Journal of Medical Physics
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   Table of Contents - Current issue
Coverpage
April-June 2020
Volume 45 | Issue 2
Page Nos. 59-141

Online since Monday, July 20, 2020

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ORIGINAL ARTICLES  

Characterization and performance evaluation of the first-proton therapy facility in India Highly accessed article p. 59
Dayananda Sharma Shamurailatpam, A Manikandan, K Ganapathy, MP Noufal, Kartikeshwar C Patro, T Rajesh, R Jalali
DOI:10.4103/jmp.JMP_12_20  
Purpose: The purpose of this study is to evaluate the performance characteristic of volumetric image-guided dedicated-nozzle pencil beam-scanning proton therapy (PT) system. Materials and Methods: PT system was characterized for electromechanical, image quality, and registration accuracy. Proton beam of 70.2–226.2 MeV was characterized for short- and long-term reproducibility in integrated depth dose; spot profile characteristics at different air gap and gantry angle; positioning accuracy of single and pattern of spot; dose linearity, reproducibility and consistency. All measurements were carried out using various X-ray and proton-beam specific detectors following standard protocols. Results: All electro-mechanical, imaging, and safety parameters performed well within the specified tolerance limit. The image registration errors along three translation and three rotational axes were ≤0.5 mm and ≤0.2° for both point-based and intensity-based auto-registration. Distal range (R90) and distal dose fall-off (DDF) of 70.2–226.2 MeV proton beams were within 1 mm of calculated values based on the international commission on radiation units and measurements 49 and 0.0156× R90, respectively. The R90and DDF were reproducible within a standard deviation of 0.05 g/cm2 during the first 8 months. Dose were linear from 18.5 (0.011 MU/spot) to 8405 (5 MU/spot) MU, reproducible within 0.5% in 5 consecutive days and consistent within 0.8% for full rotation. The cGy/MU for 70.2–226.2MeV was consistent within 0.5%. In-air X(Y) spot-sigma at isocenter varies from 2.96 (3.00) mm to 6.68 (6.52) mm for 70.2–226.2 MeV. Maximum variation of spot-sigma with air-gap of ±20 cm was ±0.36 mm (5.28%) and ±0.82 mm (±12.5%) along X- and Y-direction and 3.56% for full rotation. Relative spot positions were accurate within ±0.6 mm. The planned and delivered spot pattern of known complex geometry agreed with (γ%≤1) for 1% @ 1 mm >98% for representative five-proton energies at four gantry angle. Conclusion: The PT-system performed well within the expected accuracy level and consistent over a period of 8 months. The methodology and data presented here may help upcoming modern PT center during their crucial phase of commissioning.
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Design, fabrication, and validation of a polymethyl methacrylate head phantom for dosimetric verification of cranial radiotherapy treatment plans Highly accessed article p. 66
VS Shaiju, Rajesh Kumar, Debjani Phani, KV Rajasekhar, George Zacharia, Saju Bhasi, Raghuram K Nair
DOI:10.4103/jmp.JMP_21_20  
Purpose: The present study aims to design and fabricate a novel, versatile, and cost-effective Polymethyl Methacrylate (PMMA) head phantom for the dosimetric pretreatment verification of radiotherapy (RT) treatment plans. Materials and Methods: The head phantom designing involves slice-wise modeling of an adult head using PMMA. The phantom has provisions to hold detectors such as ionization chambers of different sizes, Gafchromic films, gel dosimeter, and optically stimulated luminescence dosimeter. For the point dose verification purpose, 15 volumetric modulated arc therapy patient plans were selected, and doses were measured using a CC13 ionization chamber. The percentage gamma passing rate was calculated for acceptance criteria 3%/3 mm and 2%/2 mm using OmniPro I'mRT film QA software, and Gafchromic EBT3 films were used for 2D planar dose verification. Results: Treatment planning system calculated, and the measured point doses showed a percentage deviation ranged from 0.26 to 1.92. The planar dose fluence measurements, for set acceptance criteria of 3%/3 mm and 2%/2 mm, percentages of points having gamma value <1 were in the range of 99.17 ± 0.25 to 99.88 ± 0.15 and 93.16 ± 0.38 to 98.89 ± 0.23, respectively. Measured dose verification indices were within the acceptable limit. Conclusions: The dosimetric study reveals that head phantom can be used for routine pretreatment verification for the cranial RT, especially for stereotactic radiosurgery/RT as a part of patient-specific quality assurance. The presently fabricated and validated phantom is novel, versatile, and cost-effective, and many institutes can afford it.
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Influence of cleaned-up commercial knowledge-based treatment planning on volumetric-modulated arc therapy of prostate cancer p. 71
Mikoto Tamura, Hajime Monzen, Kenji Matsumoto, Kazuki Kubo, Yoshihiro Ueda, Tatsuya Kamima, Masahiro Inada, Hiroshi Doi, Kiyoshi Nakamatsu, Yasumasa Nishimura
DOI:10.4103/jmp.JMP_109_19  
