乳腺癌调强放射治疗和常规切线野治疗的三维剂量学研究

背景与目的:乳房保留治疗已在早期乳腺癌患者中逐渐推广应用,其中全乳根治性放疗的标准技术通常采用常规切线野技术。调强放射治疗(intensity-modulatedradiotherapy,IMRT)技术有望在保障相同疗效的同时进一步减少放疗并发症,提高生活质量。本研究利用三维计划系统评价全乳IMRT的剂量学优势与适应证。方法:选择10例接受保乳手术的Tis～2N0M0早期乳腺癌病例,利用三维治疗计划系统为每例患者设计两种全乳放射治疗计划,切线野常规计划与IMRT计划,处方剂量均为5000cGy。用剂量体积直方图(dosevolumehistograms,DVH)来比较各种计划中计划靶体积(planningtargetvolume,PTV)、危及器官(organsatrisks,OARs)的剂量学差异。结果:靶区覆盖率在两种计划中相似,分别为98.3%和97.7%。与常规计划比较,IMRT计划的PTV接受<95%处方剂量与>103%处方剂量的体积百分比之和(inhomogeneityindex,IHI)从29.9%减少到2.9%,PTV接受至少105%处方剂量照射的体积百分比(V105%)从28.2%减少到0.6%;IMRT计划改善IHI和减少V105%的平均值在PTV较大的患者中优势更明显。左侧患者中冠状动脉的最大剂量(Dmax)以及心脏的平均剂量(Dmean)分别从5057.1cGy减少到4832.9cGy和从629.8cGy到450.7cGy;右侧患者肝脏的Dmean从283.9cGy减少到172.0cGy;所有患者中同侧肺的Dmean、至少接受20Gy照射的体积百分比(V20)分别从925.2cGy减少到765.9cGy,从16.0%到15.3%,Dmean与V20的平均值在IMRT计划中减少的百分比在不同射野中心肺厚度(centrallungdistance,CLD)亚组中分别是14.7%与20.9%,7.0%与12.9%;对侧乳腺和对侧肺的Dmean也分别从75.4cGy减少到20.3cGy和从30.9cGy到16.1cGy。结论:全乳IMRT的剂量学优势主要在于保证靶区覆盖率的前提下,显著改善靶区的剂量分布均匀性并一定程度上降低OARs的受照剂量与容积。乳房体积和CLD较大的病例可以通过IMRT技术获得更好的剂量学结果。     

Comparison of contralateral breast dose for various tangential field techniques in clinical radiotherapy

Contralateral breast (CLB) cancer is a rare but serious concern in radiotherapy. In this study, the CLB dose was measured using MOSFET dosimeter in 49 patients who underwent breast conservation surgery treated by different radiotherapy tangential field techniques, which included enhanced dynamic wedge (EDW), physical wedge, and intensity modulated radiation therapy (IMRT). The mean percent of the prescribed dose received by the contralateral areola in treatment technique using physical wedge (Cobalt), physical wedge (Linac), EDW, and IMRT were 4.27% (SD: 0.65), 3.61% (SD: 0.60), 3.38% (SD: 0.58), and 1.65% (SD: 0.24), respectively. There was a 29% CLB dose reduction at 3 cm from the medial tangential field border with IMRT compared to other wedged tangential field techniques. The study shows that the CLB dose could be reduced with IMRT or reducing or avoiding the medial wedge in conventional tangential field planning for breast cancer.     

