Shoot Intensity Modulated Radiation Therapy Research Articles

Dosimetric Impact of Radiolucent Carbon Fiber Hardware for Post-Operative Spine Stereotactic Body Radiation Therapy

The spine is the most common site of osseous metastases. In the non-operative setting, there is growing support for stereotactic body radiation therapy (SBRT) over conventional radiation therapy for improved pain relief and local control. Hybrid therapy consisting of separation surgery and post-operative SBRT is considered in patients with biomechanical instability and epidural cord compression. Surgery traditionally requires titanium (Ti) implants, which introduce artifacts on post-operative imaging in addition to increased uncertainty and beam attenuation. Use of radiolucent carbon fiber reinforced polyetheretherketone (CFR-PEEK) hardware has been shown to provide safe and comparable surgical outcomes as compared to Ti. Our primary objective is to assess the dosimetric impact of Ti versus carbon fiber implants in spine SBRT. Single institution retrospective series of post-operative spine SBRT from 2019-2020. Re-irradiation cases were excluded. The electronic medical record and treatment planning systems (TPS) were queried. Dosimetric analyses compared original Ti plans with reoptimized plans, replacing Ti hardware electronic density with carbon fiber. Maintaining clinical goals, dose calculations were performed in a treatment planning system using a collapsed cone algorithm. All treatments used step and shoot intensity modulated radiation therapy to avoid beam angles with significant metal along the beam path. Metallic artifacts were contoured and assigned the appropriate tissue density. A D'Agostino-Pearson test was used to assess data for normality. We used paired Student's t-tests to compare three dosimetric outcomes in the setting of Ti and carbon fiber implants. Planning target volume (PTV) coverage was represented by the volume receiving at least the prescribed dose (%), the maximum point dose (dmax, cGy) to the spinal cord planning risk volume (PRV, 2 mm margin), and the overall hot spot intensity (plan dmax). A series of 14 consecutive SBRT cases were evaluated (dose 27-30 Gy in 3-5 fractions). All dosimetric outcomes were normally distributed (p>0.05). We found a statistically significant difference in PTV coverage between the original SBRT treatment plans with Ti hardware (mean 85.1 ± 7.9%) and reoptimized carbon fiber hardware (87.3 ± 6.6%; p = 0.002). There was no significant difference in mean spinal cord PRV dmax between Ti and carbon fiber plans (1846 ± 483 cGy vs. 1842 ± 495 cGy; p>0.05). We observed a nonsignificant increase in mean overall dmax from 3932 ± 416 cGy in the Ti cohort to 4111 ± 906 cGy in the carbon fiber cohort (p>0.05). Carbon fiber implants provide a significant increase in SBRT target coverage, without impacting the overall plan and spinal cord PRV dmax in this retrospective series. In addition to improved post-operative imaging and reduced uncertainty, carbon fiber hardware may offer dosimetric advantages as compared to traditional Ti spinal implants, and warrants further investigation in a larger cohort.

Comparison of three Radiotherapy Techniques Volumetric Modulated Arc Therapy with Variable and Constant Dose Rate and Intensity-Modulated Radiotherapy for the Irradiation of Five Cancer Sites.

Volumetric modulated arc therapy (VMAT) is mostly considered due to its superior tumor coverage and sparing of organs at risk (OAR) with shorter treatment delivery time. This study aimed to explore the feasibility and potential benefits of VMAT with a constant dose rate (CDR). In this analytical study, 75 cancer patients (15 from each cancer) were selected. Step and shoot intensity-modulated radiation therapy (S&S IMRT), CDR, and VDR VMAT (variable dose rate VMAT) plans were generated for each patient using the Monte Carlo algorithm on the Monaco treatment planning system for 6 MV photon energy. For dosimetric comparison, some variables were compared, including doses to the planning target volume (PTV), OAR, homogeneity index, conformity index (CI), treatment delivery time, and monitor units. CI was higher in CDR and VDR VMAT plans compared to IMRT without any significant variation for PTV coverage V95 and PTV mean dose. In the sparing of OAR, no significant variation was found between CDR, VDR, and IMRT for the brain, head-neck, oesophagus, lung, and prostate. The treatment delivery time was reduced more, i.e., by up to 72-80% in the CDR VMAT technique compared to IMRT. CDR VMAT technique generates a clinically acceptable plan in terms of PTV coverage, dose conformity, and OAR sparing as IMRT and VDR VMAT in all five cancer sites.

Evaluation of Radiation Treatment Planning Algorithms in IMRT and VMAT: A Comparative Dosimetric Study in Lung Equivalent Heterogeneous Medium.

