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2.  Dosimetric and radiobiological characterizations of prostate intensity-modulated radiotherapy and volumetric-modulated arc therapy: A single-institution review of ninety cases 
This study reviewed prostate volumetric-modulated arc therapy (VMAT) plans with intensity-modulated radiotherapy (IMRT) plans after prostate IMRT technique was replaced by VMAT in an institution. Characterizations of dosimetry and radiobiological variation in prostate were determined based on treatment plans of 40 prostate IMRT patients (planning target volume = 77.8–335 cm3) and 50 VMAT patients (planning target volume = 120–351 cm3) treated before and after 2013, respectively. Both IMRT and VMAT plans used the same dose-volume criteria in the inverse planning optimization. Dose-volume histogram, mean doses of target and normal tissues (rectum, bladder and femoral heads), dose-volume points (D99% of planning target volume; D30%, D50%, V30 Gy and V35 Gy of rectum and bladder; D5%, V14 Gy, V22 Gy of femoral heads), conformity index (CI), homogeneity index (HI), gradient index (GI), prostate tumor control probability (TCP), and rectal normal tissue complication probability (NTCP) based on the Lyman-Burman-Kutcher algorithm were calculated for each IMRT and VMAT plan. From our results, VMAT plan was found better due to its higher (1.05%) CI, lower (0.83%) HI and (0.75%) GI than IMRT. Comparing doses in normal tissues between IMRT and VMAT, it was found that IMRT mostly delivered higher doses of about 1.05% to the normal tissues than VMAT. Prostate TCP and rectal NTCP were found increased (1%) for VMAT than IMRT. It is seen that VMAT technique can decrease the dose-volume evaluation criteria for the normal tissues. Based on our dosimetric and radiobiological results in treatment plans, it is concluded that our VMAT implementation could produce comparable or slightly better target coverage and normal tissue sparing with a faster treatment time in prostate radiotherapy.
PMCID: PMC5019034  PMID: 27651562
Dose-volume histogram; intensity-modulated radiotherapy; normal tissue complication probability; prostate; tumor control probability; volumetric-modulated arc therapy
3.  Measurement of eye lens dose for Varian On-Board Imaging with different cone-beam computed tomography acquisition techniques 
The objective of this work was to measure patient eye lens dose for different cone-beam computed tomography (CBCT) acquisition protocols of Varian's On-Board Imaging (OBI) system using optically stimulated luminescence dosimeter (OSLD) and to study the variation in eye lens dose with patient geometry and distance of isocenter to the eye lens. During the experimental measurements, OSLD was placed on the patient between the eyebrows of both eyes in line of nose during CBCT image acquisition to measure eye lens doses. The eye lens dose measurements were carried out for three different cone-beam acquisition protocols (standard dose head, low-dose head [LDH], and high-quality head [HQH]) of Varian OBI. Measured doses were correlated with patient geometry and distance between isocenter and eye lens. Measured eye lens doses for standard head and HQH protocols were in the range of 1.8–3.2 mGy and 4.5–9.9 mGy, respectively. However, the measured eye lens dose for the LDH protocol was in the range of 0.3–0.7 mGy. The measured data indicate that eye lens dose to patient depends on the selected imaging protocol. It was also observed that eye lens dose does not depend on patient geometry but strongly depends on distance between eye lens and treatment field isocenter. However, undoubted advantages of imaging system should not be counterbalanced by inappropriate selection of imaging protocol, especially for very intense imaging protocol.
