ABSTRACT
BACKGROUND: Two-dimensional treatment planning using radiographs or simulator films was the standard in planning brachytherapy for patients with cervical cancer. Three-dimensional (3D) treatment planning has improved treatment efficacy. This retrospective study compares conventional and 3D treatment planning of brachytherapy in patients with cervical cancer and interfraction dose variation to bladder and rectum (D2cc). METHODS: The mean doses to bladder and rectum (D2cc) were computed by computed tomography (CT)-based planning during 100 sessions of intracavitary brachytherapy for carcinoma cervix with the same source configuration as generated for conventional planning, and these estimates were compared with the doses at International Commission on Radiation Units and measurements (ICRU) rectal, bladder points and point A. Interfraction variation of doses to bladder and rectum during various sessions was also analysed. RESULT: The mean ICRU bladder dose and D2cc of the bladder for all patients was 3.7 Gy and 7.4 Gy, respectively (p < 0.001). The mean ICRU rectal dose from conventional plan was 4.3Gy and with CT planning, 4.45 Gy (p = 0.04). Interfraction dose variations for D2cc of the bladder were min -5.3 Gy and max 4.8 Gy and those of the rectum were min -1.8 Gy and max 1.72Gy. CONCLUSION: Dosimetric evaluation of conventional and 3D CT-based treatment planning for the same brachytherapy sessions demonstrated underestimation of ICRU bladder dose points (p < 0.001) and the rectal ICRU point dose and D2cc (p=0.04). The doses to organs at risk did not show a statistically significant variation between the fractions. However, large variation was noted between the interfractional maximum and minimum doses to bladder and rectum.
ABSTRACT
BACKGROUND: Inaccuracies in treatment setup during radiation therapy for breast cancers may increase risks to surrounding normal tissue toxicities, i.e. organs at risks (OARs), and compromise disease control. This study was planned to evaluate the dosimetric and isocentric variations and determine setup reproducibility and errors using an online electronic portal imaging (EPI) protocol. METHODS: A total of 360 EPIs in 60 patients receiving breast/chest wall irradiation were evaluated. Cumulative dose-volume histograms (DVHs) were analyzed for mean doses to lung (V20) and heart (V30), setup source to surface distance (SSD) and central lung distance (CLD), and shifts in anterior-posterior (AP), superior-inferior (SI), and medial lateral (ML) directions. RESULTS: Random errors ranged from 2 to 3 mm for the breast/chest wall (medial and lateral) tangential treatments and 2-2.5 mm for the anterior supraclavicular nodal field. Systematic errors ranged from 3 to 5 mm in the AP direction for the tangential fields and from 2.5 to 5 mm in the SI and ML direction for the anterior supraclavicular nodal field. For right-sided patients, V20 was 0.69-3.96 Gy, maximum lung dose was 40.5 Gy, V30 was 1.4-3 Gy, and maximum heart dose was 50.5 Gy. Similarly, for left-sided patients, the CLD (treatment planning system) was 25 mm-30 mm, CLD (EPIs) was 30-40 mm, V20 was 0.9-5.9 Gy, maximum lung dose was 45 Gy, V30 was 2.4-4.1 Gy, and maximum heart dose was 55 Gy. CONCLUSION: Online assessment of patient position with matching of EPIs with digitally reconstructed radiographs (DRRs) is a useful method in evaluation of interfraction reproducibility in breast irradiation.
ABSTRACT
PURPOSE: To compare intracavitary brachytherapy dose estimation for organs at risk (bladder and rectum) based on semi-orthogonal reconstruction of radiographs on non-isocentric X-ray unit and Computed Tomography (CT) - based volumetric planning in cervical cancer. MATERIAL AND METHODS: Bladder and rectal points as per International Commission on Radiation Units and Measurements (ICRU) report 38, were retrospectively evaluated on 15 high dose rate intracavitary brachytherapy applications for cervical cancer cases. With the same source configuration as obtained during planning on radiographs performed on a non-isocentric X-ray unit, the mean doses to 2cc of most irradiated part of bladder and rectum were computed by CT planning and these estimates were compared with the doses at ICRU bladder and rectal points. RESULTS: The mean ICRU point dose for bladder was 3.08 Gy (1.9-5.9 Gy) and mean dose to 2 cc (D2cc) bladder was 6.91 Gy (2.9-12.2 Gy). ICRU rectal dose was 3.8 Gy (2.4-4.45 Gy) and was comparable with D2cc rectum dose 4.2 Gy (2.8-5.9 Gy). Comparison of mean total dose (ICRU point vs. D2cc) for each patient was found to be significantly different for bladder (p = 0.000), but not for rectum (p = 0.08). CONCLUSIONS: On comparison of ICRU point based planning with volumetric planning on CT, it was found that bladder doses were underestimated by the film based method. However, the rectal doses were found to be similar to the D2cc doses. The results with non isocentric film based treatment planning were similar to the existing literature on orthogonal film based simulator planning.
