Dosimetric comparison between VMAT plans using the fast-rotating O-ring linac with dual-layer stacked MLC and helical tomotherapy for nasopharyngeal carcinoma.

BACKGROUND: To compare the dosimetric profiles of volumetric modulated arc therapy (VMAT) plans using the fast-rotating O-ring linac (the Halcyon system) based on a dual-layer stacked multi-leaf collimator and helical tomotherapy (HT) for nasopharyngeal cancer (NPCa). METHODS: For 30 NPCa patients, three sets of RT plans were generated, under the same policy of contouring and dose constraints: HT plan; Halcyon VMAT plan with two arcs (HL2arc); and Halcyon VMAT plan with four arcs (HL4arc), respectively. The intended dose schedule was to deliver 67.2 Gy to the planning gross target volume (P-GTV) and 56.0 Gy to the planning clinical target volume (P-CTV) in 28 fractions using the simultaneously integrated boost concept. Target volumes and organ at risks dose metrics were evaluated for all plans. Normal tissue complication probabilities (NTCP) for esophagus, parotid glands, spinal cord, and brain stem were compared. RESULTS: The HT plan achieved the best dose homogeneity index for both P_GTV and P_CTV, followed by the HL4arc and L2arc plans. No significant difference in the dose conformity index (CI) for P_GTV was observed between the HT plan (0.80) and either the HL2arc plan (0.79) or the HL4arc plan (0.83). The HL4arc plan showed the best CI for P_CTV (0.88), followed by the HL2arc plan (0.83) and the HT plan (0.80). The HL4arc plan (median, interquartile rage (Q1, Q3): 25.36 (22.22, 26.89) Gy) showed the lowest Dmean in the parotid glands, followed by the HT (25.88 (23.87, 27.87) Gy) and HL2arc plans (28.00 (23.24, 33.99) Gy). In the oral cavity (OC) dose comparison, the HT (22.03 (19.79, 24.85) Gy) plan showed the lowest Dmean compared to the HL2arc (23.96 (20.84, 28.02) Gy) and HL4arc (24.14 (20.17, 27.53) Gy) plans. Intermediate and low dose regions (40-65% of the prescribed dose) were well fit to the target volume in HL4arc, compared to the HT and HL2arc plans. All plans met the dose constraints for the other OARs with sufficient dose margins. The between-group differences in the median NTCP values for the parotid glands and OC were < 3.47% and < 1.7% points, respectively. CONCLUSIONS: The dosimetric profiles of Halcyon VMAT plans were comparable to that of HT, and HL4arc showed better dosimetric profiles than HL2arc for NPCa.

Early Clinical Outcomes of Intensity Modulated Radiation Therapy/Intensity Modulated Proton Therapy Combination in Comparison with Intensity Modulated Radiation Therapy Alone in Oropharynx Cancer Patients.

PURPOSE: To report the early clinical outcomes of combining intensity-modulated radiation therapy (IMRT) and intensity-modulated proton therapy (IMPT) in comparison with IMRT alone in treating oropharynx cancer (OPC) patients. MATERIALS AND METHODS: The medical records of 148 OPC patients who underwent definitive radiotherapy (RT) with concurrent systemic therapy, from January 2016 till December 2019 at Samsung Medical Center, were retrospectively reviewed. During the 5.5 weeks' RT course, the initial 16 (or 18) fractions were delivered by IMRT in all patients, and the subsequent 12 (or 10) fractions were either by IMRT in 81 patients (IMRT only) or by IMPT in 67 (IMRT/IMPT combination), respectively, based on comparison of adaptive re-plan profiles and availability of equipment. Propensity-score matching (PSM) was done on 76 patients (38 from each group) for comparative analyses. RESULTS: With the median follow-up of 24.7 months, there was no significant difference in overall survival and progression free survival between groups, both before and after PSM. Before PSM, the IMRT/IMPT combination group experienced grade ≥ 3 acute toxicities less frequently: mucositis in 37.0% and 13.4% (p < 0.001); and analgesic quantification algorithm (AQA) in 37.0% and 19.4% (p = 0.019), respectively. The same trends were observed after PSM: mucositis in 39.5% and 15.8% (p = 0.021); and AQA in 47.4% and 21.1% (p = 0.016), respectively. In multivariate logistic regression, grade ≥ 3 mucositis was significantly less frequent in the IMRT/IMPT combination group, both before and after PSM (p = 0.027 and 0.024, respectively). AQA score ≥ 3 was also less frequent in the IMRT/IMPT combination group, both before and after PSM (p = 0.085 and 0.018, respectively). CONCLUSIONS: In treating the OPC patients, with comparable early oncologic outcomes, more favorable acute toxicity profiles were achieved following IMRT/IMPT combination than IMRT alone.

