Dose-effect relation in stereotactic radiotherapy for brain metastases. A systematic review.

PURPOSE: Stereotactic radiotherapy (SRT) of brain metastases is considered effective when long-term local control is obtained. However, dose-effect data are scarce. We, therefore, performed a systematic literature search to assess the evidence concerning the relation of SRT dose and local control probability. METHODS AND MATERIALS: A search was performed for papers describing patients treated with SRT for brain metastases, published from 1990 through 2009, in the electronic databases Medline (Pubmed) and Embase. We selected only papers reporting actuarial local control probability, in which a fixed dose had been prescribed and in which the size of the metastases was given. Series with SRT as a boost after whole brain irradiation (WBI) or with SRT after surgery were excluded. From the selected papers we extracted data on dose, local control rates and necrosis rates. Biological effective doses of the linear-quadratic-cubic model, using an α/ß of 12Gy (BED(12)), were calculated and a dose-response curve was constructed. RESULTS: Eleven papers fulfilled the selection criteria for further analysis. Six-month local control rates were higher than 80% in almost all the series irrespective of dose. Twelve-month local control rates, however, varied and were higher than 80%, higher than 60% and lower than 50% with single doses of ≥21Gy, ≥18Gy and ≤15Gy, respectively, and 70% or higher with fractionated SRT (FSRT). A BED(12) of at least 40Gy was associated with a twelve-month local control rate of 70% or more. CONCLUSION: Local control after single fraction SRT is highly dependent upon dose and is high (>80%) after 21Gy or more, but low (<50%) after 15Gy or less. We conclude that SRT for brain metastases should preferably be applied with a BED(12) of at least 40Gy corresponding with a single fraction of 20Gy, two fractions of 11.6Gy or three fractions of 8.5Gy.

Genetic probing of homologous recombination and non-homologous end joining during meiotic prophase in irradiated mouse spermatocytes.

This study was designed to obtain a better insight into the relative contribution of homologous recombination (HR) and non-homologous end joining (NHEJ) to the repair of radiation-induced DNA double-strand breaks (DSBs) at first meiotic prophase. Early and late pachytene and early diplotene spermatocytes that had completed crossing over were sampled. We studied the kinetics of gamma-H2AX chromatin foci removal after irradiation of mice deficient for HR and mice deficient for NHEJ. Analyzing gamma-H2AX signals in unirradiated RAD54/RAD54B deficient spermatocytes indicated incomplete meiotic recombination repair due to the pronounced increase of gamma-H2AX foci in late prophase primary spermatocytes. In these mice, 8h after irradiation, early pachytene spermatocytes showed a reduction of the numbers of gamma-H2AX foci by 52% compared to 82% in the wild type, the difference being significant. However, after crossing over (in late pachytene and early diplotene), no effect of RAD54/RAD54B deficiency on the reduction of irradiation-induced foci was observed. In NHEJ deficient SCID mice, repair kinetics in early spermatocytes were similar to those in wild type mice. However, 1h after irradiation in late pachytene and early diplotene spermatocytes 1.7 times more foci were found than in wild type mice. This difference might be related to the absence of a DNA-PKcs dependent fast repair component in SCID mice. As subsequent repair is normal, HR likely is taking over. Taken together, the results obtained in RAD54/RAD54B deficient mice and in SCID mice indicate that DSB repair in early pachytene spermatocytes is mainly carried out through HR. In late spermatocytes (late pachytenes and early diplotenes) NHEJ is active. However, probably there is an interplay between these repair pathways and when in late spermatocytes the NHEJ pathway is compromised HR may take over.

Parp1-XRCC1 and the repair of DNA double strand breaks in mouse round spermatids.

