Mesenchymal differentiation mediated by NF-κB promotes radiation resistance in glioblastoma.

Despite extensive study, few therapeutic targets have been identified for glioblastoma (GBM). Here we show that patient-derived glioma sphere cultures (GSCs) that resemble either the proneural (PN) or mesenchymal (MES) transcriptomal subtypes differ significantly in their biological characteristics. Moreover, we found that a subset of the PN GSCs undergoes differentiation to a MES state in a TNF-α/NF-κB-dependent manner with an associated enrichment of CD44 subpopulations and radioresistant phenotypes. We present data to suggest that the tumor microenvironment cell types such as macrophages/microglia may play an integral role in this process. We further show that the MES signature, CD44 expression, and NF-κB activation correlate with poor radiation response and shorter survival in patients with GBM.

Using NanoDot dosimetry to study the RS 2000 X-ray biological irradiator.

PURPOSE: To use NanoDot dosimeters to study the RS 2000 X-ray Biological Irradiator dosimetry characteristics and perform in vivo dosimetry for cell or small animal experiments. METHODS AND MATERIALS: We first calibrated the Landauer NanoDot(™) Reader by irradiating some NanoDot dosimeters with a set of known doses at specific positions defined by the irradiator. A group of five NanoDot dosimeters were placed at five specific positions where the dose rates were known and provided by the irradiator. Each group was irradiated for a set of times respectively. By correlating the readings of dosimeters with the given irradiated doses, we established the dose-reading relationship for the irradiator under the specific running condition. The established calibration curve was validated by exposing arbitrary known doses to a set of dosimeters, using the Landauer NanoDot(™) Reader to measure the doses, and then making the comparison between the two doses. To study the dose gradient of the X-ray inside the irradiated target (dose variation/cm), we placed dosimeters under different thicknesses of water-equivalent bolus and irradiated them, then measured the doses to determine the dose gradient. RESULTS: Using the method described above, we were able to calibrate the Landauer InLight NanoDot(™) Reader and use NanoDot dosimeters to measure the actual doses delivered to the targets for the cell/small animal experiments that use the RS 2000 X-ray Biological Irradiator. CONCLUSIONS: NanoDots are ideal dosimeters to use for in vivo dosimetry for cell/small animal irradiation experiments. The dose decrease inside the animal tissue is about 20% per cm.

Regulation of FANCD2 by the mTOR pathway contributes to the resistance of cancer cells to DNA double-strand breaks.

Deregulation of the mTOR pathway is closely associated with tumorigenesis. Accordingly, mTOR inhibitors such as rapamycin and mTOR-selective kinase inhibitors have been tested as cancer therapeutic agents. Inhibition of mTOR results in sensitization to DNA-damaging agents; however, the molecular mechanism is not well understood. We found that an mTOR-selective kinase inhibitor, AZD8055, significantly enhanced sensitivity of a pediatric rhabdomyosarcoma xenograft to radiotherapy and sensitized rhabdomyosarcoma cells to the DNA interstrand cross-linker (ICL) melphalan. Sensitization correlated with drug-induced downregulation of a key component of the Fanconi anemia pathway, FANCD2 through mTOR regulation of FANCD2 gene transcripts via mTORC1-S6K1. Importantly, we show that FANCD2 is required for the proper activation of ATM-Chk2 checkpoint in response to ICL and that mTOR signaling promotes ICL-induced ATM-Chk2 checkpoint activation by sustaining FANCD2. In FANCD2-deficient lymphoblasts, FANCD2 is essential to suppress endogenous and induced DNA damage, and FANCD2-deficient cells showed impaired ATM-Chk2 and ATR-Chk1 activation, which was rescued by reintroduction of wild-type FANCD2. Pharmacologic inhibition of PI3K-mTOR-AKT pathway in Rh30 rhabdomyosarcoma cells attenuated ICL-induced activation of ATM, accompanied with the decrease of FANCD2. These data suggest that the mTOR pathway may promote the repair of DNA double-strand breaks by sustaining FANCD2 and provide a novel mechanism of how the Fanconi anemia pathway modulates DNA damage response and repair.

