• Progress in Medical Physics
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• v.26 no.2
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• pp.79-86
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• 2015

The purpose of this study is to evaluate efficacy and feasibility of adaptive radiotherapy according to tumor volume change (TVC) in early stage non-small cell lung cancer (NSCLC) using stereotactic body radiotherapy (SBRT). Twenty-two lesions previously treated with SBRT were selected. SBRT was usually performed with a total dose of 48 Gy or 60 Gy in four fractions with an interval of three to four days between treatments. For evaluation of TVC, gross tumor volume (GTV) was contoured on each cone-beam computed tomography (CBCT) image used for image guidance. Intensity modulated radiotherapy (IMRT) planning was performed in the first CBCT (CBCT1) using a baseline plan. For ART planning (ART), re-optimization was performed at $2^{nd}$, $3^{rd}$, and $4^{th}$ CBCTs (CBCT2, CBCT3, and CBCT4) using the same angle and constraint used for the baseline plan. The ART plan was compared with the non-ART plan, which generated copying of the baseline plan to other CBCTs. Average GTV volume was 10.7 cc. Average TVC was -1.5%, 7.3%, and -25.1% in CBCT2, CBCT3, and CBCT4 and the TVC after CBCT3 was significant (p<0.05). However, the nine lesions were increased GTV in CBCT2. In the ART plan, $V_{20\;Gy}$, $D_{1500\;cc}$, and $D_{1000\;cc}$ of lung were significantly decreased (p<0.05), and $V_{30\;Gy}$ and $V_{32\;Gy}$ of the chest wall were also decreased (p<0.05). While D min of planning target volume (PTV) decreased by 8.3% in the non-ART plan of CBCT2 compared with the baseline plan in lesions with increased tumor size (p=0.021), PTV coverage was not compromised in the ART plan. Based on this result, use of the ART plan may improve target coverage and OAR saving. Thus ART using CBCT should be considered in early stage NSCLC with SBRT.

• Journal of Radiation Protection and Research
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• v.36 no.1
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• pp.28-34
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• 2011

The measurement-based verification for intensity modulated radiation therapy (IMRT) is a time-and labor-consuming procedure. Instead, this study aims to develop a MU fluence reconstruction method for IMRT QA. Total actual fluences from treatment planning system (TPS, Eclipse 8.6, Varian) were selected as a reference. Delivered leaf positions according to MU were extracted by the dynalog file generated after IMRT delivery. An in-house software was develop to reconstruct MU fluence from the acquired delivered leaf position data using MATLAB. We investigated five patient's plans delivered by both step-and-shoot IMRT and sliding window technologies. The total actual fluence was compared with the MU fluence reconstructed by using commercial software (Verisoft 3.1, PTW) and gamma analysis method (criteria: 3%/3 mm and 2%/1 mm). Gamma pass rates were $97.8{\pm}1.33$% and the reconstructed fluence was shown good agreement with RTP-based actual fluence. The fluence from step and shoot IMRT was shown slightly higher agreement with the actual fluence than that from sliding window IMRT. If moving from IMRT QA measurements toward independent computer calculations, the developed method can be used for IMRT QA. A point dose calculation method from reconstructed fluences is under development for the routine IMRT QA purpose.

• Radiation Oncology Journal
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• v.35 no.4
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• pp.306-316
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• 2017

