Terms Of Conformity Index Research Articles

Comparison of Single and Multiple Treatment Plans Made in CyberKnife® Radiosurgery System on Phantom

While the use of CyberKnife® radiosurgery systems is increasing, the choice of treatment plan is also important. In this study, it was aimed to determine the more advantageous application by comparing the irradiation of all metastases at once and the protocols of irradiation of metastases separately in multiple brain metastases. For this, on an entirely new head phantom; 6 brain metastases and 3 critical organs, including the spinal cord, brain stem, and chiasm, were determined over the spaces where the dosimeters were placed. Computed tomography (CT) images of the head phantom were taken and these 6 tumors and 3 critical organs were drawn (contouring) on the image. In the treatment planning system, the dose we wanted to give was written and irradiation plans were created to be done separately with a single irradiation. Luminescence (OSL) dosimeters with BeO optical excitation were removed from the phantom after each irradiation and the count value obtained from the dosimeter reader device was recorded. Homogeneity index (HI), conformity index (CI), new conformity index (nCI), duration of treatment, and gradient index (GI) values of irradiation at one time and separately were compared. While it was found that irradiation of tumors with a separate treatment plan was more advantageous in terms of conformity index (CI), new conformity index (nCI), homogeneity index (HI), and coverage values, it was seen that a single plan was more suitable in terms of gradient index and duration.

A simplified non-coplanar volumetric modulated arc therapy for the whole brain radiotherapy with hippocampus avoidance.

To evaluate the feasibility of using a simplified non-coplanar volumetric modulated arc therapy (NC-VMAT) and investigate its dosimetric advantages compared with intensity modulated radiation therapy (IMRT) and coplanar volumetric modulated arc therapy (C-VMAT) for hippocampal-avoidance whole brain radiation therapy (HA-WBRT). Ten patients with brain metastase (BM) were included for HA-WBRT. Three treatment plans were generated for each case using IMRT, C-VMAT, and NC-VMAT, respectively. The dosimetric results of the three techniques complied roughly with the RTOG 0933 criteria. After dose normalization, the V30Gy of whole brain planned target volume (WB-PTV) in all the plans was controlled at 95%. Homogeneity index (HI) of WB-PTV was significantly reduced in NC-VMAT (0.249 ± 0.017) over IMRT (0.265 ± 0.020, p=0.005) and C-VMAT (0.261 ± 0.014, p=0.020). In terms of conformity index (CI), NC-VMAT could provide a value of 0.821 ± 0.010, which was significantly superior to IMRT (0.788 ± 0.019, p<0.001). According to D2% of WB-PTV, NC-VMAT could provide a value of 35.62 ± 0.37Gy, significantly superior to IMRT (36.43 ± 0.65Gy, p<0.001). According to D50% of WB-PTV, NC-VMAT can achieve the lowest value of 33.18 ± 0.29Gy, significantly different from IMRT (33.47 ± 0.43, p=0.034) and C-VMAT (33.58 ± 0.37, p=0.006). Regarding D2%, D98%, and Dmean of hippocampus, NC-VMAT could control them at 15.57 ± 0.18Gy, 8.37 ± 0.26Gy and 11.71 ± 0.48Gy, respectively. D2% and Dmean of hippocampus for NC-VMAT was significantly lower than IMRT (D2%: 16.07 ± 0.29Gy, p=0.001 Dmean: 12.18 ± 0.33Gy, p<0.001) and C-VMAT (D2%: 15.92 ± 0.37Gy, p=0.009 Dmean: 12.21 ± 0.54Gy, p<0.001). For other organs-at-risk (OARs), according to D2% of the right optic nerves and the right lenses, NC-VMAT had the lowest values of 31.86 ± 1.11Gy and 7.15 ± 0.31Gy, respectively, which were statistically different from the other two techniques. For other organs including eyes and optic chiasm, NC-VMAT could achieve the lowest doses, different from IMRT statistically. The dosimetry of the three techniques for HA-WBRT could roughly comply with the proposals from RTOG 0933. After dose normalization (D95%=30Gy), NC-VMAT could significantly improve dose homogeneity and reduce the D50% in the brain. Besides, it can reduce the D2% of the hippocampus, optic nerves, and lens. With this approach, an efficient and straightforward plan was accomplished.

