Journal of Medical Physics
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   2018| January-March  | Volume 43 | Issue 1  
    Online since March 12, 2018

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A treatment planning method for better management of radiation-induced oral mucositis in locally advanced head and neck cancer
Hao Howard Zhang, Warren D D'Souza
January-March 2018, 43(1):9-15
DOI:10.4103/jmp.JMP_78_17  PMID:29628628
Purpose/Aim: To describe a two-phase intensity-modulated radiation therapy (IMRT) treatment planning approach, that is, promising for reduction of oral mucositis risk in locally advanced head-and-neck cancer. Materials and Methods: Ten locally advanced head-and-neck cancer patients who underwent RT were retrospectively collected. Conventional IMRT and volumetric-modulated arc therapy (VMAT) plans were generated for these patients following clinical protocol. Following the first phase of generating conventional IMRT plans, our approach utilized data from Monte Carlo-based kernel superposition dose calculations corresponding to beam apertures (generated from the conventional IMRT plans) and used an exact mathematical programming-based optimization approach applying linear programming (LP) to dose optimization in the second phase. Results: Compared with conventional IMRT and VMAT treatment plans, our novel method achieved better preservation of oral cavity (16%–29% lower mean dose, P < 0.01), parotid glands (6%–17% lower mean dose, P < 0.04), and spinal cord (3-11 Gy lower maximum dose, P < 0.03) and lower doses to nonorgan-at-risk/nontarget normal tissues, with the same or better target coverage. Conclusions: Our LP-based method can be practically implemented in routine clinical use with a goal of limiting radiation-induced oral mucositis for head-and-neck cancer patients.
  1,551 153 -
Monte carlo investigation of photon beam characteristics and its variation with incident electron beam parameters for indigenous medical linear accelerator
Subhalaxmi Mishra, PK Dixit, T Palani Selvam, Sanket S Yavalkar, DD Deshpande
January-March 2018, 43(1):1-8
DOI:10.4103/jmp.JMP_125_17  PMID:29628627
Purpose: A Monte Carlo model of a 6 MV medical linear accelerator (linac) unit built indigenously was developed using the BEAMnrc user code of the EGSnrc code system. The model was benchmarked against the measurements. Monte Carlo simulations were carried out for different incident electron beam parameters in the study. Materials and Methods: Simulation of indigenously developed linac unit has been carried out using the Monte Carlo based BEAMnrc user-code of the EGSnrc code system. Using the model, percentage depth dose (PDD), and lateral dose profiles were studied using the DOSXYZnrc user code. To identify appropriate electron parameters, three different distributions of electron beam intensity were investigated. For each case, the kinetic energy of the incident electron was varied from 6 to 6.5 MeV (0.1 MeV increment). The calculated dose data were compared against the measurements using the PTW, Germany make RFA dosimetric system (water tank MP3-M and 0.125 cm3 ion chamber). Results: The best fit of incident electron beam parameter was found for the combination of beam energy of 6.2 MeV and circular Gaussian distributed source in X and Y with FWHM of 1.0 mm. PDD and beam profiles (along both X and Y directions) were calculated for the field sizes from 5 cm × 5 cm to 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 2%. Conclusions: A Monte Carlo model of indigenous linac (6 MV) has been developed and benchmarked against the measured data.
  1,212 180 -
Comparison of volumetric modulated arc therapy and intensity modulated radiation therapy for whole brain hippocampal sparing treatment plans based on radiobiological modeling
Ethan Kendall, Ozer Algan, Salahuddin Ahmad
January-March 2018, 43(1):16-22
DOI:10.4103/jmp.JMP_85_17  PMID:29628629
Introduction: In this article, we report the results of our investigation on comparison of radiobiological aspects of treatment plans with linear accelerator-based intensity-modulated radiation therapy and volumetric-modulated arc therapy for patients having hippocampal avoidance whole-brain radiation therapy. Materials and Methods: In this retrospective study using the dose-volume histogram, we calculated and compared biophysical indices of equivalent uniform dose, tumor control probability, and normal tissue complication probability (NTCP) for 15 whole-brain radiotherapy patients. Results and Discussions: Dose-response models for tumors and critical structures were separated into two groups: mechanistic and empirical. Mechanistic models formulate mathematically with describable relationships while empirical models fit data through empirical observations to appropriately determine parameters giving results agreeable to those given by mechanistic models. Conclusions: Techniques applied in this manuscript could be applied to any other organs or types of cancer to evaluate treatment plans based on radiobiological modeling.
