前立腺癌に対する高線量率組織内照射において，アプリケーター針の刺入本数や刺入位置は線量分布に大きく影響する．刺入方法は各施設の経験やポリシー，使用装置に依存する部分があり，最適な刺入法として確立された普遍的な方法はない．今回我々はアプリケーター針の刺入本数と線量体積因子の関連を解析し，最適な刺入本数を検討した．対象は2010年６月１日から2012年10月31日の間に同治療を受けた初発前立腺癌135例．治療計画にはOncentra® を用いた．治療前エコーによる前立腺体積，治療計画CT により算出された線量体積因子（PTV のDmin%，D90%，dosenon-uniformity ratio：DNR，homogeneity index：HI，conformity index：CI，尿道最大線量，直腸最大線量），治療時期（一次解析として前期：～2011年１月，中期：2011年２月～９月，後期：2011年10月～2012年５月，さらに追加解析として直近：2012年６月〜），アプリケーター針刺入本数について，相互の関連をJMP 14，Student のｔ検定を用いて検討した．一次解析の結果，刺入本数は前立腺体積と相関せず，刺入本数が多い群は少ない群に比べ尿道最大線量が有意に低かった．他の線量体積因子では有意差はないものの，刺入本数が多い群でPTV のDmin% は高値，D90% は高値，DNR は低値，HI は高値，CI は高値と，本数が多いほど良好な線量分布であることを示していた．なお，治療時期が後期の症例で刺入本数が有意に増加していた．これらの結果が判明した後に治療された直近16例においては，さらに刺入本数が増加し，線量体積因子の改善が認められていた．今回の検討から，アプリケーター針の刺入本数が多いほど線量分布が改善し，とくに16-17本の刺入により良好な線量分布が得られることが示された． In high-dose-rate brachytherapy (HDR-BT) for prostate cancer, the number and arrangement of applicator needles have a decisive impact on radiation dose distribution. Brachytherapy techniques largely depend on the operator’s experience, policy and devices. Furthermore, the procedures of needle insertion, dose prescription and plan optimization vary according to institutions. The aim of this study was to determine the optimal needle number for achieving the best quality of HDR-BT for prostate cancer by analyzing the relationship between needle number and dose-volume parameters. We included 135 patients with newly diagnosed prostate cancer who received HDR-BT between June 2010 and October 2012. Treatment planning was performed on Oncentra® using volume optimization, followed by manual graphical optimization. Dose-volume parameters, such as Dmin% and D90% of the planning target volume (PTV), dose non-uniformity ratio (DNR), homogeneity index (HI), conformity index (CI), and maximum dose to the urethra and rectum, were calculated on the treatment planning system. Student’s t-test was performed to determine the correlation of these parameters and prostate volume with needle number using the JMP® 14 software. We divided the treatment period into three phases: early, middle, and late; needle number and dose-volume parameters were analyzed according to these periods. Needle number was not correlated with prostate volume but showed correlations with several dose-volume parameters. Higher needle number was significantly correlated with lower maximum dose to the urethra; furthermore, higher needle number had a tendency to show correlations with higher Dmin% of PTV, higher D90%, lower DNR, higher HI, and higher CI. These results indicated that a higher needle number could achieve better radiation dose distribution. Concerning the treatment period, the number of needles used in patients was higher in the late period than in the earlier period. Based on these results, we started using the highest number of needles that could be inserted safely; this led to the achievement of better radiation dose distribution. In conclusion, our results show that a high needle number can achieve better quality of brachytherapy for prostate cancer. We think that using 16 or 17 needles is the most appropriate
