8% at 2-mm below the skin surface. Discussion Bolus thickness required to enhance surface dose is optimized according to surface and build-up region dosimetry. In the present study, a 1-cm bolus was used to increase skin doses. This thickness was chosen because 6-MV photon energy with a 1.5-cm maximal depth was used for tangential

fields. The skin dose contributions of 1-cm bolus material during whole or a part of treatment duration were calculated in this study. The results showed a trend of increasing minimum skin dose when the days of bolus application were increased. The minimum skin dose increments were expected to be linear among the Venetoclax in vitro bolus durations. However, the minimum skin dose increments between 20 and 25 (1.6% ± 1.0%), and 15 and 20 (4.0% ± 1.0%) days of bolus applications were significantly lower than the dose increments between 0 and 5 (5.2% ± 0.6%), 5 and 10 (5.1% ± 0.8%), and 10 and 15 (4.9% ± 0.8%) days of bolus applications while the maximum skin dose increments were significantly higher. TPS dose calculation algorithm and treatment related factors such as delivery technique, field size and angle of beam incidence are supposed to be associated with MLN0128 these non-linear dose increments. Therefore,

our results need to be clarified in further dosimetric studies using different TPS, techniques, beam energies, and bolus thicknesses. Determining the necessary frequency of bolus treatments is critically important in post-mastectomy radiotherapy, Farnesyltransferase since it influences the irradiated volume as well as the skin doses. Although the literature contains several recommendations for radiotherapy planning techniques, there are few recommendations regarding

bolus use [4, 5, 9–11]. The optimal duration and the optimal thickness of the bolus material still remain uncertain and change centre to centre [7, 12]. Wide regional variations in the use of boluses were reported by Vu et al. in an international survey of radiation oncologists and their opinions on the indications for boluses in post-mastectomy radiotherapy [12]. Determining the difference between the calculated and measured surface dose is useful when evaluating and comparing patient plans and also when optimizing the use of boluses. Many factors affect the magnitude of the surface dose, such as the delivery technique, field size, angle of beam incidence, air gap and the use of bolus material and beam modifiers [13–15]. Calculation of skin doses is difficult in most TPSs due to their inability to account for all the factors that contribute to the surface dose. However, the Monte Carlo TPSs and, to a lesser extent, the modern true 3D algorithms are able to calculate skin doses [16–18]. Doses calculated with different TPSs have been reported to underestimate and overestimate measured skin doses [15, 19–23]. Measured skin doses also may differ according to the dosimetry used [13].