The Optimal Choice of Technique for Stereotactic Radiosurgery—A LINAC-Based Dosimetric Study between DCA, DCA-SSO, DCA-SSO-VDR, and VMAT

Abstract Introduction Advanced radiation therapy delivery techniques require greater understanding of various planning sequences and methods. The aim of this study is to determine a class solution that finds the best possible technique to deliver for stereotactic radiosurgery between dynamic conformal arc (DCA) techniques using various options such as DCA, DCA + SSO (segment shape optimization), and DCA + SSO + VDR (variable dose rate) using noncoplanar beam arrangement and volumetric modulated arc therapy (VMAT) using coplanar beams. Materials and Methods In this dosimetric study, 11 brain cases were retrospectively planned for various techniques and analyzed for the Paddick conformity index (CI), Radiation Therapy Oncology Group homogeneity index (HI), Paddick gradient index (GI), treatment time in terms of monitor units (MU) and normal brain dose (V12Gy). The paired t-test was performed to know the statistical significance between the techniques. Results In terms of CI, GI, and control of the normal brain dose, the VMAT plan was superior to other techniques. But, HI was found to be better with DCA. Above all, VMAT delivered higher MU than any other technique. The p-values between DCA + SSO and DCA, DCA + SSO + VDR and DCA + SSO, and VMAT and DCA + SSO + VDR are as follows: CI: 0.0004, 0.015, and 0.03; GI: 0.03, 0.33, and 0.29; HI: 0.008, 0.04, and 0.06; V12 Gy of normal brain: 0.1, 0.01, 0.38. VMAT requires approximately 41 ± 17% more MU than DCA + SSO + VDR. Conclusion VMAT using coplanar beams is preferable among all the techniques, considering the dosimetric parameters studied. If VMAT is not available in the facility, DCA + SSO + VDR technique using non coplanar beams can be used to deliver SRS treatment.

Dosimetric characteristics of VMAT plans with respect to a different increment of gantry angle size for Ca cervix

AbstractAim:We have investigated the influence in volumetric-modulated arc therapy (VMAT) plans by a sequence of increment of gantry angle (IGA) in definitive radiotherapy treatment for cervical cancer. The plans are quantitatively analysed in terms of conformity index (CI), heterogeneity index (HI), dose–gradient index (DGI), target coverage (TC) by prescription dose, monitor unit (MU) usage, control points (CPs) and dose to organs.Materials and Methods:In this retrospective study, we selected 27 patients with cervical cancer having aged between 54 and 69. All the patients enrolled in this study were at T3N1M0 stage of cervical cancer. The prescription dose to planning target volume (PTV) was 50 Gy and was administered in 2 Gy/fraction through VMAT technique. VMAT plans were optimised by varying the parameter ‘IGA’ as 10, 20, 30 and 40°.Results:Homogenous dose distribution within PTV and TC by prescription dose was significantly enhanced (p &lt; 0·05) with larger IGA. The difference between volume receiving 15 Gy (V15Gy) in bowel was up to 10% with larger IGA (30 and 40°) and V25Gy in femoral head was up to 3% with smaller IGA (10 and 20°). CPs were enhanced and MU usage was reduced with larger IGA (30 and 40°). IGA 40° had reduced the MU usage than IGA 30° but the CI and DGI were compromised due to large MLC field segments.Conclusion:This study recommends that the larger IGA could yield better results when the number of sectors is even, for a cervical cancer patient. However, more data from more patients need to be obtained and analysed to make this an evidence-based hypothesis.

Dosimetric feasibility of brain stereotactic radiosurgery with a 0.35 T MRI-guided linac and comparison vs a C-arm-mounted linac.

