鼻咽癌半束照射的剂量分布

目的 比较鼻咽癌半束和全束照射技术射野衔接处的剂量分布以及脑和肺的受量。方法 应用Varian 600CD直线加速器，在固体水模体中采用胶片黑度法测量鼻咽癌面颈联合野和下颈切线野射野衔接处的剂量分布。应用Helax TMS-3D治疗计划系统，根据实际病例的螺旋CT模拟定位资料，在数字重建图像上设计面颈联合野和下颈切线野，分别计算半束和全束照射技术条件下脑组织和肺的受量，比较两者受照射的剂量体积直方图(DVH)及脑组织受照射的最大剂量、最小剂量、中位剂量、平均剂量、25％受较高照射剂量脑组织的下限剂量(D25％)以及受量超过75％肿瘤剂量的脑体积(V75%)。结果 两种照射技术射野衔接处均无漏照及低剂量区情况，半束照射和全束共线照射分别有约4mm、10mm的剂量重叠区，两野衔接处剂量最高点高出剂量归一点分别为28％和117％。两种照射技术脑及肺受照射的DVH相似，脑受照射的最小剂量、最大剂量、中位剂量、平均剂量、D25％、V75％及破裂孔处剂量均以全束照射略高，但相差幅度均不超过1％。结论 鼻咽癌应用面颈联合野和下颈切线野放射治疗时，与全束照射技术相比，半束照射技术照射野衔接处的剂量重叠区较小，脑和肺的照射体积和剂量没有增加。     

鼻咽癌放射治疗照射野最佳衔接方法的探讨

目的：探讨鼻咽癌患者放射治疗中面颈野或耳前野与颈切线野的最佳衔接方法。方法：用带独立准直器的直线加速器,以一个等中心、半束整体铅模照射面颈野或耳前野与颈切线野用于鼻咽癌患者的放射治疗。结果：根据测量,面颈野或耳前野与颈切线之间的剂量分布满意、无冷点和热点,与初步临床观察相符。结论：用一个等中心并半束整体铅模放射治疗鼻咽癌患者时,面颈野或耳前野与颈切线野间的剂量衔接满意。     

鼻咽癌放射治疗射野衔接设计的探讨

背景与目的:放射治疗鼻咽癌,面颈联合野已作为标准的射野设计,用一个颈部等中心半束照接野解决了面颈联合野与颈部切线野的衔接问题,但面颈联合野内存在剂量冷点与热点,剂量均匀性差。因此,本研究试图就鼻咽癌放射治疗中面颈联合野与颈部切线野最合适的射野衔接设计作一些探讨。方法:分别用两种方法设野,一种方法用一个等中心,半束照射面颈联合野与颈部切线照射,另一种用两个等中心,面颈联合野用鼻咽等中心照射,选用适当的楔形角,床转一定的角度,下颈切线照射再用颈部等中心半束照。比较两种设野衔接的区别。结果:根据治疗计划系统(treatmentplanningsystem,TPS)计算,两种设计的面颈联合野与颈部切线野之间的剂量衔接处都无冷点热点。用两个等中心设计的面颈联合野与颈部切线野,面颈联合野加角头足方向楔形板和床转一定的角度,其剂量分布比单一中心设野更均匀,更合理。99%的等剂量线包容颅底及鼻咽处大体肿瘤体积(grosstumorvolume,GTV)时,下颈及口咽部最高点剂量为103%,而且高剂量区容积也小,而用单一等中心设野时,如果要使95%的等剂量线包含颅底及鼻咽处GTV时,最高点处剂量达120%以上。结论:用两个等中心设计面颈联合野和颈部切线照,比单一颈部等中心设野时,接野处可以达到与单一等中心相同的结果,即不产生冷点及热点,而且三维TPS显示比单一等中心更合理、更均匀。     

