Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark.
Acta Oncol. 2013 Apr;52(3):521-7. doi: 10.3109/0284186X.2012.752860. Epub 2013 Feb 14.
Internal target and organ motion during treatment is a challenge in radiotherapy (RT) of the prostate and the involved elective targets, with residual motion being present also following image-guidance strategies. The aim of this study was to investigate organ motion-induced dose degradations for the prostate, seminal vesicle and the pelvic lymph node when treating these targets with proton therapy, using different image-guidance and delivery strategies.
Four patients were selected from a larger series as they displayed large inter-fractional variation in bladder and rectum volume. Intensity-modulated proton therapy plans were generated using both simultaneous integrated and sequential boost delivery. For each technique, three isotropic margin expansions (in the range of 4-10 mm) were evaluated for the clinical target volume of prostate (CTV-p), seminal vesicles (CTV-sv) and lymph nodes (CTV-ln). Simulation of the dose degradations for all treatment plans were based on dose re-calculations for the 8-9 repeat CTs available for each patient, after applying rigid registrations to reproduce set-up based on either intra-prostatic fiducials or bony anatomy.
The simulated dose received by 99% of the target volume (D(99)) and generalized equivalent dose (gEUD) showed substantial inter-patient variations. For 40% of the investigated scenarios, the patient average simulated D(99) for all targets were within 2 GyE from the planned dose. The largest difference between simulated and planned dose was seen for the CTV-sv when using SIB delivery, with an average relative reduction in D(99) of 13% and 15% for the largest margin expansion, when positioned using fiducials and bony anatomy, respectively.
The most severe dose degradations were found for CTV-sv, but they were also evident for CTV-ln. The degradations could not be completely resolved, neither by using the largest margin expansion nor with the choice of set-up. With fiducial set-up CTV-p was robust against the inter-fraction changes.
本研究旨在探讨使用质子治疗前列腺、精囊和盆腔淋巴结时，不同图像引导和治疗策略下，靶区器官运动导致的剂量衰减。
从一个更大的系列中选择了 4 名患者，因为他们在膀胱和直肠体积方面存在很大的分次间变化。使用同时集成和序贯增强两种方式生成强度调制质子治疗计划。对于每种技术，评估了临床靶区（CTV-p）、精囊（CTV-sv）和淋巴结（CTV-ln）的三个各向同性边界扩展（4-10mm 范围内）。所有治疗计划的剂量衰减模拟均基于每个患者可获得的 8-9 次重复 CT 的剂量重新计算，应用刚性配准以根据前列腺内基准或骨骼解剖结构来重现摆位。
99%靶区接受的模拟剂量（D(99)）和广义等效剂量（gEUD）显示出显著的患者间差异。对于 40%的研究情况，所有靶区的患者平均模拟 D(99)与计划剂量相差 2GyE 以内。当使用 SIB 治疗时，使用基准和骨骼解剖结构定位时，CTV-sv 的模拟剂量与计划剂量的差异最大，最大边界扩展的 D(99)平均相对减少 13%和 15%。
CTV-sv 的剂量衰减最严重，但 CTV-ln 也有明显的剂量衰减。即使使用最大边界扩展或选择摆位，也无法完全解决这些衰减。使用基准定位时，CTV-p 对分次间变化具有较强的稳健性。
