个体患者适形调强放疗计划模体内剂量实测验证技术的建立

目的建立个体患者适形调强放疗（IMRT）计划的模体内剂量实测验证技术。方法选择1例鼻咽癌患者，设计IMRT计划。将患者计划转移到模体上设计杂交计划。执行杂交计划时，用针点电离室测量感兴趣点的剂量，并与该点的计算剂量比较。用胶片剂量测量系统测量杂交计划中感兴趣平面的剂量，胶片与计划剂量矩阵登记后，依次进行计划，胶片分析、计划，胶片剖面分析和计划／胶片等剂量线分析。采用复合判断标准评价验证结果。结果针点电离室测量得到杂交计划单次照射的总剂量为121．5cGy，比计算值低约4％。计划，胶片分析得到高剂量、高梯度区域的距离差别均在4mm以内；计划／胶片剖面分析显示，计划与胶片在通过靶区的剖面具有较好的一致性；计划，胶片等剂量线分析显示，计划与胶片对应值的等剂量线重合良好。按照复合判断标准，该计划验证通过。结论初步建立了个体患者IMRT计划的模体内剂量实测验证技术，建立并优化了剂量登记技术、剂量归一方法和评价方法。     

Fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT) for small acoustic neuromas.

Eight patients with acoustic neuromas were treated using a novel method developed at our institution for delivering fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT). We present treatment parameters, dosimetry analysis, and preliminary clinical outcome. The method incorporates high-precision invasive fixation, obliquely-oriented tomotherapy arcs, and reduced dimension pencil beams. The delivered dose distributions for the 8 patients treated from April 1999 to May 2001 were assessed for dose conformality, homogeneity, and doses to organs at risk. Total doses prescribed were 54 Gy in daily doses of 1.8 Gy. Results show that the median planning target volume (gross tumor volume plus a safety margin of 2 mm) was 2.48 cm3 (1.64 to 16.86 cm3) and that the median conformality and homogeneity indices were 1.69 (1.56 to 2.16) and 1.12 (1.09 to 1.19), respectively. The respective average mean and maximum doses to the brain stem were 12.67 Gy and 53.86 Gy. The treatment parameters for the novel FS-IMRT method developed here document excellent dose conformality and normal tissue sparing. Preliminary short-term follow-up (mean 17, median 18.5 months) revealed a 100% local control and hearing preservation rate. No new persistent impairment of facial and trigeminal nerve was observed. Our current follow-up experience indicates a reasonable potential for achieving outcomes comparable to established stereotactic radiotherapy techniques.     

Commissioning of mini-multi-leaf-collimator (MMLC) for stereotactic radiosurgery and radiotherapy

Commissioning of a Radionics miniature multi-leaf collimator (MMLC) for stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) is reported. With single isocenter and multi static fields, the MMLC can provide better conformity of dose distributions to the target and/or irregularly shaped target volumes than standard arc (circular) field beams with multiple isocenters. Advantages offered by the MMLC over traditional LINAC based SRS and SRT includes greatly improved dose homogeneity to the target, reduced patient positioning time and reduced treatment time. In this work, the MMLC is attached to a Varian 2300 C/D with Varian 80-leaf multi-leaf collimator. The MMLC has 62 leaves, each measured to a width of 3.53 mm at isocenter, with fields range from 1x1 cm to less than 10 × 12 cm. Beam parameters required by the Radionics treatment planning system (XPlan version 2) for evaluating the dose include tissue maximum ratio (TMR), scatter factors (SF), off-axis ratios (OAR), output factors, penumbra function (P) and transmission factors (TF) are performed in this work. Beam data are acquired with a small stereotactic diode, standard ion chambers and radiographic films. Measured profiles of dose distribution are compared to those calculated by the software and absolute dosimetry is performed.     