乳腺癌保乳术后全乳野中野适形调强放射治疗技术

目的：探讨乳腺癌保乳术后全乳野中野适形调强照射技术方法,并与常规全乳切线野照射技术进行剂量学对比。方法：选取22例早期乳腺癌保乳术后患者在CT模拟机下对乳腺部位行薄层定位扫描,将定位图像传输至治疗计划系统进行全乳野中野计划设计：在全乳两切线适形野的基础上挡去高剂量区部分,另设计2—4个小跳数射野以降低靶区最高剂量和调整高剂量区的范围及所在位置。处方剂量50Gy／25次,要求95％的靶区接受处方剂量;然后利用其CT模拟定位资料按照常规切线野射野方法在治疗计划上模拟常规切线野治疗计划,对野中野计划和常规射野计划进行靶区适形性、靶区均匀性和危及器官受量的比较。结果：野中野适形调强放射治疗技术的适形度、均匀性优于常规切线野照射,靶区内超过110％处方剂量的体积明显小于常规切线野技术。减少了肺组织V20的体积,降低了心脏的平均剂量和受照体积。结论：乳腺癌保乳术后全乳野中野适形调强放射治疗技术是一种有益的全乳照射技术。     

早期乳腺癌保乳术后4种放疗技术的剂量参数比较

目的：比较早期乳腺癌保乳术后常规切线野（TW）、野中野调强（FIF - IMRT）、切线逆向调强（T -IMRT）和容积调强（VMAT）4种放射治疗技术的靶区和危及器官的剂量参数。方法：15例左侧早期（pT1-2 N0 M0）乳腺癌患者保乳术后接受放疗。CT 模拟定位扫描后勾画靶区和危及器官,在同一患者 CT 影像上分别做 TW、FIF - IMRT、T - IMRT 和 VMAT 4种治疗计划设计。PTV 剂量为50Gy,V47.5≥95%。4种计划的剂量限制相同。在剂量-体积直方图中读取4种计划靶区剂量的分布参数,心脏、双侧肺脏及对侧乳腺受照剂量和体积,对各参数的均数进行比较,并比较4组平均机器跳数差异。结果：4种计划都满足 V47.5≥95%。VMAT 与 T - IMRT、FIF - IMRT 和 TW 计划相比,明显提高了靶区适行指数（CI,P ﹤0.05）。VMAT、T - IMRT和 FIF - IMRT 与 TW 相比,明显改善了靶区均匀性指数（HI,P ﹤0.05）。VMAT 增加了危及器官（心脏和同侧肺脏）V 5、V10和 V20的受照射体积,但是没有增加﹥ V30的照射体积。VMAT 明显增加了右侧乳腺和右侧肺脏照射剂量（P ﹤0.05）,T - IMRT 和 FIF - IMRT 明显降低了右侧乳腺和右侧肺脏照射剂量（P ﹤0.05）。VMAT 与T - IMRT、FIF - IMRT 和 TW 相比,明显增加了机器跳数（P ﹤0.05）。结论：早期乳腺癌保乳术后放射治疗4种计划比较,VMAT 明显提高了靶区的适行性和均匀性,增加了正常组织的受照射剂量和机器跳数,延长了治疗时间。T - IMRT 和 FIF - IMRT 也提高了靶区的适行性和均匀性,降低了正常组织的受照射剂量。     

Comparision of Different Radiotherapy Planning Techniques for Breast Cancer after Breast Conserving Surgery

Objectives:To compare different radiotherapy planning techniques for breast cancer after breast conserving surgery.Materials and methods: Eighteen patients with breast cancer who underwent breast conserving surgery were selected.For each patient four different whole breast irradiation techniques including Tan, fIMRT, iIMRT and VMAT werecompared to the conventional tangential technique (Tan). Results: Mean maximum point dose (Dmax) for Tan, fIMRT,iIMRT and VMAT were 110.17% (±1.87), 105.89% (±1.13), 106.47% (±0.92) and 106.99% (±1.16) (p<0.001). Meanminimum point dose (Dmin) from Tan was 84.02% (±3.68) which was significantly higher than those from fIMRT,iIMRT and VMAT which were 76.57% (±11.4), 67.69 %( ±19.20) and 80.69% (±7.06) (p<0.001). Only the meanV95 of fIMRT was significantly less than Tan (p=0.01). Mean percentage of volume receiving ≥ 20 Gy (V20Gy) andmean doses of the ipsilateral lung were 17.09% and 953.05 cGy, 16.60% and 879.20 cGy, 14.79% and 772.26 cGy,15.32% and 984.34 cGy for Tan, fIMRT, iIMRT and VMAT. Only iIMRT had a significantly lower mean V20Gy andthe mean dose to ipsilateral lung in comparison with Tan. Significantly, high mean doses to the contralateral breast(498.07 cGy, p<0.001) were observed in VMAT. Conclusion: The conventional tangential technique provides adequatedose coverage but resulted in high dose-volumes. The iIMRT and fIMRT had significantly smaller high dose-volumesand better conformity. VMAT demonstrated excellent dose homogeneity and conformity but an increased low-dosevolume outside the target should be of concern.     

