Journal of Medical Physics
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  Citation statistics : Table of Contents
   2009| April-June  | Volume 34 | Issue 2  
    Online since June 6, 2009

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Has the time come for doing away with Cobalt-60 teletherapy for cancer treatments
R Ravichandran
April-June 2009, 34(2):63-65
DOI:10.4103/0971-6203.51931  PMID:20098538
  10 4,600 490
Skin dose estimation for various beam modifiers and source-to-surface distances for 6MV photons
Girigesh Yadav, RS Yadav, Alok Kumar
April-June 2009, 34(2):87-92
DOI:10.4103/0971-6203.51935  PMID:20098542
The purpose of this study was to learn the skin dose estimation for various beam modifiers at various source-to-surface distances (SSDs) for a 6 MV photon. Surface and buildup region doses were measured with an acrylic slab phantom and Markus 0.055 cc parallel plate (PP) ionization chamber. Measurements were carried out for open fields, motorized wedge fields, acrylic block tray fields ranging from 3 x 3 cm 2 to 30 x 30 cm 2 . Twenty-five percent of the field was blocked with a cerrobend block and a Multileaf collimator (MLC). The effect of the blocks on the skin dose was measured for a 20 x 20 cm 2 field size, at 80 cm, 100 cm and 120 cm SSD. During the use of isocentric treatments, whereby the tumor is positioned at 100 cm from the source, depending on the depth of the tumor and size of the patient, the SSD can vary from 80 cm to 100 cm. To achieve a larger field size, the SSD can also be extended up to 120 cm at times. The skin dose increased as field size increased. The skin dose for the open 10 x10 cm 2 field was 15.5%, 14.8% and 15.5% at 80 cm, 100 cm and 120 cm SSDs, respectively. The skin dose due to a motorized 60 0 wedge for the 10 x 10 cm 2 field was 9.9%, 9.5%, and 9.5% at 80 cm, 100 cm and 120 cm SSDs. The skin dose due to acrylic block tray, of thickness 1.0 cm for a 10 x 10 cm 2 field was 27.0%, 17.2% and 16.1% at 80, 100 and 120 cm SSD respectively. Due to the use of an acrylic block tray, the surface dose was increased for all field sizes at the above three SSDs and the percentage skin dose was more dominant at the lower SSD and larger field size. The skin dose for a 30 x 30 cm 2 field size at 80 cm SSD was 38.3% and it was 70.4% for the open and acrylic block tray fields, respectively. The skin doses for motorized wedge fields were lower than for open fields. The effect of SSDs on the surface dose for motorized 60 wedge fields was not significant for a small field size (difference was less than 1% up to a 15 x 15 cm 2 field size), but for a larger field (field size more than 15 x 15 cm 2 ), the difference in a percentage skin dose was significant. The skin dose for the open field was more than that for the MLC blocked field and lower than that for the acrylic blocked tray field. The block was 25% of the 20 x 20 cm 2 open field. Skin doses were increased as the SSD decreased and were dominant for larger field sizes. The surface dose was weakly dependent on the MLC block.
  8 3,593 391
Use of mobile phone in operating room
Sanjay Saraf
April-June 2009, 34(2):101-102
DOI:10.4103/0971-6203.51938  PMID:20098545
  3 5,218 227
Static versus dynamic intensity-modulated radiotherapy: Profile of integral dose in carcinoma of the nasopharynx
KS Jothybasu, Amit Bahl, V Subramani, GK Rath, DN Sharma, PK Julka
April-June 2009, 34(2):66-72
DOI:10.4103/0971-6203.51932  PMID:20098539
This study is aimed to evaluate the impact of static and dynamic intensity modulated radiotherapy (IMRT) delivery techniques planned with Eclipse TPS on the integral dose to the healthy normal tissue surrounding the tumor-bearing area and to the volume receiving doses <5 Gy in patients with carcinoma nasopharynx treated with Simultaneous Integrated Boost IMRT (SIB-IMRT). Ten patients with carcinoma nasopharynx were chosen for this dosimetric study. IMRT plans were generated with 6X using dynamic multileaf collimator (DMLC) and static multileaf collimator (SMLC) with 5, 10 and 15 intensity levels (L). Integral dose, volume receiving 5 Gy, number of monitor units (MU) is compared against DMLC. The mean difference in the MU delivered per fraction between 5, 10 and 15 L SMLC and DMLC was -13.25% ( P < 0.001, with paired t test), -11.82% ( P < 0.001) and -10.81% ( P < 0.001), respectively. The mean difference in the integral dose with 5, 10 and 15 L compared to DMLC was -2.96% ( P < 0.001), -2.67% ( P = 0.016) and -0.39% ( P = 0.430), respectively. However, the difference in low-dose volume (V5Gy) was statistically insignificant with mean difference of 0.60% ( P = 0.23), 1.18% ( P = 0.017) and 1.70% ( P = 0.078), respectively for 5, 10 and 15 L compared to DMLC. Our results show that while choosing the IMRT delivery technique using conventional MLC the concerns about integral dose and volume receiving very low doses such as 5 Gy can be ignored.
