Radiation Treatment Planning System Research Articles

CT guided coplanar template assisted in the treatment of metastatic or recurrent chest wall malignant tumor with 125 I seed implantation

Objective To evaluate the dosimetry accuracy and clinical efficacy of 125I radioactive seed implantation using coplanar template (CPT) in the treatment of metastatic or recurrent chest wall tumor. Methods Thirty-one patients with metastasis or recurrence of chest wall tumor, who had been diagnosed with pathology between July 2005 and July 2015, were retrospectively studied. All patients underwent CPT-assisted 125I radioactive seed implantation. Brachytherapy radiation treatment planning system (BTPS) was used to make preoperative plans, and the prescribed dose (PD) was 110 Gy. CPT was used to assist CT guided 125I radioactive seeds implantation. Dose evaluation was performed immediately after implantation. The difference of dose parameters was compared between preoperation and postoperation, including D90, D100, V90, V100 and the numbers of seeds. Postoperative chest CT was conducted regularly to assess the treatment efficacy based on the response evaluation criteria in solid tumors (RECIST Version 1.1). The patients were followed up till July 2016. Results All patients went through implantation procedure successfully and there was no significant statistical difference between preoperative and postoperative dose parameters (P>0.05). The conformal index(CI) was 0.951±0.13, external index(EI) was 6.5%±0.9%. Six months after implantation, CR, PR, SD and PD were 25.8% (8/31), 51.6% (16/31), 6.5% (2/31) and 16.1% (5/31), respectively. The effective rate was 77.4%, and local control rate was 83.9% (26/31). Skin pigmentation occurred in 13 patients during the follow-up period, without any special treatment. Conclusions The auxiliary of CPT in the treatment of metastatic or recurrent chest wall tumor under the guiding of CT could achieve quality control, safety and effectiveness. Key words: Coplanar template; Radioactive seeds; Chest wall malignant tumor; Metastatic tumor; Recurrent tumor

Calculation of Lung Cancer Volume of Target Based on Thorax Computed Tomography Images using Active Contour Segmentation Method for Treatment Planning System

In this research, calculation process of the lung cancer volume of target based on computed tomography (CT) thorax images was done. Volume of the target calculation was done in purpose to treatment planning system in radiotherapy. The calculation of the target volume consists of gross tumor volume (GTV), clinical target volume (CTV), planning target volume (PTV) and organs at risk (OAR). The calculation of the target volume was done by adding the target area on each slices and then multiply the result with the slice thickness. Calculations of area using of digital image processing techniques with active contour segmentation method. This segmentation for contouring to obtain the target volume. The calculation of volume produced on each of the targets is 577.2 cm3 for GTV, 769.9 cm3 for CTV, 877.8 cm3 for PTV, 618.7 cm3 for OAR 1, 1,162 cm3 for OAR 2 right, and 1,597 cm3 for OAR 2 left. These values indicate that the image processing techniques developed can be implemented to calculate the lung cancer target volume based on CT thorax images. This research expected to help doctors and medical physicists in determining and contouring the target volume quickly and precisely.

Validation of biomechanical deformable image registration in the abdomen, thorax, and pelvis in a commercial radiotherapy treatment planning system