全乳腺放疗野中野调强技术的三种设计方法对比

[目的]优化全乳腺放疗时野中野调强技术的设计方法。[方法]选取乳腺癌保乳术后患者10例．用野中野调强技术设计全乳腺放疗计划,每例患者分别用完全正向法（正向法）、完全正向加楔形板补偿法（正楔法）和正向加逆向直接射野优化（DMPO）法（正逆法）设计三个治疗计划并进行对比。[结果]只有正逆法的计划靶区（P1rV）剂量分布能达到目标要求（平均剂量5000cGy,均匀性为±5％）,其覆盖99％靶区体积的剂量为4753±28cGy,接受高于5250eGy剂量的靶区体积为0．2％,剂量不均匀性指数为1．092±0．005,均明显优于正向法和正楔法（P〈0．05）。三种方法中同侧肺、左心室和对侧乳房的受量无明显差异。[结论]正向加DMPO的正逆法得到的剂量分布最好,正向加楔形板法产生的照射野最为简单。     

Superficial doses in breast cancer radiotherapy using conventional and IMRT techniques: A film-based phantom study

Background and purpose

Superficial doses in radiotherapy are affected by the treatment technique. The implications for breast cancer treatments were evaluated.

Material and methods

Four treatment techniques relevant for breast cancer irradiation were evaluated; tangential standard, tangential IMRT, 7-field IMRT (arc-like field arrangement) and hybrid IMRT (an IMRT plan mixed with non-modulated fields). Only 6 MV photons were used. GafChromic EBT film was used for dose measurements at the surface, in the skin (0–5 mm depth) and in the superficial parts of CTV (5–10 mm depth) of an anthropomorphic thorax phantom.

Results

Only small differences in superficial doses were observed between tangential standard and tangential IMRT. Compared to the tangential standard plan, the surface and skin doses were reduced with the 7-field IMRT plan, on average by 20% and 5%, respectively, while hybrid IMRT reduced the surface and skin doses medially (by 44% and 8%, respectively) and increased the surface and skin dose laterally (by 40% and 15%, respectively). Minimum superficial CTV doses varied between regions, but were mainly between 90% and 95% of the target dose for all plans, only the hybrid IMRT plan resulted in a region with minimum dose below 90%.

Conclusions

Compared to tangential irradiation, skin sparing was achieved by the 7-field IMRT plan. The minimum dose in the superficial parts of the CTV was below 95% of the target dose for all plans investigated.     

A dosimetric evaluation of conventional helmet field irradiation versus two-field intensity-modulated radiotherapy technique

