Fixed-jaw technique to improve IMRT plan quality for the treatment of cervical and upper thoracic esophageal cancer.

The purpose of this study was to investigate the potential advantages of the fixed-jaw technique (FJT) over the conventional split-field technique (SFT) for cervical and upper thoracic esophageal cancer (EC) patients treated with intensity-modulated radiotherapy. The SFT and FJT plans were generated for 15 patients with cervical and upper thoracic EC. Dosimetric parameters and delivery efficiency were compared. An area ratio (AR) of the jaw opening to multileaf collimator (MLC) aperture weighted by the number of monitor units (MUs) was defined to evaluate the impact of the transmission through the MLC on the dose gradient outside the PTV50.4, and the correlation between the gradient index (GI) and AR was analyzed. The FJT plans achieved a better GI and AR (P < 0.001). There was a positive correlation between the GI and AR in the FJT (r = 0.883, P < 0.001) and SFT plans (r = 0.836, P < 0.001), respectively. Moreover, the mean dose (Dmean ), V5Gy -V40Gy for the lungs and the Dmean , V5Gy -V50Gy for the body-PTV50.4 in the FJT plans were lower than those in the SFT plans (P < 0.05). The FJT plans demonstrated a reduction trend in the doses to the spinal cord PRV and heart, but only the difference in the heart Dmean reached statistical significance (P < 0.05). The FJT plans reduced the number of MUs and subfields by 5.5% and 17.9% and slightly shortened the delivery time by 0.23 min (P < 0.05). The gamma-index passing rates were above 95% for both plans. The FJT combined with target splitting can provide superior organs at risk sparing and similar target coverage without compromising delivery efficiency and should be a preferred intensity-modulated radiotherapy planning method for cervical and upper thoracic EC patients.

Evaluation of fixed-jaw IMRT and tangential partial-VMAT radiotherapy plans for synchronous bilateral breast cancer irradiation based on a dosimetric study.

PURPOSE: To investigate the fixed-jaw intensity-modulated radiotherapy (F-IMRT) and tangential partial volumetric modulated arc therapy (tP-VMAT) treatment plans for synchronous bilateral breast cancer (SBBC). MATERIALS AND METHOD: Twelve SBBC patients with pTis-2N0M0 stages who underwent whole-breast irradiation after breast-conserving surgery were planned with F-IMRT and tP-VMAT techniques prescribing 42.56 Gy (2.66 Gy*16f) to the breast. The F-IMRT used 8-12 jaw-fixed tangential fields with single (sF-IMRT) or two (F-IMRT) isocenters located under the sternum or in the center of the left and right planning target volumes (PTVs), and tP-VMAT used 4 tangential partial arcs with two isocenters located in the center of the left and right PTVs. Plan evaluation was based on dose-volume histogram (DVH) analysis. Dosimetric parameters were calculated to evaluate plan quality; total monitor units (MUs), and the gamma analysis for patient-specific quality assurance (QA) were also evaluated. RESULTS: For PTVs, the three plans had similar Dmean and conformity index (CI) values. F-IMRT showed a slightly better target coverage according to the V100% values and demonstrated an obvious reduction in V105% and Dmax compared with the values observed for sF-IMRT and tP-VMAT. Compared with tP-VMAT, sF-IMRT was slightly better in terms of V100% , V105% and Dmax . In addition, F-IMRT achieved the best homogeneity index (HI) values for PTVs. Concerning healthy tissue, tP-VMAT had an advantage in minimizing the high dose volume. The MUs of the tP-VMAT plan were decreased approximately 1.45 and 1 times compared with the sF-IMRT and F-IMRT plans, respectively, and all plans passed QA. For the lungs, heart and liver, F-IMRT achieved the smallest values in terms of Dmean and showed a significant difference compared with tP-VMAT. Simultaneously, sF-IMRT was also superior to tP-VMAT. For the coronary artery, tP-VMAT achieved the lowest Dmean , while the value for F-IMRT was 2.24% lower compared with sF-IMRT. For all organs at risk (OARs), tP-VMAT was superior at the high dose level. In contrast, sF-IMRT and F-IMRT were obviously superior at the low dose level. The sF-IMRT and F-IMRT plans showed consistent trends. CONCLUSION: All treatment plans for the provided techniques were of high quality and feasible for SBBC patients. However, we recommend F-IMRT with a single isocenter as a priority technique because of the tremendous advantage of local hot spot control in PTVs and the reduced dose to OARs at low dose levels. When the irradiated dose to the lungs and heart exceed the clinical restriction, two isocenter F-IMRT can be used to maximize OAR sparing. Additionally, tP-VMAT can be adopted for improving cold spots in PTVs or high-dose exposure to normal tissue when the interval between PTVs is narrow.