PMCID: PMC5019036  PMID: 27651564
Eye lens dose; optically stimulated luminescence dosimeter; Varian cone-beam computed tomography
4.  Radioprotective effects of hesperidin on oxidative damages and histopathological changes induced by X-irradiation in rats heart tissue 
This study was carried out to evaluate radioprotective effects of hesperidin (HES) administration before the irradiation on the cardiac oxidative stress and histopathological changes in an experimental rat model. The cardiovascular complications of radiation exposure cause morbidity and mortality in patients who received radiotherapy. HES, an antioxidant flavonoid found in citrus fruits, suggests the protection against the tissue damage. Fifty-eight rats were divided into four groups: Group 1 received phosphate buffered saline (PBS) and sham radiation; Group 2, HES and sham radiation; Group 3, PBS and radiation; and Group 4, HES and radiation. The rats were exposed to single dose of 18 Gy of 6 MV X-ray. One hundred milligrams per kilogram doses of HES was administered for 7 days before irradiation. The estimation of superoxide dismutase (SOD), malondialdehyde (MDA), and histopathological analyses was performed at 24 h and 8 weeks after radiation exposure. The irradiation of chest area resulted in an elevated MDA level and decreased SOD activity. Moreover, long-term pathological lesions of radiation were inflammation, fibrosis, the increased number of mast cells and macrophages, and development of plaque, vascular leakage, myocardial degeneration, and myocyte necrosis. Although the administration of HES decreases inflammation, fibrosis, mast cell and macrophage numbers, and myocyte necrosis, it did not result in reduced thrombus, myocardium degeneration, and vascular leakage. In conclusion, these results suggest that HES can perform a radioprotection action. The protective effect of HES may be attributable to its immunomodulatory effects and free radical-scavenging properties.
PMCID: PMC5019037  PMID: 27651565
Cardiomyopathy; cardiotoxicity; hesperidin; radioprotector
5.  Comparative study of old and new versions of treatment planning system using dose volume histogram indices of clinical plans 
Recently, Eclipse treatment planning system (TPS) version 8.8 was upgraded to the latest version 13.6. It is customary that the vendor gives training on how to upgrade the existing software to the new version. However, the customer is provided less inner details about changes in the new software version. According to manufacturer, accuracy of point dose calculations and irregular treatment planning is better in the new version (13.6) compared to the old version (8.8). Furthermore, the new version uses voxel-based calculations while the earlier version used point dose calculations. Major difference in intensity-modulated radiation therapy (IMRT) plans was observed between the two versions after re-optimization and re-calculations. However, minor difference was observed for IMRT cases after performing only re-calculations. It is recommended TPS quality assurance to be performed after any major upgrade of software. This can be done by performing dose calculation comparisons in TPS. To assess the difference between the versions, 25 clinical cases from the old version were compared keeping all the patient data intact including the monitor units and comparing the differences in dose calculations using dose volume histogram (DVH) analysis. Along with DVH analysis, uniformity index, conformity index, homogeneity index, and dose spillage index were also compared for both versions. The results of comparative study are presented in this paper.
PMCID: PMC5019038  PMID: 27651566
Conformity index; dose spillage index; dose volume histogram; homogeneity index; treatment planning version; uniformity index
6.  Analysis of dose distribution in organs at risk in patients with prostate cancer treated with the intensity-modulated radiation therapy and arc technique 
This study describes a comparative analysis of treatment plans in 48 patients with prostate cancer treated with ionizing radiation. Each patient was subjected to the intensity-modulated radiation therapy (IMRT) and arc technique. In each treatment plan, the organs at risk were assessed: the urinary bladder, rectum and heads of the femur, as well as the volume of normal tissue. The following features were compared: treatment time, conformity indices for the planning target volume, mean doses and standard deviation in organs at risk, and organ volumes for each particular dose. The treatment period in the arc technique is 13.7% shorter than in the IMRT technique. Comparing the results of the IMRT and arc techniques (arc vs. IMRT), the mean values were 29.21 ± 12.91 Gy versus 28.36 ± 13.79 Gy for the bladder, 20.36 ± 3.16 Gy versus 18.17 ± 5.11 Gy for the right femoral head, and 18.98 ± 3.28 Gy versus 16.67 ± 5.15 Gy for the left femoral head. For the rectum, lower values were obtained after application of the arc technique, not the IMRT technique: 35.84 ± 12.28 Gy versus 35.90 ± 13.05 Gy. The results indicate that the applied therapy has a statistically significant influence on the volume for a particular dose with regard to the urinary bladder. It is advisable to apply the IMRT technique to patients who need the femur heads and urinary bladder protected by exposing them to low irradiation doses.
