Reducing the Risk of Xerostomia and Mandibular Osteoradionecrosis: The Potential Benefits of Intensity Modulated Radiotherapy in Advanced Oral Cavity Carcinoma

Radiation therapy for squamous cell carcinoma of the oral cavity may be curative, but carries a risk of permanent damage to bone, salivary glands, and other soft tissues. We studied the potential of intensity modulated radiotherapy (IMRT) to improve target volume coverage, and normal tissue sparing for advanced oral cavity carcinoma (OCC). Six patients with advanced OCC requiring bilateral irradiation to the oral cavity and neck were studied. Standard 3D conformal radiotherapy (3DCRT) and inverse-planned IMRT dose distributions were compared by using dose-volume histograms. Doses to organs at risk, including spinal cord, parotid glands, and mandible, were assessed as surrogates of radiation toxicity. PTV1 mean dose was 60.8 ± 0.8 Gy for 3DCRT and 59.8 ± 0.1 Gy for IMRT (p = 0.04). PTV1 dose range was 24.7 ± 6 Gy for 3DCRT and 15.3 ± 4 Gy for IMRT (p = 0.001). PTV2 mean dose was 54.5 ± 0.8 Gy for 3DCRT and for IMRT was 54.2 ± 0.2 Gy (p = 0.34). PTV2 dose range was improved by IMRT (7.8 ± 3.2 Gy vs. 30.7 ± 12.8 Gy, p = 0.006). Homogeneity index (HI) values for PTV2 were closer to unity using IMRT (p = 0.0003). Mean parotid doses were 25.6 ± 2.7 Gy for IMRT and 42.0 ± 8.8 Gy with 3DCRT (p = 0.002). The parotid V30 in all IMRT plans was <45%. The mandible V50, V55, and V60 were significantly lower for the IMRT plans. Maximum spinal cord and brain stem doses were similar for the 2 techniques. IMRT provided superior target volume dose homogeneity and sparing of organs at risk. The magnitude of reductions in dose to the salivary glands and mandible are likely to translate into reduced incidence of xerostomia and osteoradionecrosis for patients with OCC.     

Escalated median dose for pituitary macroadenomas using intensity-modulated radiation therapy.

Three-dimensional conformal radiotherapy (3D CRT) has become an established treatment for pituitary macroadenomas. This study is an investigation into the possible dosimetric advantages of intensity-modulated radiotherapy for such critically located tumors. Three consecutive patients with pituitary macroadenoma previously treated with 3D CRT were replanned with inverse-planned IMRT using Helax-TMS (V.6.0, Helax AB, Uppsala, Sweden. Fusion of computed tomography (CT) with postoperative magnetic resonance imaging (MRI) was performed within the planning system to define the gross tumor volume (GTV), planning target volume (PTV), and normal structures including the optic chiasm. Dose-volume histograms (DVHs) for the 3D CRT plans were then compared with those of the corresponding prospective IMRT plans. Both techniques maintained critical structure doses below tolerance levels while maintaining a minimum dose of 45 Gy to 100% of the PTV. While IMRT plans deliver consistently more heterogeneous dose distributions to the PTV, the median PTV dose is elevated in the IMRT plans compared with the 3D CRT plans. For critically located tumors like these pituitary macroadenomas, IMRT allows escalation of the median dose to the tumor without an accompanying loss in critical structure sparing or creating unacceptable cold spots within the PTV.     

Superiority of conventional intensity-modulated radiotherapy over helical tomotherapy in locally advanced non-small cell lung cancer

PURPOSE: To compare helical tomotherapy (HT) and conventional intensity-modulated radiotherapy (IMRT) using a variety of dosimetric and radiobiologic indexes in patients with locally advanced non-small cell lung cancer (LA-NSCLC). PATIENTS AND METHODS: A total of 20?patients with LA-NSCLC were enrolled. IMRT plans with 4-6 coplanar beams and HT plans were generated for each patient. Dose distributions and dosimetric indexes for the tumors and critical structures were computed for both plans and compared. RESULTS: Both modalities created highly conformal plans. They did not differ in the volumes of lung exposed to >?20?Gy of radiation. The average mean lung dose, volume receiving ≥?30?Gy, and volume receiving ≥?10?Gy in HT planning were 18.3?Gy, 18.5%, and 57.1%, respectively, compared to 19.4?Gy, 25.4%, and 48.9%, respectively, with IMRT (p?=?0.004, p?相似文献   