Optimization of primary jaw settings for stereotactic radiosurgery/radiotherapy

The primary goal of stereotactic radiosurgery/radiotherapy is to provide a technique by which the dose to a target volume can be maximized while minimizing the dose to uninvolved structures. Initially, circular apertures were applied through the use of multiple arcs and one or more isocenters in an effort to achieve these goals. Advances in field-shaping techniques, such as more elaborate cerrobend shaping and micromultileaf collimators, have allowed for improved target conformality with further reductions in dose to normal tissues. The shape of these secondary collimation devices is usually set at the precise size and shape necessary to encompass only the volume of interest with a small margin. Often, however, the primary collimators are set at a default setting that may be much larger than required to encompass the treatment area. This results in unnecessary transmission through the secondary collimators and added dose to the uninvolved tissues. This paper compares the dose delivered to normal tissues surrounding the target volume when a “standard” collimator setting is used to dose delivered when the primary collimator setting is optimized to only that necessary to encompass the treatment volume.     

立体定向调强放射治疗剂量验证结果分析

目的 研究测量数据插值、计划系统剂量计算网格及剂量评估阈值等因素对立体定向调强放射治疗患者计划的剂量验证结果的影响。方法 回顾性分析了50例立体定向放射治疗的患者放疗计划的剂量验证结果。剂量验证设备采用MatriXX及配套MultiCube固体水模。测量数据分别选择线性插值（1.00 mm）和不插值（7.62 mm）两种分辨率;计划系统剂量计算网格分别选择1.0、2.5和4.0 mm;剂量评估阈值分别选择10%、20%和30%,γ评估标准分别选择2%/2 mm、3%/2 mm和3%/3 mm,分析不同因素选择对平面剂量验证结果的影响。结果 测量数据插值选择线性插值和不插值,2%/2 mm标准下,γ平均通过率分别为（86.3±7.3）%和（93.7±5.5）%;3%/2 mm标准下,γ平均通过率分别为（94.1±4.4）%和（97.7±3.9）%;3%/3 mm标准下,γ平均通过率分别为（97.7 ±2.2）%和（99.1±1.7）%。相比1.0 mm的剂量计算网格,使用2.5 mm计算网格,3种标准下γ平均通过率分别降低3.8%、1.9%和0.8%（t=8.41、9.06、5.30,P<0.05）,4.0 mm分别降低6.5%、6.0%和3.5%（t=-13.76、-13.15、-9.80,P<0.05）,差异有统计学意义。相比剂量评估阈值为10%,当阈值设置为20%时,2%/2 mm、3%/2 mm和3%/3 mm标准下,γ平均通过率分别降低2.4%、1.0%和0.6%（t=-8.60、-5.86、-4.68,P<0.05）;当阈值设置为30%,3种标准下γ平均通过率分别降低4.0%、1.7%和0.9%（t=-9.45、-6.66、-5.06,P<0.05）,差异有统计学意义。结论 测量数据插值、剂量计算网格大小及剂量评估阈值对立体定向放射治疗患者计划剂量验证结果均有明显影响,因此在进行立体定向放射治疗患者计划剂量验证时需要考虑这些因素。     

A dosimetric evaluation of the Eclipse AAA algorithm and Millennium 120 MLC for cranial intensity-modulated radiosurgery

The aim of this study is to assess the accuracy of a convolution-based algorithm (anisotropic analytical algorithm [AAA]) implemented in the Eclipse planning system for intensity-modulated radiosurgery (IMRS) planning of small cranial targets by using a 5-mm leaf-width multileaf collimator (MLC). Overall, 24 patient-based IMRS plans for cranial lesions of variable size (0.3 to 15.1 cc) were planned (Eclipse, AAA, version 10.0.28) using fixed field-based IMRS produced by a Varian linear accelerator equipped with a 120 MLC (5-mm width on central leaves). Plan accuracy was evaluated according to phantom-based measurements performed with radiochromic film (EBT2, ISP, Wayne, NJ). Film 2D dose distributions were performed with the FilmQA Pro software (version 2011, Ashland, OH) by using the triple-channel dosimetry method. Comparison between computed and measured 2D dose distributions was performed using the gamma method (3%/1 mm). Performance of the MLC was checked by inspection of the DynaLog files created by the linear accelerator during the delivery of each dynamic field. The absolute difference between the calculated and measured isocenter doses for all the IMRS plans was 2.5% ± 2.1%. The gamma evaluation method resulted in high average passing rates of 98.9% ± 1.4% (red channel) and 98.9% ± 1.5% (blue and green channels). DynaLog file analysis revealed a maximum root mean square error of 0.46 mm. According to our results, we conclude that the Eclipse/AAA algorithm provides accurate cranial IMRS dose distributions that may be accurately delivered by a Varian linac equipped with a Millennium 120 MLC.     

