Purpose
To estimate and reduce uncertainties of a self-consistent set of radiobiological parameters based on the outcome of head and neck cancer (HNC) patients treated with radiotherapy (RT).
Methods
...Published studies comparing at least two RT schedules for HNC patients were selected. The method used to estimate the radiobiological parameters consists of three sequential steps that allow a significant reduction of uncertainties: the first, in which the intrinsic (
α
) and the repair (
β
) radio-sensitivities were estimated together with the doubling time (
T
d
) by an analytical/graphical method; the second, in which the kick-off time for accelerated proliferation (
T
k
) was estimated applying the hypothesis of activation for sub-populations of stem cells during the RT; the third, in which the number of clonogens (
N
) was obtained by the Tumor Control Probability (TCP) model. Independent clinical data were used to validate results.
Results
The best estimate and the 95 % confidence intervals (95 % CIs) were:
α
= 0.24 Gy
−1
(0.23–0.26),
β
= 0.023 Gy
−2
(0.021–0.025),
α
/
β
= 10.6 Gy (8.4–12.6),
T
d
= 3.5 days (3.1–3.9),
T
k
= 19.2 days (15.1–23.3),
N
= 7 × 10
7
(4 × 10
7
–1 × 10
8
). From these data, the dose required to offset repopulation occurring in 1 day (
D
prolif
) and starting after
T
k
was also estimated as 0.69 Gy/day (0.52–0.86).
Conclusions
The estimation of all the radiobiological parameters of HNC was obtained based on the hypothesis of activation for specifically tumorigenic sub-populations of stem cells. The similarity of results to those from other studies strengthens such a hypothesis that could be very useful for the predictivity of the TCP model and to design new treatment strategies for HNC.
Neutrinos could be mistaken for dark matter by certain types of detectors, so researchers are outlining ways to differentiate the two signals. Direct detection dark matter experiments looking for ...WIMP-nucleus elastic scattering will soon be sensitive to an irreducible background from neutrinos which will drastically affect their discovery potential. Here we explore how the neutrino background will affect future ton-scale experiments considering both spin-dependent and spin-independent interactions. We show that combining data from experiments using different targets can improve the dark matter discovery potential due to target complementarity. We find that in the context of spin-dependent interactions, combining results from several targets can greatly enhance the subtraction of the neutrino background for WIMP masses below 10 GeV /c super(2) and therefore probe dark matter models to lower cross sections. In the context of target complementarity, we also explore how one can tune the relative exposures of different target materials to optimize the WIMP discovery potential.
Over the last years (177)Lu has received considerable attention from the clinical nuclear medicine community thanks to its wide range of applications in molecular radiotherapy, especially in ...peptide-receptor radionuclide therapy (PRRT). In addition to short-range beta particles, (177)Lu emits low energy gamma radiation of 113keV and 208keV that allows gamma camera quantitative imaging. Despite quantitative cancer imaging in molecular radiotherapy having been proven to be a key instrument for the assessment of therapeutic response, at present no general clinically accepted quantitative imaging protocol exists and absolute quantification studies are usually based on individual initiatives. The aim of this work was to develop and evaluate an approach to gamma camera calibration for absolute quantification in tomographic imaging with (177)Lu. We assessed the gamma camera calibration factors for a Philips IRIX and Philips AXIS gamma camera system using various reference geometries, both in air and in water. Images were corrected for the major effects that contribute to image degradation, i.e. attenuation, scatter and dead- time. We validated our method in non-reference geometry using an anthropomorphic torso phantom provided with the liver cavity uniformly filled with (177)LuCl3. Our results showed that calibration factors depend on the particular reference condition. In general, acquisitions performed with the IRIX gamma camera provided good results at 208keV, with agreement within 5% for all geometries. The use of a Jaszczak 16mL hollow sphere in water provided calibration factors capable of recovering the activity in anthropomorphic geometry within 1% for the 208keV peak, for both gamma cameras. The point source provided the poorest results, most likely because scatter and attenuation correction are not incorporated in the calibration factor. However, for both gamma cameras all geometries provided calibration factors capable of recovering the activity in anthropomorphic geometry within about 10% (range -11.6% to +7.3%) for acquisitions at the 208keV photopeak. As a general rule, scatter and attenuation play a much larger role at 113keV compared to 208keV and are likely to hinder an accurate absolute quantification. Acquisitions of only the (177)Lu main photopeak (208keV) are therefore recommended in clinical practice. Preliminary results suggest that the gamma camera calibration factor can be assessed with a standard uncertainty below (or of the order of) 3% if activity is determined with equipment traceable to primary standards, accurate volume measurements are made, and an appropriate chemical carrier is used to allow a homogeneous and stable solution to be used during the measurements.
Abstract
In the framework of the Italian TOP-IMPLART project (Regione Lazio), ENEA-Frascati, ISS and IFO are developing and constructing the first proton linear accelerator based on an actively ...scanned beam for tumor radiotherapy with final energy of 150 MeV. An important feature of this accelerator is modularity: an exploitable beam can be delivered at any stage of its construction, which allows for immediate characterization and virtually continuous improvement of its performance. Currently, a sequence of 3 GHz accelerating modules combined with a commercial injector operating at 425 MHz delivers protons up to 35 MeV. Several dosimetry systems were used to obtain preliminary characteristics of the 35-MeV beam in terms of stability and homogeneity. Short-term stability and homogeneity better than 3% and 2.6%, respectively, were demonstrated; for stability an improvement with respect to the respective value obtained for the previous 27 MeV beam.
Abstract Aims To quantify the changes in dose as well as in the prediction of parotid gland toxicity due to anatomical changes during therapy of head and neck cancer patients. Materials and methods ...Fifteen patients with advanced locoregional head and neck cancer, with no evidence of distant metastasis, were enrolled in a prospective study. All patients were treated with intensity-modulated radiotherapy. Multiple computed tomography scans were repeated at the end of each treatment week. The original treatment plans were copied to the per-treatment scans to create hybrid plans. The normal tissue complication probability (NTCP) was calculated assuming the end point to be grade ≥3 xerostomia according to the Radiation Therapy Oncology Group late toxicity scale. Results The gross tumour volume dose coverage was slightly affected by the anatomical changes, whereas the mean dose (Dmean ) to the parotids changed from 26.1 ± 6.0 to 27.4 ± 7.4 Gy, with a mean increase of 0.22 Gy/treatment week. Consequently, the mean NTCP increased from 0.15 ± 0.06 to 0.18 ± 0.10, primarily due to a few patients exhibiting a marked increase. The absolute gross tumour volume shrinkage and the percentage parotids shrinkage were the best independent predictors for the NTCP variations. Conclusions On average, the increase in the parotids Dmean as well as in NTCP during treatment is limited, and the observed variations were strongly patient-dependent.
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