A comparison of a moderately hypofractionated IMRT planning technique used in a randomised UK external beam radiotherapy trial with an in-house technique for localised prostate cancer

AimTo compare the radiotherapy technique used in a randomised trial with VMAT and an in-house technique for prostate cancer.BackgroundTechniques are evolving with volumetric modulated arc therapy (VMAT) commonly used. The CHHiP trial used a 3 PTV forward planned IMRT technique (FP_CH). Our centre has adopted a simpler two PTV technique with locally calculated margins.Materials and methods25 patients treated with FP_CH to 60 Gy in 20 fractions were re-planned with VMAT (VMAT_CH) and a two PTV protocol (VMAT_60/52 and VMAT_60/48). Target coverage, conformity index (CI), homogeneity index (HI), monitor units (MU) and dose to the rectum, bladder, hips and penile bulb were compared.ResultsPTV coverage was high for all techniques. VMAT_CH plans had better CI than FP_CH (p ≤  0.05). VMAT_60/52/48 plans had better CI than VMAT_CH. FP_CH had better HI and fewer MU than VMAT (p ≤  0.05). More favourable rectum doses were found for VMAT _CH than FP_CH (V_48.6, V_52.8, V₅₇, p ≤  0.05) with less difference for bladder (p ≥  0.05). Comparing VMAT_CH to VMAT_60/52/48 showed little differences for the bladder and rectum but VMAT_CH had larger penile bulb doses (V_40.8, V_48.6, mean, D_2, p ≤  0.05). Femoral head doses (V_40.8) were similarly low for all techniques (p = ≥ 0.05).ConclusionVMAT produced more conformal plans with smaller rectum doses compared to FP_CH albeit worse HI and more MU. VMAT_60/52 and VMAT_60/48 plans had similar rectal and bladder doses to VMAT_CH but better CI and penile bulb doses which may reduce toxicity.     

VMAT-like plans for magnetic resonance guided radiotherapy: Addressing unmet needs

PurposeVMAT delivery technique is currently not applicable to Magnetic Resonance-guided radiotherapy (MRgRT) hybrid systems. Aim of this study is to evaluate an innovative VMAT-like (VML) delivery technique.Material and methodsFirst, planning and dosimetric evaluation of the MRgRT VML treatment have been performed on 10 different disease sites and the results have been compared with the corresponding IMRT plans. Then, in the second phase, 10 of the most dosimetrically challenging locally advanced pancreas treatment plans have been retrospectively re-planned using the VML approach to explore the potentiality of this new delivery technique. Finally, VML robustness was evaluated and compared with the IMRT plans, considering a lateral positioning error of ± 5 mm.ResultsIn phase one, all VML plans were within constraint for all OARs. When PTV coverage is considered, in the 50% of the cases VML PTV coverage is equal or higher than in IMRT plan. In the remaining 50%, the highest target under coverage difference in comparison with IMRT plan is −1.71%. The mean and maximum treatment time differences (VML-IMRT) is 0.2 min and 3.1 min respectively. In phase two, the treatment time variation (VML-IMRT), shows a mean, maximum and minimum variations of 1.3, 4.6 and −0.6 min respectively. All VML plans have a better target coverage if compared with IMRT plans, keeping in any case the OARs constraints within tolerance. VML doesn’t increase plan robustness.ConclusionVMAT-like treatment approach appeared to be an efficient planning solution and it was decided to clinically implement it in daily practice, especially in the frame of hypo fractionated treatments.     

Comparison between intensity modulated radiotherapy (IMRT) and 3D tangential beams technique used in patients with early-stage breast cancer who received breast-conserving therapy

Background

The most often found complications in patients with breast cancer who received radiotherapy are cardiac and pulmonary function disorders and development of second malignancies.

Aim

To compare the intensity modulated radiotherapy with the 3D tangential beams technique in respect of dose distribution in target volume and critical organs they generate in patients with early-stage breast cancer who received breast-conserving therapy.

Materials and methods

A dosimetric analysis was performed to assess the three radiotherapy techniques used in each of 10 consecutive patients with early-stage breast cancer treated with breast-conserving therapy. Radiotherapy was planned with the use of all the three techniques: 3D tangential beams with electron boost, IMRT with electron boost, and intensity modulated radiotherapy with simultaneous integrated boost.

