Cardiovascular effects after low-dose exposure and radiotherapy: what research is needed?

The authors of this report met at the Head Quarter of the International Atomic Energy Agency (IAEA) in Vienna, Austria, on 2-4 July 2012, for intensive discussions of an abundance of original publications on new epidemiological studies on cardiovascular effects after low-dose exposure and radiotherapy and radiobiological experiments as well as several comprehensive reviews that were published since the previous meeting by experts sponsored by the IAEA in June 2006. The data necessitated a re-evaluation of the situation with special emphasis on the consequences current experimental and clinical data may have for clinical oncology/radiotherapy and radiobiological research. The authors jointly arrived at the conclusions and recommendations presented here.

Microdistribution of targeted, fluorescently labeled anti-carcinoembryonic antigen antibody in metastatic colorectal cancer: implications for radioimmunotherapy.

PURPOSE: Most radioimmunotherapy studies on radiolabeled antibody distribution are based on autoradiographic and radioluminographic data, which provide a lack of detailed information due to low resolution. We used fluorescently labeled anti-carcinoembryonic antigen (CEA) antibody (A5B7) to investigate quantitatively the kinetics and microdistribution of antibody in a clinically relevant orthotopic colorectal cancer model (LS174T) using high-resolution digital microscopy. EXPERIMENTAL DESIGN: Nude mice bearing LS174T liver orthotopic tumors received a single i.v. injection of fluorescently labeled A5B7 and were sacrificed at 10 minutes, 1 hour, or 24 hours postinjection. Before sacrifice, mice were injected with the perfusion marker Hoechst 33342. An anti-CD31 antibody was used to detect blood vessel distribution. Cryostat sections were processed with immunofluorescence procedures and analyzed with fluorescence microscopy and image analysis techniques. The fluorescence images were related to morphologic images of the same or adjacent tumor sections. RESULTS: Fluorescently labeled antibody showed rapid, selective uptake into tumor deposits, with a strong negative correlation with tumor size at 10 minutes and 1 hour (P < or = 0.01). By 24 hours, the correlation was no longer significant. The study showed movement of antibody across the tumor with time and a tendency to localize more uniformly by later time points (24 hours). The rate of antibody motility was similar in small and large tumor metastases, but small deposits showed more rapid antibody localization. Intratumoral vessels were positively related to tumor size (P < or = 0.001). CONCLUSION: The obtained data suggest that radioimmunotherapy can be highly efficient in an adjuvant or minimal residual disease setting.

Epidermal growth factor receptor expression in pretreatment biopsies from head and neck squamous cell carcinoma as a predictive factor for a benefit from accelerated radiation therapy in a randomized controlled trial.

PURPOSE: Accelerated repopulation is a main reason for locoregional failure after fractionated radiotherapy for head and neck squamous cell carcinoma (HNSCC). Epidermal growth factor receptor (EGFR) is a key controller of cellular proliferation in HNSCC, which stimulated the current study to look for a direct link between EGFR status and a possible clinical advantage of accelerated radiotherapy. PATIENTS AND METHODS: Immunohistochemical staining for EGFR was performed in 304 patients with available pretreatment tumor biopsy material among 918 patients randomized to receive continuous hyperfractionated accelerated radiotherapy versus conventionally fractionated radiotherapy. The EGFR index was estimated as the proportion of tumor cells with EGFR membrane staining. RESULTS: Significant benefit in locoregional tumor control from continuous hyperfractionated accelerated radiotherapy was seen in patients with HNSCC with high EGFR expression (2P = .010) but not in those with low EGFR expression (2P = .85). EGFR status had no significant effect on survival or rate of distant metastases. The EGFR index was significantly associated with histologic grade and microvessel density. There was moderate support for an association between EGFR status and subsite within the head and neck region but no significant association with Ki-67 index, Ki-67 pattern, p53 index, p53 intensity, bcl-2 expression, or cyclin D1 index. CONCLUSION: This study indicates a key role for the EGFR receptor in determining the proliferative cellular response to fractionated radiotherapy in HNSCC. It also shows that we can select the dose-fractionation regime that has the greatest chance of benefiting the patient. These results also encourage further development of EGFR targeting combined with fractionated radiotherapy in HNSCC.

Radiation-induced genomic instability in repair deficient mutants of Chinese hamster cells.

PURPOSE: To determine the role of single (SSB) and double strand break (DSB) repair in the induction and propagation of radiation-induced instability. MATERIALS AND METHODS: Two defined hamster cell lines with known DNA repair deficiencies in DSB repair (XR-C1) and base excision repair (EM-C11) and the parental wild-type line (CHO-9) were used. The rate of micronucleus formation, apoptosis and survival were measured at 0, 7 and 14 days after X-ray radiation. RESULTS: An enhanced rate of production of damaged cells was observed in wild type and the repair deficient mutants after irradiation. This was cell type, dose and time-dependent. All cells demonstrated delayed death up to day 14 after irradiation along with an elevated apoptosis frequency. The yield of micronuclei was not significantly increased in the wild-type cells, but was in the mutant cells, over the dose and time range studied. For all three endpoints the increase in damage was most pronounced in the SSB deficient cell line. CONCLUSIONS: SSB and/or oxidized base damage play a major role, rather than DSB, in radiation induced instability.

