The dosimetric and clinical advantages of the GTV-CTV-PTV margins reduction by 6 mm in head and neck squamous cell carcinoma: Significant acute and late toxicity reduction.

PURPOSE: We aim to identify the dosimetric and clinical impact of reducing the total GTV-CTV-PTV margins in head-and-neck squamous cell carcinoma (HNSCC) treated with definitive (chemo)radiation. MATERIALS AND METHODS: The acute and late toxicity and outcomes of 155 consecutive patients treated between February 2017 and March 2019 with GTV-CTV-PTV margins of 9 mm were compared to those of 155 consecutive patients treated with total margin of 15 mm margin, before April 2015. All patients were treated with VMAT with daily-image guidance using CBCT. RESULTS: Reducing the GTV-CTV-PTV by 6 mm resulted in significant reduction of total irradiated volume (PTV-total) by a median of 28.1% and significant reduction of doses to all salivary glands (largest reduction ipsilateral parotid gland; median -9.6 Gy) and constrictor muscle (-6.1 Gy) with subsequent reduction of the incidence of overall acute grade 3 toxicity (47.7% for 9 mm and 66.5% for 15 mm groups, p = 0.001), grade 3 mucositis (18.1% vs. 35.5%, p < 0.001) and feeding tube-dependency at the end of treatment (24.5% vs. 40%, p = 0.005). The incidence of late grade ≥ 2 xerostomia and dysphagia were also significantly lower in the 9 mm group (31.7% vs. 58.6% p < 0.001, and 15.4% vs. 26.7%, p = 0.04). The 2-year rates of loco-regional control, disease-free and overall survival were 78.8% vs.75.8%, 70.9% vs. 64.4%, and 83.8% vs. 67.6%, (p > 0.05, all). CONCLUSION: Reduction of the total GTV-CTV-PTV margins from 15 to 9 mm in HNSCC significantly reduced the irradiated volumes and the dose to salivary glands and constrictor muscle with significant reduction of radiation-related toxicity. The loco-regional control rates of both groups were comparable.

Improving predictive CTV segmentation on CT and CBCT for cervical cancer by diffeomorphic registration of a prior.

PURPOSE: Automatic cervix-uterus segmentation of the clinical target volume (CTV) on CT and cone-beam CT (CBCT) scans is challenged by the limited visibility and the non-anatomical definition of certain border regions. We study the potential performance gain of convolutional neural networks by regulating the segmentation predictions as diffeomorphic deformations of a segmentation prior. MATERIALS AND METHODS: We introduce a 3D convolutional neural network that segments the target scan by joint voxel-wise classification and the registration of a given prior. We compare this network to two other 3D baseline models: One treating segmentation as a classification problem (segmentation-only), the other as a registration problem (deformation-only). For reference and to highlight the benefits of a 3D model, these models are also benchmarked against a 2D segmentation model. Network performances are reported for CT and CBCT segmentation of the cervix-uterus CTV. We train the networks on the data of 84 patients. The prior is provided by the CTV segmentation of a planning CT. Repeat CT or CBCT scans constitute the target scans to be segmented. RESULTS: All 3D models outperformed the 2D segmentation model. For CT segmentation, combining classification and registration in the proposed joint model proved beneficial, achieving a Dice score of 0.87 and a mean squared error (MSE) of the surface distance below 1.7 mm. No such synergy was observed for CBCT segmentation, for which the joint and the deformation-only model performed similarly, achieving a Dice score of about 0.80 and an MSE surface distance of 2.5 mm. However, the segmentation-only model performed notably worse in this low contrast regime. Visual inspection revealed that this performance drop translated into geometric inconsistencies between the prior and target segmentation. Such inconsistencies were not observed for the deformation-based models. CONCLUSION: Constraining the solution space of admissible segmentation predictions to those reachable by a diffeomorphic deformation of the prior proved beneficial as it improved geometric consistency. Especially for CBCT, with its poor soft-tissue contrast, this type of regularization becomes important as shown by quantitative and qualitative evaluation.

A biomechanical finite element model to generate a library of cervix CTVs.

