Portal-image IMRT verification

The aim of the present work was to develop and utilizing the use of an amorphous silicon electronic portal imaging device [EPID] in IMRT dosimetric verification. Neither pre-irradiation nor extra build-up materials was needed for EPID dosimetry applications. Accurate absolute dosimetry [output] obtained using the EPID up to 250 cGy with mean deviation of 0.39% and 0.62% while the maximum observed deviation was 0.7% and 1.9% at 250 MUs for 6 and IS MV photon energy respectively. Beam-by-beam fluence profiles obtained from portal images were used in air [i.e. without phantom presence] The EPID estimated the relative dose up to 1.5% accuracy. The in-air absolute dose [i.e. number of MUs] of an arbitrary clinical breast [aperture-based] IMRT test fields were extracted, the difference rose to 1.7% in the most severe tested field. One disadvantage of beam-by-beam verification is that the cumulative effect of dose errors from all beams is not quantified, however, it allows the potential origin of dose errors to be isolated more easily. The EPID could estimate the dose at each segment with average accuracy of around 1% for central axis positions and up to 1.7% for off-axis positions in the tested fields. The absolute dose verification plus the fluence map verification of IMRT fields may represent a sufficient procedure to examine the step-and shoot-IMRT treatment. Multi-leaf-collimator [MLC] related QA also tested using EPED. The mean difference between EPID effective penumbra results and both ion chamber and film measurements was 0.06 and 0.01 cm respectively. These results could justify the use of EPID in dosimetric applications including aperture-based IMRT verification, and quality control programs

MLC leaf position and dynalog file accuracy QA procedure using the EPID

A main concern about the IMRT dose validation tool using Monte Carlo [MC] simulation and R and V-system/Dynalog file is the potential inconsistency between the actual leaf-end positions and those recorded by the Dynalog file. The present study investigates a method to validate the accuracy of the Dynalog tiles using amorphous silicon electronic portal imaging device [aSi-EPID] images. A computer program was developed to detect the MLC segmented field edges in EPID images [l024x768 pixels, pixel size: 0.392 mm], Standard reference MLC segmented fields were designed and leaf-end positions were measured accurately. EPID images for these reference MLC fields were recorded and the leaf-end positions were calculated as the locations where the image intensity is 50% of the maximum. Small corrections were made to minimize the effect of scattered photons [background]. Daily EPII] images of the same MLC segmented fields were compared to the original images and to check the accuracy of the Dynalog files. A daily QA tool was developed to check the accuracy of the Dynalog file and MLC leaf end positions as part of the comprehensive IMRT-QA procedure. This ensures the accuracy of the MC based patient-specific IMRT dose verification using the information recorded in the Reeord and Verify system/Dynalog files

Developed technique of extra-cranial fractionated stereotactic radiotherapy with brainlab exac trac auto-positioning system

Developments in radiotherapy treatment techniques provide new options and treatment opportunities for patients. One of these is the Extra-cranial Stereotactic Radiation Oncology and Nuclear Medicine [NEMROCK]. Several clinical cases have shown that a radiotherapy treatment allows delivery of high total doses to the tumor. However, damage to healthy tissues as side effects caused from excess radiation, is a factor to be considered. Extra-cranial Stereotactic Radiotherapy, with its precise tumor definition, exact patient localization, and immobilization can reduce the damage of healthy tissues surrounding the tumor, while still allowing higher total doses to be delivered to the planning target volume [PTV]. In this study, development of Brain Lab cranial software system is achieved to be applicable for the Extra-cranial lesions using the circular collimators are-based radiosurgery. By this technique a good dosimetric results were obtained, with minimum doses delivered to health tissues and maximum target dose. The best of treatment is based on dose distribution, conformity index, and dose volume histograms for the patient

Dose distribution in thorax using measured and calculation algorithm method

In This study a trial has been done to verify the treatment planning algorithm implemented on the theraplan TP-11 system. To achieve this goal the thorax part of a humanoid [Rando] Phantom is used. The thorax part is irradiated using 10 Mev electron beam from varian accelerator and the dose distribution is monitored by Lif [700] TLD. The experimental results are compared with the results of the algorithm of the theraplan TP-11 System. The study revealed that the results due to the algorithm at the penumbral region of the radiation field, [area under rib and area between ribs] can vary and read as much as 23%. A discussion of the results is also presented