宫颈癌术后螺旋断层放疗与常规加速器调强放疗的剂量学比较

目的 研究宫颈癌术后螺旋断层放疗(helical tomotherapy,HT)与常规静态调强放疗(IMRT)的剂量学特点。方法 采用10例宫颈癌术后患者CT图像,统一勾画靶区及危及器官(膀胱、直肠、小肠及双侧股骨头),分别传输至HT计划系统和IMRT计划系统,比较两组计划剂量体积直方图、适形度指数(CI)、均匀指数(HI)和危及器官所接受的照射剂量和体积,统一给予阴道残端60 Gy/25次,亚临床病灶50 Gy/25次,同时限定膀胱、直肠、小肠、股骨头等危及器官受照射剂量与体积。统一应用50 Gy处方剂量评价和比较CI和HI。结果 HT组适形指数(0.94±0.03)和均匀指数(1.28±0.02)均明显好于IMRT组(0.85±0.01和1.36±0.03)(t =5.12和-6.34, P<0.01);HT组PTV平均剂量为51.77Gy显著低于IMRT组54.53Gy(t =-8.01, P<0.05);HT组膀胱、直肠和小肠最大剂量、平均剂量、V₃₀、V₄₀和V₅₀照射体积均显著低于IMRT组;HT组左、右侧股骨头最大剂量、平均剂量、V₃₀和V₄₀照射体积均显著低于IMRT组。结论 HT与IMRT计划均有较好的靶区剂量分布,但HT组在适形指数、均匀指数及对周围危及器官的保护均比IMRT组有明显优势。     

Helical Tomotherapy-Based STAT RT: Dosimetric Evaluation for Clinical Implementation of a Rapid Radiation Palliation Program

Helical tomotherapy–based STAT radiation therapy (RT) uses an efficient software algorithm for rapid intensity-modulated treatment planning, enabling conformal radiation treatment plans to be generated on megavoltage computed tomography (MVCT) scans for CT simulation, treatment planning, and treatment delivery in one session. We compared helical tomotherapy–based STAT RT dosimetry with standard linac-based 3D conformal plans and standard helical tomotherapy–based intensity-modulated radiation therapy (IMRT) dosimetry for palliative treatments of whole brain, a central obstructive lung mass, multilevel spine disease, and a hip metastasis. Specifically, we compared the conformality, homogeneity, and dose with regional organs at risk (OARs) for each plan as an initial step in the clinical implementation of a STAT RT rapid radiation palliation program. Hypothetical planning target volumes (PTVs) were contoured on an anthropomorphic phantom in the lung, spine, brain, and hip. Treatment plans were created using three planning techniques: 3D conformal on Pinnacle³, helical tomotherapy, and helical tomotherapy–based STAT RT. Plan homogeneity, conformality, and dose to OARs were analyzed and compared. STAT RT and tomotherapy improved conformality indices for spine and lung plans (CI spine = 1.21, 1.17; CI lung = 1.20, 1.07, respectively) in comparison with standard palliative anteroposterior/posteroanterior (AP/PA) treatment plans (CI spine = 7.01, CI lung = 7.30), with better sparing of heart, esophagus, and spinal cord. For palliative whole-brain radiotherapy, STAT RT and tomotherapy reduced maximum and mean doses to the orbits and lens (maximum/mean lens dose: STAT RT = 2.94/2.65 Gy, tomotherapy = 3.13/2.80 Gy, Lateral opposed fields = 7.02/3.65 Gy), with an increased dose to the scalp (mean scalp dose: STAT RT = 16.19 Gy, tomotherapy = 15.61 Gy, lateral opposed fields = 14.01 Gy). For bony metastatic hip lesions, conformality with both tomotherapy techniques (CI = 1.01 each) is superior to AP/PA treatments (CI = 1.21), as expected. Helical tomotherapy–based STAT RT treatment planning provides clinically acceptable dosimetry, with conformality and homogeneity that is superior to standard linac-based 3D conformal planning and is only slightly inferior to standard helical tomotherapy IMRT dosimetry. STAT RT facilitates rapid treatment planning and delivery for palliative radiation of patients with metastatic disease, with relative sparing of adjacent OARs compared with standard 3D conformal plans.     

