The response of human glioma cell lines to low-dose radiation exposure

PURPOSE: To examine the low-dose radiation response of a series of radioresistant human glioma cell lines and determine if low-dose hypersensitivity is a characteristic of these cells. MATERIALS AND METHODS: The clonogenic survival of six radioresistant human glioma cell lines was measured following exposure to graded, single, very low doses of X-rays in vitro. High resolution was achieved using either a Dynamic Microscopic Image Processing Scanner (DMIPS) or a cell sorter (CS). RESULTS: In five of the six cell lines tested, low-dose hypersensitivity (HRS) was demonstrated although in the sixth, a grade III astrocytoma line, it was not. These results are consistent with previous data indicating that low-dose hypersensitivity is more marked in more radioresistant cell lines although the difference between the glioblastoma cell lines with differing SF2 is not marked. CONCLUSION: Low-dose hypersensitivity is common in radioresistant glioma cell lines. This may have implications for the treatment of these tumours if further studies confirm that HRS translates to increased effectiveness per gray in vivo when very low doses per fraction are used.     

On the possible increase in local tumour control probability for gliomas exhibiting low dose hyper-radiosensitivity using a pulsed schedule

Using modelling, we have developed a treatment strategy for gliomas exhibiting low dose hyper-radiosensitivity (HRS) that employs both a reduced dose-rate and pulsed treatment dose delivery. The model exploits the low dose hypersensitivity observed in some glioma cell lines at low radiation doses. We show, based on in vitro data, that a pulsed delivery of external beam radiation therapy could yield significant increases in local control. We therefore propose a pulsed delivery scheme for the treatment of gliomas in which the daily treatment fraction is delivered using 0.20 Gy pulses, separated by three minutes for a time-averaged dose-rate of 0.0667 Gy/min. The dose per pulse of 0.2 Gy is near or below the transition dose observed in vitro for four of the five glioma cell lines we have studied. Using five established glioma cell lines our modelling demonstrates that our pulsed delivery scheme yields a substantial increase in tumour control probability (TCP).     

The response of human glioma cell lines to low-dose radiation exposure

Purpose: To examine the low-dose radiation response of a series of radioresistant human glioma cell lines and determine if lowdose hypersensitivity is a characteristic of these cells. Materials and methods: The clonogenic survival of six radioresistant human glioma cell lines was measured following exposure to graded, single, very low doses of X-rays in vitro. High resolution was achieved using either a Dynamic Microscopic Image Processing Scanner (DMIPS) or a cell sorter (CS). Results: In five of the six cell lines tested, low-dose hypersensitivity (HRS) was demonstrated although in the sixth, a grade III astrocytoma line, it was not. These results are consistent with previous data indicating that low-dose hypersensitivity is more marked in more radioresistant cell lines although the difference between the glioblastoma cell lines with differing SF2 is not marked. Conclusion: Low-dose hypersensitivity is common in radioresistant glioma cell lines. This may have implications for the treatment of these tumours if further studies confirm that HRS translates to increased effectiveness per gray in vivo when very low doses per fraction are used.     

Inverse dose-rate effect due to pre-mitotic accumulation during continuous low dose-rate irradiation of cervix carcinoma cells.

PURPOSE: To investigate the radiation sensitivity of asynchronous and synchronized cancer cervix cells irradiated with low dose rates. MATERIALS AND METHODS: Cells were exposed to 60Co gamma-rays at dose rates ranging from 0.33 to 0.94 Gy/h. Synchronized cells were obtained by collecting detached mitotic cells after a shaking procedure. Cell survival was measured as the ability of cells to form colonies. Cell-cycle distributions were calculated by computer analysis of a DNA histogram recorded by flow cytometry. RESULTS: Irradiation of asynchronous cells at either 0.33 or 0.86 Gy/h resulted in exponential dose-survival curves with equal alpha-values, i.e. same radiation sensitivity, when dose-survival data for irradiation periods less than 20h were considered. However, the radiation sensitivity was higher by a factor of two when analysing dose-survival data for irradiation periods exceeding 20h. This increase in radiation sensitivity occurred when 80% of the cells accumulated in a pre-mitotic stage of the cell cycle. Irradiation of synchronized cell populations confirmed that these cells were a factor of two more sensitive to radiation in G2 than in G1. CONCLUSIONS: An inverse dose-rate effect, i.e. more efficient inactivation of cells at lower rather than at higher dose rates, was observed for radiation doses exceeding 7 Gy due to pre-mitotic accumulation of cells during low dose-rate irradiation.     

