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.

The Hippocampus Sparing Volume Modulated Arc Therapy does not Influence Plan Quality on Locally Advanced Nasopharyngeal Carcinoma Patients.

Irradiation on hippocampus would lead to neuro-cognitive dysfunction in locally advanced nasopharyneal carcinoma (LA-NPC) patients accepting radiotherapy. Our study here aimed to investigate if undergoing hippocampus sparing (HS) volume modulated arc therapy (VMAT) would influence the plan quality in LA NPC patients. We designed three kinds of radiotherapeutic plans for 11 LA NPC patients: conventional VMAT (C-VMAT), HS-VMAT and HS intensity modulated radiation therapy with dynamic multileaf collimator (HS-dMLC). And the dose distribution on targets and surrounding organs at risk (OAR) were carefully evaluated. We found out that the expected doses on hippocampus were significantly lowered in HS-VMAT (899 ± 378 cGy) and HS-dMLC (896 ± 321 cGy) as compared to C-VMAT (1518 ± 337 cGy, p < 0.05), but meaningless difference was presented on plan quality of targets (p > 0.05). Moreover, lower radiation doses on brain stem were observed in HS-VMAT plan in comparison with C-VMAT plan (p < 0.05). However, there were no statistically meaningful diversities in the doses received by other OARs among all plans. Here we concluded that HS-VMAT presented promising advantages on protecting hipppcampus and brain stem as compared to C-VMAT and HS-dMLC, but enthusiastically had no effects on plan quality in LA-NPC patients.

Collimator rotation in volumetric modulated arc therapy for craniospinal irradiation and the dose distribution in the beam junction region.

PURPOSE: The purpose of this study was to investigate the role of beam collimator rotation in Volumetric Modulated Arc Therapy (VMAT) for craniospinal irradiation (CSI), and the impact on dose distribution in the beam junctions. METHODS: Six adult patients were selected for the study. Six VMAT plans with different collimator angles were generated for each patient. The patients were treated in supine position with two beam isocenters. The plans were evaluated by analysis of Dose-Volume Histogram (DVHs) data for planning target volume (PTV) and organs at risk (OAR), and conformity index (CI) and homogeneity index (HI) for the target. Dose distributions in the beam junctions were examined carefully and experimentally validated in phantom, with measurement using an ion chamber array and film. RESULTS: The mean values of HI and CI for the plans with different beam collimator angles were not significantly different. The numbers of segments, monitor units (MUs) and the delivery time of the plans with 45° beam collimator were obviously higher than those in plans with other beam collimator angles. When collimator angle for both sets of beams were set at 0°, there was a 1 mm low dose gap measured in the junction region. CONCLUSIONS: By setting the collimator angle to 45°, only two isocenters were needed for the treatment of a target with the length up to 90 cm. The HI and CI of the plans were almost the same, regardless if the collimator angles were at 0°. The collimator angles for at least one set of beams should be off 0° in order to avoid a dose gap in the beam junction region.