Optimization of low-energy electron beam production for superficial cancer treatments by Monte Carlo code

Context: Low energy electron beam has been being used widely for superficial cancer treatments. In the current study a design for production of very low energy electron beam, by different thickness of Perspex spoilers, is presented that may be used for skin cancer. Aims: MCNPX Monte Carlo code was used for modeling and simulations in the current study. An energy spoiler Perspex was modeled for degrading 4 MeV electron beam of Varian 2300 CD Linac. Materials and Methods: The thicknesses of 3, 7, and 10 mm were applied before electron applicator at a distance of 42 cm from phantom surface. Dosimetric properties of new electron beams including Rp, Dmax, E0, as well as the penumbra of the beam were investigated. Results: For the 3 mm spoiler, the superficial beam output decreased to 77%, and the Dmax, R90, R50, and RP were shifted to the depths of 4, 6, 9, and 12 mm, respectively. While for 10 mm filter the results were 5.2, 3.0 and 5.0 mm for R90, R50, and Rp, respectively. In addition, the surface dose was 93% and the Dmax was shifted to the depth of 1mm for the 10mm Perspex spoiler slab. Conclusions: The presented beam provides a novel surface dose, Dmax, and RP which can be applicable for treatment of skin cancers with minimum dose to the beyond normal tissues

Skin Dose Distrubution with Spoiler of 6 MV X-ray for head and Neck Tumor / 대한치료방사선과학회지

PURPOSE: This study was performed for adequate irradating tumor area when 6 MV linear accerelator photon was used to treat the head and neck tumor. The skin surface dose and maximum build-up ragion was measured by using a spoiler which was located between skin surface and collimator. METHODS: A spoiler was made of tissue equivalent materials and the skin surface dose and maximum build-up region was measured varing with field size, thickness of spoiler and interval between skin and collimator. The results of skin surface dose and maximum build-up dose was represented as a build-up ratio and it was compared with dose distribution by using a bolus. RESULTS: The skin surface dose was increased with appling spoiler and decreased by distance of the skin-spoiler separation. The maxium build-up region was 1.5 cm below the skin surface and it was markedly decreased near the skin surface. By using a 1.0-cm thickness spoiler, Dmax moved to 5, 10.2, 12.3, 13.9 and 14.8 mm from the skin surface by separation of the spoiler from the skin 0, 5, 10, 15, 20 cm, respectively. CONCLUSION: The skin surface dose was increased and maximum build-up region was moved to the surface by using a spoiler. Therefore spoiler was useful in treating by high energy photon in the head and neck tumor.

The Dosimetric Data of 10 MV Linear Accelerator Photon Beam for Total Body Irradiation / 대한치료방사선과학회지

PURPOSE: This study was to obtain the basic dosimetric data using the 10 MV X-ray for the total body irradiation. MATERIALS AND METHODS: A linear accelerator photon beam is planned to be used as a radiation source for total body irradiation (TBI) in Chonnam University Hospital. The planned distance from the target to the midplane of a patient is 360cm and the maximum geometric field size is 144cm' 144cm. Polystyrene phantom sized 30 30 30.2cm3 and consisted of several sheets with various thickness, and a parallel plate ionization chamber were used to measure surface dose and percent depth dose (PDD) at 345cm SSD, and dose profiles. To evaluate whether a beam modifier is necessary for TBI, dosimetry in build up region was made first with no modifier and next with an 1cm thick acryl plate 20cm far from the polystyrene phantom surface. For a fixed source-chamber distance, output factors were measured for various depth. RESULTS: As any beam modifier was not on the way of radiation of 10MV X-ray the dmax and surface dose was 1.8cm and 61%, respectively, for 345cm SSD. When an 1cm thick acryl plate was put 20cm far from polystyrene phantom for the SSD, the dmax and surface dose were 0.8cm and 94%, respectively. With acryl as a beam spoiler, the PDD at 10cm depth was 78.4% and exit dose was a little higher than expected dose at interface of exit surface. For two-opposing fields for a 30cm phantom thick phantom, the surface dose and maximum dose relative to mid-depth dose in our experiments were 102.5% and 106.3%, respectively. The off-axis distance of that point of 95% of beam axis dose were 70cm on principal axis and 80cm on diagonal axis. CONCLUSION: 1. To increase surface dose for TBI by 10MV X-ray at 360cm SAD, 1cm thick acrylic spoiler was sufficient when distance from phantom surface to spoiler was 20 cm. 2. At 345cm SSD, 10MV X-ray beam of full field produced a satisfiable dose uniformity for TBI within 7% in the phantom of 30cm thickness by two-opposing irradiation technique. 3. The uniform dose distribution region was 67cm on principal axis of the bean and 80cm on diagonal axis from beam axis. 4. The output factors at mid-point of various thickness revealed linear relation with depth, and it could be applicable to practical TBI.