PMCID: PMC5019039  PMID: 27651567
Arc technique; intensity-modulated radiation therapy technique; prostate cancer; radiotherapy
7.  Radiological risk assessment of cosmic radiation at aviation altitudes (a trip from Houston Intercontinental Airport to Lagos International Airport) 
Radiological risk parameters associated with aircrew members traveling from Houston Intercontinental Airport to Lagos International Airport have been computed using computer software called EPCARD (version 3.2). The mean annual effective dose of radiation was computed to be 2.94 mSv/year. This result is above the standard permissible limit of 1 mSv/year set for the public and pregnant aircrew members but below the limit set for occupationally exposed workers. The Risk of cancer mortality and excess career time cancer risk computed ranged from 3.5 × 10−5 to 24.5 × 10−5 (with average of 14.7 × 10−5) and 7 × 10−4 to 49 × 10−4 (with average of 29.4 × 10−4). Passengers and aircrew members should be aware of the extra cosmic radiation doses taken in during flights. All aircraft operators should monitor radiation doses incurred during aviation trips.
PMCID: PMC5019040  PMID: 27651568
Aviation; cosmic radiation; Houston; Lagos; radiological
8.  Gamma Putty dosimetric studies in electron beam 
Traditionally, lead has been used for field shaping in megavoltage electron beams in radiation therapy. In this study, we analyze the dosimetric parameters of a nontoxic, high atomic number (Z = 83), bismuth-loaded material called Gamma Putty that is malleable and can be easily molded to any desired shape. First, we placed an ionization chamber at different depths in a solid water phantom under a Gamma Putty shield of thickness (t = 0, 3, 5, 10, 15, 20, and 25 mm, respectively) and measured the ionizing radiation on the central axis (CAX) for electron beam ranging in energies from 6 to 20 MeV. Next, we investigated the relationship between the relative ionization (RI) measured at a fixed depth for several Gamma Putty shield at different cutout diameters ranging from 2 to 5 cm for various beam energies and derived an exponential fitting equation for clinical purposes. The dose profiles along the CAX show that bremsstrahlung dominates for Gamma Putty thickness >15 mm. For high-energy beams (12–20 MeV) and all Gamma Putty thicknesses up to 25 mm, RI below 5% could not be achieved due to the strong bremsstrahlung component. However, Gamma Putty is a very suitable material for reducing the transmission factor below 5% and protecting underlying normal tissues for low-energy electron beams (6–9 MeV).
PMCID: PMC5019035  PMID: 27651563
Electron beam radiotherapy; exponential function; Gamma Putty; transmission
9.  An investigation of the dose distribution effect related with collimator angle in volumetric arc therapy of prostate cancer 
To investigate the dose-volume variations of planning target volume (PTV) and organ at risks (OARs) in eleven prostate cancer patients planned with single and double arc volumetric modulated arc therapy (VMAT) when varying collimator angle. Single and double arc VMAT treatment plans were created using Monaco5.0® with collimator angle set to 0°. All plans were normalized 7600 cGy dose to the 95% of clinical target volume (CTV) volume. The single arc VMAT plans were reoptimized with different collimator angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°), and for double arc VMAT plans (0–0°, 15°–345, 30–330°, 45–315°, 60–300°, 75–285°, 90–270°) using the same optimization parameters. For the comparison the parameters of heterogeneity index (HI), dose-volume histogram and minimum dose to the 95% of PTV volume (D95 PTV) calculated and analyzed. The best plans were verified using 2 dimensional ion chamber array IBA Matrixx® and three-dimensional IBA Compass® program. The comparison between calculation and measurement were made by the γ-index (3%/3 mm) analysis. A higher D95 (PTV) were found for single arc VMAT with 15° collimator angle. For double arc, VMAT with 60–300° and 75–285° collimator angles. However, lower rectum doses obtained for 75–285° collimator angles. There was no significant dose difference, based on other OARs which are bladder and femur head. When we compared single and double arc VMAT's D95 (PTV), we determined 2.44% high coverage and lower HI with double arc VMAT. All plans passed the γ-index (3%/3 mm) analysis with more than 97% of the points and we had an average γ-index for CTV 0.36, for PTV 0.32 with double arc VMAT. These results were significant by Wilcoxon signed rank test statistically. The results show that dose coverage of target and OAR's doses also depend significantly on the collimator angles due to the geometry of target and OARs. Based on the results we have decided to plan prostate cancer patients in our clinic with double arc VMAT and 75°–285° collimator angles.