Development of a Tongue Immobilization Device Using a 3D Printer for Intensity Modulated Radiation Therapy of Nasopharyngeal Cancer Patients.

PURPOSE: This study aimed to reduce radiation doses to the tongue, a patient-specific semi-customized tongue immobilization device (SCTID) was developed using a 3D printer for helical tomotherapy (HT) of nasopharyngeal cancer (NPCa). Dosimetric characteristics and setup stability of the SCTID were compared with those of a standard mouthpiece (SMP). MATERIALS AND METHODS: For displacement and robust immobilization of the tongue, the SCTID consists of four parts: upper and lower tooth stoppers, tongue guider, tongue-tip position guide bar, and connectors. With the SCTID and SMP, two sets of planning computed tomography and HT plans were obtained for 10 NPCa patients. Dosimetric and geometric characteristics were compared. Position reproducibility of the tongue with SCTID was evaluated by comparing with planned dose and adaptive accumulated dose of the tongue and base of the tongue based on daily setup mega-voltage computed tomography. RESULTS: Using the SCTID, the tongue was effectively displaced from the planning target volume compared to the SMP. The median mucosa of the tongue (M-tongue) dose was significantly reduced (20.7 Gy vs. 27.8 Gy). The volumes of the M-tongue receiving a dose of 15 Gy, 30 Gy, and 45 Gy and the volumes of the mucosa of oral cavity and oropharynx (M-OC/OP) receiving a dose of 45 Gy and 60 Gy were significantly lower than using the SMP. No significant differences was observed between the planned dose and the accumulated adaptive dose in any dosimetric characteristics of the tongue and base of tongue. CONCLUSION: SCTID can not only reduce the dose to the M-tongue and M-OC/OP dramatically, when compared to SMP, but also provide excellent reproducibility and easy visual verification.

Impact Of Underlying Pulmonary Diseases On Treatment Outcomes In Early-Stage Non-Small Cell Lung Cancer Treated With Definitive Radiotherapy.

Purpose: Current guidelines recommend definitive radiotherapy for patients with medically inoperable early-stage non-small cell lung cancer (NSCLC). However, the impact of underlying pulmonary diseases on survival in those patients remains unclear. Methods: We retrospectively reviewed the medical records of 234 patients with stage I-II NSCLC treated with definitive radiotherapy alone at Samsung Medical Center between January 2010 and October 2017. We compared survival outcomes according to the presence of underlying pulmonary diseases, including chronic obstructive pulmonary disease (COPD), combined pulmonary fibrosis and emphysema (CPFE), and idiopathic pulmonary fibrosis (IPF). The control group in this study was stage I-II NSCLC patients who were non-COPD, non-CPFE, and non-IPF. Results: The median follow-up duration was 17 (range, 1-92) months. The median survival times of the control, COPD, CPFE, and IPF groups were 32, 49, 17, and 12 months, respectively (P<0.001). In a Cox proportional hazards analysis for factors associated with overall survival, patients with COPD showed a similar risk of death (adjusted hazard ratio [HR], 1.306; 95% confidence interval [CI], 0.723-2.358; P=0.376) compared to that of the control group, while patients with CPFE (adjusted HR, 3.382; 95% CI, 1.472-7.769; P=0.004) and IPF (adjusted HR, 4.061; 95% CI, 1.963-8.403; P<0.001) showed an increased risk of death. Conclusion: Definitive radiotherapy may be a tolerable treatment for early-stage NSCLC with COPD. However, poor survival in early-stage NSCLC patients with IPF or CPFE requires further study to identify and develop patient selection criteria as well as an optimal radiotherapy modality.

Early clinical outcomes of helical tomotherapy/intensity-modulated proton therapy combination in nasopharynx cancer.