早期鼻咽癌常规放疗相邻野衔接设计的剂量学研究

目的　应用三维治疗计划系统对早期鼻咽癌常规放疗相邻野衔接设计方案进行剂量学研究,探讨其在临床放疗中的价值。方法　对５例早期初治鼻咽癌患者,设计面颈联合野与下颈锁骨上单前野衔接移位方案,即先给予面颈联合野ＤＴ１９Ｇｙ／１０ｆ,下颈锁骨上单前野Ｄｍ２５Ｇｙ／１０ｆ,后将两野衔接上移１５ｃｍ,继续予两野至ＤＴ３８Ｇｙ／２０ｆ和Ｄｍ５０Ｇｙ／２０ｆ;面颈缩野与上后颈电子线照射野衔接时设计５°水平（９５°和２６５°）共线成角及０°水平重叠０５ｃｍ两种方案,两野ＤＴ２０Ｇｙ／１０ｆ。应用三维治疗计划系统比较其与常规衔接方案剂量分布。结果　（１）面颈联合野与下颈锁骨上单前野常规衔接方案衔接处组织受照最高剂量以及ＤＴ５２Ｇｙ以上受照体积分别为ＤＴ（５６.２７±１.８１）Ｇｙ和（１２.４９±８.２９）ｃｍ³,衔接移位方案分别为ＤＴ（５２.８２±１.３）Ｇｙ和（２.１３±４.１６）ｃｍ３,差异均有统计学意义（Ｐ＜０.０５）。（２）面颈缩野与上后颈电子线照射野衔接时,常规０°水平共线衔接两野相邻处存在低剂量区。５°水平共线成角及０°水平重叠０５ｃｍ衔接时未见明显的低剂量区,但衔接处组织受量增加,ＤＴ２３Ｇｙ以上受照体积分别为（２４.０５±９.０３）ｃｍ３和（４４.７±８.２３）ｃｍ^３,差异有统计学意义（Ｐ＜０.０５）。结论　对于早期初治鼻咽癌常规放疗时,面颈联合野与下颈锁骨上单前野衔接移位方案较常规衔接方案可以明显改善衔接处剂量分布。上后颈电子线照射野与面颈缩野衔接时推荐采用５°水平共线成角照射。     

鼻咽癌常规放射治疗加后程三维适形放射治疗近期疗效观察

目的：探讨鼻咽癌后程三维适形放射治疗（3DCRT）的疗效.方法：40例初治无远处转移的鼻咽癌患者,采用分两阶段对原发灶及颈部放射治疗.第一阶段用面颈联合野常规放疗DT 38Gy,第二阶段用3DCRT DT 30-36Gy,鼻咽癌原发灶总剂量70～74Gy,颈部用切线野常规分割放疗,射野上界保持与主野下界衔接,对颈淋巴结阴性照射DT 50Gy,淋巴结阳性照射DT66-70Gy.结果：局部肿瘤消退率（有效率） 100％,完全缓解率93.85％,1年生存率100％.无严重并发症发生.结论：鼻咽癌常规放射治疗加后程三维适型放射治疗近期疗效满意.     

后程三维适形放射治疗鼻咽癌的近期疗效观察

目的 分析鼻咽癌后程三维适形放射治疗（3DCRT）近期疗效。方法 32例初治无远处转移的鼻咽癌患者，采用分三阶段对原发灶放射治疗。第一段用面颈联合野常规放疗DT 36Gy，第二段用耳前野放疗DT 14Gy，第三段用3DCRT DT 20～25Gy。总照射剂量DT 70～75Gy。颈部用切线野或者加电子线野作常规分割照射，设野上界保持与主野下界衔接，对颈淋巴结阴性照射DT 50Gy，淋巴结阳性照射DT 66～70Gy。结果 局部肿瘤消退率（有效率）100％，完全缓解率93、75％，1年生存率100％。无严重并发症。结论 鼻咽癌后程三维适形放射治疗可以获得比较理想的剂量分布，近期疗效满意。     