肺癌立体定向放疗偏中心计划设计剂量学研究

目的研究不同程度的偏中心计划对肺癌立体定向放疗(SBRT)计划质量和执行准确度的影响, 为肺癌SBRT的临床计划设计提供参考。方法首先, 选取10例肺癌SBRT患者, 将计划等中心置于肿瘤质心位置, 设计等中心参考计划。将计划等中心置于偏离肿瘤质心1、3、5、8及10 cm位置, 设计偏中心计划, 共计60个, 分析这些偏中心计划相对于参考计划的剂量学差异。然后, 引入不同程度的位置误差(0～5 mm), 利用Octavius 4D高分辨率剂量验证系统, 测量这些计划的伽马通过率(GPR), 完成240次计划验证, 分析参考计划和偏中心计划的执行准确度对位置误差的鲁棒性。结果偏中心计划的剂量梯度指标略差于等中心计划, 差异无统计学意义(P>0.05)。随着偏中心距离增加, 正常肺平均剂量(MLD)和V20以及支气管Dmax略微有升高趋势。MLD在偏中心距离1、3和10 cm, 较等中心计划分别升高了0.8%、0.8%和1.9%, 差异具有统计学意义(z=-2.34～-1.99, P<0.05), V20在偏中心距离1、5和10 cm, 较等中心计划分别增加了2.0%、2.5...     

Trilogy image-guided stereotactic radiosurgery.

Full integration of advanced imaging, noninvasive immobilization, positioning, and motion-management methods into radiosurgery have resulted in fundamental changes in therapeutic strategies and approaches that are leading us to the treatment room of the future. With the introduction of image-guided radiosurgery (IGRS) systems, such as Trilogy, physicians have for the first time a practical means of routinely identifying and treating very small lesions throughout the body. Using new imaging processes such as positron emission tomography/computed tomography (PET/CT) scans, clinics may be able to detect these lesions and then eradicate them with image-guided stereotactic radiosurgery treatments. Thus, there is promise that cancer could be turned into a chronic disease, managed through a series of checkups, and Trilogy treatments when metastatic lesions reappear.     

头颈部肿瘤调强放射治疗后甲状腺功能减退的临床参数和剂量影响因素

目的 探讨头颈部肿瘤患者接受调强放射治疗（IMRT）后出现甲状腺功能减退（HT）与患者临床特征参数、剂量体积直方图（DVH）参数的相关性。方法 收集28例接受头颈部IMRT（颈部照射剂量 ≥ 40 Gy）联合化疗的肿瘤患者资料。治疗前后及随访观察中监测血清促甲状腺激素（TSH）、游离三碘甲状腺原氨酸（FT3）和游离甲状腺素（FT4）。原发性HT定义为血清TSH高于正常值的上限伴或不伴有FT3/FT4的降低。基于放疗计划系统DVH,记录每一位患者甲状腺体积（TV）、甲状腺平均照射剂量（MTD）、最大点剂量（D_max）、甲状腺接受≥5~50 Gy的相对体积（表示为V_x,x=5~50,5 Gy为间隔）。回顾性分析患者年龄、性别、化疗、TV、MTD、D_max及各DVH参数与HT的相关性。 结果 全组患者治疗前血清TSH、FT3和FT4中位数分别为1.51 μU/ml、5.38和18.57 pmol/L。中位随访15个月（3~57月）,14例（50.0%）患者出现HT,出现HT的中位时间为放疗后8个月（2~23月）。患者首次监测发现HT时间点的TSH、FT3和FT4中位数分别为7.48 μU/ml（4.67~60.11 μU/ml）、4.05 pmol/L（0.40~5.77 pmol/L）和12.32 pmol/L（4.12~21.25 pmol/L）,HT患者的TSH较治疗前明显升高（P<0.01）。HT患者的TV中位数为17.76 cm³,显著低于未出现HT患者的20.21 cm³（Z=-2.154,P<0.05）。单因素分析显示患者年龄和V₄₀与HT的发生风险相关（χ²=11.340、4.102,OR=30.0、9.17,P<0.05）。多因素分析证实患者年龄、V₄₀均是HT的独立影响因素（OR=34.7、6.13,P<0.05）。结论 头颈部肿瘤患者IMRT后出现HT伴随TSH的显著增高。低龄、甲状腺体积较小的患者,甲状腺V₄₀大于80%是发生HT的高风险因素。     

