Effect of Target Changes on Target Coverage and Dose to the Normal Brain in Fractionated Stereotactic Radiation Therapy for Metastatic Brain Tumors.

Purpose: We evaluated the dosimetric effect of tumor changes in patients with fractionated brain stereotactic radiation therapy (SRT) on the tumor and normal brain using repeat verification magnetic resonance imaging (MRI) in the middle of the treatment period. Methods and Materials: Fifteen large intracranial metastatic lesions with fractionated SRT were scanned employing standardized planning MRI (MRI-1). Repeat verification MRI (MRI-2) were performed during the middle of the irradiation period. Gross tumor volume (GTV) was defined as the volume of the contrast-enhancing lesion on T1-weighted MRI with gadolinium contrast agent. The doses to the tumor and normal brain were evaluated on the MRI-1 scan. Beam configuration and intensity on the initial volumetric modulated arc therapy plan were used to evaluate the dose to the tumor and the normal brain on MRI-2. We evaluated the effect of D98% (percent dose irradiating 98% of the volume) on the GTV using the plans on the MRI-1 and MRI-2 scans. For the normal brain, the V90%, V80%, and V50% (volume of the normal brain receiving >90%, 80%, and 50% of the prescribed dose, respectively) were investigated. Results: Three (20% of the total) and 4 (26% of the total) tumors exhibited volume shrinkage or enlargement changes of >10%. Five (33% of the total) tumors exhibited volume shrinkage and enlargement changes of <10%. Three tumors (20% of the total) showed no volume changes. D98% of the GTV increased in patients with tumor shrinkage because of dose inhomogeneity and decreased in patients with tumor enlargement, with a coefficient of determination of 0.28. The V90%, V80%, and V50% increase with decreasing tumor volumes and were linearly related to the tumor volume difference with a coefficient of determination values of 0.97, 0.98, and 0.97, respectively. Conclusions: Repeat verification MRI for brain fractionated SRT during the treatment period should be considered to reduce the magnitude of target underdosing or normal brain overdosing.

Interfractional Liver Positional Motion Under Exhaled Breath Holding Based on Cone Beam Computed Tomography.

BACKGROUND/AIM: We measured interfractional liver positional motion in liver stereotactic body radiotherapy (SBRT) with exhaled breath holding (BH) based on kilovoltage (kV) cone-beam computed tomography (CBCT) images. PATIENTS AND METHODS: We collected 528 pre-treatment kV-CBCT images from 132 patients who underwent liver SBRT under exhaled BH using the Abches system, a non-electronic contact-based respiratory monitoring device, and analyzed them to investigate interfractional liver positional motion. Planning computed tomography (CT) scans were obtained using the Abches system when the patients were under exhaled BH. Translational 3-degree-of-freedom (DOF) soft-tissue-based image registration was performed using the kV-CBCT images under exhaled BH after 6-DOF vertebral bone image registration. Interfractional liver positional motions in the left-right (LR), anteroposterior (AP), and craniocaudal (CC) directions were defined based on the differences in the position of the liver relative to the vertebral bones. RESULTS: For all fractions, the absolute mean±standard deviation for the interfractional liver positional motion in the LR, AP, and CC directions was 0.7±1.0 mm, 1.0±1.5 mm, and 2.8±3.1 mm, respectively. The liver interfractional systematic/random positional motions in the LR, AP, and CC directions were 0.9/1.2 mm, 1.4/1.8 mm, and 2.9/3.9 mm, respectively. For all fractions, 100.0%, 98.3%, and 86.9% of the interfractional liver positional motions in the LR, AP, and CC directions, respectively, were less than 5 mm. CONCLUSION: CBCT-guided online correction should be used to correct interfractional liver positions errors present in liver SBRT with exhaled BH.

Multicenter retrospective study of stereotactic body radiotherapy for patients with previously untreated initial small hepatocellular carcinoma.