无口咽侵犯T1～2N0鼻咽癌放射治疗设野的前瞻性研究

目的评价无口咽侵犯的T1-2N0鼻咽癌不同设野放射治疗的近期疗效。方法将56例T1，2NoM0 1992年福州分期鼻咽癌病人随机分为面颈联合野组（A组）和面颈分野组（B组），A组先设面颈联合野和下颈切线野，均照射36Gy后改双耳前野24Gy，鼻前野8—10Gy和颈前切线野14Gy；B组设置双耳前野60Gy，鼻前野8-10Gy，颈前切线野50Gy。结果放疗结束时，鼻咽原发灶消退率A组和B组分别为96.4％和92．9％，两组无显著差异。A、B组2年总生存率分别为89.3％和85．7％。面颈分野组1例发生放射性颈脊髓损伤，两组急性和慢性放射损伤差异均无显著性。结论T1-2N0M0鼻咽癌病人选用面颈联合野或面颈分野，疗效无显著性差异。5年生存率及远期放射损伤情况有待进一步观察。     

采用等中心加带多叶光栅半野技术治疗鼻咽癌

目的　探讨鼻咽癌病人放疗中面颈野或耳前野与颈切线野的最佳衔接方法。方法　用带多叶光栅(ML C)和独立准直器的直线加速器 ,以一个等中心加 ML C半野技术照射面颈野或耳前野与颈切线野用于放疗鼻咽癌病人。结果　根据测量 ,面颈野或耳前野与颈切线野之间的剂量分布满意 ,无冷点和热点。与初步临床观察相符。结论　用一个等中心加 ML C半野技术放疗鼻咽癌时 ,面颈野或耳前野与颈切线野间的剂量衔接满意     

鼻咽癌常规放射治疗加后程三维适形放射治疗近期疗效观察

目的:探讨鼻咽癌后程三维适形放射治疗(3DCRT)的疗效.方法:40例初治无远处转移的鼻咽癌患者,采用分两阶段对原发灶及颈部放射治疗.第一阶段用面颈联合野常规放疗DT 38Gy,第二阶段用3DCRT DT 30-36Gy,鼻咽癌原发灶总剂量70～74Gy,颈部用切线野常规分割放疗,射野上界保持与主野下界衔接,对颈淋巴结阴性照射DT 50Gy,淋巴结阳性照射DT66-70Gy.结果:局部肿瘤消退率(有效率) 100％,完全缓解率93.85％,1年生存率100％.无严重并发症发生.结论:鼻咽癌常规放射治疗加后程三维适型放射治疗近期疗效满意.     

鼻咽癌面颈联合野与颈切野衔接的不同方法比较

鼻咽癌是我国的常见的恶性肿瘤,有文献报道[1]采用单一等中心半野照射的技术,解决常规放疗中面颈联合野与颈部切线野的衔接。但我们发现面颈联合野的下界较低(颈部淋巴结呈阳性)时都要用楔形板进行剂量补偿,我们统计了常规放疗时的一部分患者的面颈联合野的面积,发现多数的面颈     

Dosimetric evaluation of abutted fields using asymmetric collimators for treatment of head and neck

PURPOSE: The objective of this study was to reevaluate the dose nonuniformity of abutted fields defined using asymmetric collimators and one isocenter for treatment of the head and neck region. METHODS AND MATERIALS: Bilateral parallel-opposed fields abutted to the anterior field at one isocenter were implemented in the treatment of head and neck. The effect of digital display tolerance can produce dose nonuniformity at the junction of the abutted fields. The amount of dose nonuniformity was quantified using both mathematical summation of dose profiles and by direct measurement of doses at the junction of the two abutted fields. The dose nonuniformity was obtained by irradiating the superior part of a film using bilateral parallel-opposed fields and the inferior part by an anterior field with a gap or an overlap. Dose profiles were taken at the depth of maximum dose for the anterior field across the abutted fields. The dose nonuniformity was determined for the case where the asymmetric jaw was set at -2 mm, -1 mm, 0, +1 mm, and +2 mm from the beam central axis. RESULTS: The dose at the junction increases systematically as the abutment of the fields changes from a gap to an overlap. The dose nonuniformity with 1-mm gap and 1-mm overlap is about 15% underdose and overdose, respectively. CONCLUSION: Imperfect abutment of split fields due to digital display tolerance (+/-1 mm) of asymmetric collimator can cause an underdose or overdose of 15% of the delivered dose.     

