容积旋转调强与固定野动态调强在宫颈癌术后放疗的剂量学比较

目的 比较容积旋转调强（RapidArc）与固定野动态调强（IMRT）两种宫颈癌术后放疗的剂量学参数及急性不良反应发生率,为临床治疗技术的选择提供参考依据。方法 选取35例宫颈癌术后盆腔预防放疗患者,其中,17例接受RapidArc,18例接受IMRT,处方剂量50 Gy,共25次。比较两组治疗计划的剂量-体积直方图（DVH）、靶区剂量适形度、均匀性、靶区及危及器官的剂量、机器跳数及治疗时间;对比两组患者治疗期间的急性肠道及膀胱反应发生率。结果 与IMRT相比,RapidArc靶区剂量适形度较高（t=3.13,P<0.05）,但均匀性略低（t=-4.25,P<0.05）;RapidArc计划中股骨头V₂₀、V₃₀均低于IMRT（t=2.56、2.34,P<0.05）;RapidArc计划机器跳数减少了52.1%,治疗所需时间缩短了46.8%。两组患者肠道、膀胱急性不良反应发生率相近。结论 对于宫颈癌术后盆腔预防放疗患者,采用RapidArc或IMRT技术均可达到靶区的剂量要求及保护危及器官的目的。RapidArc计划靶区剂量学参数、急性不良反应发生率与IMRT计划比较未见明显优势,但机器跳数与出束时间明显优于IMRT计划,实现了治疗效率的大幅提高。     

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.     

Effect of collimator angle on HyperArc stereotactic radiosurgery planning for single and multiple brain metastases

We assessed the effect of collimator angle on the dosimetric parameters for targets and organs at risk (OARs) for collimator-optimized HA (CO-HA) and non-CO-HA (nCO-HA) plans. The nCO-HA and CO-HA plans were retrospectively generated for 26 patients (1 to 8 brain metastases). The dosimetric parameters for planning target volume (homogeneity index [HI]; conformity index [CI]; gradient index [GI]) and for OARs were compared. The modulation complexity score for volumetric modulated arc therapy (MCSV) and monitor units (MUs) were calculated. Doses were measured using the electronic portal imaging device and compared with the expected doses. Dosimetric parameters of the HI, CI, and GI for single (n = 12) and multiple (n = 14) metastases cases were comparable (p > 0.05). For multiple metastases cases, the CO-HA plan provided lower V_4Gy, V_12Gy, V_14Gy, V_16Gy for brain tissue compared to the nCO-HA plan (p < 0.05). Doses for OARs (D_0.1cc) (brainstem, chiasm, Hippocampus, lens, optic nerves, and retinas) were comparable (p > 0.05). For multiple metastases cases, the CO-HA plan resulted in less complex multileaf collimator (MLC) patterns (MCSV = 0.19 ± 0.04, p < 0.01), lower MUs (8596 ± 1390 MUs, p < 0.01), and shorter beam-on time (6.2 ± 1.0 min, p < 0.01) compared to the nCO-HA plan (0.16 ± 0.04, 9365 ± 1630, and 6.7 ± 1.2 for MCSV, MUs, and beam-on time, respectively). For both treatment approach, the equivalent gamma passing rate was obtained with the 3%/3 mm and 2%/2 mm criteria (p > 0.05). The collimator optimization in the HA planning reduced doses to brain tissues and improved the treatment efficacy.     

Volumetric modulated arc radiotherapy for esophageal cancer

A treatment planning study was performed to evaluate the performance of volumetric arc modulation with RapidArc (RA) against 3D conformal radiation therapy (3D-CRT) and conventional intensity-modulated radiation therapy (IMRT) techniques for esophageal cancer. Computed tomgraphy scans of 10 patients were included in the study. 3D-CRT, 4-field IMRT, and single-arc and double-arc RA plans were generated with the aim to spare organs at risk (OAR) and healthy tissue while enforcing highly conformal target coverage. The planning objective was to deliver 54 Gy to the planning target volume (PTV) in 30 fractions. Plans were evaluated based on target conformity and dose-volume histograms of organs at risk (lung, spinal cord, and heart). The monitor unit (MU) and treatment delivery time were also evaluated to measure the treatment efficiency. The IMRT plan improves target conformity and spares OAR when compared with 3D-CRT. Target conformity improved with RA plans compared with IMRT. The mean lung dose was similar in all techniques. However, RA plans showed a reduction in the volume of the lung irradiated at V_20Gy and V_30Gy dose levels (range, 4.62–17.98%) compared with IMRT plans. The mean dose and D_35% of heart for the RA plans were better than the IMRT by 0.5–5.8%. Mean V_10Gy and integral dose to healthy tissue were almost similar in all techniques. But RA plans resulted in a reduced low-level dose bath (15–20 Gy) in the range of 14–16% compared with IMRT plans. The average MU needed to deliver the prescribed dose by RA technique was reduced by 20–25% compared with IMRT technique. The preliminary study on RA for esophageal cancers showed improvements in sparing OAR and healthy tissue with reduced beam-on time, whereas only double-arc RA offered improved target coverage compared with IMRT and 3D-CRT plans.     