PMCID: PMC4870998  PMID: 27217621
Collimator angle; double arc volumetric modulated arc therapy; patient quality assurances; prostate cancer
10.  Development of a deformable dosimetric phantom to verify dose accumulation algorithms for adaptive radiotherapy 
Adaptive radiotherapy may improve treatment outcomes for lung cancer patients. Because of the lack of an effective tool for quality assurance, this therapeutic modality is not yet accepted in clinic. The purpose of this study is to develop a deformable physical phantom for validation of dose accumulation algorithms in regions with heterogeneous mass. A three-dimensional (3D) deformable phantom was developed containing a tissue-equivalent tumor and heterogeneous sponge inserts. Thermoluminescent dosimeters (TLDs) were placed at multiple locations in the phantom each time before dose measurement. Doses were measured with the phantom in both the static and deformed cases. The deformation of the phantom was actuated by a motor driven piston. 4D computed tomography images were acquired to calculate 3D doses at each phase using Pinnacle and EGSnrc/DOSXYZnrc. These images were registered using two registration software packages: VelocityAI and Elastix. With the resultant displacement vector fields (DVFs), the calculated 3D doses were accumulated using a mass-and energy congruent mapping method and compared to those measured by the TLDs at four typical locations. In the static case, TLD measurements agreed with all the algorithms by 1.8% at the center of the tumor volume and by 4.0% in the penumbra. In the deformable case, the phantom's deformation was reproduced within 1.1 mm. For the 3D dose calculated by Pinnacle, the total dose accumulated with the Elastix DVF agreed well to the TLD measurements with their differences <2.5% at four measured locations. When the VelocityAI DVF was used, their difference increased up to 11.8%. For the 3D dose calculated by EGSnrc/DOSXYZnrc, the total doses accumulated with the two DVFs were within 5.7% of the TLD measurements which are slightly over the rate of 5% for clinical acceptance. The detector-embedded deformable phantom allows radiation dose to be measured in a dynamic environment, similar to deforming lung tissues, supporting the validation of dose mapping and accumulation operations in regions with heterogeneous mass, and dose distributions.
PMCID: PMC4870999  PMID: 27217622
Adaptive radiation therapy; dose accumulation; quality assurance
11.  Dosimetry of indigenously developed 192Ir high-dose rate brachytherapy source: An EGSnrc Monte Carlo study 
Clinical application using high-dose rate (HDR) 192Ir sources in remote afterloading technique is a well-established treatment method. In this direction, Board of Radiation and Isotope Technology (BRIT) and Bhabha Atomic Research Centre, India, jointly indigenously developed a remote afterloading machine and 192Ir HDR source. The two-dimensional (2D) dose distribution and dosimetric parameters of the BRIT 192Ir HDR source are generated using EGSnrc Monte Carlo code system in a 40 cm dia × 40 cm height cylindrical water phantom. The values of air-kerma strength and dose rate constant for BRIT 192Ir HDR source are 9.894 × 10−8 ± 0.06% UBq−1 and 1.112 ± 0.11% cGyh−1U−1, respectively. The values of radial dose function (gL(r)) of this source compare well with the corresponding values of BEBIG, Flexisource, and GammaMed 12i source models. This is because of identical active lengths of the sources (3.5 mm) and the comparable phantom dimensions. A comparison of gL(r) values of BRIT source with microSelectron-v1 show differences about 2% at r = 6 cm and up to 13% at r = 12 cm, which is due to differences in phantom dimensions involved in the calculations. The anisotropy function of BRIT 192Ir HDR source is comparable with the corresponding values of microSelectron-v1 (classic) HDR source.