Low-dose hypersensitivity after fractionated low-dose irradiation in vitro

Purpose : It was demonstrated previously that some radioresistant tumour cell lines respond to decreasing single, low radiation doses by becoming increasingly radiosensitive. This paper reports the response of four radioresistant human glioma cell lines to multiple low-dose radiation exposures given at various intervals. Three of the cell lines (T98G, U87, A7) were proven already to show low-dose hyper-radiosensitivity (HRS) after single low doses; the fourth, U373, does not show HRS after acute doses. Materials and methods : Clonogenic cell-survival measurements were made in vitro using the Dynamic Microscopic Image Processing Scanner (DMIPS) or Cell Sorter (CS) following exposure to 240kVp X-rays one or more times. Results : A consistent, time-dependent hypersensitive response to a second, or subsequent, dose was observed in the cell lines that demonstrated HRS. This time-dependent change in radiosensitivity did not occur in the radioresistant cell line that did not show HRS (U373). In one cell line that demonstrated strong HRS, T98G, a similar time-dependent hypersensitive response was also seen when the cells were irradiated whilst held in the G1-phase of the cell cycle. In this same cell line, significantly increased cell kill was demonstrated when three very low doses (0.4 Gy) were given per day, 4 h apart, for 5 days, compared with the same total dose given as once-daily 1.2Gy fractions. Conclusions : These data demonstrate the possibility that a multipledose per day, low-dose per fraction regimen, termed 'ultrafractionation', could produce increased tumour cell kill in radioresistant tumours compared with the same total dose given as conventional-sized 2 Gy fractions.     

Low-dose hypersensitivity after fractionated low-dose irradiation in vitro

PURPOSE: It was demonstrated previously that some radioresistant tumour cell lines respond to decreasing single, low radiation doses by becoming increasingly radiosensitive. This paper reports the response of four radioresistant human glioma cell lines to multiple low-dose radiation exposures given at various intervals. Three of the cell lines (T98G, U87, A7) were proven already to show low-dose hyper-radiosensitivity (HRS) after single low doses; the fourth, U373, does not show HRS after acute doses. MATERIALS AND METHODS: Clonogenic cell-survival measurements were made in vitro using the Dynamic Microscopic Image Processing Scanner (DMIPS) or Cell Sorter (CS) following exposure to 240kVp X-rays one or more times. RESULTS: A consistent, time-dependent hypersensitive response to a second, or subsequent, dose was observed in the cell lines that demonstrated HRS. This time-dependent change in radiosensitivity did not occur in the radioresistant cell line that did not show HRS (U373). In one cell line that demonstrated strong HRS, T98G, a similar time-dependent hypersensitive response was also seen when the cells were irradiated whilst held in the G1-phase of the cell cycle. In this same cell line, significantly increased cell kill was demonstrated when three very low doses (0.4 Gy) were given per day, 4 h apart, for 5 days, compared with the same total dose given as once-daily 1.2Gy fractions. CONCLUSIONS: These data demonstrate the possibility that a multipledose per day, low-dose per fraction regimen, termed 'ultrafractionation', could produce increased tumour cell kill in radioresistant tumours compared with the same total dose given as conventional-sized 2 Gy fractions.     

Seed-less iodine-125 ophthalmic applicator.