AIM: We aimed to verify the therapeutic efficacy and safety of stereotactic body radiotherapy (SBRT) for previously untreated initial small hepatocellular carcinoma (HCC) in a multicenter, retrospective study. METHODS: Patients who underwent SBRT for HCC at the Japanese Society of Clinical Oncology (JCOG) member hospitals in Japan between July 2013 and December 2017 and met the following eligibility criteria were included: (1) initial HCC; (2) ≤3 nodules, ≤5 cm in diameter; (3) Child-Pugh score of A or B; and (4) unsuitability for or refusal of standard treatment. We analyzed the overall survival, recurrence-free survival, and cumulative incidence of local recurrence rate, and adverse events directly related to SBRT. RESULTS: Seventy-three patients with 79 lesions from 14 hospitals were analyzed. The median age was 77 years (range: 50-89 years), and the median tumor size was 23 mm (range: 6-50 mm). The median radiation dose was 40 Gy (range: 35-60 Gy) in five fractions (range: 4-8). The median follow-up period was 45 months (range: 0-103 months). The 3-year overall survival, recurrence-free survival, and cumulative incidence of local recurrence rates were 69.9% (95% CI: 58.7%-81%), 57.9% (95% CI: 45.2%-70.5%), and 20.0% (95% CI: 11.2%-30.5%), respectively. Four cases (5.5%) of adverse events of grade 3 or higher were reported: three cases of grade 3 and one case of grade 4 (duodenal ulcer). No grade 5 toxicities were observed. CONCLUSION: SBRT is a promising treatment modality, particularly for small HCCs, as they are not suitable for standard treatment.

Improved treatment robustness of postoperative breast cancer radiotherapy including supraclavicular nodes.

A combination of a three-dimensional conformal radiation therapy (3D-CRT) plan with a dose gradient of the chest wall area and a volumetric modulated arc therapy (VMAT) plan of the supraclavicular area might improve the dose distribution robustness in the junction. To investigate the impact of patient motion on the dose distribution, hybrid 3D-CRT and VMAT plans were recalculated by shifting the isocenter of the VMAT plan. Compared to the nominal plan, the target D98% for high- vs low-dose gradients decreased by 24% vs 12%. Hybrid VMAT with a low-dose gradient 3D-CRT plan was found to be robust towards patient motion.

Treatment planning comparison between dynamic wave arc and volumetric modulated arc therapies for prostate-cancer treatment.

The aim of this study was to compare the quality of dynamic wave arc (DWA) and coplanar volumetric modulated arc therapy (co-VMAT) plans for the treatment of localized prostate cancer. The planning target volume (PTV)-rectum, a section of the PTV comprising the PTV minus that of the rectum, received 78 Gy in 39 fractions as the mean dose to the PTV-rectum. The DWA and co-VMAT plans were generated for each patient using the RayStation treatment planning system for the Vero4DRT system. The PTV-rectum dose (D95%: the percent dose irradiating 95% of the volume), homogeneity index (HI), conformity index (CI), as well as doses to the bladder wall, rectum wall (V10-70 Gy: the percent volume receiving 10-70 Gy), and bilateral femoral heads of the DWA and co-VMAT plans were compared. The output monitor unit (MU) and delivery time obtained for each set of plans were also investigated. In terms of target coverage, the DWA plans provided an average D95% of 75.5 Gy, which was comparable to the co-VMAT-plan D95% of 75.2 Gy (p < 0.05). The HI was significantly better with the DWA. As for the DWA plans, the bladder-wall volume receiving 10, 20, 30, and 40 Gy (V10-40 Gy) was significantly smaller than that of the co-VMAT plans, and the volume of the rectal wall receiving 10 Gy (V10Gy) was significantly larger than that of the co-VMAT plans. The DWA plans yielded a reduced dose to the bilateral femoral heads compared with the co-VMAT plans (p < 0.05). The values of the CI and MU, and the delivery time exhibited no significant differences between the DWA and co-VMAT plans. The DWA plan is a feasible treatment option for prostate cancer radiotherapy.

Development and psychometric testing of the nursing faculty competencies self-assessment scale.

BACKGROUND: Alongside the promotion of faculty development, further clarification on the vital faculty competencies is critical. OBJECTIVES: To develop and test the psychometric properties of the Nursing Faculty Competencies Self-Assessment Scale. DESIGN: A cross-sectional study. PARTICIPANTS: 1299 faculty members of 68 nursing universities throughout Japan. A total of 333 returned completed questionnaires, of which 326 provided valid data for analysis. METHODS: To investigate the reliability and validity of the Nursing Faculty Competencies Self-Assessment Scale, a questionnaire containing this scale, the General Self-Efficacy Scale, and questions regarding personal background was mailed to the participants. Using their responses, the reliability of the scale was analyzed in terms of internal consistency and stability. Further, scale validity was used to examine construct validity and perform criterion-related validity tests. RESULTS: After item analysis, exploratory factor analysis returned 82 items loaded onto 11 factors. Cronbach's α coefficients for each factor ranged from 0.86 to 0.98. Meanwhile, correlation coefficients based on the test-retest method ranged from 0.57 to 0.80. Correlation coefficients between the Nursing Faculty Competencies Self-Assessment Scale scores and the General Self-Efficacy Scale ranged from 0.25 to 0.42. CONCLUSIONS: The Nursing Faculty Competencies Self-Assessment Scale comprises 82 items and 11 subscales. The scale has adequate internal consistency and stability, and construct validity. However, additional investigation of criterion-related validity is essential for improving the scale's validity.