Purpose: To investigate the predictive role of maximum standardized uptake value ($SUV_{max}$) of 2-[$^{18}F$]fluoro-2-deoxy-D-glucose($^{18}F-FDG$) positron emission tomography/computed tomography (PET/CT) in nasopharyngeal cancer patients treated with intensity-modulated radiotherapy (IMRT). Materials and Methods: Between October 2006 and April 2016, 53 patients were treated with IMRT in two institutions and their PET/CT at the time of diagnosis was reviewed. The $SUV_{max}$ of their nasopharyngeal lesions and metastatic lymph nodes (LN) was recorded. IMRT was delivered using helical tomotherapy. All patients except for one were treated with concurrent chemoradiation therapy (CCRT). Correlations between $SUV_{max}$ and patients' survival and recurrence were analyzed. Results: At a median follow-up time of 31.5 months (range, 3.4 to 98.7 months), the 3-year overall survival (OS) and disease-free survival (DFS) rates were 83.2% and 77.5%, respectively. In univariate analysis, patients with a higher nodal pre-treatment $SUV_{max}$ (${\geq}13.4$) demonstrated significantly lower 3-year OS (93.1% vs. 55.5%; p = 0.003), DFS (92.7% vs. 38.5%; p < 0.001), locoregional recurrence-free survival (100% vs. 50.5%; p < 0.001), and distant metastasis-free survival (100% vs. 69.2%; p = 0.004), respectively. In multivariate analysis, high pre-treatment nodal $SUV_{max}$ (${\geq}13.4$) was a negative prognostic factor for OS (hazard ratio [HR], 7.799; 95% confidence interval [CI], 1.506-40.397; p = 0.014) and DFS (HR, 9.392; 95% CI, 1.989-44.339; p = 0.005). Conclusions: High pre-treatment nodal $SUV_{max}$ was an independent prognosticator of survival and disease progression in nasopharyngeal carcinoma patients treated with IMRT in our cohort. Therefore, nodal $SUV_{max}$ may provide important information for identifying patients who require more aggressive treatment.

• Radiation Oncology Journal
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• v.32 no.1
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• pp.23-30
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• 2014

Purpose: The goal of this study is to determine whether the magnitude of overlap between planning target volume (PTV) and rectum ($Rectum_{overlap}$) or PTV and bladder ($Bladder_{overlap}$) in prostate cancer volumetric-modulated arc therapy (VMAT) is predictive of the dose-volume relationships achieved after optimization, and to identify predictive equations and cutoff values using these overlap volumes beyond which the Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) dose-volume constraints are unlikely to be met. Materials and Methods: Fifty-seven patients with prostate cancer underwent VMAT planning using identical optimization conditions and normalization. The PTV (for the 50.4 Gy primary plan and 30.6 Gy boost plan) included 5 to 10 mm margins around the prostate and seminal vesicles. Pearson correlations, linear regression analyses, and receiver operating characteristic (ROC) curves were used to correlate the percentage overlap with dose-volume parameters. Results: The percentage $Rectum_{overlap}$ and $Bladder_{overlap}$ correlated with sparing of that organ but minimally impacted other dose-volume parameters, predicted the primary plan rectum $V_{45}$ and bladder $V_{50}$ with $R^2$ = 0.78 and $R^2$ = 0.83, respectively, and predicted the boost plan rectum $V_{30}$ and bladder $V_{30}$ with $R^2$ = 0.53 and $R^2$ = 0.81, respectively. The optimal cutoff value of boost $Rectum_{overlap}$ to predict rectum $V_{75}$ >15% was 3.5% (sensitivity 100%, specificity 94%, p < 0.01), and the optimal cutoff value of boost $Bladder_{overlap}$ to predict bladder $V_{80}$ >10% was 5.0% (sensitivity 83%, specificity 100%, p < 0.01). Conclusion: The degree of overlap between PTV and bladder or rectum can be used to accurately guide physicians on the use of interventions to limit the extent of the overlap region prior to optimization.

• Radiation Oncology Journal
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• v.30 no.4
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• pp.158-164
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• 2012