Adjuvant Radiotherapy for Gastric Cancer: A Dosimetric Comparison of 3-Dimensional Conformal Radiotherapy,Tomotherapy® and Conventional Intensity Modulated Radiotherapy Treatment Plans

Some patients with gastric cancer benefit from post-operative chemo-radiotherapy, but adequately irradiating the planning target volume (PTV) whilst avoiding organs at risk (OAR) can be difficult. We evaluate 3-dimensional conformal radiotherapy (CRT), conventional intensity-modulated radiotherapy (IMRT) and helical tomotherapy (TT). TT, 2 and 5-field (F) CRT and IMRT treatment plans with the same PTV coverage were generated for 5 patients and compared. Median values are reported. The volume of left/right kidney receiving at least 20Gy (V20) was 57/51% and 51/60% for 2 and 5F-CRT, and 28/14% for TT and 27/19% for IMRT. The volume of liver receiving at least 30Gy (V30) was 45% and 62% for 2 and 5F-CRT, and 37% for TT and 35% for IMRT. With TT, 98% of the PTV received 95-105% of the prescribed dose, compared with 45%, 34% and 28% for 2F-CRT, 5F-CRT and IMRT respectively. Using conventional metrics, conventional IMRT can achieve comparable PTV coverage and OAR sparing to TT, but at the expense of PTV dose heterogeneity. Both irradiate large volumes of normal tissue to low doses. Additional studies are needed to demonstrate the clinical impact of these technologies.     

Dosimetric comparison of 3-dimensional conformal radiotherapy,volumetric modulated arc therapy,and helical tomotherapy for postoperative gastric cancer patients

Purpose

To compare dosimetric data for the planning target volume (PTV) and organs at risk (OARs) between 3-dimensional conformal radiotherapy (3DCRT), volumetric modulated arc therapy (VMAT), and helical tomotherapy [1].

Materials and methods

The dosimetric data for 15 gastric cancer patients treated with 3DCRT, VMAT, or HT techniques were used. Cumulative dosimetric parameters, homogeneity index (HI), and conformal index (CI) were compared for the PTV and OARs.

Results

The average maximum doses of PTV were significantly higher in VMAT plans than in 3DCRT (p = 0.04) and HT (p = 0.02) plans, whereas minimum dose values were significantly lower in 3DCRT plans compared with VMAT (p < 0.001) and HT (p = 0.02) plans. Liver mean dose (D _mean) and D _mean values for both kidneys were significantly lower in HT plans than in 3DCRT and VMAT plans. The doses in high dose regions (V30–V45) using 3DCRT plans were significantly higher compared to both VMAT and HT plans. The bowel V5–V30 and V45 was significantly less in HT plans compared to VMAT plans. There were no significant differences in dose sparing of the spinal cord.

Conclusions

The HT plans reduced the maximum dose applied to the target and improved the conformality and homogeneity of radiation, while providing sufficient PTV coverage.

     

胸段食管癌患者三种放疗计划心脏和肺的剂量学比较

目的 比较胸中下段食管癌3种放疗技术心脏和肺的剂量分布。方法 搜集2015年1月至2016年2月在浙江省肿瘤医院接受治疗的15例胸中下段食管鳞癌患者资料。患者均接受胸部放射治疗,每位患者共制作3套放疗计划。调强放疗（IMRT）和容积旋转调强放疗（VMAT）在RayStation 4.0v系统制作,螺旋断层放疗（TOMO）在TomoH^TM Version 2.0.5系统制作。处方剂量60 Gy/30次。比较计划体积（PTV）、心脏、心脏亚单位以及肺剂量参数。结果 PTV、心脏和肺的平均体积为（399±355）、（671±274）和（3 907±1 717） cm³。与IMRT和VMAT相比,TOMO可以降低PTV、心脏、左心房及肺的最大剂量（H=10.889、7.433、12.080、11.401,P<0.05）。3种放疗技术的适形指数和均匀性指数差异无统计学意义（P>0.05）。结论 相较于IMRT和VMAT,TOMO可以降低PTV、心脏、左心房和肺的最大剂量,但均匀性及适形性差异无统计学意义。放疗过程中心脏与肺存在相互影响,TOMO技术可能带来的临床优势尚待进一步研究证实。     

