Foetal radiation dose in radiotherapy for breast cancer.

Management of breast cancer during pregnancy is complicated by the high risks of abortion and foetal malformation from the use of radiotherapy and chemotherapy. A case of breast cancer during pregnancy, treated with radiotherapy, and the estimated foetal dose is reported.     

Interfractional fluctuation of rectal dose in high dose rate brachytherapy for prostate cancer

Purpose The aim of the study was to explore the cause of the difference in the maximal rectal dose between the first and second high dose rate (HDR) brachytherapy applications by comparing the thickness of the anterior rectal wall. Materials and methods The rectal dose and the thickness of the anterior rectal wall were analyzed in 26 patients with prostate cancer. After undergoing external beam radiation treatment with a total isocenter dose of 50 Gy, they were treated with HDR brachytherapy of 7.5 Gy/fraction, two fractions daily. The interval between the first HDR brachytherapy session and the second was 5 h. The rectal doses were directly surveyed during irradiation of the HDR brachytherapy. Thickening of the anterior rectal wall was measured at the same level by axial computed tomography scans obtained before the first and second HDR brachytherapy applications. Results The maximal surveyed rectal doses during the first and second HDR brachytherapy applications were 188 ± 51 cGy and 220 ± 35 cGy, respectively (P < 0.01). The fluctuation ratio exceeded 1 in each case. The thickness of the anterior rectal wall before the first and second HDR brachytherapy applications was 18.78 ± 4.34 mm and 14.95 ± 4.09 mm (P < 0.01), respectively. The fluctuation difference exceeded 0 in each case. Conclusion The different rectal dose is attributable to thinning of the anterior rectal wall. The total rectal dose is within the range of doses at risk of exerting a toxic effect on the rectum.     

Interfractional variability in intensity-modulated radiotherapy of prostate cancer with or without thermoplastic pelvic immobilization

Purpose

To determine the variability of patient positioning errors associated with intensity-modulated radiotherapy (IMRT) for prostate cancer and to assess the impact of thermoplastic pelvic immobilization on these errors using kilovoltage (kV) cone-beam computed tomography (CBCT).

Materials and methods

From February 2012 to June 2012, the records of 314 IMRT sessions in 19 patients with prostate cancer, performed with or without immobilization at two different facilities in the Korea University Hospital were analyzed. The kV CBCT images were matched to simulation computed tomography (CT) images to determine the simulation-to-treatment variability. The shifts along the x (lateral)-, y (longitudinal)- and z (vertical)-axes were measured, as was the shift in the three dimensional (3D) vector.

Results

The measured systematic errors in the immobilized group during treatment were 0.46?±?1.75 mm along the x-axis, ??0.35?±?3.83 mm along the y-axis, 0.20?±?2.75 mm along the z-axis and 4.05?±?3.02 mm in the 3D vector. Those of nonimmobilized group were ??1.45?±?7.50 mm along the x-axis, 1.89?±?5.07 mm along the y-axis, 0.28?±?3.81 mm along the z-axis and 8.90?±?4.79 mm in the 3D vector. The group immobilized with pelvic thermoplastics showed reduced interfractional variability along the x- and y-axes and in the 3D vector compared to the nonimmobilized group (p?<?0.05).

Conclusion

IMRT with thermoplastic pelvic immobilization in patients with prostate cancer appears to be useful in stabilizing interfractional variability during the planned treatment course.     

Beam angle manipulation to reduce cardiac dose during breast radiotherapy

Objective

Standard tangential radiotherapy techniques after breast conservative surgery (BCS) often results in the irradiation of the tip of the left ventricle and the left anterior descending coronary artery (LAD), potentially increasing cardiovascular morbidity. The importance of minimising radiation dose to these structures has attracted increased interest in recent years. We tested a hypothesis that in some cases, by manipulating beam angles and accepting lower-than-prescribed doses of radiation in small parts of the breast distant from the surgical excision site, significant cardiac sparing can be achieved compared with more standard plans.

