Dosimetric evaluation of automatic and manual plans for early nasopharyngeal carcinoma to radiotherapy

To investigate dosimetric differences and plan qualities between manual plans and automatic plans for nasopharyngeal carcinoma (NPC) in early stage, and provide better options to maximize the benefits. Sixteen cases diagnosed with early NPC were retrospectively investigated. Conventional step and shoot IMRT with 7-fields and full arc volumetric-modulated arc therapy (VMAT) with double arcs were manually generated by experienced planners and automatically generated by Auto-Planning module in Pinnacle³ respectively, such as IMRT manual-planning (mIMRT), IMRT auto-planning (aIMRT), VMAT manual-planning (mVMAT), and VMAT auto-planning (aVMAT) for each patient. Target coverage, organs at risk sparing, monitor units, and planning times were compared and evaluated. All parameters of plans are able to fulfill International Commission on Radiation Units and Measurements repor (ICRU) 83 recommendations. Automatic plans are comparable or superior to manual plans without time-consuming planning process. The CI and HI for PTVs are better in aVMAT when compared with aIMRT and mVMAT, but those are similar between aIMRT and mVMAT. Automatic plans not only have superior dose homogeneity and conformity in PTVs, but also have better sparing for spinal cord or slightly reduce the doses received by other OARs, while the VMAT plans have better sparing for brain stem, especially the aVMAT plans. However, Dmax, V30, and V40 of brain stem are similar between aIMRT and mVMAT without significant difference. The monitor units and planning time for treatment plans have been significantly decreased through automatic planning technique. The automatic VMAT plan has greater clinical advantages and should be recommended to a better option for treating NPC in early stage, while automatic IMRT would be preferentially considered instead of manual VMAT.     

Dosimetric comparison of helical tomotherapy,volumetric-modulated arc therapy,intensity-modulated radiotherapy,and field-in-field technique for synchronous bilateral breast cancer

Purpose: To compare the dosimetric characteristics of helical tomotherapy (HT), volumetric-modulated arc therapy (VMAT), intensity-modulated radiotherapy (IMRT), and tangential field-in-field technique (FIF) for the treatment of synchronous bilateral breast cancer (SBBC). Methods and Materials: Ten patients with early-stage unilateral breast cancer were selected for simulating the patients with SBBC in this retrospective analysis. Treatment plans with HT, VMAT, IMRT, and FIF were generated for each patient with a total dose of 50.4 Gy in 28 fractions to the target. Plan quality, namely conformity index (CI), homogeneity index (HI), dose-volume statistics of organs at risk (OARs), and beam-on time (BOT), were evaluated. Results: HT plans showed a lower mean heart dose (3.53 ± 0.31Gy) compared with the other plans (VMAT = 5.6 ± 1.36 Gy, IMRT = 3.80 ± 0.76 Gy, and FIF = 4.84 ± 2.13 Gy). Moreover, HT plans showed a significantly lower mean lung dose (p < 0.01) compared with the other plans: mean right lung doses were 6.81 ± 0.67, 10.32 ± 1.04, 9.07 ± 1.21, and 10.03 ± 1.22 Gy and mean left lung doses were 6.33 ± 0.87, 8.82 ± 0.91, 7.84 ± 1.07, and 8.64 ± 0.99 Gy for HT, VMAT, IMRT, and FIF plans, respectively. The mean dose to the left anterior descending artery was significantly lower in HT plans (p < 0.01) than in the other plans: HT = 19.41 ± 0.51 Gy, VMAT = 25.77 ± 7.23 Gy, IMRT = 27.87 ± 6.48 Gy, and FIF = 30.95 ± 10.17 Gy. FIF plans showed a worse CI and HI compared with the other plans. VMAT plans showed shorter BOT (average, 3.9 ± 0.2 minutes) than did HT (average, 11.0 ± 3.0 minutes), IMRT (average, 6.1 ± 0.5 minutes), and FIF (average, 4.6 ± 0.7 minutes) plans. Conclusions: In a dosimetric comparison for SBBC, HT provided the most favorable dose sparing of OARs. However, HT with longer BOT may increase patient discomfort and treatment uncertainty. VMAT enabled shorter BOT with acceptable doses to OARs and had a better CI than did FIF and IMRT.     