The application of radiation therapy to the Pediatric Preclinical Testing Program (PPTP): results of a pilot study in rhabdomyosarcoma.

BACKGROUND: The Pediatric Preclinical Testing Program (PPTP) has been successfully used to determine the efficacy of novel agents against solid tumors by testing them within a mouse-flank in vivo model. To date, radiation therapy has not been applied to this system. We report on the feasibility and biologic outcomes of a pilot study using alveolar and embryonal rhabdomyosarcoma xenograft lines. PROCEDURES: We developed a high-throughput mouse-flank irradiation device that allows the safe delivery of radiotherapy in clinically relevant doses. For our pilot study, two rhabdomyosarcoma xenograft lines from the PPTP, Rh30 (alveolar) and Rh18 (embryonal) were selected. Using established methods, xenografts were implanted, grown to appropriate volumes, and were subjected to fractionated radiotherapy. Tumor response-rates, growth kinetics, and event-free survival time were measured. RESULTS: Once optimized, the rate of acute toxicity requiring early removal from study in 93 mice was only 3%. During the optimization phase, it was observed that the alveolar Rh30 xenograft line demonstrated a significantly greater radiation resistance than embryonal Rh18 in vivo. This finding was validated within the standardized 30 Gy treatment phase, resulting in overall treatment failure rates of 10% versus 60% for the embryonal versus alveolar subtype, respectively. CONCLUSIONS: Our pilot study demonstrated the feasibility of our device which enables safe, clinically relevant focal radiation delivery to immunocompromised mice. It further recapitulated the expected clinical radiobiology.

Diagnostic and prognostic molecular markers in common adult gliomas.

The majority of primary CNS tumors in adults are comprised of gliomas (astrocytomas, oligodendrogliomas and ependymomas). The diagnosis has historically been based on the histologic appearance of these tumors. However, as molecular data have accumulated over the years, there is considerable evidence that the molecular diversity (even within the same diagnostic entity) may account for the heterogeneity of clinical outcomes, such as response to treatment, time to progression and overall survival after diagnosis. These molecular markers are becoming more useful in the field of neuro-oncology. They can assist in diagnosis, provide prognostic information and potentially predict response to therapy. Perhaps the greatest potential for these molecular aberrations is that they may represent therapeutic targets themselves. In this article, we summarize the findings of important, published biomarker studies in adult gliomas and provide an overview of the practical uses of these markers in the clinical setting, as well as the current understanding of molecular gliomagenesis.

Identification of a CpG island methylator phenotype that defines a distinct subgroup of glioma.

We have profiled promoter DNA methylation alterations in 272 glioblastoma tumors in the context of The Cancer Genome Atlas (TCGA). We found that a distinct subset of samples displays concerted hypermethylation at a large number of loci, indicating the existence of a glioma-CpG island methylator phenotype (G-CIMP). We validated G-CIMP in a set of non-TCGA glioblastomas and low-grade gliomas. G-CIMP tumors belong to the proneural subgroup, are more prevalent among lower-grade gliomas, display distinct copy-number alterations, and are tightly associated with IDH1 somatic mutations. Patients with G-CIMP tumors are younger at the time of diagnosis and experience significantly improved outcome. These findings identify G-CIMP as a distinct subset of human gliomas on molecular and clinical grounds.

A multigene predictor of outcome in glioblastoma.

Only a subset of patients with newly diagnosed glioblastoma (GBM) exhibit a response to standard therapy. To date, a biomarker panel with predictive power to distinguish treatment sensitive from treatment refractory GBM tumors does not exist. An analysis was performed using GBM microarray data from 4 independent data sets. An examination of the genes consistently associated with patient outcome, revealed a consensus 38-gene survival set. Worse outcome was associated with increased expression of genes associated with mesenchymal differentiation and angiogenesis. Application to formalin fixed-paraffin embedded (FFPE) samples using real-time reverse-transcriptase polymerase chain reaction assays resulted in a 9-gene subset which appeared robust in these samples. This 9-gene set was then validated in an additional independent sample set. Multivariate analysis confirmed that the 9-gene set was an independent predictor of outcome after adjusting for clinical factors and methylation of the methyl-guanine methyltransferase promoter. The 9-gene profile was also positively associated with markers of glioma stem-like cells, including CD133 and nestin. In sum, a multigene predictor of outcome in glioblastoma was identified which appears applicable to routinely processed FFPE samples. The profile has potential clinical application both for optimization of therapy in GBM and for the identification of novel therapies targeting tumors refractory to standard therapy.

