Journal of Medical Physics
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   2008| October-December  | Volume 33 | Issue 4  
    Online since December 11, 2008

 
 
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REVIEW ARTICLE
Tumor delineation: The weakest link in the search for accuracy in radiotherapy
CF Njeh
October-December 2008, 33(4):136-140
DOI:10.4103/0971-6203.44472  PMID:19893706
Radiotherapy is one of the most effective modalities for the treatment of cancer. However, there is a high degree of uncertainty associated with the target volume of most cancer sites. The sources of these uncertainties include, but are not limited to, the motion of the target, patient setup errors, patient movements, and the delineation of the target volume. Recently, many imaging techniques have been introduced to track the motion of tumors. The treatment delivery using these techniques is collectively called image-guided radiation therapy (IGRT). Ultimately, IGRT is only as good as the accuracy with which the target is known. There are reports of interobserver variability in tumor delineation across anatomical sites, but the widest ranges of variations have been reported for the delineation of head and neck tumors as well as esophageal and lung carcinomas. Significant interobserver variability in target delineation can be attributed to many factors including the impact of imaging and the influence of the observer (specialty, training, and personal bias). The visibility of the target can be greatly improved with the use of multimodality imaging by co-registration of CT with a second modality such as magnetic resonance imaging (MRI) and/or positron emission tomography. Also, continuous education, training, and cross-collaboration of the radiation oncologist with other specialties can reduce the degree of variability in tumor delineation.
  6,273 610 36
ORIGINAL ARTICLES
Testicular shield for para-aortic radiotherapy and estimation of gonad doses
R Ravichandran, JP Binukumar, S Kannadhasan, MH Shariff, Kamal El Ghamrawy
October-December 2008, 33(4):158-161
DOI:10.4103/0971-6203.44477  PMID:19893710
For radiotherapy of para-aortic and abdominal regions in male patients, gonads are to be protected to receive less than 2% of the prescribed dose. A testicular shield was fabricated for abdominal radiotherapy with 15 MV X-rays ((Clinac 2300 CD, Varian AG) with low melting point alloy (Cerroband). The dimensions of the testicular shield were 6.5 cm diameter and 3.5 cm depth with 1.5 cm wall thickness. During treatment, this shield was held in position by a rectangular sponge and Styrofoam support. Phantom measurement was carried out with a humanoid phantom and a 0.6 cc ion chamber. The mean energy of the scattered photon was calculated for single scattering at selected distances from the beam edge and with different field dimensions. One patient received radiotherapy with an inverted Y field and gonad doses were estimated using calibrated thermo-luminescent detector (TLD) chips. Measured doses with the ion chamber were 7.1 and 3.5% of the mid-plane doses without a shield at 3 and 7.5 cm off-field respectively. These values decreased to 4.6 and 1.7% with the bottom shield alone, and to 1.7 and 0.8% with both bottom and top shields covering the ion chamber. The measured doses at the gonads during the patient's treatment were 0.5-0.92% for the AP field (0.74 ± 0.17%, n = 5) and 0.5-1.2% for the PA field (0.88 ± 0.24%, n = 5). The dose received by the testis for the full course of treatment was 32 cGy (0.8%) for a total mid-plane dose of 40 Gy. The first-scatter energy estimated at the gonads is around 1.14 MeV for a primary beam of 15 MV for a long axis dimension of 37 cm of primary field. During the patient's treatment, the estimated absorbed doses at the gonads were comparable with reported values in similar treatments. The testicular shield reported in this study is of light weight and could be used conveniently in treatments of abdominal fields.
  3,911 188 2
Studies on the time course of apparent diffusion coefficient and signal intensities on T2- and diffusion-weighted MR Imaging in acute cerebral ischemic stroke
Ajai K Srivastava, Gopesh Mehrotra, Satish K Bhargava, Sunil Agarwal, Rajendra P Tripathi
October-December 2008, 33(4):162-170
DOI:10.4103/0971-6203.44479  PMID:19893711
The time course of changes in apparent diffusion coefficient (ADC) and signal intensity on diffusion-weighted magnetic resonance imaging (DW MR) imaging in acute ischemic stroke is a very dynamic event. There is an initial reduction in ADCs with no change on T2-W imaging but signal intensity increase on T2-weighted takes place about 6-12 hours after onset of stroke. As necrosis begins to set in, there is a gradual reversal of ADC change, and around 3-10 days post-onset, ADC pseudonormalizes. Twenty-four patients of acute stroke underwent diffusion MR imaging in addition to conventional T1W, T2W, and Fluid Attenuated Inversion Recovery (FLAIR) sequence performed within 12 hours, at 30 days, and at 90 days. The mean signal intensity at b = 0 s/mm2 and at b = 1000 s/mm2 were significantly higher than control values for all time periods. The ratio of signal intensity at b = 0 (rSI b=0) significantly increased from 1.63 ± 0.20 in the acute stage to 2.19 ± 0.24 in the chronic stage ( P < 0.001). The ratio of signal intensity on DWI (r SIDWI) decreased from 2.54 ± 0.46 to 1.54 ± 0.22. The mean ADC in the lesion was found to be 41% lower than the mean ADC in the contralateral hemisphere .Linear regression analysis between rADC and log hours showed that pseudonormalization occurred at 6.61 days ( P < 0.001). We conclude that the above information could be useful in the management of very early stroke.
  3,520 187 5
