Differential effects of CLDR and PDR brachytherapy on cell cycle progression in a syngeneic rat prostate tumour model

Purpose: The study consisted of two treatment arms comparing the effects of CLDR (continuous low dose rate) and PDR (pulsed dose rate) brachytherapy on cell cycle progression in a radioresistant rat prostate tumour model.

Materials and methods: Interstitial PDR and CLDR brachytherapy (both 192-Ir, 0.75 Gy/h) were administered to Dunning prostate R3327-AT1 carcinomas transplanted subcutaneously into the thigh of Copenhagen rats. Increasing doses of up to 20 as well as up to 40 Gy were applied. Cell cycle distributions of the aneuploid tumour cell subpopulations were determined at 4 h (3 Gy), 24 h (18 Gy), 48 h (20 and 36 Gy), as well as during the subsequent redistribution period (20 and 40 Gy) at 72, 96, and 120 h. Tumours either implemented with an empty tubing system (n = 5) or under undisturbed growth (n = 5) served as controls. Three animals were irradiated per time point and exposure condition. At least two flow cytometrical analyses were carried out per animal.

Results: The aneuploid cells possessed a constant DNA-Index of 1.9 ± 0.06. In contrast to sham-treated controls, the aneuploid cell fraction with G2/M DNA content was significantly increased (p < 0.05) after initiation of both, CLDR and PDR brachytherapy. However, CLDR resulted in an earlier accumulation of tumour cells in G2/M (24 h: 28% CLDR vs. 19% PDR, p < 0.05) with a concomitant reduction of cells in G1, whereas PDR yielded delayed, but then more pronounced cell cycle changes, particularly expressed during the redistribution period after both 20 and 40 Gy.

Conclusion: CLDR and PDR brachytherapy showed differential effects on cell cycle progression. The induction of a significantly earlier but also less persistent G2/M cell cycle arrest after CLDR compared to PDR brachytherapy implies that a substantially higher fraction of tumour cells are irradiated in G2/M after CLDR.     

Dose-dependent differential effects of low and pulsed dose-rate brachytherapy in a radioresistant syngenic rat prostate tumour model

Purpose : To study the response of the Dunning prostate carcinoma (R3327-AT1 subline) to continuous low dose-rate (CLDR) and pulsed dose-rate (PDR) brachytherapy. Materials and methods : After subcutaneous tumour transplantation into the thigh of the Copenhagen rat, doses of 0, 20, 30, 40 and 50 Gy were applied to the tumour surface (tumour diameter 9 ±1mm). Eight animals were irradiated per dose group and exposure condition. Interstitial PDR (192 Ir source, 37 GBq) and CLDR (192 Ir seed, 150 MBq) brachytherapy were carried out with 0.75 Gy/pulse h -1 and a dose-rate of 0.75Gyh -1, respectively. Treatment response was assessed in terms of growth delay expressed as the time (T 5) required for each tumour to reach five times the initial tumour volume. Results : The median T 5 times for the CLDR groups (in the order: control, 20, 30, 40, 50 Gy) were 12 (12), 54.5 (21), 64.5 (31), 85.5 (51), and 65 (47.5) days. Values after PDR brachytherapy are given in parentheses and resulted in a significantly impaired tumour growth delay (log-rank test) in the 20Gy (p =0.006) and 30 Gy (p =0.036) groups. No significant difference was found in the 40-50 Gy dose range. Conclusions : In contrast to previous results and predictions of biological models we observed dose-dependent differential effects of PDR and CLDR brachytherapy with reduced efficacy of PDR in the lower dose range.     

Dose-dependent differential effects of low and pulsed dose-rate brachytherapy in a radioresistant syngenic rat prostate tumour model

PURPOSE: To study the response of the Dunning prostate carcinoma (R3327-AT1 subline) to continuous low dose-rate (CLDR) and pulsed dose-rate (PDR) brachytherapy. MATERIALS AND METHODS: After subcutaneous tumour transplantation into the thigh of the Copenhagen rat, doses of 0, 20, 30, 40 and 50 Gy were applied to the tumour surface (tumour diameter 9+/-1mm). Eight animals were irradiated per dose group and exposure condition. Interstitial PDR ((192)Ir source, 37 GBq) and CLDR ((192)Ir seed, 150 MBq) brachytherapy were carried out with 0.75 Gy/pulse h(-1) and a dose-rate of 0.75Gyh(-1), respectively. Treatment response was assessed in terms of growth delay expressed as the time (T(5)) required for each tumour to reach five times the initial tumour volume. RESULTS: The median T(5) times for the CLDR groups (in the order: control, 20, 30, 40, 50 Gy) were 12 (12), 54.5 (21), 64.5 (31), 85.5 (51), and 65 (47.5) days. Values after PDR brachytherapy are given in parentheses and resulted in a significantly impaired tumour growth delay (log-rank test) in the 20Gy (p =0.006) and 30 Gy (p =0.036) groups. No significant difference was found in the 40-50 Gy dose range. CONCLUSIONS: In contrast to previous results and predictions of biological models we observed dose-dependent differential effects of PDR and CLDR brachytherapy with reduced efficacy of PDR in the lower dose range.     