MRI is the gold-standard imaging modality for brain tumor diagnosis and delineation. The purpose of this work was to investigate the feasibility of performing brain stereotactic radiosurgery (SRS) with a 0.35T MRI-guided linear accelerator (MRL) equipped with a double-focused multileaf collimator (MLC). Dosimetric comparisons were made vs a conventional C-arm-mounted linac with a high-definition MLC. The quality of MRL single-isocenter brain SRS treatment plans was evaluated as a function of target size for a series of spherical targets with diameters from 0.6cm to 2.5cm in an anthropomorphic head phantom and six brain metastases (max linear dimension=0.7-1.9cm) previously treated at our clinic on a conventional linac. Each target was prescribed 20Gy to 99% of the target volume. Step-and-shoot IMRT plans were generated for the MRL using 11 static coplanar beams equally spaced over 360° about an isocenter placed at the center of the target. Couch and collimator angles are fixed for the MRL. Two MRL planning strategies (VR1 and VR2) were investigated. VR1 minimized the 12Gy isodose volume while constraining the maximum point dose to be within ±1Gy of 25Gy which corresponded to normalization to an 80% isodose volume. VR2 minimized the 12Gy isodose volume without the maximum dose constraint. For the conventional linac, the TB1 method followed the same strategy as VR1 while TB2 used five noncoplanar dynamic conformal arcs. Plan quality was evaluated in terms of conformity index (CI), conformity/gradient index (CGI), homogeneity index (HI), and volume of normal brain receiving ≥12Gy (V12Gy ). Quality assurance measurements were performed with Gafchromic EBT-XD film following an absolute dose calibration protocol. For the phantom study, the CI of MRL plans was not significantly different compared to a conventional linac (P>0.05). The use of dynamic conformal arcs and noncoplanar beams with a conventional linac spared significantly more normal brain (P=0.027) and maximized the CGI, as expected. The mean CGI was 95.9±4.5 for TB2 vs 86.6±3.7 (VR1), 88.2±4.8 (VR2), and 88.5±5.9 (TB1). Each method satisfied a normal brain V12Gy ≤10.0cm3 planning goal for targets with diameter ≤2.25cm. The mean V12Gy was 3.1cm3 for TB2 vs 5.5cm3 , 5.0cm3 and4.3cm3 , for VR1, VR2, and TB1, respectively. For a 2.5-cm diameter target, only TB2 met the V12Gy planning objective. The MRL clinical brain plans were deemed acceptable for patient treatment. The normal brain V12Gy was ≤6.0cm3 for all clinical targets (maximum target volume=3.51cm3 ). CI and CGI ranged from 1.12-1.65 and 81.2-88.3, respectively. Gamma analysis pass rates (3%/1mm criteria) exceeded 97.6% for six clinical targets planned and delivered on the MRL. The mean measured vs computed absolute dose difference was -0.1%. The MRL system can produce clinically acceptable brain SRS plans for spherical lesions with diameter ≤2.25cm. Large lesions (>2.25cm) should be treated with a linac capable of delivering noncoplanar beams.

Dosimetric and Radiobiological Comparison of External Beam Radiotherapy Using Simultaneous Integrated Boost Technique for Esophageal Cancer in Different Location.

Objectives: To compare treatment plans of intensity modulated radiotherapy (IMRT), volumetric modulated arc radiotherapy (VMAT), and helical tomotherapy (HT) with simultaneous integrated boost (SIB) technique for esophageal cancer (EC) of different locations using dosimetry and radiobiology.Methods: Forty EC patients were planned for IMRT, VMAT, and HT plans, including 10 cases located in the cervix, upper, middle, and lower thorax, respectively. Dose-volume metrics, conformity index (CI), homogeneity index (HI), tumor control probability (TCP), and normal tissue complication probability (NTCP) were analyzed to evaluate treatment plans.Results: HT showed significant improvement over IMRT and VMAT in terms of CI (p = 0.007), HI (p < 0.001), and TCP (p < 0.001) in cervical EC. IMRT yielded more superior CI, HI and TCP compared with VMAT and HT in upper and middle thoracic EC (all p < 0.05). Additionally, V30 (27.72 ± 8.67%), mean dose (1801.47 ± 989.58cGy), and NTCP (Niemierko model: 0.44 ± 0.55%; Lyman-Kutcher-Burman model: 0.61 ± 0.59%) of heart in IMRT were sharply reduced than VMAT and HT in middle thoracic EC. For lower thoracic EC, the three techniques offered similar CI and HI (all p > 0.05). But VMAT dramatically lowered liver V30 (9.97 ± 2.84%), and reduced NTCP of lungs (Niemierko model: 0.47 ± 0.48%; Lyman-Kutcher-Burman model: 1.41 ± 1.07%) and liver (Niemierko model: 0.10 ± 0.08%; Lyman-Kutcher-Burman model: 0.17 ± 0.17%).Conclusions: HT was a good option for cervical EC with complex target coverage but little lungs and heart involvement as it achieved superior dose conformity and uniformity. Due to potentially improving tumor control and reducing heart dose with acceptable lungs sparing, IMRT was a preferred choice for upper and middle thoracic EC with large lungs involvement. VMAT could ameliorate therapeutic ratio and lower lungs and liver toxicity, which was beneficial for lower thoracic EC with little thoracic involvement but being closer to heart and liver. Individually choosing optimal technique for EC in different location will be warranted.

