Journal of Medical Physics
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   Table of Contents - Current issue
Coverpage
October-December 2020
Volume 45 | Issue 4
Page Nos. 197-263

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EDITORIAL  

The ever-changing role of medical physicists in the era of personalized medicine p. 197
Loredana G Marcu
DOI:10.4103/jmp.JMP_113_20  
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ORIGINAL ARTICLES Top

Simplifying tumor volume estimation from linear dimensions for intra-cranial lesions treated with stereotactic radiosurgery Highly accessed article p. 199
Sakshi Singhal, Maneet Gill, Chinmaya Srivastava, Darpan Gupta, Ashok Kumar, Aruna Kaushik, Manoj Kumar Semwal
DOI:10.4103/jmp.JMP_56_20  
Aims: This study aims to derive simple yet robust formula(s) for the calculation of cranial tumor volume using linear tumor dimensions in anterioposterior (AP), mediolateral (ML) and craniocaudal (CC) directions and also propose a reproducible methodology for tumor dimension measurements. Materials and Methods: Magnetic resonance images (MRI) of 337 patients planned for Gammaknife Stereotactic Radiosurgery for different types of brain tumors were analyzed using Leksell Gamma Plan (LGP) software. Tumor volume in three dimensional was outlined and maximum tumor diameters were measured in three orthogonal directions AP, ML, and CC on the MRI. Formulas were derived to calculate tumor volume from AP, ML, and CC diameters using linear regression technique. An agreement between the calculated volume and standard volume observed from LGP software was determined using Bland Altman (B-A) plot. A comparison was made between the volume calculated using traditionally used formula of ellipsoid, standard volume obtained from LGP software and volume calculated from formulas derived in the present study. Results: The tumors were divided into two categories based on their size for better volume prediction. The tumors having product of their diameters in the range 0–2.5cc were called “small tumors” and the formula proposed for their volume estimation ([INSIDE:1]) was found to predict the tumor volume with an average bias of 0.0005cc. For “large tumors,” having product of diameters in the range 2.5–36cc, the proposed formula ([INSIDE:2]) predicted the tumor volume with an average bias of 0.007cc. Conclusions: The two formulas proposed in the study are more accurate as compared to the commonly used formula that considers the tumors as ellipsoids. The methodology proposed in the study for measurement of linear tumor dimensions is simple and reproducible.
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The role of plan robustness evaluation in comparing protons and photons plans - An application on IMPT and IMRT plans in skull base chordomas p. 206
Manthala Padannayil Noufal, Lamberto Widesott, Shamurailatpam Dayananda Sharma, Roberto Righetto, Marco Cianchetti, Marco Schwarz
DOI:10.4103/jmp.JMP_45_20  
Purpose: To analyze robustness of treatment plans optimized using different approaches in intensity modulated proton therapy (IMPT) and investigate the necessity of robust optimization and evaluation in intensity modulated radiotherapy (IMRT) plans for skull base chordomas. Materials and Methods: Two photon plans, standard IMRT and robustly optimized IMRT (RB-IMRT), and two IMPT plans, robustly optimized multi field optimization (MFO) and hybrid-MFO (HB-MFO), were created in RayStation TPS for five patients previously treated using single field uniform optimization (SFO). Both set-up and range uncertainties were incorporated during robust optimization of IMPT plans whereas only set-up uncertainty was used in RB-IMRT. The dosimetric outcomes from the five planning techniques were compared for every patient using standard dose volume indices and integral dose (ID) estimated for target and organs at risk (OARs). Robustness of each treatment plan was assessed by introducing set-up uncertainties of ±3 mm along the three translational axes and, only in protons, an additional range uncertainty of ±3.5%. Results: All the five nominal plans provided comparable and clinically acceptable target coverage. In comparison to nominal plans, worst case decrease in D95% of clinical target volume-high risk (CTV-HR) were 11.1%, 13.5%, and 13.6% for SFO, MFO, and HB-MFO plans respectively. The corresponding values were 13.7% for standard IMRT which improved to 11.5% for RB-IMRT. The worst case increased in high dose (D1%) to CTV-HR was highest in IMRT (2.1%) and lowest in SFO (0.7%) plans. Moreover, IMRT showed worst case increases in D1% for all neurological OARs and were lowest for SFO plans. The worst case D1% for brainstem, chiasm, spinal cord, optic nerves, and temporal lobes were increased by 29%, 41%, 30%, 41% and 14% for IMRT and 18%, 21%, 21%, 24%, and 7% for SFO plans, respectively. In comparison to IMRT, RB-IMRT improved D1% of all neurological OARs ranging from 5% to 14% in worst case scenarios. Conclusion: Based on the five cases presented in the current study, all proton planning techniques (SFO, MFO and HB-MFO) were robust both for target coverage and OARs sparing. Standard IMRT plans were less robust than proton plans in regards to high doses to neurological OARs. However, robust optimization applied to IMRT resulted in improved robustness in both target coverage and high doses to OARs. Robustness evaluation may be considered as a part of plan evaluation procedure even in IMRT.