In-vitro-Untersuchungen zur PDR-Brachytherapie

Background

Calculations on the basis on the LQ-model have been focussed on the possible radiobiological equivalence between common continuous low dose rate irradiation (CLDR) and a superfractionated irradiation (PDR=pulsed dose rate) provided that the same total dose will be prescribed in the same overall time as with the low doserate. A clinically usable fractionation scheme for brachytherapy was recommended by Brenner and Hall and should replace the classical CLDR brachytherapy with line sources with an afterloading technique using a stepping source. The hypothesis that LDR equivalency can be achieved by superfractionation was tested by means of in vitro experiments on V79 cells in monolayer and spheroid cultures as well as on HeLa monolayers.

Materials and Methods

Simulating the clinical situation in PDR brachytherapy, fractionation experiments were carried out in the dose rate gradient of afterloading sources. Different dose levels were produced with the same number of fractions in the same overall incubation time. The fractionation schedules which were to be compared with a CLDR reference curve were: 40×0.47 Gy, 20×0.94 Gy, 10×1.88 Gy, 5×3.76 Gy, 2×9.4 Gy given in a period of 20 h and 1×18.8 Gy as a “single dose” exposition. As measured by flow cytometry, the influence of the dose rate in the pulse on cell survival and on cell cycle distribution under superfractionation was examined on V79 cells.

Results

V79 spheroids as a model for a slowly growing tumor, reacted according to the radiobiological calculations, as a CLDR equivalency was achieved with increasing fractionation. Rapidly growing V79 monolayer cells showed an inverse fractionation effect. A superfractionated irradiation with pulses of 0.94 Gy/h respectively 0.47 Gy/0.5 h was significantly more effective than the CLDR irradiation. This inverse fractionation effect in log-phase V79 cells could be attributed to the accumulation of cycling cells in the radiosensitive G2/M phase (G2 block) during protected exposure which was drastically more pronounced for the pulsed scheme. HeLa cells were rather insensitive to changes of fractionation. Superfractionation as well as hypofractionation yielded CLDR equivalent survival curves.

Conclusions

The fractionation scheme, derived from the PDR theory to achieve CLDR equivalent effects, is valid for many cell lines, however not for all. Proliferation and dose rate dependend cell cycle effects modify predictions derived from the sublethal damage recovery model and can influence acute irradiation effects significantly. Dose rate sensitivity and rapid proliferation favour cell cycle effects and substantiate, applied to the clinical situation, the possibility of a higher effectiveness of the pulsed irradiation on rapidly growing tumors.     

5-Year Results of Pulsed Dose Rate Brachytherapy Applied as a Boost after Breast-Conserving Therapy in Patients at High Risk for Local Recurrence from Breast Cancer

PURPOSE: The aim of this study was to evaluate effect, toxicity, and cosmesis of a prospectively applied pulsed dose rate (PDR) brachytherapy boost schedule in patients with stage I/II/IIIa invasive breast cancer. PATIENTS AND METHODS: A total of 113 patients were treated after breast-conserving surgery (BCS) and external beam radiotherapy (median 50 Gy, range 46-52). The boost dose was graded in accordance to the pathologic tumor characteristics: 20-25 Gy: incomplete resection (n = 34), vascular invasion (n = 27), close margin resection (n = 41); 15 Gy: T2G3 stage (n = 11). PDR brachytherapy (37 GBq, (192)Ir source) was carried out after geometric volume optimization with 1 Gy/pulse/h. The implantation and dose specification were performed similar to the rules of the Paris system. RESULTS: The overall local failure rate after a median follow-up of 61 months was 4.4% (5/113). The actuarial 5- and 8-year local recurrence-free survival rates were 95% and 93%, respectively. Cosmesis was rated by 90% of the patients as excellent or good. 14/113 patients experienced grade III (all caused by planar telangiectasia) and none of the patients grade IV late toxicity of the skin (RTOG/EORTC). A boost dose of 25 Gy resulted in a significantly higher rate of late toxicity (Fisher's exact test, p < 0.01). CONCLUSIONS: PDR brachytherapy is safe, effective, and provides good cosmesis. A CLDR breast boost can be replaced by PDR brachytherapy without significant loss of therapeutic ratio.     