This study aimed to evaluate the feasibility of combining helical tomotherapy (HT) and intensity-modulated proton therapy (IMPT) in treating patients with nasopharynx cancer (NPC). From January 2016 to March 2018, 98 patients received definitive radiation therapy (RT) with concurrent chemotherapy (CCRT). Using simultaneous integrated boost and adaptive re-plan, 3 different dose levels were prescribed: 68.4 Gy in 30 parts to gross tumor volume (GTV), 60 Gy in 30 parts to high-risk clinical target volume (CTV), and 36 Gy in 18 parts to low-risk CTV. In all patients, the initial 18 fractions were delivered by HT, and, after rival plan evaluation on the adaptive re-plan, the later 12 fractions were delivered either by HT in 63 patients (64.3%, HT only) or IMPT in 35 patients (35.7%, HT/IMPT combination), respectively. Propensity-score matching was conducted to control differences in patient characteristics. In all patients, grade ≥ 2 mucositis (69.8% vs 45.7%, P = .019) and grade ≥ 2 analgesic usage (54% vs 37.1%, P = .110) were found to be less frequent in HT/IMPT group. In matched patients, grade ≥ 2 mucositis were still less frequent numerically in HT/IMPT group (62.9% vs 45.7%, P = .150). In univariate analysis, stage IV disease and larger GTV volume were associated with increased grade ≥ 2 mucositis. There was no significant factor in multivariate analysis. With the median 14 month follow-up, locoregional and distant failures occurred in 9 (9.2%) and 12 (12.2%) patients without difference by RT modality. In conclusion, comparable early oncologic outcomes with more favorable acute toxicity profiles were achievable by HT/IMPT combination in treating NPC patients.

Development of a semi-customized tongue displacement device using a 3D printer for head and neck IMRT.

PURPOSE: To reduce radiation doses to the tongue, a patient-specific semi-customized tongue displacement device (SCTDD) was developed using a 3D printer (3DP) for head and neck (H&N) radiation therapy (RT). Dosimetric characteristics of the SCTDD were compared with those of a standard mouthpiece (SMP). MATERIALS AND METHODS: The SCTDD consists of three parts: a mouthpiece, connector with an immobilization mask, and tongue displacer, which can displace the tongue to the contralateral side of the planning target volume. Semi-customization was enabled by changing the thickness and length of the SCTDD. The instrument was printed using a 3DP with a biocompatible material. With the SCTDD and SMP, two sets of planning computed tomography (CT) and tomotherapy plans were obtained for seven H&N cancer patients. Dosimetric and geometric characteristics were compared. RESULTS: Using the SCTDD, the tongue was effectively displaced from the planning target volume without significant tongue volume change compared to the SMP. The median tongue dose was significantly reduced (29.6 Gy vs. 34.3 Gy). The volumes of the tongue receiving a dose of 15 Gy, 30 Gy, 35 Gy, 45 Gy, and 60 Gy were significantly lower than using the SMP. CONCLUSION: The SCTDD significantly decreased the radiation dose to the tongue compared to the SMP, which may potentially reduce RT-related tongue toxicity.

Heart-sparing radiotherapy with three-dimensional printing technology after mastectomy for patients with left breast cancer.

The purpose of this study was to analyze the effectiveness of electron beam therapy (EBT) with patient-tailored bolus (PTB) using three-dimensional printing technology to reduce heart and lung doses during post-mastectomy radiotherapy (PMRT). For 28 patients with left breast cancer, we designed customized virtual bolus for PMRT to compensate for surface irregularities on computed tomography images and developed optimized plans for EBT. As comparison between the PTB and tangential plans, the PTB plan reduced unnecessary exposure to heart and ipsilateral lung with better target coverage compared with the tangential technique.

Normal lung sparing Tomotherapy technique in stage III lung cancer.

PURPOSE: Radiation pneumonitis (RP) has been a challenging obstacle in treating stage III lung cancer patients. Beam angle optimization (BAO) technique for Tomotherapy was developed to reduce the normal lung dose for stage III non-small cell lung cancer (NSCLC). Comparative analyses on plan quality by 3 different Intensity-modulated radiation therapy (IMRT) methods with BAO were done. MATERIALS AND METHODS: Ten consecutive stage IIIB NSCLC patients receiving linac-based static IMRT (L-IMRT) with total 66 Gy in 33 fractions to the PTV were selected. Two additional Tomotherapy-based IMRT plans (helical beam (TH-IMRT) and static beam (TD-IMRT)) were generated on each patient. To reduce the normal lung dose, Beam angles were optimized by using complete and directional block functions in Tomotherapy based on knowledge based statistical analysis. Plan quality was compared with target coverage, normal organ sparing capability, and normal tissue complication probability (NTCP). Actual beam delivery times and risk of RP related with planning target volume (PTV) were also evaluated. RESULTS: The best PTV coverage measured by conformity index and homogeneity index was achievable by TH-IMRT (0.82 and 1.06), followed by TD-IMRT (0.81 and 1.07) and L-IMRT (0.75 and 1.08). Mean lung dose was the lowest in TH-IMRT plan followed by TD-IMRT and L-IMRT, all of which were ≤20 Gy. TH-IMRT plan could significantly lower the lung volumes receiving low to medium dose levels: V5~30 when compared to L-IMRT plan; and V5~20 when compared to TD-IMRT plan, respectively. TD-IMRT plan was significantly better than L-IMRT with respects to V20 and V30 and there was no significant difference with respect to V40 among three plans. The NTCP of the lung was the lowest in TH-IMRT plan, followed by TD-IMRT and L-IMRT (6.42% vs. 6.53% vs. 8.11%). Beam delivery time was the shortest in TD-IMRT plan followed by L-IMRT. As PTV length increased, NTCP and Mean lung dose proportionally increased significantly in all three plans. CONCLUSION: Advantageous profiles by TH-IMRT could be achieved by BAO by complete and directional block functions. Current observation could help radiation oncologists to make wise selection of IMRT method for stage IIIB NSCLC.

