MAPPING OF WORKPLACE RADIATION FIELDS IN DIAGNOSTIC RADIOLOGY FACILITIES USING PERSONNEL MONITORING TLD BADGES.

The radiation protection programme is aimed at safe usage of radiation at workplace, ensuring minimum possible dose to radiation workers, patients and members of the public. Verification of the adequacy of protective measures in actual workplace is important, especially for diagnostic radiology facilities, as a substantial number of suspected overexposures are reported from these facilities. To address this issue, a study was conducted for mapping workplace radiation field at various locations in nine Diagnostic Radiology Facilities of two hospitals in India. The cumulative doses were measured for a period of 1-3 months, using personnel monitoring TLD badges. The dosemeters were placed at positions representative of two exposure situations: (1) probable locations of workers during procedures, leading to genuine exposure and (2) inappropriate storage locations of personal dosemeters at user end for probing claims of nongenuine exposures. The results indicate that the measured doses at locations (1) were just a fraction of the permissible dose, provided all safety practices are adhered to. However, the measured doses at certain locations (2) exceeded the investigation levels and indicate that any inadvertent storage of the dosemeters at such locations could lead to reporting of the overexposure from these radiology facilities. The outcome of the study will be useful for the investigation of such exposures and better understanding of the readout patterns of TLD badges in radiology workplaces.

Time trial: a prospective comparative study of the time-resource burden for three-dimensional conformal radiotherapy and intensity-modulated radiotherapy in head and neck cancers.

INTRODUCTION: An ongoing institutional randomized clinical trial comparing three-dimensional conformal radiotherapy (3D CRT) and intensity-modulated radiotherapy (IMRT) provided us an opportunity to document and compare the time-manpower burden with these high-precision techniques in head and neck cancers. MATERIALS AND METHODS: A cohort of 20 consecutive patients in the ongoing trial was studied. The radiotherapy planning and delivery process was divided into well-defined steps and allocated human resource based on prevalent departmental practice. Person-hours for each step were calculated. RESULTS: Twelve patients underwent IMRT and eight patients had 3D CRT. The prerandomization steps (upto and including approval of contours) were common between the two arms, and expectedly, the time taken to complete each step was similar. The planning step was carried out postrandomization and the median times were similar for 3D CRT (312 min, 5.2 person-hours) and IMRT (325.6 min, 5.4 person-hours). The median treatment delivery time taken per fraction varied between the two arms, with 3D CRT taking 15.2 min (0.6 person-hours), while IMRT taking 27.8 min (0.9 person-hours) (P< 0.001). The total treatment time was also significantly longer in the IMRT arm (median 27.7 versus 17.8 person-hours, P< 0.001). The entire process of IMRT took 48.5 person-hours while 3D CRT took a median of 37.3 person-hours. The monitor units delivered per fraction and the actual "beam-on" time was also statistically longer with IMRT. CONCLUSIONS: IMRT required more person-hours than 3D CRT, the main difference being in the time taken to deliver the step-and-shoot IMRT and the patient-specific quality assurance associated with IMRT.

Do all patients of breast carcinoma need 3-dimensional CT-based planning? A dosimetric study comparing different breast sizes.

Evaluation of dose distribution in a single plane (i.e., 2-dimensional [2D] planning) is simple and less resource-intensive than CT-based 3-dimensional radiotherapy (3DCRT) planning or intensity modulated radiotherapy (IMRT). The aim of the study was to determine if 2D planning could be an appropriate treatment in a subgroup of breast cancer patients based on their breast size. Twenty consecutive patients who underwent breast conservation were planned for radiotherapy. The patients were grouped in 3 different categories based on their respective chest wall separation (CWS) and the thickness of breast, as "small," "medium," and "large." Two more contours were taken at locations 5 cm superior and 5 cm inferior to the isocenter plane. Maximum dose recorded at specified points was compared in superior/inferior slices as compared to the central slice. The mean difference for small breast size was 1.93 (standard deviation [SD] = 1.08). For medium breas size, the mean difference was 2.98 (SD = 2.40). For the large breasts, the mean difference was 4.28 (SD = 2.69). Based on our dosimetric study, breast planning only on the single isocentric contour is an appropriate technique for patients with small breasts. However, for large- and medium-size breasts, CT-based planning and 3D planning have a definite role. These results can be especially useful for rationalizing treatment in busy oncology centers.

