Journal of Medical Physics
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   Table of Contents - Current issue
January-March 2021
Volume 46 | Issue 1
Page Nos. 1-57

Online since Wednesday, May 5, 2021

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Use of a checklist approach on a telecobalt in an attempt to reduce human errors in radiotherapy delivery and improve therapeutic ratio Highly accessed article p. 1
Hari Mukundan, Sankalp Singh, Nishant Lohia, Manoj Kumar Semwal, Vijendra Kumar, Sharad Bhatnagar, Arti Sarin, Gaurav Trivedi
Background: The process of radiotherapy treatment planning and delivery involves multiple steps and professionals causing it to be prone to errors. Radiotherapy centers equipped with old telecobalt machines have certain peculiar challenges to workflow. We designed and tested a checklist for radiotherapy technicians (RTTs) to reduce chances of error during treatment delivery on a telecobalt machine. Materials and Methods: A physical checklist was designed for RTTs to use in the pretreatment pause using a template advocated by the American Association of Physicists in Medicine. It was tested on 4 RTTs over 1000 radiotherapy delivery sittings. Results: The checklist helped to rectify 41 documentary lapses and 28 errors in radiotherapy treatment parameters while also identifying 12 instances where treatment plan modifications were due and 30 where the patient was due for review by the radiation oncologist. The average time to go through the checklist was between 2.5 and 3 min. Conclusions: The development and use of the checklist has helped in reducing errors and also improving workflow in our department. It is recommended to utilize such physical checklists in all radiotherapy centers with telecobalt machines. The success of the checklist depends upon leadership, teamwork, acceptance of a need to inculcate a “safety culture,” with voluntary error-reporting and a willingness to learn from such errors.
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Dosimetric evaluation of simplified knowledge-based plan with an extensive stepping validation approach in volumetric-modulated arc therapy-stereotactic body radiotherapy for lung cancer Highly accessed article p. 7
Yutaro Wada, Hajime Monzen, Mikoto Tamura, Masakazu Otsuka, Masahiro Inada, Kazuki Ishikawa, Hiroshi Doi, Kiyoshi Nakamatsu, Yasumasa Nishimura
Purpose: We investigated the performance of the simplified knowledge-based plans (KBPs) in stereotactic body radiotherapy (SBRT) with volumetric-modulated arc therapy (VMAT) for lung cancer. Materials and Methods: For 50 cases who underwent SBRT, only three structures were registered into knowledge-based model: total lung, spinal cord, and planning target volume. We performed single auto-optimization on VMAT plans in two steps: 19 cases used for the model training (closed-loop validation) and 16 new cases outside of training set (open-loop validation) for TrueBeam (TB) and Halcyon (Hal) linacs. The dosimetric parameters were compared between clinical plans (CLPs) and KBPs: CLPclosed, KBPclosed-TB and KBPclosed-Hal in closed-loop validation, CLPopen, KBPopen-TB and KBPopen-Hal in open-loop validation. Results: All organs at risk were comparable between CLPs and KBPs except for contralateral lung: V5 of KBPs was approximately 3%–7% higher than that of CLPs. V20 of total lung for KBPs showed comparable to CLPs; CLPclosed vs. KBPclosed-TB and CLPclosed vs. KBPclosed-Hal: 4.36% ± 2.87% vs. 3.54% ± 1.95% and 4.36 ± 2.87% vs. 3.54% ± 1.94% (P = 0.54 and 0.54); CLPopen vs. KBPopen-TB and CLPopen vs. KBPopen-Hal: 4.18% ± 1.57% vs. 3.55% ± 1.27% and 4.18% ± 1.57% vs. 3.67% ± 1.26% (P = 0.19 and 0.27). CI95 of KBPs with both linacs was superior to that of the CLP in closed-loop validation: CLPclosed vs. KBPclosed-TB vs. KBPclosed-Hal: 1.32% ± 0.12% vs. 1.18% ± 0.09% vs. 1.17% ± 0.06% (P < 0.01); and open-loop validation: CLPopen vs. KBPopen-TB vs. KBPopen-Hal: 1.22% ± 0.09% vs. 1.14% ± 0.04% vs. 1.16% ± 0.05% (P ≤ 0.01). Conclusions: The simplified KBPs with limited number of structures and without planner intervention were clinically acceptable in the dosimetric parameters for lung VMAT-SBRT planning.