Dosimetric study of field junction in adjacent beams using asymmetric collimators and MLC

Adjacent treatment fields are commonly employed in external beam radiation therapy, such as the mantle and inverted-Y fields for the treatment of Hodgkin＇s disease. In some cases, the adjacent fields are orthogonal, such as the cra- niospinal fields used in the treatment of medulloblastoma. Another example is the irradiation of head and neck tumors when the lateral neck fields are placed adjacent to the anterior supraclavicular field. In each of these situations, there is a possibility of introducing very large dosage errors across the junction. Consequently, this region is at risk for tumor recurrence if it is underdosed or severe complications if it is overdosed. Four millimeter overlap and gap resulted in an unacceptable dose in homogeneity in the junction. As a result of this study, the magnitudes of hot and cold spots might be clinically acceptable for 3 mm gap between photon fields.     

The effect of independent collimator misalignment on the dosimetry of abutted half-beam blocked fields for the treatment of head and neck cancer.

BACKGROUND AND PURPOSE: Independent collimation conveniently allows for the junctioning of abutting fields with non-diverging beam edges. When this technique is used at the junction of multiple fields, e.g. lateral and low anterior fields in three-field head and neck set-ups, there should be a dosimetric match with no overdose or underdose at the matchline. We set out to evaluate the actual dosimetry at the central match plane. MATERIALS AND METHODS: Independent jaws were used to mimic two half-beam blocked fields abutting at the central axis. X-Ray verification film was exposed in a water-equivalent phantom and the dose at the matchline was evaluated with laser densitometry. Collimators were then programmed to force a gap or overlap of the radiation fields to evaluate the effect of jaw misalignment within the tolerance of the manufacturer's specification. Diode measurements of the field edges were also performed. Four beam energies from four different linear accelerators were evaluated. RESULTS: Small systematic inhomogeneities were found along the matchline in all linear accelerators tested. The maximum dose on the central axis varied linearly with small programmed jaw misalignments. For a gap or overlap of 2 mm between the jaws, the matchline dose increased or decreased by 30-40%. The region of overdose or underdose around the matchline is 3-4 mm wide. The discrepancy between the width of jaw separation and the width of the region of altered dose is explained by a penumbra effect. CONCLUSION: We recommend that independent jaw alignment be evaluated routinely and provide a simple method to estimate dose inhomogeneity at the match plane. If there is a field gap or overlap resulting in a clinically significant change in dosimetry, jaw misalignment should be corrected. If it cannot be corrected, part of the benefit of asymmetric collimation is lost and other methods of field junctioning may have to be considered. We routinely use a small block over the spinal cord at the mono-isocenter set-up plane for three-field head and neck treatments to prevent an overdose.     

用MOSFET探测器进行乳腺癌放疗剂量的实时检测

目的 研究用金属氧化物半导体场效应晶体管(MOSFET)探测器测量接受高能X射线半束照射的乳腺癌患者的照射剂量。方法 采用MOSFET探测器首先在人体模型上测量,研究在6MV X射线半束照射中相邻半野剂量的分布情况和加速器相关因子的影响,然后实时测量10例乳腺癌患者腋锁野与胸壁切线野6MVX射线半束照射时匹配线上、腋锁...     

Linac-based isocentric electron–photon treatment of radically operated breast carcinoma with enhanced dose uniformity in the field gap area

Background and purpose

Isocentric treatment technique is a standard method in photon radiotherapy with the primary advantage of requiring only a single patient set-up procedure for multiple fields. However, in electron treatments the size of the standard applicators does not generally allow to use an isocentric treatment technique. In this work we have modified and dosimetrically tested electron applicators for isocentric treatments in combination with photons. An isocentric treatment technique with photons and electrons for postmastectomy radiation therapy (PMRT) has been developed with special emphasis on improving the dose uniformity in the field gap area.

