Partial–breast irradiation: towards a replacement for whole–breast irradiation?

Relative biological effectiveness of photon energies used in brachytherapy and intraoperative radiotherapy techniques for two breast cancer cell lines

BACKGROUND

Partial breast irradiation (IORT or brachytherapy) differ from external radiation of whole breast in terms of irradiated volumes, fractionation, radiation energy and dose rate; all factors influencing the treatment outcome in a complex manner. Theoretically obtained RBE values comparing effects of radiation used in IORT and external therapy are published, but experimental studies are required to confirm these data. The aim of this study is to establish such RBE values for two breast cancer cell lines.

MATERIALS AND METHODS

Colony formation of breast cancer cell lines (MCF-7 and T-47D) were studied after photon irradiation with qualities and dose rates used in IORT, brachytherapy and external radiation. RBE values from survival data were used to compare effects.

RESULTS

Increasing the photon energy (dose rate 0.2 Gy/min) from 50 kV (Intrabeam) to 380 keV (¹⁹²Ir source) and 6 MV (linear accelerator) yielded an increase in the cell survival, whereas increasing the dose rate to 6 Gy/min had minor effect. Average RBE values for 50 kV with 6 MV as reference radiation varied from about 1.4 (for doses < 5 Gy) to > 1.9 (for doses < 0.02 Gy) for MCF-7 cells and from about 1.4 to > 3.1 for T-47D cells for the same dose levels. Corresponding RBE values for 380 keV radiation were about 1.4 for MCF-7 cells and 1.3-2.3 for T-47D cells.

CONCLUSION

RBE data for breast cancer cells exposed to radiation used in IORT, brachytherapy or external radiation differ among the cell lines tested. The values are in agreement with published theoretical and experimental work.

Lung Dose-Volume Parameters and the Risk of Pneumonitis for Patients Treated With Accelerated Partial-Breast Irradiation Using Three-Dimensional Conformal Radiotherapy

Purpose

There are no data on how complication rates after accelerated partial-breast irradiation delivered by three-dimensional conformal radiotherapy are affected by treatment technique. We therefore examined the risk of pneumonitis in relation to lung dose-volume parameters.

Patients and Methods

Our prospective dose-escalation trial enrolled 198 treated patients from 2003 to 2007. Patients received 32 or 36 Gy in 4-Gy fractions, given twice daily: 29 (14%) were treated with pure photons; 149 (77%) with mixed photons and electrons; and 20 (10%) with protons.

Results

There were four cases of pneumonitis at 4, 4, 7, and 9 months after treatment. All were in the 36-Gy cohort and were treated with pure photons. The risk of pneumonitis for the two cohorts combined was: 17% (four of 24) for an ipsilateral lung volume (ILV) receiving 20 Gy or higher (ILV, 20 Gy) of 3% or higher (P = .0002 for comparison to ILV 20 Gy < 3%, Fisher's exact test); 20% (four of 20) for an ILV 10 Gy of 10% or higher (P = .0001); and 15% (four of 26) for an ILV 5 Gy of 20% or higher (P = .0002).

Conclusion

The risk of pneumonitis appeared related to the ILV treated. This volume can be reduced by using mixed photons and electron when possible. We recommend that the ILV 20 Gy should be lower than 3%, the ILV 10 Gy lower than 10%, and the ILV 5 Gy lower than 20% when purely coplanar techniques are used.

Use of radiation treatment units in breast cancer. Changes in the last 15 years

INTRODUCTION

Advances in diagnosis and treatment in oncology combined with technical advances in radiotherapy have resulted in qualitative and quantitative changes in the use of radiation to treat breast cancer.

OBJECTIVE

The objective was to analyse changes in radiation indications from 1990 to the present time and their consequences in the use of treatments units.

METHODS AND MATERIAL

From January 1990 to December 2005, 4545 radiation treatments for breast cancer were performed, classified as radical after conservative surgery, radical after mastectomy or palliative. Data are presented as relative frequencies and as 3-year period groups.

RESULTS

An increase in the proportion of treatments for breast cancer and in treatment unit use distribution is observed. Radical treatments have increased over time, ranging from 55% in the first 3-year period group to 82% in the last one. Unit treatment distribution analysis is similar, but with a less important increase, rising from 85% to 95%. A rise in conservative treatment is also observed, from 43% to 75%.

CONCLUSIONS

An increase in breast cancer incidence is observed and there was also an increase in irradiation after conservative treatment. On the contrary, probably due to the rise in the use of systemic treatments, a decrease in postmastectomy irradiation and palliative treatments is shown.