A dosimetric comparison of double-arc volumetric arc therapy, step-shoot intensity modulated radiotherapy and 3D-CRT for left-sided breast cancer radiotherapy after breast-conserving surgery.

OBJECTIVE: To compare the dosimetric and efficiency differences for left-sided breast cancer radiotherapy after breast-conserving surgery among three different planning techniques: double-arc volumetric-modulate arc therapy (VMAT), step-shoot intensity-modulated radiotherapy (sIMRT) and three-dimensional conformal radiation therapy (3D-CRT). MATERIALS AND METHODS: A total of 17 female patients with left-sided breast cancer who underwent breast-conserving surgery were selected; the prescription doses were 50 Gy in 25 fractions. For every patient VMAT, sIMRT and 3D-CRT plans were generated within the Monaco treatment planning system for an Axesse™ accelerator equipped with the Agility MLC. The Conformity Index (CI), the Homogeneity Index (HI), the dose volume histogram (DVH) parameters for the organs at risk and the delivery efficiency were evaluated. RESULTS: The VMAT plans showed on average higher CI of PTV (0.77 ± 0.03) than both sIMRT (0.68 ± 0.02) and 3D-CRT (0.55 ± 0.04) plans (P< 0.05). The HI values in the VMAT, sIMRT and 3D-CRT plans were 0.10 ± 0.01 0.09 ± 0.01 and 0.13 ± 0.01 (P> 0.05), respectively, and the differences among the three techniques were not statistically significant. In the ipsilateral lung, the VMAT plans showed lower Dmean, V30, V20, and V10 than the sIMRT and 3D-CRT (P< 0.05); however, there was no significant difference in V5. In the heart, the VMAT plans had lower V30 and V20 than the sIMRT and 3D-CRT plans (P< 0.05), but there was no significant difference in the Dmean and V5. In the contralateral lung, the VMAT plans showed higher Dmean and V5 than sIMRT and 3D-CRT (P< 0.05). In the contralateral breast, the VMAT plans had a higher V5 than the sIMRT and 3D-CRT plans (P< 0.05). The VMAT plans had higher MU's than sIMRT and 3D-CRT, while the treatment times were lower than that of sIMRT. CONCLUSION: For left-sided breast cancer radiotherapy after breast-conserving surgery, the VMAT plans had a better CI than the sIMRT and 3D-CRT plans. The VMAT and the sIMRT plans had better HI than the 3D-CRT plans, but no significant difference was observed between VMAT and sIMRT.

Single arc volumetric-modulated arc therapy is sufficient for nasopharyngeal carcinoma: a dosimetric comparison with dual arc VMAT and dynamic MLC and step-and-shoot intensity-modulated radiotherapy.

BACKGROUND: The performance of single arc VMAT (VMAT1) for nasopharyngeal carcinoma (NPC) on the Axesse linac has not been well described in previous studies. The purpose of this study is to assess the feasibility of VMAT1 for NPC by comparing the dosimetry, delivery efficiency, and accuracy with dual arc VMAT (VMAT2), dynamic MLC intensity-modulated radiotherapy (dIMRT), and step-and-shoot intensity-modulated radiotherapy (ssIMRT). METHODS: Twenty consecutive patients with non-metastatic NPC were selected to be planned with VMAT1, VMAT2, dIMRT and ssIMRT using Monaco 3.2 TPS on the Axesse™ linear accelerator. Three planning target volumes (PTVs), contoured as high risk, moderate risk and low risk regions, were set to receive median absorbed-dose (D50%) of 72.6 Gy, 63.6 Gy and 54 Gy, respectively. The Homogeneity Index (HI), Conformity Index (CI), Dose Volume Histograms (DVHs), delivery efficiency and accuracy were all evaluated. RESULTS: Mean HI of PTV72.6 is better with VMAT1(0.07) and VMAT2(0.07) than dIMRT(0.09) and ssIMRT(0.09). Mean HI of PTV63.6 is better with VMAT1(0.21) and VMAT2(0.21) than dIMRT and ssIMRT. Mean CI of PTV72.6 is also better with VMAT1(0.57) and VMAT2(0.57) than dIMRT(0.49) and ssIMRT(0.5). Mean CI of PTV63.6 is better with VMAT1(0.76) and VMAT2(0.76) than dIMRT(0.73) and ssIMRT(0.73). VMAT had significantly improved homogeneity and conformity compared with IMRT. There was no significant difference between VMAT1 and VMAT2 in PTV coverage. Dose to normal tissues was acceptable for all four plan groups. VMAT1 and VMAT2 showed no significant difference in normal tissue sparring, whereas the mean dose of the parotid gland of dIMRT was significantly reduced compared to VMAT1 and VMAT2. The mean delivery time for VMAT1, VMAT2, dIMRT and ssIMRT was 2.7 min, 3.9 min, 5.7 min and 14.1 min, respectively. VMAT1 reduced the average delivery time by 29.8%, 51.1% and 80.8% compared with VMAT2, dIMRT and ssIMRT, respectively. VMAT and IMRT could all be delivered accurately based on our quality assurance standards. CONCLUSIONS: In the treatment of NPC using the Axesse™ linear accelerator, single arc VMAT has shown superiority to double arc VMAT, dIMRT and ssIMRT in delivery efficiency, without compromise to the PTV coverage. However, there is still room for improvement in terms of OAR sparing.