Development of patient-specific phantoms for verification of stereotactic body radiation therapy planning in patients with metallic screw fixation.

A new technique for manufacturing a patient-specific dosimetric phantom using three-dimensional printing (PSDP_3DP) was developed, and its geometrical and dosimetric accuracy was analyzed. External body contours and structures of the spine and metallic fixation screws (MFS) were delineated from CT images of a patient with MFS who underwent stereotactic body radiation therapy for spine metastasis. Contours were converted into a STereoLithography file format using in-house program. A hollow, four-section PSDP was designed and manufactured using three types of 3DP to allow filling with a muscle-equivalent liquid and insertion of dosimeters. To evaluate the geometrical accuracy of PSDP_3DP, CT images were obtained and compared with patient CT data for volume, mean density, and Dice similarity coefficient for contours. The dose distribution in the PSDP_3DP was calculated by applying the same beam parameters as for the patient, and the dosimetric characteristics of the PSDP_3DP were compared with the patient plan. The registered CT of the PSDP_3DP was well matched with that of the real patient CT in the axial, coronal, and sagittal planes. The physical accuracy and dosimetric characteristics of PSDP_3DP were comparable to those of a real patient. The ability to manufacture a PSDP representing an extreme patient condition was demonstrated.

Clinical outcomes in cervical cancer patients treated by FDG-PET/CT-based 3-dimensional planning for the first brachytherapy session.

The aim of the study was to evaluate the treatment outcomes in cervical cancer patients treated with 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT)-guided 3-dimensional brachytherapy (3D-BT) planning for the first brachytherapy session.We retrospectively analyzed 87 patients with cervical cancer who received definitive radiotherapy (RT). Primary tumor size was ≤4 cm in 22 patients (25.3%), >4 cm and ≤6 cm in 45 patients (51.7%), and >6 cm in 20 patients (23.0%). The median total dose of external beam RT was 50.4 (50.4-60.4) Gy. FDG-PET/CT-guided 3D-BT with an iridium-192 source was performed. The clinical target volume (CTV) for 3D-BT included the entire cervix and the abnormal FDG-uptake with a 1-cm expansion. A planned total dose was 24 Gy at 4 Gy per insertion 3 times per week using a tandem and 2 ovoids.The mean D95 and D90 for the CTV were 73.4 (±5.9) Gy and 77.9 (±6.9) Gy, respectively (EQD2, α/ß=10). The D2cc for the rectum and bladder was 374 (±97.4) cGy and 394 (±107.6) cGy per fraction, respectively. The EQD2 (α/ß=3) for the D2cc was 74.5 (±12.4) Gy for the rectum and 77.3 (±14.6) Gy for the bladder. The median follow-up period was 40 (8-61) months. The 3-year overall survival (OS), progression-free survival (PFS), and local control (LC) rates were 84.7%, 72.1%, and 89.2%, respectively. The 3-year LC rate was 100% for tumors ≤ 4 cm, 91.1% for tumors > 4 cm and ≤ 6 cm, and 70.5% for tumors > 6 cm (P = 0.014). Local failure developed in 9 patients. Three patients had local failures outside of the CTV. Grade 1, 2, and 3 rectal bleeding developed in 5, 4, and 2 patients, respectively. One patient experienced rectovaginal fistula.FDG-PET/CT-guided 3D-BT planning is a feasible approach, which showed favorable clinical outcomes.

Effect of Radiation Therapy Techniques on Outcome in N3-positive IIIB Non-small Cell Lung Cancer Treated with Concurrent Chemoradiotherapy.