Dosimetric comparison and biological evaluation of fixed-jaw intensity-modulated radiation therapy for T-shaped esophageal cancer.

BACKGROUND: To evaluate the dosimetric and biological benefits of the fixed-jaw (FJ) intensity-modulated radiation therapy (IMRT) technique for patients with T-shaped esophageal cancer. METHODS: FJ IMRT plans were generated for thirty-five patients and compared with jaw tracking (JT) IMRT, static jaw (SJ) IMRT and JT volumetric modulated arc therapy (VMAT). Dosimetric parameters, tumor control probability (TCP) and normal tissue complication probability (NTCP), monitor units (MUs), delivery time and gamma passing rate, as a measure of dosimetric verification, were compared. The correlation between the length of PTV-C below the upper boundary of lung tissue (PTV-Cinferior) and dosimetric parameters and NTCP of the lung tissue were analyzed. RESULTS: The homogeneity and conformity of the target in the four plans were basically equivalent. When compared to the JT IMRT and SJ IMRT plans, FJ IMRT plan led to a statistically significant improvement in the NTCP and low-middle dosimetric parameters of the lung, and the improvement had a moderately positive correlation with the length of PTV-Cinferior, with a correlation coefficient ranging from 0.523 to 0.797; the FJ IMRT plan exhibited better lung sparing in low-dose volumes than the JT VMAT plan. The FJ IMRT plan had similar MUs (888 ± 99) and delivery times (516.1 ± 54.7 s) as the JT IMRT plan (937 ± 194, 522 ± 5.6 s) but higher than SJ IMRT (713 ± 137, 488.8 ± 45.2 s) and JT VMAT plan (517 ± 59, 263.7 ± 43.3 s). CONCLUSIONS: The FJ IMRT technique is superior in reducing the low-dose volumes of lung tissues for patients with T-shaped esophageal cancer.

Dosimetric and delivery comparison of helical tomotherapy with dynamic jaw and fixed jaw for cervical carcinoma.

Context: Recently, the dynamic jaw mode has been introduced in our radiation oncology center second in China. Many studies showed that dynamic jaw mode in helical tomotherapy (HT) has the potential to improve organs at risk avoidance. Aim: This study aimed to evaluate the plan quality and efficiency of dynamic jaw delivery compared to the regular HT delivery mode (fixed jaw mode) for cervical carcinoma. Settings and Design: Plan quality and efficiency were compared among the fixed jaw 2.5 cm mode, the dynamic jaw 2.5 cm mode, and the dynamic jaw 5.0 cm mode. Subjects and Methods A total of 20 patients with cervical carcinoma were chosen to compare the plan quality and treatment efficiency using regular HT mode (fixed jaw 2.5 cm field width) and HT dynamic jaw mode with width 2.5 cm and 5.0 cm field width. The prescribed dose was 50.4 Gy in 28 fractions to planning target volume. Target coverage, homogeneity, conformity, sparing of organs at risk (OARs), monitor unit, and beam-on time were evaluated. Statistical Analysis Used: : The statistical significance of any difference among plans assessed the two-sided paired t-test. The statistical analysis was conducted using SPSS 19.0 software. Results: For each of the 20 patients, the plans were clinically acceptable. The target coverage and sparing of most OARs were measured using the dynamic jaw. Conclusions: Cervical carcinoma should be treated with the dynamic jaw 2.5 cm mode. Considering the risk of long treatment time, the dynamic jaw 5.0 cm mode could be an option.

A comparative study of identical VMAT about two adjacent targets with and without fixed-jaw technique.