PURPOSE: To generate a series of physiologically plausible cervix CTVs by biomechanically modeling organ deformation as a consequence of bladder filling. This series can serve as planning CTVs for radiotherapy treatment of cervical cancer patients using a library of plans (LoP) strategy. METHODS: The model was constructed based on the full and empty bladder scans of 20 cervical cancer patients, for which the bladder, rectum and the clinical target volume (CTV) of the cervix were delineated. Finite element modeling (FEM) was used to deform empty to full bladder anatomy. This deformation comprised two steps. In the first step, the surfaces of the bladder and rectum of the empty bladder anatomy were explicitly deformed to the full bladder anatomy and imported as enforced displacements into the biomechanical model. These surface displacements cause volumetric deformations of the bladder, rectum and cervix CTV meshes, dictated by their respective elastic properties and the type of contact among them. In the second step, the residual offset between the simulated and target CTV was corrected by an additional thin plate spline warp. Intermediate structural outputs of a linear superposition of the biomechanical and residual warp then constituted the library of CTVs for each patient. The residual warp was minimized by optimizing the FEM parameters over the 20 patients. Finally, the model was tested for nine healthy volunteers for which repeat MR scans were available as the bladder filled from empty to full. Small and large movers were identified depending on the extent of CTV motion, and analyzed separately. The proposed method was compared against the method currently used in our institute, in which intermediate structures are linearly interpolated between full and empty bladder anatomy, using a thin plate spline warp. The comparison metrics used were the ability to preserve CTV volume throughout the deformation, and residual offsets between repeat and library CTV. RESULTS: Optimal model parameters were found to be compatible with published values. While for the current method, the median CTV volume shrunk by 4% for large movers halfway the deformation (and by up to 10% for individual cases), the proposed FEM-based method preserved CTV volumes throughout the deformation. Regional residual errors between repeat and library CTV reduced by up to 3 mm when averaged over the group of large movers. For individual cases this regional error reduction could be as large as 8 mm. CONCLUSIONS: We developed a robust and automatic method to create a patient-specific FEM-based LoP. The FEM-based method resulted in more accurate library of planning CTVs as compared to the current method, with the greatest improvements observed for patients with large CTV motion. The biomechanical model simulates volumetric deformations from empty to full bladder anatomy, paving the way for dose accumulation in an LoP setting.

Substantial Volume Changes and Plan Adaptations During Preoperative Radiation Therapy in Extremity Soft Tissue Sarcoma Patients.

PURPOSE: Many authors suggest that extremity soft tissue sarcomas (ESTS) do not change significantly in size during preoperative radiation therapy (RT). This cone beam computed tomography study investigates the justification to deliver the entire course with 1 initial RT plan by observing anatomic changes during RT. METHODS AND MATERIALS: Between 2015 and 2017, 99 patients with ESTS were treated with either curative (n = 80) or palliative intent (n = 19) with a regimen of at least 6 fractions. The clinical target volume to planning target volume margin was 1 cm. Action levels were assigned by radiation technicians. An extremity contour change of >1 cm and/or tumor size change >0.5 cm required a physician's action before the next fraction. RESULTS: A total of 982 cone beam computed tomography logfiles were studied. In 41 of 99 patients, the dose coverage of the initial treatment plan was fully satisfactory throughout the RT course. However, action levels were observed in 58 patients (59%). In 41 of these 58 patients, a contour increase of 5 to 23 mm was noted (29 tumor size increase only, 3 extremity contour increase, and 9 both). In 21 of 58 patients, a decrease of 5 to 33 mm was observed (20 tumor size decrease only and 1 tumor size decrease and extremity contour decrease). In 4 cases, contours initially increased and subsequently decreased. In 33 of 41 patients with increasing contours, the dose distribution adequately covered gross tumor volume because of the 1 cm planning target volume margin applied. For the remaining 8 patients (8%), the plan needed to be adapted. CONCLUSIONS: ESTS volumes may change substantially during RT in 59% of all patients, leading to plan adaptations resulting from increased volumes in 8%. Daily critical observation of these patients is mandatory to avoid geographic misses because of increases in size and overdosing of normal tissues when masses shrink.

Protocolised way to cope with anatomical changes in head & neck cancer during the course of radiotherapy.