The repair of DNA double strand breaks (DSBs) in male germ cells is slower and differently regulated compared to that in somatic cells. Round spermatids show DSB repair and are radioresistant to apoptosis induction. Mutation induction studies using ionizing irradiation, indicated a high frequency of chromosome aberrations (CA) in the next generation. Since they are in a G1 comparable stage of the cell cycle, haploid spermatids are expected to repair DSBs by the non-homologous end-joining pathway (NHEJ). However, immunohistochemical evidence indicates that not all components of the classical NHEJ pathway are available since the presence of DNA-PKcs cannot be shown. Here, we demonstrate that round spermatids, as well as most other types of male germ cells express both Parp1 and XRCC1. Therefore, we have determined whether the alternative Parp1/XRCC1 dependent NHEJ pathway is active in these nuclei and also have tested for classical NHEJ activity by a genetic method. To evaluate DSB repair in SCID mice, deficient for DNA-PKcs, and to study the involvement of the Parp1/XRCC1 dependent NHEJ pathway in round spermatids, the loss of gamma-H2AX foci after irradiation has been determined in nucleus spreads of round spermatids of SCID mice and in nucleus spreads and histological sections of Parp1-inhibited mice and their respective controls. Results show that around half of the breaks in randomly selected round spermatids are repaired between 1 and 8h after irradiation. The repair of 16% of the induced DSBs requires DNA-PKcs and 21% Parp1. Foci numbers in the Parp1-inhibited testes tend to be higher in spermatids of all epithelial stages reaching significance in stages I-III which indicates an active Parp1/XRCC1 pathway in round spermatids and a decreased repair capacity in later round spermatid stages. In Parp1-inhibited SCID mice only 14.5% of the breaks were repaired 8h after irradiation indicating additivity of the two NHEJ pathways in round spermatids.

Induction of severe cataract and late renal dysfunction following total body irradiation: dose-effect relationships.

BACKGROUND: Severe cataract and renal dysfunction are late effects following myeloablative total body irradiation (TBI) and hematopoietic stem cell transplantation in patients with hematological malignancies. The aim of the study was to determine radiation dose-response relationships for these late effects. MATERIALS AND METHODS: A retrospective review of articles reporting incidences for cataract induction and late renal dysfunction was performed, using PubMed. The radiation regimens identified were normalized using the linear-quadratic model; biologically effective doses (BEDs) were calculated. RESULTS: For cataract induction, 17 articles were identified allowing a dose-effect relationship to be derived. A threshold BED of approximately 40 Gy was indicated below which severe cataract seldom occurs. For late renal toxicity, 14 articles were found. The resulting dose-effect relationship indicates a threshold BED of approximately 16 Gy. CONCLUSION: To prevent severe cataract, fractionated TBI should be applied to keep the BED <40 Gy. Only when single-dose TBI cannot be avoided should eye shielding be applied. To prevent late renal toxicity, fractionated TBI is recommended, but kidney shielding remains necessary for almost all myeloablative TBI regimens.

Dose-effect relationships for recurrence of keloid and pterygium after surgery and radiotherapy.

PURPOSE: To show radiation dose-response relationships for recurrence of keloid and pterygium after radiotherapy following surgery. METHODS AND MATERIALS: Using PubMed, we performed a retrospective review of articles reporting incidences and/or dose-response relationships for recurrence of keloid and pterygium after radiotherapy following surgery. The irradiation regimens identified were normalized by use of the linear-quadratic model; biologically effective doses (BEDs) were calculated. RESULTS: For keloid recurrence after radiotherapy following keloid removal, with either teletherapy or brachytherapy, the recurrence rate after having delivered a BED greater than 30 Gy is less than 10%. For pterygium recurrence after bare sclera surgery and (90)Sr beta-irradiation, a BED of about 30 Gy seems to be sufficient also to reduce the recurrence rate to less than 10%. CONCLUSIONS: Most of the doses in the radiotherapy schemes used for prevention of keloid recurrence after surgery are too low. In contrast, the doses applied in most regimens to prevent pterygium recurrence are too high. A scheme with a BED of 30 to 40 Gy seems to be sufficient to prevent recurrences of keloid as well as pterygium.

Cyclopentenyl cytosine has biological and anti-tumour activity, but does not enhance the efficacy of gemcitabine and radiation in two animal tumour models.

