ABSTRACT
In this study, the physical compensator made with the high density material, Cerrobend, and the electronic compensator realized by the movement of a dynamic multileaf collimator were analyzed in order to verify the properness of a design function in the commercial RTP (radiation treatment planning) system, Eclipse. The CT images of a phantom composed of the regions of five different thickness were acquired and the proper compensator which can make homogeneous dose distribution at the reference depth was designed in the RTP. The frame for the casting of Cerrobend compensator was made with a computerized automatic styrofoam cutting device and the Millennium MLC-120 was used for the electronic compensator. All the dose values and isodose distributions were measured with a radiographic EDR2 film. The deviation of a dose distribution was +/-0.99 cGy and +/-1.82 cGy in each case of a Cerrobend compensator and a electronic compensator compared with a +/-13.93 cGy deviation in an open beam condition. Which showed the proper function of the designed compensators in the view point of a homogeneous dose distribution. When the absolute dose value was analyzed, the Cerrobend compensator showed a +3.83% error and the electronic compensator showed a -4.37% error in comparison with a dose value which was calculated in the RTP. These errors can be admtted as an reasonable results that approve the accuracy of the compensator design in the RTP considering the error in the process of the manufacturing of the Cerrobend compensator and the limitation of a film in the absolute dosimetry.
ABSTRACT
Objective To improve the external irradiation technique for Head-neck neoplasms.Methods 95 patients with Head-neck neoplasms confirmed by pathology,were fixed with head pillow mask , isocenter irradiation,technique utilizing cerrobend block.Radical therapy dose was 72 (70～80)Gy/35～40 fractions in 7～8 weeks for general carcinoma and 50～55Gy/28～31 fractions in 5 6～6 2 weeks for NHL .Preventive dose was 56 (50～60)Gy/25～30 fractions in 5～6 weeks for general carcinoma and 45～50Gy/25～28 fractions in 5～5 6 weeks for NHL.A short and a long-term clinical outcome, acute and late radiation reactions were observed.Results After 1～2 months following radiation therapy,CT scans revealed that the primary lesion complete remission rate was 58 57% , and obvious remission rate was 32 86%.The normal mucous membrane acute radiation reaction rates were G0 56 84% , GⅠ 42 10% , GⅡ 1 05%,respectively.After 1～2 years following radiation therapy,the spinal cord and brain stem radiation injury rate was zoro.Conclusions The improving external irradiation technique may elevate local control rate better,and reduce radiation reactions of patients with head-neck neoplasms.
ABSTRACT
The eye lens is known to be radiosensitive organ and catarat can be induced by relatively low dose of radiation. In the treatment of head and neck tumors, shielding blocks are frequently used to minimize dose on sensitive organs. The shielding block, which is trade of high atomic number materials (cerrobend), produce significant dose perturbations in megavoltage photos beams. The effects of these perturbations of eye shielding blocks are measured with film and ion chambers for the treatment of head and neck malignancies. Optimum parameters for the treatment are suggested.