Abstract
Many factors contribute to the accuracy of delivered dose to patients in external-beam radiotherapy (EBRT). Although some of these factors can be checked by implementing suitable quality control procedures, the main aim was to assess the radiotherapy treatment filed on portal film using image processing technique in order to increase the accuracy of treatment delivery to the tumor by measuring the actual F/S, dose uniformity and penumbra size using portal film. This research is conducted at radiation therapy department, Khartoum Oncology Center (RICK), Khartoum state, Sudan, from July-2014 up to December-2014. The field size of each type of radiotherapy Co60 is measured as (9.4 × 9.4) cm and (9.1 × 9.1) cm, for linear accelerator machines it was 10 × 10 cm exactly as the reference field size, and there is no area reduced in linacs. The penumbra size for the two types of Co60 machine was measured also and it was 1.2 cm and 1.0 cm, and penumbra size of the linear accelerator machines was found to be 4 mm. The area of the field that received radiation by 100% was measured and it was 94.1% and 91.1% in Co60 and 100% for linear accelerator machine and that means linacs deliver the 100% of the dose to the useful field size. The dose percentage in the field for Co60 was 98.0% and 94.1% and thus the dose in the border of field 83.1% and 89.0% and it’s different in linacs because the dose percentage in the field was 78.4% and 78.4% and there is no measurable dose outside its field. Penumbra Co60 machines are relatively large which increase radiation dose to normal tissue and reduce the TCP, so calculation and accuracy of such calculation are necessary to the patient in term of NTCP.
Highlights
Teletherapy cobalt-60 units were first used for patient treatment in 1951 in Canada [1] [2]
Some of these factors can be checked by implementing suitable quality control procedures, the main aim was to assess the radiotherapy treatment filed on portal film using image processing technique in order to increase the accuracy of treatment delivery to the tumor by measuring the actual F/S, dose uniformity and penumbra size using portal film
[5] stated that the field size that calculated by computerized score using Matlab program was 9.9 ± 0.36049 cm × 9.9 ± 0.1123 cm calculated form digitized film. [6], aimed to verify radiotherapy treatments: computerized analysis of the size and shape of radiation fields using portal imaging. [7] studied the high energy linear accelerator penumbra size using the Pencil Beam Convolution algorithms and self-developing GafchromicTM EBT2 film, he found that increased energy, field size and depth rise to an increased penumbra (20% - 80%) width
Summary
Teletherapy cobalt-60 units were first used for patient treatment in 1951 in Canada [1] [2]. Various beam collimators designs exist to give variable rectangular fields with sides ranging in length, typically, from 4 cm to 30 cm or even up to 40 cm on isocentric units with a source axis distance (SAD) of 100 cm. Distances from the source to the far edge of the collimators are typically between 40 cm and 50 cm for machines designed for 80 cm SSD, but this distance may be increased by penumbra trimmers that are desirable when the machine is to be used for 100 cm SSD treatment [3]
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