不同剂量X射线对同步化HeLaS3细胞周期的影响

目的　研究不同剂量Ｘ射线对同步化ＨｅＬａＳ３ 细胞周期的影响,为进一步探讨其分子调控机理和临床肿瘤放疗提供基础资料。方法　采用胸苷（ＴｄＲ） 双阻断法和流式细胞术（ＦＣＭ） 检测了ＨｅＬａＳ３ 细胞同步化后分别于其细胞周期各时相进行７５ ｍ Ｇｙ 和２－０ Ｇｙ Ｘ 射线照射以及于Ｇ２＋ Ｍ 期进行０－０２５～２－０ Ｇｙ 照射后其细胞周期进程的变化。结果　２－０ Ｇｙ 照射时细胞无论处于Ｇ０／Ｇ１ 、Ｓ期还是Ｇ２ ＋ Ｍ 期,从释放点后９～１５ 小时内均发生明显的Ｓ期延迟和Ｇ２ 阻滞,但其中以Ｇ２ 期照射者阻滞最显著;于Ｇ０／Ｇ１ 和Ｇ２ ＋ Ｍ 期进行７５ ｍ Ｇｙ 照射,分别在９ 和１２ ｈ 时发生一过性的明显的Ｇ２ 阻滞,至１１ 和１５ｈ 时完全从这一阻滞中脱离,甚至促进了其细胞周期的进程;而在Ｓ期进行７５ ｍ Ｇｙ 照射时,并没有发生这种阻滞,反而加速了其细胞周期由Ｇ２ ＋ Ｍ→Ｇ０／Ｇ１ 的移行,其中尤以９ｈ 时最为显著。剂量效应关系研究表明,于Ｇ２ ＋ Ｍ 期进行０－０２５ ～２－０ Ｇｙ 照射后,在释放点后１１ ｈ 时均发生Ｇ０／Ｇ１ 期细胞数减少,Ｇ２ 阻滞,且有剂量依赖性,而Ｓ期细胞数的变化在０－０２５ ～０－１ Ｇｙ 和０－５ ～２－０ Ｇｙ     

5-Year Results of Pulsed Dose Rate Brachytherapy Applied as a Boost after Breast-Conserving Therapy in Patients at High Risk for Local Recurrence from Breast Cancer