Results

The use of the IMRT techniques enables more homogenous dose distribution in target volume. The range of mean and median dose to the heart and lung was lower with the IMRT techniques in comparison to the 3D tangential beams technique. The range of mean dose to the heart amounted to 0.3–3.5 Gy for the IMRT techniques and 0.4–4.3 for the tangential beams technique. The median dose to the lung on the irradiated side amounted to 4.9–5 Gy for the IMRT techniques and 5.6 Gy for the 3D tangential beams technique.

Conclusion

The application of the IMRT techniques in radiotherapy patients with early-stage breast cancer allows to obtain more homogenous dose distribution in target volume, while permitting to reduce the dose to critical organs.     

Four-dimensional carbon-ion pencil beam treatment planning comparison between robust optimization and range-adapted internal target volume for respiratory-gated liver and lung treatment

We investigated the dose differences between robust optimization-based treatment planning (4DRO) and range-adapted internal target volume (rITV). We used 4DCT dataset of 20 lung cancer and 20 liver cancer patients, respectively, who had been treated with respiratory-gated carbon-ion pencil beam scanning therapy. 4DRO and rITV plans were created with the same clinical target volume (CTV) and organs at risk (OAR) contours. Four-dimensional dose distribution was calculated using deformable image registration. Dose metrics (e.g. D95, V20) were analyzed. Statistical significance was assessed by the Wilcoxon signed-rank test. For the lung cases, the mean CTV-D95 value for the rITV plan (=98.5%) was same as that for the 4DRO plan (=98.5%, P = 0.106), while the mean D95 value for the CTV + setup margin contour for the rITV plan (=98.2%) was higher than that for the 4DRO plan (95.2%, P < 0.001). For the liver cases, the mean CTV-D95 value for the rITV plan (=98.1%) was slightly lower than that for the 4DRO plan (=98.5%, P < 0.01), while the mean D95 value for the CTV + setup margin contour for the rITV plan (=98.0%) was higher than that for the 4DRO plan (94.1%, P < 0.001). For the doses to the organs at risk (OARs), the ipsilateral lung-V20/liver-V20 values for the rITV plan (=10.1%/19.7%) was significantly higher than that for the 4DRO plan (=8.6%/17.6, P < 0.001). Although the target coverage for 4DRO plan may be worse than that for rITV plan in the presence of the setup error, the 4DRO plan can improve OAR dose while preserving acceptable target dose coverage.     

Fully automatic and robust segmentation of the clinical target volume for radiotherapy of breast cancer using big data and deep learning

PurposeTo train and evaluate a very deep dilated residual network (DD-ResNet) for fast and consistent auto-segmentation of the clinical target volume (CTV) for breast cancer (BC) radiotherapy with big data.MethodsDD-ResNet was an end-to-end model enabling fast training and testing. We used big data comprising 800 patients who underwent breast-conserving therapy for evaluation. The CTV were validated by experienced radiation oncologists. We performed a fivefold cross-validation to test the performance of the model. The segmentation accuracy was quantified by the Dice similarity coefficient (DSC) and the Hausdorff distance (HD). The performance of the proposed model was evaluated against two different deep learning models: deep dilated convolutional neural network (DDCNN) and deep deconvolutional neural network (DDNN).ResultsMean DSC values of DD-ResNet (0.91 and 0.91) were higher than the other two networks (DDCNN: 0.85 and 0.85; DDNN: 0.88 and 0.87) for both right-sided and left-sided BC. It also has smaller mean HD values of 10.5 mm and 10.7 mm compared with DDCNN (15.1 mm and 15.6 mm) and DDNN (13.5 mm and 14.1 mm). Mean segmentation time was 4 s, 21 s and 15 s per patient with DDCNN, DDNN and DD-ResNet, respectively. The DD-ResNet was also superior with regard to results in the literature.ConclusionsThe proposed method could segment the CTV accurately with acceptable time consumption. It was invariant to the body size and shape of patients and could improve the consistency of target delineation and streamline radiotherapy workflows.     