MGMT promoter methylation is predictive of response to radiotherapy and prognostic in the absence of adjuvant alkylating chemotherapy for glioblastoma.

Hypermethylation of the O(6)-methylguanine-DNA-methyltransferase (MGMT) gene has been shown to be associated with improved outcome in glioblastoma (GBM) and may be a predictive marker of sensitivity to alkylating agents. However, the predictive utility of this marker has not been rigorously tested with regard to sensitivity to other therapies, namely radiation. To address this issue, we assessed MGMT methylation status in a cohort of patients with GBM who underwent radiation treatment but did not receive chemotherapy as a component of adjuvant treatment. Formalin-fixed, paraffin-embedded tumor samples from 225 patients with newly diagnosed GBM were analyzed via methylation-specific, quantitative real-time polymerase chain reaction following bisulfite treatment on isolated DNA to assess MGMT promoter methylation status. In patients who received radiotherapy alone following resection, methylation of the MGMT promoter correlated with an improved response to radiotherapy. Unmethylated tumors were twice as likely to progress during radiation treatment. The median time interval between resection and tumor progression of unmethylated tumors was also nearly half that of methylated tumors. Promoter methylation was also found to confer improved overall survival in patients who did not receive adjuvant alkylating chemotherapy. Multivariable analysis demonstrated that methylation status was independent of age, Karnofsky performance score, and extent of resection as a predictor of time to progression and overall survival. Our data suggest that MGMT promoter methylation appears to be a predictive biomarker of radiation response. Since this biomarker has also been shown to predict response to alkylating agents, perhaps MGMT promoter methylation represents a general, favorable prognostic factor in GBM.

Optimal treatment planning for skull base chordoma: photons, protons, or a combination of both?

PURPOSE: We compared dosimetry of proton (PR), intensity modulated radiation therapy (IMRT) photon (PH), and combined PR and IMRT PH (PP) irradiation of skull base chordomas to determine the most optimal technique. METHODS AND MATERIALS: Computed tomography simulation scans of 5 patients with skull base chordoma were used to generate four treatment plans: an IMRT PH plan with 1-mm planning target volume (PTV; PH1) for stereotactic treatment, an IMRT PH plan with 3-mm PTV (PH3) for routine treatment, a PR plan with beam-specific expansion margins on the clinical target volume, and a PP plan combining PR and PH treatment. All plans were prescribed 74 Gy/Cobalt Gray equivalents (CGE) to the PTV. To facilitate comparison, the primary objective of all plans was 95% or greater PTV prescribed dose coverage. Plans then were optimized to limit dose to normal tissues. RESULTS: PTVs ranged from 4.4 to 36.7 cc in size (mean, 21.6 cc). Mean % PTV receiving 74 Gy was highest in the PP plans (98.4%; range, 96.5-99.2%) and lowest in the PH3 plans (96.1%; range, 95.1-96.7%). PR plans were the least homogeneous and conformal. PH3 plans had the highest mean % volume (V) of brain, brainstem, chiasm, and temporal lobes greater than tolerance doses. The PH1 plans had the lowest brainstem mean % V receiving 67 Gy (V(67Gy); 2.3 Gy; range, 0-7.8 Gy) and temporal lobe mean % V(65Gy) (4.3 Gy; range, 0.1-7.7 Gy). Global evaluation of the plans based on objective parameters revealed that PH1 and PP plans were more optimal than either single-modality PR or PH3 plans. CONCLUSIONS: There are dosimetric advantages to using either PH1 or PP plans, with the latter yielding the best target coverage and conformality.

Stereotactic radiosurgery for metastatic brain tumors: a comprehensive review of complications.

