• Journal of the Korean Society of Radiology
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• v.13 no.7
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• pp.925-932
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• 2019

In this paper, we developed optical dosimetry system with a plastic scintillator, a commercial 50 mm, f1.8 lens, and a commercial high-sensitivity CMOS (complementary metal-oxide semiconductor) camera. And, the correction processors of vignetting, geometrical distortion and scaling were established. Using the developed system, we can measured a percent depth dose, a beam profile and a dose linearity for 6 MV medical LINAC (Linear Accelerator). As results, the optically measured percent depth dose was well matched with the measured percent depth dose by ion-chamber within 2% tolerance. And the determined flatness was 2.8%. We concluded that the optical dosimetry system was sufficient for application of absorbed dose monitoring during radiation therapy.

• Progress in Medical Physics
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• v.1 no.1
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• pp.91-95
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• 1990

The solid state detector system was constructed using commercially available rectifier diode for the assessment of quality assurance in radiotherapy. Dosimetry system which consists of the electrometer and the water phanton was used for measuring small field size scanning. The measured results, which had linearity in accordance with variation of radiation dose for gamma-ray of Co- 60 and 6 and 10MV photons of linear accelerator, showed quite linear characteristics within 1% error. The percent depth dose of 10MV photon of Mevatron KD linear accelerator was measured in small field size using diode, and the results were compared with that of using ion chambers. The results show that the difference of percent depth dose between the value of diode and that of ion chamber was negligible in large field size. However, in small size less than 4$\times$4cm, the difference of percent depth dose estimated by diode and ion chamber was 4.7% by extrapolation to 0$\times$0cm. Considering the smaller volume of diode than that of ion chamber, it might be more reliable to use diode for estimating percent depth dose. Above results suggest that diode can be used for routine check such as beam profile, flatness, symmetry and energy

• Radiation Oncology Journal
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• v.11 no.2
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• pp.455-461
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• 1993

Experimental measurements of dose characteristics with pentagonal applicator at nominal energy of 4, 6, 9, 12 and 15 MeV electron beam were performed for intraoperative radiotherapy (IORT) in ML-15MDX linear accelerator. This paper presents the percent depth dose, surface dose, beam flatness and output factors of using the IORT applicator in different electron beam energy. The output factor showed as a 24 percent higher in IORT applicator than that of reference $10{\times}10cm^2$ applicator. The surface dose of using the IORT applicator showed 7.7 and 2.7 percent higher than that of reference field in 4 and 15 MeV electron beam, respectively. In our experiments, the variation of percent depth dose was very small but the output factor and flatnees at 0.5 cm depth have showed a large value in IORT applicator.

• Radiation Oncology Journal
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• v.1 no.1
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• pp.21-24
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• 1983

The thickness of the part being irradiated is finite. Percent depth dose tables being used routinely are generally obtained from dosimetry in a phantom much thickner than usual patient. At or close to exit surface, the dose should be less than that obtained from the percent depth dose tables, because of insufficient volume for backscattering. To know the difference between the true absorbed dose and the dose obtained from percent depth dose table, the doses at or close to the exit surface were measured with plate type ionization chamber with volume of 0.5ml. The results are as follows; 1. In the case of $^{60}Co$, percent depth dose at a given depth increases with underlying phantom thickness up to the 5cm. 2. In the case of $^{60}Co$, the dose correction factor at exit surface which is less than 1, increases with part thickness and decreases with field size. 3. Exposure time may not be corrected when the part above 10cm in thickness is treated by $^{60}Co$. 4. In the case of 10MV x-ray, the dose correction factor is nearly 1 and constant for the underlying phantom thickness and field size, so the correction of monitor unit is not necessary for part thickness.