PURPOSE: To compare dosimetric differences between conventional two-beam helmet field irradiation (external beam radiotherapy, EBRT) of the brain and a two-field intensity-modulated radiotherapy (IMRT) technique. METHODS AND MATERIALS: Ten patients who received helmet field irradiation at our institution were selected for study. External beam radiotherapy portals were planned per usual practice. Intensity-modulated radiotherapy fields were created using the identical field angles as the EBRT portals. Each brain was fully contoured along with the spinal cord to the bottom of the C2 vertebral body. This volume was then expanded symmetrically by 0.5 cm to construct the planning target volume. An IMRT plan was constructed using uniform optimization constraints. For both techniques, the nominal prescribed dose was 3,000 cGy in 10 fractions of 300 cGy using 6-MV photons. Comparative dose-volume histograms were generated for each patient and analyzed. RESULTS: Intensity-modulated radiotherapy improved dose uniformity over EBRT for whole brain radiotherapy. The mean percentage of brain receiving >105% of dose was reduced from 29.3% with EBRT to 0.03% with IMRT. The mean maximum dose was reduced from 3,378 cGy (113%) for EBRT to 3,162 cGy (105%) with IMRT. The mean percent volume receiving at least 98% of the prescribed dose was 99.5% for the conventional technique and 100% for IMRT. CONCLUSIONS: Intensity-modulated radiotherapy reduces dose inhomogeneity, particularly for the midline frontal lobe structures where hot spots occur with conventional two-field EBRT. More study needs to be done addressing the clinical implications of optimizing dose uniformity and its effect on long-term cognitive function in selected long-lived patients.     

The delivery of intensity modulated radiotherapy to the breast using multiple static fields.

BACKGROUND AND PURPOSE: To develop a method of using a multileaf collimator (MLC) to deliver intensity modulated radiotherapy (IMRT) for tangential breast fields, using an MLC to deliver a set of multiple static fields (MSFs). MATERIALS AND METHODS: An electronic portal imaging device (EPID) is used to obtain thickness maps of medial and lateral tangential breast fields. From these IMRT deliveries are designed to minimize the volume of breast above 105% of prescribed dose. The deliveries are universally-wedged beams augmented with a set of low dose shaped irradiations. Dosimetric and planning QA of this method has been compared with the standard, wedged treatment and the corresponding treatment using physical compensators. Several options for delivering the MSF treatment are presented. RESULTS: The MSF technique was found to be superior to the standard technique (P value=0.002) and comparable with the compensated technique. Both IMRT methods reduced the volume of breast above 105% dose from a mean value of 12.0% of the total breast volume to approximately 2.8% of the total breast volume. CONCLUSIONS: This MSF method may be used to reduce the high dose volume in tangential breast irradiation significantly. This may have consequences for long-term side effects, particularly cosmesis.     

Dose to the contralateral breast due to primary breast irradiation

The radiation dose received by the contralateral breast during primary breast irradiation is of concern because breast tissue is subject to cancer induction from low to moderate doses of radiation. In this paper the dose to the opposite breast has been studied in detail for common breast treatment techniques. Measurements have been made on 16 patients, a water phantom, a polystyrene phantom with cork inserts to simulate lung tissue, and a body-shaped phantom with wax breasts. Thermoluminescent dosimeters (TLD), ion chambers, diodes, and film have been used in the various configurations. The patient measurements have shown that there is a wide variation in the opposite breast dose received by patients, even when all are treated with, for example, tangential fields alone. Addition of more radiation fields, such as supraclavicular/axillary and internal mammary fields, may increase the dose to the opposite breast for a particular patient. Variations in the details of the technique such as what wedges are used, the use of blocks, and the orientation of the field edges are all important to the final dose received by the patient's contralateral breast. With the phantom measurements, it has been possible to determine the contributions to the opposite breast dose from each of the relevant factors. This makes it possible to explain the wide variation in patient dose measurements, and to make some relatively simple recommendations that will allow the reduction of the dose to the opposite breast from several hundred cGy to about 50 cGy for a typical treatment course dose of 5000 cGy.     

Multileaf field-in-field forward-planned intensity-modulated dose compensation for whole-breast irradiation is associated with reduced contralateral breast dose: a phantom model comparison.