Purpose: The aim of this study was to evaluate effect, toxicity, and cosmesis of a prospectively applied pulsed dose rate (PDR) brachytherapy boost schedule in patients with stage I/II/IIIa invasive breast cancer. Patients and Methods: A total of 113 patients were treated after breast-conserving surgery (BCS) and external beam radiotherapy (median 50 Gy, range 46-52). The boost dose was graded in accordance to the pathologic tumor characteristics: 20-25 Gy: incomplete resection (n = 34), vascular invasion (n = 27), close margin resection (n = 41); 15 Gy: T2G3 stage (n = 11). PDR brachytherapy (37 GBq, ¹⁹²Ir source) was carried out after geometric volume optimization with 1 Gy/pulse/h. The implantation and dose specification were performed similar to the rules of the Paris system. Results: The overall local failure rate after a median follow-up of 61 months was 4.4% (5/113). The actuarial 5- and 8-year local recurrence-free survival rates were 95% and 93%, respectively. Cosmesis was rated by 90% of the patients as excellent or good. 14/113 patients experienced grade III (all caused by planar telangiectasia) and none of the patients grade IV late toxicity of the skin (RTOG/EORTC). A boost dose of 25 Gy resulted in a significantly higher rate of late toxicity (Fisher's exact test, p < 0.01). Conclusions: PDR brachytherapy is safe, effective, and provides good cosmesis. A CLDR breast boost can be replaced by PDR brachytherapy without significant loss of therapeutic ratio. Ziel: Diese Studie diente der Evaluierung von Effektivität, Toxizität und kosmetischen Ergebnissen eines prospektiv applizierten PDR- (pulsed dose-rate-)Brachytherapieboostkonzeptes bei Patienten mit invasivem Mammakarzinom im Stadium I/II/IIIa. Patienten und Methoden: Insgesamt wurden 113 Patienten nach brusterhaltender Therapie (BET) und externer Bestrahlung (Median 50 Gy, Range 46-52) behandelt. Die Boostdosis wurde anhand histopathologischer Tumorcharakteristika graduiert (Tabelle 1): 20-25 Gy: inkomplette Resektion (n = 34), Lymphgefäß- oder Gefäßinvasion (n = 27), "close-margin"-Resektion (n = 41); 15 Gy: T2G3 Stadium (n = 11). Die gepulste Brachytherapie (37 GBq, ¹⁹²Ir-Quelle) wurde nach geometrischer Volumenoptimierung mit 1 Gy/Puls/h durchgeführt. Applikation und Dosisspezifikation erfolgten in Anlehnung an das Pariser System. Ergebnisse: Die Lokalrezidivrate betrug nach einer medianen Nachbeobachtungszeit von 61 Monaten 4,4% (5/113). Das aktuarische lokalrezidivfreie 5- und 8-Jahres-Überleben betrug 95% bzw. 93% (Abbildungen 1 und 2). 90% der Patienten beurteilten ihre kosmetischen Ergebnisse als gut oder exzellent (Tablle 3). Bedingt durch flächige Teleangiektasien im Boostareal entwickelten 14/113 Patienten eine Grad-III-Spättoxizität (0/113 Grad IV) der haut (RTOG/EORTC, Tabelle 2). Eine Boostdosis von 25 Gy resultierte in einer signifikant erhöhten Spättoxizitätsrate (Fishers Exakt-Test, p < 0,01, Abbildung 3). Schlussfolgerung: Die gepulste Brachytherapie ist sicher und effektiv. Die kosmetischen Ergebnisse sind gut. Der interstitielle CLDR-Mammaboost kann durch die PDR-Brachytherapie ohne signifikanten Verlust an therapeutischer Breite ersetzt werden.     

Radiation-induced apoptosis in human non-small-cell lung cancer cell lines is secondary to cell-cycle progression beyond the G2-phase checkpoint

PURPOSE: To characterize the relationship between cell-cycle progression and radiation-induced apoptosis in NSCLC cell lines with different p53 status. MATERIALS AND METHODS: Cell lines with functional (H460, A549) and non-functional p53 (H661 and H520) were irradiated with 20 Gy. Multiparameter flow-cytometry was used to follow the progression of synchronized cells through the cell cycle after irradiation. RESULTS: Delayed apoptosis was observed after cell-cycle progression beyond the G2 block, either in the late G2/M-phase of the same cell cycle being irradiated (H661, H520) or in the G1-phase of the subsequent cell cycle (H460, A549). The apoptotic fraction in H661 and H520 was 60-80% at 144h after irradiation, higher than in A549 and H460 (5 and 35%, respectively). As an alternative to apoptosis in cells cycling beyond the G2 restriction point, hyperploid cells were generated by all cell lines. Inhibition of cell-cycle progression through the G2/M-phase efficiently reduced the induction of late apoptosis. After irradiation in S-phase, 50-60% of cells with functional p53 remained arrested at the G2 restriction point until 144 h post-irradiation, while only 20% of the H661 or H520 did so. CONCLUSIONS: These data characterize radiation-induced apoptosis in NSCLC cell lines as a removal pathway of clonogenically inactivated cells secondary to cell-cycle progression beyond G2/M, and is unlikely to be a critical factor for cellular radiation sensitivity.     

Radiation-induced apoptosis in human non-small-cell lung cancer cell lines is secondary to cell-cycle progression beyond the G2-phase checkpoint

Purpose : To characterize the relationship between cell-cycle progression and radiation-induced apoptosis in NSCLC cell lines with different p53 status. Materials and methods : Cell lines with functional (H460, A549) and non-functional p53 (H661 and H520) were irradiated with 20 Gy. Multiparameter flow-cytometry was used to follow the progression of synchronized cells through the cell cycle after irradiation. Results : Delayed apoptosis was observed after cell-cycle progression beyond the G2 block, either in the late G2/M-phase of the same cell cycle being irradiated (H661, H520) or in the G1-phase of the subsequent cell cycle (H460, A549). The apoptotic fraction in H661 and H520 was 60-80% at 144 h after irradiation, higher than in A549 and H460 (5 and 35%, respectively). As an alternative to apoptosis in cells cycling beyond the G2 restriction point, hyperploid cells were generated by all cell lines. Inhibition of cell-cycle progression through the G2/M-phase efficiently reduced the induction of late apoptosis. After irradiation in S-phase, 50-60% of cells with functional p53 remained arrested at the G2 restriction point until 144 h post-irradiation, while only 20% of the H661 or H520 did so. Conclusions : These data characterize radiation-induced apoptosis in NSCLC cell lines as a removal pathway of clonogenically inactivated cells secondary to cell-cycle progression beyond G2/M, and is unlikely to be a critical factor for cellular radiation sensitivity.     