Feasibility study of conformal forward planned simultaneous integrated boost technique comparable to IMRT and VMAT in pelvic irradiation for locally advanced cervical cancer

Abstract Aim: To check the feasibility of simultaneous integrated boost (SIB) using a forward planned field in field (FIF) conformal technique for the treatment of carcinoma of the cervix IIIB and compare it dosimetrically with other advanced inverse planning techniques. Methods: In our study 33 patients of carcinoma of the cervix IIIB were planned for SIB using conformal FIF technique and they were compared with retrospectively planned IMRT and VMAT techniques. SIB using conformal FIF was planned by two different methods. Results: The results of our study indicate that forward planned Conformal SIB techniques are comparable with inverse planned techniques dosimetrically, in terms of conformity Index, Homogeneity Index, Maximum dose, etc. The ability of FIF SIB plans to produce dose contrast in differential dose accumulation was compared and analyzed and the results were encouraging. To treat an advanced/bulky disease like Carcinoma of the Cervix IIIB in centers with large patient load, utilizing advanced techniques such as IMRT and VMAT is both technically and practically difficult. Despite VMAT’s shorter delivery time, the procedures involved are time-consuming. Conclusion: Hence forward planned SIB techniques may be used to achieve similar dosimetric effects of IMRT and VMAT techniques without much compromise in plan quality and patient throughput for treating bulky carcinoma of the cervix IIIB cases. However, the clinical results need to be carefully compared and evaluated and reported.

Dosimetric and radiobiological comparison of external beam radiotherapy using simultaneous integrated boost technique for esophageal cancer in different location.

e15505 Background: Based on dosimetry and radiobiology to compare treatment plans for esophageal cancer (EC) in different location using intensity modulated radiotherapy (IMRT), volumetric modulated arc radiotherapy (VMAT) and helical tomotherapy(HT) with simultaneous integrated boost (SIB) technique. Methods: A total of 20 patients including 5 cases respectively located in the cervix, upper, middle and lower thorax were generated for IMRT, VMAT and HT plans. The dose volume histogram statistics, conformity index (CI), homogeneity index (HI), tumor control probability (TCP) and normal tissues control probability (NTCP) were analyzed to evaluate treatment plans. Results: HT showed significantly improvement over IMRT and VMAT in terms of CI(0.93±0.03), HI(0.07±0.03) and TCP(88.08±0.82%) in cervical EC(p&lt;0.05). IMRT greatly developed TCP(88.29±1.79%;85.11±0.79%), and offered superior CIs (0.87±0.04;0.90±0.01) and HIs(0.10±0.01; 0.06±0.01) compared with VMAT and HT in upper and middle thoracic EC(p&lt;0.05). Meanwhile, the V30(33.30±6.49%), mean dose (2559.00±219.64cGy) and NTCP(0.50±0.61%) of heart for IMRT were significantly reduced than other two techniques in middle thoracic EC. Patients with lower thoracic EC yielded the similar CIs and HIs(all p&gt;0.05) for the 3 techniques, but VMAT showed the lowest NTCP of lungs (0.01±0.01%) with improved TCP (84.84±1.13%). Conclusions: HT was a good option with little lung and heart involvement as it achieved superior dose conformality and uniformity. IMRT was a perfect strategy with large thoracic involvement. It significantly improved tumor local control and reduced heart dose and complications with acceptable dose to lungs. VMAT was preferred with a smaller target volume but surrounded by more heart and less lungs. Individually choosing optimal technique for EC in different location will be warranted.

DoseNet: a volumetric dose prediction algorithm using 3D fully-convolutional neural networks

The goal of this study is to demonstrate the feasibility of a novel fully-convolutional volumetric dose prediction neural network (DoseNet) and test its performance on a cohort of prostate stereotactic body radiotherapy (SBRT) patients. DoseNet is suggested as a superior alternative to U-Net and fully connected distance map-based neural networks for non-coplanar SBRT prostate dose prediction. DoseNet utilizes 3D convolutional downsampling with corresponding 3D deconvolutional upsampling to preserve memory while simultaneously increasing the receptive field of the network. DoseNet was implemented on 2 Nvidia 1080 Ti graphics processing units and utilizes a 3 phase learning protocol to help achieve convergence and improve generalization. DoseNet was trained, validated, and tested with 151 patients following Kaggle completion rules. The dosimetric quality of DoseNet was evaluated by comparing the predicted dose distribution with the clinically approved delivered dose distribution in terms of conformity index, heterogeneity index, and various clinically relevant dosimetric parameters. The results indicate that the DoseNet algorithm is a superior alternative to U-Net and fully connected methods for prostate SBRT patients. DoseNet required ~50.1 h to train, and ~0.83 s to make a prediction on a 128 × 128 × 64 voxel image. In conclusion, DoseNet is capable of making accurate volumetric dose predictions for non-coplanar SBRT prostate patients, while simultaneously preserving computational efficiency.