PMCID: PMC4871000  PMID: 27217623
Brachytherapy; 192Ir high-dose rate source; TG43; EGSnrc Monte Carlo
12.  Estimation of the effects of normal tissue sparing using equivalent uniform dose-based optimization 
In this study, we intend to estimate the effects of normal tissue sparing between intensity modulated radiotherapy (IMRT) treatment plans generated with and without a dose volume (DV)-based physical cost function using equivalent uniform dose (EUD). Twenty prostate cancer patients were retrospectively selected for this study. For each patient, two IMRT plans were generated (i) EUD-based optimization with a DV-based physical cost function to control inhomogeneity (EUDWith DV) and (ii) EUD-based optimization without a DV-based physical cost function to allow inhomogeneity (EUDWithout DV). The generated plans were prescribed a dose of 72 Gy in 36 fractions to planning target volume (PTV). Mean dose, D30%, and D5% were evaluated for all organ at risk (OAR). Normal tissue complication probability was also calculated for all OARs using BioSuite software. The average volume of PTV for all patients was 103.02 ± 27 cm3. The PTV mean dose for EUDWith DV plans was 73.67 ± 1.7 Gy, whereas for EUDWithout DV plans was 80.42 ± 2.7 Gy. It was found that PTV volume receiving dose more than 115% of prescription dose was negligible in EUDWith DV plans, whereas it was 28% in EUDWithout DV plans. In almost all dosimetric parameters evaluated, dose to OARs in EUDWith DV plans was higher than in EUDWithout DV plans. Allowing inhomogeneous dose (EUDWithout DV) inside the target would achieve better normal tissue sparing compared to homogenous dose distribution (EUDWith DV). Hence, this inhomogeneous dose could be intentionally dumped on the high-risk volume to achieve high local control. Therefore, it was concluded that EUD optimized plans offer added advantage of less OAR dose as well as selectively boosting dose to gross tumor volume.
PMCID: PMC4871001  PMID: 27217624
Biological optimization; equivalent uniform dose; in-homogeneity; intensity modulated radiotherapy
13.  Determination of optimal number of beams in direct machine parameter optimization-based intensity modulated radiotherapy for head and neck cases 
This paper aims to introduce an algorithm called “sensitivity-based beam number selection (SBBNS)” for fully automated and case-specific determination of an optimal number of equispaced beams in intensity-modulated radiotherapy (IMRT). We tested the algorithm in five head and neck cases of varying complexity. We used direct machine parameter optimization method coupled with Auto Plan feature available in Pinnacle TPS (Version 9.10.0) for optimization. The Pearson correlation test shows a correlation of 0.88 between predicted and actual optimal number of beams, which indicates that SBBNS method is capable of predicting optimal number of beams for head and neck cases with reasonable accuracy. The major advantage of the algorithm is that it intrinsically takes into account various case- and machine-specific factors for the determination of optimal number. The study demonstrates that the algorithm can be effectively applied to IMRT scenarios to determine case specific and optimal number of beams for head and neck cases.
PMCID: PMC4871002  PMID: 27217625
Dose to organs at risk; inverse planning in intensity-modulated radiotherapy; Linac radiotherapy; orientation of radiotherapy beams
14.  Dosimetric and radiobiological comparison of CyberKnife M6™ InCise multileaf collimator over IRIS™ variable collimator in prostate stereotactic body radiation therapy 
The impetus behind our study was to establish a quantitative comparison between the IRIS collimator and the InCise multileaf collimator (MLC) (Accuray Inc. Synnyvale, CA) for prostate stereotactic body radiation therapy (SBRT). Treatment plans for ten prostate cancer patients were performed on MultiPlan™ 5.1.2 treatment planning system utilizing MLC and IRIS for 36.25 Gy in five fractions. To reduce the magnitude of variations between cases, the planning tumor volume (PTV) was defined and outlined for treating prostate gland only, assuming no seminal vesicle or ex-capsule involvement. Evaluation indices of each plan include PTV coverage, conformity index (CI), Paddick's new CI, homogeneity index, and gradient index. Organ at risk (OAR) dose sparing was analyzed by the bladder wall Dmax and V37Gy, rectum Dmax and V36Gy. The radiobiological response was evaluated by tumor control probability and normal tissue complication probability based on equivalent uniform dose. The dose delivery efficiency was evaluated on the basis of planned monitor units (MUs) and the reported treatment time per fraction. Statistical significance was tested using the Wilcoxon signed rank test. The studies indicated that CyberKnife M6™ IRIS and InCise™ MLC produce equivalent SBRT prostate treatment plans in terms of dosimetry, radiobiology, and OAR sparing, except that the MLC plans offer improvement of the dose fall-off gradient by 29% over IRIS. The main advantage of replacing the IRIS collimator with MLC is the improved efficiency, determined from the reduction of MUs by 42%, and a 36% faster delivery time.
