• Progress in Medical Physics
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• v.32 no.3
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• pp.70-81
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• 2021

Purpose: This study was designed to investigate the dosimetric difference between intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in head and neck cancer (HNC). The study primarily focuses on low-dose spillage evaluation between these two techniques. Methods: This retrospective study involved 45 patients with HNC. The treatment plans were generated using the IMRT and VMAT techniques for all patients. Dosimetric comparisons were performed in terms of target coverage, organ-at-risk (OAR) sparing, and various parameters, including conformity index, uniformity index, homogeneity index, conformation number, low-dose volumes, and normal tissue integral dose (NTID). Results: No significant (P>0.05) difference in planning target volume coverage (D_95%) was observed between IMRT and VMAT plans for supraglottic larynx, hard palate, and tongue cancers. A decrease in dose volumes ranging from 1 Gy to 30 Gy was observed for VMAT plans compared with those for IMRT plans, except for V_1Gy and V_30Gy for supraglottic larynx cancer and V_1Gy for tongue cancer. Moreover, decreases (P<0.05) in NTID were observed for VMAT plans compared with that for IMRT plans in supraglottic larynx (4.50%), hard palate (12.80%), and tongue (7.76%) cancers. In contrast, a slight increase in monitor units for VMAT compared with those for IMRT in supraglottic larynx (0.46%), hard palate (2.54%), and tongue (7.56%) cancers. Conclusions: For advanced-stage HNC, both IMRT and VMAT offer satisfactory clinical plans. VMAT offers a conformal and homogeneous dose distribution with comparable OAR sparing and higher dose falloff outside the target volume than IMRT, which provides an edge to reduce the risk of secondary malignancies for HNC over IMRT.

• Progress in Medical Physics
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• v.24 no.3
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• pp.145-153
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• 2013

Stereotactic body radiation therapy (SBRT) is increasingly used to treat spinal metastases. To achieve the highest steep dose gradients and conformal dose distributions of target tumors, intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques are essential to spine radiosurgery. The purpose of the study was to qualitatively compare IMRT and VMAT techniques with International Spine Radiosurgery Consortium (ISRC) contoured consensus guidelines for target volume definition. Planning target volume (PTV) was categorized as TB, $T_{BPT}$ and $T_{ST}$ depending on sectors involved; $T_B$ (vertebral body only), $T_{BPT}$ (vertebral body+pedicle+transverse process), and $T_{ST}$ (spinous process+transverse process). Three patients treated for spinal tumor in the cervical, thoracic, and lumbar region were selected. Eacg tumor was contoured by the definition from the ISRC guideline. Maximum spinal cord dose were 12.46 Gy, 12.17 Gy and 11.36 Gy for $T_B$, $T_{BPT}$ and $T_{ST}$ sites, and 11.81 Gy, 12.19 Gy and 11.99 Gy for the IMRT, RA1 and RA2 techniques, respectively. Average fall-off dose distance from 90% to 50% isodose line for $T_B$, $T_{BPT}$, and $T_{ST}$ sites were 3.5 mm, 3.3 mm and 3.9 mm and 3.7 mm, 3.7 mm and 3.3 mm for the IMRT, RA1 and RA2 techniques, respectively. For the most complicated target $T_{BPT}$ sites in the cervical, thoracic and lumbar regions, the conformity index of the IMRT, RA1 and RA2 is 0.621, 0.761 and 0.817 and 0.755, 0.796 and 0.824 for rDHI. Both IMRT and VMAT techniques delivered high conformal dose distributions in spine stereotactic radiosurgery. However, if the target volume includes the vertebral body, pedicle, and transverse process, IMRT planning resulted in insufficient conformity index, compared to VMAT planning. Nevertheless, IMRT technique was more effective in reducing the maximum spinal cord dose compared to RA1 and RA2 techniques at most sites.