Comparative dosimetric study of two strategies of intensity-modulated radiotherapy in nasopharyngeal cancer

This study compared the target volume coverage and normal tissues sparing of simultaneous integrated boost (SIB-IMRT, 1-phase) and sequential-IMRT (2-phase) for nasopharyngeal carcinoma (NPC). Fourteen consecutive patients with newly diagnosed primary NPC were enrolled in this study. The CT images were transferred to a commercial planning system for structural delineation. The gross tumor volume (GTV) included gross nasopharyngeal tumor and involved lymph nodes of more than 1-cm diameter. The clinical target volume (CTV) modeled two regions considered to represent different risks. CTV1 encompassed the GTV with 5–10-mm margin of adjacent tissues. CTV2 encompassed ipsilateral or contralateral elective nodal regions at risk of harboring microscopic tumor. A commercial IMRT treatment planning system (Eclipse Version 7.1) was used to provide treatment planning. Seven fixed-gantry (0°, 50°, 100°, 150°, 210°, 260°, 310°) angles were designated. The 14 patients were treated with sequential-IMRT, and treatment was then replanned with an SIB strategy to compare the dosimetric difference. For the sequential strategy, the dose delivered to CTV1/CTV2 in the first course was 54 Gy (1.8 Gy × 30 Fr); while CTV1 was boosted by an additional 16.2 Gy (1.8 Gy × 9 Fr) in the second course. For SIB-IMRT, the dose prescribed to CTV1 was 69.7 Gy (2.05 Gy × 34 Fr); 56.1 Gy was given to CTV2 (1.65 Gy × 34 Fr). A statistical analysis of the dose-volume-histogram of target volumes and critical organs was performed. Paired Student’s t-test was used to compare the dosimetric differences between the two techniques. The mean dose to CTV1 was 101.7 ± 2.4% and 102.3 ± 3.1% of the prescribed dose for SIB-IMRT and sequential-IMRT, respectively. The mean CTV2 dose was 109.8 ± 4.7% of the prescribed dose for SIB-IMRT and 112.6 ± 6.0% of the prescribed dose for sequential-IMRT. The maximal dose to the spinal cord was 4489 ± 495 cGy and 3547 ± 767 cGy for SIB and sequential-IMRT (p = 0.0001), respectively. The maximal dose to brain stem was significantly higher using SIB technique (5284 ± 551 cGy) than sequential-IMRT (4834 ± 388 cGy) (p = 0.0001). The mean dose to the parotid gland and ear apparatus was significantly lower using SIB-IMRT. The mean dose to the right/left parotids was 2865 ± 320 cGy/2903 ± 429 cGy and 3567 ± 534 cGy/3476 ± 489 cGy for SIB and sequential-IMRT, respectively (p = 0.0001). Target coverage was the same for both techniques; the dose distribution in the elective nodal area with SIB was superior to that with sequential-IMRT. SIB-IMRT provides better sparing of parotid gland and inner ear structures. Extra caution should be taken when applying SIB-IMRT since critical organs close to the boost volume may receive higher doses.     

Effects of multileaf collimator parameters on treatment planning of intensity-modulated radiotherapy.

