ABSTRACT
BACKGROUND: To analyze and compare dose distribution homogeneity in selected points (especially in the chest wall region) for patients irradiated with two different TBI techniques to achieve a uniform total dose (excluding lungs area) specified in the range of 11.4-14.0 Gy. MATERIAL AND METHODS: From August 2000 to December 2009, a group of 158 patients was treated by the use of 15 MV photon irradiation consisting of six fractions: four opposed lateral and two anterior-posterior/posterior-anterior (AP/PA). Patients were irradiated with the fraction dose of 2 Gy twice a day for 3 consecutive days. The prescribed dose to PC point (specified at intersection of the beam axis with the mid-plane of the patient irradiated laterally) was 12 Gy. Since January 2010 until closing the study, another group of 50 patients was treated according to a modified protocol. The treatment was carried out in six lateral fractions only, twice a day, for three following days and a lateral lung shield was used for a part of total irradiation time. The measurements of doses in 20 selected points of patient's body were carried out by means of MOSFET detectors. RESULTS: The modified TBI technique allows to achieve an expected homogenous dose in the points of interest similar to that obtained by using the initial protocol. The calculated and measured in vivo doses met the specified range of 11.4-14 Gy for both applied TBI protocols. CONCLUSIONS: Our results indicate that for all patients the homogenous dose distribution in the specified range was achieved.
ABSTRACT
AIM: The aim of the paper is to examine the relation between the increase of the photon dose in water in the region of electronic disequilibrium - so-called build-up region - and the distance of the bolus from the water surface for the applied parameters of X-ray beams. MATERIALS AND METHODS: PDD measurements were carried out using the plane-parallel ionization chamber Markus in the automatic water phantom IBA BluePhantom with OmniPro-Accept V7 (IBA Dosimetry GmbH, Schwarzenbruck, Germany). All measurements were performed for different field sizes and for 6 MV and 15 MV X-ray beams, respectively. A water-equivalent RW3 slab (Goettingen White Water) produced by PTW was used as a bolus. RESULTS: Placing a bolus in an irradiated field changes the shape of the PDD curve in the build-up region in comparison with the one obtained for an open field. All results has been inserted in tables and figures. CONCLUSION: The closer the bolus is to the water surface, the smaller the depth of the maximum dose in the phantom for all investigated fields and energies. The changes in the build-up region are important, even if the bolus does not touch the surface of the water phantom. The influence of the bolus can be ignored when the bolus-surface distance equals 25 cm for 6MV X-ray beams and 39 cm for 15 MV X-ray beams.
