Reduction of irradiated small bowel volume with Trendelenburg position in gynecologic pelvic radiotherapy.

The aim of this study was to assess the effect of Trendelenburg position in comparison to prone position on small bowel volume and treatment dose in gynecologic pelvic external beam radiotherapy using three-dimensional conformal treatment plans. Eight patients with gynecologic cancers, treated with definitive or postoperative pelvic radiotherapy were investigated. Pelvic computerized tomography (CT) scans for treatment planning were performed in prone and 25 degree Trendelenburg positions for each patient. The dose-volume histograms of small bowel within the treatment fields were obtained and compared for both positions. The clinical target volume (CTV) and the planning target volume (PTV) were also defined and evaluated in the subjects. Treatment dose was 5040 cGy to PTV with 180 cGy daily fraction doses in both techniques for all patients. The average irradiated small bowel volume was 726 cc for prone position and 458 cc for the Trendelenburg position. The average irradiated small bowel volume reduction in the Trendelenburg position was 38.0% (95% CI 19.5 +/- 38%) compared with the prone position. The average small bowel percent dose was 25.4% (1280 cGy) for Trendelenburg position and 39.9% (2010 cGy) for prone position. PTV doses were similar in both techniques. The results of this dosimetric study suggest that gynecologic pelvic radiotherapy in the Trendelenburg position decreases the volume of irradiated small bowel compared to prone position and may decrease treatment related small bowel morbidity. Clinical benefit of this position should be evaluated in further clinical studies.

Optimisation techniques in vaginal cuff brachytherapy.

The aim of this study was to explore whether an in-house dosimetry protocol and optimisation method are able to produce a homogeneous dose distribution in the target volume, and how often optimisation is required in vaginal cuff brachytherapy. Treatment planning was carried out for 109 fractions in 33 patients who underwent high dose rate iridium-192 (Ir(192)) brachytherapy using Fletcher ovoids. Dose prescription and normalisation were performed to catheter-oriented lateral dose points (dps) within a range of 90-110% of the prescribed dose. The in-house vaginal apex point (Vk), alternative vaginal apex point (Vk'), International Commission on Radiation Units and Measurements (ICRU) rectal point (Rg) and bladder point (Bl) doses were calculated. Time-position optimisations were made considering dps, Vk and Rg doses. Keeping the Vk dose higher than 95% and the Rg dose less than 85% of the prescribed dose was intended. Target dose homogeneity, optimisation frequency and the relationship between prescribed dose, Vk, Vk', Rg and ovoid diameter were investigated. The mean target dose was 99+/-7.4% of the prescription dose. Optimisation was required in 92 out of 109 (83%) fractions. Ovoid diameter had a significant effect on Rg (p = 0.002), Vk (p = 0.018), Vk' (p = 0.034), minimum dps (p = 0.021) and maximum dps (p<0.001). Rg, Vk and Vk' doses with 2.5 cm diameter ovoids were significantly higher than with 2 cm and 1.5 cm ovoids. Catheter-oriented dose point normalisation provided a homogeneous dose distribution with a 99+/-7.4% mean dose within the target volume, requiring time-position optimisation.

Dosimetric comparison of conventional helmet-field whole-brain irradiation with three-dimensional conformal radiotherapy: dose homogeneity and retro-orbital area coverage.

The aim of this study was to compare the dosimetric data from conventional two-dimensional (2D) helmet-field whole-brain irradiation (WBI) with those from three-dimensional conformal radiotherapy (3D-CRT), and to investigate the potential benefits of 3D-CRT as regards both dose coverage of the brain and retro-orbital (RO) area and ocular lens protection. Simulation CT scans of 30 patients were used. In 3D-CRT planning, the brain, optic nerves, ocular lenses and RO areas were contoured. Two opposed lateral fields were used and matched non-divergently behind the ocular lenses. The nominal prescribed photon beam dose was 1800 cGy in 10 fractions using 6 MV photons. Brain and RO areas were covered by at least 95% and 90% of the prescribed dose, respectively, and the maximum doses were limited to 110% of prescribed dose. In conventional 2D planning, the same field centre and angles were used as for the 3D-CRT plans. Fields were created using digital reconstructed radiographs and bony reference marks without information on the contour of structures. Brain, ocular lens and RO area doses were compared using cumulative dose-volume histograms. The mean value of minimum brain doses was significantly higher (p = 0.008) for 3D-CRT plans: all patients received a minimum of 95% of the prescribed dose. Mean doses of the left (p = 0.004) and right (p = 0.003) RO areas were also higher for 3D-CRT plans than for conventional 2D plans: all patients received a minimum of 90% of the prescribed dose. Furthermore, the mean values of minimum doses for both RO areas were statistically higher for 3D-CRT (p<0.001). 3D-CRT planning significantly improved the coverage of the RO areas and the dose homogeneity in WBI while protecting the ocular lenses.