PURPOSE: This study was conducted to evaluate clinical outcomes following definitive concurrent chemoradiotherapy (CCRT) for patients with N3-positive stage IIIB (N3-IIIB) non-small cell lung cancer (NSCLC), with a focus on radiation therapy (RT) techniques. MATERIALS AND METHODS: From May 2010 to November 2012, 77 patients with N3-IIIB NSCLC received definitive CCRT (median, 66 Gy). RT techniques were selected individually based on estimated lung toxicity, with 3-dimensional conformal RT (3D-CRT) and intensity-modulated RT (IMRT) delivered to 48 (62.3%) and 29 (37.7%) patients, respectively. Weekly docetaxel/paclitaxel plus cisplatin (67, 87.0%) was the most common concurrent chemotherapy regimen. RESULTS: The median age and clinical target volume (CTV) were 60 years and 288.0 cm(3), respectively. Patients receiving IMRT had greater disease extent in terms of supraclavicular lymph node (SCN) involvement and CTV ≥ 300 cm(3). The median follow-up time was 21.7 months. Fortyfive patients (58.4%) experienced disease progression, most frequently distant metastasis (39, 50.6%). In-field locoregional control, progression-free survival (PFS), and overall survival (OS) rates at 2 years were 87.9%, 38.7%, and 75.2%, respectively. Although locoregional control was similar between RT techniques, patients receiving IMRT had worse PFS and OS, and SCN metastases from the lower lobe primary tumor and CTV ≥ 300 cm(3)were associated with worse OS. The incidence and severity of toxicities did not differ significantly between RT techniques. CONCLUSION: IMRT could lead to similar locoregional control and toxicity, while encompassing a greater disease extent than 3D-CRT. The decision to apply IMRT should be made carefully after considering oncologic outcomes associated with greater disease extent and cost.

Carotid-Sparing TomoHelical 3-Dimensional Conformal Radiotherapy for Early Glottic Cancer.

PURPOSE: The purpose of this study was to investigate the dosimetric benefits and treatment efficiency of carotid-sparing TomoHelical 3-dimensional conformal radiotherapy (TH-3DCRT) for early glottic cancer. MATERIALS AND METHODS: Ten early-stage (T1N0M0) glottic squamous cell carcinoma patients were simulated, based on computed tomography scans. Two-field 3DCRT (2F-3DCRT), 3-field intensity-modulated radiation therapy (3F-IMRT), TomoHelical-IMRT (TH-IMRT), and TH-3DCRT plans were generated with a 67.5-Gy total prescription dose to the planning target volume (PTV) for each patient. In order to evaluate the plan quality, dosimetric characteristics were compared in terms of conformity index (CI) and homogeneity index (HI) for PTV, dose to the carotid arteries, and maximum dose to the spinal cord. Treatment planning and delivery times were compared to evaluate treatment efficiency. RESULTS: The median CI was substantially better for the 3F-IMRT (0.65), TH-IMRT (0.64), and TH-3DCRT (0.63) plans, compared to the 2F-3DCRT plan (0.32). PTV HI was slightly better for TH-3DCRT and TH-IMRT (1.05) compared to 2F-3DCRT (1.06) and 3F-IMRT (1.09). TH-3DCRT, 3F-IMRT, and TH-IMRT showed an excellent carotid sparing capability compared to 2F-3DCRT (p < 0.05). For all plans, the maximum dose to the spinal cord was < 45 Gy. The median treatment planning times for 2F-3DCRT (5.85 minutes) and TH-3DCRT (7.10 minutes) were much lower than those for 3F-IMRT (45.48 minutes) and TH-IMRT (35.30 minutes). The delivery times for 2F-3DCRT (2.06 minutes) and 3F-IMRT (2.48 minutes) were slightly lower than those for TH-IMRT (2.90 minutes) and TH-3DCRT (2.86 minutes). CONCLUSION: TH-3DCRT showed excellent carotid-sparing capability, while offering high efficiency and maintaining good PTV coverage.

Development of a 3D optical scanning-based automatic quality assurance system for proton range compensators.