Magnitude of shift of tumor position as a function of moderated deep inspiration breath-hold: An analysis of pooled data of lung patients with active breath control in image-guided radiotherapy
KR Muralidhar, P Narayana Murthy, D Shanker Mahadev, K Subramanyam, G Sudarshan, A Krishnam Raju
October-December 2008, 33(4):147-153
DOI:10.4103/0971-6203.44475  PMID:19893708
The purpose of this study was to evaluate the reproducibility and magnitude of shift of tumor position by using active breathing control and iView-GT for patients with lung cancer with moderate deep-inspiration breath-hold (mDIBH) technique. Eight patients with 10 lung tumors were studied. CT scans were performed in the breath-holding phase. Moderate deep-inspiration breath-hold under spirometer-based monitoring system was used. Few important bony anatomic details were delineated by the radiation oncologist. To evaluate the interbreath-hold reproducibility of the tumor position, we compared the digital reconstruction radiographs (DRRs) from planning system with the DRRs from the iView-GT in the machine room. We measured the shift in x, y, and z directions. The reproducibility was defined as the difference between the bony landmarks from the DRR of the planning system and those from the DRR of the iView-GT. The maximum shift of the tumor position was 3.2 mm, 3.0 mm, and 2.9 mm in the longitudinal, lateral, and vertical directions. In conclusion, the moderated deep-inspiration breath-hold method using a spirometer is feasible, with relatively good reproducibility of the tumor position for image-guided radiotherapy in lung cancers.
  3,049 262 4
In-air fluence profiles and water depth dose for uncollimated electron beams
Abdelkader Toutaoui, Amar Nassim Aichouche, Kenza Adjidir, Ahmed Chafik Chami
October-December 2008, 33(4):141-146
DOI:10.4103/0971-6203.44473  PMID:19893707
Advanced electron beam dose calculation models for radiation treatment planning systems require the input of a phase space beam model to configure a clinical electron beam in a computer. This beam model is a distribution in position, energy, and direction of electrons and photons in a plane in front of the patient. The phase space beam model can be determined by Monte Carlo simulation of the treatment head or from a limited set of measurements. In the latter case, parameters of the electron phase space beam model are obtained by fitting measured to calculated dosimetric data. In the present work, data for air fluence profiles and water depth doses have been presented for electron beams without an applicator for a medical linear accelerator. These data are used to parameterize the electron phase space beam model to a Monte Carlo dose calculation module available in the first commercial (MDS Nordion, now Nucletron) Monte Carlo treatment planning for electron beams.
  2,916 363 -
Interobserver variation in rectal and bladder doses in orthogonal film-based treatment planning of cancer of the uterine cervix
P Raghukumar, K Raghu Ram Nair, B Saju, G Zhenia, KT Divya, VS Shaiju, V Padmanabhan
October-December 2008, 33(4):154-157
DOI:10.4103/0971-6203.44476  PMID:19893709
Orthogonal film-based treatment planning is the most commonly adopted standard practice of treatment planning for cancer of the uterine cervix using high dose rate brachytherapy (HDR). This study aims at examining the variation in rectal and bladder doses when the same set of orthogonal films was given to different observers. Five physicists were given 35 pairs of orthogonal films obtained from patients who had undergone HDR brachytherapy. They were given the same instructions and asked to plan the case assuming the tumor was centrally placed, using the treatment-planning system, PLATO BPS V13.2. A statistically significant difference was observed in the average rectal (F = 3.407, P = 0.01) and bladder (F = 3.284, P = 0.013) doses and the volumes enclosed by the 100% isodose curve ( P < 0.01) obtained by each observer. These variations may be attributed to the differences in the reconstruction of applicators, the selection of source positions in ovoids and the intrauterine (IU) tube, and the differences in the selection of points especially for the rectum, from lateral radiographs. These variations in planning seen within a department can be avoided if a particular source pattern is followed in the intrauterine tube, unless a specific situation demands a change. Variations in the selection of rectal points can be ruled out if the posterior vaginal surface is clearly seen.
  2,417 242 1
SCIENTIFIC NOTE
Radiation burden of assistant medical technicians at a medical accelerator
M Grundel, F Guthoff
October-December 2008, 33(4):171-174
DOI:10.4103/0971-6203.44480  PMID:19893712
A survey of a CLINAC 2100 C medical accelerator showed residual short half-life radiation after switching off the accelerator. This led to a dose of radiation for the medical employees when the patient was handled. The dose rate was measured with a dose rate meter FH40G, and annual dose for an assistant medical technician (AMT) was estimated under conservative conditions. In the assumed situation of 1000 patient treatment fractions with high-energy photons, an AMT would get an annual dose of 960 µSv, while the monthly dosimeter records would show zero, if the dose received is below threshold of 100 µSv.
  2,391 195 2
EDITORIAL
A statement of the rights of scientists and engineers
William Hendee
October-December 2008, 33(4):135-135
DOI:10.4103/0971-6203.44471  PMID:19893705
  1,753 237 -
NEWS AND EVENTS
News and Events
T Ganesh
October-December 2008, 33(4):175-177
PMID:19893713
  1,766 163 -
OBITUARY
Obituary
PS Iyer
October-December 2008, 33(4):178-178
  1,295 126 -
 
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