• Journal of the Korean Society of Radiology
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• v.15 no.2
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• pp.239-246
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• 2021

Portal Dosimetry was verified using EPID to secure the clinical application and reliability of the existing research dose evaluation. The dose distribution of Geant4 was compared with the measured value by 360° rotational irradiation with a 2.5 cm cone for stereotactic brain surgery. To confirm the dose distribution of patients with brain metastasis, the dose distribution investigated by inserting a Gafchromic EBT film into the parietal phantom and the dose distribution obtained from the parietal phantom using VMAT are compared and applied to actual patients. As a result of the analysis, it was confirmed that the accuracy of the beam center and the center of the couch coincide accurately with an error within 1mm as a result of QA through a pin ball. In addition, it was confirmed that the EBT3 film has excellent linearity in the range of 0 to 10 Gy according to various dose irradiation. In the same setting as the two cervical phantoms, we confirm that the implementation and simulation results calculations of dose calculations based on Geant4 using photon beams match the experimental data within the treatment planning volume (PTV). Therefore, volume modulated arc treatment (VMAT) 360° rotational irradiation was performed, and the result of iso-dose distribution analysis by rotational irradiation confirmed that it is appropriate to include a virtual tumor.

• Progress in Medical Physics
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• v.25 no.2
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• pp.65-71
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• 2014

A Varian Portal Dosimetry system was compared to an isocentrically mounted MapCHECK 2 diode array for volumetric modulated arc therapy (VMAT) QA. A Varian TrueBeam STx with an aS-1000 digital imaging panel was used to acquire VMAT QA images for 13 plans using four photon energies (6, 8, 10 and 15 MV). The EPID-based QA images were compared to the Portal Dose Image Prediction calculated in the Varian Eclipse treatment planning system (TPS). An isocentrically mounted Sun Nuclear MapCHECK 2 diode array with 5 cm water-equivalent buildup was also used for the VMAT QAs and the measurements were compared to a composite dose plane from the Eclipse TPS. A ${\gamma}$ test was implemented in the Sun Nuclear Patient software with 10% threshold and absolute comparison at 1%/1 mm (dose difference/distance-to-agreement), 2%/2 mm, and 3%/3 mm criteria for both QA methods. The two-tailed paired Student's t-test was employed to analyze the statistical significance at 95% confidence level. The average ${\gamma}$ passing rates were greater than 95% at 3%/3 mm using both methods for all four energies. The differences in the average passing rates between the two methods were within 1.7% and 1.6% of each other when analyzed at 2%/2 mm and 3%/3 mm, respectively. The EPID passing rates were somewhat better than the MapCHECK 2 when analyzed at 1%/1 mm; the difference was lower for 8 MV and 10 MV. However, the differences were not statistically significant for all criteria and energies (p-values >0.05). The EPID-based QA showed large off-axis over-response and dependence of ${\gamma}$ passing rate on energy, while the MapCHECK 2 was susceptible to the MLC tongue-and-groove effect. The two fluence-based QA techniques can be an alternative tool of VMAT QA to each other, if the limitations of each QA method (mechanical sag, detector response, and detector alignment) are carefully considered.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.8
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• pp.3365-3370
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• 2015

Radiotherapy has an important role in the treatment of prostate cancer. Three-dimensional conformal radiation therapy (3D-CRT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques are all applied for this purpose. However, the risk of secondary radiation-induced bladder cancer is significantly elevated in irradiated patients compared surgery-only or watchful waiting groups. There are also reports of risk of secondary cancer with low doses to normal tissues. This study was designed to compare received volumes of low doses among 3D-CRT, IMRT and VMAT techniques for prostate patients. Ten prostate cancer patients were selected retrospectively for this planning study. Treatment plans were generated using 3D-CRT, IMRT and VMAT techniques. Conformity index (CI), homogenity index (HI), receiving 5 Gy of the volume (V5%), receiving 2 Gy of the volume (V2%), receiving 1 Gy of the volume (V1%) and monitor units (MUs) were compared. This study confirms that VMAT has slightly better CI while thev olume of low doses was higher. VMAT had lower MUs than IMRT. 3D-CRT had the lowest MU, CI and HI. If target coverage and normal tissue sparing are comparable between different treatment techniques, the risk of second malignancy should be a important factor in the selection of treatment.