Methods

A sample of 12 consecutive patients undergoing radiotherapy after left-sided BCS was studied. All patients were planned with a 6 MV tangential beam, beam angles were manipulated carefully and if necessary lower doses were given to small parts of the breast distant from the surgical excision site to minimise cardiac irradiation (“institutional” plan). Separate “hypothetical standard” plans were generated for seven patients using set field margins that met published guidelines.

Results

In seven patients, the institutional plans resulted in lower doses to the LAD and myocardium than the hypothetical standard plans. In the other five patients, LAD and myocardial doses were deemed minimal using the hypothetical standard plan, which in these patients corresponded to the institutional plan (the patients were actually treated using the institutional plans).

Conclusion

Much attention has been devoted to ways of minimising cardiac radiation dose. This small sample demonstrates that careful manipulation of beam angles can often be a simple, but effective technique to achieve this.Late cardiovascular morbidity associated with breast irradiation has received considerable attention recently, especially as diagnostic and therapeutic advances have translated into improvements in long-term survival [1].Most invasive breast cancers are discovered at an early localised stage and can be treated with breast conservation surgery (BCS) and adjuvant radiotherapy with equivalent survival rates to mastectomy [2-4]. Whole-breast radiation therapy conventionally uses tangential beam arrangements, which include the entire breast, a portion of the chest wall and some contents of the anterior thoracic cavity. In left-sided breast irradiation, the field can include a significant volume of the heart. The mean cardiac dose from left-sided breast irradiation can be two or three times that of right-sided breast irradiation. In women treated in the 1950s to 1990s, it has been estimated that the mean cardiac dose was 0.9–14 Gy and 0.4–6 Gy for left and right breast/chest wall irradiation, respectively [5]. Using 6 MV tangential radiotherapy, the mean cardiac doses were 4.7 Gy and 1.5 Gy, and the mean left anterior descending coronary artery (LAD) doses were 21.9 Gy and 1.4 Gy for left and right breast irradiation, respectively [5].In a meta-analysis by the Early Breast Cancer Trialists'' Collaborative Group that included 78 randomised trials of breast or chest wall irradiation after surgery, there was an excess of non-breast cancer deaths owing to heart disease and lung cancer [6]. A population study showed that the cardiac mortality is 25% higher among women treated for left-sided breast tumours than those treated for right-sided tumours 15 years after treatment [7]. In another study of women irradiated between 1973 and 1982, the cardiac mortality ratio (left vs right breast cancer) was 1.42 after 10–14 years and 1.58 after 15 years [8].Cardiovascular toxicity associated with radiation includes coronary artery disease, valvular disease, chronic pericardial disease, arrhythmia and conduction disturbances, and cardiomyopathy [9,10]. The exact mechanism of radiation-related heart disease and the threshold dose at which damage to the heart caused by radiation occurs is still unclear, which stresses the importance of striving to minimise the dose to the heart and the volume irradiated whenever possible. A review of some of the experiments investigating coronary artery disease after radiation has suggested that radiation increases myocardial infarction (MI) frequency by interacting with the pathological pathway of age-related coronary artery atherosclerosis resulting in accelerated atherosclerosis [10]. Radiation could also increase lethality of age-related MI by reducing the heart''s tolerance to acute infarctions as a result of microvascular myocardial damage [10].There is a correlation between cardiac perfusion defects and the volume of irradiated left ventricle; the defects becoming evident when 6% of the ventricle is irradiated by greater than 23–25 Gy [11]. A cardiac catheterisation study showed that there was an excess of cardiac stress test abnormalities among left-side irradiated patients; these were located in the anterior heart, which is most at risk in the tangential field and with 85% of abnormalities occur as stenoses of the LAD [12]. In a study of 50 patients treated with left tangential irradiation, the mean heart dose was 2.3 Gy and the mean LAD dose was 7.6 Gy [13]. A dosimetric study of 20 patients who had left-sided breast radiotherapy found that standard tangential radiotherapy resulted in a mean dose of 2.9 Gy to the heart, 12.05 Gy to the proximal LAD, 31.52 Gy to the distal LAD and a V₃₀ (the volume receiving more than 30 Gy) of 23.09±28.37% for the proximal LAD and 45.43±42.5% for the distal LAD [14].As patients with early breast cancer have an increasingly good prognosis, consideration of long-term effects such as cardiac toxicity and resulting complications is necessary when planning post-operative radiotherapy. It usually takes 10 years for radiation-related coronary artery disease and cardiac deaths to become apparent after breast irradiation [15]. However, it has been highlighted that delineation of anatomical subregions of the irradiated heart and LAD is challenging because it is difficult to accurately visualise these structures using current imaging modalities used in treatment planning [16].Since the 1970s, it has been estimated that left chest wall/breast tangential radiotherapy-associated heart dose has reduced from 14 Gy with 250 kV to 4.7 Gy with cobalt-60, to 2.3 Gy with CT planned 6 MV photons [13,17]. However, with the increased use of anthracyclines, taxanes and trastuzumab there may be a potential increase in cardiac toxicity in the future. The literature review on radiation dose–volume effect on the heart did not show a clear quantitative dose and/or volume dependence for cardiac toxicity owing to scarcity of data [16]. As mentioned previously, this highlights the importance of minimising both the dose to these structures and the volume being irradiated as much as possible. There has been considerable interest in developing modern technology for radiotherapy planning to avoid excess cardiac irradiation, by modulation of the dose around organs at risk (OAR) using intensity modulated radiotherapy (IMRT) [18,19], IMRT with simultaneously integrated boost [20], placement of heart blocks [21] and deep inspiratory breath-holding (DIBH) and gated techniques [22-25]. Beam angle modulation remains a very simple, and, up until now, rather neglected way of achieving this outcome.We hypothesised that in some cases, in comparison with “standard” plans, beam angle manipulation to reduce the dose to the LAD and the heart, while accepting lower-than-prescribed doses in small parts of the breast distant from the site of surgical excision, could lead to significant cardiac and LAD sparing without compromising the dose delivered to the “high-risk” part of the breast. This was done using dose–volume histograms (DVHs) of breast tissue, myocardium and LAD, taken from actually used plans, and “hypothetical standard” plans (see Methods and Materials for definition) in a series of our patients.     

