Bedford J L, Khoo V S, Webb S, Dearnaley D P
Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Trust, Surrey, United Kingdom.
Int J Radiat Oncol Biol Phys. 2000 Jan 1;46(1):231-8. doi: 10.1016/s0360-3016(99)00358-2.
To determine the optimal coplanar treatment technique for six-field conformal radiotherapy of prostate only (PO) or prostate plus seminal vesicles (PSV).
A series of 6-MV six-field coplanar treatment plans were created for PO and PSV volumes in 10 patients prescribed to both 64 and 74 Gy. All plans consisted of laterally-symmetric anterior oblique, lateral, and posterior oblique fields. The posterior oblique fields were varied through 20-45 degrees relative to the lateral fields, and for each of these angles, the anterior oblique fields were varied through 25-65 degrees relative to lateral. The plans were compared by means of rectal volumes irradiated to 80% or more of the prescribed dose (V80); normal tissue complication probability (NTCP) for rectum, bladder, and femoral heads; and tumor control probability (TCP). Femoral head tolerance was designated as 52 Gy to no more than 10% volume.
For the PO group, anterior oblique fields at 50 degrees from lateral and posterior oblique fields at 25 degrees from lateral produced the lowest V80, together with femoral head doses which were appropriate for most patients (V80 = 24.4+/-5.3% [1 SD]). Compared to a commonly-used six-field (reference) plan with both anterior and posterior oblique fields at 35 degrees from lateral (V80 = 26.3+/-5.9%), this represented an improvement (p = 0.001). For the PSV group, the optimal anterior and posterior oblique fields were at 65 degrees and 30 degrees from lateral, respectively (V80 = 47.5+/-6.3%). Relative to the reference plan (V80 = 49.4+/-5.6%), this was a marginal improvement (p = 0.07).
The optimized six-field plans provide increased rectal sparing at both standard and escalated doses. Moreover, the gain in TCP resulting from dose escalation can be achieved with a smaller increase in rectal NTCP using the optimized six-field plans.
确定仅前列腺（PO）或前列腺加精囊（PSV）的六野适形放疗的最佳共面治疗技术。
为10例患者的PO和PSV体积创建了一系列6兆伏六野共面治疗计划，处方剂量为64和74戈瑞。所有计划均由侧向对称的前斜野、侧野和后斜野组成。后斜野相对于侧野在20 - 45度范围内变化，对于这些角度中的每一个，前斜野相对于侧野在25 - 65度范围内变化。通过照射到规定剂量80%或更高剂量的直肠体积（V80）、直肠、膀胱和股骨头的正常组织并发症概率（NTCP）以及肿瘤控制概率（TCP）对计划进行比较。股骨头耐受剂量设定为不超过10%体积的52戈瑞。
对于PO组，相对于侧野成50度的前斜野和相对于侧野成25度的后斜野产生了最低的V80，同时股骨头剂量对大多数患者来说是合适的（V80 = 24.4±5.3%[1个标准差]）。与常用的六野（参考）计划相比，该计划的前斜野和后斜野相对于侧野均为35度（V80 = 26.3±5.9%），这是一种改进（p = 0.001）。对于PSV组，最佳的前斜野和后斜野分别相对于侧野成65度和30度（V80 = 47.5±6.3%）。相对于参考计划（V80 = 49.4±5.6%），这是一个微小的改进（p = 0.07）。
优化后的六野计划在标准剂量和增加剂量时都能减少直肠受量。此外，使用优化后的六野计划，剂量增加导致的TCP增加可以在直肠NTCP增加较小的情况下实现。