Second malignancies following breast cancer treatment: a case-control study based on the Peridose methodology. Allegro project (task 5.4).

AIMS AND BACKGROUND: To calculate peripheral radiation dose to the second primary site in patients who have developed a second malignancy after breast cancer radiotherapy (index cases) and to compare it with dose in the analogous anatomical site in radiotherapy-treated breast cancer patients who did not experience a second malignancy (controls). To evaluate the feasibility of Peridose-software peripheral dose calculation in retrospective case-control studies. MATERIAL AND STUDY DESIGN: A case-control study on 12,630 patients who underwent adjuvant breast radiotherapy was performed. Minimum 5-year follow-up was required. Each index case was matched with 5 controls by 1) year of birth, 2) year of radiotherapy and 3) follow-up duration. Peridose-software was used to calculate peripheral dose. RESULTS: 195 second cancers were registered (19% [corrected] of all patients treated with adjuvant irradiation). Several methodological limitations of the Peridose calculation were encountered including impossibility to calculate the peripheral dose in the patients treated with intraoperative or external electron beam radiotherapy, in case of second tumors located at <15 cm from the radiotherapy field etc. Moreover, Peridose requires full radiotherapy data and the distance between radiotherapy field and second primary site. Due to these intrinsic limitations, only 6 index cases were eligible for dose calculation. Calculated doses at the second cancer site in index cases and in an analogous site in controls ranged between 7.5 and 145 cGy. The mean index-control dose difference was -3.15 cGy (range, -15.8 cGy and +2.7 cGy). CONCLUSIONS: The calculated peripheral doses were low and the index-control differences were small. However, the small number of eligible patients precludes a reliable analysis of a potential dose-response relationship. Large patient series followed for a long period and further improvement in the methodology of the peripheral dose calculation are necessary in order to overcome the methodological challenges of the study.

The risks to healthy tissues from the use of existing and emerging techniques for radiation therapy.

As radical radiotherapy treatments become more effective, more and more cancer patients are becoming cured of their disease and surviving for decades. Damage to exposed healthy tissues that becomes manifest in the medium-to-long-term is becoming a more significant factor in the choice of individual treatment plans and treatment modality. However, currently there are no reliable objective methods for predicting in an individual patient the occurrence of normal tissue complications, or second cancers caused by radiation. This is especially needed as new competing techniques and modalities become available, such as IMRT, protons, carbon ions, etc., all advancing the ability to focus the radiation dose on the target while sparing normal tissue. ALLEGRO is a Euratom-funded project that is currently investigating the current state of knowledge, and attempting to define the priority research areas. Preliminary considerations of the problems to be solved and research priorities are presented.

MLL gene alterations in radiation-associated acute myeloid leukemia.

AIM: Although acute myelogenous leukemia (AML) arising after radiation exposure is considered to be secondary, little is known about the molecular mechanisms by which the radiation induces the leukemogenic phenotype. The aim of the study was to analyze whether the MLL translocations are as frequent in radiation-associated AML as in spontaneous AML cases. METHODS: Sixty one AML samples obtained at diagnosis were analyzed for the presence of MLL abnormalities using fluorescent in situ hybridization and/or reverse transcription polymerase chain reaction. Of these patients, 27 had experienced radiation exposure due to the Chernobyl accident, 32 were non-irradiated (spontaneous AML), and 2 developed therapy-related AML after chemotherapy with topoisomerase II inhibitors. RESULTS: MLL gene translocations were detected in both groups of spontaneous and therapy-related AML (1/32 and 1/2 cases respectively). The sole MLL rearrangement found in the group of radiation-associated AML patients was a duplication of the gene. CONCLUSION: Our data preclude the involvement of MLL gene translocations in radiation-induced leukemogenesis, but support the assumption that loss and gain of chromosomal material could be crucial in the leukemogenesis of AML patients with the history of radiation exposure due to the Chernobyl accident.

The relationship of thyroid cancer with radiation exposure from nuclear weapon testing in the Marshall Islands.

The US nuclear weapons testing program in the Pacific conducted between 1946 and 1958 resulted in radiation exposure in the Marshall Islands. The potentially widespread radiation exposure from radio-iodines of fallout has raised concerns about the risk of thyroid cancer in the Marshallese population. The most serious exposures and its health hazards resulted from the hydrogen-thermonuclear bomb test, the Castle BRAVO, on March 1, 1954. Between 1993 and 1997, we screened 3,709 Marshallese for thyroid disease who were born before the BRAVO test. It was 60% of the entire population at risk and who were still alive at the time of our examinations. We diagnosed 30 thyroid cancers and found 27 other study participants who had been operated for thyroid cancer before our screening in this group. Fifty-seven Marshallese born before 1954 (1.5%) had thyroid cancer or had been operated for thyroid cancer. Nearly all (92%) of these cancers were papillary carcinoma. We derived estimates of individual thyroid dose proxy from the BRAVO test in 1954 on the basis of published age-specific doses estimated on Utirik atoll and 137Cs deposition levels on the atolls where the participants came from. There was suggestive evidence that the prevalence of thyroid cancer increased with category of estimated dose to the thyroid.