OBJECT: Stereotactic radiosurgery (SRS) is commonly used to treat brain metastases. Complications associated with this treatment are underreported. The authors reviewed a large series of patients who underwent SRS for brain metastases to identify complications and factors predicting their occurrence. METHODS: Prospectively collected clinical data from 273 patients undergoing SRS for 1 or 2 brain metastases at The University of Texas M. D. Anderson Cancer Center between June 1993 and December 2004 were reviewed. Patients who had received prior treatment for their tumor, including whole-brain radiation, SRS, or surgery, were excluded from the study. Data on adverse neurological and nonneurological outcomes following treatment were collected. RESULTS: Three hundred sixteen lesions were treated. Complications were associated with 127 (40%) of 316 treated lesions. New neurological complications were associated with 101 (32%) of 316 lesions. The onset of seizure was the most common complication, occurring in 41 (13%) of 316 SRS cases. On multivariate analysis, progressing primary cancer (hazard ratio [HR]=2.4, 95% CI 1.6-3.6, p<0.001), tumor location in eloquent cortex (HR=2.3, 95% CI 1.6-3.4, p<0.001), and lower (<15 Gy) SRS dose (HR=2.1, 95% CI 1.1-4.2, p=0.04) were significantly associated with new complications. On multivariate analysis, a tumor location in the eloquent cortex (HR=2.5, 95% CI 1.6-3.8, p<0.001) and progressing primary cancer (HR=1.6, 95% CI 1.1-2.5, p=0.03) were significantly associated with new neurological complications. CONCLUSIONS: The authors showed that new neurological and nonneurological complications were associated with 40% of SRS treatments for brain metastases. Patients with lesions in functional brain regions have a significantly increased risk of treatment-related complications.

Elevated phospho-S6 expression is associated with metastasis in adenocarcinoma of the lung.

PURPOSE: The primary objective of this study was to determine whether markers of differentiation and activation of the Akt pathway are associated with metastasis in adenocarcinoma of the lung. EXPERIMENTAL DESIGN: Paired primary and metastatic tumor samples were obtained from 41 patients who had undergone resection of both primary lung adenocarcinoma and brain metastatic lesions. Paired samples were compared for relative expression of thyroid transcription factor 1 (TTF-1) and E-cadherin as potential markers of differentiation. Activation of the Akt pathway was assessed by expression of p-Akt and p-S6. Biomarkers that showed relative discordance in expression between the matched pairs were then assessed in a cohort of 77 primary lung adenocarcinomas. Validation was done in an independent cohort of 82 primary lung adenocarcinomas. RESULTS: Among the 41 matched pairs, E-cadherin (23 discordant pairs) and TTF-1 (18 discordant pairs) were overexpressed in primary tumors (20 of 23 and 15 of 18, respectively). In contrast, p-S6 overexpression was significantly associated with metastatic tumors (20 of 21 discordant pairs). The expression of E-cadherin, p-S6, and TTF-1 was evaluated in 77 primary lung adenocarcinomas, in which high p-S6 expression was associated with shorter time to metastasis. The association of p-S6 with metastasis was then validated in an independent set of 82 tumors. In multivariable analysis, p-S6 expression was a negative independent predictor of metastasis-free survival after adjustment for tumor stage. CONCLUSIONS: The biomarker p-S6 is overexpressed in metastatic tumors. In primary tumors, higher p-S6 expression is associated with shorter metastatic-free survival. This biomarker has the potential for risk stratification in future clinical trials.

Selective repression of YKL-40 by NF-kappaB in glioma cell lines involves recruitment of histone deacetylase-1 and -2.

Here we show that in contrast to other cancer types, tumor necrosis factor (TNF)-alpha suppresses YKL-40 expression in glioma cell lines in a nuclear factor kappaB (NF-kappaB) dependent manner. Even though TNF-alpha causes recruitment of p65 and p50 subunits of NF-kappaB to the YKL-40 promoter in all cell types, recruitment of histone deacetylases (HDAC)-1 and -2, and a consequent deacetylation of histone H3 at the YKL-40 promoter occurs only in glioma cells. Importantly, using chromatin immunoprecipitation assays in frozen glioblastoma multiforme tissues, we show that YKL-40 levels decrease consistent with HDAC1 recruitment despite high levels of nuclear p-p65. This study presents a paradigm for NF-kappaB regulation of one of its targets in a strict cell type specific manner.

