The photon dose calculation algorithm used in breast radiotherapy has significant impact on the parameters of radiobiological models

Abstract

The comparison of the pencil beam dose calculation algorithm with modified Batho heterogeneity correction (PBC‐MB) and the analytical anisotropic algorithm (AAA) and the mutual comparison of advanced dose calculation algorithms used in breast radiotherapy have focused on the differences between the physical dose distributions. Studies on the radiobiological impact of the algorithm (both on the tumor control and the moderate breast fibrosis prediction) are lacking. We, therefore, investigated the radiobiological impact of the dose calculation algorithm in whole breast radiotherapy. The clinical dose distributions of 30 breast cancer patients, calculated with PBC‐MB, were recalculated with fixed monitor units using more advanced algorithms: AAA and Acuros XB. For the latter, both dose reporting modes were used (i.e., dose‐to‐medium and dose‐to‐water). Next, the tumor control probability (TCP) and the normal tissue complication probability (NTCP) of each dose distribution were calculated with the Poisson model and with the relative seriality model, respectively. The endpoint for the NTCP calculation was moderate breast fibrosis five years post treatment. The differences were checked for significance with the paired t‐test. The more advanced algorithms predicted a significantly lower TCP and NTCP of moderate breast fibrosis then found during the corresponding clinical follow‐up study based on PBC calculations. The differences varied between 1% and 2.1% for the TCP and between 2.9% and 5.5% for the NTCP of moderate breast fibrosis. The significant differences were eliminated by determination of algorithm‐specific model parameters using least square fitting. Application of the new parameters on a second group of 30 breast cancer patients proved their appropriateness. In this study, we assessed the impact of the dose calculation algorithms used in whole breast radiotherapy on the parameters of the radiobiological models. The radiobiological impact was eliminated by determination of algorithm specific model parameters.PACS numbers: 87.55.dh, 87.55.dk

Radiation burden from modern radiation therapy techniques including proton therapy for breast cancer treatment - clinical implications

“…The cohort included patients with both WBO and BSC irradiations, which ensured a representative cross-section of patients from current clinical practice. The results of Paper I predicted increased heterogeneity in the target volume and higher doses to the ipsilateral lung, in agreement with results of other parallel studies comparing the performance of AAA with PBC (Basran et al 2010, Yoo et al 2012, Bufacchi et al 2013, Petillion et al 2014. It is interesting to note that although small, the differences between predictions of the two algorithms were statistically significant in many cases.…”

“…The range of individual values was rather broad, 4-22% in BSC and 4-44% in WBO. These findings reflect the situation of the normal tissue complication probabilities for the lung where AAA required significantly different model parameters than PBC (Bufacchi et al 2013, Hedin and Back 2013, Petillion et al 2014. Indeed, our findings indicate that the heart could be 13-22% more sensitive that thought based on PBC findings.…”

“…It should be noted that many previous comparative studies used a limited number of patients with mainly tangential irradiation of the breast, e.g., a single patient in Knoos et al (2006) or ten patients in Basran et al (2010). Only in recent years the number of patients was increased in several parallel studies, e.g., twenty in Yoo et al (2012), Bufac-chi et al (2013) and Hedin and Back (2013) and 30 in Petillion et al (2014). To the best of the knowledge, Paper I used the largest patient cohort this far (40 patients) to study the differences between AAA and PBC predictions.…”

“…More recent algorithms like AAA predict better and more realistic dose distributions, especially in heterogeneous media (Bragg andConway 2006, Van Esch et al 2006) and therefore are recommended for breast radiotherapy. However, it has been shown that changing the algorithm for dose calculations from PBC to AAA influences the evaluation of parameters for the risk of complications in normal tissues (Bufacchi et al 2013, Hedin and Back 2013, Petillion et al 2014 and in consequence influences also the dose thresholds that are associated with certain levels of complications. Knowledge on the differences in predictions between algorithms could be obtained in studies comparing their performance in patients.…”

The accuracy of the Acuros XB algorithm in external beam radiotherapy – a comprehensive review

“…Of two other studies related to breast radiotherapy in the first one by Lonski et al 53 the unknown version of the AXB algorithm was shown to be superior in out-of-field dose calculation, when comparing to measurements, the PBC algorithm and the AAA. In the other study by Petillion et al 54 the choice of dose calculation algorithm was shown to have an impact on the parameters of radiobiological models. They suggested that the most accurate solution would be to use the AXB algorithm in Dm,m dose report mode.…”