BACKGROUND/AIM:To analyze failure patterns and evaluate the clinical necessity of lower neck irradiation (LNI) during elective neck irradiation (ENI) in patients with parotid gland cancers (PGCs). PATIENTS AND METHODS:Forty patients with PGCs who received postoperative radiotherapy (PORT) following parotidectomy between 2006 and 2024 were included. LNI was defined as the elective inclusion of neck levels III and IV in the irradiated field. The primary endpoint was progression-free survival (PFS), while secondary endpoints included local-regional failure-free survival (LRFFS), distant metastasis-free survival (DMFS), and overall survival (OS). RESULTS:The median follow-up time was 68.7 months. Among the 40 patients, 19 (47.5%) received LNI as part of their PORT. Five-year rates of LRFFS, DMFS, OS, and PFS were 91.2%, 80.2%, 88.7%, and 76.3%, respectively. While LNI showed no significant association with survival outcomes, multivariate analysis confirmed that perineural invasion (PNI) was a significant prognostic factor for PFS [hazard ratio (HR)=5.17, p=0.028], OS (HR=7.97, p=0.017), and DMFS (HR=9.67, p=0.009). The major failure pattern was distant metastasis (N=8). Regional failures were infrequent (5%), involving level II (N=1) and levels Ib, II, and IV (N=1). CONCLUSION:Regional failures in PGC are rare and predominantly confined to the upper neck. Omitting LNI did not compromise regional control. Treatment strategies for PGCs with PNI should focus on the intensification of systemic therapy and close monitoring for distant metastasis.

BACKGROUND/AIM:To compare survival outcomes and radiation-related toxicities between conventional radiotherapy (CvT) and volumetric-modulated arc therapy (VMAT) in patients with early glottic cancer. PATIENTS AND METHODS:We reviewed 81 patients with Tis-T2N0 glottic cancer who underwent definitive radiotherapy between 2010 and 2018. CvT (N=47) was delivered using two opposing lateral beams (70 Gy in 35 fractions), while VMAT (N=34) utilized two arcs (65.25 Gy in 29 fractions). Hypothyroidism was defined as an elevated thyroid-stimulating hormone level with or without a decrease in free T4 or T3 levels. RESULTS:The overall median follow-up time was 80.0 months and was longer in the CvT group (116.0 months) than in the VMAT group (45.3 months). Five-year local failure-free survival (95.4% vs. 84.5%, p=0.088), regional failure-free survival (93.0% vs. 94.1%, p=0.481), locoregional failure-free survival (90.9% vs. 84.7%, p=0.319), and overall survival (89.4% vs. 90.7%, p=0.575) were comparable between the CvT and VMAT groups, respectively. No increase in regional failure was observed in the VMAT group despite exclusion of the anterior level III neck. Most local failures in the VMAT group occurred near the original tumor site and were associated with T2 disease (p=0.015). Hypothyroidism occurred more frequently in the CvT group (53.5%) than in the VMAT group (25.9%, p=0.043). Carotid artery events were noted in three patients treated with CvT (6.4%), with none in the VMAT group. CONCLUSION:VMAT demonstrated comparable survival outcomes to CvT while significantly reducing the incidence of hypothyroidism and potentially lowering carotid artery events. VMAT may be considered a preferred modality to improve quality of life in patients with early glottic cancer.

Purpose: The purpose of this study was to determine if treatment dose to the lungs can be considered in the initial treatment planning according to change in tumor size during treatment.Methods: Lung dose was evaluated in 26 patients who underwent re-planning CT (reCT) due to changes in tumor size during lung cancer treatment with intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc radiotherapy (VMAT). Relevant parameters were V5, V10, V20, V30, V40, and mean lung dose. Results: Dose parameters to most lungs followed a normal distribution, but there were no statistically significant results for changes in lung dose after reCT. Patients with only lungs surrounding the tumor tended to have a 7.6% decrease in mean bilateral lung dose (MBLD) as tumor volume decreased. In contrast, patients with ribs and vertebrae within the target region showed a 5.9% increase in MBLD. Mean dose to the bilateral lungs before and after reCT increased (positively correlated) with high-density material in the planned target volume (PTV).Conclusions: This study found a correlation of radiological dose to the lungs to presence of high-density material in the PTV. In such patients, reducing lung dose in the initial treatment plan is expected to reduce radiation side effects.