• Radiation Oncology Journal
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• v.7 no.1
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• pp.101-112
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• 1989

The treatment planning and dosimetry of small fields for stereotactic radiosurgery with 10 MV x-ray isocentrically mounted linear accelerator is presented. Special consideration in this study was given to the variation of absorbed dose with field size, the central axis percent depth doses and the combined moving beam dose distribution. The collimator scatter correction factors of small fields $(1\times1\~3\times3cm^2)$ were measured with ion chamber at a target chamber distance of 300cm where the projected fields were larger than the polystyrene buildup caps and it was calibrated with the tissue equivalent solid state detectors of small size (TLD, PLD, ESR and semiconductors). The central axis percent depth doses for $1\timesl\;and\;3\times3cm^2$ fields could be derived with the same acuracy by interpolating between measured values for larger fields and calculated zero area data, and it was also calibrated with semiconductor detectors. The agreement between experimental and calculated data was found to be under $2\%$ within the fields. The three dimensional dose planning of stereotactic focusing irradiation on small size tumor regions was performed with dose planning computer system (Therac 2300) and was verified with film dosimetry. The more the number of strips and the wider the angle of arc rotation, the larger were the dose delivered on tumor and the less the dose to surrounding the normal tissues. The circular cone, we designed, improves the alignment, minimizes the penumbra of the beam and formats ball shape of treatment area without stellate patterns. These dosimetric techniques can provide adequate physics background for stereotactic radiosurgery with small radiation fields and 10MV x-ray beam.

• Radiation Oncology Journal
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• v.7 no.2
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• pp.279-285
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• 1989

Central axis depth dose data for 6 MV X-rays, including tissue maximum ratios, were measured for wedge fields according to Tatcher's equation. In wedge fields, the differences in magnitude which increased with depth, field size, and wedge thickness increased when compared with the corresponding open field data. However, phantom scatter correction factors for wedge fields differed less than $1\%$ from the corresponding open field factors. The differences in central axis percent depth dose between two types of fields indicated beam hardening by the wedge filter The deviation of percent depth doses and scatter correction factors between the effective wedge field and the nominal wedge field at same angle was negligible. The differences were less than $3.20\%$ between the nominal or effective wedge fields and the open fields for percent depth doses to the depth 7cm in $6cm{\times}6cm$ field. For larger $(10cm{\times}10cm)$ field size, however, the deviation of percnet depth doses between the nominal or effective wedge fields and the open fields were greater-dosimetric errors were $3.56\%$ at depth 7cm and nearly $5.30\%$ at 12cm. We suggest that the percent depth doses of individual wedge and wedge transmission factors should be considered for the dose calculation or monitor setting in the treatment of deep seated tumor.

• Progress in Medical Physics
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• v.18 no.4
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• pp.209-213
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• 2007

In this work we have measured the dose distribution and the percent depth dose of 20 MeV electron beam using the X-OMAT films in order to verify the effects of transverse magnetic field on high energy elecrtron beam in a phantom. The result shows about 30% increase of the percent depth dose at 4.5 cm depth under the transverse magnetic field of 1.5 Tesla at 7.5 cm depth. We have verified that these were in an agreement with other theoretical results.

• Radiation Oncology Journal
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• v.13 no.3
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• pp.285-289
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• 1995

Purpose : We compared the calcualted percent depth dose curves of 6 MeV electron beam to that of measured to evaluate the usefulness of Monte-carlo simulation method in radiation physics. Materials and Methods : The radiation dose values of 6 MeV electron beam using EGS4 code with one million histories in water were compared values that were measured from the depth dose curve of electron beam irradiated by medical accelerator ML6M. The central axis dose values were calculated according to the changing field size. such as $5{\times}5,\;10{\times}10,\;15{\times}15,\;20{\times}20cm^2$. Results : The value calculated showed a very similar shape to depth dose curve. The calculated and measured value of $D_max$ at $10{\times}10cm^2$ cone is 15mm and 14mm respectively. The calculated value of the surface radiation dose rate is $65.52\%$ and measured one is $76.94\%$. The surface radiation dose rate has varied from $64.43\%$ to $66.99\%$. The calculated values of $D_max$ are in the range between 15mm and 18mm. The calculated value was fitted well with measured value around the $D_max$ area, excluding build up range and below the $90\%$ depth dose area. Conclusion : This result suggested that the calculation of dose value can be replace the direct measurement of the dose for radiation therapy. Also, EGS4 may be a very convenient program to assess the effect of radiation dose using by personal computers.