A prospective observational study to analyse the influence of bladder and rectal volume changes on prostate radiotherapy using IMRT

AimTo analyse the interfractional bladder and rectal volume changes and the influence on prostate position.BackgroundInterfractional displacement of prostate due to variation in bladder and rectal volume is usual. It is only rational to study the bladder and rectal volume changes and their effects on prostate position during intensity modulated radiotherapy of prostate cancer.Materials and MethodsA prospective study was conducted on twenty patients with localized prostate cancer during the first phase of radiotherapy, where 50 gray in 25 fractions was delivered by the IMRT technique with daily cone beam computed tomography Bladder and rectum volumes were delineated on CBCT images and their volumes were noted. Prostate position was noted on each set of CBCT images with respect to specific reference points defined on the ileum and coccyx, and daily prostate displacement was noted.ResultsMean setup errors in vertical, longitudinal and lateral directions were noted as 1.49, 0.498 and 0.17 cm, respectively. Mean change in bladder and rectal volumes in daily CBCT images with respect to that on the first day CT images was noted as 101.94 and 10.22, respectively. Mean lateral and vertical displacement in prostate position was noted as 0.53 and 0.49 cm respectively. No considerable changes in dosimetric parameters were observed because of bladder and rectal volume changes.ConclusionsDaily CBCT should be done for accurate treatment delivery by the IMRT technique for prostate radiotherapy as prostate shifts physiologically with changes in rectal and bladder volumes.     

Significant impact on the oncologic outcomes with intensity modulated radiotherapy and conformational radiotherapy over conventional radiotherapy in cervix cancer patients treated with radiotherapy

ObjectiveWe designed a retrospective cohort of women with cervix cancer treated by radiation therapy with an extended follow-up to evaluate if the incorporation of modern radiation techniques was a prognostic factor.Material and methodsWe studied a cohort of patients with cervix cancer FIGO stage I-IVa treated in the last fifteen years. Patients were treated with radiotherapy alone (RT) or chemoradiation alone (CRT) using conventional radiotherapy (2DRT), conformational radiotherapy (3DRT), or intensity-modulated radiotherapy (IMRT) followed by high dose rate brachytherapy. Univariate and multivariate analysis was conducted to identify significant prognostic factors (p < 0.05).Results228 patients with cervix cancer were included. The treatment groups were CRT (64.8%), and RT (34.2%), with 31.6% submitted to 2DRT and 68.4% to IMRT/3DRT. The median follow-up was 6.3 years, the OS in 5 years according to the treatment groups was 48% for CRT, and 27.8% for RT (p < 0.001). The early-stage I-IIa (p = 0.001), CRT, and IMRT/3DRT were significant factors for better overall survival (OS) in the multivariate analysis. For the cancer-specific survival (CSS), chemoradiation, age <60 years, and IMRT/3DRT were significant. Treatment with IMRT/3DRT was the only prognostic factor associated with event-free survival (EFS).ConclusionIn a long-term follow-up, chemoradiation, early-clinical stage, and age <60 years were significant factors associated with better OS and CSS at 5 and 8 years. The incorporation of new radiation techniques, such as IMRT/3DRT, over time has a significant impact on all endpoints (EFS, OS, and CSS) of this cohort. These outcomes are useful to decide about the radiation technique to achieve satisfactory oncological results outside a clinical trial.     

周剂量奈达铂联合调强放疗对复发鼻咽癌的近期疗效分析

目的:探讨周剂量奈达铂化疗联合调强放疗对于复发鼻咽癌患者的近期疗效及安全性.方法:将2009年2月至2012年2月本院收治的56例鼻咽癌复发患者随机分为联合治疗组与单纯放疗组,两组患者均给予适形调强放疗,联合治疗组患者在此基础上给予周剂量奈达铂化疗治疗,比较两组患者的临床疗效、并发症的发生情况及近期生存情况.结果:联合治疗组和单纯放疗组的有效率分别为78.6％和50.0％,联合治疗组有效率显著高于单纯放疗组(P＜0.05);联合治疗组白细胞减少发生率显著高于单纯放疗组(P＜0.05),其他并发症的发生率比较无显著差异(P＞o.05);联合治疗组1年、2年生存率分别为85.7％、64.3％,显著高于单纯放疗组的60.7％、42.9％(P＜0.05).结论:联合周剂量奈达铂化疗能够显著提高复发鼻咽癌患者调强放疗的临床疗效,且未增加严重并发症风险,值得临床推广应用.     