Intraindividual Comparison of Conventional Three-Dimensional Radiotherapy and Intensity Modulated Radiotherapy in the Therapy of Locally Advanced Non-Small Cell Lung Cancer

BACKGROUND: Local failure is the one of the most frequent cause of tumor related death in locally advanced non-small cell lung cancer (LAD-NSCLC). Dose escalation has the promise of increased loco-regional tumor control but is limited by the tolerances of critical organs. PATIENTS AND METHODS: To evaluate the potential of IMRT in comparison to conventional three-dimensional conformal planning (3DCRT) dose constraints were defined: Maximum dose (D(max)) to spinal cord < 48 Gy, mean lung dose 70 Gy in not more than 5 cm of the total length. For ten patients two plans were compared: (1) 3DCRT with 5 weekly fractions (SD) of 2 Gy to a total dose (TD) of 50 Gy to the planning target volume of second order (PTV2). If the tolerance of the critical organs was not exceeded, patients get a boost plan with a higher TD to the PTV1. (2) IMRT: concomitant boost with 5 weekly SD of 2 Gy (PTV1) and 1.5 Gy to a partial (p)PTV (pPTV=PTV2 profile of a line PTV1) to a TD of 51 Gy to the pPTV and 68 Gy to the PTV1. If possible, patients get a boost plan to the PTV1 with 5 weekly SD of 2 Gy to the highest possibly TD. RESULTS: Using 3DCRT, 3/10 patients could not be treated with TD > 50 Gy, but 9/10 patients get higher TD by IMRT. TD to the PTV1 could be escalated by 16% on average. The use of non-coplanar fields in IMRT lead to a reduction of the irradiated lung volume. There is a strong correlation between physical and biological mean lung doses. CONCLUSION: IMRT gives the possibility of further dose escalation without an increasing mean lung dose especially in patients with large tumors.     

Helical Tomotherapy-Based STAT RT: Dosimetric Evaluation for Clinical Implementation of a Rapid Radiation Palliation Program

Helical tomotherapy–based STAT radiation therapy (RT) uses an efficient software algorithm for rapid intensity-modulated treatment planning, enabling conformal radiation treatment plans to be generated on megavoltage computed tomography (MVCT) scans for CT simulation, treatment planning, and treatment delivery in one session. We compared helical tomotherapy–based STAT RT dosimetry with standard linac-based 3D conformal plans and standard helical tomotherapy–based intensity-modulated radiation therapy (IMRT) dosimetry for palliative treatments of whole brain, a central obstructive lung mass, multilevel spine disease, and a hip metastasis. Specifically, we compared the conformality, homogeneity, and dose with regional organs at risk (OARs) for each plan as an initial step in the clinical implementation of a STAT RT rapid radiation palliation program. Hypothetical planning target volumes (PTVs) were contoured on an anthropomorphic phantom in the lung, spine, brain, and hip. Treatment plans were created using three planning techniques: 3D conformal on Pinnacle³, helical tomotherapy, and helical tomotherapy–based STAT RT. Plan homogeneity, conformality, and dose to OARs were analyzed and compared. STAT RT and tomotherapy improved conformality indices for spine and lung plans (CI spine = 1.21, 1.17; CI lung = 1.20, 1.07, respectively) in comparison with standard palliative anteroposterior/posteroanterior (AP/PA) treatment plans (CI spine = 7.01, CI lung = 7.30), with better sparing of heart, esophagus, and spinal cord. For palliative whole-brain radiotherapy, STAT RT and tomotherapy reduced maximum and mean doses to the orbits and lens (maximum/mean lens dose: STAT RT = 2.94/2.65 Gy, tomotherapy = 3.13/2.80 Gy, Lateral opposed fields = 7.02/3.65 Gy), with an increased dose to the scalp (mean scalp dose: STAT RT = 16.19 Gy, tomotherapy = 15.61 Gy, lateral opposed fields = 14.01 Gy). For bony metastatic hip lesions, conformality with both tomotherapy techniques (CI = 1.01 each) is superior to AP/PA treatments (CI = 1.21), as expected. Helical tomotherapy–based STAT RT treatment planning provides clinically acceptable dosimetry, with conformality and homogeneity that is superior to standard linac-based 3D conformal planning and is only slightly inferior to standard helical tomotherapy IMRT dosimetry. STAT RT facilitates rapid treatment planning and delivery for palliative radiation of patients with metastatic disease, with relative sparing of adjacent OARs compared with standard 3D conformal plans.     