BACKGROUND/AIM:To investigate the association between the thyroid dysfunction and thyroid radiation dose in regional nodal irradiation (RNI) using volumetric modulated arc therapy (VMAT) for breast cancer.PATIENTS AND METHODS:We reviewed medical data of 67 patients with breast cancer who underwent curative surgery followed by adjuvant radiotherapy, including RNI using VMAT, between 2018 and 2021. All patients had normal thyroid functional test results, including thyroid stimulating hormone (TSH), T3, and free-T4. We defined subclinical hypothyroidism as increased TSH with or without decreased levels of free-T4 and T3 after the completion of VMAT. We calculated dose-volume histogram parameters (DVHPs), including the mean dose and relative thyroid volume receiving at least 10, 20, 30, and 40 Gy.RESULTS:The median follow-up time was 23.2 months. The 3-year locoregional failure-free survival, progression-free survival, and overall survival rates were 96.3%, 94.7%, and 96.2%, respectively. The mean thyroid dose was 21.4 Gy (range=11.5-29.4 Gy). Subclinical hypothyroidism was noted in 14 patients (20.9%) and the median time to the event was 4.1 months. Among the DVHPs, the relative volume receiving ≥20 Gy (V20Gy) was associated with subclinical hypothyroidism. The 2-year rates of subclinical hypothyroidism were 24.8% and 59.1% in patients with V20Gy ≤46.3% and >46.3%, respectively.CONCLUSION:A significant proportion of patients with breast cancer developed subclinical hypothyroidism after undergoing VMAT for RNI. Our findings highlight the importance of considering the thyroid as an organ at risk for VMAT planning, and suggest that V20Gy could be a useful dose-volume constraint.

Relative output dose was evaluated while changing the gantry angle and couch angle using an EDGE diode detector in a clinical setting. An ELEKTA cone collimator used in stereotactic radiosurgery (SRS) was used for measurements. We place the edge detector at a depth of 10 cm of solid phantom (30 × 30 × 20 cm 3 ) with a source to axis distance (SAD) of 100 cm. The relative output dose obtained by the EDGE detector was measured while the cone was mounted and the gantry angle was changed under the conditions of 0°, 45°, 90°, 315°, and 270°. As the distance of the passing beam increases as the gantry angle increases at table angle 0°, the intensity of the beam decreases and has a minimum value at the angle of 56.3°, 123.7°, 236.3°, and 303.7°. The sensitivity of output was highest in the anterior direction, and it showed a tendency to decrease in the posterior direction. It can be seen that the relative dose decreases around 60 and 120 degrees according to the change of the table angle, which is thought to be due to the change in beam transmittance according to the beam passing distance and the structure of the EDGE detector, and the sensitivity of the detector. It is also meaningful to report the dependence of the output dose on the angle when measuring using the phantom used in actual clinical practice.