The accuracy of deformable image registration tools can vary widely between imaging modalities and specific implementations of the same algorithms. A biomechanical model-based algorithm initially developed in-house at an academic institution was translated into a commercial radiotherapy treatment planning system and validated for multiple imaging modalities and anatomic sites. Biomechanical deformable registration (Morfeus) is a geometry-driven algorithm based on the finite element method. Boundary conditions are derived from the model-based segmentation of controlling structures in each image which establishes a point-to-point surface correspondence. For each controlling structure, material properties and fixed or sliding interfaces are assigned. The displacements of internal volumes for controlling structures and other structures implicitly deformed are solved with finite element analysis. Registration was performed for 74 patients with images (mean vector resolution) of thoracic and abdominal 4DCT (2.8mm) and MR (5.3mm), liver CT-MR (4.5mm), and prostate MR (2.6mm). Accuracy was quantified between deformed and actual target images using distance-to-agreement (DTA) for structure surfaces and the target registration error (TRE) for internal point landmarks. The results of the commercial implementation were as follows. The mean DTA was ≤1.0mm for controlling structures and 1.0-3.5mm for implicitly deformed structures on average. TRE ranged from 2.0mm on prostate MR to 5.1mm on lung MR on average, within 0.1mm or lower than the image voxel sizes. Accuracy was not overly sensitive to changes in the material properties or variability in structure segmentations, as changing these inputs affected DTA and TRE by ≤0.8mm. Maximum DTA >5mm occurred for 88% of the structures evaluated although these were within the inherent segmentation uncertainty for 82% of structures. Differences in accuracy between the commercial and in-house research implementations were ≤0.5mm for mean DTA and ≤0.7mm for mean TRE. Accuracy of biomechanical deformable registration evaluated on a large cohort of images in the thorax, abdomen and prostate was similar to the image voxel resolution on average across multiple modalities. Validation of this treatment planning system implementation supports biomechanical deformable registration as a versatile clinical tool to enable accurate target delineation at planning and treatment adaptation.

Tumor volume as a prognostic factor in patients (pts) with locoregionally advanced head and neck squamous cell carcinoma (LAHNSCC) treated with induction chemotherapy (IC).

e17507 Background: Tumor volume and the ratio of volumetric change have been demonstrated to have a prognostic role in head and neck cancers during definitive treatment in LAHNSCC. The aim of this study was to evaluate the prognostic value of tumor volume assessment during IC. Methods: We retrospectively assessed the tumor volume of 58 pts with LAHNSCC included in a prospective phase II trial which evaluated the safety of a non–5-fluorouracil-based IC (paclitaxel; cisplatin) followed by chemoradiotherapy (cisplatin; 70Gy/35fx) during 2009-2012. The volume of primary tumor (PrimV), all suspicious lymph nodes (LNV) and their sum (SumV) were determined on tomography before (CT1) and after (CT2) IC using a radiotherapy treatment planning system and the ratio of volumetric change was calculated for each variable (PrimV%, LNV% and SumV%). Results: The median follow-up time, the progression free survival (PFS) and the overall survival (OS) was 78,1, 19,3 and 22,5 months, respectively. Fifty-four pts were men, mean age 55,3±8,3y. Most had oropharynx (53%) and stage IV (72%) cancer. The median volume (cm3) was PrimV1= 25,5, LNV1= 7,5, SumV1= 40,7, PrimV2= 10,9, LNV2= 3,0, SumV2= 18,8 and median ratio of change (%) was PrimV% = 55, LNV% = 51 and SumV% = 54. Volume wa s associated with resectability (PrimV1, AUC ROC curve = 0,66, p = 0,04; LNV1, AUC = 0,85, p < 0,001; SumV1, AUC = 0,86, p < 0,001). Pts with SumV% reduction > 35% had better PFS (median 84,0 vs 10,1 months, 3y 52% vs 29%; HR = 0,39, p = 0,01) and OS (median 45,5 vs 17,0 months, 48% vs 21%; HR = 0,49, p = 0,04). On univariate analysis the PFS was correlated with T (p = 0,004), N (p = 0,01), stage (p = 0,03), primary site (p = 0,01), resectability (HR = 0,32, p = 0,001), PrimV1 (p = 0,002), SumV1 (p = 0,001), PrimV2 (p = 0,02), LNV2 (p = 0,04), SumV2 (p = 0,004), PrimV% (p = 0,04), LNV% (p = 0,003) and SumV% (p = 0,04) and OS was associated with T (p = 0,04), N (p = 0,02), stage (p = 0,04), primary site (p = 0,01), resectability (HR = 0,29, p < 0,001) PrimV1 (p = 0,003), LNV1 (p = 0,002) and SumV1 (p < 0,001). Conclusions: Tumor volume and the volumetric response during IC were associated with prognosis in LAHNSCC in the present study. Clinical trial information: NCT00959387.