鼻咽癌三种调强放疗计划剂量学对比研究

目的 对比鼻咽癌常规固定野调强（IMRT）、容积旋转调强（VMAT）以及断层调强（HT）3种不同调强放疗计划的剂量学差异。方法 选择18例接受VMAT治疗的鼻咽癌患者,以相同处方剂量和目标条件分别重新进行IMRT和HT计划设计。比较3种计划靶区的均匀度（HI）、适形度（CI）、最大剂量以及平均剂量。危及器官的最大量和平均量以及感兴趣区的剂量体积、计划执行时间和机器跳数（MU）。结果 3种计划在靶区的覆盖率满足临床要求。IMRT计划在靶区的HI和CI方面结果最差,HT计划结果最优。危及器官方面,IMRT计划受量最高,HT计划的脊髓、脑干和腮腺受量最低;但对于视神经、晶状体以及视交叉HT计划的受量最高而VMAT计划的受量最低。IMRT的治疗时间（8.0±0.5） min高于VMAT（3.9±0.1）min和HT（7.4±0.9）min。与VMAT相比,IMRT每次治疗为（711.4±78.7）MU,高于VMAT的（596.4±33.7）MU。结论 鼻咽癌IMRT、VMAT以及HT计划在靶区覆盖和危及器官保护上都可以达到临床要求,在靶区的适形度和均匀性上HT计划优于VMAT和IMRT,但在治疗时间和加速器的机器跳数上VMAT较有优势。     

Dosimetric comparison of volumetric modulated arc therapy and intensity-modulated radiation therapy for pancreatic malignancies

Volumetric-modulated arc therapy (VMAT) has been previously evaluated for several tumor sites and has been shown to provide significant dosimetric and delivery benefits when compared with intensity-modulated radiation therapy (IMRT). To date, there have been no published full reports on the benefits of VMAT use in pancreatic patients compared with IMRT. Ten patients with pancreatic malignancies treated with either IMRT or VMAT were retrospectively identified. Both a double-arc VMAT and a 7-field IMRT plan were generated for each of the 10 patients using the same defined tumor volumes, organs at risk (OAR) volumes, dose, fractionation, and optimization constraints. The planning tumor volume (PTV) maximum dose (55.8 Gy vs. 54.4 Gy), PTV mean dose (53.9 Gy vs. 52.1 Gy), and conformality index (1.11 vs. 0.99) were statistically similar between the IMRT and VMAT plans, respectively. The VMAT plans had a statistically significant reduction in monitor units compared with the IMRT plans (1109 vs. 498, p < 0.001). In addition, the doses to the liver, small bowel, and spinal cord were comparable between the IMRT and VMAT plans. However, the VMAT plans demonstrated a statistically significant reduction in the mean left kidney V₂₅ (9.4 Gy vs. 2.3 Gy, p = 0.018), mean right kidney V₁₅ (53.4 Gy vs. 45.9 Gy, p = 0.035), V₂₀ (32.2 Gy vs. 25.5 Gy, p = 0.016), and V₂₅ (21.7 Gy vs. 14.9 Gy, p = 0.001). VMAT was investigated in patients with pancreatic malignancies and compared with the current standard of IMRT. VMAT was found to have similar or improved dosimetric parameters for all endpoints considered. Specifically, VMAT provided reduced monitor units and improved bilateral kidney normal tissue dose. The clinical relevance of these benefits in the context of pancreatic cancer patients, however, is currently unclear and requires further investigation.     