PMCID: PMC4871003  PMID: 27217626
CyberKnife; IRIS; multileaf collimator; prostate stereotactic body radiation therapy
15.  Dosimetric impact of setup errors in head and neck cancer patients treated by image-guided radiotherapy 
To assess and analyze the impact of setup uncertainties on target volume coverage and doses to organs at risk (OAR) in head and neck cancer (HNC) patients treated by image-guided radiotherapy (IGRT). Translational setup errors in 25 HNC patients were observed by kilovoltage cone beam computed tomography (kV CBCT). Two plans were generated. Plan one – the original plan which was the initially optimized and approved plan of the patient. All patients were treated according to their respective approved plans at a defined isocenter. Plan two – the plan sum which was the sum of all plans recalculated at a different isocenter according to setup errors in x, y, and z-direction. Plan sum was created to evaluate doses that would have been received by planning target volume (PTV) and OARs if setup errors were not corrected. These 2 plans were analyzed and compared in terms of target volume coverage and doses to OARs. A total 503 kV CBCT images were acquired for evaluation of setup errors in 25 HNC patients. The systematic (mean) and random errors (standard deviation) combined for 25 patients in x, y, and z directions were 0.15 cm, 0.21 cm, and 0.19 cm and 0.09 cm, 0.12 cm, and 0.09 cm, respectively. The study showed that there was a significant difference in PTV coverage between 2 plans. The doses to various OARs showed a nonsignificant increase in the plan sum. The correction of translational setup errors is essential for IGRT treatment in terms of delivery of planned optimal doses to target volume.
PMCID: PMC4871004  PMID: 27217627
Cone beam computed tomography; head and neck neoplasm; image guided radiotherapy; setup errors
16.  Build-up material requirements in clinical dosimetry during total body irradiation treatments 
Total body irradiation (TBI) treatments are mainly used in a preparative regimen for hematopoietic stem cell (or bone marrow) transplantation. Our standard clinical regimen is a 12 Gy/6 fraction bi-daily technique using 6MV X-rays at a large extended source to surface distance (SSD). This work investigates and quantifies the dose build-up characteristics and thus the requirements for bolus used for in vivo dosimetry for TBI applications. Percentage dose build-up characteristics of photon beams have been investigated at large extended SSDs using ionization chambers and Gafchromic film. Open field measurements at different field sizes and with differing scatter conditions such as the introduction of standard Perspex scattering plates at different distances to the measurement point were made in an effort to determine the required bolus/build-up material required for accurate determination of applied dose. Percentage surface dose values measured for open fields at 300 cm SSD were found to range from 20% up to 65.5% for fields 5 cm × 5 cm to 40 cm × 40 cm, respectively. With the introduction of 1 cm Perspex scattering plates used in TBI treatments, the surface dose values increased up to 83–90% (93–97% at 1 mm depth), depending on the position of the Perspex scattering plate compared to the measurement point. Our work showed that at least 5 mm water equivalent bolus/scatter material should be placed over the EBT3 film for accurate dose assessment for TBI treatments. Results also show that a small but measurable decrease in measured dose occurred with 5 mm water equivalent thick bolus material of areas '3 cm2. As such, we recommend that 3 cm × 3 cm × 5 mm bolus build-up is the smallest size that should be placed over EBT3 Gafchromic film when used for accurate in vivo dosimetry for TBI applications.