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Estimation of skin doses for retrofit prototype multileaf collimators designed for telecobalt therapy machine p. 215
Akula Roopa Rani, Komanduri Ayyangar, AR Reddy, Ayyalasomayajula Anil Kumar, Pal Reddy Yadagiri Reddy
DOI:10.4103/jmp.JMP_25_20  
Aim: The objective of this study was to evaluate skin dose based on retrofit prototype multileaf collimators (MLCs), designed for cobalt-60 teletherapy machine. Since patient's skin is sensitive to radiation, evaluation of skin dose is of utmost importance for investigating the risk of late effects. Materials and Methods: Measurements were performed with a Phoenix cobalt-60 teletherapy machine and the detector used was EBT3 radiochromic film. The experiments were performed in a solid water phantom with two prototype MLCs mounted to the machine. Dose readings were taken by placing the films at source-to-surface distance (SSD) of 60 cm, 65 cm, 70 cm, 75 cm, 80 cm, 85 cm, and 90 cm for various MLC-generated field sizes starting from 2 cm × 2 cm to 14 cm × 14 cm. The films were analyzed using custom made programs. The measured doses were normalized to the dose at dmax for that particular measurement of SSD. Results: The skin dose is expressed as a percentage of dose at dose maximum. In general, the skin dose increases with field size and decreases with SSD. The measurements indicate surface doses within 20%–60% for the investigated SSD range. Furthermore, there is no significant difference between the surface doses of two prototype MLCs studied. Conclusions: From the measurements, it can be concluded that there is good skin sparing even at close distance to the MLCs. The skin dose is <50% for SSDs >65 cm. A minimum gap of 5 cm is required to produce acceptable skin dose.
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Spatial mesh-based surface source model for the electron contamination of an 18 MV photon beams p. 221
Ahad Ollah Ezzati, Matthew T Studenski, Masuomeh Gohari
DOI:10.4103/jmp.JMP_29_20  
Background: Source modeling is an approach to reduce computational burden in Monte Carlo simulations but at the cost of reduced accuracy. Although this method can be effective, one component of the source model that is exceptionally difficult to model is the electron contamination, a significant contributor to the skin and shallow dose. Aims and Objectives: To improve the accuracy for the electron contamination component of the overall source model, we have generated a spatial mesh based surface source model. Methods and Materials: The source model is located downstream from the flattening filter and mirror but upstream from the movable jaws. A typical phase space file uses around ten parameters per particle, but this method simplifies this number to five components. By using only the electron distance from the central axis, angles from the central axis and energy, the computational time and disk space required is greatly reduced. Results and Conclusion: Despite the simplification in the source model, the electron contamination is still accurate to within 1.5%.