Multimodality treatment of osteosarcoma: radiation in a high-risk cohort.

PURPOSE: Chemotherapy during radiation and/or bone-seeking radioisotope therapy (153-samarium; 1 mCi/kg) during radiation may improve osteosarcoma cancer control. PATIENTS AND METHODS: We analyzed our preliminary radiation experience in high-risk, metastatic, and/or recurrent patients during a consecutive period of 20 months (May 2005-December 2006). RESULTS: Thirty-nine high-risk osteosarcoma patients had radiotherapy; 119 sites were irradiated. A median four sites were irradiated per patient (range 1-14). The median radiation dose and number of fractions of radiation was 30 Gy in 10 fractions (range 10-70 Gy in 4-35 fractions). Chemotherapy, most commonly ifosfamide or methotrexate, was used in 80% (100/119) radiotherapy courses. Of 38 painful sites, 29 had improvement (76%), 4 had no change (10%), and 5 had more pain (13%). Objective and potentially durable responses were documented using PET-CT and bone scans with persistent and sustained reduction of standard uptake values (SUVs; initial SUV of indication lesion 9.5 became <4 at all subsequent time points) and serial bone scans [improvement in 29/39 (72%); stable 10/39 (25%), worse 1/39 (3%)]. The actuarial 4-year survival from development of metastasis was 39%. CONCLUSIONS: Our early results suggest that the use of multimodality therapy including chemotherapy with radiation in unresectable osteosarcoma may be beneficial.

Epidermal growth factor receptor variant III status defines clinically distinct subtypes of glioblastoma.

PURPOSE: The clinical significance of epidermal growth factor receptor variant III (EGFRvIII) expression in glioblastoma multiforme (GBM) and its relationship with other key molecular markers are not clear. We sought to evaluate the clinical significance of GBM subtypes as defined by EGFRvIII status. PATIENTS AND METHODS: The expression of EGFRvIII was assessed by immunohistochemistry in 649 patients with newly diagnosed GBM. These data were then examined in conjunction with the expression of phospho-intermediates (in a subset of these patients) of downstream AKT and Ras pathways and YKL-40 as well as with known clinical risk factors, including the Radiation Therapy Oncology Group's recursive partitioning analysis (RTOG-RPA) class. RESULTS: The RTOG-RPA class was highly predictive of survival in EGFRvIII-negative patients but much less predictive in EGFRvIII-positive patients. These findings were seen in both an initial test set (n = 268) and a larger validation set (n = 381). Similarly, activation of the AKT/MAPK pathways and YKL-40 positivity were predictive of poor outcome in EGFRvIII-negative patients but not in EGFRvIII-positive patients. Pair-wise combinations of markers identified EGFRvIII and YKL-40 as prognostically important. In particular, outcome in patients with EGFRvIII-negative/YKL-40-negative tumors was significantly better than the outcome in patients with the other three combinations of these two markers. CONCLUSION: Established prognostic factors in GBM were not predictive of outcome in the EGFRvIII-positive subset, although this requires confirmation in independent data sets. GBMs negative for both EGFRvIII and YKL-40 show less aggressive behavior.

Prognostic associations of activated mitogen-activated protein kinase and Akt pathways in glioblastoma.