A method of preparation a seed-less active insert of iodine-125 ophthalmic applicator is described. Internal electrolysis was applied for fixing iodine-125 on the concave surface of the silver shell which is afterwards hermetically sealed inside a spherically shaped acrylic insert. The current-voltage characteristics of the galvanic cell used for deposition of silver iodide were determined. The results of the measurements of the energy spectra of the radiation emitted by a seed-less and seed-containing applicator are presented. The iodine-125 surface distribution uniformity on a silver shell was measured. The depth dose rate measurements indicate that the total activity incorporated in a seed-less applicator can be lower than that in seed-containing, while simultaneously assuring the desired dose rate.     

A simple method for verifying activity of iodine-125 seeds in rigid absorbable suture

A simple system which facilitates the verification of the calibration of iodine-125 sources in rigid absorbable suture, on the remote traceability basis, was developed. It consists of a plastic jig accommodating a sterile closed-end 16 gauge plastic catheter. The iodine-125 source in rigid absorbable suture is placed into the sterile closed-end 16 gauge plastic catheter. The jig fits in a standard dose calibrator. The sterility of the strand is maintained while a reasonable number of seeds used for an actual implant can be easily measured. This is an improvement over the current recommended practice of assaying just one separate seed of the same strength designation. This system brings the calibration procedure for the rigid sterile seed strands in line with the AAPM TG-40 recommendation for the rest of radioactive seed products.     

Development of a rat solid tumor model for continuous low-dose-rate irradiation studies using 125I and 103Pd sources

PURPOSE: To develop an experimental technique for studying the radiobiology of continuous low-dose-rate irradiation (CLDRI) using clinical brachytherapy sources emitting low energy photons for a rat solid tumor model. METHODS AND MATERIALS: BA1112 tumors were grown between the ears of 14-week-old male WAG/Rij rats by interdermal inoculation. A radioactive source afterloading system, which consists of a lightweight helmet sutured to the rat and a nine-source polystyrene applicator, was fabricated for in vivo tumor irradiation by (125)I and (103)Pd brachytherapy sources. This system has a 12 x 12 mm opening in the center to accommodate the tumor and its growth during irradiation (the diameter of a typical BA1112 tumor was about 6 mm when radiation was applied). The spatial locations of the nine sources were optimized to produce an as uniform as possible three-dimensional dose distribution to the central portion of the applicator for both the (125)I and (103)Pd sources. Absolute dose delivered by the applicator was verified by point dose measurements using calibrated TLD in a polystyrene phantom that mimics the scattering environment of the tumor on the rat. RESULTS: The feasibility of tumor cure experiments using the experimental technique presented in this work was demonstrated. The technique was used to study the influence of initial dose rate on the in vivo tumor cure probability of BA1112 tumors irradiated by (125)I and (103)Pd sources at dose rates varying from 8-20 cGy/h. The technique was also used for studying the in vitro tumor cell survival following in vivo CLDRI irradiation of the tumor. CONCLUSION: An experimental technique using an in vivo tumor model has been developed for studying the radiobiological effects of continuous low-dose-rate irradiations using (125)I sources alone, (103)Pd sources alone, or a mixture of (125)I and (103)Pd sources.     

放射性125I粒子离体照射模型的建立和测量

目的建立放射性^125I粒子离体照射模型,研究模型中离体细胞照射平面的剂量和剂量分布。方法应用14颗粒子环形排布的照射模型,用临床上常用的6711型^125I粒子。实验前随机抽取20%的粒子校正,应用TLD元件对模型进行测量。先用37MBq的^125I粒子照射6d,测量细胞平面受照剂量并计算初始剂量率;然后用同样活度的^125I粒子照射10d后测量,与用公式计算的照射剂量值进行比较。结果TLD标定：测量读数和照射剂量拟合为线性关系。单颗粒子活度测量值与出厂标定值相差〈±5%。照射6d测量细胞平面累积剂量为1.58Gy,计算初始剂量率为0.273Gy/d;照射10d的测量值和理论计算值分别为2.43和2.57Gy,两者相差5.76%。根据对模型的测量和计算,可推导出在不同的初始剂量率下受照剂量和照射时间的关系。结论建立的放射性125I粒子离体照射模型简便实用,可用于放射生物学实验研究。受照剂量与照射时间关系的建立,为今后开展放射性125I粒子相对生物效应的研究和对肿瘤细胞作用机制的研究奠定基础。     