In Radiotherapy, computation of dose is important since in a small field with heterogeneity, dose is usually computed with discrepancies. The present study was aimed to evaluate the dosimetry of treatment planning algorithms in lung equivalent heterogeneous medium for Volumetric Modulated Arc Therapy (VMAT) with step and shoot Intensity-Modulated Radiation Therapy (ss-IMRT), and dynamic Intensity-Modulated Radiation Therapy (d-IMRT). In this experimental study, Computerized Imaging Reference System (CIRS) phantom was used with an inhomogeneous Racemosa wood cylinder for two types of tumors, namely, Left Lung Central Tumor (LCT) and Left Lung Peripheral Tumor (LPT) in the CIRS left lung cavity. The computed tomography (CT) datasets were employed with the generation of VMAT, d-IMRT and ss-IMRT plans for the LCT and LPT irradiated with 6 MV photon beams. In this study, the accuracy and efficacy of two algorithms: Monte Carlo (MC) and the Pencil Beam (PB), from the Monaco treatment planning system (TPS), were tested by using Gafchromic EBT3 films and CIRS thorax phantom. Regardless of treatment techniques, both algorithms exhibited higher divergence in LPT than LCT. In both LCT and LPT, the highest deviation was near the tumor-lung junction. However, the deviation was higher in the PB algorithm than MC algorithm, with a minimally acceptable variation of -0.8%. The MC algorithm shows more consistency for EBT3 measured dose in lung equivalent heterogeneous medium. However, accurate dose predictions are complicated due to electronic disequilibrium within and at the interface of inhomogeneity. These constraints may cause variations from the anticipated outcomes of the treatments.

Evaluation of internal margins for prostate for step and shoot intensity-modulated radiation therapy and volumetric modulated arc therapy using different margin formulas.

PurposeThis feasibility study evaluated the intra‐fractional prostate motion using an ultrasound image‐guided system during step and shoot intensity‐modulated radiation therapy (SS‐IMRT) and volumetric modulated arc therapy (VMAT). Moreover, the internal margins (IMs) using different margin formulas were calculated.MethodsFourteen consecutive patients with prostate cancer who underwent SS‐IMRT (n = 5) or VMAT (n = 9) between March 2019 and April 2020 were considered. The intra‐fractional prostate motion was observed in the superior–inferior (SI), anterior–posterior (AP), and left–right (LR) directions. The displacement of the prostate was defined as the displacement from the initial position at the scanning start time, which was evaluated using the mean ± standard deviation (SD). IMs were calculated using the van Herk and restricted maximum likelihood (REML) formulas for SS‐IMRT and VMAT.ResultsFor SS‐IMRT, the maximum displacements of the prostate motion were 0.17 ± 0.18, 0.56 ± 0.86, and 0.18 ± 0.59 mm in the SI, AP, and LR directions, respectively. For VMAT, the maximum displacements of the prostate motion were 0.19 ± 0.64, 0.22 ± 0.35, and 0.14 ± 0.37 mm in the SI, AP, and LR directions, respectively. The IMs obtained for SS‐IMRT and VMAT were within 2.3 mm and 1.2 mm using the van Herk formula and within 1.2 mm and 0.8 mm using the REML formula.ConclusionsThis feasibility study confirmed that intra‐fractional prostate motion was observed with SS‐IMRT and VMAT using different margin formulas. The IMs should be determined according to each irradiation technique using the REML margin.

A Systematic Approach to Optimise the Number of Beams for Intensity Modulated Radiotherapy in Pituitary Adenoma using Radiobiological Parameters

Introduction: The number of beams used in a Radiotherapy (RT) plan effects the overall quality of the plan and hence the treatment. The inclusion of radiobiological concepts in finding the optimum number of beams for a particular planning technique has the potential to provide a step ahead of the routine clinical practice where clinical decisions are more dependent on the physical dose parameters. Aim: To optimise the number of beams for Intensity Modulated Radiotherapy (IMRT) plan based on Tumour Control Probability (TCP) and Normal Tissue Complication Probability (NTCP) biological parameters. Materials and Methods: This retrospective study was done on 30 patients with pituitary macro-adenoma who underwent radiotherapy with a prescribed dose of 50.4 Gy in 28 fractions in Delhi State Cancer Institutes, Delhi, India from December 2012 to August 2018. The study data was collected and analysed between June 2018 and April 2020. These patients were treated with step and shoot IMRT technique on ONCORTM Expression linear accelerator (Siemens Healthineers, USA). But, the number of beams used to deliver IMRT plans were different as decided by the medical physicist and hence planner dependent rather than the disease. Being a centrally located disease, a symmetric beam arrangement was adopted for IMRT planning. For dosimetric comparison, three IMRT plans with five, seven, and nine equispaced beams were generated in Monaco treatment planning system for each patient and thus, a total of 90 IMRT plans were created and evaluated. For fair comparison, same IMRT planning parameters were utilized in all three plans of each patient. Monte Carlo (MC) dose calculation algorithm was used for all the plans. Resulting Cumulative Dose Volume Histograms (CDVHs) were exported to MATLAB, where these cDVHs were processed as per Niemierko’s radiobiological model to calculate the values of TCP and NTCP based on the Equivalent Uniform Dose (EUD). After this, the analysis of variance, ANOVA test was conducted over the resulting values of EUD, TCP, and NTCP to assess the difference of quality among plans having different beam arrangements at 0.05 level of significance. Results: The mean tumour control probability (TCP) for IMRT plans with seven and nine beams were found to be 89.0±0.8% and 89.1±0.9% respectively for planning target volume (PTV). These values were not significantly different from each other. However, the mean TCP value for IMRT plans with five beams was found to be 88.4±1.1% for PTV. Further, this TCP value was proved to be significantly lower as compared to IMRT plans with seven and nine beams with a p-value of 0.008 and 0.004 respectively. On the other hand, the mean Normal Tissue Complication Probability (NTCP) was assessed to be less than 1% for all critical organs irrespective of the beam arrangement, indicating almost no probability of radiation induced toxicity in any of the organ. Conclusion: This study concludes that the plan efficiency can be improved by using optimum number of beams for IMRT planning of pituitary adenoma.