Background/Aim: To evaluate the early effect of radiation dose on liver function in breast cancer patients undergoing free-breathing volumetric modulated arc therapy (FB-VMAT). Patients and Methods: Medical records of 125 patients with breast cancer who underwent curative surgery followed by postoperative radiotherapy using FB-VMAT during 2018-2021 were reviewed. Results of the liver function test (LFT), performed within 1-week before and 6-months after radiotherapy, were collected and compared. The LFTs analyzed albumin, total and direct bilirubin, aspartate transaminase, alanine transferase, and alkaline phosphatase levels. The mean dose and relative liver volume receiving at least 10 Gy, 20 Gy, or 30 Gy were calculated. Results: Median follow-up time was 21.4 months. One patient experienced locoregional and distant failures. The mean liver irradiation dose was 325.9 centigray (cGy) for all patients. The liver irradiation dose was higher in patients with right breast cancer than in those with left breast cancer (mean, 434.1 cGy vs. 260.6 cGy, p<0.001). Direct bilirubin and aspartate transaminase levels showed significant differences after FB-VMAT. LFT results outside normal limits were noted in 31 patients at follow-up, but nobody met the criteria of radiation-induced liver disease. Underlying liver disease, breast laterality, systemic treatment, or dose-volume histogram parameters were not associated with abnormal LFT results. Conclusion: FB-VMAT can deliver radiation doses safely without adversely affecting the liver. The mean dose ≤4 Gy could be a useful dose criterium of the liver for FB-VMAT plans.

Background/Aim: Lymphocyte-to-monocyte ratio, neutrophil-to-lymphocyte ratio, and platelet-to-lymphocyte ratio represent systemic immune-inflammatory responses. We evaluated the association between immune-inflammatory cell ratios and prognosis in esophageal squamous cell carcinoma (ESCC) patients who underwent definitive concurrent chemoradiotherapy (dCCRT). Patients and Methods: Medical records of 68 ESCC patients in three institutions who underwent dCCRT between 2006 and 2017 were reviewed. The immune-inflammatory cell ratios were calculated before and after dCCRT. Results: The median follow-up time was 11.4 months. The 3-year overall survival (OS) rate was 21.6%. Among the immune-inflammatory cell ratios, lower post-dCCRT neutrophil-to-lymphocyte ratio (NLRpost) was associated with better OS (median 15.2 vs. 9.7 months, p=0.030). Patients with lower NLRpost had more improved OS when adjuvant chemotherapy was administered following dCCRT (median 16.6 vs. 4.8 months, p<0.001). Conclusion: NLRpost may be useful in predicting OS in ESCC patients after dCCRT. Furthermore, NLRpost might play a role in establishing adjuvant therapy plans following dCCRT.

Background/Aim: To validate the effect of treatment intensification on survival in esophageal squamous cell carcinoma (ESCC) patients undergoing definitive concurrent chemoradiotherapy (dCCRT). Patients and Methods: We reviewed the medical records of 73 ESCC patients who underwent dCCRT between 2006 and 2017 in 3 institutions. Results: The median follow-up time was 13.3 months. The median overall survival (OS) and locoregional recurrence-free survival (LRFS) were 13.3 and 11.2 months, respectively. The median radiotherapy dose was 55.8 Gy, and the median biologically effective dose (BED) was 65.8 Gy. Chemotherapy was given in all patients during dCCRT, and adjuvant chemotherapy was administered in 56 patients (76.7%). Adjuvant chemotherapy improved OS (3-year, 24.2% vs. 11.8%, p=0.004). Higher BED ≥70 Gy improved LRFS (3-year, 41.7% vs. 23.6%, p=0.035). Conclusion: The addition of chemotherapy after dCCRT improves OS. A higher radiotherapy dose improved LRFS, but not OS. Adjuvant chemotherapy should be considered after dCCRT for better outcomes.

Recent radiation therapy has overcome the effect of internal organ motion by limiting the range of movements, gating the beam irradiation or tracking the target movement. A successful strategy requires accurate real-time estimation of target location during radiation treatment. In this study, we propose a relatively simple technique to predict patient’s respiratory pattern (RP) one step before the breathing using a Bayesian approach. Patients’ respiratory signals (RSs) were analyzed using the in-house RPM signal analyzer, and parameters (period (τ), baseline (β) and amplitude (ϕ)) characterizing an RP were extracted. Based on each parameter, we obtained the probability density function (PDF) and transition probability matrix defined as ‘likelihood’. We predicted the following RP based on the PDF and the likelihood, then compared the estimated RP with the actual one. The proposed method was applied to five lung cancer patients who were treated with radiation therapy in our facility. Prediction error was analyzed using root-mean-square error (RMSE;ε, in mm) and relative RMSE (ϵ, in %) for each breathing cycle in all RP. The ε range was [0.45,2.66], and ϵ range was [5,18.8]. The prediction accuracy was strongly dependent on the irregularity of RP. Although the prediction errors were more significant than expected, we could confirm the feasibility of the proposed algorithm. The proposed algorithm is more intuitive than other sophisticated methods and requires less computation time.

