Salagean Ghizela A-M, Bálint Zoltán, Poortmans Philip, Portik Daniel
Faculty of Physics, Babes Bolyai University Cluj-Napoca, Romania.
TopMed Medical Centre, Targu Mures, Romania.
Rep Pract Oncol Radiother. 2025 Feb 19;29(6):732-739. doi: 10.5603/rpor.104013. eCollection 2024.
Daily bolus positioning implies a high degree of variability, which can affect the dose distribution within the planning target volume (PTV) and the organs at risk (OAR). We carried out a retrospective study to evaluate bolus positioning in patients with breast cancer.
We evaluated 7 cases with left and 5 cases with right chest-wall with comprehensive nodal region irradiation in which bolus material was used to obtain better skin surface coverage. The bolus positioning on the daily cone-beam computed tomography (CBCT) images was compared to the reference image from the treatment planning system. Deviations from the reference position of the bolus were categorized as positive shifts (PosS) or negative shifts (NegS), depending on the material's overlapping with its planned position. Subsequently, a second plan was calculated using the information from the CBCT images for comparison with the original treatment plan. We performed a statistical and dosimetric analysis on the results.
For both the 95% dose coverage for the PTV for the chest wall and for the lymph node regions, about 2% variation between initial and recalculated plans was seen, with a shift of the hotspots' position in some cases. The average mean heart dose was 4.1 ± 0.3 Gy, whereas the values for PosS and NegS mean heart doses were 3.8 ± 0.4 Gy and 4.0 ± 0.6 Gy, respectively. In contrast to the original values for the ipsilateral lung V5 (57.1 ± 12.9%), V20 (30.2 ± 2.7%), and Dmean (15.0 ± 1.7 Gy), the values for PosS were 56.1 ± 4.2% for V5:, 30.1 ± 3.3% for V20, and 14.9 ± 1.2 Gy for Dmean while for NegS we obtained 56.9 ± 8.9% for V5, 30.0 ± 2.3% for V20, and 15.2 ± 1.8 Gy for Dmean.
We observed dosimetric differences between the initial and given treatment plans depending on the position of the bolus for all cases, indifferent of the shift direction. Although the differences were not statistically significant, we identified a few specific instances where the variations might cause uncertainties regarding doses to the organs at risk (OAR). We suggest therefore that strategies for correct daily reproducibility of the bolus need to be implemented on a departmental level.
每日推量的定位存在高度变异性，这可能会影响计划靶区（PTV）和危及器官（OAR）内的剂量分布。我们开展了一项回顾性研究，以评估乳腺癌患者的推量定位情况。
我们评估了7例左侧胸壁和5例右侧胸壁伴综合淋巴结区域照射的病例，这些病例使用了推量材料以获得更好的皮肤表面覆盖。将每日锥形束计算机断层扫描（CBCT）图像上的推量定位与治疗计划系统的参考图像进行比较。根据推量材料与其计划位置的重叠情况，将推量相对于参考位置的偏差分类为正向偏移（PosS）或负向偏移（NegS）。随后，利用CBCT图像的信息计算第二个计划，以便与原始治疗计划进行比较。我们对结果进行了统计和剂量学分析。
对于胸壁和淋巴结区域的PTV的95%剂量覆盖，初始计划和重新计算的计划之间出现了约2%的变化，在某些情况下热点位置发生了偏移。平均平均心脏剂量为4.1±0.3 Gy，而PosS和NegS的平均心脏剂量值分别为3.8±0.4 Gy和4.0±0.6 Gy。与同侧肺V5（57.1±12.9%）、V20（30.2±2.7%）和Dmean（15.0±1.7 Gy）的原始值相比，PosS的V5值为56.1±4.2%，V20为30.1±3.3%，Dmean为14.9±1.2 Gy，而NegS的V5值为56.9±8.9%，V20为30.0±2.3%，Dmean为15.2±1.8 Gy。
我们观察到，在所有病例中，根据推量的位置，初始治疗计划和给定治疗计划之间存在剂量学差异，与偏移方向无关。尽管差异无统计学意义，但我们确定了一些特定情况，其中这些变化可能会导致危及器官（OAR）剂量的不确定性。因此，我们建议在科室层面实施确保推量每日正确可重复性的策略。