Dosimetric difference amongst 3 techniques: TomoTherapy,sliding-window intensity-modulated radiotherapy (IMRT), and RapidArc radiotherapy in the treatment of late-stage nasopharyngeal carcinoma (NPC)

To investigate the dosimetric difference amongst TomoTherapy, sliding-window intensity-modulated radiotherapy (IMRT), and RapidArc radiotherapy in the treatment of late-stage nasopharyngeal carcinoma (NPC). Ten patients with late-stage (Stage III or IV) NPC treated with TomoTherapy or IMRT were selected for the study. Treatment plans with these 3 techniques were devised according to departmental protocol. Dosimetric parameters for organ at risk and treatment targets were compared between TomoTherapy and IMRT, TomoTherapy and RapidArc, and IMRT and RapidArc. Comparison amongst the techniques was done by statistical tests on the dosimetric parameters, total monitor unit (MU), and expected delivery time. All 3 techniques achieved similar target dose coverage. TomoTherapy achieved significantly lower doses in lens and mandible amongst the techniques. It also achieved significantly better dose conformity to the treatment targets. RapidArc achieved significantly lower dose to the eye and normal tissue, lower total MU, and less delivery time. The dosimetric advantages of the 3 techniques were identified in the treatment of late-stage NPC. This may serve as a guideline for selection of the proper technique for different clinical cases.     

三维适形、逆向调强和旋转调强放疗技术治疗胸段食管癌的剂量学比较

目的 比较胸段食管癌3种放疗技术( 3D-CRT、IMRT、RapidArc)的剂量学特点,并分析3种技术的优劣及应用特点.方法 15例胸段食管癌患者入组,依据CT图像,勾画靶区,针对患者的同一套CT图像的相同靶区分别制定3D-CRT、5野IMRT(IMRT5)、7野IMRT( IMRT7)、9野IMRT(IMRT9)、单弧Arc( Arc1)、双弧Arc( Arc2)共6套计划.PTV处方剂量为40 Gy分20次4周+19.6 Gy分14次7d.结果 3D-CRT计划各项靶区剂量学参数明显差于IMRT计划及RapidArc计划(t=5.77、3.52,P＜0.05),6套计划的PTV V95(％)分别为:3D-CRT (91.55 ±2.90),IMRT5(96.66±1.05),IMRT7 (96.87±1.23),IMRT (96.81±1.16),Arcl (94.98±1.41),Arc2 (95.93±1.32).RapidArc计划的靶区适形度(CI)最好(t=3.76,10.01,P＜0.05),IMRT计划的靶区均匀性(HI)最好(t =3.93、3.37,P＜0.05).危及器官参数RapidArc与IMRT各计划之间差异无统计学意义.3D-CRT和RapidArc计划的机器跳数明显少于IMRT计划,差异高达75％.结论 对于胸段食管癌患者,采用IMRT或RapidArc技术可以在保护正常组织的同时,涵盖临床必需的治疗靶区.3D-CRT计划对降低正常组织低剂量散射区方面优势明显.RapidArc计划靶区剂量学参数与IMRT计划比较未见明显优势.     

HybridArc: A novel radiation therapy technique combining optimized dynamic arcs and intensity modulation

