Background and Purpose: Loco-regional radiotherapy after breast conserving surgery significantly reduces the risk of recurrence but may induce complications in the lungs. The complications are related to the lung volume irradiated and the lung dose delivered. The purpose of this study was to evaluate three tangential breast irradiation techniques i.e. conventional technique, gantry tilting technique and half-beam block technique in terms of the percentage of irradiated lung volume and high dose lung volume for patients of different sizes.

Materials and Method: Treatment planning of the three tangential breast irradiation techniques was performed using the CT scans of 20 patients with early-stage breast cancer after lumpectomy.

Results: When compared with conventional technique, both half beam block technique and gantry tilting technique irradiated a significantly smaller percentage of lung volume and delivered a smaller percentage of high dose (above 30 Gy) volume in the lung. Patients with large breasts had a significantly higher percentage of lung volume irradiated to above 30Gy than those patients with small and medium breasts. The combined effect of tangential separation and technique only produced significant effect on the percentage of total lung volume irradiated but not on the high dose volume.

Conclusions: Gantry tilting and half-beam block techniques can reduce a significant amount of lung volume and high dose lung volume. Half-beam block technique is recommended for small and medium breast size while for large breast size, gantry tilting technique is preferred.

Ten patients with prostate cancer were each planned with 3 conventional and 3 conformal isocentric treatment techniques to compare the relative radiation doses to the bladder and rectal walls, and femoral head using dose volume histograms (DVH). The DVH were calculated for each organ and each technique, and the plans were ranked using the area under the curve method and also by the relative radiation dose given to specific normal tissue volumes.

The results show that for the planning target volume chosen, the 4 field non-coplanar technique delivers the least dose to the bladder, the 6 field coplanar technique delivers the least dose to the rectum and the 3 field oblique technique delivers the least dose to the femoral heads. The 4-field technique with no shielding contributes the most dose to the bladder and rectum and the 6 field coplanar technique contributes the most dose to the femoral heads.

No technique was shown to be optimal for all the organs at risk, but both the 6 field and 4 field non-coplanar field arrangements were shown to be superior techniques for minimising both the bladder and rectal dosage. The choice of technique will therefore depend on other factors such as the total prescribed dose, the ease of set-up and the ease of verification of isocentre reproducibility.