Comparing “triangular”, “V” and conventional patterns of dose delivery in optimizing cell kill when applied to tumour types with low α/ß ratios

Abstract

The aim: To compare mean inactivation doses between the triangular and the V-shaped; the triangular and conventional; and V-shaped and conventional patterns of dose delivery on prostate tumour cells, with α/ß ratios of 1 Gy, 1.5 Gy and 3 Gy. Design and method: A total of 45 treatment plans created for prostate tumours, using conformal radiotherapy techniques, six treatment fields, and dose per fraction of 2 Gy were sequentially collected. The beam weightings and treatment field positions used in the creation of these treatment plans, as well as prostate tumour cell kinetic parameters from literature, were then used to perform computational simulations, using the Virtual Cell Radiobiology programme Version 2 to calculate tumour cell survival. The mean inactivation doses for each α/ß ratio and for each dose delivery pattern were calculated. Results: For the comparison between: (i) the triangular and conventional dose delivery patterns across the three α/ß ratios, the results showed a non- significant difference, with p=0.5436; (ii) for the triangular and V-shaped patterns of dose delivery across the three α/ß ratios, the results indicate that the triangular pattern is not statistically different from the V-shaped pattern, with p=0.5436; and (iii) for the V-shaped and conventional patterns of dose delivery, a non-significant difference with p=0.5436 was observed. Discussion: The observed non-significant differences in mean inactivation dose from the different dose delivery patterns is attributed to 1) treatment times that are shorter than the sub-lethal damage repair half times; (2) high dose rates used in conformal radiotherapy techniques; and (3) the small size of individual dose fields. Conclusions: The study demonstrated that the suggested triangular and V-shaped patterns of dose delivery do not result in different biological effect when implemented to 3-D conformal treatment techniques.