Purpose: This study aimed to investigate the influence of cleaned-up knowledge-based treatment planning (KBP) models on the plan quality for volumetric-modulated arc therapy (VMAT) of prostate cancer. Materials and Methods: Thirty prostate cancer VMAT plans were enrolled and evaluated according to four KBP modeling methods as follows: (1) model not cleaned – trained by fifty other clinical plans (KBPORIG); (2) cases cleaned by removing plans that did not meet all clinical goals of the dosimetric parameters, derived from dose–volume histogram (DVH) (KBPC-DVH); (3) cases cleaned outside the range of ±1 standard deviation through the principal component analysis regression plots (KBPC-REG); and (4) cases cleaned using both methods (2) and (3) (KBPC-ALL). Rectal and bladder structures in the training models numbered 34 and 48 for KBPC-DVH, 37 and 33 for KBPC-REG, and 26 and 33 for KBPC-ALL, respectively. The dosimetric parameters for each model with one-time auto-optimization were compared. Results: All KBP models improved target dose coverage and conformity and provided comparable sparing of organs at risks (rectal and bladder walls). There were no significant differences in plan quality among the KBP models. Nevertheless, only the KBPC-ALLmodel generated no cases of >1% V78 Gy(prescribed dose) to the rectal wall, whereas the KBPORIG, KBPC-DVH, and KBPC-REG modelsincluded two, four, and three cases, respectively, which were difficult to overcome with KBP because the planning target volume (PTV) and rectum regions overlapped. Conclusions: The cleaned-up KBP model based on DVH and regression plots improved plan quality in the PTV–rectum overlap region.
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Evaluation of dose distribution and normal tissue complication probability of a combined dose of cone-beam computed tomography imaging with treatment in prostate intensity-modulated radiation therapy p. 78
Tetsuya Tomita, Tomonori Isobe, Yoshinobu Furuyama, Hideyuki Takei, Daisuke Kobayashi, Yutaro Mori, Toshiyuki Terunuma, Eisuke Sato, Hiroshi Yokota, Takeji Sakae
DOI:10.4103/jmp.JMP_4_20  
Purpose: The purpose of this study is to evaluate the effects of cone-beam computed tomography (CBCT) on dose distribution and normal tissue complication probability (NTCP) by constructing a comprehensive dose evaluation system for prostate intensity-modulated radiation therapy (IMRT). Methods: A system that could combine CBCT and treatment doses with MATLAB was constructed. Twenty patients treated with prostate IMRT were studied. A mean dose of 78 Gy was prescribed to the prostate region, excluding the rectal volume from the target volume, with margins of 4 mm to the dorsal side of the prostate and 7 mm to the entire circumference. CBCT and treatment doses were combined, and the dose distribution and the NTCP of the rectum and bladder were evaluated. Results: The radiation dose delivered to 2% and 98% of the target volume increased by 0.90 and 0.74 Gy on average, respectively, in the half-fan mode and on average 0.76 and 0.72 Gy, respectively, in the full-fan mode. The homogeneity index remained constant. The percent volume of the rectum and bladder irradiated at each dose increased slightly, with a maximum increase of <1%. The rectal NTCP increased by approximately 0.07% from 0.46% to 0.53% with the addition of a CBCT dose, while the maximum NTCP in the bladder was approximately 0.02%. Conclusions: This study demonstrated a method to evaluate a combined dose of CBCT and a treatment dose using the constructed system. The combined dose distribution revealed increases of <1% volume in the rectal and bladder doses and approximately 0.07% in the rectal NTCP.
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Study of asymmetric margins in prostate cancer radiation therapy using fuzzy logic p. 88
Santosh Kumar Patnaikuni, Sapan Mohan Saini, Rakesh Mohan Chandola, Pradeep Chandrakar, Vivek Chaudhary
DOI:10.4103/jmp.JMP_110_19  
Purpose: The purpose of present study is to estimate asymmetric margins of prostate target volume based on biological limitations with help of knowledge based fuzzy logic considering the effect of organ motion and setup errors. Materials and Methods: A novel application of fuzzy logic modelling technique considering radiotherapy uncertainties including setup, delineation and organ motion was used in this study to derive margins. The new margin was applied in prostate cancer treatment planning and the results compared very well to current techniques Here volumetric modulated arc therapy treatment plans using stepped increments of asymmetric margins of planning target volume (PTV) were performed to calculate the changes in prostate radiobiological indices and results were used to formulate the rule based and membership function for Mamdani-type fuzzy inference system. The optimum fuzzy rules derived from input data, the clinical goals and knowledge-based conditions imposed on the margin limits. The PTV margin obtained using the fuzzy model was compared to the commonly used margin recipe. Results: For total displacement standard errors ranging from 0 to 5 mm the fuzzy PTV margin was found to be up to 0.5 mm bigger than the vanHerk derived margin, however taking the modelling uncertainty into account results in a good match between the PTV margin calculated using our model and the one based on van Herk et al. formulation for equivalent errors of up to 5 mm standard deviation (s. d.) at this range. When the total displacement standard errors exceed 5 mm s. d., the fuzzy margin remained smaller than the van Herk margin. Conclusion: The advantage of using knowledge based fuzzy logic is that a practical limitation on the margin size is included in the model for limiting the dose received by the critical organs. It uses both physical and radiobiological data to optimize the required margin as per clinical requirement in real time or adaptive planning, which is an improvement on most margin models which mainly rely on physical data only.
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Appraisal of deep-learning techniques on computer-aided lung cancer diagnosis with computed tomography screening p. 98
S Akila Agnes, J Anitha
DOI:10.4103/jmp.JMP_101_19  