左乳癌保乳术后混合调强放疗中利用多叶准直器遮挡技术减少心脏受照剂量的研究

目的 利用多叶准直器（MLC）遮挡技术减少左侧乳腺癌患者保乳术后混合调强放疗中心脏的受照剂量,降低放射性心脏损伤发生的风险。方法 选取18例左乳癌保乳术后患者,在自由呼吸状态下获取3DCT和4DCT图像。利用4DCT在3DCT图像上确定出靶区并分别制定混合调强治疗计划（H_IMRT）和为降低心脏受量而引入MLC遮挡技术的治疗计划（HSH_IMRT）,利用Compass系统对治疗计划进行剂量学验证。靶区处方剂量为50 Gy,分25次完成。比较两种治疗计划结果与剂量验证结果中靶区及危及器官的剂量学参数。结果 计划结果显示,与H_IMRT比较,HSH_IMRT靶区剂量均匀性更好,适形度差异无统计学意义（P>0.05）;全心脏D_mean较前者降低23.67%（t=13.693,P<0.05）,心脏其他亚结构的D_max和D_mean均较前者下降。剂量验证结果显示,两种计划靶区剂量均匀性与适形度差异无统计学意义（P>0.05）;HSH_IMRT与H_IMRT比较,全心脏的D_mean降低24.88%（t=13.782,P<0.05）;除左心室、右心室外,其他心脏亚结构的D_max以及所有心脏亚结构的D_mean均降低。患侧肺的V₂₀和D_mean在计划结果与验证结果中均显示HSH_IMRT更低。结论 在H_IMRT中合理引入MLC遮挡技术能够在保证其剂量学优势的前提下更多地减少心脏组织的受量,进一步降低心脏发生放射性损伤的风险。     