• The Journal of Korean Society for Radiation Therapy
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• v.13 no.1
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• pp.38-46
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• 2001

Purpose : The aim of this study is to investigate the effect of tissue inhomogeneities when appling to contrast medium among Homogeneous, Batho and ETAR dose calculation method in RTP system. Method and Material : We made customized heterogeneous phantom it filled with water or contrast medium slab. Phantom scan data have taken PQ 5000 (CT scanner, Marconi, USA) and then dose was calculated in 3D RTP (AcQ-Plan, Marconi, USA) depends on dose calculation algorithm (Homogeneous, Batho, ETAR). The dose comparisons were described in terms of 2D isodose distribution, percent depth dose data, effective path length and monitor unit. Also dose distributions were calculated with homogeneous and inhomogeneous correction algorithm, Batho and ETAR, in each patients with different clinical sites. Results : Result indicated that Batho and ETAR method gave rise to percent depth dose deviation $1.5{\sim}2.7\%,\;2.3{\sim}3.5\%$ (6MV, field size $10{\times}10cm^2$) in each status with and without contrast medium. Also show that effective path lengths were more increase in contrast status (23.14 cm) than Non-contrast (22.07 cm) about $4.9\%$ or 10.7 mm (In case Hounsfield Unit 270) and these results were similary showned in each patient with different clinical site that was lung. prostate, liver and brain region. Concliusion : In conclusion we shown that the use of inhomogeneity correction algorithm for dose calculation in status of injected contrast medium can not represent exact dose at GTV region. These results mean that patients will be more irradiated photon beam during radiation therapy.

• Radiation Oncology Journal
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• v.13 no.1
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• pp.95-100
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• 1995

Purpose : To evaluate the effect on surface dose due to Aquaplast used for immobilizing the patients with head and neck cancers in photon beam radiotherapy Materials and Methods: To assess surface and buildup region dose for 6MV X-ray from linear accelerator(Siemens Mevatron 6740), we measured percent ionization value with the Markus chamber model 30-329 manufactured by PTW Frieburg and Capintec electrometer, model WK92. For measurement of surface ionization value, the chamber was embedded in $25{\times}25{\times}3cm^3$ acrylic phantom and set on $25{\times}25{\times}5cm^3$ polystyrene phantom to allow adequate scattering. The measurements of percent depth ionization were made by placing the polystyrene layers of appropriate thickness over the chamber. The measurements were taken at 100cm SSD for $5{\times}5cm^2$, $10{\times}10cm^2$ and $15{\times}15cm^2$ field sizes, respectively. Placing the layer of Aquaplast over the chamber, the same procedures were repeated. We evaluated two types of Aquaplast: 1.6mm layer of original Aquaplast(manufactured by WFR Aquaplast Corp.) and transformed Aquaplast similar to moulded one for immobilizing the patients practically. We also measured surface ionization values with blocking tray in presence or absence of transformed Aquaplast. In calculating percent depth dose, we used the formula suggested by Gerbi and Khan to correct overresponse of the Markus chamber. Results : The surface doses for open fields of $5{\times}5cm^2$, $10{\times}10cm^2$, and $15{\times}15cm^2$ were $79\%$, $13.6\%$, and $18.7\%$, respectively. The original Aquaplast increased the surface doses upto $38.4\%$, $43.6\%$, and $47.4\%$, respectively. For transformed Aquaplast, they were $31.2\%$, $36.1\%$, and $40.5\%$, respectively. There were little differences in percent depth dose values beyond the depth of Dmax. Increasing field size, the blocking tray caused increase of the surface dose by $0.2\%$, $1.7\%$, $3.0\%$ without Aquaplast, $0.2\%$, $1.9\%$, $3.7\%$ with transformed Aquaplast, respectively. Conclusion: The original and transformed Aquaplast increased the surface dose moderately. The percent depth doses beyond Dmax, however, were not affected by Aquaplast. In conclusion, although the use of Aquaplast in practice may cause some increase of skin and buildup region dose, reductioin of skin-sparing effect will not be so significant clinically.