This investigation focuses on possible dosimetric and efficiency advantages of HybridArc—a novel treatment planning approach combining optimized dynamic arcs with intensity-modulated radiation therapy (IMRT) beams. Application of this technique to two disparate sites, complex cranial tumors, and prostate was examined. HybridArc plans were compared with either dynamic conformal arc (DCA) or IMRT plans to determine whether HybridArc offers a synergy through combination of these 2 techniques. Plans were compared with regard to target volume dose conformity, target volume dose homogeneity, sparing of proximal organs at risk, normal tissue sparing, and monitor unit (MU) efficiency. For cranial cases, HybridArc produced significantly improved dose conformity compared with both DCA and IMRT but did not improve sparing of the brainstem or optic chiasm. For prostate cases, conformity was improved compared with DCA but not IMRT. Compared with IMRT, the dose homogeneity in the planning target volume was improved, and the maximum doses received by the bladder and rectum were reduced. Both arc-based techniques distribute peripheral dose over larger volumes of normal tissue compared with IMRT, whereas HybridArc involved slightly greater volumes of normal tissues compared with DCA. Compared with IMRT, cranial cases required 38% more MUs, whereas for prostate cases, MUs were reduced by 7%. For cranial cases, HybridArc improves dose conformity to the target. For prostate cases, dose conformity and homogeneity are improved compared with DCA and IMRT, respectively. Compared with IMRT, whether required MUs increase or decrease with HybridArc was site-dependent.     

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 RapidArc with Fixed Gantry Intensity-Modulated Radiotherapy Treatment for Multiple Liver Metastases Radiotherapy

We wanted to compare the dosimetric difference and treatment efficiency of RapidArc and fixed gantry intensity-modulated radiotherapy treatment (IMRT) for multiple liver metastases. Computed tomography datasets of 10 patients were studied retrospectively. IMRT plans were generated using 5 fields and RapidArc using either 1 or 2 arcs. The dose distribution of planning target volume (PTV), organs at risk (OARs), and the normal tissue were compared. Monitor units and treatment time were scored to measure expected treatment efficiency. Both RapidArc and IMRT plans resulted in equivalent target coverage. There was no statistically significant difference for the maximum and the minimum dose of PTV. RapidArc plans achieved an improved conformity index compared with IMRT (RA1 = 1.68 ± 0.27, RA2 = 1.61 ± 0.25, IMRT = 1.80 ± 0.37). For OARs, all techniques respected planning objectives. RapidArc plans had a lower dose in V₄₀ of small bowel than IMRT, but were higher in mean dose of kidneys. Concerning the V₅, V₁₀, and V₁₅ of healthy tissue, RapidArc plans were higher than IMRT. However, the V₂₀, V₂₅, and V₃₀ of healthy tissue in RapidArc plans were lower than IMRT. Monitor units per fraction of RapidArc plans were about 40% or 46% of IMRT. Compared with IMRT plans, treatment time of RapidArc plans were reduced by 60% or 70%. All techniques respected planning objectives. RapidArc showed statistical improvements in conformity index and healthy tissue sparing with uncompromised target coverage. This, in combination with fewer monitor units and short delivery time, can lead to clinically significant advances for the treatment of multiple liver metastases.     

Superiority of Equivalent Uniform Dose (EUD)-Based Optimization for Breast and Chest Wall*

We investigate whether IMRT optimization based on generalized equivalent uniform dose (gEUD) objectives for organs at risk (OAR) results in superior dosimetric outcomes when compared with multiple dose-volume (DV)–based objectives plans for patients with intact breast and postmastectomy chest wall (CW) cancer. Four separate IMRT plans were prepared for each of the breast and CW cases (10 patients). The first three plans used our standard in-house, physician-selected, DV objectives (phys-plan); gEUD-based objectives for the OARs (gEUD-plan); and multiple, “very stringent,” DV objectives for each OAR and PTV (DV-plan), respectively. The fourth plan was only beam-fluence optimized (FO-plan), without segmentation, which used the same objectives as in the DV-plan. The latter plan was to be used as an “optimum” benchmark without the effects of the segmentation for deliverability. Dosimetric quantities, such as V_20Gy for the ipsilateral lung and mean dose (D_mean) for heart, contralateral breast, and contralateral lung were used to evaluate the results. For all patients in this study, we have seen that the gEUD-based plans allow greater sparing of the OARs while maintaining equivalent target coverage. The average ipsilateral lung V_20Gy reduced from 22 ± 4.4% for the FO-plan to 18 ± 3% for the gEUD-plan. All other dosimetric quantities shifted towards lower doses for the gEUD-plan. gEUD-based optimization can be used to search for plans of different DVHs with the same gEUDs. The use of gEUD allows selective optimization and reduction of the dose for each OAR and results in a truly individualized treatment plan.     