Aims: Deep-learning methods are becoming versatile in the field of medical image analysis. The hand-operated examination of smaller nodules from computed tomography scans becomes a challenging and time-consuming task due to the limitation of human vision. A standardized computer-aided diagnosis (CAD) framework is required for rapid and accurate lung cancer diagnosis. The National Lung Screening Trial recommends routine screening with low-dose computed tomography among high-risk patients to reduce the risk of dying from lung cancer by early cancer detection. The evolvement of clinically acceptable CAD system for lung cancer diagnosis demands perfect prototypes for segmenting lung region, followed by identifying nodules with reduced false positives. Recently, deep-learning methods are increasingly adopted in medical image diagnosis applications. Subjects and Methods: In this study, a deep-learning-based CAD framework for lung cancer diagnosis with chest computed tomography (CT) images is built using dilated SegNet and convolutional neural networks (CNNs). A dilated SegNet model is employed to segment lung from chest CT images, and a CNN model with batch normalization is developed to identify the true nodules from all possible nodules. The dilated SegNet and CNN models have been trained on the sample cases taken from the LUNA16 dataset. The performance of the segmentation model is measured in terms of Dice coefficient, and the nodule classifier is evaluated with sensitivity. The discriminant ability of the features learned by a CNN classifier is further confirmed with principal component analysis. Results: Experimental results confirm that the dilated SegNet model segments the lung with an average Dice coefficient of 0.89 ± 0.23 and the customized CNN model yields a sensitivity of 94.8 on categorizing cancerous and noncancerous nodules. Conclusions: Thus, the proposed CNN models achieve efficient lung segmentation and two-dimensional nodule patch classification in CAD system for lung cancer diagnosis with CT screening.
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Assessment of four scatter correction methods in In-111 SPECT imaging: A simulation study p. 107
Mahsa Noori-Asl
DOI:10.4103/jmp.JMP_5_20  
Introduction: Detection of compton scattered photons is one of the most important factors affecting the quality of single-photon emission computed tomography (SPECT) images. In most cases, the multiple-energy window acquisition methods are used for estimation of the scatter contribution into the main energy window(s) used in imaging. Aims and Objectives: The purpose of this study is to evaluate and compare the performance of four different scatter correction methods in In-111 SPECT imaging. Due to the lack of sufficient studies in this field, it can be useful to perform a more detailed and comparative study. Materials and Methods: Four approximations for scatter correction of In-111 SPECT images are evaluated by using the Monte Carlo simulation. These methods are firstly applied on each of photopeak windows, separately. Then, the effect of the correction methods is investigated by considering both the photopeak windows. The images obtained from a simulated multiple-spheres phantom are used for the evaluation of the correction methods by using three assessment criteria, including the image contrast, relative noise, and the recovery coefficient. Results: The results of this study show that the correction methods, when using the single photopeak windows, result in increase in image contrast with a significant level of noise. In return, when both the photopeak energy windows are used for imaging, it is possible to achieve the better image characteristics. Conclusion: The use of the proposed correction methods, by considering both the photopeak windows, leads to improve the image contrast with a reasonable level of image noise.
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Monte carlo calculation of the energy spectrum of a 6 MeV electron beam using penetration and energy loss of positrons and electrons code p. 116
Danny Giancarlo Apaza Veliz, Jorge Homero Wilches Visbal, Felipe Chen Abrego, José Luis Vega Ramírez
DOI:10.4103/jmp.JMP_104_19  
Background: The limited bibliographic existence of research works on the use of Monte Carlo simulation to determine the energy spectra of electron beams compared to the information available regarding photon beams is a scientific task that should be resolved. Aims: In this work, Monte Carlo simulation was performed through the PENELOPE code of the Sinergy Elekta accelerator head to obtain the spectrum of a 6 MeV electron beam and its characteristic dosimetric parameters. Materials and Methods: The central-axis energy spectrum and the percentage depth dose curve of a 6 MeV electron beam of an Elekta Synergy linear accelerator were obtained by using Monte Carlo PENELOPE code v2014. For this, the linear accelerator head geometry, electron applicators, and water phantom were simplified. Subsequently, the interaction process between the electron beam and head components was simulated in a time of 86.4x104 s. Results: From this simulation, the energy spectrum at the linear accelerator exit window and the surface of the phantom was obtained, as well as the associated percentage depth dose curves. The validation of the Monte Carlo simulation was performed by comparing the simulated and the measured percentage depth dose curves via the gamma index criterion. Measured percentage depth- dose was determined by using a Markus electron ionization chamber, type T23343. Characteristic parameters of the beam related with the PDD curves such as the maximum dose depth (R100), 90% dose depth (R90), 90% dose depth or therapeutic range (R85), half dose depth (R50), practical range (Rp), maximum range (Rmax), surface dose (Ds), normalized dose gradient (G0) and photon contamination dose (Dx) were determined. Parameters related with the energy spectrum, namely, the most probable energy of electrons at the surface (Ep,0) and electron average energy (E0) were also determined. Conclusion: It was demonstrated that PENELOPE is an attractive and accurate tool for the obtaining of dosimetric parameters of a medical linear accelerator since it can reliably reproduce important clinical data such as the energy spectrum, depth dose, and dose profile.
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TECHNICAL NOTE Top