Dosimetric comparison of left-sided whole-breast irradiation with 3DCRT,forward-planned IMRT,inverse-planned IMRT,helical tomotherapy,and volumetric arc therapy

PurposeThis study evaluated the dose distribution and homogeneity of four different types of intensity-modulated radiotherapy (IMRT) in comparison with standard wedged tangential-beam three-dimensional conformal radiotherapy (3DCRT) of the left breast in patients who had undergone lumpectomy.Materials and methodsFive radiotherapy treatment plans, including 3DCRT, forward-planned IMRT (for-IMRT), inverse IMRT (inv-IMRT), helical tomotherapy (HT) and volumetric-modulated arc therapy (VMAT), were created for 15 consecutive patients.ResultsAll modalities presented similar target coverage. Target max doses were reduced with for-IMRT compared to 3DCRT, and these doses were further reduced with inv-IMRT and HT. HT resulted in the lowest max doses delivered to the heart, left anterior descending artery (LAD), and ipsilateral lung, but had higher mean, max, and low doses delivered to contralateral breast. HT resulted in increased low doses to a large volume of healthy tissue. Compared to other techniques, all inverse-planned modalities significantly improved conformity number; however, VMAT had worse homogeneity. The for-IMRT plan significantly lowered monitor unit (MU) compared to the inverse-planned techniques.ConclusionAll modalities evaluated provide adequate coverage of the whole breast. For-IMRT improves target homogeneity compared with 3DCRT, but to a lesser degree than the inverse-planned inv-IMRT and HT. HT decreases the ipsilateral OAR volumes receiving higher and mean doses with an increase in the volumes receiving low doses, which is known to lead to an increased rate of radiation-induced secondary malignancies.     

影像引导对乳腺癌调强放射治疗精度的影响

目的：分析在乳腺癌图像引导放射治疗（IGRT）过程中,图像引导对于放射治疗的精确度的影响;同时观察图像引导放射治疗的毒性反应及放射治疗近期的治疗效果。方法：搜集2012年1月-2013年2月间,于哈尔滨医科大学附属第三医院放疗科收治的乳腺癌患者25例。使用医科达SynergyTM锥形束CT（CBCT）进行治疗前扫描,通过图像引导放射治疗技术对25例患者进行误差纠正,调整后行调强放疗。患者在进行放疗前,用锥形柬CT对射野的偏差进行校正,其偏差利用锥形束CT图像与计划螺旋CT图像进行手动匹配,在X、Y、Z三个方向上进行调整。根据误差调整治疗床位置后治疗。对急性放射性反应采用RTOG5级评价标准进行评价：急性放射性皮肤反应、急性放射性肺损伤及急性放射性心脏损伤。结果：25例乳腺癌患者治疗前经锥形束CT扫描采集的图像与计划参考图像比较在X、Y、Z方向上平均误差分别为0．429±1．683mm、0．431±1．728mm、0．583±2．041mm：摆位误差纠正后,误差值分别为：0．068±0．429、0．019±0．438、0．158±0．697,调整后摆位误差控制在1mm之内进行治疗。放疗后2周急性皮肤反应为0级23例、1级2例;4周为0级21例、1级4例。无急性放射性肺损伤及心脏损伤的病例出现。结论：目前调强放疗是乳腺癌临床放射治疗的重要手段,图像引导放射治疗的应用能够使放疗精度显著提高。     

Assessing the need for adaptive radiotherapy in head and neck cancer patients using an automatic planning tool

BackgroundUnbiased analysis of the impact of adaptive radiotherapy (ART) is necessary to evaluate dosimetric benefit and optimize clinics’ workflows. The aim of the study was to assess the need for adaptive radiotherapy (ART) in head and neck (H&N) cancer patients using an automatic planning tool in a retrospective planning study.Materials and methodsThirty H&N patients treated with adaptive radiotherapy were analysed. Patients had a CT scan for treatment planning and a verification CT during treatment according to the clinic’s protocol. Considering these images, three plans were retrospectively generated using the iCycle tool to simulate the scenarios with and without adaptation: 1) the optimized plan based on the planning CT; 2) the optimized plan based on the verification CT (ART-plan); 3) the plan obtained by considering treatment plan 1 re-calculated in the verification CT (non-ART plan). The dosimetric endpoints for both target volumes and OAR were compared between scenarios 2 and 3 and the SPIDERplan used to evaluate plan quality.ResultsThe most significant impact of ART was found for the PTVs, which demonstrated decreased D98% in the non-ART plan. A general increase in the dose was observed for the OAR but only the spinal cord showed a statistical significance. The SPIDERplan analysis indicated an overall loss of plan quality in the absence of ART.ConclusionThese results confirm the advantages of ART in H&N patients, especially for the coverage of target volumes. The usage of an automatic planning tool reduces planner-induced bias in the results, guaranteeing that the observed changes derive from the application of ART.     

Current status of IMRT in head and neck cancer

Background

IMRT provides highly conformal dose distributions creating non uniform spatial intensity using different segments in the beam.