旋转调强与固定野调强治疗肝癌的剂量学比较

目的 比较旋转调强(RapidArc)与固定野调强放疗(IMRT)在肝癌治疗计划中的剂量学差异。方法 选择10例肝癌患者的CT数据,分别设计IMRT计划与单弧(RA1)和双弧(RA2)计划,比较设计计划的靶区剂量分布、危及器官受量、正常组织受量、机器跳数以及治疗时间。结果 RA1和RA2计划靶区剂量的最大值都低于IMRT(Z=-2.090、-2.666,P＜0.05),计划90%的处方剂量的适形指数低于IMRT(Z=-2.805、-2.809,P＜0.05);危及器官胃与小肠的V40也比IMRT计划低。但IMRT左肾平均剂量低于RapidArc计划组(Z=-1.988、-2.191,P＜0.05);正常组织的V₅、V₁₀和V₁₅IMRT计划低于RapidArc计划组,V20、V25和V30IMRT计划高于RapidArc计划组。RapidArc计划机器跳数是IMRT计划的40%和46%,治疗时间是IMRT计划30%和40%。结论 两种技术设计的计划剂量分布均能满足临床要求,并且剂量分布基本一致。RapidArc计划的适形指数优于IMRT,危及器官剂量也比IMRT计划略有降低,正常组织的低剂量区RapidArc计划组与IMRT相比有先高后低的趋势,并且机器跳数少,治疗时间短。     

Dosimetric comparison of different multileaf collimator leaves in treatment planning of intensity-modulated radiotherapy for cervical cancer

To study the effect of multileaf collimator (MLC) leaf widths (standard MLC [sMLC] width of 10 mm and micro-MLC [mMLC] width of 4 mm) on intensity-modulated radiotherapy (IMRT) for cervical cancer. Between January 2010 and August 2010, a retrospective analysis was conducted on 12 patients with cervical cancer. The treatment plans for all patients were generated with the same machine setup parameters and optimization methods in a treatment planning system (TPS) based on 2 commercial Elekta MLC devices. The dose distribution for the planning tumor volume (PTV), the dose sparing for organs at risk (OARs), the monitor units (MUs), and the number of IMRT segments were evaluated. For the delivery efficiency, the MUs were significantly higher in the sMLC-IMRT plan than in the mMLC-IMRT plan (802 ± 56.9 vs 702 ± 56.7; p < 0.05). The number of segments in the plans were 58.75 ± 1.8 and 59 ± 1.04 (p > 0.05). For the planning quality, the conformity index (CI) between the 2 paired IMRT plans with the mMLC and the sMLC did not differ significantly (average: 0.817 ± 0.024 vs 0.810 ± 0.028; p > 0.05). The differences of the homogeneity index (HI) between the 2 paired plans were statistically significant (average: 1.122 ± 0.010 vs 1.132 ± 0.014; p < 0.01). For OARs, the rectum, bladder, small intestine, and bony pelvis were evaluated in terms of V₁₀, V₂₀, V₃₀, and V₄₀, percentage of contoured OAR volumes receiving 10, 20, 30, and 40 Gy, respectively, and the mean dose (D_mean) received. The IMRT plans with the mMLC protected the OARs better than the plans with the sMLC. There were significant differences (p < 0.05) in evaluated parameters between the 2 paired IMRT plans, except for V₃₀ and V₄₀ of the rectum and V₁₀, V₂₀, V₄₀, and D_mean of the bladder. IMRT plans with the mMLC showed advantages over the plans with the sMLC in dose homogeneity for targets, dose sparing of OARs, and fewer MUs in cervical cancer.     

Dosimetric research on intensity-modulated arc radiotherapy planning for left breast cancer after breast-preservation surgery

Intensity-modulated radiotherapy (IMRT) has played an important role in breast cancer radiotherapy after breast-preservation surgery. Our aim was to study the dosimetric and implementation features/feasibility between IMRT and intensity-modulated arc radiotherapy (Varian RapidArc, Varian, Palo Alto, CA). The forward IMRT plan (f-IMRT), the inverse IMRT, and the RapidArc plan (RA) were generated for 10 patients. Afterward, we compared the target dose distribution of the 3 plans, radiation dose on organs at risk, monitor units, and treatment time. All 3 plans met clinical requirements, with RA performing best in target conformity. In target homogeneity, there was no statistical significance between RA and IMRT, but both of homogeneity were less than f-IMRT's. With regard to the V₅ and V₁₀ of the left lung, those in RA were higher than in f-IMRT but were lower than in IMRT; for V₂₀ and V₃₀, the lowest was observed in RA; and in the V₅ and V₁₀ of the right lung, as well as the mean dose in normal-side breast and right lung, there was no statistically significance difference between RA and IMRT, and the lowest value was observed in f-IMRT. As for the maximum dose in the normal-side breast, the lowest value was observed in RA. Regarding monitor units (MUs), those in RA were higher than in f-IMRT but were lower than in IMRT. Treatment time of RA was 84.6% and 88.23% shorter than f-IMRT and IMRT, respectively, on average. Compared with f-IMRT and IMRT, RA performed better in target conformity and can reduce high-dose volume in the heart and left lung—which are related to complications—significantly shortening treatment time as well. Compared with IMRT, RA can also significantly reduce low-dose volume and MUs of the afflicted lung.     