Accidental overexposure related to new radiation therapy technologies

The aim of this review paper is to examine medical overexposure accidents related to new technologies in radiation therapy during the period 2000–2009. Reported radiation therapy overexposures from 2000 to 2009 were searched in English (mainly) and Japanese. Radiation therapy accidental overexposure incidents relating to new radiation therapy technology reported in the period 2000–2009 were included. Radiotherapy root causes of overexposure were classified into three main groups: “human-,” “system-,” and “equipment-” related errors. A total of 24 of the most serious radiation therapy overexposure accidents were reviewed. The accidents occurred most frequently in patients treated with 3D conformal radiation therapy (11) and stereotactic radiosurgery (7). The majority of the accidents were related to treatment planning procedure (8) and calibration (7) of new equipment or radiotherapy treatment planning system software, followed by accidents in treatment delivery (5), and treatment setup (4). The main causes of the accidents were related to human error—62.5% (15), equipment—29.2% (7), and system—8.3% (2). Several factors have been identified that can have a significant impact on reduction of the number of accidents related to the use of new radiation therapy technologies. These include thorough preparation and management of resources, such as having sufficient number of staff, adequate staff training, risk audits of new technology, quality assurance, and an enhanced safety culture.

Analysis of measurement deviations for the patient-specific quality assurance using intensity-modulated spot-scanning particle beams

To analyze measurement deviations of patient-specific quality assurance (QA) using intensity-modulated spot-scanning particle beams, a commercial radiation dosimeter using 24 pinpoint ionization chambers was utilized. Before the clinical trial, validations of the radiation dosimeter and treatment planning system were conducted. During the clinical trial 165 measurements were performed on 36 enrolled patients. Two or three fields of particle beam were used for each patient. Measurements were typically performed with the dosimeter placed at special regions of dose distribution along depth and lateral profiles. In order to investigate the dosimeter accuracy, repeated measurements with uniform dose irradiations were also carried out. A two-step approach was proposed to analyze 24 sampling points over a 3D treatment volume. The mean value and the standard deviation of each measurement did not exceed 5% for all measurements performed on patients with various diseases. According to the defined intervention thresholds of mean deviation and the distance-to-agreement concept with a Gamma index analysis using criteria of 3.0% and 2 mm, a decision could be made regarding whether the dose distribution was acceptable for the patient. Based measurement results, deviation analysis was carried out. In this study, the dosimeter was used for dose verification and provided a safety guard to assure precise dose delivery of highly modulated particle therapy. Patient-specific QA will be investigated in future clinical operations.

MEASUREMENT OF ABSORPTION DOSE OUTSIDE IRRADIATION FIELD IN IMRT.

The absorption dose outside the irradiation field for prostate intensity-modulated radiation therapy was measured and evaluated by comparison with calculated values of radiation treatment planning system (TPS). The values of TPS calculated were using Varian CLINAC21EX/Eclipse and TomoTherapy Planning System for constant irradiation time. The absorption dose was measured by placing a glass-element dosemeter in a human-bone enclosure phantom with a planning target volume inside the irradiation field. The organs at risk were the rectum, spinal cord, thyroid, eyeball and the left lung. The calculated values of TPS, Varian CLINAC21EX/Eclipse and TomoTherapy Planning System were calculated, up to 17 and 55 cm from the isocenter, respectively. The absorbed dose outside the irradiation field diverged with increased distance from the isocenter (Varian/Eclipse: p = 0.03, TomoTherapy Planning System: p = 0.25). The calculated values for the absorbed dose outside the irradiation field were underestimated.