The Effect of Modulation Complexity Score (MCS) on the IMRT Treatment Planning Delivery Accuracy

Intensity modulated radiation therapy (IMRT) is an effective treatment planning technique for various types of tumors such as head and neck (H&N) or pelvis. A complexity algorithm was invented to predict the deliverability and the accuracy for IMRT plans called the Modulation Complexity Score ranging from 0 to 1. The %GP is a metric depends on %DD /DTA to find the variation between the calculated dose from TPS and the measured dose from the phantom during the QA. This study is trying to assess the correlation between the MCS and planning verification outcome. Thirty-four patients treated with step and shoot IMRT technique for anatomical sites: H&N and pelvis. The planning process performed using Monaco 5.1 TPS then exported to Elekta Synergy linear accelerator. The phantom is used for the QA procedure is Octavius 4D-1500 with Verisoft 7.1 software analysis to evaluate the gamma passing rate for commonly used criteria 3%/3 mm at a 5% threshold. The MCS calculated using MATLAB 2019a. It results that the H&N plans are significantly more complex than the pelvis once with p-value 0.0192. The analysis shows a weak correlation between the MCS and MU for both treated sites. The complex H&N plans give a good value for %GP. Also, simpler pelvis plans obtain better global %GP results. Thus, modulation Complexity score can give a simple indication for pretreatment verifications of the IMRT plans for H&N and pelvis sites.

Dosimetric comparison of constant dose rate volumetric modulated arc therapy (CDR-VMAT) and intensity-modulated radiation therapy (IMRT) for gallbladder cancer

AbstractAim:To study the feasibility of constant dose rate volumetric modulated arc therapy (CDR-VMAT) in radiotherapy for gallbladder cancer by comparing dosimetric parameter suggested by International Commission on Radiation Units and Measurements-83 (ICRU-83) with step and shoot intensity-modulated radiation therapy (SS IMRT).Methods:For this study, we selected 21 post-operative gallbladder cancer patients, which were treated with the IMRT technique from 2016 to 2019. For each patient, we generated SS IMRT plan and CDR-VMAT plan and were dosimetrically compared by parameters suggested by ICRU-83 for PTV. Homogeneity Index (HI) and Conformity Index (CI) were also calculated. For evaluation of Organ at Risk (OAR), we compared the mean doses, volume doses to the right kidney, left kidney, both kidneys combined, liver and max dose to the spinal cord. Monitor units (MUs) and treatment delivery time were also compared.Results:On comparing, we found that CDR-VMAT plans were highly conformed as CI and PCI (CI define by Paddick) were found more (0·98 ± 0·01 vs. 0·97 ± 0·03 and 0·86 ± 0·05 vs. 0·85 ± 0·05) than IMRT plans but not statistically significant. Better dose HI was found for IMRT plans with statistical significant difference (p < 0·001). The tumour coverage was found similar 98·24% and 97·83% for SS IMRT and CDR-VMAT, respectively. For D2%, the maximum dose to PTV was significantly lower in IMRT (p = 0·001). D50% and mean dose to PTV were also comparable to IMRT with no statistically significant difference. The OAR parameters were comparable in both the techniques. The mean doses and volume doses V10, V20 and V30 to the right kidney, left kidney and liver were also comparable with no significant difference (p > 0·05) was noted among them. However, the maximum dose to the spinal cord was significantly less in CDR-VMAT (21·1 Gy vs. 25·1Gy) than SS IMRT with p = 0·006. More MUs were associated with the CDR-VMAT technique, but shorter treatment delivery time than the IMRT technique.Conclusions:On dosimetric comparison of two treatment techniques, we conclude that CDR-VMAT can be a valid option in radiotherapy as it achieved highly conformed dose distribution, comparable tumour coverage and OAR sparing as IMRT technique for gallbladder cancer.

Radiation Oncology-External-Beam Radiation Therapy.

