• Progress in Medical Physics
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• v.25 no.3
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• pp.139-142
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• 2014

The purpose of this study was to develop a system of clinical application of reconstructed dose that includes dose reconstruction, reconstructed dose registration between fractions of treatment, and dose-volume-histogram generation and to demonstrate the system on a deformable prostate phantom. To achieve this purpose, a deformable prostate phantom was embedded into a 20 cm-deep and 40 cm-wide water phantom. The phantom was CT scanned and the anatomical models of prostate, seminal vesicles, and rectum were contoured. A coplanar 4-field intensity modulated radiation therapy (IMRT) plan was used for this study. Organ deformation was simulated by inserting a "transrectal" balloon containing 20 ml of water. A new CT scan was obtained and the deformed structures were contoured. Dose responses in phantoms and electronic portal imaging device (EPID) were calculated by using the XVMC Monte Carlo code. The IMRT plan was delivered to the two phantoms and integrated EPID images were respectively acquired. Dose reconstruction was performed on these images using the calculated responses. The deformed phantom was registered to the original phantom using an in-house developed software based on the Demons algorithm. The transfer matrix for each voxel was obtained and used to correlate the two sets of the reconstructed dose to generate a cumulative reconstructed dose on the original phantom. Forwardly calculated planning dose in the original phantom was compared to the cumulative reconstructed dose from EPID in the original phantom. The prescribed 200 cGy isodose lines showed little difference with respect to the "prostate" and "seminal vesicles", but appreciable difference (3%) was observed at the dose level greater than 210 cGy. In the rectum, the reconstructed dose showed lower volume coverage by a few percent than the plan dose in the dose range of 150 to 200 cGy. Through this study, the system of clinical application of reconstructed dose was successfully developed and demonstrated. The organ deformation simulated in this study resulted in small but observable dose changes in the target and critical structure.

• Journal of radiological science and technology
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• v.35 no.3
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• pp.265-273
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• 2012

Aquisition of accurate beam data is very important to calculate a reliable dose distribution of the treatment planning system for small radiation fields in intensity-modulated radiation therapy(IMRT) and stereotactic radiosurgery(SRS). For the measurement of small fields, the choice of a suitable detector is important due to the shape gradient in profile penumbra, the lack of lateral electronic equilibrium, and the effect of effective detector volume. Therefore, this study was to analyze the dosimetric characteristics of various detectors in measurement of beam data for small fields of linear accelerator. 0.01cc and 0.13cc ion chambers (CC01 and CC13) and a stereotactic diode detector(SFD) were used for measurement of small fields. The beam data, including the percent depth dose, output factor, and beam profile were acquired under 6 MV and 15 MV photon beams. Measurements were performed with the field size ranging from $2{\times}2cm^2$ to $5{\times}5cm^2$. For $2{\times}2cm^2$ field size, the differences of the ratios of $PDD_{20}$ and $PDD_{10}$ measured by CC01 and SFD detectors were 1.02% and 0.12% for 6 MV and 15 MV photon beams, respectively. For field sizes larger than $3{\times}3cm^2$, the differences of values of $PDD_{20}/PDD_{10}$ obtained from each detector were 1.15% and 0.71% for 6 MV and 15 MV photon beams, respectively. The output factors obtained from CC01 and SFD for $2{\times}2cm^2$ field size were within 0.5% and 1.5% for 6 MV and 15 MV, respectively. The differences in output factor of three detectors for $3{\times}3cm^2$ to $5{\times}5cm^2$ field sizes were within 0.5%. Profile penumbras measured by the SFD, CC01, and CC13 detectors at three depths were average 2.7 mm and 3.5 mm, 3.4 mm and 4.3 mm, and 5.2 mm and 6.1 mm for 6 MV and 15 MV photon beams, respectively. In conclusion, it could be possible to use of the CC01 and SFD detectors for the measurement of percent depth dose and output factor for $2{\times}2cm^2$ field size, and to use of three detectors for $3{\times}3cm^2$ to $5{\times}5cm^2$ field sizes. CC01 and SFD detectors, consider ably smaller than the radiation field, should be used in order to accurately measure the profile penumbra for small field sizes.