Simultaneous measurement of In vivo and transit mid-plane doses with ionization chambers in gynecological malignancy patients undergoing three-dimensional conformal radiotherapy p. 123
Putha Suman Kumar, Challapalli Srinivas, BM Vadhiraja, Sourjya Banerjee, R Shreyas, PU Prakash Saxena, Ramamoorthy Ravichandran, Dilson Lobo
DOI:10.4103/jmp.JMP_3_20  
Purpose: The aim of this study is to estimate delivered radiation doses inside planning tumor volume (PTV) using the in vivo (mid-plane dose) measurement and transit measurement methods in gynecological malignancy patients undergoing three-dimensional conformal radiotherapy (3DCRT) using calibrated ionization chambers. Materials and Methods: Six patients with histopathologically proven carcinoma of the cervix or endometrium were planned with four-field 3DCRT to the pelvic site. Isocenter was at the geometric mid-plane of PTV with a dose prescription of 50 Gy in 25 fractions. Clinical mid-plane dose (Diso,Transit) estimates were done in one method (transit) using the FC-65 positioned at electronic portal imaging device level. In another method, a repeat computerized tomography scan was performed (at the 11th fraction) using CC-13 having a protective cap in the vaginal cavity for in vivo measurements (Din vivo). Simultaneous measurements were performed with the two chambers from the 11th fraction onward at least 3–4 times during the remaining course of treatment. Results: The agreement of mean doses from these two described methods and treatment planning system reference doses was in the range of −4.4 ± 1.1% (minimum) to −0.3 ± 2.0% (maximum) and −4.0 ± 1.7% (minimum) to 1.9 ± 2.4% for Dinvivoand Diso,Transit, respectively, which are an acceptable range of daily radiation dose delivery. Conclusion: The fundamental importance of this study lies in simultaneous validation of delivered dose in real time with two methods. A study in this small number of patients has given the confidence to apply transit measurements for quality assurance on a routine basis as an accepted clinical dosimetry for the selected patients.
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LETTER TO THE EDITOR Top

Revision in standard operating procedures of radiation oncology department and quality assurance schedule under COVID-19 pandemic p. 130
Suresh Chaudhari, Sunil Dutt Sharma, Shyam Kishore Shrivastava
DOI:10.4103/jmp.JMP_37_20  
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BOOK REVIEWS Top

Khan's the physics of radiation therapy p. 134
Manoj Kumar Semwal
DOI:10.4103/jmp.JMP_17_20  
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Leadership and challenges in medical physics: A strategic and robust approach p. 136
Arun Chougule
DOI:10.4103/jmp.JMP_34_20  
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Guidance on the personal monitoring requirements for personnel working in healthcare p. 139
KM Ganesh
DOI:10.4103/jmp.JMP_35_20  
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ERRATUM Top

Erratum: Superparamagnetic Iron Oxide-C595: Potential MR imaging contrast agents for ovarian cancer detection p. 141

DOI:10.4103/0971-6203.290236  
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