High Dose-rate Irradiation Research Articles

Time course of enhanced activity of deoxycytidine kinase and thymidine kinase 1 and 2 in cultured human squamous lung carcinoma cells, SW-1573, induced by γ-irradiation

Single high dose rate irradiation of 4 Gy in SW-1573 cells, derived from non-small cell lung cancer, led to increased activities of deoxycytidine kinase (dCK) and thymidine kinase 1 and 2 (TK1 and 2). The activity of dCK increased by approximately 30% between 1 and 5 h after irradiation, after which the activity returned to the level of control cells by 8 h after irradiation. TK1 activity also increased by 30-50% between 1 and 6 h after irradiation. The decline to normal levels of dCK concurred with a further increase in the activity of TK1, 8 h after irradiation. TK2 activity was below control levels during the first 4 h after irradiation but rose 3-fold at 8 and 16 h after treatment. The activities of TK1 and TK2 had returned to approximate control levels 24 h after irradiation. The observation that mitochondrial TK2 activity increased to a very high level after irradiation may indicate that the activity of this enzyme is not only important for the damage to mitochondrial DNA, the increased activity may also be instrumental for repair of damage to nuclear DNA. We presume that the increase in activity of TK1 after irradiation is limited to cells in S-phase. Recruitment of cells into S-phase, to replace cells killed by irradiation, is probably too slow to offer an explanation for the enhanced activity of TK1 8 h after irradiation. The increase in activity of both dCK, and TK1 and 2 might be involved in an adaptive response of the cells to radiation by facilitation of DNA repair. The expression of protein kinase C (PKC) decreased during the first 5 h after irradiation. At 5 h after irradiation the level of expression had decreased by >50%. The decrease in PKC expression is concurrent with the increase in dCK activity. This suggests a role of PKC in the signal transduction from DNA damage to the increase in activity of enzymes instrumental in DNA repair.

161 A 3D Imaging Technique for Brachytherapy Planning and Treatment in a Single High Dose Rate (HDR) Radiation Operating Suite

161 A 3D Imaging Technique for Brachytherapy Planning and Treatment in a Single High Dose Rate (HDR) Radiation Operating Suite

Current controversies in high‐dose‐rate versus low‐dose‐rate brachytherapy for cervical cancer

The use of brachytherapy in the treatment of cervical cancer has increased worldwide since its initial introduction over 100 years ago. However, certain aspects of the use of high-dose-rate (HDR) versus low-dose-rate (LDR) brachytherapy continue to be controversial, particularly the role of HDR in FIGO Stage III cervical cancer and the use of HDR with concurrent chemotherapy. This study represents a systematic literature review of prospective and retrospective series of patients with cervical carcinoma treated with external-beam radiation (EBRT) followed by either HDR or LDR radiation. The local control rates, survival rates, and treatment-related complications in patients with Stage III cervical cancer treated with HDR or LDR and those treated with concomitant chemotherapy are examined. Patients with Stage III cervical cancer treated with EBRT and brachytherapy have a local control rate of >50% in most series. Randomized prospective and retrospective studies show overall statistically equivalent local control, overall survival, and complication rates between HDR and LDR. However, LDR may be preferable for large, bulky tumors at the time of brachytherapy. Retrospective studies of HDR and concurrent chemotherapy are limited but have demonstrated toxicity rates similar to those with LDR. Selected patients with Stage III cervical carcinoma who have an adequate response to EBRT and concomitant chemotherapy may be treated with HDR brachytherapy. The existing literature shows no significant increase in complications in patients treated with HDR and concurrent chemotherapy; however, sufficient tumor shrinkage prior to HDR and careful monitoring of the dose to the normal tissues are imperative.