INTRODUCTION: During a course of radiotherapy for head-and-neck-cancer (HNC), non-rigid anatomical changes can be observed on daily Cone Beam CT (CBCT). To objectify responses to these changes, we use a decision support system (traffic light protocol). Action levels orange and red may lead to re-planning. The purpose of this study was to evaluate how often re-planning was done for non-rigid anatomical changes, which anatomical changes led to re-planning and in which subgroups of patients treatment adaptation was deemed necessary. MATERIALS AND METHODS: A consecutive series of 388 HNC patients were retrospectively selected using the digital log of CBCT scans. The logs were analyzed for the number of new plans on an original planning CT scan (O-pCT) or a new pCT scan (N-pCT). Reasons for re-planning were categorized into: target volume increase/decrease, body contour decrease/increase and local shift of target volume. Subgroup analysis was performed to investigate relative differences of re-planning between treatment modalities. RESULTS: For 33 patients the treatment plan was adapted due to anatomical changes, resulting in 37 new plans in total. Re-planning on a N-pCT with complete re-delineation was done 22 times. In fifteen cases a new plan was created after adjustment of contours on the O-pCT. Main reasons for re-planning were target volume increase, body contour decrease and local shifts of target volume. Most re-planning (23%) was seen in patients treated with chemoradiotherapy. CONCLUSION: Visual detection of anatomical changes on CBCT during treatment of HNC, results in re-planning in 1 out of 10 patients.

Margin and PTV volume reduction using a population based library of plans strategy for rectal cancer radiotherapy.

PURPOSE: Day-to-day shape variation in the rectum CTV results in considerable geometric uncertainties during rectal cancer radiotherapy. To ensure coverage a large CTV-to-PTV margin is required. The purpose of this study was to increase the accuracy of treatment delivery by building a population based library of planning CTVs for rectal cancer patients and to evaluate its potential for rectum PTV margin and PTV volume reduction. METHODS: Analysis was done retrospectively on 33 early-stage rectal cancer patients with daily repeat CTs who received short-course pre-operative radiotherapy in 5 fractions of 5 Gy. We created signed distance maps from the planning rectum CTV to each of the repeat CTVs, from which we calculated the group mean, systematic and random error. The correlation between different regions of the rectum CTV was analyzed and used in combination with the distance maps to create the library of nine planning CTVs. For each of the repeat CTVs the best fitting CTV structure in the library was automatically selected defined by the plan that minimized the mean absolute distance between the repeat and library CTV. Residual distance maps were calculated from which a new PTV margin was constructed. Bootstrapping was performed on the margin difference to assess its significance. RESULTS: Residual errors were found to decrease with the number of plans in the library, but adding more than five plans yields negligible further error reduction. Margin reduction of up to 50% was achieved at the upper-anterior site of the mesorectum. The average PTV volume decreased by 15.5% when a library is introduced. CONCLUSIONS: A library of plans strategy for rectal cancer based on population statistics is feasible and results in a considerably reduced average rectum PTV volume compared to conventional radiotherapy.

Pre-clinical experience of an adaptive plan library strategy in radiotherapy of rectal cancer: An inter-observer study.

BACKGROUND AND PURPOSE: The clinical target volume (CTV) in radiotherapy of rectal cancer is subject to large deformations. With a plan library strategy, the treatment may be adapted to these deformations. The purpose of this study was to determine feasibility and consistency in plan selection for a plan library strategy in radiotherapy of rectal cancer. MATERIAL AND METHODS: Thirty rectal cancer patients were included in this retrospective study with in total 150 CBCT scans. A library of CTVs was constructed with in-house built software using population statistics on daily rectal deformations. The library consisted of five plans based on: the original CTV, two larger, and two smaller CTVs. An inter-observer study (study-I) was performed to test the consistency in plan choices between four observers (all RTTs). After five months the observers were asked to re-evaluate (study-II) the same set of scans based on refined guidelines. RESULTS: In study-I the observers reached accordance with the majority choice in 69% of cases. This improved to 87% in study-II. The consensus meeting revealed that inconsistency in choices mainly arose from inadequate instructions, which were later clarified and formulated more accurately. CONCLUSION: Plan selection based on daily CBCT scans for rectal cancer patients is feasible, and can be performed consistently by well-trained RTTs.

Geometric changes of parotid glands caused by hydration during chemoradiotherapy.

