ABSTRACT
Objective To evaluate the radiation method and resuh of 450 patients received TBI(total body irradiation).Methods Single-dose Measurement was used to mark dose of TLD(thermo luminescence dosimeter).The values of actual dose in body midline were evaluated by calculating and correcting mean dose of incidence and emergence.Radiation methods:In four-field Irradiation.diagonals of fields coinside with the longitudinal axis of the patients,patient in supine and lateral positions received two pairs of parallel opposite radiation.Scheme of TBI came from a preparative radiation about one week before,and this four-field and equal-in-dose(about 10%of TBI)preparative radiation offered US the optimal scheme with aminimal dose non-uniformity by adjusting different dose proportion of supine and lateral position.In small field irradiation,patients received one pair of parallel opposite radiation from lateral side sitting on a special stool with backrest,the stool can be rotated CW or CCW,pedals can be move forward or backward and fixed.In opposite lateral irradiation,similar to four-field irradiation,patients received one pair of horizontal opposite radiation only in supine position.Five of these patients received FTBI(Fractional TBI). Results The average non-uniformity in midline of patients in four-field irradiation group(87 patients).small field irradiation group(91patients)and opposite lateral irradiation group(272 patients)is respectively ±8.1%,±7.4% and ±4.9%. Conclusions It iS a important process for QA and Qc to measure the dose of incidence and emergence real-timely with TLD or semiconductor dosimeter.We can adopt small field irradiation when the field iS not large enough to contain the patient from head to foot,and it showed advantages over four-field irradiation in treatment process and outcomes.We found the uniformity in body midline would be much better in supine position with diagonal＞180 cm than that in four-field irradiation and small field irradiation with diagonal＜110 cm.We compared supine position irradiation with opposite lateral irradiation,only to find which has its strong point.And actually we considered that FTBI treatment booth can be used more often in anterior and posterior parallel fields irradiation,patient semi-sitted,repeatedly received forward and backward radiation. In spit of not possessing radio-biological advantages as FTBI,STBI(Single TBI)is still a practical form of TBI.
ABSTRACT
The work suggested in this paper addresses a method for collecting beam data for small circular fields. Beam data were obtained from Philips 6 and 8 MV LINAC at Dept. Radiation Therapy at Gainesville Incorporated and Shands Teaching Hospital. Specific quantities measured include tissue maximum ratio (TMR), off-axis ration (OAR) and relative output factor (ROF). In small field irradiation, special collimators were used to produce circular fields of 1 cm to 3 cm diameter in 2 mm steps, measured at SAD (soura axis distance) of 100 cm. Diode detector was chosen for primary beam measurement and compared with measurements made with photographic film and TLD dosimeters. The measured TMRs and OARs were formulated from limited measurements to generate basic beam data for reference set-up. The empirical formula were later, extended and generalized for any possible set-up using the trends of fitting parameters. The measured TMRs and OARs were well represented by the fitting formula developed.