Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
Department of Radiation Oncology, University of Massachusetts Memorial Medical Center, Worcester, Massachusetts, USA.
J Appl Clin Med Phys. 2022 Nov;23(11):e13772. doi: 10.1002/acm2.13772. Epub 2022 Aug 27.
For breast cancer patients treated in the prone position with tangential fields, a diamond-shaped light field (DSLF) can be used to align with corresponding skin markers for image-guided radiation therapy (IGRT). This study evaluates and compares the benefits of different DSLF setups. Seventy-one patients who underwent daily tangential kilovoltage (kV) IGRT were categorized retrospectively into four groups: (1) DSLF field size (FS) = 10 × 10 cm , gantry angle = 90° (right breast)/270° (left breast), with the same isocenter as treatment tangential beams; (2) same as group 1, except DSLF FS = 4 × 4 cm ; (3) DSLF FS = 4 × 4-6 × 8 cm , gantry angle = tangential treatment beam, off-isocenter so that the DSLF was at the approximate breast center; and (4) No-DSLF. We compared their total setup time (including any DSLF/marker-based alignment and IGRT) and relative kV-based couch shift corrections. For groups 1-3, DSLF-only dose distributions (excluding kV-based correction) were simulated by reversely shifting the couch positions from the computed tomography plans, which were assumed equivalent to the delivered dose when both DSLF and IGRT were used. For patient groups 1-4, the average daily setup time was 2.6, 2.5, 5.0, and 8.3 min, respectively. Their mean and standard deviations of daily kV-based couch shifts were 0.64 ± 0.4, 0.68 ± 0.3, 0.8 ± 0.6, and 1.0 ± 0.6 cm. The average target dose changes after excluding kV-IGRT for groups 1-3 were-0.2%, -0.1%, and +0.4%, respectively, whereas DSLF-1 was most efficient in sparing heart and chest wall, DSLF-2 had lowest lung D ; and DSLF-3 maintained the highest target coverage at the cost of highest OAR dose. In general, the use of DSLF greatly reduces patient setup time and may result in smaller IGRT corrections. If IGRT is limited, different DSLF setups yield different target coverage and OAR dose sparing. Our findings will help DSLF setup optimization in the prone breast treatment setting.
对于采用切线野俯卧位治疗的乳腺癌患者，可以使用菱形光野（DSLF）与相应的皮肤标记物对齐，以进行图像引导放射治疗（IGRT）。本研究评估并比较了不同 DSLF 设置的优势。回顾性地将 71 名接受每日切线千伏（kV）IGRT 的患者分为四组：（1）DSLF 野大小（FS）= 10×10cm，机架角度= 90°（右乳）/270°（左乳），与治疗切线束的相同等中心；（2）与组 1 相同，只是 DSLF FS= 4×4cm；（3）DSLF FS= 4×4-6×8cm，机架角度=切线治疗束，偏心等中心，使 DSLF 位于乳房中心附近；（4）无 DSLF。我们比较了他们的总设置时间（包括任何 DSLF/基于标记的对准和 IGRT）和相对的基于千伏的床面移动校正。对于组 1-3，通过从计算机断层扫描计划中反向移动床面位置来模拟仅 DSLF 的剂量分布（不包括基于千伏的校正），假设当同时使用 DSLF 和 IGRT 时，该位置相当于所给予的剂量。对于患者组 1-4，平均每日设置时间分别为 2.6、2.5、5.0 和 8.3 分钟。他们每日基于千伏的床面移动的平均值和标准差分别为 0.64±0.4、0.68±0.3、0.8±0.6 和 1.0±0.6cm。排除组 1-3 的千伏 IGRT 后，平均靶区剂量变化分别为-0.2%、-0.1%和+0.4%，而 DSLF-1 对心脏和胸壁的保护最有效，DSLF-2 的肺 D 值最低；而 DSLF-3 则以最高的 OAR 剂量为代价维持了最高的靶区覆盖率。一般来说，使用 DSLF 可大大减少患者的设置时间，并且可能导致较小的 IGRT 校正。如果 IGRT 受到限制，不同的 DSLF 设置会产生不同的靶区覆盖率和 OAR 剂量节省。我们的研究结果将有助于俯卧位乳腺癌治疗中 DSLF 设置的优化。