Inverse-planned, dynamic, multi-beam, intensity-modulated radiation therapy (IMRT): A promising technique when target volume is the left breast and internal mammary lymph nodes

The purpose of this study was to determine the optimum beam number and orientation for inverse-planned, dynamic intensity-modulated radiation therapy (IMRT) for treatment of left-sided breast cancer and internal mammary nodes (IMNs) to improve target coverage while reducing cardiac and ipsilateral lung irradiation. Computed tomography (CT) data was used from 5 patients with left-sided breast cancer in whom the heart was close to the chest wall. The planning target volume (PTV) was the full breast plus ipsilateral IMNs. Two geometric beam arrangements were investigated, 240° and 190° sector angles, and the number of beams was increased from 7 to 9 to 11. Dose comparison metrics included: PTV homogeneity and conformity indices (HI, CI), heart V30, left lung V20, and mean doses to surrounding structures. To assess clinical application, the IMRT plans with 11 beams equally spaced in a 190° sector angle were compared to conventional plans. Treatment times were modeled. The 190° IMRT plans improved PTV HI and CI and reduced mean dose to the heart, lungs, contralateral breast, and total healthy tissue (all p < 0.05) compared to a 240° sector angle. The 11-beam plan significantly improved PTV HI and CI, heart V30, left lung V20, and healthy tissue V5 compared to a 7-beam plan (all p < 0.05). The 11-beam plan reduced heart V30 and left lung V20 (p < 0.05) without compromising PTV coverage, compared to a 9-beam plan. Compared to a conventional plan, the IMRT class solution significantly improved PTV HI and CI (both p < 0.01), heart V30 (p = 0.01), and marginally reduced left lung V20 (p = 0.07) but increased contralateral breast and lung mean dose (p < 0.001) and healthy tissue V5 (p < 0.001). An 11-beam 190° sector angle IMRT technique as a class solution is clinically feasible.     

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.     

Adaptive Radiation Therapy for Localized Mesothelioma with Mediastinal Metastasis Using Helical Tomotherapy

The purpose of this study was to compare 2 adaptive radiotherapy strategies with helical tomotherapy. A patient having mesothelioma with mediastinal nodes was treated using helical tomotherapy with pretreatment megavoltage CT (MVCT) imaging. Gross tumor volumes (GTVs) were outlined on every MVCT study. Two alternatives for adapting the treatment were investigated: (1) keeping the prescribed dose to the targets while reducing the dose to the OARs and (2) escalating the target dose while maintaining the original level of healthy tissue sparing. Intensity modulated radiotherapy (step-and-shoot IMRT) and 3D conformal radiotherapy (3DCRT) plans for the patient were generated and compared. The primary lesion and nodal mass regressed by 16.2% and 32.5%, respectively. Adapted GTVs and reduced planning target volume (PTV) margins of 4 mm after 22 fractions decrease the planned mean lung dose by 19.4%. For dose escalation, the planned prescribed doses may be increased from 50.0 to 58.7 Gy in PTV₁ and from 60.0 to 70.5 Gy in PTV₂. The step-and-shoot IMRT plan was better in sparing healthy tissue but did not provide target coverage as well as the helical tomotherapy plan. The 3DCRT plan resulted in a prohibitively high planned dose to the spinal cord. MVCT studies provide information both for setup correction and plan adaptation. Improved healthy tissue sparing and/or dose escalation can be achieved by adaptive planning.     