Interstitial high dose rate (HDR) brachytherapy for early stage breast cancer

10551 Background: External Beam Radiation Therapy (EBRT) has been the standard of care for breast conservation radiation therapy. Recent data indicates that Interstitial Implant and High Dose Rate (HDR) radiation afterloading compares favorably to EBRT in selected patients. Methods: Patients with Tis, T1, and T2 tumors measuring ≤ 3 cm, negative surgical margins, and negative axillary lymph nodes were judged to be candidates for Interstitial Implant. Results: Between 2000 and 2006, 112 patients underwent Interstitial HDR Implant under Stereotactic Mammographic guidance with conscious sedation and local anesthesia. Conscious sedation consisted of Morphine and Versed. Local anesthesia was given with a mixture of 1% Lidocaine, 0.25% Marcaine, 1:100,000 Epinephrine, and 4% Sodium Bicarbonate neutralizing solution. The implants were placed using a Template with from 3 to 6 planes, and 8 to 43 needles. Catheters were subsequently threaded thru the needles, and the needles removed. Catheter spacing was 1.0 to 1.5 cm. Radiation Treatment planning was performed using CT Scanning. Treatment volumes ranged from 25 cm3 to 359 cm3. The breast implant volume received 3400 cGy in 10 fractions via HDR prescribed to the Planning Target Volume, given BID over 5 days. The procedure was well tolerated. No patient required hospital admission. With a median follow-up 36 months (range 6–60 months), local recurrence occurred in 2.7% (3/112). Cosmetic results were good to excellent in 85.7% (96/112) of the patients. Wound healing complications developed in 7.1% (8/112). Three of these patients had received anthracycline based Chemotherapy. The other five had large (> 200 cm3) implant volumes and catheter spacing of 1.5 cm. Two patients healed after 6 months of conservative treatment. Surgery was required in six patients who developed fat necrosis. Conclusions: With median 36 month follow-up, Breast Conservation radiation therapy utilizing Interstitial HDR Implant has yielded local recurrence rates and cosmetic results which compare favorably to EBRT in selected patients. Treatment with anthracycline based Chemotherapy and large (> 200 cm3) implant volumes appear to be relative contraindications to Interstitial HDR Implant. Finally, catheter spacing of 1 cm yielded optimal dosimetry and minimized complications. No significant financial relationships to disclose.

Determination of ambient and personal dose equivalent for personnel and cargo security screening

In the past few years, imaging technology using ionising radiation has been gaining in importance for the screening of goods and persons for security reasons and in order to detect contraband. For radiation protection purposes it is extremely important to know that dose persons are exposed to when passing through a personnel scanner or, as a stowaway, in a cargo scanner, so as to remain within the prescribed dose limits. Within the scope of a research project, measurements were performed on different types of personnel X-ray scanners as well as cargo X-ray scanners, using the transmission and/or the backscattering method. All scanners investigated operate with a high dose rate and use short irradiation time. Owing to this method of scanning reliable values can only be determined for the personal and ambient dose equivalents, H(p)(10) and H(*)(10), by using a specially developed measuring system. The aim of this project was to determine the range of magnitudes of doses for representative personnel and cargo X-ray scanner systems. Depending on the type of scanner, the determined dose values for personnel scanners range from 0.07 microSv to 6 microSv. Measurements and instruments used in this study are described and the dose values obtained are discussed in detail.

Dermatological applications of HDR using surface applicators using a shorter treatment schedule

Purpose: To present our preliminary results using high-dose-rate (HDR) radiotherapy with a shortened treatment schedule in patients with skin caner. HDR radiotherapy using surface molds offers an alternative radiotherapy modality to electrons for the treatment of skin lesions with a shortened treatment schedule. Custom made surface molds used in conjunction with HDR brachytherapy make possible a uniform dose distribution with a sharp dose gradient.