PMCID: PMC4871005  PMID: 27217628
Bolus; build up dose; dosimetry; radiochromic; radiotherapy; total body irradiation
19.  Dosimetric differences in flattened and flattening filter-free beam treatment plans 
This study investigated the dosimetric differences in treatment plans from flattened and flattening filter-free (FFF) beams from the TrueBeam System. A total of 104 treatment plans with static (sliding window) intensity-modulated radiotherapy beams and volumetric-modulated arc therapy (VMAT) beams were generated for 15 patients involving three cancer sites. In general, the FFF beam provides similar target coverage as the flattened beam with improved dose sparing to organ-at-risk (OAR). Among all three cancer sites, the head and neck showed more important differences between the flattened beam and FFF beam. The maximum reduction of the FFF beam in the mean dose reached up to 2.82 Gy for larynx in head and neck case. Compared to the 6 MV flattened beam, the 10 MV FFF beam provided improved dose sparing to certain OARs, especially for VMAT cases. Thus, 10 MV FFF beam could be used to improve the treatment plan.
PMCID: PMC4871009  PMID: 27217620
Flattening filter-free beam; intensity-modulated radiotherapy; treatment plan
20.  Surface dose measurements and comparison of unflattened and flattened photon beams 
The purpose of this study was to evaluate the central axis dose in the build-up region and the surface dose of a 6 MV and 10 MV flattened photon beam (FB) and flattening filter free (FFF) therapeutic photon beam for different square field sizes (FSs) for a Varian Truebeam linear accelerator using parallel-plate ionization chamber and Gafchromic film. Knowledge of dosimetric characteristics in the build-up region and surface dose of the FFF is essential for clinical care. The dose measurements were also obtained empirically using two different commonly used dosimeters: a p-type photon semiconductor dosimeter and a cylindrical ionization chamber. Surface dose increased linearly with FS for both FB and FFF photon beams. The surface dose values of FFF were higher than the FB FSs. The measured surface dose clearly increases with increasing FS. The FFF beams have a modestly higher surface dose in the build-up region than the FB. The dependence of source to skin distance (SSD) is less significant in FFF beams when compared to the flattened beams at extended SSDs.
PMCID: PMC4871008  PMID: 27217619
Flattening filter-free; Gafchromic films; NACP chamber; photon beams; surface dose
22.  Analysis of small field percent depth dose and profiles: Comparison of measurements with various detectors and effects of detector orientation with different jaw settings 
The advent of modern technologies in radiotherapy poses an increased challenge in the determination of dosimetric parameters of small fields that exhibit a high degree of uncertainty. Percent depth dose and beam profiles were acquired using different detectors in two different orientations. The parameters such as relative surface dose (DS), depth of dose maximum (Dmax), percentage dose at 10 cm (D10), penumbral width, flatness, and symmetry were evaluated with different detectors. The dosimetric data were acquired for fields defined by jaws alone, multileaf collimator (MLC) alone, and by MLC while the jaws were positioned at 0, 0.25, 0.5, and 1.0 cm away from MLC leaf-end using a Varian linear accelerator with 6 MV photon beam. The accuracy in the measurement of dosimetric parameters with various detectors for three different field definitions was evaluated. The relative DS(38.1%) with photon field diode in parallel orientation was higher than electron field diode (EFD) (27.9%) values for 1 cm ×1 cm field. An overestimation of 5.7% and 8.6% in D10 depth were observed for 1 cm ×1 cm field with RK ion chamber in parallel and perpendicular orientation, respectively, for the fields defined by MLC while jaw positioned at the edge of the field when compared to EFD values in parallel orientation. For this field definition, the in-plane penumbral widths obtained with ion chamber in parallel and perpendicular orientation were 3.9 mm, 5.6 mm for 1 cm ×1 cm field, respectively. Among all detectors used in the study, the unshielded diodes were found to be an appropriate choice of detector for the measurement of beam parameters in small fields.