Purpose: The poor quality of megavoltage (MV) images from electronic portal imaging device (EPID) hinders visual verification of tumor targeting accuracy particularly during markerless tumor tracking. The aim of this study was to investigate the effect of a few representative image processing treatments on visual verification and detection capability of tumors under auto tracking. Methods: Images of QC-3 quality phantom, a single patient's setup image, and cine images of two-lung cancer patients were acquired. Three image processing methods were individually employed to the same original images. For each deblurring, contrast enhancement, and denoising, a total variation deconvolution, contrast-limited adaptive histogram equalization (CLAHE), and median filter were adopted, respectively. To study the effect of image enhancement on tumor auto-detection, a tumor tracking algorithm was adopted in which the tumor position was determined as the minimum point of the mean of the sum of squared pixel differences (MSSD) between two images. The detectability and accuracy were compared. Results: Deblurring of a quality phantom image yielded sharper edges, while the contrast-enhanced image was more readable with improved structural differentiation. Meanwhile, the denoising operation resulted in noise reduction, however, at the cost of sharpness. Based on comparison of pixel value profiles, contrast enhancement outperformed others in image perception. During the tracking experiment, only contrast enhancement resulted in tumor detection in all images using our tracking algorithm. Deblurring failed to determine the target position in two frames out of a total of 75 images. For original and denoised set, target location was not determined for the same five images. Meanwhile, deblurred image showed increased detection accuracy compared with the original set. The denoised image resulted in decreased accuracy. In the case of contrast-improved set, the tracking accuracy was nearly maintained as that of the original image. Conclusions: Considering the effect of each processing on tumor tracking and the visual perception in a limited time, contrast enhancement would be the first consideration to visually verify the tracking accuracy of tumors on MV EPID without sacrificing tumor detectability and detection accuracy.

We designed an in-house phantom for mechanical quality assurance (QA) and compared its performance against commercial available QA tools. The QA phantom is an acrylic cubic shape with dimensions of 150 mm × 150 mm × 150 mm, and with a pocket into which various adapter plates can be inserted. The plates were classified into three types (A, B, and C) according to their location and shape. An additional accessory can be used to check the alignment of lasers to the center of CT image scans. We evaluated the usefulness of the phantom by checking mechanical isocentricity, field size accuracy, isocenter and position coincidence between the treatment beam and the image guidance systems, and alignment of the lasers. All the tests carried out were within the tolerance limits. The isocenter of the gantry and collimator was within 1 mm and the field size was within 2 mm for both the commercial tool and the new phantom. The kV image of the isocenter was within 0.5 mm for both the commercial tool and the new phantom and that of the displacement of the off-center position from the isocenter was within 0.5 mm for both phantoms. Displacement between the laser origin and the center of a CT image scan was within 0.5 mm for the commercial tool and new phantom. The developed phantom can also be used to easily check the geometrical and mechanical parameters of medical linear accelerators (LINAC) and CT simulators.