Prospective Study of Quality of Life of Patients Receiving Treatment for Prostate Cancer

No research was found that compared quality of life (QOL) outcomes of prostate cancer patients receiving intensity-modulated radiation therapies with prostate cancer patients receiving radical prostatectomy. To (a) describe differences in QOL before and after three types of treatment for prostate cancer: radical prostatectomy, intensity-modulated radiation therapy + seed implantation (permanent brachytherapy), or intensity-modulated radiation therapy + high dose rate radiotherapy (temporary brachytherapy); and (b) investigate demographic, physical, and psychosocial variables that impact QOL of men with prostate cancer. Data were collected on three occasions: baseline (prior to treatment), 1 month, and 3 months after beginning treatment. Measures included biographic data, physiological, and psychological measures. Analysis of variance and hierarchical regression were used to examine patterns, describe differences, and identify predictors of QOL in the three treatment groups. QOL was conceptualized as a multidimensional construct that included physical, psychological, social, and functional well-being and prostate cancer concerns. Groups differed significantly in bowel and urinary symptom scores and prostate cancer concerns at baseline, and in urinary and depressive symptoms at 3 months. There were no significant group differences at 1 month. Significant differences were found in QOL as measured with the Functional Assessment of Cancer Treatment-Prostate after treatment with radical prostatectomy, intensity-modulated radiation therapy + seed implantation, or intensity-modulated radiation therapy + high dose rate radiotherapy. Findings may provide healthcare providers with knowledge about treatment sequelae for prostate cancer, enable healthcare providers to educate patients about QOL outcomes of treatment for prostate cancer, and enable patients to make more informed treatment decisions.

Patterns of brachytherapy practice for patients with carcinoma of the cervix (1996–1999): A Patterns of Care Study

To analyze the details of brachytherapy practice in patients treated for carcinoma of the cervix in the United States between 1996 and 1999. Radiation facilities were selected from a stratified random sample. Patients were randomly selected from lists of eligible patients treated at each facility. A total of 442 patients' records were reviewed in 59 facilities to obtain data about patients' characteristics, evaluation, tumor extent, and treatment. National estimates were made using weights that reflected the relative contribution of each institution and of each patient within the sampled institutions. From our survey we estimate that 16,375 patients were treated in the United States during this study period. Unless otherwise specified, brachytherapy practice was based on the 408 patients who had their brachytherapy or all their treatment at the surveyed facility. A total of 91.5% of patients underwent brachytherapy at the initial treating institution; 8.5% were referred to a second site for brachytherapy. Forty-two percent of U.S. facilities referred at least some patients to a second facility for brachytherapy. Of U.S. facilities that treated < or =2 eligible patients per year, 61% referred all of their patients to a second facility for brachytherapy or treated with external RT alone; none of the U.S. facilities with larger experience (>2 eligible patients per year) referred all their patients to a second facility for brachytherapy treatment, but 28% referred some patients to an outside facility for brachytherapy. Overall, 94% of patients who completed treatment with curative intent received brachytherapy. Of these patients who had brachytherapy, 77.8%, 13.3%, and 0.9%, respectively, were treated with low-dose-rate (LDR), high-dose-rate (HDR), or a combination of HDR and LDR brachytherapy; 7.9% had interstitial brachytherapy (5.7% LDR and 1.9% HDR, 0.3% mixed). In facilities that treated >2 patients per year, 15.5% and 9.4% of brachytherapy procedures included HDR or interstitial, respectively; in facilities that treated fewer patients, 3.4% had HDR brachytherapy, and only 1.2% had interstitial brachytherapy. Patients treated with LDR intracavitary radiotherapy had one (23.5%), two (74.1%), or three (2.4%) implants. For patients treated with curative intent who completed radiation therapy with LDR intracavitary radiation therapy without hysterectomy, the median brachytherapy dose to Point A was 40.3 Gy, and the median total dose to Point A was 82.9 Gy. Patients were treated with HDR intracavitary radiation therapy using a variety of treatment schedules using 1-2 fractions (7.5%), 3-4 fractions (17.4%), 5-6 fractions (38.5%), 7-9 fractions (33.5%), or 12 fractions (3%). Fraction sizes were <500 cGy (29.5%), 500-<600 (25.2%), 600 (28.1%), >600 (8%), or unknown (9.2%). For patients treated with HDR, the median total dose to Point A (corrected for fraction size using a alpha/beta = 10) was 85.8 Gy (range: 56.2-116.1 Gy). At institutions treating <500 new patients per year, the percentage of patients receiving a brachytherapy dose <40 Gy was significantly higher than at institutions treating > or =500 new patients per year (p < 0.0001). For LDR intracavitary radiation therapy, 5.8% had neither bladder nor rectal doses recorded for any of their implants, whereas in HDR intracavitary radiation therapy, 73.4% had neither bladder nor rectal doses recorded for any of their implants. The median total duration of radiation therapy was identical for patients who had HDR or LDR intracavitary radiation therapy (57 days). For LDR at institutions treating <500 new patients per year, the percentage of patients with treatment duration >56 days was significantly greater than at institutions > or =500 new patients per year (p = 0.002). Of the patients who had LDR intracavitary radiation therapy implants, 65% were treated using tandem and shielded Fletcher-Suit-Delclos colpostats; other patients had mini ovoids (10.9%), cylinders (3.9%), Henschke (3.7%), or other/mixed applicators (16.5%). In contrast, of patients treated with HDR intracavitary radiation therapy, 68.7% had tandem and rings, 18.2% Fletcher-Suit-Delclos ovoids, 7.5% mini ovoids, 2.3% cylinders, and 3.2% other or mixed applicators. The median duration of treatment and median Point A dose were very similar for patients treated with HDR or LDR. Patients with HDR were treated using a variety of treatment schedules. Different applicator types were favored for LDR vs. HDR. Of patients treated with HDR, 73.4% had no brachytherapy bladder or rectal doses recorded, suggesting that full dosimetric calculations were performed only for the first fraction in many institutions. Facility size significantly impacted on referral to another institution for brachytherapy, brachytherapy dose, and treatment duration.

