Update on clinical radiobiology

Radiation therapy is an important local cytotoxic modality for cancer treatment whose aim is to control the disease while minimising damage to normal tissue. The combination of different treatment modalities offers a more effective cure and reduction in normal tissue toxicity. However, the differences in genetic profiles can cause diverse treatment outcomes. Multidisciplinary research, where technologies and knowledge from different areas are integrated, is necessary to design the optimal regimen for individualised cancer treatment. This paper offers an overview of some new cancer treatment strategies; the impact of molecular imaging on radiation oncology; and a computer simulation model to optimise treatment planning based on patient information. It briefly discusses molecular targeted therapy, tumour microenvironment and bioreductive agents, and evidence for making individualised medicine a reality. Using DNA microarrays and proteomic technologies, information on defined molecular targets and genetic profiling for individual patients can be obtained and new algorithms for radiation oncology-related diagnosis, treatment response and prognosis can be developed.

High-dose-rate afterloading brachytherapy in carcinoma of the cervix: an experience of 1992 patients

PURPOSE

To report the results of radiation therapy in carcinoma of the cervix treated by external irradiation and high-dose-rate (HDR) intracavitary brachytherapy.

METHODS AND MATERIALS

This is a retrospective analysis of 2,063 patients with histologically proven carcinoma of the cervix treated by external irradiation and HDR intracavitary brachytherapy between March 1985-December 1991. The Kaplan-Meier method was used for survival and disease-free survival analysis. Late complications in the bowel and bladder were calculated actuarially.

RESULTS

There were 71 patients who did not complete the course of irradiation so only 1992 patients were retrospectively analyzed for survival. There were 2 patients (0.1%) in Stage IA, 211 (10.2%) Stage IB, 225 (10.9%) in Stage IIA, 902 (43. 7%) in Stage IIB, 14 (0.7%) in Stage IIIA, 675 (32.7%) in Stage IIIB, 16 (0.8%) in Stage IVA, and 16 (0.8%) in Stage IVB. The median follow-up time was 96 months. The actuarial 5-year disease-free survival rate was 79.5%, 70.0%, 59.4%, 46.1%, 32.3%, 7.8%, and 23.1% for Stage IB, IIA, IIB, IIIA, IIIB, IVA, and IVB respectively. The actuarial 5-year disease-free survival rate for Stage IB(1) and IB(2) squamous cell carcinoma was 88.7% and 67.0%. The actuarial 5-year overall survival rate was 86.3%, 81.1%, 73.0%, 50.3%, 47.8%, 7.8%, and 30.8% for Stage IB, IIA, IIB, IIIA, IIIB, IVA, and IVB respectively. Pattern of failure revealed 20.8% local recurrence, 18. 7% distant metastases, and 4% in both. The late complication rate Grade 3 and 4 (RTOG) for bowel and bladder combined was 7.0% with 1. 9% Grade 4.

CONCLUSION

HDR brachytherapy used in this series produced pelvic control and survival rates comparable to other LDR series.

The neoplastic transformation of SCID cells by radiation

Severe combined immunodeficiency (SCID) cells are hypersensitive to killing by ionizing radiation because of deregulation of DNA-dependent protein kinase (DNA-PK) and a concomitant deficiency in the repair of DNA double-strand breaks. The effect of this condition on the neoplastic transformation of SCID fibroblasts, designated SCID 3T1, has been investigated. The spontaneous transformation rate was approximately 2 x 10(-5) at early passages and increased up to approximately 7 x l0(-3) at later passages. The radiation survival curves of transformed cells had thresholds and therefore appeared to be qualitatively similar to the survival curves of C3H 10T(1/2) mouse fibroblast cells, but the initial slopes were steeper. In contrast, per unit dose, SCID cells were more sensitive to transformation than 10T(1/2) cells. Eight transformed clones were tested for tumorigenicity, and all produced fibrosarcomas in athymic nude mice. Properties associated with the tumor suppressor Trp53 (formerly known as p53) were examined in three of the clones. In these clones, although Trp53 protein was overexpressed, a lower expression of Cdkn1a (formerly known as p21, Cip1) protein was observed compared to parental cells. The expression of Trp53 and Cdkn1a and the G(1)-phase arrest (one set of data on G(1)-phase delay is included as an example) was not induced by ionizing radiation in these transformed clones; each clone carried a point mutation in Trp53. This suggests that the deficiency in the repair of DNA double-strand breaks increased the tumorigenicity and the genomic instability of transformed SCID cells.