Impact of radiation attenuation by a carbon fiber couch on patient dose verification

The aim of this study was to understand the difference between the measured and calculated irradiation attenuations obtained using two algorithms and to identify the influence of couch attenuation on patient dose verification. We performed eight tests of couch attenuation with two photon energies, two longitudinal couch positions, and two rail positions. The couch attenuation was determined using a radiation treatment planning system. The measured and calculated attenuations were compared. We also performed 12 verifications of head-and-neck and rectum cases by using a Delta phantom. The dose deviation (DD), distance to agreement (DTA), and gamma index of pencil-beam convolution (PBC) verifications were nearly the same. The agreement was least consistent for the anisotropic analytical algorithm (AAA) without the couch for the head-and-neck case, in which the DD, DTA, and gamma index were 74.4%, 99.3%, and 89%, respectively; for the rectum case, the corresponding values were 56.2%, 95.1%, and 92.4%. We suggest that dose verification should be performed using the following three metrics simultaneously: DD, DTA, and the gamma index.

Lung volume reproducibility under ABC control and self-sustained breath-holding.

An Active Breathing Coordinator (ABC) can be employed to induce breath‐holds during CT imaging and radiotherapy of lung, breast and liver cancer, and recently during lung cancer MRI. The apparatus measures and controls respiratory volume, hence subject lung volume reproducibility is its principal measure of effectiveness. To assess ABC control quality, the intra‐session reproducibility of ABC‐induced lung volumes was evaluated and compared with that reached by applying the clinical standard of operator‐guided self‐sustained breath‐holds on healthy volunteers during MRI. Inter‐session reproducibility was investigated by repeating ABC‐controlled breath‐holds on a second visit. Additionally, lung volume agreement with ABC devices used with different imaging modalities in the same institution (MR, CT), or for a breast trial treatment, was assessed. Lung volumes were derived from three‐dimensional (3D) T1‐weighted MRI datasets by three observers employing semiautomatic lung delineation on a radiotherapy treatment planning system. Inter‐observer variability was less than 6% of the delineated lung volumes. Lung volume agreement between the different conditions over all subjects was investigated using descriptive statistics. The ABC equipment dedicated for MR application exhibited good intra‐session and inter‐session lung volume reproducibility (1.8% and 3% lung volume variability on average, respectively). MR‐assessed lung volumes were similar using different ABC equipment dedicated to MR, CT, or breast radiotherapy. Overall, lung volumes controlled by the same or different ABC devices agreed better than with self‐controlled breath‐holds, as suggested by the average ABC variation of 1.8% of the measured lung volumes (99 mL), compared to the 4.1% (226 mL) variability observed on average with self‐sustained breath‐holding.

Validation of a method for retroperitoneal tumor segmentation.

In 2005, an application for surgical planning called AYRA[Formula: see text] was designed and validated by different surgeons and engineers at the Virgen del Rocío University Hospital, Seville (Spain). However, the segmentation methods included in AYRA and in other surgical planning applications are not able to segment accurately tumors that appear in soft tissue. The aims of this paper are to offer an exhaustive validation of an accurate semiautomatic segmentation tool to delimitate retroperitoneal tumors from CT images and to aid physicians in planning both radiotherapy doses and surgery. A panel of 6 experts manually segmented 11 cases of tumors, and the segmentation results were compared exhaustively with: the results provided by a surgical planning tool (AYRA), the segmentations obtained using a radiotherapy treatment planning system (Pinnacle[Formula: see text]), the segmentation results obtained by a group of experts in the delimitation of retroperitoneal tumors and the segmentation results using the algorithm under validation. 11 cases of retroperitoneal tumors were tested. The proposed algorithm provided accurate results regarding the segmentation of the tumor. Moreover, the algorithm requires minimal computational time-an average of 90.5% less than that required when manually contouring the same tumor. A method developed for the semiautomatic selection of retroperitoneal tumor has been validated in depth. AYRA, as well as other surgical and radiotherapy planning tools, could be greatly improved by including this algorithm.

Impact of Different Independent Dose Verification Software Programs for Secondary Check.