Hydrogel spacer shrinkage during external-beam radiation therapy following low-dose-rate brachytherapy for high-risk prostate cancer: a case series.

BACKGROUND: Few studies have assessed hydrogel spacer shrinkage during external-beam radiation therapy following brachytherapy for localized high-risk prostate cancer. This case presentation evaluated the changes in hydrogel spacer appearance by magnetic resonance imaging during external-beam radiation therapy after brachytherapy for prostate cancer and analyzed the effect of this shrinkage on the dose distribution in four cases. CASE PRESENTATION: In all cases, we implanted 125I sources using a modified peripheral loading pattern for seed placement. The prescribed dose for each implant was 110 Gy. After delivering the sources, a hydrogel spacer was injected. All cases underwent external-beam radiation therapy approximately 1-2 months after brachytherapy. The prescribed dose of external-beam radiation therapy was 45 Gy in 1.8-Gy fractions. Magnetic resonance imaging was performed for evaluation on the day following seed implantation (baseline), at external-beam radiation therapy planning, and during external-beam radiation therapy. The median hydrogel spacer volume was 16.2 (range 10.9-17.7) cc at baseline, 14.4 (range, 9.4-16.1) cc at external-beam radiation therapy planning, and 7.1 (range, 2.0-11.4) cc during external-beam radiation therapy. The hydrogel spacer volume during external-beam radiation therapy was significantly lower than that at external-beam radiation therapy planning. The rectum V60-80 (rectal volume receiving at least 60-80% of the prescribed dose of external-beam radiation therapy) during external-beam radiation therapy was significantly higher than that at external-beam radiation therapy planning. CONCLUSIONS: The potential reduction in hydrogel spacer size during external-beam radiation therapy following brachytherapy can lead to unexpected irradiation to the rectum. This case presentation would be helpful for similar cases.

Uncertainty in the positioning of patients receiving treatment for brain metastases and wearing surgical mask underneath thermoplastic mask during COVID-19 crisis.

Thermoplastic masks, used along with surgical masks, enable immobilization methods to reduce the risk of infection in patients undergoing intracranial stereotactic radiosurgery and stereotactic radiotherapy (SRS/SRT) during the COVID-19 crisis. The purpose of this study was to investigate the feasibility of thermoplastic mask immobilization with a surgical mask using an ExacTrac system. Twelve patients each with brain metastases were immobilized using a thermoplastic mask and a surgical mask and only a thermoplastic mask. Two x-ray images were acquired to correct (XC) and verify (XV) the patient's position at a couch angle of 0°. Subsequently, the XC and XV images were acquired at each planned couch angle for non-coplanar beams. When the position errors were detected after couch rotation for non-coplanar beams, the errors were corrected at each planned couch angle until a clinically acceptable tolerance was attained. The position errors in the translational and rotational directions (vertical, lateral, longitudinal, pitch, roll, and yaw) were retrospectively investigated using data from the ExacTrac system database. A standard deviation of XC translational and rotational position errors with and without a surgical mask in the lateral (1.52 vs 2.07 mm), longitudinal (1.59 vs 1.87 mm), vertical (1.00 vs 1.73 mm), pitch (0.99 vs 0.79°), roll (1.24 vs 0.68°), and yaw (1.58 vs 0.90°) directions were observed at a couch angle of 0°. Most of patient positioning errors were less than 1.0 mm or 1.0° after the couch was rotated to the planned angle for non-coplanar beams. The overall absolute values of the translational and rotational XV position errors with and without the surgical mask were less than 0.5 mm and 0.5°, respectively. This study showed that a thermoplastic mask with a surgical mask is a feasible immobilization technique for brain SRS/SRT patients using the ExacTrac system.

