Journal of Medical Physics
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   2018| July-September  | Volume 43 | Issue 3  
    Online since September 26, 2018

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Voxel based BED and EQD2Evaluation of the radiotherapy treatment plan
Gaganpreet Singh, Arun S Oinam, Rose Kamal, Bhumika Handa, Vivek Kumar, Bhavana Rai
July-September 2018, 43(3):155-161
DOI:10.4103/jmp.JMP_29_18  PMID:30305772
Introduction: Three-dimensional (3D) treatment planning of patient undergoing radiotherapy uses complex and meticulous computational algorithms. These algorithms use 3D voxel data of the patient to calculate the radiation dose distribution and display it over the CT image dataset for treatment plan evaluation. Aims and Objective: The purpose of the present study is the development and implementation of radiobiological evaluation of the radiotherapy treatment plan incorporating the tissue-specific radiobiological parameters. Material and Method: An indigenous program was written in MATLAB® software (version 2011b of Mathworks Inc.) to extract the patient treatment plan data from DICOM-RT files which are exported from the treatment planning system. CT-, Structures- and Dose-Cube matrices are reconstructed from the exported patient plan data. BED and EQD2based dose volume histograms (DVHs), colorwash and iso-effective dose curves were generated from the physical Dose-Cube using the linear-quadratic (LQ) formalism and tissue-specific radiobiological parameters (α/β). Results and Conclusion: BED-and EQD2-colorwash and iso-effective curves along with BED and EQD2dose volume histograms provide superior radiobiological information as compared to those of physical doses. This study provides supplementary recipes of radiobiological doses along with the physical doses which are useful for the evaluation of complex radiotherapy treatment plan of the patients.
  3,467 344 -
A dose falloff gradient study in RapidArc planning of lung stereotactic body radiation therapy
Ganesh Narayanasamy, Dharmin Desai, Sanjay Maraboyina, Jose Penagaricano, Robert Zwicker, Ellis Lee Johnson
July-September 2018, 43(3):147-154
DOI:10.4103/jmp.JMP_38_18  PMID:30305771
Introduction: Radiation Therapy Oncology Group (RTOG) report #0813 and 0915 recommends using D2cmand R50%as plan quality metrics for evaluation of normal tissue sparing in stereotactic body radiation therapy (SBRT) of lung lesion. This study introduces dose falloff gradient (DFG) as a tool for analyzing the dose beyond the planning target volume (PTV) extending into normal tissue structures. In ascertaining the impact of PTV size and SBRT planning techniques in DFG, this study questions the independence of the RTOG recommended metrics. Materials and Methods: In this retrospective study, 41 RapidArc lung SBRT plans with 2 or 3 complete or partial arcs were analyzed. PTV volumes ranged between 5.3 and 113 cm3 and their geographic locations were distributed in both lungs. 6MV, 6 MV-FFF, 10 MV, or 10 MV-FFF energies were used. RTOG-0915 metrics conformity index, homogeneity index, D2cm, R50%, and HDlocwere evaluated. DFG was computed from the mean and maximum dose in seven concentric 5 mm wide rings outside the PTV. DFG was investigated against the volume of normal lung irradiated by 50% isodose volume. Treatment plans with alternate energy and couch rotations were generated. Results: The dose falloff beyond PTV was modeled using a double exponential fit and evaluated for relationship with intermediate lung dose. Photon energy and beam configuration had a minimal impact on the dose falloff outside. The product of normalized D2cmand R50%was estimated to have a slowly varying value. Conclusions: Dose falloff outside PTV has been studied as a function of radial distance and ascertained by intermediate dose to normal lung. DFG can serve as a complementary plan quality metric.