不同照射方式对结直肠癌CL187细胞的抑制作用和分子机制初探

目的 研究单次、分次和125Ⅰ粒子持续低剂量率照射对结直肠癌CL187细胞生物学效应的影响.方法 实验分高剂量率单次照射组(400 cGy/min,单次组)、分次照射组(2 Gy/次/d,400 cGy/min,分次组)和125Ⅰ粒子持续低剂量率照射组(2.77 cGy/h,125Ⅰ组).3组细胞照射0、2、4和8 Gy后,24和48 h进行细胞计数和锥虫蓝染色,比较细胞总数和细胞存活率的差异.利用克隆形成实验比较3组细胞增殖能力的差异.通过流式细胞仪检测细胞凋亡.蛋白免疫印迹法分析PHLPP2、PTEN和Bax蛋白表达的变化.结果 与单次组和分次组相比,125Ⅰ组细胞总数减少(t=34.28和29.48,P＜0.05)、存活细胞比例减少(t=-12.38和-14.61,P＜0.05),细胞克隆形成能力下降,相对生物学效应是1.41.照射后48 h细胞凋亡检测发现125Ⅰ组细胞凋亡比例增加(t=-15.08和-11.99,P＜0.05).蛋白免疫印迹法检测发现125Ⅰ组Bax表达量升高,PHLPP2和PTEN的表达量3组间差异无统计学意义.结论 单次、分次和持续低剂量率照射后细胞PHLPP2蛋白表达水平均升高,但剂量率的高低并不影响其表达水平.不同方式照射后,凋亡相关蛋白Bax的表达水平上升,125Ⅰ组升高更加明显,125Ⅰ持续低剂量粒子照射可能通过影响凋亡相关蛋白Bax的表达水平实现对结直肠癌CL187细胞的杀伤作用.     

甲状腺乳头状癌患者术后首次131I治疗后辐射剂量率的影响因素及出院时间的探讨

目的 探讨甲状腺乳头状癌(PTC)患者术后首次131I治疗后影响辐射剂量率降低的相关因素,并预估其住院隔离时间。方法 选取2015年5月至2018年11月于南方医科大学珠江医院住院并首次行131I治疗的PTC患者167例,其中男性43例、女性124例,年龄(37.14± 12.00)岁。将所有患者按治疗剂量分为高剂量组(63例)和低剂量组(104例),于治疗后24、48、72、96 h时测量距离患者1 m处的辐射剂量率,将治疗后患者体内滞留131I活度为400 MBq时的时间点定为出院时间。采用多重线性回归方法分析影响辐射剂量率降低的相关因素。组间比较采用两独立样本非参数检验或两独立样本t检验。结果 PTC患者首次行131I治疗后的辐射剂量率随时间推移迅速下降,高剂量组治疗后的24、48 h辐射剂量率[(70.62±34.45)、15.64 μSv/h]明显高于低剂量组[(11.27±5.13)、2.03 μSv/h],且差异均有统计学意义(t=-13.581、-7.952,均P <0.01)。81.0%(51/63)和90.5%(57/63)的高剂量组患者分别可在治疗48 h和72 h后出院,99%(103/104)的低剂量组患者可在治疗24 h后出院。多重线性回归分析显示,131I剂量和2 h摄碘率对高剂量组24 h辐射剂量率的影响有统计学意义(F=9.23,复相关系数R2=0.212,P<0.01),高剂量组24 h辐射剂量率与2 h摄碘率和131I剂量呈正相关;性别、24 h摄碘率和残甲法3对高剂量组48 h辐射剂量率的影响有统计学意义(F=34.45,复相关系数R2=0.622,P<0.01),48 h辐射剂量率与24 h摄碘率和残留甲状腺体积呈正相关,与性别呈负相关;131I剂量和24 h饮水量对低剂量组24 h辐射剂量率的影响有统计学意义(F=12.76,复相关系数R2=0.186 ,P<0.01),低剂量组24 h辐射剂量率与131I剂量呈正相关,与24 h饮水量呈负相关。结论 PTC术后患者首次131I治疗24 h后,影响其辐射剂量率降低的主要因素是服用131I的剂量,而48 h后的主要影响因素是24 h甲状腺摄碘率、残留甲状腺体积和性别。低剂量组和高剂量组平均住院时间分别为1 d和2 d左右。     