The application of structural shielding design techniques and goals as outlined in the National Council on Radiation Protection and Measurements Report 151, Structural Shielding Design and Evaluation for Megavoltage X- and Gamma-Ray Radiotherapy Facilities (2005), continues to be the basis for treatment vault design in 2018 with some updated information. Treatment techniques have changed significantly with the dominant usage of intensity-modulated radiation therapy techniques today based on concurrent imaging. Some of the developments in linear accelerator technology over the past 15 y include flattening filter-free modes, which enable higher instantaneous dose rates; three-dimensional conformal radiation therapy resulting in potentially higher workloads since healthy tissue is spared; improved intensity-modulated radiation therapy treatment delivery systems with lower monitor units per centigray delivered than traditional step and shoot intensity-modulated radiation therapy; stereotactic body radiation therapy with higher treatment fractions and increased workloads; and increased use of stereotactic radiosurgery with conventional linear accelerators as well as robotic arm-mounted linear accelerators with higher treatment fractions. These new treatment units also incorporate multiple-energy x-ray beams (2 to 5 MV typical), which require a significant change in the specification of a workload to be used in each vault. As the equipment in radiation oncology departments has evolved to state-of-the-art modalities, the requirements for adequate radiation shielding for these modalities has become more rigorous. Architectural designs no longer depend on standard maze design rectangular rooms. Innovative layouts and utilization of multiple layers of shielding materials allow much greater flexibility in room designs. Maze-less rooms with direct-shielded doors are part of these challenging designs and are very common today. Use of multiple-density concrete blocks allows quicker construction of vaults and requires less space for the equivalent shielding provided. Combinations of high-density or normal-density concrete, steel, and lead are used in designs to make optimum use of available space and cost. Additional shielding needed at the edges of these single- or bi-parting sliding doors as well as baffle designs for heating, ventilation, and air conditioning systems and communication cable penetrations require detailed calculations. Examples of these designs will be given in this presentation. Consideration of the radiation levels around the planned vault must also include adjacent multistory buildings.

192. Evaluation of a commercial orthopedic metal artefact reduction tool in radiation therapy

Purpose In radiotherapy process image artifacts can lead either a wrong definition of structure contours by the clinician either an erroneous computation of dose due to inaccuracies in the Hounsfield Unit (HU) values. Radiotherapy patients have often metal implants and this causes several image artifacts. This study is focused on the advantages using a commercial metal artifacts reduction algorithm, O-MAR (Philips Healthcare System, Cleveland, OH). Methods and materials The study is performed on five head and neck cases with metal dental implants. Patients were scanned on a large bore CT Brilliance Philips. The scanned images were reconstructed with standard and O-MAR algorithm for each patient. The structures drawing by the clinicians on the O-MAR series were copied, on the originally CT images to evaluate the dose distribution on the same volume. The plans have been made on Pinnacle TPS in nine field steep and shoot intensity modulated radiation therapy (IMRT). The treatment provided two or three PTVs, respectively with 54/66 Gy and 54/60/66 Gy and constraints were evaluated on different OARs, close to the artifacts region, such as bone marrow, parotids, mandibule. Hounsfield Units (HU) variation were analyzed also in additional region of interest (ROI) near the dental implant. Results In the OMAR images, noise values were generally reduced, standard deviation of HU is lower than standard images. Statistical analysis on HU values was performed, but without significant difference between the two data sets. Evaluating the dose distribution and the dose volume histogram (DVH) with the clinicians, no significant difference were detected. Conclusion In head and neck case, when patients have dental implants, the use of O-MAR improve the entire radiation treatment planning process, especially for contouring because increase the accuracy of CT HU and reduce the noise. No significant changes in dose calculation had been found.

Use of lung treatment plans to evaluate DIR algorithms.

The purpose of the study is to evaluate the accuracy of two deformable image registration algorithms by examining their influence on the dose summation results obtained using 4DCT (four dimensional computed tomography) dose distributions based on '4D' planned and '4D optimal' IMRT (intensity modulated radiation therapy) plans. For ten lung cancer patients, 4D step and shoot IMRT plans were produced. The breathing cycle was divided into ten parts and for each part a set of CT images was acquired. For each patient the treatment plan was copied to the CTs of each phase and subsequently recalculated. Each phase CT was then registered to the average intensity projection (AIP) CT using a deformable image registration (DIR) algorithm and the composite dose distribution was then calculated by summing up the deformed dose distributions from all the phases ('4D' treatment plan). The '4D optimal' treatment plan was created by producing an optimal plan on the CTs of each phase of the respiratory cycle and summing up the deformed dose distributions from all the phases. The results indicate that it is possible to map the dose distributions of different breathing phases in lung using DIR, and that different DIR methods and target characteristics (motion amplitude, size, location) affect the differences between original plan, '4D' and '4D optimal' dose distributions. Although the '4D optimal' plans were designed to achieve 95% target coverage, both of the used DIR methods failed to translate that coverage in some instances. The same variation between these methods was also observed in the '4D' plan comparison. This study shows that it is feasible to perform an acceptably accurate calculation of the composite deformed dose. However, it is important to account for tumor motion and body deformation especially when the tumor volume is small and/or located in the lower lobe of the lung.