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Is synchronous bilateral breast irradiation using flattening filter-free beam-based volumetric-modulated arc therapy beneficial? A dosimetric study p. 226
Jagadheeskumar Nagaraj, K Veluraja
DOI:10.4103/jmp.JMP_32_20  
Objective: The aim of this study is to validate the clinical use of flattening filter-free (FFF) beam-based volumetric-modulated arc therapy (VMAT) in synchronous bilateral breast carcinoma (SBBC) patient treatments and to compare with flattening filtered (FF) beam-based VMAT. Materials and Methods: Computed tomography images of 15 SBBC patients were taken for this study. A dose of 50 Gy in 25 fractions was prescribed to planning target volume (PTV). VMAT plans were generated using both FFF and FF 6 MV X-ray beams in Eclipse treatment planning system. PTV and organs at risk (OARs) doses were analyzed quantitatively using dose–volume histograms (DVHs) to meet plan objectives. Pretreatment point and planar dosimetry were performed. Results: The findings were reported as mean ± 1 standard deviation. PTV volume receiving 95% of the prescribed dose was 95.71% ± 0.65% for FF-VMAT and 95.45% ± 1.33% for FFF-VMAT (P = 0.743). Conformity index was 1.12 ± 0.31 (FF-VMAT) and 1.12 ± 0.02 (FFF-VMAT). Right lung mean dose was 10.95 ± 1.33 Gy (FF-VMAT) and 10.60 ± 98.5 (FFF-VMAT). Left lung mean dose was 9.73 ± 1.56 (FF-VMAT) and 9.61 ± 1.53 Gy (FFF-VMAT). Tumor control probability (TCP) was 99.68% ± 0.02% (FF-VMAT) and 99.67% ± 0.01% (FFF-VMAT) (P = 0.390). Uncomplicated TCP was 98.72% ± 0.02% (FF-VMAT) and 98.72% ± 0.01% (FFF-VMAT) (P = 0.508). Conclusion: The planning objective parameters achieved using FFF-based VMAT showed that FFF can also be used clinically to treat bilateral breast carcinomas and the low-dose lung volumes were still lesser with FFF-VMAT plans than FF-VMAT.
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Evaluation of optimal combination of planning parameters (Field width, pitch, and modulation factor) in helical tomotherapy for bilateral breast cancer p. 234
CA Muthuselvi, TK Bijina, A Pichandi
DOI:10.4103/jmp.JMP_31_20  
Aim: The aim of the study was to find the most balanced plan with an optimal combination of planning parameters in helical tomotherapy (HT) for bilateral breast irradiation by evaluating dosimetric indices and time factors. In particular, we investigated the best combination of field width (FW), pitch, and modulation factor (MF). Materials and Methods: A total of 90 plans (18 plans for each patient) was created in this study, with different combination of planning parameters (FW: 2.5 cm [F1] and 5 cm [F2]; pitch: 0.215 [P1], 0.287 [P2], and 0.43 [P3]; and MF: 2.0 [M1], 2.5 [M2], and 3.0 [M3]). Plans were analyzed using several dosimetric indices: homogeneity index, conformity index, dose near minimum D98%, dose near maximum D2%, and the coverage by D95% of the target. Organ at risk (OAR) doses were evaluated by mean dose, V5Gy and V25Gy for the heart and mean dose V5Gy and V20Gy for both the lungs. Treatment time was also reported for all plans. Results: Reducing FW from 5 cm to 2.5 cm increased the treatment time by 40%–50% and improved homogeneity of the target. Tightening the pitch value from 0.43 to 0.215 improved target as well as OAR doses without increasing the treatment time. Increasing MF from 2 to 3 improved all the dosimetric indices and also increased treatment time. Conclusions: On the basis of our analysis, a plan with FW 5 cm, pitch 0.215, and MF 2.5 can be considered as an optimal combination of planning parameters for bilateral breast irradiation in HT technique.