• Journal of Radiation Protection and Research
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• v.40 no.1
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• pp.17-24
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• 2015

To improve accuracy of dose calculation on kilovoltage cone beam computed tomography (kV CBCT) images, a custom-made phantom was fabricated to acquire an accurate CT number to electron density curve by full scatter of cone beam x-ray. To evaluate the dosimetric accuracy, 9 volumetric modulated arc therapy (VMAT) plans for head and neck (HN) cancer and 9 VMAT plans for lung cancer were generated with an anthropomorphic phantom. Both CT and CBCT images of the anthropomorphic phantom were acquired and dose-volumetric parameters on the CT images with CT density curve (CTCT), CBCT images with CT density curve ($CBCT_{CT}$) and CBCT images with CBCT density curve ($CBCT_{CBCT}$) were calculated for each VMAT plan. The differences between $CT_{CT}$ vs. $CBCT_{CT}$ were similar to those between $CT_{CT}$ vs. $CBCT_{CBCT}$ for HN VMAT plans. However, the differences between $CT_{CT}$ vs. $CBCT_{CT}$ were larger than those between $CT_{CT}$ vs. $CBCT_{CBCT}$ for lung VMAT plans. Especially, the differences in $D_{98%}$ and $D_{95%}$ of lung target volume were statistically significant (4.7% vs. 0.8% with p = 0.033 for $D_{98%}$ and 4.8% vs. 0.5% with p = 0.030 for $D_{95%}$). In order to calculate dose distributions accurately on the CBCT images, CBCT density curve generated with full scatter condition should be used especially for dose calculations in the region of large inhomogeneity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.10
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• pp.6187-6192
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• 2014

The use of WBRT(whole brain radiation therapy) has increased due to the increase in the incidence of metastatic brain tumors. The development of radiation therapy techniques is expected to improve the quality of life. The VMAT (Volumetric Modulated Arc Therapy) is an excellent treatment technique that can distinguish the dose in each volume. Therefore, this study compared conventional WBRT and VMAT for hair loss according to the scalp dose using a head phantom. The CI (Conformity Index), HI (Homogeneity Index) and QOC (Quality of Coverage) were measured brain tissue. A 20 percent and 50 percent dose was measured at the scalp, eyeball, lens, and c-spine. Conventional WBRT is excellent at 10 percent of brain tissue. VMAT is far superior at 1000 percent at the other organs. VMAT at the prescribed dose can be used as radiation therapy of metastatic brain tumors with less hair loss.

• Journal of Radiation Protection and Research
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• v.44 no.1
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• pp.43-52
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• 2019

Background: The mid-term performance of clinical linear accelerator (LINAC) during volumetric modulated arc therapy (VMAT) treatment period is not performed in clinical practice and usually replaced with one-time plan quality assurance (QA). In this research we aim to monitor daily reproducibility of VMAT delivery from tracking individual leaf movement error and dosimetric error to evaluate the mid-term quality of the machine used. Materials and Methods: First, multileaf collimator (MLC) information was imported into MATLAB program to determine which of the MLC leaves in the leaf bank had the maximum RMS position error (maxRMS). We estimated where the maximum positional errors (maxPE) of the chosen leaf occur along its path length and tracked its daily variations over the entire treatment period. Secondly, picture information of dosimetric error from portal dosimetry was imported into MATLAB where representative high gamma index region (HGR) was determined as HGR with length of > 1 cm and their centers were daily tracked. Results and Discussion: The maxPEs in the brain and tongue cases were distributed broader than in other cases, but all data were found located within ${\pm}0.5mm$. From first day to last day all of five cases show the similar visual pattern of HGRs and Centers of the longest HGRs remained within ${\pm}1mm$ of that in first day. These findings prove excellent mid-term performance of the LINAC used in VMAT treatments over a full course of treatment. Conclusion: Tracking the daily location changes of leaf movement and dosimetric error can be a good indicator of predicting the daily quality like stability and reproducibility of beam delivering in VMAT treatment.