Treatment and Dosimetric Advantages Between VMAT, IMRT, and Helical TomoTherapy in Prostate Cancer

We investigated the possible treatment and dosimetric advantage of volumetric modulated arc therapy (VMAT) over step-and-shoot intensity-modulated radiation therapy (step-and-hhoot IMRT) and helical tomotherapy (HT). Twelve prostate cancer patients undergoing VMAT to the prostate were included. Three treatment plans (VMAT, step-and-shoot IMRT, HT) were generated for each patient. The doses to clinical target volume and 95% of planning target volume were both ≥78 Gy. Target coverage, conformity index, dose to rectum/bladder, monitor units (MU), treatment time, equivalent uniform dose (EUD), normal tissue complication probability (NTCP) of targets, and rectum/bladder were compared between techniques. HT provided superior conformity and significantly less rectal volume exposed to 65 Gy and 40 Gy, as well as EUD/NTCP of rectum than step-and-shoot IMRT, whereas VMAT had a slight dosimetric advantage over step-and-shoot IMRT. Notably, significantly lower MUs were needed for VMAT (309.7 ± 35.4) and step-and-shoot IMRT (336.1 ± 16.8) than for HT (3368 ± 638.7) (p < 0.001). The treatment time (minutes) was significantly shorter for VMAT (2.6 ± 0.5) than step-and-shoot IMRT (3.8 ± 0.3) and HT (3.8 ± 0.6) (p < 0.001). Dose verification of VMAT using point dose and film dosimetry met the accepted criteria. VMAT and step-and-shoot IMRT have comparable dosimetry, but treatment efficiency is significantly higher for VMAT than for step-and-shoot IMRT and HT.     

Nasopharyngeal carcinoma radiotherapy with hybrid technique

The aim of the study was to investigate the effect of the Hybrid technique which was created by combining of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for the treatment of nasopharyngeal cancer (NPC) patients. 7 to 9 field IMRT, triple arc VMAT, and Hybrid plans were generated for 10 advanced stage NPC patients. The homogeneity index (HI) and the conformity index (CI) of planning target volumes (PTVs) were calculated for each technique to evaluate the plan quality. The techniques were compared in terms of plan quality, sparing of organs at risk (OARs), monitor units (MUs), and delivery time. Hybrid technique significantly improved the target dose homogeneity and the conformity for PTV70 and PTV60 compared to IMRT and VMAT. Hybrid plans significantly reduced the maximum dose of the brainstem sparing compared to the VMAT plans and also improved the sparing of spinal cord compared to IMRT and VMAT. The MUs and the delivery time of Hybrid plans were found to be between values for IMRT and VMAT plans. Hybrid technique can be useful when IMRT and VMAT techniques are not adequate alone in the treatment of NPC patients.     

Locoregional irradiation including internal mammary nodal region for left-sided breast cancer after breast conserving surgery: Dosimetric evaluation of 4 techniques

The present study aimed to compare 4 techniques in the planning of locoregional irradiation including internal mammary nodal region for left-sided breast cancer. Ten patients with left-sided breast cancer undergoing breast conservation surgery were enrolled. For each patient, 4 treatment plans were performed: a helical tomotherapy (HT) plan, a volumetric modulated arc therapy (VMAT) plan, a static intensity modulated radiation therapy (IMRT) plan, and a hybrid IMRT plan, designed to encompass the whole breast, internal mammary, and supraclavicular nodal regions. The prescribed dose of radiation was 50 Gy in 25 fractions. The dosimetric parameters of the target and organs at risk, as well as the dose delivery time, were evaluated and compared using an independent-samples t-test. The HT and VMAT plans had the best conformity and homogeneity. For the HT, VMAT, IMRT, and hybrid IMRT plans, the mean conformity index (CI) and homogeneity index (HI) were 0.83, 0.82, 0.8, and 0.77 (p < 0.001); and 1.07, 1.11, 1.14, and 1.14 (p < 0.001), respectively. The corresponding V₅₅ values were 0.3%, 11.4%, 27.02%, and 23.29% (p < 0.001). The D_mean and V₂₀ of the left lung obtained using the HT plan were significantly lower than those of VMAT, IMRT, and hybrid IMRT plans (p = 0.002, p = 0.004). There were no significant differences in D max of LAD descending coronary artery, or the D_mean of the heart among the 4 types of plans. The HT and VMAT plans had a lower dose to other organ at risk (OARs) compared with the IMRT and hybrid IMRT plans. The mean delivery times were 1042 ± 33 seconds, 136 ± 12 seconds, 450 ± 65 seconds, and 451 ± 70 seconds for the HT, VMAT, IMRT, and hybrid IMRT plans, respectively (p < 0.001). For whole breast plus supraclavicular and internal mammary nodal irradiation in left-sided breast cancer, the VMAT technique is recommended considering both the dose distribution and the delivery time. Under circumstances in which dose distribution is a priority, the HT technique is a valid option.     

