Quantifying inter- and intra-fraction variations of breast cancer radiotherapy with skin dose measurements

Aim. The aim of the current study was to compare between the deep inspiration breath-hold (DIBH) technique and free-breathing (FB) method in the treatment delivery uncertainty of breast cancer radiotherapy using skin dose measurements.Methods. In a prospective manner, eighty patients were randomly selected for skin dose measurements, and they were assigned to two groups. DIBH (40 patients) and FB (40 patients). The systematic inter-fraction dose variation was quantified using the mean percentage error (MPE) between the average measured total dose per session in three consecutive sessions and the corresponding calculated point dose from the treatment planning system. The random inter-fraction dose variation was quantified using the standard deviation (SD) of the dose delivered by the medial or lateral tangential fields, or the total session dose in the three sessions (SD_MT, SD_LT, or SD_total, respectively). While the random intra-fraction dose variation was quantified using the SD of the dose difference between the medial and lateral tangential fields in three consecutive sessions (SD_MT-LT).Results. There was no statistically significant difference in MPE between the DIBH and FB groups (p = 0.583). Moreover, the mean SD_totaland SD_MTof the DIBH group were significantly lower than that of the FB group (2.75 ± 2.33 cGy versus 4.45 cGy ± 4.33, p = 0.048) and (1.94 ± 1.63 cGy versus 3.76 ± 3.42 cGy, p = 0.007), respectively. However, there was no significant difference in the mean SD_LTand SD_MT-LTbetween the two groups (p > 0.05).Conclusion. In addition to the advantage of reducing the cardiopulmonary radiation doses in left breast cancer, the DIBH technique could reduce the treatment delivery uncertainty compared to the FB method due to the significant reduction in the random inter-fraction dose variations.