Hybrid Tri-Co-60 MRI radiotherapy for locally advanced rectal cancer: An in silico evaluation.

Aim of this paper is to investigate the plan quality of a tri-Co-60 MRI-Hybrid system for intensity-modulated radiation therapy (IMRT) in patients affected by locally advanced rectal cancer (LARC) undergoing neo-adjuvant radiotherapy. Ten consecutive LARC patients were selected. Tri-Co-60 step and shoot IMRT plans were generated simulating the presence of the magnetic field (Bon) or not (Boff) with the dedicated treatment planning system (TPS).The total planned dose was 45 Gy in 25 fractions to the mesorectum and the pelvic nodes (planning target volume 2, PTV2) and 55 Gy to the tumor and correspondent mesorectum (PTV1) through simultaneous integrated boost (SIB). Tri-Co-60 IMRT plans were compared with Volumetric Modulated Arc Therapy (VMAT) and IMRT plans for Linear Accelerator (Linac). Bon and Boff tri-Co-60 IMRT plans showed no relevant differences. Mean values of PTV1 and PTV2 receiving at least 95% of the Dp (V95%) were higher than 95% in all treatment plans. All plans met the V105% constraint for the PTV1. Mean values of V105% for the PTV2 were 14.8, 5.0, and 7.3% respectively for tri-Co-60, VMAT and IMRT. Mean Wu's HI values were similar in all plans (7.4-7.8%). All plans met the V45Gy constraint for small bowel, but mean V45Gy value was higher with tri-Co-60.Bladder irradiation was comparable and always lower than the chosen D max 65 Gy constraint.Mean values of V5Gy and V20Gy to the body and median skin doses were higher with tri-Co-60 plans. Treatment plans with Tri-Co-60 step and shoot IMRT met the dose-volume objectives in patients with LARC. Nevertheless, a larger volume of normal tissue received low-moderate doses when compared with Linac based VMAT and IMRT.

Is volumetric modulated arc therapy with constant dose rate a valid option in radiation therapy for head and neck cancer patients?

Intensity-modulated radiotherapy (IMRT) improves dose distribution in head and neck (HN) radiation therapy. Volumetric-modulated arc therapy (VMAT), a new form of IMRT, delivers radiation in single or multiple arcs, varying dose rates (VDR-VMAT) and gantry speeds, has gained considerable attention. Constant dose rate VMAT (CDR-VMAT) associated with a fixed gantry speed does not require a dedicated linear accelerator like VDR-VMAT. The present study explored the feasibility, efficiency and delivery accuracy of CDR-VMAT, by comparing it with IMRT and VDR-VMAT in treatment planning for HN cancer. Step and shoot IMRT (SS-IMRT), CDR-VMAT and VDR-VMAT plans were created for 15 HN cancer patients and were generated by Pinnacle3 TPS (v 9.8) using 6MV photon energy. Three PTVs were defined to receive respectively prescribed doses of 66Gy, 60Gy and 54Gy, in 30 fractions. Organs at risk (OARs) included the mandible, spinal cord, brain stem, parotids, salivary glands, esophagus, larynx and thyroid. SS-IMRT plans were based on 7 co-planar beams at fixed gantry angles. CDR-VMAT and VDR-VMAT plans, generated by the SmartArc module, used a 2-arc technique: one clockwise from 182° to 178° and the other one anti-clockwise from 178° to 182°. Comparison parameters included dose distribution to PTVs (Dmean, D2%, D50%, D95%, D98% and Homogeneity Index), maximum or mean doses to OARs, specific dose-volume data, the monitor units and treatment delivery times. Compared with SS-IMRT, CDR-VMAT significantly reduced the maximum doses to PTV1 and PTV2 and significantly improved all PTV3 parameters, except D98% and D95%. It significantly spared parotid and submandibular glands and was associated with a lower Dmean to the larynx. Compared with VDR-VMAT, CDR-VMAT was linked to a significantly better Dmean, to the PTV3 but results were worse for the parotids, left submandibular gland, esophagus and mandible. Furthermore, the Dmean to the larynx was also worse. Compared with SS-IMRT and VDR-VMAT, CDR-VMAT was associated with higher average monitor unit values and significantly shorter average delivery times. CDR-VMAT appeared to be a valid option in Radiation Therapy Centers that lack a dedicated linear accelerator for volumetric arc therapy with variable dose-rates and gantry velocities, and are unwilling or unable to sanction major expenditure at present but want to adopt volumetric techniques.