BACKGROUND: Plan adaptation during the course of (chemo)radiotherapy of H&N cancer requires repeat CT scanning to capture anatomy changes such as parotid gland shrinkage. Hydration, applied to prevent nephrotoxicity from cisplatin, could temporarily alter the hydrogen balance and hence the captured anatomy. The aim of this study was to determine geometric changes of parotid glands as function of hydration during chemoradiotherapy compared to a control group treated with radiotherapy only. METHODS: This study included an experimental group (n = 19) receiving chemoradiotherapy, and a control group (n = 19) receiving radiotherapy only. Chemoradiotherapy patients received cisplatin with 9 l of saline solution during hydration in the first, fourth and seventh week. The delineations of the parotid glands on the planning CT scan were automatically propagated to Cone Beam CT scans using deformable image registration. Relative volume and position of the parotid glands were determined at the second chemotherapy cycle (week four) and at fraction 35. RESULTS: When saline solution was administrated, the volume temporarily increased on the first day (7.2 %, p < 0.001), second day (10.8 %, p < 0.001) and third day (7.0 %, p = 0.016). The gland positions shifted lateral, the distance between glands increased on the first day with 1.5 mm (p < 0.001), on the second day 2.2 mm (p < 0.001). At fraction 35, with both groups the mean shrinkage was 24 % ± 11 % (1SD) and the mean medial distance between the parotid glands decreased by 0.47 cm ± 0.27 cm. CONCLUSIONS: Hydration significantly modulates parotid gland geometry. Unless, in the context of adaptive RT, a repeat CT scan is timed during a chemotherapy cycle, these effects are of minor clinical relevance.

Local interfractional setup reproducibility for 2 individual head and neck supports in head and neck cancer patients.

PURPOSE: In radiation therapy, head and neck (H&N) supports and thermoplastic masks are used to reproduce the setup of patients for H&N treatment. Individualized supports that include the shoulders may improve the immobilization of the upper thorax region. The purpose of this study was to compare the local misalignment of the supraclavicular region using a vacuum cushion H&N support to a more simple in-house modified, clinically standard H&N support. METHODS AND MATERIALS: Two groups of 15 patients were evaluated: the first group of patients was positioned using a vacuum cushion as an individual head support and the second group with a modified Posifix headrest (MPH). A total of 316 cone beam computed tomography (CBCTs; ~ 10 scans per patient) were evaluated using a multiple region of interest registration protocol. Local setup errors were measured using chamfer matching on the CBCT scan to the planning CT scan for 9 bony structures (cervical vertebrae 1, 3, 5, and 7 [C7], lower jaw, hyoid bone, larynx, skull, and jugular notch). In this study, we compared the local residual misalignments of the bony structures and in particular those of the jugular notch and C7 as surrogates of the shoulders and thorax region. The workload was qualitatively evaluated on the basis of open interviews. RESULTS: The significant differences in group mean, systematic error, and random error of the local residual misalignments between the 2 groups for jugular notch and C7 were equal or smaller than 0.5 mm and 0.1 degrees, and for the other 7 bony structures were equal to or smaller than 0.6 mm and 1.2 degrees (larynx). There were no large differences in workload. CONCLUSIONS: No clinically relevant differences were found between a modified Posifix headrest and an individual vacuum cushion for H&N cancer patients in local posture change at the level of the clavicle and upper thorax.

Deformable image registration for adaptive radiation therapy of head and neck cancer: accuracy and precision in the presence of tumor changes.