CT导引下125I粒子植入治疗外照射后复发的恶性肿瘤

目的 评价外照射后复发的恶性肿瘤行CT导引下瘤体内^125I粒子植入治疗的可行性、安全性及疗效。资料与方法 2001年12月至2004年12月,14例外照射后局部复发的恶性肿瘤行CT导引下瘤体内^125I粒子植入,其中原发肿瘤8例,转移瘤6例（11个病灶）,病灶的平均直径为3．25cm。依据粒子植入术前CT图像应用计算机治疗计划系统制定粒子植入计划,按治疗计划在CT导引下穿刺植入^125I粒子。植入^125I粒子数为9．48粒（中位数为28粒）。植入术后立即CT扫描及术后2～6个月CT扫描观察粒子在瘤体内的分布、有无并发症发生及疗效。结果 14例粒子植入均顺利完成,瘤体内粒子分布满意,其中1例植入术后有2粒粒子脱落到体外,未见急性并发症和治疗相关的放射损伤。4例疼痛患者粒子植入术后疼痛均有明显减轻。14例19个病灶粒子植入后完全缓解（CR）5个,部分缓解（PR）9个,无变化（NC）4个,进展（PD）1个,近期总有效率73．7％。结论 对于外照射后复发的恶性肿瘤CT导引下瘤体内^125I粒子植入近距离放射治疗是一种安全、可行的治疗方法,近期肿瘤局部控制率满意,远期疗效有待大组病例进一步观察。     

Dose-response study on thyrotoxic patients undergoing positron emission tomography and radioiodine therapy

With the acknowledged problems associated with assessment of functioning thyroid mass and hence radiation dose, our policy had been to give 75 MBq iodine-131 at 6-monthly intervals to patients with Graves' disease until they became euthyroid. Since positron emission tomography (PET) has been available at this hospital, the radiation dose to the thyroid has been calculated with an accuracy of 20%, the thyroid mass being determined from an iodine-124 PET scan. A dose-response study has been carried out on 65 patients who have received single or cumulative radiation doses of <80 Gy. The results show that patients who receive a low radiation dose (<20 Gy) at their first treatment have a high probability of remaining toxic at 12 months. In contrast, patients who receive higher radiation doses (>40 Gy) at their first treatment have a high probability of control. The probability of becoming euthyroid increases more rapidly with increasing radiation dose than the probability of becoming hypothyroid. Following this dose-response study, a new treatment protocol has been introduced. A ¹²⁴I PET tracer study prior to ¹³¹I therapy will be performed to enable a prescribed thyroid dose of 50 Gy to be delivered to patients with Graves' disease. Further ¹³¹I therapy will only be considered if patients are still toxic at 12 months.     

The radiobiology of human cells and tissues. In vitro radiosensitivity. The picture has changed in the 1980s

Substantial developments have been made during the 1980s in the radiobiology of human tumours, in particular in studies of the radiosensitivity of human tumour cells. It is now clear that tumour cells differ considerably in radiosensitivity, to an extent that by itself is capable of explaining the clinical response of tumours to radiotherapy. There also is evidence that the radiosensitivity of human tumour cell lines to low radiation doses correlates with clinical experience. Irradiation at low dose rate amplifies the differences between cell lines. In conjunction with mathematical modelling, a study of the dose-rate effect also allows a distinction to be drawn between repairable and non-repairable damage. The differences seen between cell lines at low acute doses or low dose rates are associated with the non-repairable component. The most radiosensitive cell lines have a steep component of non-repairable damage and they give the impression of being recovery-deficient; this may, however, be incorrect for when evaluated at constant dose levels recovery is found to increase with increasing radiosensitivity. This leads to the view that recovery from radiation damage may reflect the amount of recoverable damage inflicted rather than the 'capacity' of the cells to recover.     