  1,198 131 -
Dosimetric comparison of treatment plans using physical wedge and enhanced dynamic wedge for the planning of breast radiotherapy
Zhenia Gopalakrishnan, Raghuram K Nair, P Raghukumar, B Sarin
January-March 2018, 43(1):46-51
DOI:10.4103/jmp.JMP_40_17  PMID:29628633
The aim of this study is to compare the physical wedge (PW) with enhanced dynamic wedge (EDW) to determine the difference in the dose distribution affecting the treated breast and the contralateral breast, lungs, heart, esophagus, spine, and surrounding skin in the radiotherapy of breast cancer. Computed tomography (CT) data sets of 30 breast cancer patients were selected from the database for the study. The treatment plans which were executed with PW were re-planned with EDW without changing the beam parameters. Keeping the wedge angles same, the analytic anisotropic algorithm (AAA) with heterogeneity correction was used for dose calculation in all plans. The prescription was 50 Gy in 25 fractions. The dose- volume histogram (DVH) of the planning target volume (PTV) and critical structures of both PW and EDW plans were analyzed. The analysis showed that the maximum dose within the target volume is higher in EDW plan compared to PW plan. However the PTV conformity index (CI) remained the same in both plans. For all the critical structures, the EDW technique offered less dose compared to PW technique. The effect of volume of the contralateral breast on the dose to contralateral breast and the effect of volume of PTV breast for patients with carcinoma left breast on the dose to heart were studied and analyzed for the two wedges. No correlation between volumes and dose parameters was found for the two techniques. The number of monitor units to deliver a particular dose with EDW field is less than that of PW field due to change in wedge factor. As EDW produces less scattered dose to structures outside the treatment field, the risk of a second malignancy can be reduced with this technique.
  952 121 -
Dosimetric and radiobiological evaluation of patient setup accuracy in head-and-neck radiotherapy using daily computed tomography-on-rails-based corrections
Ines-Ana Jurkovic, Esengul Kocak-Uzel, Abdallah Sherif Radwan Mohamed, Eleftherios Lavdas, Sotirios Stathakis, Nikos Papanikolaou, David C Fuller, Panayiotis Mavroidis
January-March 2018, 43(1):28-40
DOI:10.4103/jmp.JMP_113_17  PMID:29628631
Introduction: This study evaluates treatment plans aiming at determining the expected impact of daily patient setup corrections on the delivered dose distribution and plan parameters in head-and-neck radiotherapy. Materials and Methods: In this study, 10 head-and-neck cancer patients are evaluated. For the evaluation of daily changes of the patient internal anatomy, image-guided radiation therapy based on computed tomography (CT)-on-rails was used. The daily-acquired CT-on-rails images were deformedly registered to the CT scan that was used during treatment planning. Two approaches were used during data analysis (“cascade” and “one-to-all”). The dosimetric and radiobiological differences of the dose distributions with and without patient setup correction were calculated. The evaluation is performed using dose–volume histograms; the biologically effective uniform dose ([INSIDE:1]) and the complication-free tumor control probability (P+) were also calculated. The dose–response curves of each target and organ at risk (OAR), as well as the corresponding P+ curves, were calculated. Results: The average difference for the “one-to-all” case is 0.6 ± 1.8 Gy and for the “cascade” case is 0.5 ± 1.8 Gy. The value of P+ was lowest for the cascade case (in 80% of the patients). Discussion: Overall, the lowest PIis observed in the one-to-all cases. Dosimetrically, CT-on-rails data are not worse or better than the planned data. Conclusions: The differences between the evaluated “one-to-all” and “cascade” dose distributions were small. Although the differences of those doses against the “planned” dose distributions were small for the majority of the patients, they were large for given patients at risk and OAR.
