Research on improvement of precision in high-dose-rate brachytherapy for prostate cancer

从1995年5月至2005年12月，122名前列腺癌患者在大阪大学医院接受了高剂量率近距离放射治疗作为单一疗法（即不进行外部放射治疗）。中位随访时间为33个月（范围6-129）。在LQ模型假设a/β =1.5 Gy的情况下，大多数患者接受54 Gy/9次/5天的治疗，相当于116 Gy/ 2 Gy/次。所有患者5年总生存率94%，局部控制率97%，PSA控制率77%。低、中、高危组5年PSA控制率分别为91%、92%和67%。6例出现急性3级毒性，24例出现急性2级毒性，59例出现急性1级毒性。2例观察到晚期3级毒性，13例观察到2级毒性，28例观察到1级毒性。采用本方案的高剂量率近距离放疗是可行的，其毒性也可接受。初步和中期结果均与其他文献具有可比性。由于它可以治疗囊外病变，并且可以对前列腺施加高剂量，因此表明高剂量率近距离放疗作为单药治疗局部晚期前列腺癌是有效的。在治疗计划过程中，我们显示了基于解剖的居住位置的优势，其中居住位置根据前列腺的形状排列，而不是传统的圆柱形居住位置；以及逆优化的优越性。其次，我们应用了原始的吸引-排斥模型，并展示了新算法克服基于商业的算法的可能性。我们还发明并报告了一种新方法，使患者在接受近距离治疗时可以走动，目的是提高他们在治疗期间的生活质量，否则他们应该卧床4到5天。

From May 1995 through December 2005, 122 patients with prostate cancer were treated with high-dose-rate brachytherapy as monotherapy (i.e. without external beam radiotherapy) at Osaka University Hospital. The median follow-up time was 33 months (range, 6-129). Most of the patients were treated with 54 Gy/9 fractions/5 days, which corresponded to 116 Gy with 2 Gy/fraction on the assumption of a/β =1.5 Gy using LQ model. The 5-year overall survival rate for all patients was 94%, local control rate 97%, and PSA control rate 77%. The 5-year PSA control rates for low-, intermediate-, and high-risk groups were 91%, 92%, and 67%, respectively. Acute Grade 3 toxicity was observed in 6 patients, Grade 2 in 24 patients, and Grade 1 in 59 patients. Late Grade 3 toxicity was observed in 2 patients, Grade 2 in 13 patients, and Grade 1 in 28 patients. High-dose-rate brachytherapy with our regimen was feasible and its toxicity acceptable. The preliminary and interim results were both comparable with other literature. Because it can treat even extracapsular lesion and because it can administer a high dose to the prostate, it was suggested that high-dose-rate brachytherapy as monotherapy was effective to the locally advanced prostate cancer.In the field of treatment planning process, we showed superiority of Anatomy-based dwell positions, where dwell positions were arranged according to the figure of prostate to conventional cylindrical dwell positions; and also superiority of Inverse optimization. Second, we applied our original Attraction-Repulsion Model, and showed a possibility that the new algorithm overcame commercial-based ones.We also invented and reported a new method that enabled the patients to walk around while they were implanted the needles for brachytherapy, with the intention to improve their quality of life during treatment when otherwise they should be on bed for 4 or 5 days.