Investigation of interfractional variation in lung tumor position under expiratory-phase breath hold using cone-beam computed tomography in stereotactic body radiation therapy.

PURPOSE: We investigated the interfractional variation in the tumor position during lung stereotactic body radiotherapy (SBRT) under expiratory-phase breath hold (BH) using cone-beam computed tomography (CBCT). METHODS: A total of 79 patients with lung cancer were treated with lung SBRT, wherein the Abches system under expiratory-phase BH was used to study interfractional variation. The tumors were located in the upper lobe in 31 cases, in the middle lobe in 11 cases, and in the lower lobe in 37 cases. Planning CTs were scanned under expiratory-phase BH with the Abches system. The 3-degrees-of-freedom (DOF) tumor-based setup using CBCT images under expiratory-phase BH was performed after a 6-DOF bony vertebrae-based setup using an ExacTrac X-ray system. Interfractional variation in the lung tumor position was defined as the difference in the position of the lung tumor relative to the bone anatomy in the left-right (LR), antero-posterior (AP), and craniocaudal (CC) directions represented as absolute values. RESULTS: The interfractional variation in the lung tumor position was very similar in all the lung regions, and its mean ± standard deviation values in all patients were 1.0 ± 1.1, 1.6 ± 1.9, and 1.6 ± 1.9 mm in the LR, AP, and CC directions, respectively. Further, 99.1%, 92.4%, and 92.7% of all the fractions for the interfractional tumor positional variation in the LR, AP, and CC directions were less than 5 mm, respectively. CONCLUSION: The interfractional variation in the tumor position was small for lung cancer patients treated with the Abches system under expiratory-phase BH.

Impact on liver position under breath-hold by computed tomography contrast agents in stereotactic body radiotherapy of liver cancer.

BACKGROUND: We investigated variations in liver position relative to the vertebral bone for liver cancer treated with stereotactic body radiation therapy under expiratory phase breath-hold (BH) for treatment with contrast-enhanced-computed tomography (CECT), non-CECT, and cone-beam computed tomography (CBCT). MATERIALS AND METHODS: Seventeen consecutive patients using a contrast enhancement (CE) agent for the CT simulation session for this retrospective study were selected. The first computed tomography (CT) scan without the use of CE agent in the expiratory phase was used for treatment planning (pCT). The remaining three CT scans without a CE agent under expiratory phase BH were acquired successively without repositioning to evaluate the intra-fraction variation in liver position. Furthermore, a three-phase CT scan (arterial, portal, and late phases) accompanied by a CE agent under expiratory phase BH was acquired for target delineation. CBCT scans without the use of a CE agent under expiratory phase BH were acquired for treatment. Inter-fractional variations (non-CECT or CECT) in liver position were measured using the difference between CBCT and pCT or each 3 phase CECT images, respectively. RESULTS: The average ± standard deviations for intrafractional, non-CECT interfractional variations, and CECT interfractional variations were 1.0 ± 1.3, 2.5 ± 2.6, and 6.4 ± 6.4 mm, respectively, in the craniocaudal (CC) direction. Intra- and inter-fractional variations in liver position were relatively small for non-CECT. However, significant inter-fractional liver position variations in CECT were observed in the expiratory phase BH. The position of the liver should be carefully considered when applying CECT images for image-guided radiotherapy.

Hybrid volumetric-modulated arc therapy for postoperative breast cancer including regional lymph nodes: the advantage of dosimetric data and safety of toxicities.

To improve the homogeneity and conformity of the irradiation dose for postoperative breast cancer including regional lymph nodes, we planned Hybrid volumetric-modulated arc therapy (VMAT), which combines conventional tangential field mainly for the chest area and VMAT mainly for the supraclavicular area and marginal zone. In this study, we compared the dosimetric impact between traditional 3D conformal radiotherapy (3DCRT) and Hybrid VMAT and observed toxicities following Hybrid VMAT. A total of 70 patients indicated between October 2016 and December 2017 were included. The prescribed dose was 50 Gy/25 fractions. For the dosimetric impact, 3DCRT and Hybrid VMAT plans were compared in each patient with respect to the dosimetric parameters. Toxicities were followed using the Common Terminology Criteria for Adverse Events version 4.0. The median follow-up duration was 319 days. For the dosimetric impact, the homogeneity index (HI) and conformity index (CI) of PTV were significantly improved in the Hybrid VMAT plan compared with that in the 3DCRT plan (HI, 0.15 ± 0.07 in Hybrid VMAT vs 0.41 ± 0.19 in 3DCRT, P < 0.001; CI, 1.61 ± 0.44 in Hybrid VMAT vs 2.10 ± 0.56 in 3DCRT, P < 0.001). The mean irradiated ipsilateral lung dose was not significantly different in both plans (12.0 ± 2.4 Gy in Hybrid VMAT vs 11.8 ± 2.8 Gy in 3DCRT, P < 0.533). Regarding toxicity, there were no patients who developed ≥grade 3 acute toxicity and ≥grade 2 pneumonitis during the follow-up. Hybrid VMAT for postoperative breast cancer including regional lymph nodes was a reasonable technique that improved the homogeneity and conformity of the irradiation dose to the planning target volume while keeping the irradiation dose to organs at risk to a minimum.