• The Journal of Korean Society for Radiation Therapy
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• v.25 no.1
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• pp.77-85
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• 2013

Purpose: The accurate movement of gantry rotation, collimator and correct application of dose rate are very important to approach the successful performance of Volumetric Modulated Arc Therapy (VMAT), because it is tightly interlocked with a complex treatment plan. The interruption and restart of dose delivery, however, are able to occur on treatment by various factors of a treatment machine and treatment plan. If unexpected problems of a treat machine or a patient interrupt the VMAT, the movement of treatment machine for delivering the remaining dose will be restarted at the start point. In this investigation, We would like to know the effect of interruptions and restart regarding dose delivery at VMAT. Materials and Methods: Treatment plans of 10 patients who had been treated at our center were used to measure and compare the dose distribution of each VMAT after converting to a form of digital image and communications in Medicine (DICOM) with treatment planning system (Eclipse V 10.0, Varian, USA). We selected the 6 MV photon energy of Trilogy (Varian, USA) and used OmniPro I'mRT system (V 1.7b, IBA dosimetry, Germany) to analyze the data that were acquired through this measurement with two types of interruptions four times for each case. The door interlock and the beam-off were used to stop and then to restart the dose delivery of VMAT. The gamma index in OmniPro I'mRT system and T-test in Microsoft Excel 2007 were used to evaluate the result of this investigation. Results: The deviations of average gamma index in cases with door interlock, beam-off and without interruption on VMAT are 0.141, 0.128 and 0.1. The standard deviations of acquired gamma values are 0.099, 0.091, 0.071 and The maximum gamma value in each case is 0.413, 0.379, 0.286, respectively. This analysis has a 95-percent confidence level and the P-value of T-test is under 0.05. Gamma pass rate (3%, 3 mm) is acceptable in all of measurements. Conclusion: As a result, We could make sure that the interruption of this investgation are not enough to seriously affect dose delivery of VMAT by analyzing the measured data. But this investigation did not reflect all cases about interruptions and errors regarding the movement of a gantry rotation, collimator and patient So, We should continuously maintain a treatment machine and program to deliver the accurate dose when we perform the VMAT for the many kinds of cancer patients.

• Progress in Medical Physics
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• v.24 no.4
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• pp.295-302
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• 2013

We estimated secondary scattered and leakage doses for intensity-modulated radiotherapy (IMRT), volumetric arc therapy (VMAT) and tomotherapy (TOMO) in patients with liver cancer. Five liver patients were planned by IMRT, VMAT and TOMO. Secondary scatter (and leakage) dose and organ equivalent doses (OEDs) are measured and estimated at various points 20 to 80 cm from the iso-center by using radiophotoluminescence glass dosimeter (RPLGD). The secondary dose per Gy from IMRT, VMAT and TOMO for liver cancer, measured 20 to 80 cm from the iso-center, are 0.01~3.13, 0.03~2.34 and 0.04~1.29 cGy, respectively. The mean values of relative OED of secondary dose of VMAT and TOMO for five patients, which is normalized by IMRT, measured as 75.24% and 50.92% for thyroid, 75.14% and 40.61% for bowel, 72.30% and 47.77% for rectum, 76.21% and 49.93% for prostate. The secondary dose and OED from TOMO is relatively low to those from IMRT and VMAT. OED based estimation suggests that the secondary cancer risk from TOMO is less than or comparable to the risks from conventional IMRT and VMAT.