  635 111 -
Safety, security and regulations in handling radiation sources
Bhuwan Chandra Bhatt
January-March 2018, 43(1):66-68
  642 101 -
Interfraction variations in organ filling and their impact on dosimetry in CT image based hdr intracavitary brachytherapy
Ramya Rangarajan
January-March 2018, 43(1):23-27
DOI:10.4103/jmp.JMP_90_17  PMID:29628630
Aim: Since anatomical and geometric variations occur with every fraction, planning, and dose optimization is necessary for every fraction of high-dose rate intracavitary brachytherapy of carcinoma cervix. In this study, we have tried to quantify the differences in doses to organs at risk (OAR) for each fraction of brachytherapy. Methods and Materials: One hundred and seventy computed tomography datasets of cervical cancer patients receiving intracavitary brachytherapy at our institution between January and April 2015 were analyzed. The volumes of the high-risk clinical target volume and OAR contoured were recorded for every insertion. Dose-volume histograms were generated and D90 and D100CTV and D0.1, D1, and D2cc were recorded for bladder, rectum, and sigmoid for each insertion. Results: Sixty-one percent had a decrease in bladder volume in the second fraction, 35% had an increase in bladder volume and 4% had no change in bladder volume. There was a strong positive correlation between increase in volume and dose (D2cc), which was statistically significant, rs = 0.441, P = 0.013. Nearly 49.4% of patients had an increase in rectal volume during the second fraction. 45.9% had decrease in rectal volume during the second fraction. There was a positive correlation between the increase in volume and dose (D2cc), which was statistically significant, rs = 0.393, P = 0.010. About 63.5% of the patients had a decrease in sigmoid volume during the second fraction, whereas 30.6% had an increase in volume and 5.9% had no change in volume. Conclusion: First, this study emphasizes the importance of imaging and planning for every fraction of brachytherapy to quantify the exact doses to the target and OAR s. Second, it is important to follow a uniform bladder protocol for every fraction, and adequate bowel preparation is needed for every fraction to minimize the interfraction variations. Finally, it also opens the realm of an adaptive planning strategy in cervical cancers which are known for rapid tumor regression during radiotherapy.
  615 124 -
Dosimetric effect of jaw tracking in volumetric-modulated arc therapy
Sangutid Thongsawad, Chirasak Khamfongkhruea, Chirapha Tannanonta
January-March 2018, 43(1):52-57
DOI:10.4103/jmp.JMP_75_17  PMID:29628634
The aim of this study was to investigate the potential of jaw tracking with the volumetric-modulated arc therapy (VMAT) to reduce the normal tissue dose. Plans of nasopharynx, lung, and prostate cancers (10 plans for each) were used to perform VMAT with and without jaw tracking. The dose reduction was evaluated in terms of organ doses and integral doses. Organ-dose reduction with jaw tracking was statistically significant in the volume receiving a dose of 5 Gy (V5) of bladder, rectum, and lung, the volume receiving a dose of 10 Gy (V10) of bladder, rectum, and lung, and the mean dose of lung (P < 0.05). Integral-dose reduction with jaw tracking was statistically significant in almost all the treatment plans (P < 0.05). For organ-dose reduction, jaw tracking in VMAT plan was effective in reducing V5and V10. For integral-dose reduction, jaw tracking in VMAT plan is an efficient method for decreasing V5.