PURPOSE: A new automatic quality assurance (AutoRCQA) system using a three-dimensional scanner (3DS) with system automation was developed to improve the accuracy and efficiency of the quality assurance (QA) procedure for proton range compensators (RCs). The system performance was evaluated for clinical implementation. METHODS: The AutoRCQA system consists of a three-dimensional measurement system (3DMS) based on 3DS and in-house developed verification software (3DVS). To verify the geometrical accuracy, the planned RC data (PRC), calculated with the treatment planning system (TPS), were reconstructed and coregistered with the measured RC data (MRC) based on the beam isocenter. The PRC and MRC inner surfaces were compared with composite analysis (CA) using 3DVS, using the CA pass rate for quantitative analysis. To evaluate the detection accuracy of the system, the authors designed a fake PRC by artificially adding small cubic islands with side lengths of 1.5, 2.5, and 3.5 mm on the inner surface of the PRC and performed CA with the depth difference and distance-to-agreement tolerances of [1 mm, 1 mm], [2 mm, 2 mm], and [3 mm, 3 mm]. In addition, the authors performed clinical tests using seven RCs [computerized milling machine (CMM)-RCs] manufactured by CMM, which were designed for treating various disease sites. The systematic offsets of the seven CMM-RCs were evaluated through the automatic registration function of AutoRCQA. For comparison with conventional technique, the authors measured the thickness at three points in each of the seven CMM-RCs using a manual depth measurement device and calculated thickness difference based on the TPS data (TPS-manual measurement). These results were compared with data obtained from 3DVS. The geometrical accuracy of each CMM-RC inner surface was investigated using the TPS data by performing CA with the same criteria. The authors also measured the net processing time, including the scan and analysis time. RESULTS: The AutoRCQA system accurately detected all fake objects in accordance with the given criteria. The median systematic offset of the seven CMM-RCs was 0.08 mm (interquartile range: -0.25 to 0.37 mm) and -0.08 mm (-0.58 to 0.01 mm) in the X- and Y-directions, respectively, while the median distance difference was 0.37 mm (0.23-0.94 mm). The median thickness difference of the TPS-manual measurement at points 1, 2, and 3 was -0.4 mm (-0.4 to -0.2 mm), -0.2 mm (-0.3 to 0.0 mm), and -0.3 mm (-0.6 to -0.1 mm), respectively, while the median difference of 3DMS was 0.0 mm (-0.1 to 0.2 mm), 0.0 mm (-0.1 to 0.3 mm), and 0.1 mm (-0.1 to 0.2 mm), respectively. Thus, 3DMS showed slightly better values compared to the manual measurements for points 1 and 3 in statistical analysis (p < 0.05). The average pass rate of the seven CMM-RCs was 97.97% ± 1.68% for 1-mm CA conditions, increasing to 99.98% ± 0.03% and 100% ± 0.00% for 2- and 3-mm CA conditions, respectively. The average net analysis time was 18.01 ± 1.65 min. CONCLUSIONS: The authors have developed an automated 3DS-based proton RC QA system and verified its performance. The AutoRCQA system may improve the accuracy and efficiency of QA for RCs.

The first private-hospital based proton therapy center in Korea; status of the Proton Therapy Center at Samsung Medical Center.

PURPOSE: The purpose of this report is to describe the proton therapy system at Samsung Medical Center (SMC-PTS) including the proton beam generator, irradiation system, patient positioning system, patient position verification system, respiratory gating system, and operating and safety control system, and review the current status of the SMC-PTS. MATERIALS AND METHODS: The SMC-PTS has a cyclotron (230 MeV) and two treatment rooms: one treatment room is equipped with a multi-purpose nozzle and the other treatment room is equipped with a dedicated pencil beam scanning nozzle. The proton beam generator including the cyclotron and the energy selection system can lower the energy of protons down to 70 MeV from the maximum 230 MeV. RESULTS: The multi-purpose nozzle can deliver both wobbling proton beam and active scanning proton beam, and a multi-leaf collimator has been installed in the downstream of the nozzle. The dedicated scanning nozzle can deliver active scanning proton beam with a helium gas filled pipe minimizing unnecessary interactions with the air in the beam path. The equipment was provided by Sumitomo Heavy Industries Ltd., RayStation from RaySearch Laboratories AB is the selected treatment planning system, and data management will be handled by the MOSAIQ system from Elekta AB. CONCLUSION: The SMC-PTS located in Seoul, Korea, is scheduled to begin treating cancer patients in 2015.

Evaluation of radiation dose to organs during kilovoltage cone-beam computed tomography using Monte Carlo simulation.

Image-guided techniques for radiation therapy have improved the precision of radiation delivery by sparing normal tissues. Cone-beam computed tomography (CBCT) has emerged as a key technique for patient positioning and target localization in radiotherapy. Here, we investigated the imaging radiation dose delivered to radiosensitive organs of a patient during CBCT scan. The 4D extended cardiac-torso (XCAT) phantom and Geant4 Application for Tomographic Emission (GATE) Monte Carlo (MC) simulation tool were used for the study. A computed tomography dose index (CTDI) standard polymethyl methacrylate (PMMA) phantom was used to validate the MC-based dosimetric evaluation. We implemented an MC model of a clinical on-board imager integrated with the Trilogy accelerator. The MC model's accuracy was validated by comparing its weighted CTDI (CTDIw) values with those of previous studies, which revealed good agreement. We calculated the absorbed doses of various human organs at different treatment sites such as the head-and-neck, chest, abdomen, and pelvis regions, in both standard CBCT scan mode (125 kVp, 80 mA, and 25 ms) and low-dose scan mode (125 kVp, 40 mA, and 10 ms). In the former mode, the average absorbed doses of the organs in the head and neck and chest regions ranged 4.09-8.28 cGy, whereas those of the organs in the abdomen and pelvis regions were 4.30-7.48 cGy. In the latter mode, the absorbed doses of the organs in the head and neck and chest regions ranged 1.61-1.89 cGy, whereas those of the organs in the abdomen and pelvis region ranged between 0.79-1.85 cGy. The reduction in the radiation dose in the low-dose mode compared to the standard mode was about 20%, which is in good agreement with previous reports. We opine that the findings of this study would significantly facilitate decisions regarding the administration of extra imaging doses to radiosensitive organs.