PURPOSE: To compare deformable image registration (DIR) accuracy and precision for normal and tumor tissues in head and neck cancer patients during the course of radiation therapy (RT). METHODS AND MATERIALS: Thirteen patients with oropharyngeal tumors, who underwent submucosal implantation of small gold markers (average 6, range 4-10) around the tumor and were treated with RT were retrospectively selected. Two observers identified 15 anatomical features (landmarks) representative of normal tissues in the planning computed tomography (pCT) scan and in weekly cone beam CTs (CBCTs). Gold markers were digitally removed after semiautomatic identification in pCTs and CBCTs. Subsequently, landmarks and gold markers on pCT were propagated to CBCTs, using a b-spline-based DIR and, for comparison, rigid registration (RR). To account for observer variability, the pair-wise difference analysis of variance method was applied. DIR accuracy (systematic error) and precision (random error) for landmarks and gold markers were quantified. Time trend of the precisions for RR and DIR over the weekly CBCTs were evaluated. RESULTS: DIR accuracies were submillimeter and similar for normal and tumor tissue. DIR precision (1 SD) on the other hand was significantly different (P<.01), with 2.2 mm vector length in normal tissue versus 3.3 mm in tumor tissue. No significant time trend in DIR precision was found for normal tissue, whereas in tumor, DIR precision was significantly (P<.009) degraded during the course of treatment by 0.21 mm/week. CONCLUSIONS: DIR for tumor registration proved to be less precise than that for normal tissues due to limited contrast and complex non-elastic tumor response. Caution should therefore be exercised when applying DIR for tumor changes in adaptive procedures.

Adaptive radiotherapy with an average anatomy model: evaluation and quantification of residual deformations in head and neck cancer patients.

BACKGROUND AND PURPOSE: To develop and validate an adaptive intervention strategy for radiotherapy of head-and-neck cancer that accounts for systematic deformations by modifying the planning-CT (pCT) to the average misalignments in daily cone beam CT (CBCT) measured with deformable registration (DR). METHODS AND MATERIALS: Daily CBCT scans (808 scans) for 25 patients were retrospectively registered to the pCT with B-spline DR. The average deformation vector field () was used to deform the pCT for adaptive intervention. Two strategies were simulated: single intervention after 10 fractions and weekly intervention with an from the previous week. The model was geometrically validated with the residual misalignment of anatomical landmarks both on bony-anatomy (BA; automatically generated) and soft-tissue (ST; manually identified). RESULTS: Systematic deformations were 2.5/3.4mm vector length (BA/ST). Single intervention reduced deformations to 1.5/2.7 mm (BA/ST). Weekly intervention resulted in 1.0/2.2mm (BA/ST) and accounted better for progressive changes. 15 patients had average systematic deformations >2mm (BA): reductions were 1.1/1.9 mm (single/weekly BA). ST improvements were underestimated due to observer and registration variability. CONCLUSIONS: Adaptive intervention with a pCT modified to the average anatomy during treatment successfully reduces systematic deformations. The improved accuracy could possibly be exploited in margin reduction and/or dose escalation.

Evaluation of tumor shape variability in head-and-neck cancer patients over the course of radiation therapy using implanted gold markers.

PURPOSE: This study quantifies tumor shape variability in head-and-neck cancer patients during radiation therapy using implanted markers. METHODS AND MATERIALS: Twenty-seven patients with oropharyngeal tumors treated with (chemo)radiation were included. Helical gold markers (0.35 × 2 mm, 3-10/patient, average 6) were implanted around the tumor. Markers were identified on planning computed tomography (CT) and daily cone beam CT (CBCT). After bony anatomy registration, the daily vector length on CBCT in reference to the planning CT and daily marker movement perpendicular to the gross tumor volume (GTV) surface at planning CT (d(normal)) of each marker were analyzed. Time trends were assessed with linear regression of the (markers). In 2 patients, 2 markers were implanted in normal tissue to evaluate migration by measuring intermarker distances. RESULTS: Marker implantation was feasible without complications. Three-dimensional vectors (4827 measurements, mean 0.23 cm, interquartile ratio 0.24 cm) were highest in base of tongue sublocalization (P<.001) and bulky tumors (vectors exceeded 0.5 cm in 5.7% [0-20 mL], 12.0% [21-40 mL], and 21.7% [≥ 41 mL], respectively [P<.001] of measurements). The measured inward time trend in 11/27 patients correlated with the visual observed marker pattern. In patients with an outward trend (5/27) or no trend (11/27), visual observation showed predominantly an inhomogeneous pattern. Remarkably, in 6 patients, outward marker movement was observed in the posterior pharyngeal wall. The difference in distance between normal tissue markers (1 SD) was 0.05-0.06 cm without time trend, indicating that implanted markers did not migrate. CONCLUSIONS: During head-and-neck radiation therapy, normal tissue markers remained stable. Changes in position of tumor markers depended on sublocalization and tumor volume. Large differences in marker patterns between patients as well as within patients were observed. Based on our study, the cranial and caudal border in the posterior pharyngeal wall are at highest risk to be covered insufficiently. Furthermore, implanted markers could help identify patients with an actual shrinkage of the GTV who might benefit from mid-radiation therapy redelineation to reduce toxicity.