PMCID: PMC4795411  PMID: 27051165
Beam profile; detector orientation; penumbra; percent depth dose; small field dosimetry
23.  Investigation of grid performance using simple image quality tests 
Antiscatter grids improve the X-ray image contrast at a cost of patient radiation doses. The choice of appropriate grid or its removal requires a good knowledge of grid characteristics, especially for pediatric digital imaging. The aim of this work is to understand the relation between grid performance parameters and some numerical image quality metrics for digital radiological examinations. The grid parameters such as bucky factor (BF), selectivity (Σ), Contrast improvement factor (CIF), and signal-to-noise improvement factor (SIF) were determined following the measurements of primary, scatter, and total radiations with a digital fluoroscopic system for the thicknesses of 5, 10, 15, 20, and 25 cm polymethyl methacrylate blocks at the tube voltages of 70, 90, and 120 kVp. Image contrast for low- and high-contrast objects and high-contrast spatial resolution were measured with simple phantoms using the same scatter thicknesses and tube voltages. BF and SIF values were also calculated from the images obtained with and without grids. The correlation coefficients between BF values obtained using two approaches (grid parameters and image quality metrics) were in good agreement. Proposed approach provides a quick and practical way of estimating grid performance for different digital fluoroscopic examinations.
PMCID: PMC4795412  PMID: 27051166
Bucky factor; contrast; grid performance; image quality
24.  Application of Chang's attenuation correction technique for single-photon emission computed tomography partial angle acquisition of Jaszczak phantom 
The acquisition and processing of the Jaszczak phantom is a recommended test by the American College of Radiology for evaluation of gamma camera system performance. To produce the reconstructed phantom image for quality evaluation, attenuation correction is applied. The attenuation of counts originating from the center of the phantom is greater than that originating from the periphery of the phantom causing an artifactual appearance of inhomogeneity in the reconstructed image and complicating phantom evaluation. Chang's mathematical formulation is a common method of attenuation correction applied on most gamma cameras that do not require an external transmission source such as computed tomography, radionuclide sources installed within the gantry of the camera or a flood source. Tomographic acquisition can be obtained in two different acquisition modes for dual-detector gamma camera; one where the two detectors are at 180° configuration and acquire projection images for a full 360°, and the other where the two detectors are positioned at a 90° configuration and acquire projections for only 180°. Though Chang's attenuation correction method has been used for 360° angle acquisition, its applicability for 180° angle acquisition remains a question with one vendor's camera software producing artifacts in the images. This work investigates whether Chang's attenuation correction technique can be applied to both acquisition modes by the development of a Chang's formulation-based algorithm that is applicable to both modes. Assessment of attenuation correction performance by phantom uniformity analysis illustrates improved uniformity with the proposed algorithm (22.6%) compared to the camera software (57.6%).
PMCID: PMC4795413  PMID: 27051167
American College of Radiology testing; attenuation correction; single-photon emission computed tomography
25.  Analyzing the characteristics of 6 MV photon beam at low monitor unit settings 
Analyzing the characteristics of a low monitor unit (MU) setting is essential, particularly for intensity-modulated techniques. Intensity modulation can be achieved through intensity-modulated radiotherapy (IMRT) or volumetric-modulated arc therapy (VMAT). There is possibility for low MUs in the segments of IMRT and VMAT plans. The minimum MU/segment must be set by the physicist in the treatment planning system at the time of commissioning. In this study, the characteristics such as dose linearity, stability, flatness, and symmetry of 6 MV photon beam of a Synergy linear accelerator at low MU settings were investigated for different dose rates. The measurements were performed for Synergy linear accelerator using a slab phantom with a FC65-G chamber and Profiler 2. The MU linearity was studied for 1–100 MU using a field size of 10 cm ×10 cm. The linearity error for 1 MU was 4.2%. Flatness of the beam was deteriorated in 1 MU condition. The beam stability and symmetry was well within the specification. Using this study, we conclude that the treatment delivered with <3 MU may result in uncertainty in dose delivery. To ensure the correct dose delivery with less uncertainty, it is recommended to use ≥3 MU as the minimum MU per segment in IMRT and VMAT plans.
PMCID: PMC4795415  PMID: 27051168
Flatness; gated volumetric-modulated arc therapy; linearity; low monitor unit; stability; symmetry

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