Material & Methods and Results

Different retrospective studies have shown a high capability of IMRT to treat tumours close to the base of skull. Prospective studies have shown a decrease in xerostomia compared with conventional 3D conformal treatment (3DCRT). Modulation of intensity is performed by the movement of the multileaf collimator (MLC) that can deliver the radiation in different ways, such as static field segments, dynamic field segments and rotational delivery (arc therapy and tomotherapy). There are slight differences among the different techniques in terms of homogeneity, dose conformity and treatment delivery time.

Conclusions

The best method to deliver IMRT will depend on multiple factors such as deliverability, practicality, user training and plan quality.     

Evaluation of high-grade astrocytoma recurrence patterns after radiotherapy in the era of temozolomide: A single institution experience

Aim

Evaluating the recurrence patterns of high-grade astrocytomas in patients who were treated with radiotherapy (RT) plus temozolomide (TMZ).

食管癌调强放射治疗的初期疗效及急性放射性肺损伤的影响因素分析

摘要 目的：探讨食管癌调强放射治疗的初期疗效及急性放射性肺损伤的影响因素。方法：选取2015年1月-2019年1月在我院进行调强放射治疗的食管癌患者322例,评价食管癌调强放射治疗后一个月的疗效;按照是否发生急性放射性肺损伤（RILI）分为急性RILI组和无急性RILI组,采用多因素Logistic回归分析分析急性RILI的影响因素。结果：调强放射治疗的完全缓解和部分缓解的患者占98.45%;322例患者中90例（27.95%）出现急性RILI,其中36例（11.18%）出现2级及以上的急性RILI;急性RILI组和无急性RILI组间卡氏（KPS）评分、淋巴结转移、基础肺疾病、V5、V10、V20、V30和全肺平均剂量（MLD）差异有统计学意义（P<0.05）;多因素Logistic回归分析显示,KPS评分<80分、有淋巴结转移、有基础肺疾病,V5≥60%、V10≥40%、V20≥28%、V30≥20%和MLD≥10Gy是食管癌调强放射治疗后急性放射性肺损伤的危险因素（P<0.05）。结论：使用调强放射治疗技术治疗食管癌的初期疗效较好,治疗过程中,应充分考虑病患的临床特征,优化放疗方案和靶区,减少急性RILI的发生,提高食管癌患者放疗后的生存质量。     

The effectiveness of gadolinium MRI to improve target delineation for radiotherapy in hepatocellular carcinoma: A comparative study of rigid image registration techniques

To achieve consistent target delineation in radiotherapy for hepatocellular carcinoma (HCC), image registration between simulation CT and diagnostic MRI was explored.Twenty patients with advanced HCC were included. The median interval between MRI and CT was 11 days. CT was obtained with shallow free breathing and MRI at exhale phase. On each CT and MRI, the liver and the gross target volume (GTV) were drawn. A rigid image registration was taken according to point information of vascular bifurcation (Method[A]) and pixel information of volume of interest only including the periphery of the liver (Method[B]) and manually drawn liver (Method[C]). In nine cases with an indefinite GTV on CT, a virtual sphere was generated at the epicenter of the GTV. The GTV from CT (V_GTV[CT]) and MRI (V_GTV[MR]) and the expanded GTV from MRI (V_+GTV[MR]) considering geometrical registration error were defined. The underestimation (uncovered V[CT] by V[MR]) and the overestimation (excessive V[MR] by V[CT]) were calculated. Through a paired T-test, the difference between image registration techniques was analyzed.For method[A], the underestimation rates of V_GTV[MR] and V_+GTV[MR] were 16.4 ± 8.9% and 3.2 ± 3.7%, and the overestimation rates were 16.6 ± 8.7% and 28.4 ± 10.3%, respectively. For V_GTV[MR] and V_+GTV[MR], the underestimation rates and overestimation rates of method[A] were better than method[C]. The underestimation rates and overestimation rates of the V_GTV[MR] were better in method[B] than method[C]. By image registration and additional margin, about 97% of HCC could be covered. Method[A] or method[B] could be recommended according to physician preference.     