Dosimetric effects of multileaf collimator leaf width on intensity-modulated radiotherapy for head and neck cancer.

PURPOSE: The authors evaluated the effects of multileaf collimator (MLC) leaf width (2.5 vs. 5 mm) on dosimetric parameters and delivery efficiencies of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) for head and neck (H&N) cancers. METHODS: The authors employed two types of mock phantoms: large-sized head and neck (LH&N) and small-sized C-shape (C-shape) phantoms. Step-and-shoot IMRT (S&S_IMRT) and VMAT treatment plans were designed with 2.5- and 5.0-mm MLC for both C-shape and LH&N phantoms. Their dosimetric characteristics were compared in terms of the conformity index (CI) and homogeneity index (HI) for the planning target volume (PTV), the dose to organs at risk (OARs), and the dose-spillage volume. To analyze the effects of the field and arc numbers, 9-field IMRT (9F-IMRT) and 13-field IMRT (13F-IMRT) plans were established for S&S_IMRT. For VMAT, single arc (VMAT1) and double arc (VMAT2) plans were established. For all plans, dosimetric verification was performed using the phantom to examine the relationship between dosimetric errors and the two leaf widths. Delivery efficiency of the two MLCs was compared in terms of beam delivery times, monitor units (MUs) per fraction, and the number of segments for each plan. RESULTS: 2.5-mm MLC showed better dosimetric characteristics in S&S_IMRT and VMAT for C-shape, providing better CI for PTV and lower spinal cord dose and high and intermediate dose-spillage volume as compared with the 5-mm MLC (p < 0.05). However, no significant dosimetric benefits were provided by the 2.5-mm MLC for LH&N (p > 0.05). Further, beam delivery efficiency was not observed to be significantly associated with leaf width for either C-shape or LH&N. However, MUs per fraction were significantly reduced for the 2.5-mm MLC for the LH&N. In dosimetric error analysis, absolute dose evaluations had errors of less than 3%, while the Gamma passing rate was greater than 95% according to the 3%/3 mm criteria. There were no significant differences in dosimetric error between the 2.5- and 5-mm MLCs. CONCLUSIONS: As compared with MLC of 5-mm leaf widths, MLC with finer leaf width (2.5-mm) can provide better dosimetric outcomes in IMRT for C-shape. However, the MLC leaf width may only have minor effects on dosimetric characteristics in IMRT for LH&N. The results of the present study will serve as a useful assessment standard when assigning or introducing equipment for the treatment of H&N cancers.

New technique for developing a proton range compensator with use of a 3-dimensional printer.

PURPOSE: A new system for manufacturing a proton range compensator (RC) was developed by using a 3-dimensional printer (3DP). The physical accuracy and dosimetric characteristics of the new RC manufactured by 3DP (RC_3DP) were compared with those of a conventional RC (RC_CMM) manufactured by a computerized milling machine (CMM). METHODS AND MATERIALS: An RC for brain tumor treatment with a scattered proton beam was calculated with a treatment planning system, and the resulting data were converted into a new format for 3DP using in-house software. The RC_3DP was printed with ultraviolet curable acrylic plastic, and an RC_CMM was milled into polymethylmethacrylate using a CMM. The inner shape of both RCs was scanned by using a 3D scanner and compared with TPS data by applying composite analysis (CA; with 1-mm depth difference and 1 mm distance-to-agreement criteria) to verify their geometric accuracy. The position and distal penumbra of distal dose falloff at the central axis and field width of the dose profile at the midline depth of spread-out Bragg peak were measured for the 2 RCs to evaluate their dosimetric characteristics. Both RCs were imaged on a computed tomography scanner to evaluate uniformity of internal density. The manufacturing times for both RCs were compared to evaluate the production efficiency. RESULTS: The pass rates for the CA test were 99.5% and 92.5% for RC_3DP and RC_CMM, respectively. There was no significant difference in dosimetric characteristics and uniformity of internal density between the 2 RCs. The net fabrication times of RC_3DP and RC_CMM were about 18 and 3 hours, respectively. CONCLUSIONS: The physical accuracy and dosimetric characteristics of RC_3DP were comparable with those of the conventional RC_CMM, and significant system minimization was provided.