直肠癌术后盆腔不同放疗技术的剂量学研究

目的 比较直肠癌术后盆腔三维适形放疗(3DCRT)、适形调强放疗(IMRT)和简化调强(sIMRT)技术的三维剂量学特点,为直肠癌术后辅助放疗照射方法的优选提供依据。方法 选择Ⅱ～Ⅲ期直肠癌经腹前切除(Dixon手术)术后盆腔放疗的10例患者分别行3DCRT、sIMRT和IMRT3种计划设计,利用剂量体积直方图评价不同照射技术对靶区和正常组织照射剂量和靶区适形指数(CI)及剂量不均匀性指数(HI)。结果 不同放疗技术的剂量学研究:1CI为IMRT＞sIMRT＞3DCRT(t=7.48、9.13,P＜0.05)。23种治疗计划PTV靶区剂量分布的均匀度3DCRT最好,IMRT和sIMRT相似,但两者差异无统计学意义。3对膀胱的保护,IMRT明显优于3DCRT,sIMRT稍低于IMRT;对小肠的保护,sIMRT优于3DCRT,但IMRT并不比sIMRT具有更多优势;对结肠的保护,3种计划差异无统计学意义;对股骨头的保护,IMRT及sIMRT均明显好于3DCRT。IMRT、sIMRT对上述危及器官的保护优势主要体现在高剂量区。43种不同放疗技术的机器子野跳数sIMRT的子野跳数(543.0±69.8)与3DCRT技术(569.7±48.7)相当,但显著低于IMRT计划(770.3±73.1)。结论 在直肠癌术后放疗中sIMRT放疗技术具有最优性价比。     

Simultaneous Integrated Boost (SIB) for Nasopharynx Cancer with Helical Tomotherapy

PURPOSE: To explore the potential of helical tomotherapy (HT) in the treatment of nasopharynx cancer. PATIENTS AND METHODS: Six T1-4 N1-3 patients were considered. A simultaneous integrated boost (SIB) technique was planned with inversely optimized conventional intensity-modulated radiotherapy (IMRT; dynamic multileaf collimator using the Eclipse-Helios Varian system) and HT. The prescribed (median) doses were 54 Gy, 61.5 Gy, and 64.5 Gy delivered in 30 fractions to PTV1 (planning target volume), PTV2, and PTV3, respectively. The same constraints for PTV coverage and for parotids, spinal cord, mandible, optic structures, and brain stem were followed in both modalities. The planner also tried to reduce the dose to other structures (mucosae outside PTV1, larynx, esophagus, inner ear, thyroid, brain, lungs, submental connective tissue, bony structures) as much as possible. RESULTS: The fraction of PTV receiving >95% of the prescribed dose (V95%) increased from 97.6% and 94.3% (IMRT) to 99.6% and 97% (HT) for PTV1 and PTV3, respectively (p<0.05); median dose to parotids decreased from 30.1 Gy for IMRT to 25.0 Gy for HT (p<0.05). Significant gains (p<0.05) were found for most organs at risk (OARs): mucosae (V30 decreased from 44 cm(3) [IMRT] to 18 cm(3) [HT]); larynx (V30: 25 cm(3) vs. 11 cm(3)); thyroid (mean dose: 48.7 Gy vs. 41.5 Gy); esophagus (V45: 4 cm(3) vs. 1 cm(3)); brain stem (D1%: 45.1 Gy vs. 37.7 Gy). CONCLUSION: HT improves the homogeneity of dose distribution within PTV and PTV coverage together with a significantly greater sparing of OARs compared to linac five-field IMRT.     

Optimization of Stereotactic Radiotherapy Treatment Delivery Technique for Base-Of-Skull Meningiomas