Multi-institutional comparison of simulated treatment delivery errors in ssIMRT, manually planned VMAT and autoplan-VMAT plans for nasopharyngeal radiotherapy

PurposeTo quantify the impact of simulated errors for nasopharynx radiotherapy across multiple institutions and planning techniques (auto-plan generated Volumetric Modulated Arc Therapy (ap-VMAT), manually planned VMAT (mp-VMAT) and manually planned step and shoot Intensity Modulated Radiation Therapy (mp-ssIMRT)). MethodsTen patients were retrospectively planned with VMAT according to three institution’s protocols. Within one institution two further treatment plans were generated using differing treatment planning techniques. This resulted in mp-ssIMRT, mp-VMAT, and ap-VMAT plans. Introduced treatment errors included Multi Leaf Collimator (MLC) shifts, MLC field size (MLCfs), gantry and collimator errors. A change of more than 5% in most selected dose metrics was considered to have potential clinical impact. The original patient plan total Monitor Units (MUs) were correlated to the total number of dose metrics exceeded. ResultsThe impact of different errors was consistent, with ap-VMAT plans (two institutions) showing larger dose deviations than mp-VMAT created plans (one institution). Across all institutions’ VMAT plans the significant errors included; ±5° for the collimator angle, ±5mm for the MLC shift and +1, ±2 and ±5mm for the MLC field size. The total number of dose metrics exceeding tolerance was positively correlated to the VMAT total plan MUs (r=0.51, p<0.001), across all institutions and techniques. ConclusionsDifferences in VMAT robustness to simulated errors across institutions occurred due to planning method differences. Whilst ap-VMAT was most sensitive to MLC errors, it also produced the best quality treatment plans. Mp-ssIMRT was most robust to errors. Higher VMAT treatment plan complexity led to less robust plans.

Simultaneous integrated boost therapy of carcinoma of the hypopharynx/larynx with and without flattening filter - a treatment planning and dosimetry study

BackgroundThe aim of this study was to investigate if the flattening filter free (FFF) irradiation mode of a linear accelerator (linac) is advantageous as compared to the flat beam (FF) irradiation mode in intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for carcinoma of the hypopharynx / larynx.MethodsFour treatment plans were created for each of 10 patients for an Elekta Synergy linac with Agility collimating device, a dual arc VMAT and a nine field step and shoot IMRT each with and without flattening filter. Plan quality was compared considering target coverage and dose to the organs at risk. All plans were verified by a 2D–ionization-chamber-array and delivery times were compared. Peripheral point doses were determined as a measure of second cancer risk. The Wilcoxon test was used for statistical analysis with a significance level of 0.05.ResultsPlan quality was similar for all four treatment plans without statistically significant differences of clinical relevance. The clinical goals were met in all plans for the PTV-SIB (V95% > 95%), the spinal cord (D1ccm < 45 Gy) and the brain stem (D1ccm < 48 Gy). For the parotids, the goal of D50% < 30 Gy was met in 70% and 60% of the plans for the left and right parotid respectively, and the V95% of the SIB reached an average of 94%. Delivery times were similar for FF and FFF and significantly decreased by around 70% for VMAT as compared to IMRT. Peripheral doses were significantly reduced by 18% in FFF mode as compared to FF and by 26% for VMAT as compared to IMRT. Lowest peripheral doses were found for VMAT FFF, followed by VMAT FF.ConclusionsThe FFF mode of a linear accelerator is advantageous for the treatment of hypopharynx/larynx carcinoma only with respect to reduction of second cancer induction in peripheral organs for the combination of Elekta Synergy linacs and Oncentra® External Beam v4.5 treatment planning system. This might be of interest in a therapy with curative intent.

Neutron contamination in conventional 3DCRT treatment and step and shoot IMRT technique using 10 mv photon beam

Introduction Linear accelerator is a device that can able to generate high energy photon from 4 MV to 25 MV, and these beams are used for radiation therapy. There are different treatment techniques using now a days to deliver radiation externally but most common is 3DCRT (3D conformal radiotherapy) and Intensity modulated radiation therapy. The major issue arises using photon beam having energy ∼10 MV and above is the productions of secondary neutron which can maximize the patient absorb doses. Purpose The aim of the study is to evaluate 3D conformal radiation therapy and step and shoot intensity modulated radiation therapy (ssIMRT) techniques for less neutron contamination that lead to minimum patient exposure from neutrons. Material and methods For this purpose five treatment plan of breast were made on both 3DCRT and ssIMRT using 10MV photon. Linear accelerator Elekta Synergy is used to deliver these plans and for measuring neutrons dose in primary beam, a portable, Ludlum neutron detector is used which is placed on patient’s couch. Results Obtained data shows that the mean values with standard error for each technique was found to be 14.56 mSv ± 0.38 and 25.07 mSv ± 1.2 for 3D CRT and ssIMRT, respectively. Mean difference between two techniques for neutron contamination was found to be 10.5 mSv. Conclusion It can be concluded from the study that contamination of neutrons increases by a factor of 10.5 when we move from 3D CRT to ssIMRT. This is because of increase no. of MUs that are being used in ssIMRT. Although ssIMRT therapy provides better plan optimization for target than 3DCTR but contains greater neutron contamination.