Response of SOI bipolar transistors exposed to /spl gamma/-rays under different dose rate and bias conditions

This work is devoted to the analysis of /spl gamma/-ray effects on the behavior of bipolar junction transistors belonging to a silicon on insulator technology. Such a process is currently being investigated in order to assess its suitability for use in radiation-resistant applications, namely in the design of readout electronics for radiation detectors in high energy physics experiments and for operation in the space environment. Possible sensitivity to low dose-rate was tested by exposing the devices to /spl gamma/-ray sources with different activities. High dose rate irradiations were performed with the devices biased in different operating regions in order to evaluate the effects of bias conditions on the device sensitivity to radiation. Radiation tolerant, low noise design of charge preamplifiers is discussed in the last section of the paper, on the basis of the results relevant to single device characterization.

Development of High Dose Rate Sensing Method Based on Cavity Ring-Down Laser Spectroscopy

We have developed a new method for high radiation dose rate monitoring based on cavity ring-down laser absorption spectroscopy and have measured 60Co gamma-ray induced chemical species in stationary and flowing air at the wavelength of 532 nm to check the basic performance of the new method. In the stationary air measurement, we confirmed linearity between the absorbed dose and the measured light absorbance by the radiation induced chemical species. Furthermore, in the flowing air measurement, we found the response time and the magnitude of the light absorbance largely depend on the air flow rate. In addition, a preliminary experiment was done to demonstrate the applicability to an intensity monitor for the intense undulator X-rays of BL47XU beamline at SPring-8. Results showed that the measured ring-down rate is proportional to the photon intensity and the detectable range is from 2×1011 to 3×1015 photons/s with time resolution around 3×102 s.

