Search

Objective To compare the dosimetric difference between the two beams formed by low melting-point lead (LML) and multileaf collimator (MLC) in orbit radiotherapy, so as to select the one with a lower lens dose for treatment of Graves' ophthalmopathy. Methods Patients with unilateral and bilateral Graves' ophthalmopathy (10 cases each) suitable for radiotherapy were selected for dosimetric comparison. The identical sketching principle of target volume was employed, and the prescribed dose of planning target volume (PTV) was 2000 cGy/10 times. The distribution of radiation field in unilateral group was 3 fields (2 X-ray fields + 1 electron field), and in bilateral group was 4 fields (2 X-ray fields + 2 electron fields), and LML and MLC were employed to form the radiation field. The conformity index (CI) and dose volume histogram (DVH) were compared between the two formation methods of radiation field; the effective penumbra area of the half radiation field formed by the two methods and its influence on the lens dose were analyzed with flushing-free film and dose analysis software. Results The average dose of the affected side lens in MLC unilateral group was 582±34cGy, and of the lens of uninjured side was 160±22cGy, the CI of target volume was 0.69; the average dose of the left and right lens in MLC bilateral group was 591±47cGy and 585±52cGy, respectively, and the CI was 0.67. The average dose of the affected side lens in LML unilateral group was 252±45cGy, and that of the uninjured side lens was 148±19cGy, and the CI was 0.71; the average dose of the left and right lens in LML bilateral group was 247±44cGy and 256±42cGy, respectively, and the CI was 0.68. When the X-ray energy was setup at 4MV and 8MV, the half radiation field was 5cm×5cm with a depth of 4cm, and the effective penumbra area of LML was 3mm smaller than that of MLC. Conclusion A small radiation area formed by LML may be more appropriate, and it may not only diminish the penumbra of radiation field, also it significantly reduce the irradiation dose imparted to patients' affected side lens.

Objective To investigate the range of inter-fraction and intra-fraction motion of crystalline lens in radiotherapy. Methods The CT and MRI images of 17 patients were registered, and the profile of crystalline lens was delineated to determine the respective center coordinates, thus simulating and analyzing inter-fraction and intra-fraction motion of lens in radiotherapy. Results Both left and right lens moved in different degree during both inter-or intra-fraction phase. The range of lens movement was larger in inter-fraction than in intra-fraction phase in all directions. Conclusion When radiotherapy is given in the free state, considering the distance of lens movement alone in inter-and intra-fraction and without considering the setup error, the lens planning organs at risk should increase 1.5mm outside the lens boundary.

Objective To compare the dosimetric characteristics of intensity-modulated radiation therapy(IMRT),three-dimensional conformal radiation therapy(3D-CRT) and super gamma knife arc conformal radiotherapy(SGS-CRT) for patients with recurrence of cervical cancer.Methods Treatment planning of IMRT,3D-CRT and SGS-CRT for 15 patients with recurrence of cervical cancer was designed,and the prescription dose(50Gy,2.0Gy×25) covered 95% of the planning target volume(PTV).The dosimetric characteristics of the 3 irradiation technologies in target region and organs at risk were compared by analyzing dose-volume histogram(DVH).Results The target volume of 95% prescription dose was significantly higher in 3D-CRT(99.9%±0.2%) than in IMRT(99.5%±0.5%) and SGS-CRT(99.3%±0.8%,P < 0.05);the dose gradient of target region was significantly higher in SGS-CRT(85%±20%) than in IMRT(10%±7%) and 3D-CRT(8%±5%,P < 0.05);the conformal index of target region was higher in IMRT(0.9±0.3) than in SGS-CRT(0.8±0.2,P < 0.05),and the latter was higher than that in 3D-CRT(0.7±0.5,P < 0.05).The DVH showed that the radiation volumes of bladder was lower in SGS-CRT(27.8%) than in IMRT(40.1%) and 3D-CRT(57.4%,P < 0.05) when the dosage ranged from 10 to 30 Gy,and the radiation volumes of rectum was lower in SGS-CRT(25.4%) than in IMRT(48.9%) and 3D-CRT(73.2%,P < 0.05) when the dosage ranged from 5 to 45 Gy,while there was no significant difference among the 3 irradiation technologies of the radiation volumes of small bowel.Conclusion SGS-CRT shows some dosimetric advantages in treating patients with recurrence of cervical cancer.