A multi-institutional study was performed to identify the impact of different independent dose verification programs on independent dose verification software program. Data for 1,543 treatment fields were collected in three institutions. RADCALC and Simple MU Analysis (Simple MU) using the Clarkson-based algorithm were used. RADCALC needs the input of radiological path length (RPL) from radiotherapy treatment planning systems (RTPSs) (Eclipse or Pinnacle3). The Simple MU computes the RPL using CT images independently from the RTPSs. Ion-chamber measurements were performed for commissioning the two programs and the RTPSs. Next, the results of the two programs were compared to the RTPSs obtained in the clinically-approved plans in all three institutions. The commissioning results showed ±1.5% variation in the ion-chamber measurements and there was slight difference between the institutions. The RADCALC (0.9±2.2%) and the Simple MU (1.7±2.1%) results showed a slight systematic difference. Pinnacle3 computed longer RPLs because it used CT-physical density tables. Thus, there was an impact on the accuracy in the treatment plans involving bone and other high-density materials. Dose calculation algorithms in different dose verification programs provided similar results. However, care must be taken because different RPL calculation methods in the RTPSs may affect dose difference between different independent dose verification programs by 1%.

Evaluation of a commercial automatic treatment planning system for prostate cancers

Recent developments in Radiation Oncology treatment planning have led to the development of software packages that facilitate automated intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) planning. Such solutions include site-specific modules, plan library methods, and algorithm-based methods. In this study, the plan quality for prostate cancer generated by the Auto-Planning module of the Pinnacle3 radiation therapy treatment planning system (v9.10, Fitchburg, WI) is retrospectively evaluated. The Auto-Planning module of Pinnacle3 uses a progressive optimization algorithm. Twenty-three prostate cancer cases, which had previously been planned and treated without lymph node irradiation, were replanned using the Auto-Planning module. Dose distributions were statistically compared with those of manual planning by the paired t-test at 5% significance level. Auto-Planning was performed without any manual intervention. Planning target volume (PTV) dose and dose to rectum were comparable between Auto-Planning and manual planning. The former, however, significantly reduced the dose to the bladder and femurs. Regression analysis was performed to examine the correlation between volume overlap between bladder and PTV divided by the total bladder volume and resultant V70. The findings showed that manual planning typically exhibits a logistic way for dose constraint, whereas Auto-Planning shows a more linear tendency. By calculating the Akaike information criterion (AIC) to validate the statistical model, a reduction of interoperator variation in Auto-Planning was shown. We showed that, for prostate cancer, the Auto-Planning module provided plans that are better than or comparable with those of manual planning. By comparing our results with those previously reported for head and neck cancer treatment, we recommend the homogeneous plan quality generated by the Auto-Planning module, which exhibits less dependence on anatomic complexity.

Optimization of Couch Modeling in the Change of Dose Calculation Methods and Their Versions.

In external radiotherapy, the X-ray beam passes through the treatment couch, leading to the dose reduction by the attenuation of the couch. As a method to compensate for the reduction, radiation treatment planning systems (RTPS) support virtual couch function, namely "couch modeling method". In the couch modeling method, the computed tomography (CT) numbers assigned to each structure should be optimized by comparing calculations to measurements for accurate dose calculation. Thus, re-optimization of CT numbers will be required when the dose calculation algorithm or their version changes. The purpose of this study is to evaluate the calculation accuracy of the couch modeling method in different calculation algorithms and their versions. The optimal CT numbers were determined by minimizing the difference between measured transmission factors and calculated ones. When CT numbers optimized by Anisotropic Analytical Algorithm (AAA) Ver. 8.6 were used, the maximum and the mean difference of transmission factor were 5.8% and 1.5%, respectively, for Acuros XB (AXB) Ver. 11.0. However, when CT numbers optimized by AXB Ver. 11.0 were used, they were 2.6% and 0.6%, respectively. The CT numbers for couch structures should be optimized when changing dose calculation algorithms and their versions. From the comparison of the measured transmission to calculation, it was found that the CT numbers had high accuracy.