EBT3 film is utilized as a dosimetry quality assurance tool for the verification of clinical radiotherapy treatments. In this work, we suggest a percentage-depth-dose (PDD) calibration method that can calibrate several EBT3 film pieces together at different dose levels because photon beams provide different dose levels at different depths along the axis of the beam. We investigated the feasibility of the film PDD calibration method based on PDD data and compared the results those from the traditional film calibration method. Photon beams at 6 MV were delivered to EBT3 film pieces for both calibration methods. For the PDD-based calibration, the film pieces were placed on solid phantoms at the depth of maximum dose (dmax) and at depths of 3, 5, 8, 12, 17, and 22 cm, and a photon beam was delivered twice, at 100 cGy and 400 cGy, to extend the calibration dose range under the same conditions. Fourteen film pieces, to maintain their consistency, were irradiated at doses ranging from approximately 30 to 400 cGy for both film calibrations. The film pieces were located at the center position on the scan bed of an Epson 1680 flatbed scanner in the parallel direction. Intensity-modulated radiation therapy (IMRT) plans were created, and their dose distributions were delivered to the film. The dose distributions for the traditional method and those for the PDD-based calibration method were evaluated using a Gamma analysis. The PDD dose values using a CC13 ion chamber and those obtained by using a FC65-G Farmer chamber and measured at the depth of interest produced very similar results. With the objective test criterion of a 1% dosage agreement at 1 mm, the passing rates for the four cases of the three IMRT plans were essentially identical. The traditional and the PDD-based calibrations provided similar plan verification results. We also describe another alternative for calibrating EBT3 films, i.e ., a PDD-based calibration method that provides an easy and time-saving approach to film calibration.

The dose constraint during prostate intensity-modulated radiation therapy (IMRT) optimization should be patient-specific for better rectum sparing. The aims of this study are to suggest a novel method for automatically generating a patient-specific dose constraint by using an experience-based dose volume histogram (DVH) of the rectum and to evaluate the potential of such a dose constraint qualitatively. The normal tissue complication probabilities (NTCPs) of the rectum with respect to V %ratio in our study were divided into three groups, where V %ratio was defined as the percent ratio of the rectal volume overlapping the planning target volume (PTV) to the rectal volume: (1) the rectal NTCPs in the previous study (clinical data), (2) those statistically generated by using the standard normal distribution (calculated data), and (3) those generated by combining the calculated data and the clinical data (mixed data). In the calculated data, a random number whose mean value was on the fitted curve described in the clinical data and whose standard deviation was 1% was generated by using the ‘randn’ function in the MATLAB program and was used. For each group, we validated whether the probability density function (PDF) of the rectal NTCP could be automatically generated with the density estimation method by using a Gaussian kernel. The results revealed that the rectal NTCP probability increased in proportion to V %ratio , that the predictive rectal NTCP was patient-specific, and that the starting point of IMRT optimization for the given patient might be different. The PDF of the rectal NTCP was obtained automatically for each group except that the smoothness of the probability distribution increased with increasing number of data and with increasing window width. We showed that during the prostate IMRT optimization, the patient-specific dose constraints could be automatically generated and that our method could reduce the IMRT optimization time as well as maintain the IMRT plan quality.

Purpose:Despite the importance of accurately estimating the respiration regularity of a patient in motion compensation treatment, an effective and simply applicable method has rarely been reported. The authors propose a simple respiration regularity index based on parameters derived from a correspondingly simplified respiration model.Methods:In order to simplify a patient's breathing pattern while preserving the data's intrinsic properties, we defined a respiration model as a power of cosine form with a baseline drift. According to this respiration formula, breathing‐pattern fluctuation could be explained using four factors: sample standard deviation of respiration period, sample standard deviation of amplitude and the results of simple regression of the baseline drift (slope and standard deviation of residuals of a respiration signal. Overall irregularity (δ) was defined as a Euclidean norm of newly derived variable using principal component analysis (PCA) for the four fluctuation parameters. Finally, the proposed respiration regularity index was defined as ρ=ln(1+(1/ δ))/2, a higher ρ indicating a more regular breathing pattern. Subsequently, we applied it to simulated and clinical respiration signals from real‐time position management (RPM; Varian Medical Systems, Palo Alto, CA) and investigated respiration regularity. Moreover, correlations between the regularity of the first session and the remaining fractions were investigated using Pearson's correlation coefficient.Results:The respiration regularity was determined based on ρ; patients with ρ<0.3 showed worse regularity than the others, whereas ρ>0.7 was suitable for respiratory‐gated radiation therapy (RGRT). Fluctuations in breathing cycle and amplitude were especially determinative of ρ. If the respiration regularity of a patient's first session was known, it could be estimated through subsequent sessions.Conclusions:Respiration regularity could be objectively determined using a respiration regularity index, ρ. Such single‐index testing of respiration regularity can facilitate determination of RGRT availability in clinical settings, especially for free‐breathing cases.This work was supported by a Korea Science and Engineering Foundation (KOSEF) grant funded by the Korean Ministry of Science, ICT and Future Planning (No. 2013043498).