Preferential radiosensitization in p53-mutated human tumour cell lines by pentoxifylline-mediated disruption of the G2/M checkpoint control

PURPOSE: There is evidence that the duration of the G2/M delay following irradiation is correlated with cell survival. We studied the radiosensitizing potential of pentoxifylline (PTX) and the PTX-mediated modulation of cell-cycle progression dependent on the p53 status of various human tumour cell lines. MATERIALS AND METHODS: The cellular radiosensitivity of human MCF-7 (wild-type p53) and HT-29 (p53-defective) tumour cells, which were exposed to PTX (2 mM) immediately after gamma-irradiation was determined by colony forming assay. The influence on cell cycle progression after irradiation (6 Gy) was assessed by flow cytometric analysis using p53 wild-type MCF-7 and HPR600 cells, and p53-defective HT-29 and WiDr cells. RESULTS: Clonogenic survival assays up to 8 Gy demonstrated that p53-defective HT-29 cells (sensitizer enhancement ratio [SER]=1.54) were sensitized by PTX (2 mM) to a significantly higher degree than p53 wild-type MCF-7 (SER=1.14) cells. Exposure of irradiated (6 Gy) cells to PTX (2 mM) resulted in abrogation of the radiation-induced G2/M arrest in the p53-defective HT-29 and WiDr cells, whereas the p53 wild-type-expressing MCF-7 and HPR600 cells showed less significant impairment of the G2/M checkpoint. In HT-29 cells, the rate of transition into mitosis was even higher than in the sham-treated control cells. G2/M abrogation was accompanied by an increase of apoptosis only in HPR600 cells. CONCLUSIONS: Since PTX was less effective in cells expressing intact p53, the application of PTX suggests a promising strategy of pharmacological disruption of the G2/M checkpoint control by which preferentially radiation-resistant tumours with defective p53 function might be rendered more sensitive to ionizing radiation.     

Preferential radiosensitization in p53-mutated human tumour cell lines by pentoxifylline-mediated disruption of the G2/M checkpoint control

Purpose : There is evidence that the duration of the G2/M delay following irradiation is correlated with cell survival. We studied the radiosensitizing potential of pentoxifylline (PTX) and the PTX-mediated modulation of cell-cycle progression dependent on the p53 status of various human tumour cell lines. Materials and methods : The cellular radiosensitivity of human MCF-7 (wild-type p53) and HT-29 (p53-defective) tumour cells, which were exposed to PTX (2 mM) immediately after γ-irradiation was determined by colony forming assay. The influence on cell cycle progression after irradiation (6 Gy) was assessed by flow cytometric analysis using p53 wild-type MCF-7 and HPR600 cells, and p53-defective HT-29 and WiDr cells. Results : Clonogenic survival assays up to 8 Gy demonstrated that p53-defective HT-29 cells (sensitizer enhancement ratio [SER]=1.54) were sensitized by PTX (2 mM) to a significantly higher degree than p53 wild-type MCF-7 (SER=1.14) cells. Exposure of irradiated (6 Gy) cells to PTX (2 mM) resulted in abrogation of the radiation-induced G2/M arrest in the p53-defective HT-29 and WiDr cells, whereas the p53 wild-type-expressing MCF-7 and HPR600 cells showed less significant impairment of the G2/M checkpoint. In HT-29 cells, the rate of transition into mitosis was even higher than in the sham-treated control cells. G2/M abrogation was accompanied by an increase of apoptosis only in HPR600 cells. Conclusions : Since PTX was less effective in cells expressing intact p53, the application of PTX suggests a promising strategy of pharmacological disruption of the G2/M checkpoint control by which preferentially radiation-resistant tumours with defective p53 function might be rendered more sensitive to ionizing radiation.     