P1.05-031 Primary Results of Dose Escalated Stereotactic Body Radiotherapy for Stage IA Non-Small Cell Lung Cancer

JCOG 0403 showed excellent overall survival in stereotactic body radiotherapy (SBRT) for stage IA non-small cell lung cancer (NSCLC). In Japan, 48Gy/4Fr for isocenter have been the standard dose fractionation of SBRT for stage IA NSCLC. JCOG0702 showed that dose escalation of 55Gy for PTVD95% was feasible in SBRT for peripheral small (PTV volume 100cc or less) NSCLC. Intensification of local treatment with dose escalation is considered to be one of the measures for improvement of overall survival. In 2011, we adopted dose escalated regimen (50Gy/4Fr for PTVD95%) for SBRT for stage IA NSCLC, expected improvement of local control and overall survival. The purpose of this study was to review and report the primary results of dose escalated SBRT for stage IA NSCLC. From August 2011 to April 2015, 31 patients with stage IA NSCLC were treated with dose escalated SBRT at the University of Yamanashi. The patients' ages ranged from 61 to 86 (median 79) years. Twenty two patients were male, 9 were female. Performance status was 0 in 26, 1 in 5 patients. Tumor histology was squamous cell carcinoma in 6 and adenocarcinoma in 23, other NSCLC in 2 patients. Clinical stage was T1a in 19, T2b in 12 patients. A multiple static ports radiation planned by a radiation treatment planning system (Pinnacle3 Version 9.2-9.8) was performed with linac using 6MV x-ray beams. The Breath hold technique and CT image guided set-up were used in all cases. A total dose of 50Gy was delivered in 4 fractions over 4-5days. Radiation doses were prescribed to the 95% of planning target volume (PTVD95%). A superposition algorithm with heterogeneity correction was used for dose calculations. The follow-up period for all patients was 3.3-43.1 (median 23.7) months. The overall survival rate at one year and two years were 87.1%, 79.3%, respectively. The local control rate at one year and two years were both 96.4%. Local recurrence, regional lymph node metastases, and distant metastases were observed in 1, 4 and 3 patients, respectively. Regarding to the toxicities, grade 3 radiation pneumonitis were observed in 3 patients. Grade 2 rib fractures were observed in 3 patients. There were no Grade 4 or greater adverse events in the follow-up period. The toxicity was considered to be acceptable. The local control effect was considered to be sufficient. Longer follow- up durations are needed to validate the clinical benefits of dose escalated SBRT for stage IA NSCLC.

Assessment of the accuracy of dose calculation in the build-up region of the tangential field of the breast for a radiotherapy treatment planning system.

Aim of the studyOur objective was to quantify the accuracy of dose calculation in the build-up region of the tangential field of the breast for a TiGRT treatment planning system (TPS).Material and methodsThermoluminescent dosimeter (TLD) chips were arranged in a RANDO phantom for the dose measurement. TiGRT TPS was also used for the dose calculation. Finally, confidence limit values were obtained to quantify the accuracy of the dose calculation of the TPS at the build-up region.ResultsIn the open field, for gantry angles of 15°, 30°, and 60°, the confidence limit values were 17.68, 19.97, and 34.62 at a depth of 5 mm, and 24.01, 19.07, and 15.74 at a depth of 15 mm, respectively. In the wedge field, for gantry angles of 15°, 30°, and 60°, the confidence limit values were 21.64, 26.80, and 34.87 at a depth of 5 mm, and 27.92, 22.04, and 20.03 at a depth of 15 mm, respectively. Additionally, the findings showed that at a depth of 5 mm, the confidence limit values increased with increasing gantry angle while at a depth of 15 mm, the confidence limit values decreased with increasing gantry angle.ConclusionsOverall, TiGRT TPS overestimated doses compared to TLD measurements, and the confidence limit values were greater for the wedge field than for the open fields. Our findings suggest that the assessment of dose distributions in large-dose gradient regions (i.e. build-up region) should not entirely rely on TPS calculations.