A systematic review and meta-analysis of radiotherapy planning studies comparing multi leaf collimator designs.

Background and purposeSeveral studies have investigated multi leaf collimator (MLC) leaf design. We performed a systematic review and meta-analysis of those studies to compare the impact of MLC leaf width used for different radiotherapy techniques.Materials and methodsWe decided to focus on 2.5, 3.0 and 5.0 mm leaf width MLCs as it appeared to be the most contentious area from literature. We adopted Cochrane and PRISMA guidelines and computed the association between MLC leaf width and conformity index (CI) across the selected studies as pooled mean difference (PMD) with 95% confidence interval.ResultsA total of 43 papers were selected from the literature search, of which ten compare MLC leaf width of 2.5 mm or 3.0 mm (MLC2.5 mm) versus 5.0 mm (MLC5 mm) in terms of CI. There was a slight, but significant, difference between MLC2.5 mm and MLC5 mm in favor of the former (mean difference −0.036; 95% confidence interval: −0.068 to −0.005). A subgroup analysis was performed by comparing techniques (intensity modulated radiation therapy vs conformal). In the intensity modulated radiation therapy (IMRT) subgroup, the difference between MLC2.5 mm and MLC5 mm appeared to be negligible (mean difference: −0.006; 95% confidence interval: −0.013 to 0.001) and not significantly different from zero. In the subgroup of studies which used conformal techniques, there was a significant difference between MLC2.5 mm and MLC5 mm (mean difference: −0.054; 95% confidence interval: −0.096 to −0.012).ConclusionsIntroduction of IMRT produced comparable target coverage (CI) between 2.5 or 5.0 mm leaf width MLCs.

Differentiation of Using Flattening Filter Free Energy in Vmat Plans for Prostate Cancer

It is aimed to compare the values of conformity index (CI), homogeneity index (HI), monitor unit (MU) of volumetrically adjusted arthritis therapy (VMAT) plans using 10 prostate cancer patients with flattened filter (FF) and without flattening filter (FFF). In the study, treatment plans were prepared using 6 FF and 6 FFF in the Eclipse (ver.13.6) treatment planning system with Varian Trilogy Linear Accelerator. When planning was completed, CI averaged 0.87, HI averaged 0.44 and MU values were found to be 591 ± 26.8, 650 ± 33.06, respectively. When the PTV coverage, CI, HI and MU comparisons were made as a result of planning, there was no significant difference when comparing VMAT plans in FFF and FF energies. When we compare the MU values, the MU increase is seen when the straightening filter is removed. In both energy modes, good homogeneity in PTV was achieved with conventional francitation and close dose rates. No significant advantages and disadvantages of the unfiltered energy mode were observed in the assessment of plan quality in terms of CI, HI.

Optimization of Treatment Planning Parameters used in Tomotherapy for Breast Cancer Patients

Aim: To study the effect of various planning parameters viz field width (FW), pitch factor (PF) on breast tumor and evaluate the relation among these parameters and their influence on the quality of plan and the treatment time. Material and method: Nine plans for each of the ten breast cancer patients were created taking various combinations of field width (FW) and pitch keeping the Modulation factor (MF) constant 3. The reference plan selected for the study is field width of 1, pitch 0.215. Other plans were created keeping the same constraints and penalty as the reference plan and 1000 iterations. Target coverage was evaluated in terms of conformity index (CN) and homogeneity index (HI) while the sparing of organs at risk (OARs) were evaluated in terms of mean, maximum and relevant dose volumes. Low dose spillages in normal tissues were also evaluated. The plans are compared with the reference plan using the Wilcoxon Signed Ranks Test. Concept of plan Quality index is also used to evaluate the plans qualitatively. Results: The mean treatment delivery time for 5, 2.5 and 1.0 cm FW plans were 5.04 ± 0.4, 8.51 ± 0.87 and 20.67 ± 2.02 minutes respectively. There was no significant variation in doses for OARs and COIN and HI of targets for 1 cm and 2.5 cm plans except for 5 cmplans. But the low dose spillage increased by 9-14% and 23-43% for 2.5 and 5 cm respectively. Conclusion: Dose to the OARs was not significantly higher for 2.5_FW plans from the reference plan but, significantly higher for 5_FW. Larger the FW and higher the pitch, spillage were more. On the basis of our analysis, 2.5_0.215 plan with MF=3, can be considered as the optimum plan for unilateral breast treatment using Tomotherapy.