PURPOSE: Activation of mitogen-activated protein kinase (MAPK) and members of the Akt pathway have been shown to promote cell proliferation, survival, and resistance to radiation. This study was conducted to determine whether any of these markers are associated with survival time and response to radiation in glioblastoma. EXPERIMENTAL DESIGN: The expression of phosphorylated (p-)Akt, mammalian target of rapamycin (p-mTOR), p-p70S6K, and p-MAPK were assessed by immunohistochemical staining in 268 cases of newly diagnosed glioblastoma. YKL-40, a prognostic marker previously examined in these tumors, was also included in the analysis. Expression data were tested for correlations with response to radiation therapy in 131 subtotally resected cases and overall survival (in all cases). Results were validated in an analysis of 60 patients enrolled in clinical trials at a second institution. RESULTS: Elevated p-MAPK expression was most strongly associated with poor response to radiotherapy, a finding corroborated in the validation cohort. For survival, higher expressions of p-mTOR, p-p70S6K, and p-MAPK were associated with worse outcome (all P < 0.03). YKL-40 expression was associated with the expressions of p-MAPK, p-mTOR, and p-p70S6K (all P < 0.02), with a trend toward association with p-Akt expression (P = 0.095). When known clinical variables were added to a multivariate analysis, only age, Karnofsky performance score, and p-MAPK expression emerged as independent prognostic factors. CONCLUSIONS: p-MAPK and activated members of the Akt pathway are markers of outcome in glioblastoma. Elevated expression of p-MAPK is associated with increased radiation resistance and represents an independent prognostic factor in these tumors.

FoxM1B is overexpressed in human glioblastomas and critically regulates the tumorigenicity of glioma cells.

The transcription factor Forkhead box M1 (FoxM1) is overexpressed in malignant glioma. However, the functional importance of this factor in human glioma is not known. In the present study, we found that FoxM1B was the predominant FoxM1 isoform expressed in human glioma but not in normal brain tissue. The level of FoxM1 protein expression in human glioma tissues was directly correlated with the glioma grade. The level of FoxM1 protein expression in human glioblastoma tissues was inversely correlated with patient survival. Enforced FoxM1B expression caused SW1783 and Hs683 glioma cells, which do not form tumor xenografts, to regain tumorigenicity in nude mouse model systems. Moreover, gliomas that arose from FoxM1B-transfected anaplastic astrocytoma SW1783 cells displayed glioblastoma multiforme phenotypes. Inhibition of FoxM1 expression in glioblastoma U-87MG cells suppressed their anchorage-independent growth in vitro and tumorigenicity in vivo. Furthermore, we found that FoxM1 regulates the expression of Skp2 protein, which is known to promote degradation of the cell cycle regulator p27(Kip1). These results showed that FoxM1 is overexpressed in human glioblastomas and contributes to glioma tumorigenicity. Therefore, FoxM1 might be a new potential target of therapy for human malignant gliomas.

A three-dimensional computed tomography-assisted Monte Carlo evaluation of ovoid shielding on the dose to the bladder and rectum in intracavitary radiotherapy for cervical cancer.

PURPOSE: To determine the effects of Fletcher Suit Delclos ovoid shielding on dose to the bladder and rectum during intracavitary radiotherapy for cervical cancer. METHODS AND MATERIALS: The Monte Carlo method was used to calculate the dose in 12 patients receiving low-dose-rate intracavitary radiotherapy with both shielded and unshielded ovoids. Cumulative dose-difference surface histograms were computed for the bladder and rectum. Doses to the 2-cm(3) and 5-cm(3) volumes of highest dose were computed for the bladder and rectum with and without shielding. RESULTS: Shielding affected dose to the 2-cm(3) and 5-cm(3) volumes of highest dose for the rectum (10.1% and 11.1% differences, respectively). Shielding did not have a major impact on the dose to the 2-cm(3) and 5-cm(3) volumes of highest dose for the bladder. The average dose reduction to 5% of the surface area of the bladder was 53 cGy. Reductions as large as 150 cGy were observed to 5% of the surface area of the bladder. The average dose reduction to 5% of the surface area of the rectum was 195 cGy. Reductions as large as 405 cGy were observed to 5% of the surface area of the rectum. CONCLUSIONS: Our data suggest that the ovoid shields can greatly reduce the radiation dose delivered to the rectum. We did not find the same degree of effect on the dose to the bladder. To calculate the dose accurately, however, the ovoid shields must be included in the dose model.

YKL-40 expression is associated with poorer response to radiation and shorter overall survival in glioblastoma.