In inverse planning of intensity-modulated radiotherapy (IMRT), the setting of multileaf collimator (MLC) parameters affects the optimization algorithms and dose distribution. We investigated the effects of varying the MLC leaf width, leaf insertion percentage, and leaf increment in treatment planning of IMRT in 3 cancer cases: nasopharynx, esophagus, and prostate. Inverse planning of the 3 cancer cases was performed using the XiO treatment planning system. MLCs with 0.5 and 1.0 cm were used to evaluate the leaf width effect, whereas leaf insertions of 20%, 50%, and 80% were used to demonstrate the effect of leaf insertion percentage, and leaf increments of 0.5, 1.0, and 2.0 cm were used to study the leaf increment effect. The treatment plans were evaluated by dose profiles, tumor control probability (TCP), and normal tissue complication probability (NTCP). The 0.5-cm MLC leaves showed better TCPs and NTCPs than the 1.0-cm leaves in the 3 cancer cases, although the differences were less than 2.5%. For the leaf insertion percentage, the dose profile differences among the 3 levels of increments were minimal, and their differences in TCP and NTCP were extremely small (< 1.5%). The effect of leaf increment was more prominent, dose profile, TCPs, and NTCPs were best for the smallest leaf increment and they deteriorated as the leaf increment increased. Narrower leaves gave slightly better sparing of organs at risk (OAR)s; changing the leaf insertion percentage brought about negligible changes, whereas increasing the leaf increment significantly degraded the treatment plans.     

Comparative dosimetric study of two strategies of intensity-modulated radiotherapy in nasopharyngeal cancer

This study compared the target volume coverage and normal tissues sparing of simultaneous integrated boost (SIB-IMRT, 1-phase) and sequential-IMRT (2-phase) for nasopharyngeal carcinoma (NPC). Fourteen consecutive patients with newly diagnosed primary NPC were enrolled in this study. The CT images were transferred to a commercial planning system for structural delineation. The gross tumor volume (GTV) included gross nasopharyngeal tumor and involved lymph nodes of more than 1-cm diameter. The clinical target volume (CTV) modeled two regions considered to represent different risks. CTV1 encompassed the GTV with 5–10-mm margin of adjacent tissues. CTV2 encompassed ipsilateral or contralateral elective nodal regions at risk of harboring microscopic tumor. A commercial IMRT treatment planning system (Eclipse Version 7.1) was used to provide treatment planning. Seven fixed-gantry (0°, 50°, 100°, 150°, 210°, 260°, 310°) angles were designated. The 14 patients were treated with sequential-IMRT, and treatment was then replanned with an SIB strategy to compare the dosimetric difference. For the sequential strategy, the dose delivered to CTV1/CTV2 in the first course was 54 Gy (1.8 Gy × 30 Fr); while CTV1 was boosted by an additional 16.2 Gy (1.8 Gy × 9 Fr) in the second course. For SIB-IMRT, the dose prescribed to CTV1 was 69.7 Gy (2.05 Gy × 34 Fr); 56.1 Gy was given to CTV2 (1.65 Gy × 34 Fr). A statistical analysis of the dose-volume-histogram of target volumes and critical organs was performed. Paired Student’s t-test was used to compare the dosimetric differences between the two techniques. The mean dose to CTV1 was 101.7 ± 2.4% and 102.3 ± 3.1% of the prescribed dose for SIB-IMRT and sequential-IMRT, respectively. The mean CTV2 dose was 109.8 ± 4.7% of the prescribed dose for SIB-IMRT and 112.6 ± 6.0% of the prescribed dose for sequential-IMRT. The maximal dose to the spinal cord was 4489 ± 495 cGy and 3547 ± 767 cGy for SIB and sequential-IMRT (p = 0.0001), respectively. The maximal dose to brain stem was significantly higher using SIB technique (5284 ± 551 cGy) than sequential-IMRT (4834 ± 388 cGy) (p = 0.0001). The mean dose to the parotid gland and ear apparatus was significantly lower using SIB-IMRT. The mean dose to the right/left parotids was 2865 ± 320 cGy/2903 ± 429 cGy and 3567 ± 534 cGy/3476 ± 489 cGy for SIB and sequential-IMRT, respectively (p = 0.0001). Target coverage was the same for both techniques; the dose distribution in the elective nodal area with SIB was superior to that with sequential-IMRT. SIB-IMRT provides better sparing of parotid gland and inner ear structures. Extra caution should be taken when applying SIB-IMRT since critical organs close to the boost volume may receive higher doses.     

Re-irradiation of recurrent anaplastic ependymoma using radiosurgery or fractionated stereotactic radiotherapy

Purpose

Recurrent ependymomas were retreated with stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (FSRT). The efficacy, toxicities, and differences between SRS and FSRT were analyzed.