A Multi-Institutional Retrospective Study of Repeated Stereotactic Body Radiation Therapy for Intrahepatic Recurrent Hepatocellular Carcinoma.

PURPOSE: Through this multi-institutional study, we aimed to retrospectively evaluate the safety and efficacy of repeated stereotactic body radiation therapy (SBRT) for intrahepatic recurrent hepatocellular carcinoma (HCC). METHODS AND MATERIALS: Between 2005 and 2017, 709 patients with 835 HCCs underwent SBRT; those treated with repeated SBRT were eligible. The median prescribed dose was 40 Gy in 5 fractions. RESULTS: Eighty-one patients with 189 tumors underwent repeated SBRT (≥ 2 courses [median 2 times; range, 2-5 times]). The median follow-up periods from the first to the second SBRT were 41.5 (range, 12-99) and 20 (range, 1-81) months, respectively. The median interval between the first and second SBRT was 18 (range, 3-74) months. The 5-year local recurrence rate was 6.3% (95% confidence interval [CI], 2.3%-13.4%). The 5-year overall survival (OS) and liver-related death rates from the first SBRT were 60.4% (95% CI, 47.0%-73.8%) and 32.9% (95% CI, 20.3%-46.0%), respectively, and the 3-year rates from the second SBRT were 61.0% (95% CI, 49.9%-75.2%) and 34.5% (95% CI, 20.6%-48.9%), respectively. The frequency of grade 3 toxicity was not significantly different between the first and second SBRT (first: 11% [95% CI, 5.2%-20%]; second: 15% [95% CI, 7.9%-24%]; P = .48). Among 39 patients with no intrahepatic recurrence for 1 year after the first and second SBRT, the deterioration in liver function after the first and second SBRT was not significantly different; the albumin-bilirubin score increased 1 year after the first versus second SBRT (first, 0.143 ± 0.23; second, 0.195 ± 0.38; P = .48). Multivariate analysis revealed that the intrahepatic recurrence-free interval was the only significant factor for OS. CONCLUSIONS: Repeated SBRT for intrahepatic recurrent HCC resulted in high local control with safety and a satisfactory OS comparable with that of other curative local treatments for patients with well-preserved liver function.

Effectiveness of robust optimization in volumetric modulated arc therapy using 6 and 10 MV flattening filter-free beam therapy planning for lung stereotactic body radiation therapy with a breath-hold technique.

We investigated the feasibility of a robust optimization with 6 MV X-ray (6X) and 10 MV X-ray (10X) flattening filter-free (FFF) beams in a volumetric modulated arc therapy (VMAT) plan for lung stereotactic body radiation therapy (SBRT) using a breath-holding technique. Ten lung cancer patients were selected. Four VMAT plans were generated for each patient; namely, an optimized plan based on the planning target volume (PTV) margin and a second plan based on a robust optimization of the internal target volume (ITV) with setup uncertainties, each for the 6X- and 10X-FFF beams. Both optimized plans were normalized by the percentage of the prescription dose covering 95% of the target volume (D95%) to the PTV (1050 cGy × 4 fractions). All optimized plans were evaluated using perturbed doses by specifying user-defined shifted values from the isocentre. The average perturbed D99% doses to the ITV, compared to the nominal plan, decreased by 369.1 (6X-FFF) and 301.0 cGy (10X-FFF) for the PTV-based optimized plan, and 346.0 (6X-FFF) and 271.6 cGy (10X-FFF) for the robust optimized plan, respectively. The standard deviation of the D99% dose to the ITV were 163.6 (6X-FFF) and 158.9 cGy (10X-FFF) for the PTV-based plan, and 138.9 (6X-FFF) and 128.5 cGy (10X-FFF) for the robust optimized plan, respectively. Robust optimized plans with 10X-FFF beams is a feasible method to achieve dose certainty for the ITV for lung SBRT using a breath-holding technique.

