Vaarkamp Jaap, Adams Elizabeth J, Warrington Alan P, Dearnaley David P
Joint Department of Physics, Royal Marsden NHS Trust and Institute of Cancer Research, Sutton, Surrey, UK.
Radiother Oncol. 2004 Oct;73(1):65-72. doi: 10.1016/j.radonc.2004.07.015.
Full inverse planned intensity modulated radiotherapy (IMRT) may be indicated to treat concave targets like prostate and pelvic nodes, because concave dose distributions cannot be generated with conformal radiotherapy (CRT). We investigated whether this concave dose distribution can be produced using simplified forward planned multi segment radiotherapy (MSRT).
CRT, MSRT and IMRT dose distributions were calculated and compared for five patients treated in our current IMRT prostate and pelvic node dose escalation trial. The same beam arrangement was used for CRT, MSRT and IMRT, increasing the number of segments. The MSRT concave dose distribution was realised regarding left and right pelvic nodes as two separate targets. The IMRT dose distribution had been used to treat the patients using a step and shoot delivery.
Contrary to CRT, forward planned MSRT concave dose distributions had improved target coverage at lower or equivalent bowel doses than inverse planned IMRT. The five MSRT beams had a maximum of three segments per beam. Both lateral beams had two segments to deliver the two dose levels to prostate and nodes. The posterior field needed a third segment to avoid using a central block. The two anterior oblique beams needed a third segment to account for the different beam weighting because the nodes were irradiated partially using four and partially using five beams. Inverse planned IMRT used up to 15 segments in any one beam, with an average of 11.4 per beam.
Concave dose distributions for prostate and pelvic node treatment were generated using forward planned multi segment techniques. The plans met clinical constraints used in our IMRT protocol. MSRT presented a significant advantage over both CRT and IMRT.
全逆向计划调强放疗（IMRT）可能适用于治疗如前列腺和盆腔淋巴结等凹陷靶区，因为适形放疗（CRT）无法生成凹陷的剂量分布。我们研究了能否使用简化的正向计划多野放疗（MSRT）产生这种凹陷剂量分布。
对在我们当前的IMRT前列腺和盆腔淋巴结剂量递增试验中治疗的5例患者，计算并比较了CRT、MSRT和IMRT的剂量分布。CRT、MSRT和IMRT使用相同的射野布置，增加了子野数量。将左、右盆腔淋巴结视为两个独立靶区来实现MSRT凹陷剂量分布。IMRT剂量分布已用于采用步进式射野技术治疗患者。
与CRT相反，正向计划的MSRT凹陷剂量分布在较低或同等肠道剂量下比逆向计划的IMRT具有更好的靶区覆盖。五条MSRT射野每条射野最多有三个子野。两条侧野各有两个子野，用于向前列腺和淋巴结提供两个剂量水平。后野需要第三个子野以避免使用中央挡块。两条前斜野需要第三个子野来考虑不同的射野权重，因为淋巴结部分使用四条射野部分使用五条射野照射。逆向计划的IMRT在任何一条射野中最多使用15个子野，平均每条射野11.4个子野。
采用正向计划多野技术生成了用于前列腺和盆腔淋巴结治疗的凹陷剂量分布。这些计划符合我们IMRT方案中使用的临床限制条件。MSRT相对于CRT和IMRT均具有显著优势。
