The impact of scanning data measurements on the Acuros dose calculation algorithm configuration.

BACKGROUND: Many dose calculation algorithms for radiotherapy planning need to be configured for each clinical beam using pre-defined measurements. An optimization process adjusts the physical parameters able to estimate the energy released in the medium in any geometrical condition. This work investigates the impact of measured input data quality on the configuration of the type "c" Acuros-XB dose calculation algorithm in the Eclipse (Varian Medical Systems) treatment planning system. METHODS: Different datasets were acquired with the BeamScan water phantom (PTW) to configure 6 MV beams, for both flattened (6X) and flattening filter free mode (6FFF) for a Varian TrueBeam: (i) a correct dataset measured using a Semiflex-3D ion chamber, (ii) a set in missing lateral scatter conditions (MLS), (iii) a set with incorrect effective point of measurement (EPoM), (iv) sets acquired with PinPoint-3D chamber, DiodeP, microDiamond detectors. The Acuros-XB dose calculation algorithm (version 15.6) was configured using the reference dataset, the sets measured with the different detectors, with intentional errors, and using the representative beam data (RBD) made available by the vendor. The physical parameters obtained from each optimization process (spectrum, mean radial energy, electron contamination), were analyzed and compared. Calculated data were finally compared against the input and reference measurements. RESULTS: Concerning the physical parameters, the configurations presenting the largest differences were the MLS conditions (mean radial energy) and the incorrect EPoM (electron contamination). The calculation doses relative to the input data present low accuracy, with mean differences > 2% in some conditions. The PinPoint-3D ion chamber presented lower accuracy for the 6FFF beam. Regarding the RBD, calculations compared well with the input data used for the configuration, but not with the reference data. CONCLUSION: The MLS conditions and the incorrect setting of the EPoM lead to erroneous configurations and should be avoided. The choice of an appropriate detector is important. Whenever the representative beam data is used, a careful check under more clinical geometrical conditions is advised.

Small field characterization of a Nanochamber prototype under flattening filter free photon beams.

INTRODUCTION: Nanochambers present some advantages in terms of energy independence and absolute dose measurement for small field dosimetry in the SBRT scenario. Characterization of a micro-chamber prototype was carried out both under flattened and flattening-filter-free (FFF) beams with particular focus on stem effect. METHODS: The study included characterization of leakage and stem effects, dose rate and dose per pulse dependence, measurement of profiles, and percentage depth doses (PDDs). Ion collection efficiency and polarity effects were measured and evaluated against field size and dose per pulse. The 6_MV, 6_MV_FFF and 10_MV FFF beams of a Varian EDGE were used. Output factors were measured for field sizes ranging from 0.8×0.8cm2 to 20×20cm2 and were compared with other detectors. RESULTS: The 2mm diameter of this chamber guarantees a high spatial resolution with low penumbra values. In orthogonal configuration a strong stem (and cable) effect was observed for small fields. Dose rate and dose per pulse dependence were <0.3% and 0.6% respectively for the whole range of considered values. The Nanochamber exhibits a field size (FS) dependence of the polarity correction >2%. The OF values were compared with other small field detectors showing a good agreement for field sizes >2×2cm2. The large field over-response was corrected applying kpol(FS). CONCLUSIONS: Nanochamber is an interesting option for small field measurements. The spherical shape of the active volume is an advantage in terms of reduced angular dependence. An interesting feature of the Nanochamber is its beam quality independence and, as a future development, the possibility to use it for small field absolute dosimetry.

Actualización de la estadificación del cáncer de próstata

En nuestro país el cáncer de próstata es la neoplasia más frecuente en hombres de edad avanzada. Por ello, resulta indispensable una adecuada estadificación al momento de establecer la estrategia terapéutica. En este artículo se presenta la 7.a edición del sistema TNM de estadifi cación para el cáncer de próstata, vigente desde el 1.º de enero de 2010. El mismo ha tenido modifi caciones mayores con respecto a la 6.a edición.

In our country prostate cancer is the most common malignancy in older men. An accurate staging is very important to establish treatment strategies.This article presents the 7th edition TNM staging system for prostate cancer, effective January 1, 2010. This has undergone major changes over the 6th edition.

Pulmonary intravascular lymphoma detected by FDG PET-CT: a case report.

Intravascular lymphoma is a rare subtype of extranodal Non-Hodgkin's lymphoma. Its prognosis is poor in a high percentage of cases due to its insidious appearance and low clinical suspicion. Its diagnosis is usually only reached after an autopsy. It may affect different organs as a whole or only one organ. It is extremely rare that the lung is the only damaged organ. Its diagnosis depends of the clinician's suspicion and proper evaluation with imaging studies as well as correct selection of the organ to be biopsied. When detected on time, the treatment of choice is a combination of a series of chemotherapy associated to a monoclonal antibody (anti-CD20). We present the case of a male patient who underwent a positron emission tomography-computed tomography with 2-[F-18]-fluoro-2 deoxy-D-glucose (FDG) due to symptoms suggestive of a lymphoproliferative disease with no clear structural abnormalities. The images led to a diagnosis of pulmonary intravascular large B cell lymphoma.