Radiobiological analysis of human melanoma cells on the 62 MeV CATANA proton beam

PURPOSE: To measure the ability of protons and gamma-rays to effect cell viability and cell survival of human HTB140 melanoma cells. MATERIALS AND METHODS: Exponentially growing HTB140 cells were irradiated close to the Bragg peak maximum of the 62 MeV protons or with 60Co gamma-rays with single doses, ranging from 8 - 24 Gy. Cell viability using the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assay was evaluated at 6 h, 24 h, 48 h or 7 days after irradiation and clonogenic survival was assessed at 7 days after irradiation. Cell cycle phase redistribution and the level of apoptosis were evaluated at 6 h and 48 h after irradiation. RESULTS: The study of cell viability as a function of time (cell survival progression) and cell survival, using a clonal assay, demonstrated the considerably stronger inactivation effect of protons compared to gamma-rays with a relative biological effectiveness (RBE) of approximately 1.64. Cell cycle phase distribution and apoptosis levels with time enabled us to investigate the development and the character of the damage induced by irradiation. Due to the high radio-resistance of HTB140 cells, cell cycle phase redistribution exhibited only a modest cell accumulation in G2/M phase. Protons but not gamma-rays induced apoptosis. CONCLUSIONS: It appears that protons reduce the number of HTB140 cells by apoptosis as well as by severe DNA damage, while gamma-rays eliminate viable cells primarily by the production of irreparable DNA damage. Protons have an increased RBE relative to gamma-rays.     

Daytime pulsed dose rate brachytherapy as a new treatment option for previously irradiated patients with recurrent oesophageal cancer

The aim of this study was to evaluate the feasibility, effects, and toxicity of pulsed dose rate (PDR) brachytherapy for re-irradiation of oesophageal carcinoma. A total of 16 patients (median age 67 years) with inoperable recurrences from oesophageal cancer after primary radio-(chemo)-therapy (median 50 Gy) were re-irradiated using PDR brachytherapy ((192)Ir, 37 GBq). Treatment was carried out on an outpatient basis applying a weekly 5 Gy daytime schedule (0.5 Gy pulse(-1) h(-1), total dose 15-20 Gy). The dose was prescribed 10 mm from the mid-dwell position and encompassed the clipped tumour extension with 2 cm margins. The use of clips for delineation of tumour extent and catheter movement during irradiations was evaluated. All 61 PDR treatments were applied safely. The median catheter movement was 5 mm, range 2-12 mm. After a median follow-up of 8 months, three patients had a complete and five a partial remission. Body weight increased in 5 of 16 (31%) and was stable in 4 of 16 (25%) patients, respectively. The median grade 2 (RTOG/EORTC) dysphagia-free survival was 17 months. Seven patients experienced grade 1, five grade 2, and one grade 3 late toxicity. Three patients with uncontrolled locoregional disease showed grade 4 complications (oesophago-tracheal fistulae (n=2), fatal arterial bleeding (n=1). Daytime PDR brachytherapy proved to be feasible and provided effective palliation. Toxicity remains a major problem. Thus, total dose should be restricted to <15 Gy in this palliative situation.     

β射线内照射抑制血管内皮细胞和平滑肌细胞增殖的研究

目的 探讨β射线对血管内皮细胞和平滑肌细胞的细胞效应。方法 培养人脐静脉内皮细胞和牛主动脉平滑肌细胞,接受0、1.25、2.5、5.0、10、20、40 Gy β射线后,以四唑盐(MTT)比色实验评价剂量-效应关系,用划痕实验研究β射线对两种细胞增殖的影响。血管内皮细胞经0、2.5、5.0、10、20 Gy照射后,进行透射电镜超微结构观察和使用流式细胞仪进行DNA倍体及凋亡率分析。结果 血管内皮细胞在照射后2、24 h,在1.25～40 Gy其增殖呈剂量依赖性抑制;在照射后48、72 h,其剂量依赖性抑制在10 Gy时处于平台期。血管平滑肌细胞在照射后2、24和48 h,其增殖抑制在10Gy时处于平台期;在照射后72h,其增殖抑制在5 Gy时处于平台期。在照射后72 h,吸收剂量为5 Gy时,血管平滑肌细胞和内皮细胞的抑制率分别为27.9％和19.0％(P=0.016);吸收剂量为10 Gy时,血管平滑肌细胞和内皮细胞的抑制率分别为33.7％和20.9％(P=0.002)。划痕实验示吸收剂量为5Gy时血管内皮细胞几乎完全充填裂隙,而平滑肌细胞较少充填裂隙;10 Gy照射后,内皮细胞充填裂隙数量减少,而平滑肌细胞几乎未充填裂隙。透射电镜未发现典型的凋亡征象,流式细胞仪检查各实验组和对照组的凋亡率均<4.4％。DNA倍体分析发现对照组G_2/M期细胞数百分比为13.09％,各照射组依次为16.     

