الفهرس 
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Abstract
The basic goal of radiotherapy treatment is the irradiation of a target volume while minimizing the amount of radiation absorbed in normal tissue-. Shaping the beam is an important way of minimizing the absorbed dose in healthy tissue and Organs At Risk. Conventional collimator jaws are used for shaping a rectangular treatment field; but, as usually the treatment volume is not rectangular, additional shaping is required. On a linear accelerator, Cerrobend blocks are attached onto the treatment head under standard collimating system. A multileaf collimator (MLC) provides another option.
The aim of this study is to evaluate and compare the planning and dosimetric measurements of mantle irradiation field technique for 6 MeV linear accelerator shielded with cerrobend blocks and multileaf collimators (MLCs) in the way to choose the best method of shielding technique.
This study involved 10 patients of different age with Mantle lymphoma, treated with opposed anteroposterior fields from a 6 MeV linear accelerator.
Each patient has been subjected to the following:
1. CT scanning image to define the tumor site.
2. Focal contouring systems, which define the planning target volumes (PTV) and relevant Organs at Risk (OARs).
3. Each patient planned using 3DCRT Precise treatment system, to achieve a conformal uniform dose distribution in PTV and reduce the dose to surrounding tissues, The treatment target volume included the PTV and an additional - 0.7cm margin for beam penumbra in all directions.
4. For each patient mantle irradiation field technique was carried out using the two shielding techniques, to achieve the optimum plans for a specific target to give the required dose for radiotherapy by the treatment planning system.
5. The DVHs and the DVH parameters for the two shielding techniques were compared and analyzed statistically.
6. The dose distributions in the fields shaped with the MLC and cerrobend blocks were measured with TLD chips at different depths using a Perspex Phantom.
The results showed that the cerrobend blocks shielding provide target volume coverage better than that of the MLC. The analysis suggest that the MLCs’ dosimetry is less favorable than that of the cerrobond blocks in the treatment of two-field irradiation of Mantle lymphoma without daily setup variations taken into account, as the cerrobond blocks provide dose distributions better than that of the MLCs, due to the large amounts of scattered radiation and Interleaf leakage of the MLC.
However, none of the Organs at risk (OARs) e.g. right lung, left lung and heart were irradiated to the critical doses and thus with each of the beam shaping configurations, higher volumes did not receive critical doses of irradiation. Even though the scalloping effect and larger penumbra, MLCs shaped fields seems to be problematic features; it’s reported that when the set up uncertainties and the multifield treatments are taken into account, these features would also reduce the differences between using conformal blocks and MLCs.