Ruifrok A C, Levendag P C, Lakeman R F, Deurloo I K, Visser A G
Department of Radiation Oncology, Dr. Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
Int J Radiat Oncol Biol Phys. 1990 Jan;18(1):31-6. doi: 10.1016/0360-3016(90)90263-j.
One way to deliver high doses of radiation to deep seated tumors without damaging the surrounding tissue is by interstitial techniques. This is commonly applied clinically; however, biological data of tumor response to interstitial low-dose-rate gamma irradiation are scarce. Therefore, we have studied the response of rhabdomyosarcoma R1 tumors implanted in the flanks of female Wag/Rij rats using an interstitial Ir192 afterloading system. A template was developed by which four catheters can be implanted in a square geometry with a fixed spacing. Subsequently four Ir192 wires of 2 cm length each are inserted. For dose prescription the highest isodose enveloping the tumor volume was chosen. Interstitial irradiation was performed using tumor volumes of 1500-2000 mm3. A range of minimum tumor doses of 20 up to 115 Gy were given at a mean dose-rate of 48 cGy/hr. Dose-effect relations were obtained from tumor growth curves and tumor cure data, and compared to data from external irradiation. The dose required for 50% cures with interstitial irradiation (TCD50) appears to be 95 +/- 9 Gy. The TCD50 for low-dose-rate interstitial gamma irradiation is 1.5 times the TCD50 for single dose external X ray irradiation at high dose rates, but is comparable to the TCD50 found after fractionated X ray irradiation at high dose rate. Sham treatment of the tumors had no effect on the time needed to reach twice the treatment volume. The growth rate of tumors regrowing after interstitial radiotherapy is not markedly different from the growth rate of untreated (control) tumors (volume doubting time 5.6 +/- 1 day), in contrast to the decreased growth rate after external X ray irradiation. It is argued that the absence of a clear tumor bed effect may be explained by some sparing of the stroma by the low-dose-rate of the interstitial irradiation per se as well as by the physical dose distribution of the interstitial Ir192 sources, giving a relative low dose of radiation to the surrounding normal tissues.
一种在不损伤周围组织的情况下将高剂量辐射传递至深部肿瘤的方法是采用间质技术。这在临床上已普遍应用；然而，关于肿瘤对间质低剂量率伽马射线照射反应的生物学数据却很匮乏。因此，我们使用间质铱 - 192后装系统，研究了植入雌性Wag/Rij大鼠侧腹的横纹肌肉瘤R1肿瘤的反应。开发了一种模板，通过该模板可以将四根导管以固定间距呈方形植入。随后插入四根长度均为2厘米的铱 - 192导线。对于剂量处方，选择包围肿瘤体积的最高等剂量线。使用体积为1500 - 2000立方毫米的肿瘤体积进行间质照射。以48厘戈瑞/小时的平均剂量率给予一系列最低肿瘤剂量，范围从20戈瑞到115戈瑞。从肿瘤生长曲线和肿瘤治愈数据中获得剂量 - 效应关系，并与外照射数据进行比较。间质照射实现50%治愈所需的剂量（TCD50）似乎为95±9戈瑞。低剂量率间质伽马射线照射的TCD50是高剂量率单次外照射X射线TCD50的1.5倍，但与高剂量率分次X射线照射后的TCD50相当。对肿瘤进行假处理对达到两倍治疗体积所需的时间没有影响。间质放疗后复发肿瘤的生长速度与未治疗（对照）肿瘤的生长速度没有明显差异（体积倍增时间为5.6±1天），这与外照射X射线后生长速度降低形成对比。有人认为，间质照射低剂量率本身以及间质铱 - 192源的物理剂量分布对基质有一定的保护作用，从而使周围正常组织接受相对较低剂量的辐射，这可以解释为何没有明显的肿瘤床效应。