  2,691 252 4
Comparison of measured and Monte Carlo calculated dose distributions from indigenously developed 6 MV flattening filter free medical linear accelerator
Bibekananda Mishra, Subhalaxmi Mishra, T Palani Selvam, ST Chavan, SN Pethe
July-September 2018, 43(3):162-167
DOI:10.4103/jmp.JMP_58_18  PMID:30305773
Purpose: Monte Carlo simulation was carried out for a 6 MV flattening filter-free (FFF) indigenously developed linear accelerator (linac) using the BEAMnrc user-code of the EGSnrc code system. The model was benchmarked against the measurements. A Gaussian distributed electron beam of kinetic energy 6.2 MeV with full-width half maximum of 1 mm was used in this study. Methods: The simulation of indigenously developed linac unit has been carried out by using the Monte Carlo-based BEAMnrc user-code of the EGSnrc code system. Using the simulated model, depth and lateral dose profiles were studied using the DOSXYZnrc user-code. The calculated dose data were compared against the measurements using an RFA dosimertic system made by PTW, Germany (water tank MP3-M and 0.125 cm3 ion chamber). Results: The BEAMDP code was used to analyze photon fluence spectra, mean energy distribution, and electron contamination fluence spectra. Percentage depth dose (PDD) and beam profiles (along both X and Y directions) were calculated for the field sizes 5 cm × 5 cm - 25 cm × 25 cm. The dose difference between the calculated and measured PDD and profile values were under 1%, except for the penumbra region where the maximum deviation was found to be around 3%. Conclusions: A Monte Carlo model of indigenous FFF linac (6 MV) has been developed and benchmarked against the measured data.
  1,980 164 -
Monte Carlo simulation on the imaging contrast enhancement in nanoparticle-enhanced radiotherapy
Ferdos Albayedh, James C. L. Chow
July-September 2018, 43(3):195-199
DOI:10.4103/jmp.JMP_141_17  PMID:30305778
This study focused on the imaging in radiotherapy by finding the relationship between the imaging contrast ratio and appropriate gold, iodine, iron oxide, silver, and platinum nanoparticle concentrations; the relationship between the imaging contrast ratio and different beam energies for the different nanoparticle concentrations; the relationship between the contrast ratio and various beam energies for gold nanoparticles; and the relationship between the contrast ratio and different thicknesses of the incident layer of the phantom including variety of gold nanoparticles (GNPs) concentration. Monte Carlo simulation was used to model the gold, iodine, iron oxide, silver, and platinum nanoparticle concentration which were infused within a heterogeneous phantom (50 cm × 50 cm × 10.5 cm) choosing different concentrations (3, 7, 18, 30, and 40 mg), and beams (100, 120, 130, and 140 kVp) correspondingly that were delivered into the phantom. The results showed obvious connection between the high concentration and having a high imaging contrast ratio, low energy and a high contrast ratio, small thickness, and a high contrast ratio. The superior nanoparticle obtained was GNP, the better concentration was 40 mg, the better beam energy was 100 kVp, and the better thickness was 0.5 cm. It is concluded that our study successfully proved that medical imaging contrast could be improved by increasing the contrast ratio using GNP as the finest choice to accomplish this improvement considering a high concentration, low beam energy, and a small thickness.
  1,502 156 7
Assessment of diagnostic reference level in radiography of neonatal chest anteroposterior examination: A hospital-based study
Jibon Sharma, Jogesh Sarma, Sushant Agarwal
July-September 2018, 43(3):200-203
DOI:10.4103/jmp.JMP_37_18  PMID:30305779
Radiological imaging is an important modality of today's overall practicum. Imaging can begin as early as the 1st day of life. Neonates are 3–4 times more sensitive to radiation than adults. The purpose of the work was to assess the diagnostic reference level (DRL), the radiation organ dose, and effective organ dose for both sexes from chest anteroposterior radiograph, which is the most common radiographic examination performed at the Neonatal Intensive Care Unit (NICU). The entrance air kerma was measured using a solid-state PIN type detector, and the value was used as the input factor to PCXMC-2.0 software to calculate the entrance surface air kerma (ESAK), patient-specific organ dose, and effective dose originated from chest anteroposterior examinations of neonates at NICU. The mean value of ESAK is taken as a diagnostic reference level (DRL) for neonates (both male and female). The mean ESAK value of male neonates is (79.6 ± 1.4) μGy and for female is (79.9 ± 1.9) μGy, and the institutional diagnostic reference level (DRL) is 80.35 μGy for male and 81.2 μGy for female (i.e., third quartile value). A statistical dependency (correlation) between neonates body mass index (BMI) and ESAK was defined for both the sexes. Significant positive correlation was found between ESAK per patient with respect to BMI of both male (R = 0.83, P = 0.00001) and female (R = 0.72, P = 0.00055) neonates. The results for neonatal dose in NICU were compatible with the literature. The result presented will serve as baseline data for the selection of technical parameters in neonatal chest anteroposterior X-ray examination.