BACKGROUND: The radiation transmission through the multileaf collimators is undesired in modern techniques such as volumetric modulated arc therapy (VMAT). According to identical plans, in this study, we aim to investigate the dosimetric impact of jaw tracking on the VMAT plans on two adjacent targets. METHODS: Two treatment plans were designed for eight pelvic (cervical) patients with two targets using the same optimization parameters. The original plan (O-plan) used automatically selected jaw positions. In the new plan (F-plan), the jaws were fixed to block two targets in two beams. The dosimetric parameters of the two plans were compared to evaluate the improvement of dose sparing for the body volume between two targets (named interOAR) in F-VMAT. RESULTS: The mean dose of interOAR reduced significantly from 654.96 ± 113.38 cGy for O-VMAT, to 490.84 ± 80.26 cGy for F-VMAT (p = 0.018). The monitor units (MUs) in the F-plans were 1.49-fold higher than that in the O-plan. The F and O-plan performed similarly in target dose homogeneity. The differences in Dmax of spinal cord, Dmax of spinal cord planning organ at risk volume, and V20, V30, and V40 of the intestine were insignificant. CONCLUSIONS: VMAT plans with the fixed-jaw method can reduce the volume between two targets effectively. However, despite the plan quality, the method can only be used when the regular methods cannot reach the clinical requirements for critical organs because of additional MUs.

Analysis of dosimetric differences between active control and passive tracking of jaws / 中国辐射卫生

Objective To analyze the effect of the fixed-jaw technique on dosimetric parameters during dynamic intensity-modulated radiotherapy (DIMRT) planning. Methods Ten patients each with nasopharyngeal carcinoma, postoperative cervical cancer, and right breast cancer after radical surgery were selected for this study; all patients underwent DIMRT in our hospital in 2020. After administration at the prescribed dose, two methods were used to design the radiotherapy plan for each patient: split-field technique (SFT) and fixed-jaw technique (FJT). The two plans were compared for the differences in the dosimetric parameters and plan verification pass rate. Results Compared with SFT, FJT showed significant decreases (P <0.05) in the following parameters for patients with nasopharyngeal carcinoma, postoperative cervical cancer, and right breast cancer after radical surgery: number of radiation fields (down by 41.5%, 47.3%, and 34.9%, respectively, t = 7.954, 24.2, and 4.949, respectively), total number of monitor units (MUs) (down by 5.6%, 5.3%, and 13.5%, respectively, t = 3.211, 2.423, and 5.481, respectively), and actual beam-on time (down by 25.3%, 23.8%, and 13.6%, respectively, t = 5.814, 9.208, and 5.655, respectively). There were significant differences in some of the dosimetric parameters for all three types of cancer patients between the two plans (P <0.05). There were no significant differences in the plan verification pass rate (P >0.05). Conclusion FJT can reduce the total number of MUs and actual beam-on time while meeting the requirements for clinically prescribed doses in DIMRT planning.

A novel IMRT planning study by using the fixed-jaw method in the treatment of peripheral lung cancer with mediastinal lymph node metastasis.

Intensity-modulated radiotherapy (IMRT) is an important technology in cancer radiotherapy. In the current planning system, such as in the Pinnacle3 system, jaw positions are automatically set to cover all target volumes, and many medical centers in developing countries are not equipped with linear accelerators with a jaw tracing function. As solitary lesions are often located in patients, the resulting radiation leakage and transmission increase the dose exposure in surrounding critical organs, although blocked by multileaf collimator (MLC) leaves. We therefore designed a method to manually fix jaw positions, which further reduces doses. We particularly focused on the patients of peripheral lung cancer combined with mediastinal lymph node metastasis, as our medical center mainly targets lung cancer. We designed 2 treatment plans for each patient with the same optimization parameters, i.e., the plan of automatically chosen jaw positions (jaw auto-chosen plan) and the plan of fixed-jaw positions (fixed-jaw plan). In the latter plan, jaws were manually fixed for tumors in lung and in mediastinal lymph node metastases, respectively. We found that both plans met the clinical requirements, and the D2, D98, conformation number (CN), and homogeneity index (HI) for planning target volume (PTV) had no significant differences between the 2 plans. Importantly, the machine units (MUs) for fixed-jaw plans were 50%~60% more than routine jaw auto-chosen plans, whereas the V5, V10, V20, V30, and the mean dose in the total lung and the ipsilateral lung were less than the routine jaw auto-chosen plans. Dose-volume values D1 for the spinal cord and D2, V40, V60 for the heart existed no significant differences for 2 plans. In the fixed-jaw method, the total lung TLV5-△Vab and TLV10-△Vab values had a moderate positive correlation with the lung radiation leakage and the transmission area reduction. We concluded that the fixed-jaw plan is superior to the routine jaw auto-chosen plan in reducing the radiation exposure of surrounding critical organs, which will benefit the IMRT application.

A fixed-jaw method to protect critical organs during intensity-modulated radiotherapy.