RapidArc radiotherapy planning for prostate cancer: Single-arc and double-arc techniques vs. intensity-modulated radiotherapy

RapidArc is a novel technique using arc radiotherapy aiming to achieve intensity-modulated radiotherapy (IMRT)-quality radiotherapy plans with shorter treatment time. This study compared the dosimetric quality and treatment efficiency of single-arc (SA) vs. double-arc (DA) and IMRT in the treatment of prostate cancer. Fourteen patients were included in the analysis. The planning target volume (PTV), which contained the prostate gland and proximal seminal vesicles, received 76 Gy in 38 fractions. Seven-field IMRT, SA, and DA plans were generated for each patient. Dosimetric quality in terms of the minimum PTV dose, PTV hotspot, inhomogeneity, and conformity index; and sparing of rectum, bladder, and femoral heads as measured by V70, V-40, and V20 (% of volume receiving >70 Gy, 40 Gy, and 20 Gy, respectively), treatment efficiency as assessed by monitor units (MU) and treatment time were compared. All plan objectives were met satisfactorily by all techniques. DA achieved the best dosimetric quality with the highest minimum PTV dose, lowest hotspot, and the best homogeneity and conformity. It was also more efficient than IMRT. SA achieved the highest treatment efficiency with the lowest MU and shortest treatment time. The mean treatment time for a 2-Gy fraction was 4.80 min, 2.78 min, and 1.30 min for IMRT, DA, and SA, respectively. However, SA also resulted in the highest rectal dose. DA could improve target volume coverage and reduce treatment time and MU while maintaining equivalent normal tissue sparing when compared with IMRT. SA achieved the greatest treatment efficiency but with the highest rectal dose, which was nonetheless within tolerable limits. For busy units with high patient throughput, SA could be an acceptable option.     

胸上段食管癌无均整器容积弧形调强与固定野调强放疗计划的剂量学比较

目的 探讨在瓦里安TrueBeam^TM直线加速器中使用无均整器出束容积弧形调强(RA-FFF)及常规固定野调强(IMRT)两种计划剂量学差异.方法 选择10例分期为cT_2-3N_0-1M_0-1a胸上段食管癌患者定位CT资料,使用ECLIPSE^TM 10.0.4治疗计划系统分别设计RA-FFF、IMRT根治性放疗计划,处方剂量为60 Gy/30次,比较2种计划的剂量学参数和执行效率.结果 2种计划靶区适形度相似,差异无统计学意义;IMRT计划的均匀性指数高于RA-FFF计划(t=7.298,P=0.008);RA-FFF计划中肺组织的V₂₀、V₅低于IMRT计划(t=2.451、2.604,P<0.05).RA-FFF及IMRT两种计划制定时间分别为(5.3±1.4)、(3.5±1.7)h(t=2.585,P<0.05),机器总跳数分别为632±213及734±132(t=-1.287,P=0.084),治疗执行时间分别为(2.2±0.9)、(4.5±1.3)min(t=4.60,P<0.01).结论 与IMRT计划相比,RA-FFF在胸上段食管癌治疗中具有相似的靶区剂量分布,可更好地保护肺组织,计划制定时间较长但执行效率较高.     

The effect of the target-organ geometric complexity on the choice of delivery between RapidArc and sliding-window IMRT for nasopharyngeal carcinoma