An overview of stereotactic body radiation therapy for hepatocellular carcinoma.

Introduction: According to several guidelines, stereotactic body radiation therapy (SBRT) for early hepatocellular carcinoma (HCC) can be considered an alternative to other modalities, such as resection, radiofrequency ablation (RFA), and transarterial chemoembolization (TACE), or when these therapies have failed or are contraindicated. This article reviews the current status of SBRT for the treatment of HCC.Areas covered: From the results of many retrospective reports, SBRT is a promising modality with an excellent local control of almost 90% at 2-3 years and acceptable toxicities. Currently there are no randomized trials to compare SBRT and other modalities, such as resection, RFA, and TACE, but many retrospective reports and propensity score matching have shown that SBRT is comparable to the different modalities. Repeated SBRT for intra-hepatic recurrent HCC also resulted in high local control with safety and satisfactory overall survival, which were comparable to those of other curative local treatments.Expert opinion: Despite the good results of SBRT, the conclusions of the comparisons of SBRT and other modalities are still controversial. Further studies, including randomized phase III studies to define that patients are more suitable for each curative local treatment, are needed.

Characterization of robust optimization for VMAT plan for liver cancer.

PURPOSE: We investigated the feasibility of robust optimization for volumetric modulated arc therapy (VMAT) stereotactic body radiation therapy (SBRT) for liver cancer in comparison with planning target volume (PTV)-based optimized plans. Treatment plan quality, robustness, complexity, and accuracy of dose delivery were assessed. METHODS: Ten liver cancer patients were selected for this study. PTV-based optimized plans with an 8-mm PTV margin and robust optimized plans with an 8-mm setup uncertainty were generated. Plan perturbed doses were evaluated using a setup error of 8 mm in all directions from the isocenter. The dosimetric comparison parameters were clinical target volume (CTV) doses (D98%, D50%, and D2%), liver doses, and monitor unit (MU). Plan complexity was evaluated using the modulation complexity score for VMAT (MCSv). RESULTS: There was no significant difference between the two optimizations with respect to CTV doses and MUs. Robust optimized plans had a higher liver dose than did PTV-based optimized plans. Plan perturbed dose evaluations showed that doses to the CTV for the robust optimized plans had small variations. Robust optimized plans were less complex than PTV-based optimized plans. Robust optimized plans had statistically significant fewer leaf position errors than did PTV-based optimized plans. CONCLUSIONS: Comparison of treatment plan quality, robustness, and plan complexity of both optimizations showed that robust optimization could be feasibile for VMAT of liver cancer.

Evaluation of interbreath-hold lung tumor position reproducibility with vector volume histogram using the breath-hold technique.

Tumor geometric reproducibility for lung stereotactic body radiotherapy (SBRT) is an important issue in the breath-hold (BH) technique. We investigated the inter-BH reproducibility of the tumor position in expiratory BH using our proposed vector volume histogram (VVH) method. Subjects comprising 14 patients with lung cancer who were treated with lung SBRT under expiratory BH conditions were monitored by the Abches system. Multiple computed tomography (CT) scans were performed to evaluate the inter-BH reproducibility of the tumor position at the expiratory BH in the simulation session. Gross tumor volume was delineated by a physician. Deformable image registration was used to deform the images from the 3 expiratory BH-CTs to the treatment planning expiratory BH-CT. To evaluate the inter-BH reproducibility of the tumor positions, we measured the largest motion extent within the organ of 3 dimensions (left-right, LR; anterior-posterior, AP; cranio-caudal, CC) and a 3D vector using the VVH method. The average and standard deviations of the inter-BH reproducibility of the tumor position in the LR, AP, and CC directions, and the 3D vector were 1.7 ± 0.5, 2.0 ± 0.7, 2.1 ± 0.7, and 2.7 ± 0.7 mm, respectively. Ten patients exhibited inter-BH displacements of the lung tumor >3 mm in the 3D vector. No displacement >5 mm was observed in any direction for all patients. Our study indicated that the inter-BH variation of the tumor position was small for lung cancer patients, using the Abches system and the VVH method.