Radiation therapy of synchronous bilateral breast carcinoma (SBBC) using multiple techniques

The purpose of this study was to establish intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) treatment plans for synchronous bilateral breast cancer (SBBC) and to compare those plans with the previous treatment plans using 3D conformal radiation therapy (3DCRT). The differences among the treatments were also statistically compared regarding dosimetry distribution and treatment efficiency. The research was conducted with 10 SBBC patients. The study established IMRT (12 fields with a single isocenter) and VMAT (2 partial arcs with a single isocenter) treatment plans for SBBC patients and then compared those plans with 3DCRT (8 fields with multiple isocenters). The plans were evaluated based on a dose-volume histogram analysis. For planning target volumes (PTVs), the mean doses and the values of V95%, V105%, conformity index, and homogeneity index were reported. For the organs at risk, the analysis included the mean dose, maximum dose, and VXGy, depending on the organs (lungs, heart, and liver). To objectively evaluate the efficiency of the treatment plans, each plan's beam times, treatment times (including set-up time), and monitor units were compared. Tukey test and one-way analysis of variance were used to compare the PTV and organs at risk values of the 3 techniques. Additionally, the independent-samples t-test was used to compare the 2 techniques (IMRT and VMAT) based on the values of Rt. PTV and Lt. PTV (p < 0.05). For PTV dose distribution, IMRT showed increases of approximately 1.2% in Dmean and of approximately 5.7% in V95% dose distribution compared with 3DCRT. In comparison to VMAT, 3DCRT showed about 3.0% higher dose distribution in Dmean and V95%. IMRT was the best in terms of conformity index and homogeneity index (p < 0.05), whereas 3DCRT and VMAT did not significantly differ from each other. In terms of dose distribution on lungs, heart, and liver, the percentage of volume at high doses such as V30Gy and V40Gy was approximately 70% lower for IMRT and approximately 40% lower for VMAT than for 3DCRT. For distribution volumes of low doses such as V5% and V10%, that for 3DCRT was approximately 60% smaller than for IMRT and approximately 70% smaller than for VMAT. Comparison between IMRT and VMAT showed that the IMRT was superior in all distribution factors. VMAT showed better treatment efficiency than 3DCRT or IMRT. Among the SBBC radiotherapy treatment plans, IMRT was superior to 3DCRT and VMAT in terms of PTV dose distribution, whereas VMAT showed the most outstanding treatment efficiency.

The evaluation of the feasibility of carotid sparing intensity modulated radiation therapy technique for comprehensive breast irradiation

PurposeTo investigate the feasibility of carotid sparing intensity modulated radiation therapy (CS-IMRT) to minimize the radiation dose to carotid arteries for comprehensive irradiation of breast cancer patients who have risk factors for atherosclerosis. The dose distribution of CS-IMRT technique and the conventional irradiation technique were also compared. Patients and methodsTen patients who were previously treated with comprehensive three-dimensional conformal radiation therapy (3DCRT) were selected. DICOM data were used to contour the carotid artery and to create the virtual CS-IMRT plans for each patient. 3DCRT and CS-IMRT plans were compared in terms of conformity index, homogeneity index, and the doses to organ at risk and carotid arteries. ResultsThe homogeneity and conformity indices were better with CS-IMRT plans compared to 3DCRT plan. The homogeneity index was 1.13 vs 1.11 (p=0.007) for 3DCRT and CS-IMRT and the conformity index was 0.96 vs 0.97 (p=0.006) for 3DCRT and CS-IMRT. The radiation dose to the carotid arteries were reduced by applying CS-IMRT without compromising the target volume coverage. When the carotid artery was considered as organ at risk for CS-IMRT planning, the median of V50 was decreased to 0% from 12.5% compared to 3DCRT plans (p=0.017). The median of the maximum dose to the carotid artery was decreased under 50Gy with CS-IMRT. ConclusionsCS-IMRT can significantly reduce the unnecessary radiation dose to the carotid arteries compared with conventional 3DCRT technique while maintaining target volume coverage. CS-IMRT technique can be considered for breast cancer patient with high risk of atherosclerosis.