This study compares static conformal field (CF), intensity modulated radiotherapy (IMRT), and dynamic arcs (DA) for the stereotactic radiotherapy of base-of-skull meningiomas. Twenty-one cases of base-of-skull meningioma (median planning target volume [PTV] = 21.3 cm³) previously treated with stereotactic radiotherapy were replanned with each technique. The plans were compared for Radiation Therapy Oncology Group conformity index (CI) and homogeneity index (HI), and doses to normal structures at 6 dose values from 50.4 Gy to 5.6 Gy. The mean CI was 1.75 (CF), 1.75 (DA), and 1.66 (IMRT) (p < 0.05 when comparing IMRT to either CF or DA plans). The CI (IMRT) was inversely proportional to the size of the PTV (Spearman's rho = −0.53, p = 0.01) and at PTV sizes above 25 cm³, the CI (IMRT) was always superior to CI (DA) and CI (CF). At PTV sizes below 25 cm³, there was no significant difference in CI between each technique. There was no significant difference in HI between plans. The total volume of normal tissue receiving 50.4, 44.8, and 5.6 Gy was significantly lower when comparing IMRT to CF and DA plans (p < 0.05). There was significantly improved dose sparing for the brain stem and ipsilateral temporal lobe with IMRT but no significant difference for the optic chiasm or pituitary gland. These results demonstrate that stereotactic IMRT should be considered to treat base-of-skull meningiomas with a PTV larger than 25 cm³, due to improved conformity and normal tissue sparing, in particular for the brain stem and ipsilateral temporal lobe.     

Inverse planning in three-dimensional conformal and intensity-modulated radiotherapy of mid-thoracic oesophageal cancer

The aim of this study is to demonstrate the use of inverse planning in three-dimensional conformal radiation therapy (3DCRT) of oesophageal cancer patients and to evaluate its dosimetric results by comparing them with forward planning of 3DCRT and inverse planning of intensity-modulated radiotherapy (IMRT). For each of the 15 oesophageal cancer patients in this study, the forward 3DCRT, inverse 3DCRT and inverse IMRT plans were produced using the FOCUS treatment planning system. The dosimetric results and the planner's time associated with each of the treatment plans were recorded for comparison. The inverse 3DCRT plans showed similar dosimetric results to the forward plans in the planning target volume (PTV) and organs at risk (OARs). However, they were inferior to that of the IMRT plans in terms of tumour control probability and target dose conformity. Furthermore, the inverse 3DCRT plans were less effective in reducing the percentage lung volume receiving a dose below 25 Gy when compared with the IMRT plans. The inverse 3DCRT plans delivered a similar heart dose as in the forward plans, but higher dose than the IMRT plans. The inverse 3DCRT plans significantly reduced the operator's time by 2.5 fold relative to the forward plans. In conclusion, inverse planning for 3DCRT is a reasonable alternative to the forward planning for oesophageal cancer patients with reduction of the operator's time. However, IMRT has the better potential to allow further dose escalation and improvement of tumour control.     

Left-sided breast cancer irradiation using rotational and fixed-field radiotherapy

The 3-dimensional conformal radiotherapy (3DCRT) technique is the standard for breast cancer radiotherapy. During treatment planning, not only the coverage of the planning target volume (PTV) but also the minimization of the dose to critical structures, such as the lung, heart, and contralateral breast tissue, need to be considered. Because of the complexity and variations of patient anatomy, more advanced radiotherapy techniques are sometimes desired to better meet the planning goals. In this study, we evaluated external-beam radiation treatment techniques for left breast cancer using various delivery platforms: fixed-field including TomoDirect (TD), static intensity-modulated radiotherapy (sIMRT), and rotational radiotherapy including Elekta volumetric-modulated arc therapy (VMAT) and tomotherapy helical (TH). A total of 10 patients with left-sided breast cancer who did or did not have positive lymph nodes and were previously treated with 3DCRT/sIMRT to the entire breast were selected, their treatment was planned with Monaco VMAT, TD, and TH. Dosimetric parameters including PTV coverage, organ-at-risk (OAR) sparing, dose-volume histograms, and target minimum/maximum/mean doses were evaluated. It is found that for plans providing comparable PTV coverage, the Elekta VMAT plans were generally more inhomogeneous than the TH and TD plans. For the cases with regional node involvement, the average mean doses administered to the heart were 9.2 (± 5.2) and 8.8 (± 3.0) Gy in the VMAT and TH plans compared with 11.9 (± 6.4) and 11.8 (± 9.2) Gy for the 3DCRT and TD plans, respectively, with slightly higher doses given to the contralateral lung or breast or both. On average, the total monitor units for VMAT plans are 11.6% of those TH plans. Our studies have shown that VMAT and TH plans offer certain dosimetric advantages over fixed-field IMRT plans for advanced breast cancer requiring regional nodal treatment. However, for early-stage breast cancer fixed-field radiotherapy is potentially more beneficial in terms of OAR sparing.