Dosimetric comparison of robotic- and LINAC-based treatment of spine stereotactic body radiotherapy

To determine which treatment technique and modality would offer better dosimetric results and be preferable for spinal stereotactic body therapy (SBRT) depending on the three different regions of the vertebrae. Linear accelerator (LINAC)- and CyberKnife (CK)-based treatment techniques were compared in terms of their dosimetric quality, treatment efficiency, and delivery accuracy. Thirty previously treated patients were included in this study. Intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques were used for LINAC-based treatment, whereas CK-based treatment plans were generated for two different collimator systems: fixed and multileaf collimator (MLC). The plans were compared based on spinal cord sparing, dose homogeneity, conformity index (CI), gradient index (GI), monitor unit (MU), and beam-on time. The percentage volumes of V2Gy, V5Gy (representing volume low of the dose spillage region), V10Gy, and V20Gy (representing the volume of the high-dose spillage region) of the healthy tissue were analyzed. The CI and GI of the VMAT plans were better than those of the IMRT plans. For spinal cord sparing, the VMAT and MLC-based CK (CK-MLC) techniques were superior. The percentage of low-dose spillage regions was the lowest for IMRT and fixed cone-based CK (CK-FIX) plans. The percentage of the high-dose spillage region was the lowest for the VMAT and CK-MLC plans. In terms of treatment efficiency, the VMAT and CK-MLC plans were superior to the IMRT and CK-FIX plans. The VMAT technique lowered the MU and beam-on time values. The plan delivery accuracy of the VMAT and CK-FIX plans was better than that of the IMRT plans. VMAT is the best option for LINAC-based spinal SBRT. For CK-based spinal SBRT, MLC-based plans are preferred. If the clinic has both treatment modalities and the patient can tolerate long treatment times, CK-MLC-based treatment should be chosen because of its superiority in sparing the spinal cord and sharp dose fall-off.     

A dosimetric evaluation of dose escalation for the radical treatment of locally advanced vulvar cancer by intensity-modulated radiation therapy

The purpose of this planning study was to determine whether intensity-modulated radiation therapy (IMRT) reduces the radiation dose to organs at risk (OAR) when compared with 3D conventional radiation therapy (3D-CRT) in patients with vulvar cancer treated by irradiation. This study also investigated the use of sequential IMRT boost (seq-IMRT) and simultaneous integrated boost (SIB-IMRT) for dose escalation in the treatment of locally advanced vulvar cancer. Five vulvar cancer patients treated in the postoperative setting and 5 patients treated with definitive intent (def-group) were evaluated. For the postoperative group, 3D-CRT and IMRT plans to a total dose (TD) of 45 Gy were generated. For the def-group, 4 plans were generated: a 3D-CRT and an IMRT plan to a TD of 56.4 Gy, a SIB-IMRT plan to a TD of 56 Gy, and a SIB-IMRT with dose escalation (SIB-IMRT-esc): TD of 67.2 Gy. Mean dose and dose-volume histograms were compared using Student's t-test. IMRT significantly (all p < 0.05) reduced the D_mean, V30, and V40 for all OAR in the adjuvant setting. The V45 was also significantly reduced for all OAR except the bladder. For patients treated in the def-group, all IMRT techniques significantly reduced the D_mean, V40, and V45 for all OAR. The mean femur doses with SIB-IMRT and SIB-IMRT-esc were 47% and 49% lower compared with 3D-CRT. SIB-IMRT-esc reduced the doses to the OAR compared with seq-3D-CRT but increased the D_max. for the small bowel, rectum, and bladder. IMRT reduces the dose to the OAR compared with 3D-CRT in patients with vulvar cancer receiving irradiation to a volume covering the vulvar region and nodal areas without compromising the dosimetric coverage of the target volume. IMRT for vulvar cancer is feasible and an attractive option for dose escalation studies.     