Unlabelled iododeoxyuridine increases the cytotoxicity and incorporation of [1251]-iododeoxyuridine in two human glioblastoma cell lines

Iododeoxyuridine (IUdR), labelled with radioiodines emitting Auger, alpha or beta- radiation, has been proposed as a therapeutic tool in the treatment of cancer. However, the low per cent incorporation in tumour cells and limited cytotoxicity are major obstacles for such an application. Using unlabelled IUdR as a modulator, we have studied the in vitro cytotoxicity of [125I]-IUdR in two human glioblastoma cell lines. Surprisingly, an enhanced cytotoxicity of [125I]-IUdR was observed in the presence of 0.3-10 microM concentrations of unlabelled IUdR in U251 glioblastoma cells and to a lesser extent in LN229 cells. The presence of unlabelled IUdR unexpectedly increased the incorporation of [125I]-IUdR in both cell lines. Thymidine competitively blocked the cytotoxic effects of combined unlabelled and [125I]-labelled IUdR in these cells and DNA-incorporation of radiolabelled IUdR.     

The 4Rs in radiation therapy

It has been realized that the 4Rs (repair, repopulation, redistribution, and reoxygenation) would affect the result of cell irradiation, and thus radiation treatment. The 4Rs each occurs at different dose rates, usually very low dose rates. Depending on the dose rate used for treatment, the corresponding R should be included in the linear-quadratic equation (LQ) and biological effective dose (BED) calculation. For low dose rate brachytherapy(LDR) especially permanent implant, all the 4Rs should be included in LQ for BED calculation. The 4Rs, especially repair and repopulation, play a critical role in dose fractionation. Various dose fractionation schemes such as hyperfractionation and hypofractionation are determined in consideration of the 4Rs. Stereotactic radiation therapy uses hypofractionation with high fractional doses and combine with high accuracy target localization techniques to achieve high local control rates compared to conventional dose fractionation schemes. The 4Rs have been taken into account for LDR and permanent implant. Recently, LQ for permanent implant brachytherapy has been modified to include all the 4Rs for gynecological malignancy ¹³¹Cs permanent implants. Including the 4Rs in radiation therapy has significantly improved the effectiveness and efficiency of radiation therapy for cancer treatment.     

Radiation exposure to medical personnel during iodine-125 seed implantation of the prostate.

Radiation exposure to operating room personnel was measured by thermoluminescent dosimeters and an ionization chamber during a simulated iodine-125 seed implantation of the prostate gland. The exposure rates at points around the implanted phantom were measured and compared with the calculated values. The data suggested that even with a schedule of 25 prostate implants per year, exposure levels would not exceed 5% of the recommended maximum limits for occupationally exposed personnel.     

Isolation of mammalian cell variants with enhanced endogenous thiol content at low survival levels following irradiation

Approximately half of a group of Chinese hamster V79 cell clones isolated from radiation survivors at low surviving fractions had significantly higher endogenous levels of non-protein and protein thiols than unirradiated cells. A similar group of cell lines cloned from unirradiated cells had thiol levels in the same range as the original unirradiated population. In some cases, clones isolated following irradiation are also more resistant to misonidazole toxicity and to radiation. This phenotype can persist through many cell generations for weeks or months of continuous growth; however, in many clones with altered phenotypes isolated following irradiation, reversion of the population to the same phenotype as that of unirradiated populations has been observed. Induction of elevated thiol levels in tumours by radiotherapy could reduce both the efficacy of the radiation itself and of radiation-modifying or chemotherapeutic drugs given in combination with the radiation.