Methods

Eight patients with recurrent ependymomas fulfilling the criteria described below were evaluated. Inclusion criteria were: (1) the patient had previously undergone surgery and conventional radiotherapy as first-line treatment; (2) targets were located in or adjacent to the eloquent area or were deep-seated; and (3) the previously irradiated volume overlapped the target lesion.

Results

FSRT was delivered to 18 lesions, SRS to 20 lesions. A median follow-up period was 23 months. The local control rate was 76 % at 3 years. No significant differences in local control were observed due to tumor size or fractionation schedule. Lesions receiving >25 Gy/5 fr or 21 Gy/3 fr did not recur within 1 year, whereas no dose–response relationship was observed in those treated with SRS. No grade ≥2 toxicity was observed.

Conclusion

Our treatment protocol provided an acceptable LC rate and minimal toxicities. Because local recurrence of tumors may result in patient death, a minimum dose of 21 Gy/3 fr or 25 Gy/5 fr or higher may be most suitable for treatment of these cases.

     

直肠癌调强放疗计划中六维随机摆位误差的剂量学影响研究

目的 设计一种软件将随机六维摆位误差引入到直肠癌调强放疗(IMRT)计划中,并评估其剂量学影响。方法 随机选取21例直肠癌IMRT计划作为参考计划(单次剂量 2 Gy, 共50 Gy;PTV为CTV均匀外扩5 mm)。对参考计划的每个分次,通过调整射野几何参数的方法引入随机生成的六维摆位误差,并重新完成剂量计算。再将各分次剂量累加后得到存在摆位误差情况下的总剂量分布。基于美国瓦里安Eclipse脚本应用程序接口(ESAPI)开发能够自动完成上述流程的治疗模拟软件,将服从两种预设分布[分布1:平移误差服从N(0,4²),旋转误差服从N(0,2²);分布2:平移误差服从N(0,2²),旋转误差服从N(0,1²)]的六维摆位误差引入参考计划,并评估剂量学影响。结果 参考计划、误差分布1和误差分布2情况下,CTV的D_min分别为(49.4±0.41)、(47.56±0.76)和(49.17±0.64)Gy;CTV的D_98%分别为(50.23±0.07)、(49.98±0.10)和(50.27±0.09)Gy;主体靶区(靶区除去边缘后的内核部分)D_98%为(50.25±0.08)、(50.42±0.13)和(50.33±0.10)Gy;边缘靶区D_98%为(50.22±0.10)、(49.88±0.11) 和(50.26±0.10)Gy。另外,相比参考计划,误差分布1和2的情况下,膀胱和股骨头平均受量的变化差异均无统计学意义(P>0.05),剂量分布的适形指数虽有微弱降低,但临床意义有限。结论 本方法及据此开发的治疗模拟软件可以根据需要将服从不同分布的六维摆位误差引入到直肠癌IMRT计划中,并给出总体剂量学变化情况。     

快速旋转调强与五野动态调强在乳腺癌 保乳术后放疗中的剂量学比较

目的 比较乳腺癌保乳术后RapidArc计划与五野动态调强(5F-IMRT)计划的剂量学差异。方法 选择8例左侧乳腺癌保乳术后女性患者,处方剂量为50 Gy/ 25次。分别设计RapidArc计划与5F-IMRT计划。比较两种计划的靶区适形度指数、均匀性指数、靶区覆盖度和危及器官的受照剂量体积,同时比较两组计划实施时的治疗时间和机器跳数。结果 在两种计划的靶区比较中,RapidArc计划的靶区适形度指数为(0.88±0.03),高于5F-IMRT计划的(0.79±0.02)(t=8.28,P<0.05);RapidArc计划的均匀性指数为(9.01±0.73),优于5F-IMRT计划的(10.44±1.08)(t=-2.73,P<0.05)。两组计划在同侧肺受照剂量体积比较中RapidArc计划的D_mean、V₁₀、V₂₀、V₃₀小于5F-IMRT计划(t=-7.53、-7.20、-8.39、-7.80,P<0.05),但RapidArc计划中的V₅较5F-IMRT计划增加了约16% (t=5.67,P<0.05);心脏的受照剂量体积比较中RapidArc计划中的D_mean、V₅、V₁₀均高于5F-IMRT(t=10.46、28.76、5.40,P<0.05),但在RapidArc计划中心脏的V₃₀低于5F-IMRT (t=-6.12,P<0.05)。对侧肺和对侧乳腺的V₅在RapidArc计划中明显高于5F-IMRT计划 (肺:t=21.50,P<0.05;乳腺:t=5.44,P<0.05)。RapidArc计划中机器跳数减少了25%,平均治疗时间节省了60%。结论 乳腺癌保乳术后RapidArc计划与5F-IMRT计划比较提高了靶区的适形度和均匀度,减少了高剂量区的受照体积,降低了机器跳数,缩短了治疗时间,但增加了正常组织低剂量区的受照体积。     