Dosimetric benefits of automation in the treatment of lower thoracic esophageal cancer: Is manual planning still an alternative option?

This study aimed to design automated volumetric-modulated arc therapy (VMAT) plans in Pinnacle auto-planning and compare it with manual plans for patients with lower thoracic esophageal cancer (EC). Thirty patients with lower thoracic EC were randomly selected for replanning VMAT plans using auto-planning in Pinnacle treatment planning system (TPS) version 9.10. Historical plans of these patients were then compared. Dose-volume histogram (DVH) statistics, dose uniformity, and dose homogeneity were analyzed to evaluate treatment plans. Auto-planning was superior in terms of conformity index (CI) and homogeneity index (HI) for planning target volume (PTV), significantly improving 8.2% (p = 0.013) and 25% (p = 0.007) compared with manual planning, respectively, and decreasing dose of heart and liver irradiated by 20 to 40 Gy and 5 to 30 Gy, respectively (p < 0.05). Meanwhile, auto-planning further reduced the maximum dose (Dmax) of spinal cord by 6.9 Gy compared with manual planning (p = 0.000). Additionally, manual planning showed the significantly lower low-dose volume (V5) for the lung (p = 0.005). For auto-planning, the V5 of the lung was significantly associated with the relative volume index (the volume ratio of PTV to the lung), and the correlation coefficient (R) and p-value were 0.994 and 0.000. Pinnacle auto-planning achieved superior target conformity and homogeneity and similar target coverage compared with historical manual planning. Most of organs at risk (OARs) sparing was significantly improved by auto-planning except for the V5 of the lung, and the low dose distribution was highly associated with PTV volume and lung volume in auto-planning.

SU-F-T-334: Has IMRT Changed the Impact of MLC Leaf Width? A Systematic Review and Meta-Analysis of TPS Studies

Purpose: We have performed a systematic review and meta-analysis in order to compare MLC leaf width used for different treatment techniques such as conformal and IMRT. Methods: Medline and Google scholar databases have been searched using the “MLC leaf width” keywords with a cut-off date of 31st December 2015, considering only peer-reviewed papers. We have defined as intervention the MLC leaf width of 5 and 2.5 mm. We used the Conformity Index (CI) as the outcome subjected to the analysis. The mean and standard deviation of each group has been either extracted or calculated. The association between MLCs and Conformity Index reduction across the selected studies was then computed as Pooled Mean Difference (PMD) with 95% CI. Results: From the literature search 43 studies were selected, 12 of them compared MLC 2.5 or 3 mm vs. 5 mm in terms of Conformity Index. On the whole there is a slight significant difference between MLC2.5 and MLC5.0 in favour of the former. The pooled mean difference is −0.036 with a 95% confidence interval ranging between −0.068 and −0.005 (p=0.026). The analysis highlights a very large heterogeneity (I2=87.7%) suggesting the results could be different in specific subgroups. Therefore a subgroup analysis has been performed by comparing techniques (IMRT/VMAT vs 3DCRT/DCA). In the subgroup of IMRT/VMAT the difference between MLC2.5 and MLC5.0 appears to be negligible (mean diff:-0.006; 95%CI: −0.013–0.001) and not significantly different from zero (p=0.064). On the contrary in the subgroup of studies which used the conformal 3DCRT/ DCA techniques, the MLC2.5 resulted significantly different from the MLC5.0 (mean difference: −0.054; 95% CI: −0.096–0.012; p=0.02). Conclusion: A systematic review of TPS studies have been performed. In this analysis, using IMRT/VMAT shows identical capability of achieving good target coverage ability (CI) with 2.5 and 5mm MLC, differently from 3DCRT/DCA. Marco Luzzara and Kevin Brown are Elekta employees. Luigi Santoro has a scientific collaboration with Elekta

SU-E-T-302: Dosimetric Comparison Between Volumetric Modulated Arc Radiotherapy and Intensity-Modulated Radiotherapy for Locally Recurrent Nasopharyngeal Carcinoma