  1,463 176 3
Optimization of variance reduction techniques used in EGSnrc Monte Carlo Codes
Sangeetha Shanmugasundaram, Sureka Chandrasekaran
July-September 2018, 43(3):185-194
DOI:10.4103/jmp.JMP_132_17  PMID:30305777
Monte Carlo (MC) simulations are often used in calculations of radiation transport to enable accurate prediction of radiation-dose, even though the computation is relatively time-consuming. In a typical MC simulation, significant computation time is allocated to following non-important events. To address this issue, variance reduction techniques (VRTs) have been suggested for reducing the statistical variance for the same computation time. Among the available MC simulation codes, electron gamma shower (National Research Council of Canada) (EGSnrc) is a general-purpose coupled electron-photon transport code that also features an even-handed, rich set of VRTs. The most well-known VRTs are the photon splitting, Russian roulette (RR), and photon cross-section enhancement (XCSE) techniques. The objective of this work was to determine the optimal combination of VRTs that increases the simulation speed and the efficiency of simulation, without compromising its accuracy. Selection of VRTs was performed using EGSnrc MC User codes, such as cavity and egs_chamber, for simulating various ion chamber geometries using 6 MV photon beams and 1.25 MeV60Co photon beams. The results show that the combination of XCSE and RR yields the highest efficiency for ion-chamber dose calculations inside a 30 cm × 30 cm × 30 cm water phantom. Hence, properly selecting a different VRT without altering the underlying physics increases the efficiency of MC simulations for ion-chamber dose calculation.
  1,354 235 3
A pilot study on the comparison between planning target volume-based intensity-modulated proton therapy plans and robustly optimized intensity-modulated proton therapy plans
Bojarajan Perumal, Harikrishna Etti Sundaresan, Ranganathan Vaitheeswaran
July-September 2018, 43(3):179-184
DOI:10.4103/jmp.JMP_45_18  PMID:30305776
The objective of this work is to compare the planning target volume (PTV)-based intensity-modulated proton therapy (IMPT) plans with robustly optimized IMPT plans using the robust optimization tools available in Pinnacle Treatment Planning System. We performed the study in five cases of different anatomic sites (brain, head and neck, lung, pancreas, and prostate). Pinnacle IMPT nonclinical version was used for IMPT planning. Two types of IMPT plans were created for each case. One is PTV-based conventionally optimized IMPT plan and the other is robustly optimized plan considering setup uncertainties. For the PTV-based plans, margins were on top of clinical target volume (CTV) to account for the setup errors, whereas in the robustly optimized plan, the setup errors were directly incorporated into the optimization process. The plan evaluation included target (CTV) coverage and dose uniformity. Our interest was to see how the target coverage and dose uniformity were perturbed on imposing setup errors in +X, −X, +Y, −Y, +Z, and −Z directions for both PTV-based and robust optimization (RO)-based plans. On the average, RO-based IMPT plans have shown a good consistency of target coverage and dose uniformity for all six setup errors scenarios as compared to PTV-based plans. In addition, RO-based plans have a better target coverage and dose uniformity under uncertainty conditions as compared to the PTV-based plans. The study demonstrates the superiority of robustly optimized IMPT plans over the PTV-based IMPT plans in terms of dose distribution under the uncertainty conditions.