Dosimetric validation of first helical tomotherapy Hi-Art II machine in India.

A Helical Tomotherapy (HT) Hi-Art II machine, Hi ART (TomoTherapy, Inc., Madison, WI, USA) was installed at our center in July 2007, and was the first machine in India. Image-guided HT is a new modality for delivering intensity modulated radiotherapy (IMRT). Dosimetric tests done include (a) primary beam alignment (b) secondary beam alignment (c) water tank measurements (profiles and depth doses) (d) dose rate measurements (e) IMRT verification, and (f) Mega voltage Computed Tomography (MVCT) dose. Primary and secondary beam alignment revealed an acceptable linear accelerator (linac) alignment in both X and Y axes. In addition, it was observed that the beam was aligned in the same plane as gantry and the jaws were not twisted with respect to gantry. The rotational beam stability was acceptable. Multi-leaf collimators (MLC) were found to be stable and properly aligned with the radiation plane. The jaw alignment during gantry rotation was satisfactory. Transverse and longitudinal profiles were in good agreement with the "Gold" standard. During IMRT verification, the variation between the measured and calculated dose for a particular plan at the central and off-axis was found to be within 2% and 1mm in position, respectively. The dose delivered during the TomoImage scan was found to be 2.57 cGy. The Helical Tomotherapy system is mechanically stable and found to be acceptable for clinical treatment. It is recommended that the output of the machine should be measured on a daily basis to monitor the fluctuations in output.

Performance characterization of siemens primus linear accelerator under small monitor unit and small segments for the implementation of step-and-shoot intensity-modulated radiotherapy.

Implementation of step-and-shoot intensity-modulated radiotherapy (IMRT) needs careful understanding of the accelerator start-up characteristic to ensure accurate and precise delivery of radiation dose to patient. The dosimetric characteristic of a Siemens Primus linear accelerator (LA) which delivers 6 and 18 MV x-rays at the dose rate of 300 and 500 monitor unit (MU) per minutes (min) respectively was studied under the condition of small MU ranging from 1 to 100. Dose monitor linearity was studied at different dose calibration parameter (D1_C0) by measuring ionization at 10 cm depth in a solid water phantom using a 0.6 cc ionization chamber. Monitor unit stability was studied from different intensity modulated (IM) groups comprising various combinations of MU per field and number of fields. Stability of beam flatness and symmetry was investigated under normal and IMRT mode for 20×20 cm(2) field under small MU using a 2D Profiler kept isocentrically at 5 cm depth. Inter segment response was investigated form 1 to 10 MU by measuring the dose per MU from various IM groups, each consisting of four segments with inter-segment separation of 2 cm.In the range 1-4 MU, the dose linearity error was more than 5% (max -32% at 1 MU) for 6 MV x-rays at factory calibrated D1_C0 value of 6000. The dose linearity error was reduced to -10.95% at 1 MU, within -3% for 2 and 3 MU and ±1% for MU ≥4 when the D1_C0 was subsequently tuned at 4500. For 18 MV x-rays, the dose linearity error at factory calibrated D1_C0 value of 4400 was within ±1% for MU ≥3 with maximum of -13.5 observed at 1 MU. For both the beam energies and MU/field ≥4, the stability of monitor unit tested for different IM groups was within ±1% of the dose from the normal treatment field. This variation increases to -2.6% for 6 MV and -2.7% for 18 MV x-rays for 2 MU/field. No significant variation was observed in the stability of beam profile measured from normal and IMRT mode. The beam flatness was within 3% for 6 MV x-rays and more than 3% (Max 3.5%) for 18 MV x-rays at lesser irradiation time ≤3 MU. The beam stability improves with the increase in irradiation time. Both the beam energies show very good symmetry (≤2%) at all irradiation time.For all the three segment sizes studied, the nonlinearity was observed at smaller MU/segment in both the energies. When the MU/segment is ≥4, all segment size shows fairly linear relation with dose/MU. The smaller segment size shows larger nonlinearity at smaller MU/segment and become more linear at larger MU/segment. Based on our study, we conclude that the Primus LA from Siemens installed at our hospital is ideally suited for step-and-shoot IMRT preferably for radiation ON time ≥4MU per segment.