Prognostic factors in breast cancer. Consequences for radiotherapy

Even today the therapeutic strategy in the treatment of breast cancer is governed by prognostic factors, such as the size and type of the tumor, histological grading, and the number of lymph node metastases. In addition to other criteria, a decision must also be made as to whether changes in the radiotherapy technique (dosage, means of boostering) might lead to better results in the treatment of carcinoma of the breast in patients in poor condition. Several studies indicate that the effectiveness of irradiation can be improved (even with respect to longterm results) by alterations in the technique and careful adaptation to the surgical procedure.     

Assessment of contralateral mammary gland dose in the treatment of breast cancer using accelerated hypofractionated radiotherapy

AIM:To measure the dose distribution,related to the treatment planning calculations,in the contralateral mammary gland of breast cancer patients treated with accelerated hypofractionated 3-dimensional conformal radiotherapy.METHODS:Thirty-four prospectively selected female patients with right breast cancer (pN0,negative surgical margins) were treated with breast-conserving surgery.A total dose of 42.5 Gy (2.66 Gy/fraction) was prescribed;it was requested that planning target volumes be covered by the 95% isodose line.The contralateral mam-mary gland was defined on CT simulation.The dose received was evaluated by dose volume histograms.RESULTS:The measured contralateral breast doses were:(1) Dose maximum:290-448 cGy [Equivalent (Eq) 337-522 cGy];(2) Mean dose:45-70 cGy (Eq 524815 cGy);and (3) Median dose:29-47 cGy (337-547 cGy) for total primary breast dose of 42.5 Gy in 16 equal fractions.The spearman rho correlation showed statistical significance between the contralateral breast volume and maximum dose (P=0.0292),as well as mean dose (P=0.0025) and median dose (P=0.046) to the breast.CONCLUSION:Minimizing the dose to the contralateral breast has to be one of the priorities of the radiation oncologist when using short schedules because of the radiosensitivity of this organ at risk.Further study is necessary to assess the long-term clinical impact of this schedule.     

Side effects of radiotherapy in breast cancer patients

Aim

Breast cancer is the most common cancer type among women necessitating adjuvant radiotherapy. As the Internet has become a major source of information for cancer patients, this study aimed to evaluate the quality of websites giving information on side effects of radiotherapy for breast cancer patients.

Methods

A patients’ search for the English terms “breast cancer – radiotherapy – side effects” and the corresponding German terms “Brustkrebs – Strahlentherapie – Nebenwirkungen” was carried out twice (5 months apart) using the search engine Google. The first 30 search results each were evaluated using the validated 16-question DISCERN Plus instrument, the Health on the Net Code of Conduct (HONcode) certification and the Journal of the American Medical Association (JAMA) benchmark criteria. The overall quality (DISCERN score) of the retrieved websites was further compared to queries via Bing and Yahoo search engines.

Results

The DISCERN score showed a great range, with the majority of websites ranking fair to poor. Significantly superior results were found for English websites, particularly for webpages run by hospitals/universities and nongovernmental organizations (NGO), when compared to the respective German categories. In general, only a minority of websites met all JAMA benchmarks and was HONcode certified (both languages). We did not determine a relevant temporal change in website ranking among the top ten search hits, while significant variation occurred thereafter. Mean overall DISCERN score was similar between the various search engines.

Conclusion

The Internet can give breast cancer patients seeking information on side effects of radiotherapy an overview. However, based on the currently low overall quality of websites and the lack of transparency for the average layperson, we emphasize the value of personal contact with the treating radio-oncologist in order to integrate and interpret the information found online.