Long-term results in malignant pleural mesothelioma treated with neoadjuvant chemotherapy, extrapleural pneumonectomy and intensity-modulated radiotherapy.

IntroductionWe investigated the clinical outcome and the toxicity of trimodal therapy of malignant pleural mesothelioma (MPM) treated with neoadjuvant chemotherapy, extrapleural pneumonectomy (EPP) and adjuvant intensity-modulated radiotherapy (IMRT).MethodsChemotherapy regimens included Cisplatin/Pemetrexed, Carboplatin/Pemetrexed and Cisplatin/Gemcitabine, followed by EPP. 62 patients completed the adjuvant radiotherapy. IMRT was carried out in two techniques, either step&shoot or helical tomotherapy. Median target dose was 48 Gy to 54 Gy. Toxicity was scored with the Common Terminology Criteria (CTC) for Adverse Events. We used Kaplan-Meier method to estimate actuarial rate of locoregional control (LRC), distant control (DC) and overall survival (OS), measured from the date of surgery. Rates were compared using the logrank test. For multivariate analysis the Cox proportional hazard model was used.ResultsThe median OS, LRC and DC times were 20.4, 31.4 and 21.4 months. The 1-, 2-, 3-year OS rates were 63, 42, 28 %, the LRC rates were 81, 60, 40 %, and the DC rates were 62, 48, 41 %. We observed no CTC grade 4 or grade 5 toxicity. Step&shoot and helical tomotherapy were equivalent both in dosimetric characteristics and clinical outcome. Biphasic tumor histology was associated with worse clinical outcome compared to epitheloid histology.ConclusionsMature clinical results of trimodal treatment for MPM were presented. They indicate that hemithoracic radiotherapy after EPP can be safely administered by either step&shoot IMRT and tomotherapy. However, the optimal prospective patient selection for this aggressive trimodal therapy approach remains unclear. This study can serve as a benchmark for current and future therapy concepts for MPM.Electronic supplementary materialThe online version of this article (doi:10.1186/s13014-015-0575-5) contains supplementary material, which is available to authorized users.

SU‐E‐T‐740: The Optimization in Segment Numbers for Nasopharyngeal Carcinoma (NPC) Treated by Intensity Modulated

Purpose:In premise of uninfluenced to dose distribution of tumor target and organ at risk(OAR) in Nasopharyngeal carcinoma (NPC),the number of segment was changed to increase efficacy and optimize treatment method by designing different plan of intensity modulated radiotherapy(IMRT).Methods:10 cases of NPC were confirmed in pathology and treated with step and shoot IMRT. The target volumes were defined: GVT‐T (the primary tumor); GVT‐N (the metastasis lymph nodes in neck); CTV‐T and CTV‐N (the clinical targets of GVT‐T and GTV‐N); and PTV (incidental lymph nodal region). Dose of GTV/CTV/PTV was 70/64/54Gy for 30 fractions.Every patient was designed 7 treatment plans of IMRT by Pinnacle 8.0m planning system,each plan was used with 9 beams of uniform distribution and fixing incidence direction(200°,240°,280°,320°,0°,40°,80°,120°and 160°respectively),and designed for delivery on Elekta Synergy linear accelerator.All plans were optimized with the direct machine parameter optimization(DMPO) algorithm.Minimum MU in each segment was defined at 4MU,and minimal segment area was 4cm2.Number of maximum segment field was defined at 120,110,100,90,80,70,60, respectively.Coverage and conformity of GTV/CTV/PTV,sparing of OARs(spinal cord, brain, parotids, lens and optic nerves) were compared.Results:In this group,mean volume of GTV(GTV‐T+GTV‐N),CTV(CTV‐T+CTV‐N)and PTV were 91.39±71.13cm3,177.27±92.16cm3 and 1028.05±167.03cm3,.respectively. Compared with the number of segment decreased from 120 to 60, there were no difference in MU(p&gt;0.05),and the dose distribution of targets(GTV/CTV/PTV),OARs and CI were not different too(p&gt;0.05).But when the segment number was &lt;60, CI of PTV was changed compared with others(p&lt;0.05).Conclusion:The minimal segment number of IMRT plan designed by Pinnacle 8.0m planning system in NPC should be decreased reasonably and the limit of minimal segment number was recommended by 70.