  2 4,057 454
Initial dosimetric experience with mega voltage computed tomography detectors and estimation of pre and post-repair dosimetric parameters of a first helical Hi-Art II tomotherapy machine in India
Rajesh A Kinhikar, Zubin Master, Dipak S Dhote, Deepak D Deshpande
April-June 2009, 34(2):73-79
DOI:10.4103/0971-6203.51933  PMID:20098540
A Helical Tomotherapy TM (HT) Hi-Art II (TomoTherapy, Inc., Madison, WI, USA) has been one of the important innovations to help deliver IMRT with image guidance. On-board, mega voltage computed tomography (MVCT) detectors are used for imaging and dosimetric purpose. The two objectives of this study are: (i) To estimate the dosimetric and general capability (TomoImage registration, reconstruction, contrast and spatial resolution, artifacts-free image and dose in TomoImage) of on-board MVCT detectors. (ii) To measure the dosimetric parameters (output and energy) following major repair. The MVCT detectors also estimated the rotational output constancy well. During this study, dosimetric tests were repeated after replacing MVCT detectors and the target. fixed-gantry/fixed-couch measurements were measured daily to investigate; the system stability. Thermoluminescense dosimeter (TLD) was used during both the measurements subsequently. The MVCT image quality with old and new detectors was comparable and hence acceptable clinically. The spatial resolution was optimal and the dose during TomoImage was 2 cGy (well within the manufacturer tolerance of 4 cGy). The results of lateral beam profiles showed an excellent agreement between the two normalized plots. The output from the rotational procedure revealed 99.7% while the energy was consistent over a period of twelve months. The Hi-Art II system has maintained its calibration to within +/- 2% and energy to within +/- 1.5% over the initial twelve-month period. Based on the periodic measurements for rotational output and consistency in the lateral beam profile shape, the on-board detector proved to be a viable dosimetric quality assurance tool for IMRT with Tomotherapy. Tomotherapy was stable from the dosimetric point of view during the twelve-month period.
  1 3,067 290
A quantitative analysis of the structure of human sternum
Azim Arbabi
April-June 2009, 34(2):80-86
DOI:10.4103/0971-6203.51934  PMID:20098541
An extensive study of the human sternum has been carried out to obtain estimates of the omnidirectional path-length distributions and structural parameters for trabeculation and marrow spaces. Data for sternum samples have been collected, using an object plane scanning microscope. These data have been used to produce the omnidirectional path-length distributions and values of structural parameters for the whole sternum. For a typical adult man the mean trabecular and marrow space path lengths are 224 and 1364 m, respectively. The percentage bone volume is 13.8 and the surface to volume ratio is 190 cm. Data on the structural variations within the whole sternum are presented. They show a percentage difference in bone volume between the manubrium and the body of sternum of about 36%.
  1 2,773 168

April-June 2009, 34(2):106-106
  - 1,278 98
News and Events
T Ganesh
April-June 2009, 34(2):103-105
  - 2,059 129
Rectal dosimetry in intracavitary brachytherapy by HDR at rural center of Maharashtra: Comparison of two methods
Rajeev Shrivastava, Rahul B Umbarkar, MB Sarje, KK Singh
April-June 2009, 34(2):93-96
DOI:10.4103/0971-6203.51936  PMID:20098543
The purpose of this study was to calculate the radiation dose at the anterior rectal wall as per the International Commission on Radiation Units and Measurements (ICRU 38) recommendations and compare it with the dose calculated by the commonly used intrarectal catheter. Dose delivery by brachytherapy to the cervix is limited by the critical structure of the bladder and rectum. In this study the ICRU-38 rectal point was derived by using a radio-opaque gauze piece on the posterior vaginal wall, and the intrarectal point was derived by inserting a rubber catheter with a wire, inside the rectum. A total of 146 applications were performed in 81 patients. Rectal doses were compared for complementary rectal points R1 and R5, R2 and R6, R3 and R7, and R4 and R8, obtained by both methods. The rectal doses at each complementary pair were compared with each other. The average dose at R1 was 5% higher than at R5 (60.57% vs. 55.57%). The average dose at R2 was 1% higher than at R6 (58% vs. 57%). The average dose at R3 was 1.29% higher than at R7 (52.71% vs. 51.42%), and the average dose at R4 was 1.15% higher than at R8 (43% vs. 41.85%). There were many instances where the rectal dose exceeded by more than 15%, from the R1 to R4 points (43, 22, 21, and 11 times, respectively, for R1-R5, R2-R6, R3-R7, and R4-R8 pairs). The difference in dose between R1 and R5 was significant as seen on the statistical tests, i.e., Pair T test, Wilcoxan Signed Ranks test, and Sign test (p value 0.002). The rectal dose obtained by the intrarectal wire method underestimates the actual dose to the rectum when compared to the ICRU-38 method. Thus ICRU-38 recommendations should be strictly adhered to, to reduce late complications.
  - 2,475 286
Radiation exposure levels within timber industries in Calabar, Nigeria
SO Inyang, IS Inyang, NO Egbe
April-June 2009, 34(2):97-100
DOI:10.4103/0971-6203.51937  PMID:20098544
The UNSCEAR (2000) observed that there could be some exposure at work which would require regulatory control but is not really considered. This study was, therefore, set up to evaluate the effective dose in timber industries in Calabar, Nigeria to determine if the evaluated dose levels could lead to any radiological health effect in the workers, and also determine if the industries require regulatory control. The gamma ray exposure at four timber industries measured using an exposure meter were converted to effective dose and compared with the public and occupational values. The evaluated effective dose values in the timber industries were below public and occupational exposure limits and may not necessarily result in any radiological health hazard. Therefore, they may not require regulatory control.
  - 2,740 174
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