     

乳腺癌放疗中两种不同摆位方式的剂量分布及摆位误差比较

目的 比较研究乳腺癌放射治疗成角度胸前板（ABB）和平板胸前板（PBB）两种摆位方法治疗计划的剂量学参数及摆位误差。方法 选取2017年3月至2018年1月在浙江大学医学院附属第一医院就诊的20例左侧乳腺癌术后患者病例资料,按不同摆位方法分ABB组和PBB组,每组10例,在定位扫描的CT图像上勾画靶区、心脏和肺等结构。计划设计采用切线野中野（FIF）技术,比较两种摆位方法治疗计划的计划靶区体积（PTV）、肺、心脏的剂量学参数及摆位误差。结果 两种摆位方式治疗计划在肿瘤靶区覆盖方面差异无统计学意义（P>0.05）。患侧肺V₂₀ ABB组和PBB组分别为（11.2±3.2）%和（15.9±5.3）%,两组比较差异有统计学意义（t=-2,47,P<0.05）,V₃₀ ABB组和PBB组分别为（9.8±1.5）%和（12.9±2.2）%,两组比较差异有统计学意义（t=-4.46,P<0.05）。心脏剂量V₂₅ ABB组和PBB组分别为（1.9±0.2）%和（2.8±0.4）%,两组比较差异有统计学意义（t=-8.28,P<0.05）,V₃₀ ABB组和PBB组分别为（1.8±0.1）%和（2.7±0.3）%,两组比较差异有统计学意义（t=-8.34,P<0.05）,心脏平均剂量D_mean ABB组和PBB组分别为（3.0±0.5）和（5.3±1.2）Gy,两组比较差异有统计学意义（t=5.58,P<0.05）。ABB摆位在左右（LR）、上下（SI）、前后（AP）的平移误差分别为（3.23±2.63）、（5.42±3.22）、（4.58±2.30）mm,在θ、Φ、ψ方向的旋转误差分别为（1.60±0.56）°、（3.40±1.65）°、（2.50±1.72）°。PBB摆位误差在LR、SI、AP的平移误差分别为（2.35±1.22）、（2.17±1.29）、（2.27±1.58）mm,在θ、Φ、ψ方向的旋转误差分别为（1.37±0.43）°、（1.79±0.71）°、（2.06±0.63）°,且进出SI、前后AP、侧翻Φ误差,两组比较差异均有统计学意义（t=3.06,2.80,3.33,P<0.05）。结论 两种摆位方式治疗计划在肿瘤靶区覆盖方面差异无统计学意义,ABB摆位方式对正常组织的保护效果优于PBB摆位方式。但摆位精度PBB比ABB摆位方式更具优势。     

Surface dose and acute skin reactions in external beam breast radiotherapy

The biologically relevant depth for acute skin reactions in radiotherapy is 70 µm. The dose at this depth is difficult to measure or calculate and can be quite different than the dose at a depth of as little as 1 mm. For breast radiotherapy with medial and lateral tangential beams, the skin dose depends on both the contribution from the entrance beam and the exit beam. The skin dose has been estimated in a breast model hemi-ellipse accounting for field size, beam energy, obliquity, lack of backscatter, fractionation, size and shape of the hemi-ellipse. The dose has been held constant along the axis of symmetry of the hemi-ellipse by introducing modulation as in clinical IMRT practice. Dose distributions have been computed as a function of the polar angle from the center of the hemi-ellipse. The exit dose always dominates the entrance dose for all realistic parameters. As a result, the surface dose is higher for 18 MV than 6 MV over the entire surface for all reasonable sizes and shapes of the hemi-ellipse. The results of these calculations suggest that substituting an 18 MV beam for a 6 MV beam to achieve greater skin sparing may have just the opposite effect. The ratio of the surface dose to the mid-depth dose ranges from about 35% at polar angle 0^o to up to 70% at polar angle 80^o. The dose rises sharply at angles above 30^o. The surface dose rises moderately at all angles as the size of the hemi-ellipse increases. The effect of shape is somewhat complex: as the breast becomes flatter, doses at intermediate angles increase, but doses at small and large angles decrease. The biologically effective dose for erythema and moist desquamation is about 2 to 3 Gy higher at all polar angles for conventional fractionation (2.00 Gy × 25 fractions) than for hypofractionation (2.66 Gy × 16).