Cyclopentenyl cytosine (CPEC), targetting the de novo biosynthesis of cytidine triphosphate (CTP), increases the cytotoxicity of gemcitabine (2',2'-difluoro-2'-deoxycytidine, dFdC) alone and in combination with irradiation in several human tumour cells in vitro. We investigated whether CPEC enhances the therapeutic ratio of gemcitabine and irradiation in human pancreatic BxPC-3 xenografts and in rat syngeneic L44 lung tumours. These models were selected because gemcitabine and radiation are used to treat both pancreatic and lung cancer patients and both models differ in growth capacity and in gemcitabine-induced radiosensitisation. A profound dose-dependent CTP-depletion was observed after a single injection of CPEC in both tumour tissue and in normal jejunum. In both models, CPEC alone induced a slight but significant tumour growth delay. The combination of CPEC with gemcitabine, at time intervals that showed CTP-depletion after CPEC, enhanced neither tumour growth delay nor toxicity as compared to gemcitabine alone. In addition, no beneficial effect of CPEC was observed in combination with gemcitabine and radiation. These results suggest that CPEC and gemcitabine alone as well as in combination with radiation target a similar cell population in both tumour models. In conclusion, future clinical development of CPEC as a modulator of gemcitabine combined with radiation is unlikely.

Proliferative activity in vitro and DNA repair indicate that adult mouse and human Sertoli cells are not terminally differentiated, quiescent cells.

Sertoli cells isolated from the adult mouse and human testis resume proliferation in culture. After 20 days of culture in Dulbecco modified Eagle medium/Ham F12 (DMEM/F12) medium containing 5%% fetal calf serum, about 36%% of the mouse Sertoli cells, identified by their immunohistochemical staining for the Sertoli cell marker vimentin, incorporated bromodeoxyuridine (BrdU). The renewed proliferation was associated with a 70%% decrease in expression of the cell cycle inhibitor CDKN1B (P27(kip1)) and a 2-fold increase in the levels of the proliferation inducer ID2. In vivo, the balance between cell cycle inhibitors and inducers probably is such that the cells remain quiescent, whereas in culture the balance is disturbed such that Sertoli cells start to proliferate again. The renewed proliferative activity of Sertoli cells in culture was further confirmed by double staining for BrdU and the Sertoli cell marker clusterin (CLU), showing about 25%% of the CLU-positive Sertoli cells to be also positive for BrdU after 13 days of culture. Radiobiologically, Sertoli cells are also different from other quiescent somatic cells in the testis because they express several DNA repair proteins (XRCC1, PARP1, and others). Indeed, a comet assay on irradiated Sertoli cells revealed a 70%% reduction in tail length and tail moment at 20 h after irradiation. Hence, Sertoli cells repair DNA damage, whereas other quiescent somatic testicular cells do not. This repair may be accomplished by nonhomologous end joining via XRCC1 and PARP1. In conclusion, cell kinetic and radiobiological data indicate that Sertoli cells more resemble arrested proliferating cells than the classic postmitotic and terminally differentiated somatic cells that they have always been assumed to be.

Concurrent versus sequential chemotherapy and radiotherapy in limited disease small cell lung cancer: a retrospective comparative study.

BACKGROUND: Patients with limited-disease small cell lung cancer are treated with chemotherapy and chemotherapy combined with radiotherapy. Treatment schemes with curative intention include sequential or concurrent chemoradiotherapy, both combined with prophylactic cranial irradiation (PCI). It is unclear which scheme is superior. PATIENTS AND METHODS: Until 2001, patients received 4-5 cycles of chemotherapy. In cases of no complete response, palliative radiotherapy (RT) was given in 13 fractions of 3 Gy (CT-RT group, N=26). A total of 89 patients did not receive RT after chemotherapy (CT group). After complete response, curatively intended RT was given, of 16x2.5 Gy, concurrently with PCI of 15x2 Gy (SCT-RT group, N=111). From 2001, 40 patients received 4-5 cycles of chemotherapy concurrently with RT of 25x1.8 Gy. PCI was applied to patients with complete response (CCT-RT group). Endpoints were median survival time (MST) and overall survival (OS). RESULTS: MST of CT, CT-RT, SCT-RT and CCT-RT were 8.1, 12.5, 14.0 and 21.8 months, and 5-year OS 3.5, 4.8, 10.5 and 26.9%, respectively. Frequencies of brain metastasis after PCI in SCT-RT and CCT-RT patients were 16.4% and 8.7%, respectively. CONCLUSION: Concurrent chemoradiotherapy resulted in longer MST and higher OS than sequential chemoradiotherapy, chemotherapy with palliative radiotherapy or chemotherapy alone. Results may improve further by applying PCI at an earlier stage and increasing the RT dose.

