ABSTRACT
Objective:To compare three fixed-field intensity-modulated radiotherapy (IMRT) plans for nasal cavity and paranasal sinus tumors, including the coplanar IMRT (C-IMRT) plan and the non-coplanar IMRT(NC-IMRT) plan which were based on a conventional C-arm LINAC (Trilogy), and the coplanar IMRT (H-IMRT) plan based on an O-ring LINAC (Halcyon).Methods:Based on the data of 10 patients in the Ningbo First Hospital from December 2018 to December 2021 with nasal cavity and paranasal sinus tumors who underwent postoperative radiotherapy, this study redesigned three IMRT plans with the same prescribed doses and optimization objectives. Then, this study compared the doses of target volumes and organ at risks(OARs), the validation pass rates, and the execution time of these plans. Friedman test was employed in this study, and multiple comparisons were further made in cases of different results.Results:The differences in the conformal index (CI) of PTV and PTV boost of the three plans were statistically significant ( χ2 = 7.51, 9.69, P < 0.05). The multiple comparisons showed that the median CI of the H-IMRT plan was higher than that of the NC-IMRT plan ( Z = 2.53, 2.68, P < 0.05). The differences in other parameters of target volumes were not statistically significant. Compared with the C-IMRT plan, the H-IMRT plan reduced the Dmax of bilateral lenses, bilateral corneas, ipsilateral optic nerve, and ipsilateral eyeball ( Z = 2.80, 2.80, 2.80, 2.80, 2.81, 2.09, P < 0.05). Compared with the C-IMRT plan, the NC-IMRT reduced the Dmax of bilateral lenses, corneas, and eyeballs and contralateral optic nerve ( Z = 2.80, 2.66, 2.80, 2.70, 2.29, 2.29, 2.65, P < 0.05) and reduced the Dmean of bilateral eyeballs ( Z = 2.80, 2.80, P < 0.05). Compared with the NC-IMRT plan, the H-IMRT plan reduced the Dmax of the ipsilateral lens and cornea ( Z = 2.50, 2.08, P < 0.05), but increased the Dmax of the contralateral optic nerve and the Dmean of bilateral eyeballs ( Z = 2.80, 2.80, 2.80, P < 0.05). The validation pass rate of the three plans met the institutional standards, and the differences were not statistically significant. Moreover, the H-IMRT plan had the shortest median execution time (172.00 s), followed by the C-IMRT plan (337.50 s), and the NC-IMRT plan (388.00 s). Conclusions:The verification pass rate of the three plans can achieve the requirements of treatment implementation. The three plans had similar dosimetric differences in target volumes. However, the H-IMRT and NC-IMRT plans can protect the normal tissues (especially optical organs) more effectively than the C-IMRT plan, which is conducive to reducing the toxicity after radiotherapy and provides space for local dose increase or the radiotherapy for the treatment of tumor recurrence. The execution efficiency of the three plans is in the order of H-IMRT > C-IMRT > NC-IMRT. It is necessary to select appropriate radiotherapy equipment and technology according to actual situations.
ABSTRACT
Objective To investigate the effects of bolus thickness and use frequency on skin dose in postmastectomy intensity-modulated radiotherapy. Methods We retrospectively reviewed 20 cases receiving postmastectomy fixed-field intensity-modulated radiotherapy, to analyze the homogeneity index (HI) and conformity index (CI) of the target volume and the skin dose (Dmax, Dmean, and Dmin) of radiotherapy plans with 0.5 cm-thick bolus or 1 cm-thick bolus alone at a use frequency of 5 F, 10 F, 15 F, 20 F, and 25 F versus a combination of 0.5 cm and 1 cm-thick bolus, and fit the relationship between skin dose and bolus use frequency. Results As the bolus use frequency increased, the skin dose increased, the hot spot of the target volume decreased, and the low-dose volume decreased. The HI of the target volume with the 1 cm bolus was better than that with the 0.5 cm bolus at all use frequencies (P < 0.05), and HI decreased with the increase of bolus use frequency. For both 0.5 cm and 1 cm bolus, the CI of the target volume increased initially and then decreased, reaching the maximum value at a frequency of around 15 F; the CI showed significant differences only at 20 F and 25 F between the two types of bolus (P < 0.05). The skin Dmax and Dmean were significant higher with the 0.5 cm bolus than with the 1 cm bolus (P < 0.05). The equation for the relationship between skin dose (D) and bolus use frequency (F) was D = A × F + B × F2 + C. The Dmax and HI with the combination of 0.5 cm bolus (6 F) plus 1 cm bolus (8 F) fell between those with the 0.5 cm bolus (15 F) and those with the 1 cm bolus (15 F) (P < 0.05). Conclusion In postmastectomy fixed-field intensity-modulated radiotherapy, skin dose can be calculated based on bolus use frequency. Mixed use of bolus may be more suitable than use of 0.5 cm bolus or 1 cm bolus alone.
ABSTRACT
Objective To investigate dosimetric advantage of fixed field intensity-modulated radiotherapy (FF-IMRT),volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) for cervix uteri cancer.Methods CT datasets of ten patients with cervix uteri cancer were enrolled in the study.FF-IMRT,VMAT and HT plans were designed on Eclipse and HT treatment planning system.Plans were optimized with the aim to assess OAR while enforcing highly conformal target coverage.Institutional dose-volume constraints used in cervix uteri cancer were kept the same for three techniques.The different of three plan was play by single factor analysis of variance and compared to two groups by LSD method.Results All FF-IMRT,VMAT and HT resulted in equivalent target coverage but HT had an improved homogeneity index (P =0.000) and conformity index (P =0.000),or PTV of 105％ prescription dose (47.12％,45.83％ and 0.05％,P=0.000) and lowest Dmax dose (54.53 Gy,53.65 Gy,52.69 Gy,P=0.000).Compared with FF-IMRT and VMAT,the bladder V40 and Dmax of HT were lowest (50.01％,46.84％,42.98％,P=0.001 and 54.49 Gy,52.96 Gy,52.78 Gy,P=0.000),with the rectum V40 lowest (54.61％,48.34％,46.78％,P =0.006),the intestine Dmax lowest (54.53 Gy,53.65 Gy,52.66 Gy,P =0.000) and marrow Dmax lowest (54.51 Gy,54.44 Gy,52.13 Gy,P=0.000).But the delivery MU per fraction were highest (1429.20 MU,617.80 MU,7002.04 MU,P =0.000).Conclusions HT technology is feasible for clinical applications in cervical uteri cancer and can be used as a new method to promote.