Long-term results of pulsed irradiation of skin metastases from breast cancer. Effectiveness and sequelae.

PURPOSE: The concept of pulsed brachytherapy suggested by Brenner and Hall requires an unusual fractionation scheme. Effectiveness and sequelae of this new irradiation method were observed in patients with disseminated cutaneous metastases of breast cancer. PATIENTS AND METHODS: A flexible, reusable skin mold (weight 110 g) was developed for use with a pulsed dose rate (PDR) afterloader. An array of 18 parallel catheters (2 mm diameter) at equal distances of 10 or 12 mm was constructed by fixation of the catheters in a plastic wire mesh. The array is sewn between 2 foam rubber slabs of 5 mm thickness to provide a defined constant distance to the skin. Irradiations are possible up to a maximum field size of 20 x 23.5 cm using a nominal 37 GBq Ir-192 source. Pulses of 1 Gy reference dose at the skin surface are applied at a rate of 1 pulse every 1.2 hours (0.8 Gy per hour). The dose distribution is geometrically optimized to provide a homogeneous skin dose (100% +/- 10%). The 80% dose level lies at 5 mm below the skin surface. Between April 1994 and December 1997, 52 patients suffering from cutaneous metastases at the thoracic wall were treated with 54 fields and total doses of 38 to 50 Gy (median 42 Gy) applying 2 PDR courses with a pause of 4 to 5 weeks. RESULTS: Forty-six patients (48 fields) were eligible for evaluation in June 1998. The median follow-up was 16 months (range 7.1 to 46.2 months). Local control was achieved in 40 out of 48 fields (83%) or 41 of 46 patients (89%), respectively. Moist desquamation occurred in 52% of the patients. Late reactions were judged after a minimum follow-up of 6 months. Thirty-two fields had been previously irradiated with external beam therapy to doses of 40 to 60 Gy. Regardless of whether the skin was preirradiated or not all patients surviving long enough developed telangiectasia within 2 years after PDR irradiation. In preirradiated patients (n = 32) skin contractures and/or skin necrosis occurred in 12% each. In newly irradiated patients (n = 14) no contractures or skin necrosis were observed. CONCLUSIONS: Pulsed brachytherapy is an effective and time-sparing method for the treatment of cutaneous metastases from breast cancer. Skin reactions are comparable to the sequelae of orthovoltage therapy. Two sessions of approximately 20 Gy PDR were tolerated on preirradiated skin without severe sequelae.     

Role of Interstitial PDR Brachytherapy in the Treatment of Oral and Oropharyngeal Cancer

PURPOSE: To evaluate the role of pulsed-dose-rate interstitial brachytherapy (PDR IBT) in patients with head-and-neck malignancies. PATIENTS AND METHODS: From October 1997 to December 2003, 236 patients underwent PDR IBT for head-and-neck cancer at the authors' department. 192 patients received brachytherapy as part of their curative treatment regimen after minimal non-mutilating surgery, 44 patients were treated with irradiation alone. 144 patients had sole IBT (median D(REF) = 56 Gy), in 92 patients IBT procedures (median D(REF) = 24 Gy) were performed in combination with external irradiation. The pulses (0.4-0.7 Gy/h) were delivered 24 h a day with a time interval of 1 h between two pulses. The analysis of tumor control, survival and treatment-related toxicity was performed after a median follow-up of 26 months (6-75 months). RESULTS: At the time of analysis permanent local tumor control was registered in 208 of 236 patients (88%). At 5 years overall survival and local recurrence-free survival of the entire group were 82-73% and 93-83% for T1/2, and 56% and 83% for T3/4, respectively. Soft-tissue necrosis was seen in 23/236 patients (9.7%) and bone necrosis in 17/236 patients (7.2%). No other serious side effects were observed. CONCLUSION: PDR IBT with 0.4-0.7 Gy/h and 1 h between pulses is safe and effective. These results confirm that PDR IBT of head-and-neck cancer is comparable with low-dose-rate (LDR) brachytherapy - equally effective and less toxic.     