SU-E-T-592: Relationship Between Dose of Distribution and Area of Segment Fields Among Different Intensity-Modulated Radiotherapy Planning in Cervix Cancer

Purpose: In premise of uninfluenced to dose distribution of tumor target and organ at risk(OAR) in cervical cancer,area of segment fields was changed to increase efficacy and optimize treatment method by designing different plan of intensity modulated radiotherapy(IMRT). Methods: 12 cases of cervical cancer were confirmed in pathology and treated with step and shoot IMRT. Dose of PTV was 50Gy/25fractions. Every patient was designed 9 treatment plans of IMRT by Pinnacle 8.0m planning system,each plan was used with 9 beams of uniform distribution and fixing incidence direction(200°,240°,280°,320°,0°,40°,80°,120°and 160°respectively),and designed for delivery on Elekta Synergy linear accelerator. All plans were optimized with the direct machine parameter optimization(DMPO) algorithm using the same set of optimization objectives. Number of maximum segment field was defined at 80 and minimum MU in each segment was 5MU,and minimal segment area was 2*1cm2,2*2cm2,3*3cm2,4*4cm2,5*5cm2,6*6cm2,7*7cm2,8*8cm2and 9*9cm2,respectively.Coverage,homogeneity and conformity of PTV,sparing of OAR, MU and number of segment were compared. Results: In this group, mean volume of PTV was 916.8±228.7 cm3. Compared with the area of minimal segment field increased from 2*1cm2 to 9*9 cm2,the number of mean MU was decreased from 1405±170 to 490±47 and the number of segment field was reduced from 76±4 to 39±7 respectively(p 0.05),but when the minimal segment area was 8*8 cm2 and 9*9 cm2,they were changed compared with 7*7 cm2 and below(p<0.05). Conclusion: The minimal segment field of IMRT plan designed by Pinnacle 8.0m planning system in cervical carcinoma should be enlarge reasonably and minimal segment area of 7*7 cm2 was recommend.

Which T Category of Nasopharyngeal Carcinoma May Benefit Most from Volumetric Modulated Arc Therapy Compared with Step and Shoot Intensity Modulated Radiation Therapy

BackgroundTo compare volumetric modulated arc therapy (VMAT) with conventional step and shoot intensity modulated radiation therapy (s-IMRT) in nasopharyngeal carcinoma (NPC) patients, and identify which T category patient gains the maximum benefit from VMAT.MethodsFifty-two patients that randomly selected from 205 patients received VMAT at a single center were retrospectively replanned with s-IMRT. For a fair comparison, the planning target volume (PTV) coverage of the 2 plans was normalized to the same level. A standard planning constraint set was used; the constraints for the organs at risk (OARs) were individually adapted. The calculated doses to the PTV and OARs were compared for s-IMRT and VMAT plans generated using the Monaco treatment planning system.ResultsVMAT and s-IMRT plans had similar PTV coverage and OAR sparing within all T categories. However, in stratified analysis, VMAT plans lead to better or similar sparing of the OARs in early T category patients; and lead to poorer sparing of the OARs in advanced T category patients (P<0.05). VMAT shows significant advantages for low dose burden (P<0.05) compared with s-IMRT. The delivery time per fraction for VMAT (424±64 s) was shorter than s-IMRT (778 ± 126 s, p<0.01).ConclusionsVMAT provides similar dose coverage of the PTVs and similar/better normal tissue sparing in early T category NPC, and poorer OARs sparing in advanced T category NPC. And VMAT shows significant advantages for low dose burden and delivery time.

Improvement in clinical step and shoot intensity modulated radiation therapy delivery accuracy on an integrated linear accelerator control system

PurposeThe dose delivery accuracy of 30 clinical step and shoot intensity modulated radiation therapy plans was investigated using the single integrated multileaf collimator controller of the Varian Truebeam linear accelerator (linac) (Varian Medical Systems, Palo Alto, CA) and compared with the dose delivery accuracy on a previous generation Varian 2100CD C-Series linac. Methods and MaterialsTen prostate, 10 prostate and pelvic node, and 10 head-and-neck cases were investigated in this study. Dose delivery accuracy on each linac was assessed using Farmer ionization chamber point dose measurements, 2-dimensional planar ionization chamber array measurements, and the corresponding Varian dynamic log files. Absolute point dose measurements, fluence delivery accuracy, leaf position accuracy, and the overshoot effect were assessed for each plan. ResultsAbsolute point dose delivery accuracy increased by 1.5% on the Truebeam compared with the 2100CD linac. No improvement in fluence delivery accuracy between the linacs, at a gamma criterion of 3%/3 mm was measured using the 2-dimensional ionization chamber array, with median (interquartile range) gamma passing rates of 98.99% (97.70%-99.72%) and 99.28% (98.26%-99.75%) for the Truebeam and 2100CD linacs, respectively. Varian log files also showed no improvement in fluence delivery between the linacs at 3%/3 mm, with median gamma passing rates of 99.97% (99.93%-99.99%) and 99.98% (99.94%-100%) for the Truebeam and 2100CD linacs, respectively. However, log files revealed improved leaf position accuracy and fluence delivery at 1%/1 mm criterion on the Truebeam (99.87%; 99.78%-99.94%) compared with the 2100CD linac (97.87%; 91.93%-99.49%). The overshoot effect, characterized on the 2100CD linac, was not observed on the Truebeam. ConclusionsThe integrated multileaf collimator controller on the Varian Truebeam improves clinical treatment delivery accuracy of step and shoot intensity modulated radiation therapy fields compared with delivery on a Varian C-series linac.