容积旋转调强放疗和常规调强放疗技术在乳腺癌保乳术后同步推量中的剂量学比较

 目的 比较容积旋转调强放疗(VMAT)和常规调强放疗(IMRT)两种技术在乳腺癌保乳术后同步推量放疗中剂量学差异。方法 随机选择10例左侧乳腺癌保乳术后患者,使用MONACO 5.1计划系统,分别设计VMAT和IMRT计划,处方剂量均为PTV_50Gy/25 f、PGTVtb60 Gy/25 f,评估两种计划靶区剂量适形指数(CI)、均匀性指数(HI),以及正常器官受照剂量(Gy)、机器跳数(MU)及治疗时间。结果 VMAT计划中靶区剂量的适形度明显优于IMRT(P<0.05),而患侧肺V₅、V₁₀、V₂₀及健侧肺V₅稍高于IMRT组(P<0.05)。结论 对于乳腺癌保乳术后同步推量放疗,VMAT和IMRT计划都可以满足临床剂量学的要求,VMAT在适形度方面对于IMRT计划有优势,并缩短了治疗时间。     

Conformal breast irradiation with the arm of the affected side parallel to the body

Purpose

To propose a simple, forward-planned three-dimensional conformal radiotherapy (3D-CRT) technique for breast cancer patients with frozen shoulder.

Materials and methods

A technique is described that avoids lateral beams transmitting through the arm of the affected side. One medial, tangentially applied beam deposits most of the dose. Further beams with little weight are used to attain dose homogeneity. In order to quantify dose distribution and homogeneity in the planning target volume (PTV), as well as the scattered dose in organs at risk (OAR), the parameters D95, D5, D1, mean and median dose were determined for the individual volumes. Intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were created in order to compare these with the proposed technique.

Results

The described technique achieved homogenous dose deposition within the PTV. A regimen comprising 25 fractions of 2 Gy prescribed to the PTV resulted in the following dose parameters: PTV(D95): 44.3 Gy, PTV(D5): 52.7 Gy, PTV(D1): 54.8 Gy, PTV(mean): 49.3 Gy and PTV(median): 49.9 Gy. Mean lung dose was 7.0 Gy. The ipsilateral lung received a mean dose of 9.9 Gy. This plan was accepted for treatment. The IMRT and VMAT plans achieved a similar dose distribution in the PTV. These techniques also reduced dose deposition in the OAR.

Conclusion

The proposed 3D-CRT technique allows treatment of breast cancer patients who are not able to raise their arms above their head. Homogenous dose distribution in the PTV was achieved while avoiding lateral beams that transmit through the arm of the affected side. Mean lung dose was comparable to that of the conventional technique using opposed tangential beams. IMRT and VMAT also provide good target dose homogeneity with good sparing of OAR. However, these techniques are more demanding in terms of planning and quality assurance.     

不同调强方式在胸中上段食管癌放疗中的剂量学研究

目的 对胸中上段食管癌患者进行静态调强（IMRT）和容积旋转调强（VMAT）两种放疗方式的剂量学对比研究。方法 对20例IMRT治疗的食管癌患者行VMAT（单弧和双弧）计划的重新设计。在单弧的VMAT计划中,对其中5例患者行不同子野间隔（4°、3°、2°）以及不同计划系统（Monaco和MasterPlan）的计划设计。比较靶区和危及器官（OAR）的剂量学差异及治疗参数。结果 双弧VMAT计划各项靶区剂量学参数明显好于IMRT计划和单弧VMAT计划（P<0.05）,靶区均匀性（HI）（P<0.05）和适形度（CI）（P<0.05）最好。危及器官参数VMAT可在一定程度上降低OAR的受照剂量,但是IMRT对肺组织和正常组织（E-P）的低剂量保护要优于VMAT（P<0.05）;不同子野间隔的VMAT计划中,2°相对于3°和4°其OAR的受照剂量是减小的（P<0.05）,除了心脏的D_mean;不同计划系统设计的VMAT计划,以Monaco对OAR的保护为最优（P<0.05）;VMAT的机器跳数少于IMRT,而且有效节省了治疗时间。 结论 VMAT方式相对于IMRT能够实现更好的靶区覆盖、均匀性和适形度,同时能降低脊髓、肺组织、心脏和E-P的受照剂量;对于VMAT来说,双弧技术、小子野角度间隔能够进一步地改善靶区和OAR的受照剂量;此外,在物理参数和优化参数一致的前提下,Monaco可以更好地保护OAR。     