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Assessment of single- and double-strand breaks in DNA induced by auger electrons of radioisotopes used in diagnostic and therapeutic applications p. 240
Mahdi Seifi Moradi, Babak Shirani Bidabadi
DOI:10.4103/jmp.JMP_79_19  
Introduction: Most of the radionuclides that are used for diagnostic purposes emit Auger electrons and can thus cause damage to the DNA molecule on a nanometer scale. Therefore, the nanodosimetric calculation of these radioisotopes is necessary to achieve better understanding on their effects. Aim: The aim of this study was to calculate the mean number of DNA strand breaks (single-strand breaks and double-strand breaks) caused by direct and indirect effects for six widely used Auger electron-emitting diagnostic radioisotopes, including 123I, 125I, 99mTc, 67Ga, 201Tl, 111In and two therapeutic radioisotopes of 131I(beta + Auger + CK emitter) and 211At(alpha + Auger + CK emitter). Materials and Methods: Geant4-DNA simulation tool was used to evaluate the effects of Auger electrons, beta and alpha particles of these radioisotopes on DNA molecules. Two different DNA molecule geometric models were simulated and the results of these two models were compared with each other as well as with the results of previous studies. Results and Conclusion: The results showed that the geometric shape of the sugar-phosphate groups may have a significant effect on the number of single-strand breaks (SSBs) and double-strand breaks (DSBs) of the DNA molecule. Among the most widely used diagnostic radioisotopes, 201Tl and 125I, had the greatest impact on the number of SSBs and DSBs, respectively, while therapeutic radioisotope of 131I almost had no effect, therapeutic radioisotope of 211At had the moderate effect on the number of breaks in the DNA chain.
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Texture analysis on ultrasound: The effect of time gain compensation on histogram metrics and gray-level matrices p. 249
Giulio Vara, Arianna Rustici, Andrea Sechi, Cristina Mosconi, Vincenzo Lucidi, Rita Golfieri
DOI:10.4103/jmp.JMP_82_20  
Aims: Texture analysis (TA) is becoming an increasingly used tool in radiological research. Some papers have been published on its use in ultrasound (US), but the way in which the machine settings affect the features has not yet been fully explored. With this research, we analyze how the time gain compensation (TGC) influences the features of the gray-level matrices in the abdominal US setting. Subjects and Methods: We analyzed the images acquired from the hepatorenal acoustic window of a healthy 29-year-old volunteer acquired with different TGC settings. TA was carried out using the LifeX software. Results: Several both 1st and 2nd order gray-level matrices features showed a strong correlation with TGC settings. Conclusions: TGC settings must be accounted for when carrying out further TA studies.
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TECHNICAL NOTE Top

Effect of three-dimensional detector orientation on small-field output factors p. 256
Zakithi Lungile Mpumelelo Msimang, Debbie Van Der Merwe, Nkosingiphile Maphumulo
DOI:10.4103/jmp.JMP_50_20  
The IAEA TRS 483 has recommended that the orientation for cylindrical ionization chambers be perpendicular to the beam for small-field output factor (OF) measurements. The recommendation was based on the unavailability of field output correction factor data for measurements using parallel orientation at the time of publication. Two three-dimensional (3D) air ionization chambers were used to perform measurements in parallel and perpendicular orientations and compared to data determined using a PTW 31018. The aim of the study was to establish whether the 3D detectors behaved as spherical or cylindrical devices. From the results, it was confirmed that the PTW 31016 and PTW 31021 detectors are suitable for OF measurements in both orientations for field sizes down to an equivalent square field of 1.8 cm and 0.96 cm, respectively, using the field output correction factor data published in the IAEA TRS 483. The preferred orientation is parallel to the beam to facilitate beam profile measurements and minimize the irradiation of the chamber stem and detector cable and decrease the volume averaging factor.
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BOOK REVIEW Top

The computed tomography handbook: Optimizing Protocols for Todays' feature-rich scanners p. 261
Roshan Samuel Livingstone
DOI:10.4103/jmp.JMP_112_20  
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