Interstitial high dose rate (HDR) brachytherapy for early stage breast cancer

819 Background: External Beam Radiation Therapy (EBRT) has been the standard of care for breast conservation radiation therapy. Recent data indicates that Interstitial Implant and High Dose Rate (HDR) radiation afterloading compares very favorably to EBRT in selected patients. Methods: Patients with Tis, T1, and T2 tumors measuring ≤ 3 cm, negative surgical margins, and negative axillary lymph nodes were judged to be candidates for Interstitial Implant. Subsequently, patients who had, or were scheduled to receive anthracycine based Chemotherapy were excluded. Results: Between 2000 and 2004, 94 patients underwent Interstitial HDR Implant under Stereotactic Mammographic guidance with conscious sedation and local anesthesia. The implants were placed using a customized Lucite Template utilizing from 3 to 4 planes, and 8 to 26 needles. Catheters were subsequently threaded thru the needles, and the needles removed. Catheter spacing was 1.5 cm. Radiation Treatment planning was performed using CT Scanning and the Plato System. Treatment volumes ranged from 25 cm3 to 359 cm3. HDR treatment was given using the Nucletron afterloading system. The breast implant volume received 4,000 cGy in 10 fractions prescribed to the 100% Isodose line, given BID over 5 days. The procedure was well tolerated. No patient required hospital admission. With a median follow-up 35 months (range 6–56 months), local recurrence occurred in 2.1% (2/94). Cosmetic results were good to excellent in 86.1% (81/94) of the patients. Wound healing complications developed in 8.5% (8/94). Three of these patients had received anthracycline based Chemotherapy. The other five had large (> 200 cm3) implant volumes. Two patients healed after 6 months of conservative treatment. Surgery was required in six patients who developed fat necrosis. Conclusions: Breast Conservation radiation therapy utilizing Interstitial HDR Implant appears to yield local recurrence rates and cosmetic results which compare favorably to EBRT in selected patients. Longer follow-up is needed. Treatment with anthracycline based Chemotherapy and large (> 200 cm3) implant volumes appear to be relative contraindications to Interstitial HDR Implant. No significant financial relationships to disclose.

Chain terminations in the decomposition reactions of chloroethylenes in air through the deposition of alkylperoxy radicals on the wall of an irradiation vessel

The decomposition reactions of chloroethylenes in air were studied for electron beams and 60Co γ -rays at different dose rates using irradiation vessels having different S/V ratios. The chain termination of their decomposition reactions involves the bimolecular reactions of alkylperoxy radicals (RO 2 •) for high dose-rate irradiations, while it involves the deposition of RO 2 • on the wall of the irradiation vessel beside this bimolecular reaction for low dose-rate irradiations, and/or irradiations using vessels having larger inner surface area to volume ratio.

The biological effect of pentoxifylline on the survival of human head and neck cancer cells treated with continuous low and high dose-rate irradiation

The aim of this study was to compare the radiosensitivity effect of the G2/M arrest-abrogating substance, pentoxifylline (PTX), with high dose-rate irradiation (HDRI) and low dose-rate irradiation (LDRI), during which DNA repair and cell proliferation occur. Three squamous cell carcinoma cell lines, FaDu, RPMI 2650 and SCC-61, with differences in genomic imbalance and intrinsic radiosensitivity, were irradiated with 140 cGy/min (HDRI) and 0.7 cGy/min (LDRI) in the presence and absence of 2.0 mM PTX. The surviving fraction at 2.0 Gy (SF2) and cell-cycle phase distribution were assessed by DNA flow cytometry analysis and bromodeoxyuridine incorporation. With HDRI and LDRI the SF2 of FaDu cells decreased by 38.5% and 27.6%, respectively, while the corresponding figures for RPMI 2650 were 28.5% and 48.5%, and for SCC-61 were 44.2% and 28.6%. Increases in G2 populations were evident after both HDRI and LDRI of all cell lines. The enhancement in the cytotoxic effect of PTX was statistically significant after HDRI as well as after LDRI in all three cell lines. We therefore conclude that PTX in combination with LDRI is worth further study, both in vitro, for disclosing underlying mechanisms, and in vivo, to confirm the findings.

