Three-dimensional dose distribution of tangential breast treatment: a national dosimetry intercomparison.

From August 1990 to February 1991, a dosimetry intercomparison of breast treatment was performed at all 21 radiotherapy centres in The Netherlands. The absorbed dose was measured in three planes in a breast phantom during tangential breast irradiation, according to a prescribed technique. The beam energy could be chosen by the radiotherapy centre as normally applied for this type of "patient", and varied between 60Co and 8 MV X rays. The dose measured by the visiting team in 22 points inside the phantom was compared with the dose calculated by the institution using their local treatment planning system. In the institutions the mean ratio (the mean value of the ratios of the absolute calculated dose and the measured absolute dose in the 22 points) varied between 0.92 and 1.08 with an overall mean ratio of 1.04. There was no significant difference in this ratio between the three planes in a particular institution. In the isocentre the mean ratio of calculated and measured dose was 1.021 with a SD of 0.028, i.e. the algorithms in the six different commercial treatment planning systems calculate the dose generally somewhat too high. In order to explain the results, a measurement of the output under reference conditions was performed at each treatment unit. The mean ratio of the dose stated by the institution and the dose measured by the visiting team was 1.011 with a SD of 0.015 with a maximum deviation of 0.040. This small deviation explains therefore only part of the variation in the ratio of calculated and measured dose for tangential breast irradiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Quality assurance of the EORTC trial 22881/10882: "assessment of the role of the booster dose in breast conserving therapy": the Dummy Run. EORTC Radiotherapy Cooperative Group.

The EORTC trial 22881/10882 is a randomised trial with the aim to assess the role of the boost dose in breast conserving therapy in stage I and II breast cancer. In order to detect potential protocol deviations concerning irradiation technique and in the dose specification procedure of participating institutions before actual patient accrual, a Dummy Run was performed. Three transverse sections of a patient were sent to 16 participating institutions with a request to make a three-plane treatment plan according to the protocol prescriptions. A treatment chart and beam data were also requested for recalculation of the dose. Additional information was asked in a questionnaire. On evaluation, the techniques differed considerably with respect to photon beam energy, varying between 60Co gamma-rays and 8 MV X-rays, and the use of wedge filters. Two institutions did not apply wedges, whereas wedge angles in the other institutions varied between 6 degrees and 45 degrees. Twelve institutions used collimator rotation and/or a table wedge to diminish the amount of irradiated lung volume. The dose was specified in a point according to the protocol prescription in 11 institutions and to the 90, 95 or 100% isodose curve in four. Twelve institutions applied lung density corrections during treatment planning, while nine reported problems with their planning system in off-axis dose distribution calculation and/or the simulation of collimator rotation. Recalculation of the dose at the isocentre showed agreement within 2% compared with the stated dose. The dose reported in the tumour excision area varied between 93 and 100%.(ABSTRACT TRUNCATED AT 250 WORDS)

Film dosimetry for radiotherapy treatment planning verification of a 6 MV tangential breast irradiation.

Film dosimetry has been applied to measure relative dose distributions in an anthropomorphic polystyrene breast phantom having cork lungs, simulating a radiation therapy treatment with 6 MV opposing tangential beams. Measured relative dose distributions showed good reproducibility (about 1.5%, 1 SD) and good agreement (< 2%) with calculations performed with a three-dimensional treatment planning system. These results demonstrate that film dosimetry is a useful tool for treatment planning verification.

Should inhomogeneity corrections be applied during treatment planning of tangential breast irradiation?

Due to the inclusion of lung tissue in the treatment volume, some parts of the breast will get a higher dose during tangential breast irradiation because of the lower lung density. Data on the accuracy of dose calculation algorithms, investigated by phantom measurements, determinations of the geometry and density of the actual lung in the patient and the results of in vivo dose measurements, are presented. From this information it can be concluded that a lung correction varying between about 3% and 7% is needed but its magnitude is slightly overpredicted in a number of commercial treatment planning systems. Because this increase in dose is already in a high dose region, it is recommended that inhomogeneity corrections should be applied during tangential breast irradiation.