Bedford J L, Khoo V S, Oldham M, Dearnaley D P, Webb S
Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Trust, Sutton, Surrey, UK.
Radiother Oncol. 1999 Jun;51(3):225-35. doi: 10.1016/s0167-8140(99)00057-2.
Conformal radiotherapy of the prostate is an increasingly common technique, but the optimal choice of beam configuration remains unclear. This study systematically compares a number of coplanar treatment plans for four-field irradiation of two different clinical treatment volumes: prostate only (PO) and the prostate plus seminal vesicles (PSV).
A variety of four-field coplanar treatment plans were created for PO and PSV volumes in each of ten patients. Plans included a four-field 'box' plan, a symmetric plan having bilateral anterior and posterior oblique fields, a plan with anterior oblique and lateral fields, a series of asymmetric plans, and a three-field plan having anterior and bilateral fields for comparison. Doses of 64 and 74 Gy were prescribed to the isocentre. Plans were compared using the volume of rectum irradiated to greater than 50% (V50), 80% (V80) and 90% (V90) of the prescribed dose. Tumour control probabilities (TCP) and normal tissue complication probabilities (NTCP) for the rectum, bladder and femoral heads were also evaluated. Femoral head dose was limited such that less than 10% of each femoral head received 70% of the prescribed dose.
For the PO group, the optimal plan consisted of anterior oblique and lateral fields (Rectal V80 = 23.8+/-5.0% (1 SD)), while the box technique (V80 = 26.0+/-5.8%) was less advantageous in terms of rectal sparing (P = 0.001). Similar results were obtained for the PSV group (Rectal V80 = 43.9+/-5.0% and 47.3+/-5.5% for the two plan types, respectively, P = 0.001). The three-field plan was comparable to the optimal four-field plan but gave higher superficial body dose. With dose escalation from 64 to 74 Gy, the mean TCP for the optimal plan rose from 52.0+/-2.8% to 74.1+/-2.0%. Meanwhile, rectal NTCP for the optimal plan rose by 3.5% (PO) or 8.4% (PSV), compared to 4.7% (PO) or 10.1% (PSV) for the box plan.
For PO volumes, a plan with gantry angles of 35 degrees, 90 degrees, 270 degrees and 325 degrees offers a high level of rectal sparing and acceptable dose to the femoral heads for all patients, while for PSV volumes, the corresponding plan has gantry angles of 20 degrees, 90 degrees , 270 degrees and 340 degrees. Using these plans, the gain in TCP resulting from dose escalation can be achieved with a smaller increase in anticipated rectal NTCP.
前列腺适形放疗是一种日益常见的技术，但射野配置的最佳选择仍不明确。本研究系统地比较了针对两种不同临床靶区（仅前列腺（PO）和前列腺加精囊（PSV））的四野照射的多种共面治疗计划。
为十名患者中的每一位的PO和PSV靶区创建了多种四野共面治疗计划。计划包括一个四野“盒式”计划、一个具有双侧前后斜野的对称计划、一个具有前斜野和侧野的计划、一系列不对称计划以及一个具有前野和双侧野的三野计划用于比较。等中心处的处方剂量为64 Gy和74 Gy。使用照射到大于处方剂量50%（V50）、80%（V80）和90%（V90）的直肠体积来比较计划。还评估了直肠、膀胱和股骨头的肿瘤控制概率（TCP）和正常组织并发症概率（NTCP）。股骨头剂量限制为每个股骨头接受小于70%处方剂量的比例小于10%。
对于PO组，最佳计划由前斜野和侧野组成（直肠V80 = 23.8±5.0%（1标准差）），而盒式技术（V80 = 26.0±5.8%）在直肠保护方面优势较小（P = 0.001）。PSV组也得到了类似结果（两种计划类型的直肠V80分别为43.9±5.0%和47.3±5.5%，P = 0.001）。三野计划与最佳四野计划相当，但体表剂量更高。随着剂量从64 Gy增加到74 Gy，最佳计划的平均TCP从52.0±2.8%升至74.1±2.0%。同时，最佳计划的直肠NTCP上升了3.5%（PO）或8.4%（PSV），相比之下，盒式计划为4.7%（PO）或10.1%（PSV）。
对于PO靶区，机架角度为35度、90度、270度和325度的计划对所有患者而言都能高度保护直肠并使股骨头接受可接受剂量，而对于PSV靶区，相应计划的机架角度为20度、90度、270度和340度。使用这些计划，剂量增加所带来的TCP增益可以在预期直肠NTCP增加较小的情况下实现。
