Department of Radiation Oncology, Hiroshima University Hospital, 1-2-3 Kasumi Minami-ku Hiroshima-shi, Hiroshima, 734-8553, Japan.
Hiroshima High-Precision Radiotherapy Cancer Center, 2-2 Futabanosato Higashi-ku Hiroshima-shi, Hiroshima, 732-0057, Japan.
J Med Case Rep. 2021 May 26;15(1):296. doi: 10.1186/s13256-021-02864-9.
Few studies have assessed hydrogel spacer shrinkage during external-beam radiation therapy following brachytherapy for localized high-risk prostate cancer. This case presentation evaluated the changes in hydrogel spacer appearance by magnetic resonance imaging during external-beam radiation therapy after brachytherapy for prostate cancer and analyzed the effect of this shrinkage on the dose distribution in four cases.
In all cases, we implanted I sources using a modified peripheral loading pattern for seed placement. The prescribed dose for each implant was 110 Gy. After delivering the sources, a hydrogel spacer was injected. All cases underwent external-beam radiation therapy approximately 1-2 months after brachytherapy. The prescribed dose of external-beam radiation therapy was 45 Gy in 1.8-Gy fractions. Magnetic resonance imaging was performed for evaluation on the day following seed implantation (baseline), at external-beam radiation therapy planning, and during external-beam radiation therapy. The median hydrogel spacer volume was 16.2 (range 10.9-17.7) cc at baseline, 14.4 (range, 9.4-16.1) cc at external-beam radiation therapy planning, and 7.1 (range, 2.0-11.4) cc during external-beam radiation therapy. The hydrogel spacer volume during external-beam radiation therapy was significantly lower than that at external-beam radiation therapy planning. The rectum V60-80 (rectal volume receiving at least 60-80% of the prescribed dose of external-beam radiation therapy) during external-beam radiation therapy was significantly higher than that at external-beam radiation therapy planning.
The potential reduction in hydrogel spacer size during external-beam radiation therapy following brachytherapy can lead to unexpected irradiation to the rectum. This case presentation would be helpful for similar cases.
很少有研究评估近距离放射治疗后行外照射放射治疗时水凝胶间隔物的收缩情况。本病例报告评估了前列腺癌近距离放射治疗后行外照射放射治疗期间磁共振成像中水凝胶间隔物外观的变化，并分析了这种收缩对 4 例患者中剂量分布的影响。
所有病例均采用改良的外周加载模式植入 I 源。每个植入物的处方剂量为 110 Gy。放置好源后，注射水凝胶间隔物。所有病例均在近距离放射治疗后 1-2 个月接受外照射放射治疗。外照射放射治疗的处方剂量为 45 Gy，分 1.8 Gy 剂量进行。在种子植入后第 1 天（基线）、外照射放射治疗计划时和外照射放射治疗期间进行磁共振成像评估。基线时水凝胶间隔物体积中位数为 16.2（范围 10.9-17.7）cc，外照射放射治疗计划时为 14.4（范围 9.4-16.1）cc，外照射放射治疗期间为 7.1（范围 2.0-11.4）cc。外照射放射治疗期间水凝胶间隔物体积明显小于外照射放射治疗计划时。外照射放射治疗期间直肠 V60-80（直肠接受至少 60-80%外照射放射治疗处方剂量的体积）明显高于外照射放射治疗计划时。
近距离放射治疗后行外照射放射治疗时水凝胶间隔物体积的潜在减少可能导致直肠意外照射。本病例报告对类似病例有帮助。
