Journal of Medical Physics
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   2016| July-September  | Volume 41 | Issue 3  
    Online since August 30, 2016

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Dosimetric and radiobiological characterizations of prostate intensity-modulated radiotherapy and volumetric-modulated arc therapy: A single-institution review of ninety cases
Muhammad Isa Khan, Runqing Jiang, Alexander Kiciak, Jalil ur Rehman, Muhammad Afzal, James C.L. Chow
July-September 2016, 41(3):162-168
DOI:10.4103/0971-6203.189479  PMID:27651562
This study reviewed prostate volumetric-modulated arc therapy (VMAT) plans with intensity-modulated radiotherapy (IMRT) plans after prostate IMRT technique was replaced by VMAT in an institution. Characterizations of dosimetry and radiobiological variation in prostate were determined based on treatment plans of 40 prostate IMRT patients (planning target volume = 77.8-335 cm 3 ) and 50 VMAT patients (planning target volume = 120-351 cm 3 ) treated before and after 2013, respectively. Both IMRT and VMAT plans used the same dose-volume criteria in the inverse planning optimization. Dose-volume histogram, mean doses of target and normal tissues (rectum, bladder and femoral heads), dose-volume points (D 99% of planning target volume; D 30% , D 50% , V 30 Gy and V 35 Gy of rectum and bladder; D 5% , V 14 Gy , V 22 Gy of femoral heads), conformity index (CI), homogeneity index (HI), gradient index (GI), prostate tumor control probability (TCP), and rectal normal tissue complication probability (NTCP) based on the Lyman-Burman-Kutcher algorithm were calculated for each IMRT and VMAT plan. From our results, VMAT plan was found better due to its higher (1.05%) CI, lower (0.83%) HI and (0.75%) GI than IMRT. Comparing doses in normal tissues between IMRT and VMAT, it was found that IMRT mostly delivered higher doses of about 1.05% to the normal tissues than VMAT. Prostate TCP and rectal NTCP were found increased (1%) for VMAT than IMRT. It is seen that VMAT technique can decrease the dose-volume evaluation criteria for the normal tissues. Based on our dosimetric and radiobiological results in treatment plans, it is concluded that our VMAT implementation could produce comparable or slightly better target coverage and normal tissue sparing with a faster treatment time in prostate radiotherapy.
  2,056 161 -
Radioprotective effects of hesperidin on oxidative damages and histopathological changes induced by X-irradiation in rats heart tissue
Abolhasan Rezaeyan, Gholam Hassan Haddadi, Massood Hosseinzadeh, Maryam Moradi, Masoud Najafi
July-September 2016, 41(3):182-191
DOI:10.4103/0971-6203.189482  PMID:27651565
This study was carried out to evaluate radioprotective effects of hesperidin (HES) administration before the irradiation on the cardiac oxidative stress and histopathological changes in an experimental rat model. The cardiovascular complications of radiation exposure cause morbidity and mortality in patients who received radiotherapy. HES, an antioxidant flavonoid found in citrus fruits, suggests the protection against the tissue damage. Fifty-eight rats were divided into four groups: Group 1 received phosphate buffered saline (PBS) and sham radiation; Group 2, HES and sham radiation; Group 3, PBS and radiation; and Group 4, HES and radiation. The rats were exposed to single dose of 18 Gy of 6 MV X-ray. One hundred milligrams per kilogram doses of HES was administered for 7 days before irradiation. The estimation of superoxide dismutase (SOD), malondialdehyde (MDA), and histopathological analyses was performed at 24 h and 8 weeks after radiation exposure. The irradiation of chest area resulted in an elevated MDA level and decreased SOD activity. Moreover, long-term pathological lesions of radiation were inflammation, fibrosis, the increased number of mast cells and macrophages, and development of plaque, vascular leakage, myocardial degeneration, and myocyte necrosis. Although the administration of HES decreases inflammation, fibrosis, mast cell and macrophage numbers, and myocyte necrosis, it did not result in reduced thrombus, myocardium degeneration, and vascular leakage. In conclusion, these results suggest that HES can perform a radioprotection action. The protective effect of HES may be attributable to its immunomodulatory effects and free radical-scavenging properties.
  1,780 119 -
Gamma Putty dosimetric studies in electron beam
Aime M Gloi
July-September 2016, 41(3):169-176
DOI:10.4103/0971-6203.189480  PMID:27651563
Traditionally, lead has been used for field shaping in megavoltage electron beams in radiation therapy. In this study, we analyze the dosimetric parameters of a nontoxic, high atomic number (Z = 83), bismuth-loaded material called Gamma Putty that is malleable and can be easily molded to any desired shape. First, we placed an ionization chamber at different depths in a solid water phantom under a Gamma Putty shield of thickness (t = 0, 3, 5, 10, 15, 20, and 25 mm, respectively) and measured the ionizing radiation on the central axis (CAX) for electron beam ranging in energies from 6 to 20 MeV. Next, we investigated the relationship between the relative ionization (RI) measured at a fixed depth for several Gamma Putty shield at different cutout diameters ranging from 2 to 5 cm for various beam energies and derived an exponential fitting equation for clinical purposes. The dose profiles along the CAX show that bremsstrahlung dominates for Gamma Putty thickness >15 mm. For high-energy beams (12-20 MeV) and all Gamma Putty thicknesses up to 25 mm, RI below 5% could not be achieved due to the strong bremsstrahlung component. However, Gamma Putty is a very suitable material for reducing the transmission factor below 5% and protecting underlying normal tissues for low-energy electron beams (6-9 MeV).