A multi-institutional study for tolerance and action levels of IMRT dose quality assurance measurements in Korea.

The purpose of this study was to suggest tolerance levels for IMRT DQA measurements using confidence limits determined by a multi-institutional study in Korea. Ten institutions were grouped into LINAC (seven linear accelerators) and TOMO (three tomotherapy machines). The DQA processes consisted of point (high- and low-dose regions) and planar (per-field and composite-field) dose measurements using an ion chamber and films (or 2D detector array) inserted into a custom-made acryl phantom (LINAC) or a cheese phantom (TOMO). The five mock structures developed by AAPM TG-119 were employed, but the prostate as well as the H&N structures were modified according to Korean patients' anatomy. The point measurements were evaluated in a ratio of measured and planned doses, while the planar dose distributions were assessed using two gamma criteria of 2 mm/2% and 3 mm/3%. The confidence limit (|mean + 1.96 σ|) for point measurements was determined to be 3.0% in high-dose regions and 5.0% in low-dose regions. The average percentage of points passing the gamma criteria of 2 mm/2% and 3mm/3% for per-field measurements was 92.7 ± 6.5% and 98.2 ± 2.8%, respectively. Thus, the corresponding confidence limit was 79.1% and 92.7%, respectively. The gamma passing rate averaged over all mock tests and institutions for composite-field measurements was 86.1 ± 6.5% at 2 mm/2% and 95.3 ± 3.8% at 3 mm/3%, leading to the confidence limit of 73.3% and 87.9%, respectively. There was no significant difference in the tolerance levels of point dose measurements between LINAC and TOMO groups. In spite of the differences in mock structures and dosimetry tools, our tolerance levels were comparable to those of AAPM and ESTRO guidelines.

Early response of patients undergoing concurrent chemoradiotherapy for cervical cancer: a comparison of PET/CT and MRI.

OBJECTIVE: To investigate the efficacy of positron emission tomography/computed tomography (PET/CT) and magnetic resonance imaging (MRI) for early response evaluation of cervical cancer patients undergoing concurrent chemoradiotherapy (CCRT). METHODS: Fifty-two patients were prospectively enrolled in the study. The pathologic findings were squamous cell carcinoma in 47 patients and adenocarcinoma in 5 patients. All patients underwent PET/CT and MRI scans before, during and within 1 month after completion of CCRT. The percent change in tumor volume during and after CCRT based on PET/CT and MRI images was compared. RESULTS: There were significant differences (p < 0.001) between the initial tumor volume and tumor volume during and after CCRT as measured by both PET/CT and MRI. During CCRT, the percent volume reduction based on PET/CT images was significantly greater than the percent volume reduction calculated from MRI images (p = 0.024). However, after the completion of CCRT, no significant differences were found in volume reduction as calculated based on PET/CT versus MRI images (p = 0.289). The percent volume reduction of adenocarcinomas was significantly smaller than that of squamous cell carcinomas based on both PET/CT (p = 0.041) and MRI images (p < 0.001). CONCLUSIONS: Significant decreases in tumor volume were observed during and after CCRT in patients with cervical cancer. Tumor volume reduction on PET/CT images was greater than that on MRI images during CCRT. We suggest that early PET/CT as well as MRI scans could be taken during CCRT to evaluate tumor response and allow personalized treatment of cervical cancer.

Different effects of bladder distention on point A-based and 3D-conformal intracavitary brachytherapy planning for cervical cancer.

This study sought to evaluate the differential effects of bladder distention on point A-based (AICBT) and three-dimensional conformal intracavitary brachytherapy (3D-ICBT) planning for cervical cancer. Two sets of CT scans were obtained for ten patients to evaluate the effect of bladder distention. After the first CT scan, with an empty bladder, a second set of CT scans was obtained with the bladder filled. The clinical target volume (CTV), bladder, rectum, and small bowel were delineated on each image set. The AICBT and 3D-ICBT plans were generated, and we compared the different planning techniques with respect to the dose characteristics of CTV and organs at risk. As a result of bladder distention, the mean dose (D50) was decreased significantly and geometrical variations were observed in the bladder and small bowel, with acceptable minor changes in the CTV and rectum. The average D2 cm(3)and D1 cm(3)showed a significant change in the bladder and small bowel with AICBT; however, no change was detected with the 3D-ICBT planning. No significant dose change in the CTV or rectum was observed with either the AICBT or the 3D-ICBT plan. The effect of bladder distention on dosimetrical change in 3D-ICBT planning appears to be minimal, in comparison with AICBT planning.