Surgical stress and accelerated tumor growth.

BACKGROUND: Delay in the initiation of radiotherapy after surgery is associated with an increase in local regional recurrence. A possible mechanism might be that remaining tumor cells proliferate significantly faster as a result of induced angiogenic cytokines. The growth rate of tumors arising from the inoculation of L44 tumor cells in the wound bed after surgical removal of L44 tumors was determined. MATERIALS AND METHODS: L44 tumors growing in the flank of female BN rats were surgically removed. In the wound bed, 5x10(6) L44 cells, harvested from the in vitro cell line, were injected. L44 cells were also injected in the contralateral flank and in control rats with and without surgical intervention. Tumor volumes as a function of time after injection of cells were recorded. From the attained volume at day 7, the cell doubling time was calculated, assuming 10(9) cells per cm3. RESULTS: Tumors arising in the wound bed had the fastest growth rate as compared to the tumors in the contralateral flank or tumors in control rats with or without surgical intervention. CONCLUSION: The results clearly indicate accelerated tumor growth after surgical stress. This indicates that delay in the initiation of radiotherapy after surgery with tumor cells remaining, results in a larger tumor burden and hence a higher probability of local recurrence.

Results of hematopoietic stem cell transplantation after treatment with different high-dose total-body irradiation regimens in five Dutch centers.

PURPOSE: To evaluate results of high-dose total-body irradiation (TBI) regimens for hematopoietic stem cell transplantation. METHODS AND MATERIALS: A total of 1,032 patients underwent TBI in one or two fractions before autologous or allogeneic hematologic stem cell transplantation for acute leukemia and non-Hodgkin's lymphoma. The TBI regimens were normalized by using the biological effective dose (BED) concept. The BED values were divided into three dose groups. Study end points were relapse incidence (RI), non-relapse mortality (NRM), relapse-free survival (RFS), and overall survival (OS). Multivariate analysis was performed, stratified by disease. RESULTS: In the highest TBI dose group, RI was significantly lower and NRM was higher vs. the lower dose groups. However, a significant influence on RFS and OS was not found. Relapses in the eye region were found only after shielding to very low doses. Age was of significant influence on OS, RFS, and NRM in favor of younger patients. The NRM of patients older than 40 years significantly increased, and OS decreased. There was no influence of age on RI. Men had better OS and RFS and lower NRM. Type of transplantation significantly influenced RI and NRM for patients with acute leukemia and non-Hodgkin's lymphoma. There was no influence on RFS and OS. CONCLUSIONS: Both RI and NRM were significantly influenced by the size of the BED of single-dose or two-fraction TBI regimens; OS and RFS were not. Age was of highly significant influence on NRM, but there was no influence of age on RI. Hyperfractionated TBI with a high BED might be useful, assuming NRM can be reduced.

Postoperative high-dose-rate brachytherapy in the prevention of keloids.

BACKGROUND: The aim of this study is to show the efficiency of keloidectomy and postoperative interstitial high-dose-rate (HDR) brachytherapy in the prevention of keloids. METHODS AND MATERIALS: Between 1998 and 2004, 35 patients with 54 keloids were treated postoperatively with HDR brachytherapy. The first HDR dose was applied within 6 hours after surgery, and two additional HDR doses were administered on the next day with a six-hour interval. The majority of patients received 6 Gy as the first dose postsurgery and two fractions of 4 Gy (38 keloids) on the next day. Seven keloids were treated postoperatively with three fractions of 6 Gy. The biologically effective dose (BED), derived from the linear quadratic concept, was applied to calculate the BED for the various radiation regimens. The keloid recurrence rates at specific BED values were compared with those derived for other fractionation schemes in the literature. RESULTS: Four recurrences/nonsatisfactory results out of nine treated keloids were observed after treatments with 1 x 4 Gy + 2 x 3 Gy. Only one recurrence out of 38 was found after 1 x 6 Gy + 2 x 4 Gy and none after 3 x 6 Gy. Better cosmetic results were found at the higher-dose schemes. CONCLUSION: The results of this study prove the effectiveness of HDR brachytherapy after keloidectomy provided that the total HDR dose is sufficient. Currently our scheme is 3 x 6 Gy.