  1,225 153 2
Incidence of suboptimal applicator placement and the resulting dosimetric impact in image-based intracavitary brachytherapy
Ramya Rangarajan
July-September 2018, 43(3):168-172
DOI:10.4103/jmp.JMP_28_18  PMID:30305774
Aim: With the advent of computed tomography (CT)-based brachytherapy, it is possible to view the appropriate placement of the applicator within the uterine canal and detect uterine perforation. In this study, the incidence of suboptimal placement of the intracavitary applicator and the resulting dosimetric impact were analyzed and compared with a similar set of ideal applicator placement. Materials and Methods: CT datasets of 282 (141 patients) high dose rate brachytherapy insertions between January and April 2016 were analyzed. The target volumes and organs at risk (OAR) were contoured as per the Groupe Européen de Curiethérapie European Society of Therapeutic Radiation Oncology guidelines. The position of the applicator in the uterine cavity was analyzed for each application. Results: The suboptimal insertion rate was 11.7%. There were 26 perforations and 7 subserosal insertions. The most common site of perforation was through the posterior wall of the uterus (42.4%). Fundus perforation and anterior wall perforation were seen in 24.2% and 12.1% of patients, respectively. The average dose to 90% of the target volume (D90 to high-risk clinical target volume) was the highest (9.15 Gy) with fundal perforation. Average dose to 2 cc (D2cc) bladder was highest for fundus perforation (7.65 Gy). The average dose received by 2 cc of rectum (D2cc) was highest (4.49 Gy) with posterior wall perforation. The average D2cc of the sigmoid was highest with anterior perforation (3.18 Gy). Conclusion: In order to achieve better local control and to decrease doses to OAR, it is important to perform a technically accurate applicator placement. A cost-effective, real-time image guidance modality like ultrasound is recommended for all insertions to ensure optimal applicator insertion.
  1,222 120 1
Dosimetry of 175Ytterbium-poly (amidoamine) therapy for humans' organs
Navideh Aghaei-Amirkhizi, Sodeh Sadjadi, Leila Moghaddam-Banaem, Mitra Athari-Allaf, Fariba Johari-Deha
July-September 2018, 43(3):173-178
DOI:10.4103/jmp.JMP_8_18  PMID:30305775
Purpose: This investigation focuses on biodistribution of irradiated dendrimer encapsulated ytterbium-175 (175Yb) and to estimate the absorbed dose from intravenous injection of PAMAM encapsulated 175Yb to human organs. Methods: A dendrimer compound containing an average of 55 Yb+3 ions per dendrimer was prepared and irradiated with neutrons for 2h at 3×1011 neutron flux. The resulting mixture was injected into a group of tumor bearing mice and the mice were excised, weighed and counted at certain times to study the biodistribution. The human organs absorbed dose was assessed by MIRD schema and MCNP simulation. Results: The specific activity and radiochemical purity of the irradiated nano-composite were 7MBq/mg and >99% respectively. The rapid up take of dendrimer was in liver, lung, and, spleen. MIRD and MCNPX were applied for dose estimation. The human absorbed dose in liver, lung, spleen, kidney and bone that simulated by MCNP are 1.266, 0.8081, 0.8347, 0.03979 and 0.01706 mGy/MBq respectively and these values for MIRD schema are 1.351, 0.73, 1.03, 0.039, and 0.0097 mGy/MBq respectively. Conclusion: The results showed that 175Yb-PAMAM nano-radiopharmaceutical has potential of application for liver and lung tumors.
  1,125 118 -
Review of the book entitled “Cancer, Radiation Therapy, and the Market” by Ms. Barbara Bridgman
Deepak Dattatray Deshpande
July-September 2018, 43(3):204-206
  780 166 -
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