para muchas neoplasias, la progresión del compromiso hepático es la principal causa de mortalidad. En la actualidad, la resección quirúrgica es la principal opción curativa, con una mediana de sobrevida de 21 a 46 meses, sin embargo, sólo alrededor del 20% de los tumores son resecables. En pacientes que presentan escasas lesiones, en ausencia de enfermedad extrahepática, las técnicas de ablación son una alternativa terapéutica válida. Otras opciones de tratamiento son la quimioterapia, radioterapia, radioembolización, quimioembolización y radiofrecuencia. TECNOLOGÍA: La radioterapia (RT) consiste en la administración de radiaciones ionizantes capaces de eliminar las células neoplásicas al dañar de manera irreversible la molécula de ADN. Antes de iniciar el tratamiento se realiza una planificación para delimitar la localización exacta del área a tratar (volumen objetivo) y calcular la dosis que se desea administrar. OBJETIVO: El objetivo del presente informe es evaluar la evidencia disponible acerca de la eficacia, seguridad y aspectos relacionados a las políticas de cobertura del uso de radioterapia corporal estereotáxica para tumores hepáticos primarios y secundarios en pacientes adultos. MÉTODOS: Se realizó una búsqueda en las principales bases de datos bibliográficas, en buscadores genéricos de internet, y financiadores de salud. Se priorizó la inclusión de revisiones sistemáticas (RS), ensayos clínicos controlados aleatorizados (ECAs), evaluaciones de tecnologías sanitarias (ETS), evaluaciones económicas, guías de práctica clínica (GPC) y políticas de cobertura de diferentes sistemas de salud. RESULTADOS: Se incluyeron tres RS, un análisis retrospectivo de base de datos, dos estudios de cohorte, dos estudios de costo efectividad, cuatro GPC, y ocho informes de políticas de cobertura radioterapia corporal estereotáxica para tratamiento de tumores hepáticos. No se encontraron estudios controlados y aleatorizados que comparen SBRT con otras modalidades de tratamiento en pacientes con tumores hepáticos primarios y secundarios. CONCLUSIONES: Evidencia de baja calidad sugiere resultados contradictorios acerca de la efectividad de la radioterapia corporal estereotáxica en pacientes con tumores hepáticos primarios o metastásicos en comparación con otras modalidades terapéuticas. Algunas de las Guías de Práctica Clínica relevadas consideran a la radioterapia corporal estereotáxica como una alternativa a otras técnicas existentes (radiofrecuencia, quimioembolización transarterial, otros tipos de radioterapia, etc.) para el tratamiento local de tumores hepáticos, mientras que otras, solo la contemplan en pacientes que no son candidatos o presentan contraindicaciones para otras terapias. De las políticas de cobertura relevadas, solo algunos financiadores privados estadounidenses prestan cobertura para radioterapia corporal estereotáxica en pacientes seleccionados. No se encontraron estudios de costo-efectividad o análisis de impacto presupuestario en Argentina.

The impact of MRI steady-state sequences as an additional assessment modality in vestibular schwannoma patients after LINAC stereotactic radiotherapy or radiosurgery.

PURPOSE: Data concerning the clinical usefulness of steady-state sequences (SSS) for vestibular schwannomas (VS) after linear accelerator (LINAC) stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT) are scarce. The aim of the study was to investigate whether SSS provide an additional useful follow-up (FU) tool to the established thin-layered T1 sequences with contrast enhancement. METHODS: Pre- and post-treatment SSS were identified in 45 consecutive VS patients (2012-2016) with a standardized FU protocol including SSS at 2-3 months and 6 months/yearly in our prospective database and were retrospectively re-evaluated. The SSS were used throughout for the segmentation of the cochlea and partly of the trigeminal nerve in the treatment planning. Data analysis included signal conversion in SSS and possible correlation with neuro-otological outcome and volumetric assessment after a certain time interval. RESULTS: The series included 42 SRS and 3 SRT patients (31 female/14 male; mean age 59.3 years, range: 25-81 years). An SSS signal conversion was observed in 20 tumors (44.4%) within a mean time of 11 months (range: 7-15 months). Mean FU time was 26 months (median of 4 FU visits) and demonstrated tumor volume shrinkage in 29 cases (64.4%) correlating with FU time (p = 0.07). The incidence rate of combined shrinkage and signal conversion (48.3%) compared to those without signal conversion (51.7%) did not differ significantly (p = 0.49). In case of an early signal conversion at the first FU, a weak statistical significance (p = 0.05) for a higher shrinkage rate of VS with signal conversion was found. Side effects in cases with signal conversion (9/20, 45%) were more frequently than without signal conversion (6/25, 24%) without reaching statistical significance (p = 0.13). CONCLUSION: Our data confirmed the usefulness of SSS for anatomical segmentation of VS in LINAC-SRS/SRT treatment planning and add data supporting their potential as an adjunctive FU option in VS patients.