Bench tests with La-doped PbWO [formula omitted] crystals

Bench tests of 20 lanthanum-doped PbWO 4 crystals with dimensions 23.8 × 23.8 × 200 mm 3 , delivered in 1997 from BTCP, Bogoroditsk, demonstrated excellent qualities. Together with an optimized optical readout 1240 photoelectrons/GeV were achieved. More than 99% of the scintillation light signal was emitted within 100 ns . Online measurements during low dose rate irradiations showed 20% transmittance loss through 20 cm length after only a few Gray but at this value the damage was already saturated. Annealing times were long enough to allow a reasonable calibration correction of crystals in calorimeters, when irradiation rates were constant. However, sharp changes in irradiation rates require a corresponding rate increase in the re-calibration of the calorimeter. An observed correlation between the radiation-induced absorbance and the transmittance before irradiation at 380 nm could help to find radiation stable crystals without copious investigations. High dose rate irradiations confirmed the low dose rate results. Although the properties of the 20 crystals differ relatively strongly from one another they fulfil, in contrast to prior crystals, the stringent demands for a small compact calorimeter at ZEUS/DESY which in the meantime has been confirmed by beam tests. Although the 1997 crystals showed a marked improvement over previous batches, newer crystals may be better still.

Precise assay of weight per cent sodium in high-level processed nuclear tank waste using a 252Cf neutron source

A basis for production assessment of the vitrification of Hanford nuclear fuel reprocessing wastes will be high precision measurements of the elemental sodium content. However, the chemical analysis of both radioactive and non-radioactive components in nuclear waste can be challenged by high radiation dose rates. In many cases, reduction of dose rates through dilution compromises the precision and sensitivity for certain key components. The use of neutron activation analysis provides a method of analysis which avoids the need for dilutions or extensive sample preparation. The recently developed analysis process is traced with iron-manganese wire referenced to weight per cent sodium standards. The procedure uses a nominal 80 mg 252Cf neutron source to activate the natural sodium to 24Na, followed by gamma-energy analysis. Assay of direct waste samples containing weight per cent sodium has shown precision of less than one per cent standard deviation of total propagated uncertainty.

Array CGH analysis of chromosome aberrations in mice Acute Myeloid Leukemia induced by high dose rate radiation

Array CGH analysis of chromosome aberrations in mice Acute Myeloid Leukemia induced by high dose rate radiation

Dose rate dependence of the relative biological effectiveness of 103Pd for continuous low dose rate irradiation of BA1112 rhabdomyosarcoma cells in vitro relative to acute exposures

Purpose: To measure the relative biological effectiveness (RBE) of continuous low dose rate irradiation (CLDRI) using 103Pd sources relative to acute high dose rate irradiations (AHDRI) from a 250 kVp x-ray beam and an x-ray beam having an equivalent mono-energetic photon energy equal to the average energy of the 103Pd source for BA1112 rhabdomyosarcoma cells.Materials and methods: A customized 103Pd irradiator was built to provide CLDRI using 103Pd at different dose rates relevant to clinical interstitial brachytherapy to BA1112 rhabdomyosarcoma cells growing in exponential phase in culture. A special x-ray beam that simulates the photon energies emitted by the 103Pd source was also developed to provide acute high dose rate irradiation at those energies. Cell survival curves from different irradiation conditions were measured. The RBE with respect to AHDRI using standard 250 kVp x-rays was determined from the doses required to achieve a cell surviving faction of 0.01.Results: For acute irradiation, the RBE of the x-rays simulating 103Pd was 1.24 relative to 250 kVp x-rays. A profound dose rate effect was observed at low dose rates in the range of 6.8 – 14.4 cGy/h that are typical of permanent interstitial brachytherapy. At cell-surviving fraction of 0.01, the RBE of CLDRI at 6.8 and 14.4 cGy/h using 103Pd sources was reduced by a factor of 3 and 2, respectively, relative to the acute exposure. This observation is in good agreement with recent in vivo tumor cure studies performed on BA1112 tumor.Conclusion: The relative biological effectiveness of the photons emitted by 103Pd depends on both the linear energy transfer (LET) of the low energy photons and the dose rate of the irradiation. The higher LET of 103Pd photons is biologically more effective in killing BA1112 tumor cells compared to conventional 250 kVp x-rays when both are delivered at the same dose rate. But the gain in RBE that results from the higher LET can be quickly negated by the reduced dose rate of the irradiation.