  624 111 -
Expression of Bax and Bcl2 genes in peripheral blood lymphocytes of patients with differentiated thyroid cancer
Zari Hamivand, Gholamhassan Haddadi, Reza Fardid
January-March 2018, 43(1):41-45
DOI:10.4103/jmp.JMP_104_17  PMID:29628632
Context: Thyroid cancer is the most common endocrine malignancy worldwide. Iodine-131 is used in the treatment of thyroid cancer with dosage of 100 mCi. In the medical applications of ionizing radiation besides the advantages such as diagnosis and treatment of diseases, the risks arising from exposure should be considered as well. Aims: The present study aimed to evaluate the changes in expression levels of apoptotic Bax and Bcl-2 and the ratio of Bax/Bcl-2, in the peripheral blood lymphocytes (PBLs) of patients with differentiated thyroid cancer (DTC). Settings and Design: This study was conducted on fifty thyroid cancer patients who had undergone surgery and were under treatment with 100 and 150 mCi doses. Subjects and Methods: Blood samples were taken from the patients, one before iodine treatment and another 48 h after therapy. Bax and Bcl-2 gene expression levels were measured by using real-time reverse transcriptase polymerase chain reaction. Statistical Analysis Used: The data were analyzed using one-way analysis of variance followed by samples t-test and independent samples t-test. Results: Significant changes were observed in the percentage of apoptotic cells, in groups, after radioiodine therapy compared with before treatment. The ratio of Bax/Bcl-2 in both groups showed a significant increase (P < 0.001). The relative expression level of Bax gene showed a significant increase in comparison with the control group. Conclusions: Iodine therapy reduced expression of Bcl-2 and a significant expression of Bax and finally increased the ratio of Bax/Bcl-2. Iodine therapy led to apoptosis in the PBLs of patients with DTC. Therefore, it can be suggested that this method can be useful for monitoring and detecting destructive effects of ionizing radiation in nuclear medicine patients.
  610 83 -
Bismuth-silicon and bismuth-polyurethane composite shields for breast protection in chest computed tomography examinations
Parinaz Mehnati, Mehran Arash, Parisa Akhlaghi
January-March 2018, 43(1):61-65
DOI:10.4103/jmp.JMP_74_17  PMID:29628636
The article aims at constructing protective composite shields for breasts in chest computed tomography and investigating the effects of applying these new bismuth composites on dose and image quality. Polyurethane and silicon with 5% of bismuth were fabricated as a protective shield. At first, their efficiency in attenuating the X-ray beam was investigated by calculating the total attenuation coefficients at diagnostic energy range. Then, a physical chest phantom was scanned without and with these shields at tube voltage of 120 kVp, and image parameters together with dose values were studied. The results showed that these two shields have great effects on attenuating the X-ray beam, especially for lower energies (<40 kV), and in average, the attenuation coefficients of bismuth-polyurethane composite are higher in this energy range. The maximum relative differences between the average Hounsfield units (HUs) and noises of images without and with shield for both composites in 13 regions of interest were 4.5% and 15.7%, respectively. Moreover, primary investigation confirmed the ability of both shields (especially polyurethane-bismuth composite) in dose reduction. Comparing these two composites regarding the amount of dose reduction, the changes in HU and noise, and attenuation coefficients in diagnostic energy range, it seems that polyurethane composite is more useful for dose reduction, especially for higher tube voltages.
  563 83 -
Brachytherapy localization radiographs with conventional diagnostic x-ray machine
Ramamoorthy Ravichandran, Bandana Barman, Purnendu Deb Roy, Gopal Datta, Ravi Kannan
January-March 2018, 43(1):58-60
DOI:10.4103/jmp.JMP_97_17  PMID:29628635
With conventional diagnostic X-ray machines with over couch X-ray tubes, it is not possible to obtain anteroposterior (AP) and lateral (Lat) radiographs without changing the posture of the patients. In an old 300 mA X-ray machine with a fluoroscopy screen (12.4 kg) (1995 model), by substituting the screen with suitable counterweight and making provision to take the hoist pillar up to the edge of the wall, we could get isocentric setup for a hospital stretcher kept near the chest stand. This setup provided acceptable AP–Lat radiographs for brachytherapy localization using “Perspex jig” (Nucletron, Netherlands) and field check radiographs in head and neck, esophagus patients for treatment planning.
  462 97 -
Dosimetric studies in image-guided adaptive brachytherapy in gynecological cancers: A journey to successful implementation
Christian Kirisits, Umesh Mahantshetty, Kari Tanderup
January-March 2018, 43(1):69-71
  446 111 -
Dosimetric evaluation and optimization of fractionated stereotactic radio-surgery
Arun Chougule
January-March 2018, 43(1):72-73
  368 125 -
Pratik Kumar
January-March 2018, 43(1):74-76
  310 81 -
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