Variation in the isocentre of a Philips linear accelerator (SL-20) used for stereotactic radiosurgery/stereotactic radiotherapy

Stereotactic irradiation, either in the form of stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT) of brain lesions requires high precision and submillimetre accuracy in the isocentre, the main determinants being gantry and couch rotations. It is thus necessary to evaluate the isocentre variation due to gantry and couch rotations in the particular setup for SRS/SRT. This paper describes variation in the isocentre of a Philips (now Elekta) SL-20 linear accelerator modified for adapting a couch-mounted radiosurgery system. By considering the isocentre as defined by a mechanical index as the standard, the variations in the isocentre of the linear accelerator were independently measured for the gantry and for couch rotations. The variation in the isocentre for gantry rotation was found to be between 0.1 mm and 0.9 mm, conforming to the submillimetre accuracy required for SRS/SRT. However, the isocentre variation due to couch rotation varied considerably, possibly because the couch is of the RAM type. The isocentre variation due to couch rotation is rectified by microadjusting the couch mount at the time of treatment using a laser target localizing frame. It is our conclusion that a modified linear accelerator can be used for performing SRS/SRT after careful and separate evaluation of the isocentre stability due to gantry and couch rotations.     

A comparative dosimetric analysis of virtual stereotactic body radiotherapy to high-dose-rate monotherapy for intermediate-risk prostate cancer

PurposeStereotactic body radiotherapy (SBRT) is being used with increasing frequency as definitive treatment of early stage prostate cancer. Much of the justification for its adoption was derived from earlier clinical results using high-dose-rate (HDR) brachytherapy. We determine whether HDR's dosimetry can be achieved by virtual SBRT.Methods and MaterialsPatients with intermediate-risk prostate cancer on a prospective trial evaluating the efficacy of HDR monotherapy treated to dose of 9.5 Gy × 4 fractions were used for this study. A total of 5 patients were used in this analysis. Virtual SBRT plans were developed to reproduce the planning target volume (PTV) HDR dose distributions. Both normal tissue– and PTV-prioritized plans were generated.ResultsFrom the normal tissue–prioritized plan, HDR and virtual SBRT achieved similar PTV V₁₀₀ (93.8% vs. 93.1%, p = 0.20) and V₁₅₀ (40.3% vs. 42.9%, p = 0.69) coverage. However, the PTV V₂₀₀ was not attainable with SBRT (15.2% vs. 0.0%, p < 0.001). The rectal D_max was significantly lower with HDR (94.2% vs. 99.42%, p = 0.05). The rectal D_{2 cc} was also lower (60.8% vs. 71.1%, p = 0.07). Difference in D_{1 cc} urethral dose was not significantly different (87.7% vs. 75.2%, p = 0.33). Comparing the PTV-prioritized plans, the rectal D_max (94.2% vs. 111.1%, p = 0.05) and mean dose (27.1% vs. 33.3%, p = 0.03) were significantly higher using SBRT, and the rectal D_{2 cc} was higher using SBRT (60.8% vs. 81.8%, p = 0.07).ConclusionsHDR achieves significantly higher intraprostatic doses while achieving a lower maximum rectal dose compared with our virtual SBRT treatment planning. Future studies should compare clinical outcomes and toxicity between these modalities.