Considerations on treatment efficiency of different conformal radiation therapy techniques for prostate cancer

To evaluate the treatment efficiency of different conformal radiation therapy techniques in prostate cancer.

Three major classes of intensity-modulated radiation therapy (IMRT) delivery as well as a conformal rotation technique have been evaluated: sequential tomotherapy, dynamic multileaf collimation (DMLC) with conventional MLC, DMLC with miniMLC and dynamic field shaping arc. Treatment planning for the IMRT techniques has been performed with inverse planning. Forward planning was used for the dynamic arc technique. The four techniques have been compared to treat two different prostate cases with a conservative target dose of 70 Gy: a convex shaped target volume and one containing concavities formed by the bladder and rectum. Cumulative dose volume histograms, tumor control probability and normal tissue complication probability, conformity index and dose heterogeneity, and finally efficiency of treatment delivery have been evaluated.

For the convex shaped target, all treatment modalities met the desired treatment goals, although the conventional MLC delivered more dose to the bladder. Compared to the dynamic arc modality, both tomotherapy and the conventional MLC technique needed a tenfold higher number of monitor units per target dose, and the miniMLC a twofold higher number. The same trend has been observed for the concave target, yet the dynamic arc did not meet the desired dose reduction for the rectum. The miniMLC configuration represented the best compromise for both targets with respect to treatment goals and delivery efficiency. Sequential tomotherapy performed adequately with respect to conformity at the cost of efficiency.

Together with conformity and delivery efficiency the shape of the target should be considered as an important parameter in the selection of the treatment modality.