What should we know about photon dose calculation algorithms used for radiotherapy? Their impact on dose distribution and medical decisions based on TCP/NTCP

The dose calculation algorithms, integrated in a radiotherapy treatment planning system, use different approximations to swiftly compute the dose distributions. Any biological effect is somehow related to the dose delivered to the tissues. Thus, the optimization of treatment planning in radiation oncology requires, as a basis, the most accurate dose calculation to carry out the best possible prediction of the Normal Tissue Complication Probability (NTCP), as well as Tumor Control Probability (TCP). Presently, a number of bio-mathematical models exist to estimate TCP and NTCP from a physical calculated dose using the differential dose volume histogram (dDVH). The purpose of this review is to highlight the link between any change of algorithms and possible significant changes of DVH metrics, TCP, NTCP and even more of estimated Quality-adjusted life years (QALY) based on predicted NTCP. The former algorithms, such as pencil beam convolution (PBC) algorithm with 1D or 3D density correction methods, overestimated the TCP while underestimating NTCP for lung cancer. The magnitude of error depends on the algorithms, the radiobiological models and their assumed radiobiological parameters setting. The over/under estimation of radiotherapy outcomes can reach up to 50% relatively. Presently, the anisotropic analytical algorithm (AAA), collapsed cone convolution algorithm (CCC), Acuros-XB or Monte Carlo are the most recommended algorithms to consistently estimate the TCP/ NTCP outcomes and QALY score, to rank and compare radiotherapy plans, to make a useful medical decision regarding the best plan. This paper points out also that the values of the NTCP radiobiological parameters should be adjusted to each dose calculation algorithm to provide the most accurate estimates.

Source modeling for Monte Carlo dose calculation of CT examinations with a radiotherapy treatment planning system.

Radiation dose to patients undergoing examinations with Multislice Computed Tomography (MSCT) as well as Cone Beam Computed Tomography (CBCT) is a matter of concern. Risk management could benefit from efficient replace rational dose calculation tools. The paper aims to verify MSCT dose calculations using a Treatment Planning System (TPS) for radiotherapy and to evaluate four different variations of bow-tie filter characterizations for the beam model used in the dose calculations. A TPS (RayStation™, RaySearch Laboratories, Stockholm, Sweden) was configured to calculate dose from a MSCT (GE Healthcare, Wauwatosa, WI, USA). The x-ray beam was characterized in a stationary position the by measurements of the Half-Value Layer (HVL) in aluminum and kerma along the principal axes of the isocenter plane perpendicular to the beam. A Monte Carlo source model for the dose calculation was applied with four different variations on the beam-shaping bow-tie filter, taking into account the different degrees of HVL information but reconstructing the measured kerma distribution after the bow-tie filter by adjusting the photon sampling function. The resulting dose calculations were verified by comparison with measurements in solid water as well as in an anthropomorphic phantom. The calculated depth dose in solid water as well as the relative dose profiles was in agreement with the corresponding measured values. Doses calculated in the anthropomorphic phantom in the range 26-55 mGy agreed with the corresponding thermo luminescence dosimeter (TLD) measurements. Deviations between measurements and calculations were of the order of the measurement uncertainties. There was no significant difference between the different variations on the bow-tie filter modeling. Under the assumption that the calculated kerma after the bow-tie filter replicates the measured kerma, the central specification of the HVL of the x-ray beam together with the kerma distribution can be used to characterize the beam. Thus, within the limits of the study, a flat bow-tie filter with an HVL specified by the vendor suffices to calculate the dose distribution. The TPS could be successfully configured to replicate the beam movement and intensity modulation of a spiral scan with dose modulation, on the basis of the specifications available in the metadata of the digital images and the log file of the CT.