PURPOSE: Static multileaf collimated field-in-field forward-planned intensity-modulated radiation treatment (FiF-IMRT) has been shown to improve dose homogeneity compared to conventional wedged fields. However, a direct comparison of the scattered dose to the contralateral breast resulting from wedged and FiF-IMRT plans remains to be documented. METHODS: The contralateral scattered breast dose was measured in a custom-designed anthropomorphic breast phantom in which 108 thermoluminescent dosimeters (TLDs) were volumetrically placed every 1-2cm. The target phantom breast was treated to a dose of 50Gy using three dose compensation techniques: No medial wedge and a 30-degree lateral wedge (M0-L30), 15-degree lateral and medial wedges (M15-L15), and FiF-IMRT. TLD measurements were compared using analysis of variance. RESULTS: For FiF-IMRT, the mean doses to the medial and lateral quadrants of the contralateral breast were 112cGy (range 65-226cGy) and 40cGy (range 18-91 cGy), respectively. The contralateral breast doses with FiF-IMRT were on average 65% and 82% of the doses obtained with the M15-L15 and M0-L30 techniques, respectively (p<0.001). Compared to the M15-L15 technique, the maximum dose reduction obtained with FiF-IMRT was 115cGy (range 13-115cGy). CONCLUSIONS: The dose to the contralateral breast is significantly reduced with FiF-IMRT compared to wedge-compensated techniques. Although long-term follow-up is needed to establish the clinical relevance of this finding, these results, along with the previously reported improvement in ipsilateral dose homogeneity, support the use of FiF-IMRT if resources permit.     

An improved breast irradiation technique using three-dimensional geometrical information and intensity modulation.

BACKGROUND AND PURPOSE: In spite of the complex geometry of the breast, treatment planning for tangential breast irradiation is conventionally performed using two-dimensional patient anatomy information. The purpose of this work was to develop a new technique which takes the three-dimensional (3D) patient geometry into account. MATERIALS AND METHODS: An intensity-modulated radiotherapy (IMRT) technique was developed based on the division of the tangential fields in four multi-leaf collimator (MLC) shaped segments. The shape of these segments was obtained from an equivalent path length map of the irradiated volume. Approximately 88% of the dose was delivered by two open fields covering the whole treated volume. Dose calculations for the IMRT technique and the conventional technique were performed for five patients, using computer tomography (CT) data and a 3D calculation algorithm. A planning target volume (PTV) and ipsilateral lung volume were delineated in these CT data. RESULTS: All patients showed similar equivalent path length patterns. Analysis of the dose distribution showed an improved dose distribution using the IMRT technique. The dose inhomogeneity in the PTV was 9.0% (range 6.4-11.4%) for the conventional and 7.6% (range 6.5-10.3%) for the IMRT technique. The mean lung dose was reduced for the IMRT technique by approximately 10% compared with the conventional technique. CONCLUSION: A new breast irradiation technique has been developed which improves the dose homogeneity within the planning target volume and reduces the dose to the lung. Furthermore, the IMRT technique creates the possibility to improve the field matching in case of multiple field irradiations of the breast and lymph nodes.     

Dosimetric comparison of intensity modulated radiotherapy techniques and standard wedged tangents for whole breast radiotherapy*

Prior to introducing intensity modulated radiotherapy (IMRT) for whole breast radiotherapy (WBRT) into our department we undertook a comparison of the dose parameters of several IMRT techniques and standard wedged tangents (SWT). Our aim was to improve the dose distribution to the breast and to decrease the dose to organs at risk (OAR): heart, lung and contralateral breast (Contra Br). Treatment plans for 20 women (10 right‐sided and 10 left‐sided) previously treated with SWT for WBRT were used to compare (a) SWT; (b) electronic compensators IMRT (E‐IMRT); (c) tangential beam IMRT (T‐IMRT); (d) coplanar multi‐field IMRT (CP‐IMRT); and (e) non‐coplanar multi‐field IMRT (NCP‐IMRT). Plans for the breast were compared for (i) dose homogeneity (DH); (ii) conformity index (CI); (iii) mean dose; (iv) maximum dose; (v) minimum dose; and dose to OAR were calculated (vi) heart; (vii) lung and (viii) Contra Br. Compared with SWT, all plans except CP‐IMRT gave improvement in at least two of the seven parameters evaluated. T‐IMRT and NCP‐IMRT resulted in significant improvement in all parameters except DH and both gave significant reduction in doses to OAR. As on initial evaluation NCP‐IMRT is likely to be too time consuming to introduce on a large scale, T‐IMRT is the preferred technique for WBRT for use in our department.     