Background: The study examined the correlations among the results of the European Organization for Research and Treatment of Cancer (EORTC)-Quality of Life Questionnaire, Core 30 (QLQ-C30) completed by elderly cancer patients and their family caregivers and the Eastern Cooperative Oncology Group (ECOG)-performance status (PS) evaluated by medical doctors. Methods: The study sample included 269 persons with cancer aged 55 years or older and their family care- givers recruited from hospitals located in Seoul and Gyeonggi-do. The results of the ECOG-PS evaluated by medical doctors were obtained from medical records. Intra-class correlation analysis was used to assess rater reliability between the elderly cancer patients and their family caregivers. Correlations among the EORTC QLQ-C30 and the ECOG-PS were tested using the Kruskal-Wallis test and Spearmen's correlation. Results: The results showed that four subscales of quality of life (physical functioning, emotional functioning, social functioning, and global health status) and three items under symptoms (fatigue, pain, and financial diffi- culties) in the EORTC QLQ-C30 were highly consistent between patients and their family caregivers. From the EORTC QLQ-C30 results, social functioning, role functioning, health status, fatigue, pain, and appetite loss (patients results) and physical functioning (family caregivers results) were highly consistent with the results of the ECOG-PS by the physicians. Conclusions: The findings suggest that when the older persons with cancer have difficulty expressing their own thoughts or feelings, the EORTC QLQ-C30 completed by their family caregivers and the results of the ECOG-PS completed by the physicians could be used as substitutes.

Study of the absorption spectrum in film dosimetry is important because the spectral absorbance of the film is related to the film’s total absorption dose. We investigated the absorption spectra of Gafchromic EBT2 film at various rotational angles in a visible wavelength band. The film was irradiated with 6- MV photon beams for a total dose of 300 cGy. The absorption spectra for different angles of rotation were obtained 24 h after the irradiation and we fitted the spectra by using Lorentzian functions. Two dominant absorption peaks, one at approximately 586 nm (green) and the other at 634 nm (red) were observed. The measured spectrum was decomposed into peaks at 542 nm, 558 nm, 578 nm, 586 nm, 626 nm, 634 nm, and 641 nm. The maximum total area of the red absorption band occurred at 45° (225°) and the minimum at 90° (270°). As the angle of rotation changed, the intensities and integrated areas of the blue and the green peaks also changed with a 180° period, with minima at 90° and 270°, and maxima at 0° and 180°, although the overall absorbance was very low. The spectral peak wavelengths remained constant within ±1.2 nm for all angles. The absorption spectrum of the film should no hysteresis of; spectra taken at 0° and 360° were substantially the same and showed similar behaviors for all rotational angles. The change in the absorbance with the rotational angle of the film affected the dosimetric properties, resulting in rotational variations of the film’s dosimetry in each red-green-blue channel.

