SPECT and PET need a good pixel identification to obtain high quality images. This is why new generations of PSPMT with anode array with smaller step have been developed till the recent flat panel PMT H9500 with 2" square area, 256 anodes array, 3 mm individual pitch. The realization of electronic chains with so high number channels demands dedicated electronics readout with high cost and high management difficulty. In this work we propose a new method of anode number reduction in parallel readout limiting the total chain number to 64. Starting from the evidence that event charge distribution is always contained inside a portion of the FP PMT anodic plane, we assume that only a quarter of the anodes are involved in the detection. Our approach consists on virtually dividing 16times16 anodes in 4 arrays with 64 anodes per each. Once the charge distribution is collected by the 4 anodic planes, each individual anodic charge is projected on one plane. Physically, each i,j-element of one quadrant is associated to the corresponding i,j-element of the other three matrices. In terms of hardware, it is simply realized connecting one to each other the set of four i,j-anodes of the 4 quadrants. In this work an image reconstruction software has been developed and tested by measured charge distribution collected by 256 anodes Hamamatsu FP PMT. The final results, in term of spatial resolution and position linearity, are in agreement with ones collected by the total number of anodes
Purpose/Objective: To validate the 'mid-position' approach for lung tumor motion management in helical tomotherapy with 4D Monte Carlo planning simulation, in comparison with conventional ITV.Materials and Methods: 8 patients with stage I non-small cell lung cancer (NSCLC) treated by SBRT were included, as well as 6 patients with stage II-III NSCLC treated by Simultaneous Integrated Boost (SIB) and participating in a dose escalation protocol.Prior to treatment, a contrast-enhanced CT (CE-CT) and a 4DCT (for SBRT) or a combined 4D FDG-PET-CT (for SIB) were acquired.The GTV, CTV, and OARs were delineated on the CE-CT according to our clinical protocol.Next, 4D data were used to generate first the ITV and then the MidP volume in its exact time-weighted mean position of the respiratory motion, using a validated Morphon non-rigid registration algorithm.The PTVs were finally drawn according to the margin formula for geometric uncertainties developed by Van Herk et al. and adapted to the specific features of lung tumor tomotherapy.For each patient, two treatments were planned based on margins derived from the ITV and MidP volume.Volumetric and dosimetric parameters, as well as conformity indexes were compared with both strategies.Moreover, dose distributions were computed using a 4D Monte Carlo (MC) model, in order to assess the impact of intra-fraction tumor motion on tumor coverage (quantified by D 95 ), with and without the interplay effect.Results: For SBRT and SIB patients, the PTVs defined with the ITV approach were on average 1.2 times larger than those derived from MidP.Consequently, the dose to all the OARs was on average lower when using the MidP.Nonetheless, the planned dose conformity to TVs was identical between both strategies (0,92 ± 0,03 and 0,84 ± 0,05 for DICE and Paddick indexes, respectively).For all SBRT patients, D 95 to the GTV computed from 4D MC dose distributions complied within 1% of the planning recommendations when using the ITV approach.In contrast, MidP failed to ensure adequate GTV coverage in 3 patients.For one patient, the simulated interplay effect lowered the D 95 to the GTV by 4.35% compared to the planned dose distribution (Fig a).Although the interplay effect did not affect the two other patients, simulated MC calculations demonstrated significant GTV underdosages, with D 95 to GTV reduced by 2.16% and 2.61% compared to the planned doses (Fig b).4D MC computations are ongoing for the SIB group.
A phantom model was used to study the effect of breast compression on signal-to-noise ratio (SNR) for a dedicated high-resolution gamma camera (Single Photon Emission Mammography, or 'SPEM') and a conventional camera as typically employed in prone scintimammography. The phantom was designed to simulate the effects of lesion size and of scatter from nearby torso activity. The phantom studies showed that lesions SNR was higher with the SPEM camera than with the conventional camera, and that SNR was always improved with compression for both cameras. Since the stage of breast cancer diagnosis affects patient prognosis, it is important to optimize breast examinations for small (i.e. Tla and Tlb) lesions. For one cm size lesions (clinical stage Tlc). SNR was maximized when compression was less than 12 cm, and little additional benefit was derived from further compression. For subcentimeter (clinical stage Tlb) lesions. SNR was maximized when compression was less than 6 cm. These data are consistent with a short clinical study in which detection sensitivity for small cancers was improved with the SPEM camera as compared to a conventional gamma camera. It is concluded that, in order to image early breast cancers (stage Tlb), it is important to apply breast compression.