Differences in DNA double strand breaks repair in male germ cell types: lessons learned from a differential expression of Mdc1 and 53BP1.

In male germ cells the repair of DNA double strand breaks (DSBs) differs from that described for somatic cell lines. Irradiation induced immunofluorescent foci (IRIF's) signifying a double strand DNA breaks, were followed in spermatogenic cells up to 16 h after the insult. Foci were characterised for Mdc1, 53BP1 and Rad51 that always were expressed in conjecture with gamma-H2AX. Subsequent spermatogenic cell types were found to have different repair proteins. In early germ cells up to the start of meiotic prophase, i.e. in spermatogonia and preleptotene spermatocytes, 53BP1 and Rad51 are available but no Mdc1 is expressed in these cells before and after irradiation. The latter might explain the radiosensitivity of spermatogonia. Spermatocytes from shortly after premeiotic S-phase till pachytene in epithelial stage IV/V express Mdc1 and Rad51 but no 53BP1 which has no role in recombination involved repair during the early meiotic prophase. Mdc1 is required during this period as in Mdc1 deficient mice all spermatocytes enter apoptosis in epithelial stage IV when they should start mid-pachytene phase of the meiotic prophase. From stage IV mid pachytene spermatocytes to round spermatids, Mdc1 and 53BP1 are expressed while Rad51 is no longer expressed in the haploid round spermatids. Quantifying foci numbers of gamma-H2AX, Mdc1 and 53BP1 at various time points after irradiation revealed a 70% reduction after 16 h in pachytene and diplotene spermatocytes and round spermatids. Although the DSB repair efficiency is higher then in spermatogonia where only a 40% reduction was found, it still does not compare to somatic cell lines where a 70% reduction occurs in 2 h. Taken together, DNA DSBs repair proteins differ for the various types of spermatogenic cells, no germ cell type possessing the complete set. This likely leads to a compromised efficiency relative to somatic cell lines. From the evolutionary point of view it may be an advantage when germ cells die from DNA damage rather than risk the acquisition of transmittable errors made during the repair process.

Biologically effective dose in total-body irradiation and hematopoietic stem cell transplantation.

BACKGROUND AND PURPOSE: Total-body irradiation (TBI) is an important part of the conditioning regimen for hematopoietic stem cell transplantation (HSCT) in patients with hematologic malignancies. The results after treatment with various TBI regimens were compared, and dose-effect relationships for the endpoints relapse incidence, disease-free survival, treatment-related mortality, and overall survival were derived. The aim was to define requirements for an optimal treatment schedule with respect to leukemic cell kill and late normal-tissue morbidity. MATERIAL AND METHODS: A literature search was performed. Three randomized studies, four studies comparing results of two or three TBI regimens, and nine reports with results of one specific TBI regimen were identified. Biologically effective doses (BEDs) were calculated. The results of the randomized studies and the studies comparing results of two or three TBI regimens were pooled, and the pooled relative risk (RR) was calculated for the treatments with high BED values versus treatments with a low BED. BED-effect relationships were obtained. RESULTS: RRs for the high BED treatments were significantly lower for relapse incidence, not significantly different for disease- free survival and treatment-related mortality, and significantly higher for overall survival. BED-effect relationships indicate a decrease in relapse incidence and treatment-related mortality and an increase in disease-free and overall survival with higher BED values. CONCLUSION: "More dose is better", provided that a TBI setting is used limiting the BEDs of lungs, kidneys, and eye lenses.

Renal dysfunction after total body irradiation: dose-effect relationship.

PURPOSE: Late complications related to total body irradiation (TBI) as part of the conditioning regimen for hematopoietic stem cell transplantation have been increasingly noted. We reviewed and compared the results of treatments with various TBI regimens and tried to derive a dose-effect relationship for the endpoint of late renal dysfunction. The aim was to find the tolerance dose for the kidney when TBI is performed. METHODS AND MATERIALS: A literature search was performed using PubMed for articles reporting late renal dysfunction. For intercomparison, the various TBI regimens were normalized using the linear-quadratic model, and biologically effective doses (BEDs) were calculated. RESULTS: Eleven reports were found describing the frequency of renal dysfunction after TBI. The frequency of renal dysfunction as a function of the BED was obtained. For BED>16 Gy an increase in the frequency of dysfunction was observed. CONCLUSIONS: The tolerance BED for kidney tissue undergoing TBI is about 16 Gy. This BED can be realized with highly fractionated TBI (e.g., 6x1.7 Gy or 9x1.2 Gy at dose rates>5 cGy/min). To prevent late renal dysfunction, the TBI regimens with BED values>16 Gy (almost all found in published reports) should be applied with appropriate shielding of the kidneys.