Comparison of whole-field simultaneous integrated boost VMAT and IMRT in the treatment of nasopharyngeal cancer

To study the feasibility of using volumetric-modulated arc therapy (VMAT) to deliver whole-field simultaneous integrated boost (WF-SIB) to treat patients with nasopharyngeal cancer (NPC).WF-SIB intensity-modulated radiotherapy (IMRT) plans, one-arc WF-SIB VMAT plans, and two-arc WF-SIB VMAT plans were generated with identical objective functions for 8 patients with NPC of various stages. Isodose distributions and dose-volume histograms were evaluated. Dosimetric and biological quality indices of clinical target volume (CTV) and organs at risk (OARs) were calculated to study the optimization capability of these 3 modalities in the treatment of patients with NPC. The optimization time, delivery time, required monitor units (MUs), and delivery accuracy were also compared to investigate the feasibility of these 3 modalities.There was no significant difference (p = 0.92) in target coverage (TC) between WF-SIB IMRT (99.00 ± 0.79) and two-arc WF-SIB VMAT (97.98 ± 1.29). However, both had higher TC than one-arc VMAT plans (89.92 ± 6.32, p < 0.01). IMRT demonstrated the best protection of the spinal cord, whereas two-arc VMAT showed the minimum D_max to OARs. No other significant differences were observed among these 3 modalities on CTV coverage and OAR sparing. The delivery and MU efficiency of one-arc and two-arc WF-SIB VMAT were greatly improved compared with WF-SIB IMRT. The optimization time of one-arc and two-arc WF-SIB VMAT plans were 5 and 10 times greater than that of WF-SIB IMRT, respectively. The delivery accuracy of WF-SIB VMAT was not affected by the increased freedom.For patients with NPC, one-arc WF-SIB VMAT might not be able to achieve sufficient TC, whereas two-arc WF-SIB VMAT was able to achieve reasonable TC. No significant advantage on OAR protection was demonstrated by VMAT compared with IMRT. WF-SIB VMAT has significantly shorter delivery times, but WF-SIB IMRT may still be the first treatment choice for patients with NPC.     

Dosimetric assessment of the mono and dual-isocentric VMAT technique based on flattening filter-free beams for SBRT with non-contiguous spinal targets

The study aimed to evaluate the planning characteristics of spinal stereotactic body radiotherapy (SBRT) using mono- and dual-isocentric volumetrically modulated arc therapy (VMAT) techniques. The dosimetric indices were compared between different beam arrangement techniques for spinal SBRT planning, including spinal cord avoidance, planning target volume (PTV) dose coverage, conformity, homogeneity, and gradient index. A total of 8 PTVs were contoured on RANDO phantom computed tomography (CT) images, with 4 PTVs per section of the spine (thoracic and lumbar). VMAT plans for each PTV were generated using 4 different beam arrangement techniques with a 6-MV FFF photon beam, two of which were mono-isocentric (MI) and 2 of which were dual-isocentric (DI). Dose calculations for all plans were performed using the Acuros XB algorithm. The study found that when non-contiguous spinal lesions are widely spaced, it may be more effective to use 4-Arcs DI to generate a better homogeneity index and gradient index, whereas 2-Arcs MI was beneficial for closely spaced lesions. Furthermore, the use of more arcs with a dual isocenter reduced the volume of partial cord receiving 10 Gy (V_10Gy), maximum dose to 0.03 cc of partial cord (D_0.03cc), and monitor units (MUs). The results showed that DI has a higher plan quality than MI for treating non-contiguous spine SBRT, with better homogeneity and a lower dose to the spinal cord, as well as comparable tumor coverage, delivery accuracy, and adequate tumour coverage. 4-Arcs DI had the sharpest dose falloff and achieved the lowest overall spinal cord doses at the expense of twice the treatment time as 2Arcs-MI. These results could help figure out which VMAT beam arrangements are best for treating non-contiguous spinal tumors.