Differences in toxicity and outcome associated with circadian variations between patients undergoing daytime and evening radiotherapy for prostate adenocarcinoma

This retrospective study tested the hypothesis that disease control and treatment-related toxicity in patients undergoing high-dose radiotherapy (HDRT) for prostate cancer varies in a circadian manner. Patients with localized prostate adenocarcinoma receiving HDRT (median 78 Gy) to the prostate and involved seminal vesicle(s) without elective pelvic irradiation were divided into a daytime treatment (before 5 PM) group (n = 267) and evening treatment (after 5 PM) group (n = 142). Biochemical failure (Phoenix definition), acute and late gastrointestinal (GI) and genitourinary toxicities (Common Terminology Criteria for Adverse Events version 4), biochemical failure-free survival (BFFS) and freedom from late toxicity were assessed. Analyses were performed by binary logistic regression and Cox proportional hazard regression. The median follow-up was 68 months, and 75% of patients were ≥70 years old. Evening HDRT was significantly associated with worse freedom from ≥grade 2 late GI complications (hazard ratio = 2.96; p < 0.001). The detrimental effect of evening HDRT was significant in patients older than 70 years old (p < 0.001) but not in younger patients (p = 0.63). In a subgroup of propensity score-matched cohort with T2b–T3 disease (n = 154), the 5-year BFFS was worse in the evening group than the daytime group (72% vs. 85%, hazard ratio = 1.95, p = 0.05). Our study indicates that evening HDRT may lead to more GI complications, especially in older patients, and worse BFFS in patients with T2b–T3 disease.     

三维适形放疗与调强放疗对晚期非小细胞肺癌患者血清肿瘤标志物及剂量学参数比较研究

目的:对比晚期非小细胞肺癌患者经三维适形放疗(3D-CRT)与调强放疗(IMRT)后,其血清肿瘤标志物及剂量学参数的变化。方法:选择2015年1月-2016年12月期间我院收治的非小细胞肺癌患者120例,根据放疗方案将其分为IMRT组60例与3D-CRT组60例。比较两组临床疗效、药物毒副反应、1年内的生存率、放射剂量参数,以及治疗前与治疗后血清肿瘤标志物的变化。结果:IMRT组治疗的总有效率与3D-CRT组对比差异无统计学意义(P0.05)。IMRT组血小板减少、Ⅲ度放射性食管炎、Ⅲ度消化道反应、Ⅲ度放射性肺炎、Ⅲ度白细胞减少的发生率均低于3D-CRT组(P0.05)。IMRT组1年内的生存率90.00%,高于3D-CRT组的75.00%(P0.05)。IMRT组CI值与HI值均高于3D-CRT组(P0.05),IMRT组与3D-CRT组平均剂量对比差异无统计学意义(P0.05)。治疗后两组鳞状细胞癌抗原(SCC)、细胞角蛋白19片段抗原21-1(CYFRA21-1)与肿瘤特异性生长因子(TSGF)水平均显著降低,且IMRT组低于3D-CRT组(P0.05)。结论:IMRT与3D-CRT对于晚期非小细胞肺癌患者的临床疗效相当,但IMRT药物毒副反应少、放射剂量低,可能通过控制肿瘤来降低肿瘤标志物水平。     

Assessment and clinical validation of margins for adaptive simultaneous integrated boost in neo-adjuvant radiochemotherapy for rectal cancer

PurposeAn adaptive concomitant boost (ACB) for the neo-adjuvant treatment of rectal cancer was clinically implemented. In this study population margins M(90,90) considering rectal deformation were derived for 10 consecutive patients treated at 18 × 2.3 Gy with Helical Tomotherapy (HT) and prospectively validated on 20 additional patients treated with HT, delivering ACB in the last 6 fractions.MethodsSectorial margins M(90,90) of the whole and second treatment parts were assessed for 90% population through a method combining the 90% coverage probability maps of rectal positions (CPC90%) with 3D local distance measurements between the CPC90% and a reference rectal contour. M(90,90) were compared with the margins M(90,90)^95%/99%, ensuring CPC90% coverage with 95%/99% confidence level. M(90,90) of the treatment second part were chosen as ACB margins which were clinically validated for each patient by means of %volume missing of CPC5/6 excluded by the ACB margins.ResultsThe whole treatment M(90,90) ranged between 1.9 mm and 9 mm in the lower-posterior and upper-anterior sectors, respectively. Regarding ACB, M(90,90) were 7 mm in the anterior direction and <5 mm elsewhere. M(90,90)^95%/99% did not significantly differ from M(90,90). The %volume excluded by the ACB margin was<2% for all male and <5% for 9/10 female patients. The dosimetry impact on R_adapt for the patients with the largest residual error was negligible.ConclusionsLocal deformation measurements confirm an anisotropic motion of rectum once set-up error is rigidly corrected. Margins of 7 mm anterior and 5 mm elsewhere are adequate for ACB. Female patients show a slightly larger residual error.