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Dosimetric comparison of robotic and linear accelerator multi-leaf collimator-based stereotactic radiosurgery for arteriovenous malformation p. 16
Venkatesan Kaliyaperumal, Susan Abraham, Maragatha Veni, Susovan Banerjee, S Tamilselvan, Deepak Gupta, K Dayanithi, D Manigandan, Saumyaranjan Mishra, Shyam Singh Bisht, Tejinder Kataria
Purpose: To investigate the dosimetric comparison of different collimators which are used in robotic radiosurgery (cyberknife-CK) and linear accelerator (LINAC) for stereotactic radiosurgery (SRS) in arteriovenous malformation (AVM). Materials and Methods: Twenty-five AVM patients were planned in CK using FIXED cone, IRIS collimator, and multi-leaf collimator (MLC) based in LINAC. Dosimetric comparison was performed using Paddick conformity index (CIPaddick) and International Commission on Radiation Units and measurements (ICRU) homogeneity index (HIICRU), gradient score (GS), normal brain dose received by 10cc (D10cc) and critical structure (brain stem, optic chiasma, optic nerves) doses. Paired sample t-test was used for statistical analysis. Results: Mean treatment volume was 3.16cc (standard deviation ± 4.91cc). No significant deviation (P =0.45, 0.237 for FIXED vs. IRIS and FIXED vs. MLC, respectively) was found in target coverage. For CIPaddick, the mean difference (MD) between FIXED- and MLC-based plans was 0.16(P = 0.001); For HIICRU, difference between FIXED and IRIS was insignificant (0.5, P = 0.823); but, when FIXED versus MLC, the deviation was 7.99% (P = 0.002). In FIXED- and MLC-based plans, significant difference was found in GS70 and GS40 (P < 0.041 and 0.005, respectively). MD between FIXED- and MLC-based plans for normal brain for 5Gy, 10Gy, 12Gy, and 20Gy were 36.08cc (P = 0.009), 7.12cc (P = 0.000), 5.84cc (P = 0.000) and 1.56cc (P = 0.000), respectively. AVM volume <0.7cc should be treated with CK FIXED and >0.7cc were treated by using FIXED or IRIS collimators. AVM volume > 1.4cc can be treated by either LINAC MLC-based SRS or CK. Conclusion: Our study shows CK collimator (IRIS and FIXED) could be able to treat brain AVMs in any size. Linac MLC-based SRS has some limitations in terms of conformity and low-dose spillage, and advantages like reduced treatment time and MU.
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Probability distribution of pixel intensities of ebt3 films and its application in the correction of uncertainty budget p. 26
Rahul Kumar Chaudhary, Munir Pathan, Rajesh Kumar, SD Sharma, BK Sapra
Background and Aim: Modern radiotherapy modalities, such as Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy involve complex dose delivery. The dose delivery is complex as it involves beam modulation, hence, manual dose calculations for these techniques are not possible. Film dosimetry is commonly used method of dose verification for these modalities because of the advantages associated with it. The quantification of uncertainty associated with a film dosimetry system under clinical use becomes important for accurate dosimetry. The spread in the distribution of the pixel values (PV) of the irradiated film contributes to the uncertainty. The probability distribution (PD) of the PV was studied for the clinical photon beam energies of 6, 10, and 15 MV. Methods and Materials: Gafchromic EBT3 film and EPSON 10000XL flatbed scanner were used for this purpose and using the resulting PD, the uncertainty budgets for these energies in the red, green and blue color channels were estimated. Results: The PV of exposed films for the energies studied follows t-distribution, the sum of the squares of the deviation of the measured data from the fitted value was of the order of 10−7, this indicates the goodness of fit. The “t” value corrected combined standard uncertainty (CSU) at 1σ confidence level for exposed film and dose measurement at 200 cGy were 1.42%, 1.48%, and 1.63% and 1.99%, 3.23%, and 5.08% for 6, 10, and 15 MV energies, respectively, in the red colour channel. Conclusion: In the case of the limited number of measurements of a quantity, the SU values must be corrected using the “t” value to get the correct CSU.