We attempted to assess the effect of target-organ geometric complexity on the plan quality of sliding-window intensity-modulated radiotherapy (IMRT), double-arc (RA2), and triple-arc (RA3) RapidArc volumetric-modulated arc radiotherapy for nasopharyngeal carcinoma (NPC). Plans for 9-field sliding-window IMRT, RA2, and RA3 were optimized for 36 patients with NPC ranging from T1 to T4 tumors. Initially the patients were divided into 2 groups, with group A representing the most simple early stage (T1 and T2) cases, whereas group B represented the more complex advanced cases (T3 and T4). Evaluation was performed based on target conformity, target dose homogeneity, organ-sparing capability, and delivery efficiency. Based on the plan quality results, a subgroup of advanced cases, group B2, representing the most demanding task was distinguished and reported separately from the rest of the group B cases, B1. Detailed analysis was performed on the anatomic features for each group of cases, so that planners can easily identify the differences between B1 and B2. For the group A cases, RA3 plans were superior to the IMRT plans in terms of organ sparing, whereas target conformity and dose homogeneity were similar. For the group B1 cases, the RA3 plans produced almost equivalent plan quality as the IMRT plans. For the group B2 cases, for most of which large target volumes were adjacent to (5 mm or less) and wrapping around the brain stem, RA2 and RA3 were inferior to the IMRT regarding both target dose homogeneity and conformity. RA2 plans were slightly inferior to IMRT and RA3 plans for most cases. The plan comparison results depend on the target to brain stem distances and the target sizes. The plan quality results together with the anatomic information may allow the evaluation of the 3 treatment options before actual planning.     

Improvement in plan quality after Implementation of clinical goals in a large network of cancer centers

Clinical Goals (CG) is a tool available in the Varian Eclipse planning system to objectively and visually evaluate the quality of treatment plans based upon user-defined dose-volume parameters. We defined a set of CG for Stereotactic Radiosurgery (SRS) and Intensity-Modulated Radiotherapy (IMRT) based on published data and guidelines and implemented this in a network of cancer centers in India (American Institute of Oncology). A dosimetric study was performed to compare brain SRS and breast IMRT plan quality before and after CG implementation.The CG defined for SRS plans were target V_100% ≥ 98%, dose gradient measure (GM) ≤ 0.5 cm, conformity index (CI) 1.0 to 1.2. For breast IMRT plans, CG defined target V_100% ≥ 97%, V_95% ≥ 95%, V_107% ≤ 2%, V_105% ≤ 10%, and D_max ≤ 2.4 Gy. Dose limits to organs-at-risk (OAR) were summarize in supplemental materials. Twenty brain SRS and 10 breast IMRT treatment plans that were previously delivered on patients were selected and re-planned using CG. The pre and postoptimized plan parameters were compared using student t-tests.For brain SRS plans, the V₁₀₀, GM, and CI for the pre- and post-Clinical-Goals plans were 93.22% ± 7.2% vs 97.96% ± 0.29% (p = 0.009), 0.63 ± 0.16 vs 0.42 ± 0.05 (p < 0.001) and 1.07 ± 0.18 vs 1.06 ± 0.06 (p = 0.79), respectively. There were no differences in max dose to OARs. In breast IMRT plans, the target V_107% for pre and postimplemented plans were 16.50% ± 10.98% vs 0.32% ± 0.32%, respectively (p = 0.001). The average target V_105% were 44.00% ± 15.72% and 8.69% ± 4.53%, respectively (p < 0.001). No differences were found in the average target V_100% (p = 0.128) and V_95% (p = 0.205). The average target D_max were 112.28% ± 1.59% and 109.14% ± 0.73%, respectively (p < 0.001). There were only minor differences in doses to OARs.The implementation of CG in Varian Eclipse significantly improved SRS and IMRT plan quality with enhanced coverage, dose GM, and CI without increased dose to OARs.     

Comparison of IMRT and VMAT plans with different energy levels using Monte-Carlo algorithm for prostate cancer

Purpose

To make dosimetric comparisons of volumetric-modulated arc therapy (VMAT) and 7-field intensity-modulated radiotherapy (IMRT) with dynamic MLCs using the Monaco treatment planning system with Monte Carlo algorithm.

Materials and methods

Single-arc VMAT and 7-field IMRT treatment plans were compared for 12 intermediate risk prostate cancer patients treated with prostate and seminal vesicle radiotherapy. For all patients, the prescribed dose was 78 Gy delivered in 39 fractions. The dosimetric data of IMRT and VMAT plans with 6, 10 and 15 MV energies were compared. The comparison was made for target volume, organs at risk (OAR) doses, and for monitor units (MU).

Results

The normal tissue surrounding the target were lower in VMAT plans compared to IMRT plans. VMAT plans achieved lower doses to all OARs for nearly all dosimetric endpoints. VMAT plans achieved 9.4, 9.0 and 7.0 % relative decrease in MUs required for RT delivery, for 6, 10 and 15 MV energy levels, respectively. The target volume and OAR dosimetric values did not differ significantly between 6, 10 and 15 MV photon energies.

Conclusion

VMAT plans were found to be dosimetrically equivalent to IMRT plans for prostate cancer patients, with better rectum and bladder sparing and fewer MUs required.