PURPOSE: YKL-40 is a secreted protein that has been reported to be overexpressed in epithelial cancers and gliomas, although its function is unknown. Previous data in a smaller sample set suggested that YKL-40 was a marker associated with a poorer clinical outcome and a genetically defined subgroup of glioblastoma. Here we test these findings in a larger series of patients with glioblastoma, and in particular, determine if tumor YKL-40 expression is associated with radiation response. EXPERIMENTAL DESIGN: Patients (n=147) with subtotal resections were studied for imaging-assessed changes in tumor size in serial studies following radiation therapy. An additional set (n=140) of glioblastoma patients who underwent a gross-total resection was tested to validate the survival association and extend them to patients with minimal residual disease. RESULTS: In the subtotal resection group, higher YKL-40 expression was significantly associated with poorer radiation response, shorter time to progression and shorter overall survival. The association of higher YKL-40 expression with poorer survival was validated in the gross-total resection group. In multivariate analysis with both groups combined (n = 287), YKL-40 was an independent predictor of survival after adjusting for patient age, performance status, and extent of resection. YKL-40 expression was also compared with genetically defined subsets of glioblastoma by assessing epidermal growth factor receptor amplification and loss at chromosome 10q, two of the common recurring aberrations in these tumors, using fluorescent in situ hybridization. YKL-40 was significantly associated with 10q loss. CONCLUSIONS: The findings implicate YKL-40 as an important marker of therapeutic response and genetic subtype in glioblastomas and suggest that it may play an oncogenic role in these tumors.

Comparison between CT-based volumetric calculations and ICRU reference-point estimates of radiation doses delivered to bladder and rectum during intracavitary radiotherapy for cervical cancer.

PURPOSE: To compare CT-based volumetric calculations and International Commission on Radiation Units and Measurements (ICRU) reference-point estimates of radiation doses to the bladder and rectum in patients with carcinoma of the uterine cervix treated with definitive low-dose-rate intracavitary radiotherapy (ICRT). METHODS AND MATERIALS: Between November 2001 and March 2003, 60 patients were prospectively enrolled in a pilot study of ICRT with CT-based dosimetry. Most patients underwent two ICRT insertions. After insertion of an afterloading ICRT applicator, intraoperative orthogonal films were obtained to ensure proper positioning of the system and to facilitate subsequent planning. Treatments were prescribed using standard two-dimensional dosimetry and planning. Patients also underwent helical CT of the pelvis for three-dimensional reconstruction of the radiation dose distributions. The systems were loaded with 137Cs sources using the Selectron remote afterloading system according to institutional practice for low-dose-rate brachytherapy. Three-dimensional dose distributions were generated using the Varian BrachyVision treatment planning system. The rectum was contoured from the bottom of the ischial tuberosities to the sigmoid flexure. The entire bladder was contoured. The minimal doses delivered to the 2 cm3 of bladder and rectum receiving the highest dose (DBV2 and DRV2, respectively) were determined from dose-volume histograms, and these estimates were compared with two-dimensionally derived estimates of the doses to the corresponding ICRU reference points. RESULTS: A total of 118 unique intracavitary insertions were performed, and 93 were evaluated and the subject of this analysis. For the rectum, the estimated doses to the ICRU reference point did not differ significantly from the DRV2 (p = 0.561); the mean (+/- standard deviation) difference was 21 cGy (+/- 344 cGy). The median volume of the rectum that received at least the ICRU reference-point dose was 2.1 cm3. In 66 (71%) of 93 cases, <5 cm3 was treated to this dose. However, for the bladder, the estimated doses to the ICRU reference point were significantly lower than the D(BV2) (p <0.001); the mean difference was 680 cGy (+/- 543 cGy). The median volume of the bladder that received at least the ICRU reference-point dose was 13.0 cm3. CONCLUSIONS: Our data suggest that the estimated dose to the ICRU rectal point may be a reasonable surrogate for the DRV2. However, this result may not be applicable to other treatment guidelines and ICRT applicator systems. In contrast, the dose to the ICRU bladder point does not appear to be a reasonable surrogate for the DBV2. Correlation with late complications are needed to define the role of three-dimensional dosimetry in treatment planning.