Purpose: To evaluated the patterns of failure, survival rate, treatment-related toxicity and prognostic factors in postoperative radiotherapy of patients with ependymoma. Materials and Methods: Thirty patients who underwent surgery and postoperative radiotherapy for ependymoma between the period of June 1994 and June 2008 were reviewed retrospectively. The age of patients ranged from 21 months to 66 years (median, 19 years). Seventeen patients had grade II ependymoma, and 13 had grade III anaplastic ependymoma according to the World Health Organization grading system. The postoperative irradiation was performed with 4 or 6 MV photon beam with median dose of 52.8 Gy (range, 45 to 63 Gy), and radiation field including 2 cm beyond the preoperative tumor volume. Median follow-up period was 51 months (range, 12 to 172 months). Results: Fourteen out of 30 (46.7%) patients experienced recurrence, and 12 of those died. Among those 14 patients who experienced recurrence, 11 were in-field and 3 were out-of-field recurrence. The 5-year overall survival (OS) and progression-free survival (PFS) rates were 66.7% and 56.1%, respectively. On univariate analysis, tumor grade was a statistically significant prognostic factor for OS and PFS. There were two complications after surgery and postoperative radiotherapy, including short stature and facial palsy on the left side. Conclusion: We observed good survival rates, and histologic grade was a prognostic factor affecting the OS and PFS. Almost all recurrence occurred in primary tumor site, thus we suggest further evaluation on intensity-modulated radiotherapy or stereotatic radiosurgery for high-risk patients such as who have anaplastic ependymoma.

• Journal of radiological science and technology
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• v.35 no.4
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• pp.335-343
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• 2012

Intensity-modulated radiotherapy(IMRT) have the ability to provide better dose conformity and sparing of critical normal tissues than three-dimensional radiotherapy(3DCRT). Especially, with the benefit of health insurance in 2011, its use now increasingly in many modern radiotherapy departments. Also the use of linear accelerator with high-energy photon beams over 10 MV is increasing. As is well known, these linacs have the capacity to produce photonueutrons due to photonuclear reactions in materials with a large atomic number such as the target, flattening filters, collimators, and multi-leaf collimators(MLC). MLC-based IMRT treatments increase the monitor units and the probability of production of photoneutrons from photon-induced nuclear reactions. The purpose of this study is to quantitatively evaluate the dose of photoneutrons produced from 3DCRT and IMRT technique for Rando phantom in cervical cancer. We performed the treatment plans with 3DCRT and IMRT technique using Rando phantom for treatment of cervical cancer. An Rando phantom placed on the couch in the supine position was irradiated using 15 MV photon beams. Optically stimulated luminescence dosimeters(OSLD) were attached to 4 different locations (abdomen, chest, head and neck, eyes) and from center of field size and measured 5 times each of locations. Measured neutron dose from IMRT technique increased by 9.0, 8.6, 8.8, and 14 times than 3DCRT technique for abdomen, chest, head and neck, and eyes, respectively. When using IMRT with 15 MV photonbeams, the photoneutrons contributed a significant portion on out-of-field. It is difficult to prevent high energy photon beams to produce the phtoneutrons due to physical properties, if necessary, It is difficult to prevent high energy photon beams to produce the phtoneutrons due to physical properties, if necessary, it is need to provide the additional safe shielding on a linear accelerator and should therefore reduce the out-of-field dose.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.5
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• pp.1897-1900
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• 2015

Purpose: To evaluate acute toxicity in nasopharyngeal cancer (NPC) patients treated with intensity modulated radiotherapy (IMRT)/volumetric modulated arc therapy (VMAT) with or without cisplatin-based chemotherapy. Materials and Methods: A total of 45 newly diagnosed, histologically proven non-metastatic NPC patients treated with IMRT between May 2010 and December 2012, were evaluated retrospectively, 37 planned with Eclipse and 8 with Prowess Panther treatment planning system. The doses to the planning target volumes of primary tumor and involved lymph nodes, high risk region, and uninvolved regional nodal areas were 70 Gy, 60 Gy, and 54 Gy respectively and delivered simultaneously over 33 fractions to 39 patients. Another 6 patients irradiated with sequential boost technique. Some 84.4% of patients received chemotherapy. Acute toxicities were graded according to the Radiation Therapy Oncology Group scoring criteria and Common Terminology Criteria for Adverse Events (CTCAE) for chemotherapy side effects. Results: Median age was 43 years (14-79) and all patients were WHO type II. Grade 1 mucositis and dysphagia were observed in 17 (37.8%), and 10 (22.2%) patients, respectively. The incidence of acute grade 2 mucositis and dysphagia was 55.6% and 68.9%, respectively. The most common chemoradiotherapy related acute toxicities were nausea, leucopenia and thrombocytopenia. Grade 3 toxicity was detected in 13 (28.8%) cases. No grade 4 toxicity was occurred. Mean weight loss was 9%. None of the patients required the insertion of percutaneous endoscopic gastrostomy for nutritional support. Radiation therapy was completed without interruption in all patients. Conclusions: IMRT is a safe and effective treatment modality, and well tolerated by patients in the treatment of nasopharyngeal carcinoma. No unexpected side effects were observed.