Intensity-modulated radiotherapy (IMRT) plays an important role in cancer radiotherapy. For some patients being treated with IMRT, the extremely low tolerances of critical organs (such as lens, ovaries, and testicles) cannot be met during treatment planning. The aim of this article is to introduce a new planning method to overcome that problem. In current planning practice, jaw positions are automatically set to cover all target volumes by the planning system (e.g., Pinnacle(3) system). Because of such settings, critical organs may be fully blocked by the multileaf collimator (MLC), but they still sit in the field that is shaped by collimator jaws. These critical organs receive doses from the transmission and leakage of MLC leaves. We manually fixed jaw positions to block them to further reduce such doses. This method has been used for different treatment sites in our clinic, and it was thoroughly evaluated in patients with radical hysterectomy plus ovarian transposition after surgery. For each patient, 2 treatment plans were designed with the same optimization parameters: the original plan with automatically chosen jaw positions (called O-plan) and the plan with fixed-jaw positions (named F-plan). In the F-plan, the jaws were manually fixed to block the ovaries. For target coverage, the mean conformity index (CI) of the F-plan (1.28 ± 0.02) was remarkably lower than that of the O-plan (1.53 ± 0.09) (p < 0.05). The F-plan and the O-plan performed similarly in target dose homogeneity. Meanwhile, for the critical organ sparing, the mean dose of both ovaries were much lower in the F-plan than that in the O-plan (p < 0.05). The V20, V30, and V40 of bladder were also lower in the F-plan (93.57 ± 1.98, 73.99 ± 5.76, and 42.33 ± 3.7, respectively) than those in the O-plan (97.98 ± 1.11, 85.07 ± 4.04, and 49.71 ± 3.63, respectively) (p < 0.05). The maximum dose to the spinal cord planning organ at risk (OAR) volume (PRV) in the O-plan (3940.24 ± 102.8) was higher than that in the F-plan (3628.18 ± 131.45) with significant differences (p < 0.01). For other OARs, there were no significant differences in doses between these 2 plans except that the high-dose regions of the rectum were higher for V40 in the O-plan than that in the F-plan (p < 0.01). But the monitor units (MUs) in the F-plan were 1.4 times as much as that in the O-plan. Thus the treatment time could be longer by using the F-plan. As it results in more MUs in spite of better plan quality, it is recommended to be used only in situations in which clinical requirements to critical organs cannot be met with the regular method.

A study of lung protection in intensity?modulated radiotherapy with split field and fixed jaw techniques for peripheral lung cancer with mediastinal lymph node metastasis / 中华放射肿瘤学杂志

Objective To retrospectively design an intensity?modulated radiotherapy ( IMRT) plan with split field and fixed jaw techniques for peripheral lung cancer with mediastinal lymph node metastasis, to compare dosimetric characteristics between the IMRT plans with fixed jaw and dynamic jaw, and to study lung protection by the plan with split field and fixed jaw. Methods Treatment plans were collected from 12 patients with peripheral lung cancer and mediastinal lymph node metastasis who were treated with IMRT in our hospital. All plans used the dynamic jaw technique. The plans with split field and fixed jaw were designed based on the identical computed tomography images and planning target volume ( PTV) . Each jaw position in split field depended on each separate PTV. The prescription dose was 60 Gy in 30 fractions. 95%PTV was planned to receive 100% of the prescription dose. Dosimetric parameters of PTV, conformity index ( CI) , heterogeneity index ( HI) , number of monitor units ( MUs) , and dose?volume values of the lung and heart were obtained from dose?volume histogram. Comparison between the two plans was made by paired t test. Results Both plans met clinical requirements. There were no significant differences in D2 , D98 , CI, or HI of PTV between the two plans ( all P>005) . Compared with the dynamic jaw plan, the fixed jaw plan had MUs increased by 15%?20%( P=0010) . The V5 , V10 , V20 , V30 , and mean dose for the whole lungs were significantly lower in the fixed jaw plan than in the dynamic jaw plan ( P=0000, 0000, 0000, 0002,0000) . The V5 , V20 , and mean dose for the healthy lung were also significantly lower in the fixed jaw plan than in the dynamic jaw plan ( P=0000,0017,0000) . There were no significant differences in dose?volume values for the spinal cord or heart between the two plans ( all P>005) . Conclusions IMRT with split field and fixed jaw is recommended for patients with peripheral lung cancer and mediastinal lymph node metastasis. The therapy to a certain extent reduces low?dose volume for the lung and the incidence of radiation?induced pneumonitis.