Prognostic Factors in Computed Tomography–Guided Brachytherapy for Stage I-II Cervical Cancer (original) (raw)

2015, International Journal of Radiation Oncology*Biology*Physics

Materials/Methods: This study was performed on 6 cervical-cancer BT cases with different applicators including tandem and ovoid, ovoid with needles and ring applicators. Computed tomography was used as an imagining modality for the first 3 cases and MRI for the other 3. For each case and imaging modality, participants from 6 different institutions each created 2 BT plans: the first was a plan normalized to point A, and the second was an optimized plan. The high-dose-rate (HDR) BT plans were created as boost plans under the assumption that the patients had previously received 45 Gy, during the initial course. The prescription dose for the HDR treatment was 27.5 Gy in 5 fractions. Plan construction required that the tumor D90 receive the highest possible total dose while respecting maximum dose constraints to the rectum, bladder and sigmoid (75, 90 and 75 Gy). The EQD2 calculation was performed so total dose from treatments could be evaluated. Data collected for statistical analysis included: CTV and high-risk CTV (D90, D100, V100, V150 and V200); D0.1cm 3 , D2cm 3 and D5cm 3 for the bladder, rectum and sigmoid. Results: On an institutional level, differences were most noted in the ovoid and needles plans, irrespective of the imaging modality. The average coverage (D90) of CTV for MR-based optimized and non-optimized plans were 4.92 (SD Z 0.74) Gy and 4.88 (SD Z 0.89) Gy, respectively, indicating the increase of variations with increase of the plan complexity. The table shows the average values of the optimized plans across 6 institutions; D90 for the optimized plans was 5.25 (SD Z 0.61) Gy per fraction resulting in a total equivalent dose of 77.6AE5.2 Gy. The average D2 doses for bladder, rectum and sigmoid for the optimized plans were 77.6 (SD Z 5.2) Gy, 68.2 (SD Z 5.8) Gy and 63.8 (SD Z 3.3) Gy, respectively. A high level of consistency between the dosimetric parameters for all plans was noted (all P>.05). Conclusion: No significant differences in target coverage were recorded in any plans. This conclusion is valid for both optimized plans and point A normalized plans, indicating the consistency of the treatment plans among the institutions. The differences in the doses to the OARs should not translate into meaningful clinical outcomes.