The aim of this study was to quantitatively estimate the dosimetric benefits of the image-guided radiation therapy (IGRT) system for the prostate intensity-modulated radiation therapy (IMRT) delivery. The cases of eleven patients who underwent IMRT for prostate cancer without a prostatectomy at our institution between October 2012 and April 2014 were retrospectively analyzed. For every patient, clinical target volume (CTV) to planning target volume (PTV) margins were uniformly used: 3 mm, 5 mm, 7 mm, 10 mm, 12 mm, and 15 mm. For each margin size, the IMRT plans were independently optimized by one medical physicist using Pinnalce3 (ver. 8.0.d, Philips Medical System, Madison, WI) in order to maintain the plan quality. The maximum geometrical margin (MGM) for every CT image set, defined as the smallest margin encompassing the rectum at least at one slice, was between 13 mm and 26 mm. The percentage rectum overlapping PTV (%V ROV ), the rectal normal tissue complication probability (NTCP) and the mean rectal dose (%RD mean ) increased in proportion to the increase of PTV margin. However the bladder NTCP remained around zero to some extent regardless of the increase of PTV margin while the percentage bladder overlapping PTV (%V BOV ) and the mean bladder dose (%BD mean ) increased in proportion to the increase of PTV margin. Without relatively large rectum or small bladder, the increase observed for rectal NTCP, %RD mean and %BD mean per 1-mm PTV margin size were 1.84%, 2.44% and 2.90%, respectively. Unlike the behavior of the rectum or the bladder, the maximum dose on each femoral head had little effect on PTV margin. This quantitative study of the PTV margin reduction supported that IG-IMRT has enhanced the clinical effects over prostate cancer with the reduction of normal organ complications under the similar level of PTV control.

The aim of this study is to set up statistical quality control for monitoring of volumetric modulated arc therapy (VMAT) delivery error using machine log data. Eclipse and Clinac iX linac with the RapidArc system (Varian Medical Systems, Palo Alto, USA) is used for delivery of the VMAT plan. During the delivery of the RapidArc fields, the machine determines the delivered motor units (MUs) and gantry angle position accuracy and the standard deviations of MU (sigma_MU; dosimetric error) and gantry angle (sigma_GA; geometric error) are displayed on the console monitor after completion of the RapidArc delivery. In the present study, first, the log data was analyzed to confirm its validity and usability; then, statistical process control (SPC) was applied to monitor the sigma_MU and sigma_GA in a timely manner for all RapidArc fields: a total of 195 arc fields for 99 patients. The sigma_MU and sigma_GA were determined twice for all fields, that is, first during the patient-specific plan QA and then again during the first treatment. The sigma_MU and sigma_GA time series were quite stable irrespective of the treatment site; however, the sigma_GA was strongly dependent on the gantry rotation speed. The sigma_GA of the RapidArc delivery for stereotactic body radiation therapy (SBRT) was smaller than that for the typical VMAT. Therefore, SPC was applied for SBRT cases and general cases respectively. Moreover, the accuracy of the potential meter of gantry rotation is important, since the sigma_GA can be dramatically changed due to its condition. By applying SPC to the sigma_MU and sigma_GA, we could monitor the delivery error efficiently. However, the upper and lower limits of SPC need to be determined carefully with full knowledge of the machine and log data.

A metallic contact eye shield has sometimes been used for eyelid treatment, but dose distribution has never been reported for a patient case. This study aimed to show the shield-incorporated CT-based dose distribution using the Pinnacle system and Monte Carlo (MC) calculation for 3 patient cases. For the artifact-free CT scan, an acrylic shield machined as the same size as that of the tungsten shield was used. For the MC calculation, BEAMnrc and DOSXYZnrc were used for the 6-MeV electron beam of the Varian 21EX, in which information for the tungsten, stainless steel, and aluminum material for the eye shield was used. The same plan was generated on the Pinnacle system and both were compared. The use of the acrylic shield produced clear CT images, enabling delineation of the regions of interest, and yielded CT-based dose calculation for the metallic shield. Both the MC and the Pinnacle systems showed a similar dose distribution downstream of the eye shield, reflecting the blocking effect of the metallic eye shield. The major difference between the MC and the Pinnacle results was the target eyelid dose upstream of the shield such that the Pinnacle system underestimated the dose by 19 to 28% and 11 to 18% for the maximum and the mean doses, respectively. The pattern of dose difference between the MC and the Pinnacle systems was similar to that in the previous phantom study. In conclusion, the metallic eye shield was successfully incorporated into the CT-based planning, and the accurate dose calculation requires MC simulation.