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Establishment and dissemination of radiological standards in the field of diagnostic radiology in India p. 33
Vinatha Sumanth Panyam, Sougata Rakshit, Sanjay Daga Dhole, Bhushankumar Jagnnath Patil, Amaren Prasanna Das, Greeshma Anantharaman Kossery, Sathian Vilippalil, Probal Chaudhury
Background: The increased use of ionizing radiation for diagnostic purpose has resulted in an increase in the world population dose. Patient dosimetry in X-ray diagnostic radiology is required to establish diagnostic reference levels (DRLs) and to assess the average dose received by organs and tissues. International bodies have recommended DRLs to be based on dosimetric quantities. Aim: To cater to the increased requirement for dosimetry in diagnostic radiology, international guidelines are provided to establish and disseminate traceable calibration for dosimeters used in X-ray diagnostic radiology. X-ray diagnostic beams established are standardized using a diagnostic range free-air ionization chamber (DFAIC) (20-150 kV). Materials and Methods: Characterization of the DFAIC and determination of the correction factors for the air kerma measurements were evaluated experimentally and by theoretical calculations. Results: The paper details the establishment of 18 diagnostic beam qualities using DFAIC along with the associated uncertainties. The overall uncertainty for the air kerma measurements was within ±0.5% at 1 sigma level. Eight diagnostic range air kerma measurements using DFAIC were compared with the medium energy primary standard FAIC (50–300 kV) maintained in the laboratory. Conclusion: The air kerma rates agreed within ±1% and are within the overall standard uncertainty of both the chambers at the time of the comparison. Dissemination to the users in the field of diagnostic radiology in the country has been carried out by calibrating their ionization chambers and solid-state detector-based instruments against the DFAIC. The methodology followed to standardize the beams using DFAIC and calibration of dosimeters is presented in this work.
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Use of multiple-tube phantom: A method to globally correct native T1 relaxation time inhomogeneity in dedicated molecular magnetic resonance breast coil p. 41
Pradeep Singh Negi, Shashi Bhushan Mehta, Amarnath Jena
Background: Native T1 relaxation time (T10) presents an important prerequisite to reliably quantify pharmacokinetic parameter like Ktrans (volume transfer constant). Native T1 value can be varied because of the inhomogeneity in the breast coil, thus influencing the Ktrans measurement. Purpose: The current study aims to design and use a phantom with multiple tubes for both breast cuffs to assess native T1 inhomogeneity across the dedicated molecular magnetic resonance (mMR) breast coil and adopt corrective method to spatially normalize T1 values to improve homogeneity. Materials and Methods: Two phantoms with multiple tubes (19 tubes) specially designed and filled with contrast medium with known T1 value were placed in each mMR breast coil cuff. Native T1 at various spatial locations was calculated applying dual flip angle sequence. Correction factors were derived at various spatial locations as a function of deviation of the native T1 value from phantom and applied to correct the native T1 relaxation time. Results: A statistically significant difference between native T1 values of the right and left anterior (P = 0.0095), middle (P = 0.0081), and posterior (P = 0.0004) parts of the breast coil. No significant difference was seen in the corrected T1 values between anterior (P = 0.402), middle (P = 0.305), and posterior (P = 0.349) aspects of both sides of the breast coil. Conclusion: Inhomogeneity in the native T1 value exists in dedicated mMR breast coil, and significant improvement can be achieved using specially designed external phantom with multiple tubes.
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Repeatability of small field output factor measurements with various detectors p. 47
Zakithi Lungile Mpumelelo Msimang, Debbie van der Merwe, Nkosingiphile Maphumulo
There are well established dosimetry reference standards for broad beams; however, there are no reference standards that can be used for both broad and small fields. The variation of the equivalent square fields and field output factors in small static photon fields when using a synthetic diamond, an electron diode, and ionization chambers (pin point, semiflex, and liquid filled) was investigated over time. Data from this study were compared to the data from other hospitals in the country and standard data sets, i.e., the British Journal of Radiology Supplement No. 25 of 1996 (BJR25) and the Radiological Physics Centre (RPC) 2012 data. The results showed that reliance on one detector and one measurement session, could yield incorrect field output factors (FOFs) for small fields. At least one of the detectors should be a solid state type with published field output correction factors and at least three measurement sessions should be performed for each FOF data point. Comparing measured data with published datasets, like RPC, will assist in verifying data. BJR25 datasets should not be used for Sclin ≤4 cm.
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Role of LQ model to address effect of missed treatment days in external-beam radiotherapy p. 52
Ramamoorthy Ravichandran, Tarani Mondal, Bandana Barman, Gopal Datta, Ravi Kannan
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Book review of the modern technology of radiation oncology (Volume 4): A compendium for medical physicists and radiation oncologists for the Journal of Medical Physics p. 55
Rajesh A Kinhikar
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