Comparison of hybrid volumetric modulated arc therapy (VMAT) technique and double arc VMAT technique in the treatment of prostate cancer

Dosimetric comparison of fixed field dynamic IMRT and VMAT techniques in simultaneous integrated boost radiotherapy of prostate cancer

High-risk prostate cancer can take advantage of the combination of hypofractionated radiotherapy and pelvic conventional fraction radiotherapy. The comparison between fixed field dynamic IMRT and VMAT techniques can provide suggestions for clinical treatment. We selected 10 high-risk prostate cancer patients who received radiotherapy at the cancer center of Sun Yat-sen University from January 2016 to December 2019. The targets contained in prostate, seminal vesicles and pelvic lymph nodes. With the same prescription and optimized parameters, 9F, single-arc (1ARC) and double-arc (2ARC) treatment plans were developed. The dose distribution of the targets, OAR, MU, treatment time and gamma pass ratios of dose verification was compared. The D2% (69.37 ± 0.89) Gy, D50% (66.92 ± 0.63) Gy, HI (0.09 ± 0.02), and CI (0.83 ± 0.05) of PTV1 in 9F were slightly better than those of 1ARC which were (71.13 ± 1.21) Gy, (68.50 ± 0.76) Gy, (0.12 ± 0.02), (0.74 ± 0.07), except D98%, the difference was significant (P < .05). All dosimetry indices of PTV1 in 9F and 2ARC were close and have no significant differences (P > .05). The V95% (99.45 ± 0.78)% of PTV2 in 9F was slightly better than that in 1ARC (99.35 ± 1.28)%. The difference was significant (P < .05). All dosimetry indices of PTV2 in 9F and 2ARC were close and the difference was not significant (P > .05). The Dmean of the bladder and the V67.5 Gy of rectum between all three plans were similar. The Dmean of left and right femoral in 1ARC and 2ARC were lower than that in 9F, and the difference was significant (P < .05). Other dosimetry indices of OARs in 9F were lower than those in 1ARC and 2ARC, and much lower than 1ARC. The difference was significant (P < .05). Mean monitor units in 1ARC and 2ARC were fewer by 70.0% and 67.2% in comparison with 9F. The treatment mean time in 1ARC and 2ARC was shorter by 81.7% and 61% in comparison with 9F. Verification pass ratios of γ (3%/3 mm) were 97.8% (9F), 98.9% (1ARC) and 99.4% (2ARC) respectively. The difference was significant (P < .05). Compared with IMRT, VMAT improved delivery efficiency noticeably. Two arcs provided comparable tumor dosimetry coverage, but performed worse in dose sparing for bladder, rectum and small bowel. The IMRT plan was preferable to VMAT in prostate cancer simultaneous integrated boost radiotherapy.

Hybrid Tomo-Helical and Tomo-Direct radiotherapy for localized prostate cancer

PURPOSE

The aim of the study is to present a new planning approach to provide better planning target volume (PTV) coverage and reduce bladder and rectum dose with hybrid Tomo-Helical (TH)/Tomo-Direct (TD) radiotherapy (RT) for localized prostate cancer (LPC).

METHODS

Twenty-five LPC patients were included in this retrospective study. TH plans, TD plans, and hybrid TH/TD plans were created. Lateral beams were used for the hybrid TD plan and the prescribed dose was 70 Gy in 28 fractions (hybrid plans were combined 45 Gy/ 18 fxs for TH and 25 Gy/10 fxs for TD). Doses of PTV (D2%, D98%, D50%, homogeneity index (HI), conformity index (CI), coverage) and organs at risk (OARs) (V50%, V35%, V25%, V5%, and V95%) were analyzed. The Wilcoxon signed-rank test was used to analyze the difference in dosimetric parameters. p-Value < 0.05 was considered statistically significant.

RESULTS

TH plans showed better CI, and target coverage (p < 0.01) than TD and hybrid plans in all patient plan evaluations. However, TD plans D2%, D98%, and D50% doses were better than TH and hybrid plans. The HI values were similar between the three plans. Significant reductions in bladder and rectum V50%, V35%, and V25% doses (p < 0.001) were observed with hybrid plans compared to TH and TD. Penile bulb V95% and bowel V5% doses were better in the hybrid plans. Left and right femoral head V5% doses were higher in the hybrid plan compared to others (p < 0.001).

CONCLUSION

Concurrently hybrid TH/TD RT plan can be a good option to reduce the doses of the rectum and bladder in the RT of LPC.

Hybrid volumetric modulated arc therapy for whole breast irradiation: a dosimetric comparison of different arc designs

PURPOSE

To find an optimal arc design for hybrid volumetric modulated arc therapy (H-VMAT), a combination of conventional 3DCRT and VMAT plans for left-sided whole breast radiation therapy.

METHODS AND MATERIALS

A total of 26 left-sided early-stage breast cancer patients were selected for this study. To find the superior plan, H-VMAT with three different arc designs including, two partial arcs (2A), four partial arcs (4A) and four tangential arcs (TA) were created for each study case by combining 3DCRT and VMAT with 75% 3DCRT/25% VMAT dose proportion of prescription dose.

RESULTS

All H-VMAT plans achieved the expected target coverage. A higher conformity index and homogeneity index were achieved for 2A and 4A H-VMAT plans and significantly differ from TA H-VMAT (p < 0.003). The heart and ipsilateral lung dose parameters were comparable among all plans except heart V_40Gy which was significantly less in 4A H-VMAT plan (p < 0.05). The contralateral lung, contralateral breast, spinal cord, normal tissue doses and MU were significantly less in TA H-VMAT (p < 0.03). The beam-on time was significantly less in 2A H-VMAT (p < 0.0001).

CONCLUSION

2A and 4A H-VMAT techniques are effective in improving the PTV dosimetric parameters as well as reducing the OAR doses. Further, 2A H-VMAT delivers less MU and beam-on time compared to 4A H-VMAT.