Reduction of cardiac and lung complication probabilities after breast irradiation using conformal radiotherapy with or without intensity modulation.

PURPOSE: The main purpose of this work is to reduce the cardiac and lung dose by applying conformal tangential beam irradiation of the intact left breast with and without intensity modulation, instead of rectangular tangential treatment fields. The extension of the applicability of the maximum heart distance (MHD) to conformal tangential fields as a simple patient selection criterion, identifying patients for which rectangular and conformal tangential fields without intensity modulation will result in unacceptable normal tissue complication probability (NTCP) values for late cardiac mortality (e.g. >2%), was also investigated. MATERIALS AND METHODS: Three-dimensional treatment planning was performed for 17 left-sided breast cancer patients. Three different tangential beam techniques were compared: (1) optimized wedges without blocks, (2) optimized wedges with conformal blocks and (3) intensity modulation. Plans were evaluated using dose-volume histograms (DVHs) for the planning target volume (PTV), the heart and the lungs. NTCPs for radiation pneumonitis and late cardiac mortality were calculated using the DVH data. The MHD was measured for all rectangular (MHD(rectangular)) and conformal (MHD(conformal)) treatment plans. RESULTS: For all patients, on average, part of the PTV receiving a dose between 95 and 107% of the prescribed dose of 50Gy in 25 fractions of 2Gy was 90.8% (standard deviation (SD): 5.0%), 92.8% (SD: 3.5%) and 92.8% (SD: 3.6%) for the intensity modulation radiation therapy (IMRT), conformal and rectangular field treatment techniques, respectively. The NTCP for radiation pneumonitis was 0.3% (SD: 0.1%), 0.4% (SD: 0.4%) and 0.5% (SD: 0.6%) for the IMRT, conformal and rectangular field techniques, respectively. The NTCP for late cardiac mortality was 5.9% (SD: 2.2%) for the rectangular field technique. This value was reduced to 4.0% (SD: 2.3%) with the conformal technique. A further reduction to 2.0% (SD: 1.1%) could be accomplished with the IMRT technique. The NTCP for late cardiac mortality could be described as a second order polynomial function of the MHD. This function could be described with a high accuracy and was independent of the technique for which the MHD was determined (r(2)=0.88). In order to achieve a NTCP value for late cardiac mortality below 1, 2 or 3%, the MHD should be equal to or smaller than 11, 17 or 23 mm, respectively. If such a maximum complication probability cannot be accomplished, a treatment using the IMRT technique should be considered. CONCLUSIONS: The use of conformal tangential fields decreases the NTCP for late cardiac toxicity on average by 30% compared to using rectangular fields, while the tangential IMRT technique can further reduce this value by an additional 50%. The MHD can be used to estimate the NTCP for late cardiac mortality if rectangular or conformal tangential treatment fields are used.     

A mobile shield to reduce scatter radiation to the contralateral breast during radiotherapy for breast cancer: preclinical results

Purpose: To design a practical breast shield and to investigate its efficacy in reducing scattered radiation to the contralateral breast of patients undergoing radiation therapy for breast cancer.

Methods and Materials: We constructed a mobile shield consisting of (a) a mobile base and a counterweight; (b) a vertical column adjustable in height and a diagonal arm adjustable in angle; (c) a curved, 2.5-cm thick lead sheet with a 1-cm thick polystyrene liner for blocking scattered radiation; and (d) diode detectors to verify that the edge of the lead sheet is not in the useful beam in addition to the use of the field light. Measurements were performed with thermoluminescent dosimeters on 10 patients without the shield and on an anthropomorphic phantom with a pair of wax breasts with and without the shield. All of the patients were treated with 6-MV photons (Varian 6/100). The scattered radiation from the medial and lateral fields was measured separately.