Purpose: To compare volumetric modulated arc radiotherapy (VMAT) technique with fixed-gantry intensity-modulated radiotherapy (IMRT) technique for locally recurrent nasopharyngeal carcinoma. Methods: CT datasets of eleven nasopharyngeal-carcinoma patients were included. Dual-arc VMAT and seven-field IMRT plans were created for each case, and were then compared in terms of conformity index (CI), homogeneity index (HI) of the planning target volume (PTV), organ-at-risk (OAR) sparing, monitor unit (MU) and delivery time. Results: The D98% (near-minimal dose) of PTV in the VMAT plans was slightly lower than that of the IMRT plans (P 0.05). Compared with the IMRT plans, the VMAT plans demonstrated lower Dmean (mean dose) of the bilateral temporal lobes and the whole surrounding normal tissue (P 0.05). The MUs of the VMAT plans (672 ± 112) was significantly lower than that of the IMRT plans (917 ± 206), by 25 ± 13% (P < 0.05). The average delivery time of the VMAT plans (2.3 ± 0.1 min) was less than that of the IMRT plans (5.1 ± 0.4 min), by 54 ± 3%. Conclusion: For locally recurrent nasopharyngeal carcinoma, the VMAT technique could achieve equivalent or superior dose distribution of the target and better protect the bilateral temporal lobes, compared with the IMRT technique. Moreover, it could reduce the MU and delivery time effectively.

SU‐E‐T‐57: A Novel Method to Improve Dose Heterogeneity of Target and Organs at Risk Sparing in the Intensity‐Modulated Radiotherapy for Stage III Lung Cancer

Purpose:Intensity‐modulated radiotherapy (IMRT) treatment for lung cancer is difficult due to the heterogeneous dose distribution and excessive dose to the organs at risk (OARs). We introduce a simple method based on the base dose function (BDF) in Eclipse treatment planning system to overcome the difficulties.Methods:Thirteen patients suffered from stage III non‐small cell lung cancer (NSCLC) were enrolled in the study. Three kinds of approaches were applied to obtain clinically acceptable treatment plans: 1) conventionally optimizing method with hot and cold spots re‐optimization (CO); 2) target‐divided optimizing method (TDO) in which the optimization objective in the lung density of planning target volume (PTV) was set to 2 to 4 Gy higher than in the soft tissue density; 3) base dose function (BDF) in which the treatment plan was produced based on the original plan for re‐optimization. CO, TDO and BDF methods were then compared in terms of conformity index (CI), homogeneity index (HI), OARs sparing and monitor units (MUs). Additionally, delta4, portal dosimetry and IMSure were used to measure the dose delivering accuracy.Results:The BDF technique provided more superior CI and HI than the other two methods. Moreover, the new method also reduced the lung, esophagus, heart and spinal cord dose. However, the BDF plans needed extra 15% and 10% MUs than the CO and TDO methods. Dose verification results demonstrated good and comparable γ pass rates among the three methods.Conclusion:The proposed BDF method greatly improves the dose homogeneity and OARs sparing in the IMRT treatment for lung cancer.

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

PurposeThe 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 MethodsTen 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. ResultsThe 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). ConclusionTH-3DCRT showed excellent carotid-sparing capability, while offering high efficiency and maintaining good PTV coverage.

Dosimetric evaluation and clinical outcome in post-operative patients of carcinoma vulva treated with intensity-modulated radiotherapy.

To compare dosimetric parameters of intensity-modulated radiation therapy (IMRT) with 3D conformal radiotherapy (3DCRT) in post-operative patients of vulvar cancer and to assess clinical outcome and toxicity with IMRT. A total of 8 post-operative patients of vulvar cancer were treated with IMRT. All patients were also planned by 3DCRT for comparison with IMRT. The two plans were compared in terms of conformity index, homogeneity index, tumor control probability (TCP) and normal tissue complication probability (NTCP) for the planning target volume and organs at risk (OAR). IMRT resulted in significantly lesser doses to rectum, bladder, bowel and femoral head as compared with 3DCRT plans. Mean conformity and homogeneity indices were better and within range with IMRT. The TCP was comparable between the two treatment plans and NTCP for rectum, bladder, bowel and femoral head was significantly less with IMRT as compared with 3DCRT. Treatment was well-tolerated and none of the patients developed Grade 3 or higher toxicity. IMRT yielded superior plans with respect to target coverage, homogeneity and conformality while lowering dose to adjacent OAR as compared with 3DCRT. Thus, IMRT offers a reduction in NTCP while maintaining TCP.