MRI appearance change during stereotactic radiotherapy for large brain metastases and importance of treatment plan modification during treatment period.

PURPOSE: We aimed to evaluate the magnetic resonance imaging (MRI) appearance changes during stereotactic radiotherapy (SRT) for large sized brain metastases, and analyze the lesions necessitating treatment plan modification. MATERIALS AND METHODS: A total of 23 patients (27 lesions, >2 cm in tumor diameter) underwent SRT and all lesions were evaluated the appearance changes which had the necessity of the treatment plan modification. The appearance change of tumor during SRT was evaluated using gadolinium-enhanced MRI. The reasons of the modification were classified into tumor reduction, tumor enlargement, displacement, and shape change. RESULTS: Among the 27 lesions, 55.6% required the treatment plan modification. The reasons were tumor reduction in six lesions, tumor enlargement in three lesions, displacement in three lesions, and shape change in three lesions. The planning target volume (PTV) size changed up to 43.0% and the shift of center of PTV was a maximum of 1.7 mm. The pathological status (adenocarcinoma vs others) and timing of steroid administration (prior vs after SRT start) were the predictive factors of tumor changes required the modification. CONCLUSIONS: As tumor changes might occur even during short period of SRT, the treatment plan evaluation and modification were important in SRT for large brain metastases.

Automatic gas detection in prostate cancer patients during image-guided radiation therapy using a deep convolutional neural network.

PURPOSE: The detection of intestinal/rectal gas is very important during image-guided radiation therapy (IGRT) of prostate cancer patients because intestinal/rectal gas increases the inter- and intra-fractional prostate motion. We propose a deep convolutional neural network (DCNN) to detect intestinal/rectal gas in the pelvic region. MATERIAL AND METHODS: We selected 300 anterior-posterior kilo-voltage (kV) X-ray images from 30 prostate cancer patients. Thirty images were randomly chosen for a test set, and the remaining 270 images used as the training set. The intestinal/rectal gas was manually delineated on kV X-ray images and segmented. The training images were augmented by applying artificial shifts and fed into a DCNN. The network models were trained to keep the quality of the output image close to the quality of the input image by pooling and upsampling. The training set was used to adjust the parameters of the DCNN, and the test set was used to assess the performance of the model. The performance of the DCNN was evaluated using a fivefold cross-validation procedure. The dice similarity coefficient (DSC) was calculated to evaluate the detection accuracy between the manual contour and auto-segmentation. RESULTS: The DCNN was trained within approximately 17 min with a time step of 20 s/epoch. The training and validation accuracy of the models after 50epochs were 0.94 and 0.85, respectively. The average ±â€¯standard deviation of the DSC for 30 test images was 0.85 ±â€¯0.08. CONCLUSIONS: The proposed DCNN method can automatically detect the intestinal/rectal gas in kV images with good accuracy.

Volumetric modulated arc therapy with robust optimization for larynx cancer.

PURPOSE: The aim of this study was to perform a comparison between robust optimization and planning target volume (PTV)-based optimization plans using volumetric modulated arc-therapy (VMAT) by evaluating perturbed doses induced by localization offsets for setup uncertainties in larynx cancer radiation therapy. METHODS: Ten patients with early-stage (T1-2N0) glottis carcinoma were selected. The clinical target volume (CTV), carotid arteries, and spinal cord were contoured by a radiation oncologist. PTV-based and robust optimization plans were normalized at D50% to the PTV and D98% to the CTV, respectively. Both optimization plans were evaluated using perturbed doses by specifying user defined shifted values from the isocenter. CTV dose (D98%, D50%, and D2%), homogeneity index (HI) and conformity index (CI95%, CI80%, and CI50%), as well as doses to the carotid arteries and spinal cord were compared between PTV-based and robust optimization plans. RESULTS: The robust optimization plans exhibited superior CTV coverage and a reduced dose to the carotid arteries compared to the PTV-based optimization plans (p < 0.05). HI, CI95% and the dose to the spinal cord did not significantly differ between the PTV-based and robust optimization plans (p > 0.05). The robust optimization plans showed better CI80% and CI50% compared to the PTV-based optimization plans (p < 0.05). Plan perturbed evaluations showed that the robust optimization plan has small variations in the doses to the CTV, carotid arteries, and spinal cord compared to the PTV-based optimization plan. CONCLUSIONS: The robust optimization plan may be a suitable treatment method in radiotherapy for larynx cancer patient.