Results: The contribution of the medial field to the total scattered dose was 70% to 75%, whether a medial wedge was used or not. However, without a medial wedge, the scattered dose was reduced by nearly 33% at 3 to 9 cm away from the medial border. In the anthropomorphic phantom study with wax breast, the mobile shield reduced the medial field contribution to the total scatter dose to less than the contribution from the lateral field without a shield. With a prescribed dose of 50 Gy and a medial wedge, the median scatter dose to the contralateral breast from 6 patients was 5.3 Gy; without a medial wedge, it was 3.8 Gy from 4 patients at 6 cm from the medial border. In the phantom study, with the shield the total dose to the contralateral breast was 1.0 Gy at 6 cm from the medial border with a same prescribed dose.

Conclusion: The mobile shield reduced the scatter dose to the contralateral breast from the linear accelerator (Varian 6/100, 6-MV photons) by a factor of 3 to 4. The shield greatly reduced the scattered dose in the wax phantom. Equivalent reductions in patients may be clinically significant by reducing the risk of radiation-induced breast cancer in the contralateral breast of woman undergoing radiation therapy for breast cancer. The shield is safe and easy to adjust to each patient.     

Analysis of axillary coverage during tangential radiation therapy to the breast

PURPOSE: To evaluate the percent of the prescribed radiation dose to the breast delivered to the axillary tissue and to evaluate the volume of the axilla receiving 95% of the prescribed dose with normal and with high tangential fields. METHODS AND MATERIALS: Computed tomographic scan images with 5-mm sections were retrospectively analyzed for 35 patients who had undergone three-dimensional (3D) planning for whole-breast radiation. The axillary nodal region was identified and divided into Levels I to III and Rotter's nodes (RN). Digitally reconstructed radiographs were created, and two plans were developed: (a) the standard clinical opposed tangential irradiation fields and (b) the high-tangential irradiation fields. Axillary coverage was examined by use of dose-volume histograms (DVH), and the average coverage for the four nodal groups was obtained. RESULTS: The data show that with the standard tangential irradiation fields, the average dose delivered to Levels I, II, III, and RN is 66% (standard deviation, or SD = 13%), 44% (SD = 18%), 31% (SD = 20%), and 70% (SD = 19%) of the prescribed dose, respectively. The coverage increases to 86% (SD = 9%), 71% (SD = 19%), 73% (SD = 17%), and 94% (SD = 8%) of the prescribed dose, respectively, for Levels I, II, III, and RN when the high tangential irradiation fields are used. 51% of Level I, 26% of Level II, and 15% of Level III receive 95% of the prescribed dose with normal tangents. The volume increases to 79%, 51%, and 49% of Levels I, II, and III, respectively, with high tangents. CONCLUSION: The tangential fields designed to treat only the breast do not adequately cover the axillary region and, therefore, cannot be relied upon for prophylactic therapy of the axilla. The high tangential irradiation fields increase the dosages received by the axillary region, but the average dosages received by the lower axillary regions are still less than 90% of the prescribed dose.     

A comparison of different intensity modulation treatment techniques for tangential breast irradiation

Purpose: Several intensity modulation (IM) treatment techniques for tangential breast irradiation were evaluated in terms of dose uniformity in the treated breast volume, contralateral breast dose, and treatment irradiation time.

Methods and Materials: Contralateral breast dose was measured via TLD chips, and the dose uniformity was calculated on two anthropomorphic phantoms. IM was applied to all beams or to the lateral-medial (LM) beam only. The techniques evaluated include (a) IM via “step & shoot” multileaf collimator (MLC), (b) IM via intensity modulator (compensator), (c) virtual wedge, and (d) physical wedge. A dose optimization algorithm was used for the first two techniques.

Results: Collimator-generated IM techniques (MLC-IM and the virtual wedge) produced 50% (average) less contralateral breast dose than the conventional two-wedge technique. When the compensator or the physical wedge was used, contralateral breast dose was reduced 30% (average) by leaving the ML beam open.