Re-irradiation with interstitial pulsed-dose-rate brachytherapy for unresectable recurrent head and neck carcinoma

PurposeTo assess the long-term results of protocol-based interstitial pulsed-dose-rate (PDR) brachytherapy combined with simultaneous chemotherapy in selected patients with recurrent head and neck tumors not amenable to salvage surgery.Methods and MaterialsA total of 51 patients with recurrent head and neck cancer were treated with interstitial PDR brachytherapy. Forty patients (78%) had salvage brachytherapy alone using a median total dose of 60 Gy. Salvage brachytherapy in combination with external beam therapy was performed in 11 patients (22%) using a median total dose of D_REF = 27 Gy. Simultaneously with the PDR brachytherapy, a concomitant chemotherapy was administered in 35/51 (69%) of patients. The analysis was performed after a median followup of 58 months.ResultsLocal control rates calculated according to Kaplan–Meier after 2 and 5 years were 71% and 57%, respectively. Comparing results of salvage PDR brachytherapy with or without simultaneous chemotherapy, the 5-year local recurrence-free survival rates were 78.9% vs. 38.5% (p = 0.01), respectively. No other patient or treatment-related parameters had a significant influence on treatment results. A total of 9/51 (17.7%) and 6/51 (11.8%) patients developed soft-tissue necrosis or bone necrosis, respectively, but only 2% of patients required surgical treatment.ConclusionsPDR interstitial brachytherapy with pulse doses between 0.4 and 0.7 Gy/h/24 h with simultaneous chemotherapy is an effective and safe option for curative therapy in selected patients with head and neck cancer in previously irradiated areas, which are not suitable for salvage surgery.     

Induction of radiation resistance by a heat shock protein inhibitor, KNK437, in human glioblastoma cells

PURPOSE: We examined the effects of a heat shock protein (hsp) inhibitor, N-formyl-3, 4-methylenedioxy-gamma-butyrolactam (KNK437), on the radiosensitivity of human glioblastoma cells (A-172). MATERIALS AND METHODS: Effects of KNK437 on radiosensitivity and cell cycle regulation were examined using colony formation assays, flow cytometry analysis and Western blot analysis. KNK437 was added to the culture medium 1 h before X-ray irradiation at 50, 100 or 300 microM final concentration. RESULTS: KNK437 induced the resistance of A-172 cells and human squamous cell carcinoma cells (SAS) to X-rays. Flow cytometry analysis showed that KNK437 alone efficiently induced A-172 cells to enter G2/M phase. Though A-172 cells irradiated with X-rays at 6 Gy showed no clear change in the cell cycle, the irradiated cells were induced to enter G2/M phase when they had been pre-treated with KNK437. By Western blot analysis, p53, 14-3-3sigma and cell division cycle 2 (cdc2) proteins that function in G2 arrest were observed to be persistently accumulated or phosphorylated in KNK437-treated cells, regardless of X-ray irradiation. CONCLUSIONS: These results show that KNK437 causes cells to be resistant to radiation, and that this might be correlated with maintenance of G2 arrest in the cell cycle regulation.     

Low-dose hyper-radiosensitivity in human hepatocellular HepG2 cells is associated with Cdc25C-mediated G2/M cell cycle checkpoint control

Purpose: Although the significance of cell cycle checkpoints in overcoming low-dose hyper-radiosensitivity (HRS) has been proposed, the underlying mechanism of HRS in human hepatocellular cells remains unclear. Therefore, the aim of this study was to characterize HRS inhuman hepatocellular HepG2 cells and to explore the molecular mechanism(s) mediating this response.

Materials and methods: HepG2 cells were exposed to various single doses of γ radiation (from 0?Gy to 4?Gy), and then were assayed at subsequent time-points. Survival curves were then generated using a linear-quadratic (LQ) equation and a modified induced repair model (MIRM). The percentage of cells in the G1, G2/M, and S phases of the cell cycle were also examined using propidium iodide (PI) staining and flow cytometry. Levels of total cell division cyclin 25C (Cdc25C) and phosphorylated Cdc25C were examined by Western blotting.

Results: Low-dose γ radiation (<0.3?Gy) induced HRS in HepG2 cells, while doses of 0.3, 0.5, and 2.0?Gy γ radiation significantly arrested HepG2 cells in the G2/M phase. While total Cdc25C levels remained unchanged after irradiation, levels of phosphorylated Cdc25C markedly increased 6, 16, and 24?h after treatment with 0.5 or 2.0?Gy radiation, and they peaked after 16?h. The latter observation is consistent with the G2/M arrest that was detected following irradiation.

Conclusions: These findings indicate that low-dose HRS in HepG2 cells may be associated with Cdc25C-mediated G2/M cell cycle checkpoint control.