Comparison of 3DCRT Dose Distribution in Radiotherapy for Lung Cancer Patient by Using AAA and PBC Algorithms

The Pencil Beam Convolution (PBC) algorithm in radiation treatment planning system is widely used to calculate the radiation dose distribution in radiotherapy planning. A new photon dose calculation algorithm known as Anisotropic Analytical Algorithm (AAA) by Varian Medical Systems is applied to investigate the difference of dose distribution by using AAA and PBC algorithms for the lung cancer with an inhomogeneity of its low density. In the present work, radiotherapy treatment planning of 10 lung cancer patients are designed with 6 MV photon beam using three-dimensional conformal radiation therapy (3DCRT) and dose distribution was calculated by the AAA and the PBC Algorithms. The dose distribution performance is evaluated by dose profile curve along transversal slice of PTV and Dose Volume Histogram (DVH) covered by the 95% isodose of PTV. The mean dose of organ at risks did not changed significantly but the volume of the PTV covered by the 95% isodose curve was decreased by 6% with inhomogeneity due to the algorithms. The dose distribution and the accuracy in calculating the absorbed dose of the AAA algorithm of the Varian Eclipse treatment planning system is analyzed and discussed.

Energy Dependence of Measured CT Numbers on Substituted Materials Used for CT Number Calibration of Radiotherapy Treatment Planning Systems.

IntroductionFor accurate dose calculations, it is necessary to provide a correct relationship between the CT numbers and electron density in radiotherapy treatment planning systems (TPSs). The purpose of this study was to investigate the energy dependence of measured CT numbers on substituted materials used for CT number calibration of radiotherapy TPSs and the resulting errors in the treatment planning calculation doses.Materials and MethodsIn this study, we designed a cylindrical water phantom with different materials used as tissue equivalent materials for the simulation of tissues and obtaining the related CT numbers. For evaluating the effect of CT number variations of substituted materials due to energy changing of scanner (kVp) on the dose calculation of TPS, the slices of the scanned phantom at three kVp's were imported into the desired TPSs (MIRS and CorePLAN). Dose calculations were performed on two TPSs.ResultsThe mean absolute percentage differences between the CT numbers of CT scanner and two treatment planning systems for all the samples were 3.22%±2.57% for CorePLAN and 2.88%±2.11% for MIRS. It was also found that the maximum absolute percentage difference between all of the calculated doses from each photon beam of linac (6 and 15 MV) at three kVp's was less than 1.2%.DiscussionThe present study revealed that, for the materials with effective low atomic number, the mean CT number increased with increasing energy, which was opposite for the materials with an effective high atomic number. We concluded that the tissue substitute materials had a different behavior in the energy ranges from 80 to 130 kVp. So, it is necessary to consider the energy dependence of the substitute materials used for the measurement or calibration of CT number for radiotherapy treatment planning systems.

Effects of inaccurate small field dose measurements on calculated treatment doses

Given the difficulty and potential time- or financial-costs associated with accurate small field dosimetry, this study aimed to establish the clinical necessity of obtaining accurate small field output factor measurements and toevaluate the effects on planned doses that could arise if accurate measurements are not used in treatment planning dose calculations. Isocentre doses, in heterogeneous patient anatomy, were calculated and compared for 571 beams from 48 clinical radiotherapy treatments, using a clinical radiotherapy treatment planning system, with reference to two different sets of beam configuration data. One set of beam configuration data included field output factors (total scatter factors) from precisely positioned and response-corrected diode measurements and the other included field output factors measured using a conventional technique that would have been better suited to larger field measurements. Differences between the field output factor measurements made with the two different techniques equated to 14.2% for the 6[Formula: see text]6mm[Formula: see text] field, 1.8% for the 12[Formula: see text]12mm[Formula: see text] field, and less than 0.5% for the larger fields. This led to isocentre dose differences of up to 3.3% in routine clinical fields smaller than 9mm across and and up to 11% in convoluted fields smaller than 15mm across. If field widths smaller than 15mm are used clinically, then accurate measurement (or-remeasurement) of small field output factors in the treatment planning system's beam data is required in order to achieve dose calculation accuracy within 3%. If such measurements are not completed, then errors in excess of 10% may occur if very small,narrow, concave or convoluted treatment fields are used.