Materials and methods

Standard electron applicators of two Varian Clinac 2100CD linear accelerators were shortened by 10 cm allowing isocentric treatments of 90 cm < SSD < 100 cm in electron fields. Shortened applicators were commissioned and configured for the electron calculation algorithm of the treatment planning system. The field arrangement of PMRT was modified by combining three photon field segments with different gaps and overlaps with the electron field to improve dose uniformity. The developed technique and two other methods for PMRT were compared with each other in the group of 20 patients.

Results

Depth dose characteristics of the shortened applicators remained unchanged from those of the standard applicators. Penumbrae were broadened by 0-3 mm depending on electron energy and depth as the air gap was increased from 5 cm (standard applicator at SSD = 100 cm) to 10 cm (shortened applicator at SSD = 95 cm). The dose calculation performance of the modified applicators at 95 cm < SSD < 100 cm was considered similar as with standard applicators at SSD = 100 cm using the Gaussian pencil beam electron dose calculation algorithm of the treatment planning system (Varian Eclipse). The modified isocentric treatment technique for PMRT was superior than the traditional two-dimensional technique. However, with the tangential photon fields without electrons the even better dose uniformity within PTV could be achieved but with increased irradiation of healthy tissues (lung, heart, and contralateral breast). The modified isocentric technique was also found faster than the traditional technique with SSD = 100 cm fields.

Conclusions

It is possible to apply an isocentric treatment technique in PMRT with electrons and photons. The homogeneity of the dose distribution can be improved by adding more photon field segments. With the isocentric technique it is possible to achieve even some time sparing in treatment delivery compared with the traditional SSD = 100 cm technique.     

Delta-4探测MLC细小位置偏差敏感性研究

目的 研究Delta-4对MLC细小位置误差的探测敏感性。方法 利用瓦里安Trubeam型直线加速器配置EPID对MLC模拟细小位置偏差能力进行测量。设置2.0 cm (x)×6.0 cm (y)、7.0 cm (x)×6.0 cm (y)2个射野,MLC的x₁、x₂方向同时分别外扩0.1、0.2、0.3……0.9 mm和1.0、2.0……5.0 mm,使用3 mm 3%、2.5 mm2.5%、2 mm 2%、1.5 mm1.5%和1 mm1%标准γ分析。分析Delta-4测量的相对应剂量分布与TPS计算MLC位置不变时的剂量分布间差异。结果 Trubeam型直线加速器MLC具有移动丝米级位置能力。2.0 cm (x)×6.0 cm (y)射野2.5 mm2.5%标准下γ通过率100%,在MLC的x₁、x₂方向各打开0.3 mm时γ通过率下降至95.9%,打开0.5 mm时γ通过率下降至89.4%。7.0 cm (x)×6.0 cm (y)射野1.5 mm1.5%标准下γ通过率为96.5%,x₁、x₂方向各打开0.3 mm时γ通过率下降至95%以下,在打开3.0 mm内γ通过率都>90%。结论 适当提高γ分析标准有可能会改善Delta-4探测MLC位置细小偏差的敏感性,但不能对所有MLC丝米级位置误差探测出来。对不同大小射野,建议Delta-4选择不同分析标准。     

Matchline dosimetry of a three field technique for breast treatment using cobalt or 6 MV X rays

The matchline dose distribution between the tangential and supraclavicular fields used for treatment of breast cancer was investigated using 60Co and 6 MV X rays. Techniques which allow minimum, moderate, and maximum overlap between the fields as well as a geometric alignment technique were studied. For a given technique, comparable matchline widths and doses were obtained with either machine. Average matchline doses were slightly greater with 6 MV X rays, however, more tissue was irradiated to higher dose levels with 60Co. Among the techniques which do not geometrically align the three fields, doses as high as 150% or as low as 70% were observed depending on the amount of overlap between the fields. Matching the tangents 3.5 cm medial and lateral to the supraclavicular field center yielded average maximum and minimum matchline doses within ten percent of those with geometric alignment techniques. However, these distributions will vary with patient size and matchline length. Geometric alignment techniques offer the advantages of matchline dose uniformity and reproducibility over the patient population with maximum matchline doses of only 110-115%.