• Progress in Medical Physics
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• v.29 no.2
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• pp.66-72
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• 2018

The proper position of a multi-leaf collimator (MLC) is essential for the quality of intensity-modulated radiation therapy (IMRT) and volumetric modulated arc radiotherapy (VMAT) dose delivery. Task Group (TG) 142 provides a quality assurance (QA) procedure for MLC position. Our study investigated the QA validation of the mechanical leaf gap measurement and the maintenance procedure. Two $VitalBeam^{TM}$ systems were evaluated to validate the acceptance of an MLC position. The dosimetric leaf gaps (DLGs) were measured for 6 MV, 6 MVFFF, 10 MV, and 15 MV photon beams. A solid water phantom was irradiated using $10{\times}10cm^2$ field size at source-to-surface distance (SSD) of 90 cm and depth of 10 cm. The portal dose image prediction (PDIP) calculation was implemented on a treatment planning system (TPS) called $Eclipse^{TM}$. A total of 20 VMAT plans were used to confirm the accuracy of dose distribution measured by an electronic portal imaging device (EPID) and those predicted by VMAT plans. The measured leaf gaps were 0.30 mm and 0.35 mm for VitalBeam 1 and 2, respectively. The DLG values decreased by an average of 6.9% and 5.9% after mechanical MLC adjustment. Although the passing rates increased slightly, by 1.5% (relative) and 1.2% (absolute) in arc 1, the average passing rates were still within the good dose delivery level (>95%). Our study shows the existence of a mechanical leaf gap error caused by a degenerated MLC motor. This can be recovered by reinitialization of MLC position on the machine control panel. Consequently, the QA procedure should be performed regularly to protect the MLC system.

• 대한두경부종양학회:학술대회논문집
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• 2004.11a
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• pp.262-262
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• 2004

• Radiation Oncology Journal
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• v.37 no.2
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• pp.127-133
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• 2019

Purpose: The aim of this study was to identify volume changes and dose variations of rectum and bladder during radiation therapy in prostate cancer (PC) patients. Materials and Methods: We analyzed 20 patients with PC treated with helical tomotherapy. Daily image guidance was performed. We re-contoured the entire bladder and rectum including its contents as well as the organ walls on megavoltage computed tomography once a week. Dose variations were analyzed by means of Dmedian, Dmean, Dmax, V₁₀ to V₇₅, as well as the organs at risk (OAR) volume. Further, we investigated the correlation between volume changes and changes in Dmean of OAR. Results: During treatment, the rectal volume ranged from 62% to 223% of its initial volume, the bladder volume from 22% to 375%. The average Dmean ranged from 87% to 118% for the rectum and 58% to 160% for the bladder. The Pearson correlation coefficients between volume changes and corresponding changes in Dmean were -0.82 for the bladder and 0.52 for the rectum. The comparison of the dose wall histogram (DWH) and the dose volume histogram (DVH) showed that the DVH underestimates the percentage of the rectal and bladder volume exposed to the high dose region. Conclusion: Relevant variations in the volume of OAR and corresponding dose variations can be observed. For the bladder, an increase in the volume generally leads to lower doses; for the rectum, the correlation is weaker. Having demonstrated remarkable differences in the dose distribution of the DWH and the DVH, the use of DWHs should be considered.