External photon radiation treatment for prostate cancer: Uncomplicated and cancer-free control probability assessment of 36 plans.

PURPOSE: To perform a systematic and thorough assessment, using the Uncomplicated and Cancer-Free Control Probability (UCFCP) function, of a broad range of photon prostate cancer RT treatments, on the same scenario (a unique pelvic CT set). UCFCP considers, together with the probabilities of local tumour control (TCP) and deterministic (late) sequelae (NTCP), the second primary cancer risk (SPCR) due to photon and neutron peripheral doses. METHODS AND MATERIALS: Thirty-six radiotherapy plans were produced for the same CT. 6, 10, 15 and 18 MV 3DCRT, IMRT and VMAT (77.4 Gy in 43 fractions) and 6 and 10 MV SBRT (36.25 Gy in 5 fractions with flattened and FFF beams) for Elekta, Siemens and Varian Linacs plans were included. DVH and peripheral organ dosimetry were used to compute TCP, NTCP, and SPCR (the competition and LNT models) for further plan ranking. RESULTS: Biological models (and parameters) used predicted an outcome which is in agreement with epidemiological findings. SBRT plans showed the lowest SPCR and a below average NTCPrectal. High energy plans did not rank worse than the low energy ones. Intensity modulated plans were ranked above the 3D conformal techniques. CONCLUSIONS: According to UCFCP, the best plans were the10 MV SBRTs. SPCR rates were low and did not show a substantial impact on plan ranking. High energy intensity-modulated plans did not increase in excess the average of SPCR. Even more, they ranked among the best, provided that MU were efficiently managed.

In vitro modulation of gut microbiota by whey protein to preserve intestinal health.

The effect of several types of whey milk - cow, sheep, goat and a mixture of them (60 : 20 : 20, respectively) - was assessed in the human gut microbiota. The prebiotic potential of these substrates was evaluated through in vitro gastrointestinal digestion following faecal batch culture fermentations (mimicking colonic fermentation) for 48 hours, using faeces from normal-weight (NW) and obese (OB) donors. Throughout the fermentation process, pH, gas production, short chain and branched fatty acids (SCFA-BCFA) were measured, as well as the changes of microbiota using qPCR. The pH decreased in all whey samples during the fermentation process. Gas production was higher in all whey samples than in controls, especially at 12 hours (p < 0.05). The diversity of SCFA and BCFA production was significantly different between the donors, in particular cow and mixed whey. Whey milk had a strong prebiotic effect on the gut microbiota of NW and OB donors, showing a significant increase of Bifidobacterium (p < 0.05) with cow, sheep and mixed whey and increase in the Lactobacillus group, particularly in OB donors. Bacteria associated with obesity did not show an increase in any of the groups of donors. Therefore, supplementing a diet with these types of whey can selectively stimulate the growth of probiotic bacteria, enhancing SCFA production, which could improve intestinal disorders. In addition, it may be an interesting approach to the prevention of overweight and obesity and related diseases. Whey milk has a potent prebiotic effect. It can selectively stimulate desirable bacteria and SCFA profile, in both OB and NW donors, contributing to improved intestinal health and reducing obesity.

Estimation of neutron-equivalent dose in organs of patients undergoing radiotherapy by the use of a novel online digital detector.

Neutron peripheral contamination in patients undergoing high-energy photon radiotherapy is considered as a risk factor for secondary cancer induction. Organ-specific neutron-equivalent dose estimation is therefore essential for a reasonable assessment of these associated risks. This work aimed to develop a method to estimate neutron-equivalent doses in multiple organs of radiotherapy patients. The method involved the convolution, at 16 reference points in an anthropomorphic phantom, of the normalized Monte Carlo neutron fluence energy spectra with the kerma and energy-dependent radiation weighting factor. This was then scaled with the total neutron fluence measured with passive detectors, at the same reference points, in order to obtain the equivalent doses in organs. The latter were correlated with the readings of a neutron digital detector located inside the treatment room during phantom irradiation. This digital detector, designed and developed by our group, integrates the thermal neutron fluence. The correlation model, applied to the digital detector readings during patient irradiation, enables the online estimation of neutron-equivalent doses in organs. The model takes into account the specific irradiation site, the field parameters (energy, field size, angle incidence, etc) and the installation (linac and bunker geometry). This method, which is suitable for routine clinical use, will help to systematically generate the dosimetric data essential for the improvement of current risk-estimation models.

SU-E-T-466: TCP and NTCP: Is That All?

PURPOSE: Concerns about the secondary cancer risks associated to the peripheral neutron and photon contamination in photon modern radiotherapy (RT) techniques (e.g., Intensity Modulated RT -IMRT- or Intensity Modulated Arc Therapy -IMAT) have been widely raised. Benefits in terms of better tumor coverage have to be balanced against the drawbacks of poorer organ at risk sparing and secondary cancer risk in order to make the decision on the optimum treatment technique. The aim of this study was to develop a tool which estimates treatment success taking into consideration the neutron secondary cancer probability. METHODS: A methodology and benchmark dataset for radiotherapy real time assessment of patient neutron dose and application to a novel digital detector (DD) has been carried out (submitted to PMB, 2011). Our DD provides real time neutron equivalent dose distribution in relevant organs along the patient. This information, together with TCP and NTCP estimated from the DVH of target and organs at risks, respectively, have been built into a general biological model which allows us to evaluate the success of the treatments (Sánchez-Nieto et al., ESTRO meeting 2012). This model has been applied to make estimation of treatment success in a variety of treatment techniques (3DCRT, forward and inverse IMRT, RapidArc, Volumetric Modulated Arc Therapy and Helical Tomotherapy) to low and high energy. RESULTS: MU-demanding techniques at high energies were able to deliver treatment plans with the highest complicated-free tumour control. Nevertheless, neutron peripheral dose must be taken into consideration as the associated risk could be of the same order of magnitude than the usually considered NTCPs. CONCLUSIONS: The methodology developed to provide an online organ neutron peripheral dose can be successfully combined with biological models to make predictions on treatment success taking into consideration secondary cancer risks.

A liquid-filled ionization chamber for high precision relative dosimetry.

Radiosurgery and intensity modulated radiation therapy (IMRT) treatments are based on the delivery of narrow and/or irregularly shaped megavoltage photon beams. This kind of beams present both lack of charged particle equilibrium and steep dose gradients. Quality assurance (QA) measurements involved in these techniques must therefore be carried out with a dosimeter featuring high small volume. In order to obtain a good signal to noise ratio, a relatively dense material is needed as active medium. Non-polar organic liquids were proposed as active mediums with both good tissue equivalence and showing high signal to noise ratio. In this work, a liquid-filled ionization chamber is presented. Some results acquired with this detector in relative dosimetry are studied and compared with results obtained with unshielded diode. Medium-term stability measurements were also carried out and its results are shown. The liquid-filled ionization chamber presented here shows its ability to perform profile measurements and penumbrae determination with excellent accuracy. The chamber features a proper signal stability over the period studied.