Development of High Dose Rate Sensing Method Based on Cavity Ring-Down Laser Spectroscopy

We have developed a new method for high radiation dose rate monitoring based on cavity ring-down laser absorption spectroscopy and have measured 60Co gamma-ray induced chemical species in stationary and flowing air at the wavelength of 532 nm to check the basic performance of the new method. In the stationary air measurement, we confirmed linearity between the absorbed dose and the measured light absorbance by the radiation induced chemical species. Furthermore, in the flowing air measurement, we found the response time and the magnitude of the light absorbance largely depend on the air flow rate. In addition, a preliminary experiment was done to demonstrate the applicability to an intensity monitor for the intense undulator X-rays of BL47XU beamline at SPring-8. Results showed that the measured ring-down rate is proportional to the photon intensity and the detectable range is from 2×1011 to 3×1015 photons/s with time resolution around 3×102 s.

Non-invasive assessment of radiation injury with electrical impedance spectroscopy

A detailed understanding of non-targeted normal tissue response is necessary for the optimization of radiation treatment plans in cancer therapy. In this study, we evaluate the ability of electrical impedance spectroscopy (EIS) to non-invasively determine and quantify the injury response in soft tissue after high dose rate (HDR) irradiation, which is characterized by large localized dose distributions possessing steep spatial gradients. The HDR after-loading technique was employed to irradiate small volumes of muscle tissue with single doses (26–52 Gy targeted 5 mm away from the source). Impedance measurements were performed on 29 rats at 1, 2 and 3 month post-irradiation, employing 31 frequencies in the 1 kHz to 1 MHz range. Over the first 3 months, conductivity increased by 48% and 26% following target doses of 52 Gy and 26 Gy 5 mm from the HDR source, respectively. Injury, assessed independently through a grid-based scoring method showed a quadratic dependence on distance from source. A significant injury (50% of cells atrophied, necrotic or degenerating) in 1.2% of the volume, accompanied by more diffuse injury (25% of cells atrophied, necrotic or degenerating) in 9% of the tissue produced a conductivity increase of 0.02 S m−1 (8% over a baseline of 0.24 S m−1). This was not statistically significant at p = 0.01. Among treatment groups, injury differences in 22% of the volume led to statistically significant differences in conductivity of 0.07 S m−1 (23% difference in conductivity). Despite limitations, the success of EIS in detecting responses in a fraction of the tissue probed, during these early post-irradiation time-points, is encouraging. Electrical impedance spectroscopy may provide a useful metric of atrophy and the development of fibrosis secondary to radiation that could be further developed into a low-cost imaging method for radiotherapy monitoring and assessment.

Evidence for 'bystander effects' in vivo.

The observation of bystander effects in vitro have raised some serious questions as to the appropriate target size for calculation radiation dose. This has implications on the risk from ionizing radiation since dose is often directly related to radiation risk. This paper demonstrates that bystander effects do occur in vivo. It demonstrates that at low dose rates the bystander effects and risk are limited to the organ where the radiation dose is delivered. On the other hand, exposure to high radiation dose rates produces clastogenic factors that are released into the blood. These factors have been demonstrated both in vitro and in vivo and may influence risk in organs not directly exposed to the radiation. Bystander effects suggest that organs respond as a unit and are not just a bag of individual cells acting independently. Dose and risk must consider this unit.