Conclusion: The treatments generated by dose optimization algorithm and delivered via the compensator and MLC techniques offered superior dose uniformity. Single-beam IM techniques in general use less irradiation time without significant degradation of dose uniformity. The MLC-IM technique in this study required the longest treatment irradiation time, while the virtual wedge and compensator IM techniques required the least.     

The use of compensators to optimise the three dimensional dose distribution in radiotherapy of the intact breast

Background and purpose: Dose heterogeneity in tangential breast irradiation has been shown to be as high as 20% and may lead to problems in local control and cosmesis. In this study, dose heterogeneity in three dimensions (3D) in the breast irradiated with wedged tangential beams is assessed and the improvement which can be made by the use of individualised two dimensional (2D) compensators is established. The compensation required is calculated in two ways: (I) by an iterative technique giving a uniform dose on a plane through the isocentre normal to the central axis of each beam, and (II) by inverse planning using an optimisation technique based on simulated annealing.

Materials and methods: A total of 17 patients with histologically proven T0-3, N0, N1, M0 breast cancer undergoing breast irradiation following wide local excision, were CT scanned using contiguous 1 cm slices from approximately 2 cm superior to 2 cm inferior of the irradiated volume. The dose distributions are determined using a 3D algorithm that calculates primary and scatter dose separately using a differential scatter air ratio method and corrects both for the presence of heterogeneities. The iterative technique achieves a dose variation of better than 0.5% on the plane through the isocentre with compensation on both beams. Compensation for the lateral beam only is calculated using the optimisation technique in order to minimise the scatter dose to the contralateral breast. The optimisation algorithm minimises the dose variance over the target and sets upper dose limits for the lung and the remainder of the irradiated volume.

Results: For the group of patients the average dose heterogeneity in 3D using wedges is 12% (range 8–17%), which reduces to 8% (5–16%) using compensation on a plane and to 5% (4–7%) using the optimisation technique.

Conclusions: Inverse planning is normally used for complex radiotherapy techniques but when applied to tangential breast irradiation, can reduce the dose heterogeneity through the breast as a whole to as little as 4%, with potential benefits in local control and cosmesis.     

大分割模式下左侧乳腺癌保乳术后调强放疗方式的探索

目的:比较左侧乳腺癌保乳术后大分割放疗时,野中野正向调强（field-in-field intensity modulated radiation therapy,FIF-IMRT）、逆向调强（intensity modulated radiation therapy,IMRT）两种模式对改善靶区剂量分布和保护正常组织的差异。方法:对30例左侧乳腺癌保乳术后患者予以CT定位,分别制定FIF-IMRT及IMRT二种照射计划,总剂量均为42.65 Gy,共照射16次。分别比较两组计划的靶区剂量分布、危及器官,如心脏、肺脏、脊髓等所受剂量以及加速器总跳数（accelerator monitor unit,MU）的差异。结果:FIF-IMRT与IMRT组PTV(planning target volume)的Dmax分别为4 762.35 cGy（4 710.08,4 829.10）cGy、4 714.60 cGy（4 659.55,4 740.85）cGy（P=0.001）,均匀性指数分别为0.10（0.09,0.11）和0.09（0.08,0.10）（P=0.008）;在危及器官受量方面,FIF-IMRT组较IMRT组明显降低心脏V5、V10和左肺V5、V10（P值分别为<0.001、<0.001、0.003、0.014）,右乳Dmax、Dmean和脊髓Dmax、DmeanFIF-IMRT组均显著低于IMRT组（P值分别为0.048、0.044、<0.001、<0.001）。FIF-IMRT组MU低于IMRT组（P=0.001）。结论:两种大分割调强模式均能满足左侧乳腺癌保乳术后的治疗要求。IMRT提高靶区剂量分布均匀性,但FIF-IMRT能更好降低心脏和左肺V5、V10等低剂量照射范围,且对机器损耗更小,可能是更好的选择。