Gemcitabine as a radiosensitizer in undifferentiated tumors.

BACKGROUND: Gemcitabine (dFdC) may cause radiosensitization by specific interference with homologous recombination-mediated DNA double-strand break repair. The radiosensitizing effect of dFdC might be less in normal healthy tissue and more restricted to undifferentiated tumor cells, making it a tumor-selective radiosensitizer. Whether dFdC acts as a radiosensitizer in undifferentiated and well-differentiated rat tumors and on rat foot skin was tested. MATERIALS AND METHODS: Undifferentiated L44 lung tumors in BN rats, MLL prostate tumors in Copenhagen rats, and well-differentiated L42 lung tumors in WAG/Rij rats were used. The tumors were treated with a single X-ray dose, combined or not with dFdC (30 mg/kg) administered 24 h earlier. Tumor volume growth delay was the end-point used. In addition, rat foot skin was treated with a single dose of 22.5 Gy, with or without dFdC. The degree of skin damage was determined according to a scoring system. RESULTS: For tumor growth delay, the dose-enhancement ratios were 1.37 and 1.23-1.36 for the L44 and MLL tumors, respectively. No radiosensitization was observed for the well-differentiated L42 tumor and foot skin. CONCLUSION: Radiosensitization by dFdC was observed in the undifferentiated tumors, but not in the well-differentiated tumor and skin. Our data support further trials to evaluate the usefulness of dFdC as a radiosensitizer in undifferentiated tumors.

Biologically effective doses of postoperative radiotherapy in the prevention of keloids. Dose-effect relationship.

PURPOSE: To review the recurrence rates of keloids after surgical excision followed by radiotherapy, and to answer the question whether after normalization of the dose, a dose-effect relationship could be derived. MATERIAL AND METHODS: A literature search was performed to identify studies dealing with the efficacy of various irradiation regimens for the prevention of keloids after surgery. Biologically effective doses (BEDs) of the various irradiation regimens were calculated using the linear-quadratic concept. A distinction between recurrence rates of keloids in the face and neck region and those in other parts of the body was made. RESULTS: 31 reports were identified with PubMed with the search terms keloids, surgery, radiation therapy, radiotherapy. 13 reports were excluded, because no link could be found between recurrence rate and dose, or if less than ten patients per dose group. The recurrence rate for surgery only was 50-80%. For BED values > 10 Gy the recurrence rate decreased as a function of BED. For BED values > 30 Gy the recurrence rate was < 10%. For a given dose, the recurrence rates of keloids in the sites with high stretch tension were not significantly higher than in sites without stretch tension. CONCLUSION: The results of this study indicate that for effectively treating keloids postoperatively, a relatively high dose must be applied in a short overall treatment time. The optimal treatment probably is an irradiation scheme resulting in a BED value of at least 30 Gy. A BED value of 30 Gy can be obtained with, for instance, a single acute dose of 13 Gy, two fractions of 8 Gy or three fractions of 6 Gy, or a single dose of 27 Gy at low dose rate. The radiation treatment should be administered within 2 days after surgery.

Radiotherapy during pregnancy: fact and fiction.

Radiotherapy during pregnancy might cause harm to the developing fetus. Generally, pregnant women with malignant diseases are advised to delay radiotherapy until after delivery. However, this advice is not based on knowledge of the risks of radiation to the unborn child. In general, the expected radiation effects, such as mental retardation and organ malformations probably only arise above a threshold dose of 0.1-0.2 Gy. This threshold dose is not generally reached with curative radiotherapy during pregnancy, provided that tumours are located sufficiently far from the fetus and that precautions have been taken to protect the unborn child against leakage radiation and collimator scatter of the teletherapy machine; such precautions also reduce the risk of radiation-induced childhood cancer and leukaemia in the unborn child.