  1,558 130 -
Analysis of dose distribution in organs at risk in patients with prostate cancer treated with the intensity-modulated radiation therapy and arc technique
Michal Biegala, Adam Hydzik
July-September 2016, 41(3):198-204
DOI:10.4103/0971-6203.189490  PMID:27651567
This study describes a comparative analysis of treatment plans in 48 patients with prostate cancer treated with ionizing radiation. Each patient was subjected to the intensity-modulated radiation therapy (IMRT) and arc technique. In each treatment plan, the organs at risk were assessed: the urinary bladder, rectum and heads of the femur, as well as the volume of normal tissue. The following features were compared: treatment time, conformity indices for the planning target volume, mean doses and standard deviation in organs at risk, and organ volumes for each particular dose. The treatment period in the arc technique is 13.7% shorter than in the IMRT technique. Comparing the results of the IMRT and arc techniques (arc vs. IMRT), the mean values were 29.21 ± 12.91 Gy versus 28.36 ± 13.79 Gy for the bladder, 20.36 ± 3.16 Gy versus 18.17 ± 5.11 Gy for the right femoral head, and 18.98 ± 3.28 Gy versus 16.67 ± 5.15 Gy for the left femoral head. For the rectum, lower values were obtained after application of the arc technique, not the IMRT technique: 35.84 ± 12.28 Gy versus 35.90 ± 13.05 Gy. The results indicate that the applied therapy has a statistically significant influence on the volume for a particular dose with regard to the urinary bladder. It is advisable to apply the IMRT technique to patients who need the femur heads and urinary bladder protected by exposing them to low irradiation doses.
  1,533 118 -
Medical physics aspects in accreditation of radiation oncology practice
Surendra Nath Rustgi
July-September 2016, 41(3):157-161
DOI:10.4103/0971-6203.189452  PMID:27651561
  1,416 143 -
Comparative study of old and new versions of treatment planning system using dose volume histogram indices of clinical plans
Gangarapu Sri Krishna, Vuppu Srinivas, KM Ayyangar, Palreddy Yadagiri Reddy
July-September 2016, 41(3):192-197
DOI:10.4103/0971-6203.189489  PMID:27651566
Recently, Eclipse treatment planning system (TPS) version 8.8 was upgraded to the latest version 13.6. It is customary that the vendor gives training on how to upgrade the existing software to the new version. However, the customer is provided less inner details about changes in the new software version. According to manufacturer, accuracy of point dose calculations and irregular treatment planning is better in the new version (13.6) compared to the old version (8.8). Furthermore, the new version uses voxel-based calculations while the earlier version used point dose calculations. Major difference in intensity-modulated radiation therapy (IMRT) plans was observed between the two versions after re-optimization and re-calculations. However, minor difference was observed for IMRT cases after performing only re-calculations. It is recommended TPS quality assurance to be performed after any major upgrade of software. This can be done by performing dose calculation comparisons in TPS. To assess the difference between the versions, 25 clinical cases from the old version were compared keeping all the patient data intact including the monitor units and comparing the differences in dose calculations using dose volume histogram (DVH) analysis. Along with DVH analysis, uniformity index, conformity index, homogeneity index, and dose spillage index were also compared for both versions. The results of comparative study are presented in this paper.
  1,395 129 -
Measurement of eye lens dose for Varian On-Board Imaging with different cone-beam computed tomography acquisition techniques
Sudesh Deshpande, Deepak Dhote, Kalpna Thakur, Amol Pawar, Rajesh Kumar, Munish Kumar, MS Kulkarni, SD Sharma, V Kannan
July-September 2016, 41(3):177-181
DOI:10.4103/0971-6203.189481  PMID:27651564
The objective of this work was to measure patient eye lens dose for different cone-beam computed tomography (CBCT) acquisition protocols of Varian's On-Board Imaging (OBI) system using optically stimulated luminescence dosimeter (OSLD) and to study the variation in eye lens dose with patient geometry and distance of isocenter to the eye lens. During the experimental measurements, OSLD was placed on the patient between the eyebrows of both eyes in line of nose during CBCT image acquisition to measure eye lens doses. The eye lens dose measurements were carried out for three different cone-beam acquisition protocols (standard dose head, low-dose head [LDH], and high-quality head [HQH]) of Varian OBI. Measured doses were correlated with patient geometry and distance between isocenter and eye lens. Measured eye lens doses for standard head and HQH protocols were in the range of 1.8-3.2 mGy and 4.5-9.9 mGy, respectively. However, the measured eye lens dose for the LDH protocol was in the range of 0.3-0.7 mGy. The measured data indicate that eye lens dose to patient depends on the selected imaging protocol. It was also observed that eye lens dose does not depend on patient geometry but strongly depends on distance between eye lens and treatment field isocenter. However, undoubted advantages of imaging system should not be counterbalanced by inappropriate selection of imaging protocol, especially for very intense imaging protocol.
  1,238 134 -
Radiological risk assessment of cosmic radiation at aviation altitudes (a trip from Houston Intercontinental Airport to Lagos International Airport)
Paschal Ikenna Enyinna
July-September 2016, 41(3):205-209
DOI:10.4103/0971-6203.189491  PMID:27651568
Radiological risk parameters associated with aircrew members traveling from Houston Intercontinental Airport to Lagos International Airport have been computed using computer software called EPCARD (version 3.2). The mean annual effective dose of radiation was computed to be 2.94 mSv/year. This result is above the standard permissible limit of 1 mSv/year set for the public and pregnant aircrew members but below the limit set for occupationally exposed workers. The Risk of cancer mortality and excess career time cancer risk computed ranged from 3.5 × 10−5 to 24.5 × 10−5 (with average of 14.7 × 10−5 ) and 7 × 10−4 to 49 × 10−4 (with average of 29.4 × 10−4 ). Passengers and aircrew members should be aware of the extra cosmic radiation doses taken in during flights. All aircraft operators should monitor radiation doses incurred during aviation trips.
  1,090 117 -
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