Correction strategies to manage deformations in head-and-neck radiotherapy.

BACKGROUND AND PURPOSE: To optimize couch shifts based on multiple region-of-interest (ROI) registrations and derive criteria for adaptive replanning for management of deformations in head-and-neck (H&N) cancer patients. MATERIALS AND METHODS: Eight ROIs containing bony structures were defined on the planning-CT and individually registered to daily cone-beam CTs for 19 H&N cancer patients. Online couch shifts were retrospectively optimized to correct the mean setup error over all ROIs (mean correction) or to minimize the maximum error (MiniMax correction). Residual error distributions were analyzed for both methods. The number of measurements before adaptive-intervention and corresponding action-level were optimized. RESULTS: Overall residual setup errors were smallest for the mean corrections, while MiniMax corrections reduced the largest errors. The percentage of fractions with residual errors >5 mm was 38% versus 19%. Reduction of deformations by single plan adaptation was most effective after eight fractions: systematic deformations reduced from 1.7 to 0.9 mm. Fifty percent of this reduction can already be achieved by replanning 1/3 of the patients. CONCLUSION: Two correction methods based on multiple ROI registration were introduced to manage setup errors from deformations that either minimize overall geometrical uncertainties or maximum errors. Moreover, the registrations could be used to select patient with large deformations for replanning.

First clinical experience with a multiple region of interest registration and correction method in radiotherapy of head-and-neck cancer patients.

PURPOSE: To discuss the first clinical experience with a multiple region of interest (mROI) registration and correction method for high-precision radiotherapy of head-and-neck cancer patients. MATERIALS AND METHODS: 12-13 3D rectangular-shaped ROIs were automatically placed around bony structures on the planning CT scans (n=50 patients) which were individually registered to subsequent CBCT scans. mROI registration was used to quantify global and local setup errors. The time required to perform the mROI registration was compared with that of a previously used single-ROI method. The number of scans with residual local setup error exceeding 5mm/5 degrees (warnings) was scored together with the frequency ROIs exceeding these limits for three or more consecutive imaging fractions (systematic errors). RESULTS: In 40% of the CBCT scans, one or more ROI-registrations exceeded the 5mm/5 degrees . Most warnings were seen in ROI "hyoid", 31% of the rotation warnings and 14% of the translation warnings. Systematic errors lead to 52 consults of the treating physician. The preparation and registration time was similar for both registration methods. CONCLUSIONS: The mROI registration method is easy to use with little extra workload, provides additional information on local setup errors, and helps to select patients for re-planning.

Setup uncertainties of anatomical sub-regions in head-and-neck cancer patients after offline CBCT guidance.

PURPOSE: To quantify local geometrical uncertainties in anatomical sub-regions during radiotherapy for head-and-neck cancer patients. METHODS AND MATERIALS: Local setup accuracy was analyzed for 38 patients, who had received intensity-modulated radiotherapy and were regularly scanned during treatment with cone beam computed tomography (CBCT) for offline patient setup correction. In addition to the clinically used large region of interest (ROI), we defined eight ROIs in the planning CT that contained rigid bony structures: the mandible, larynx, jugular notch, occiput bone, vertebrae C1-C3, C3-C5, and C5-C7, and the vertebrae caudal of C7. By local rigid registration to successive CBCT scans, the local setup accuracy of each ROI was determined and compared with the overall setup error assessed with the large ROI. Deformations were distinguished from rigid body movements by expressing movement relative to a reference ROI (vertebrae C1-C3). RESULTS: The offline patient setup correction protocol using the large ROI resulted in residual systematic errors (1 SD) within 1.2 mm and random errors within 1.5 mm for each direction. Local setup errors were larger, ranging from 1.1 to 3.4 mm (systematic) and 1.3 to 2.5 mm (random). Systematic deformations ranged from 0.4 mm near the reference C1-C3 to 3.8 mm for the larynx. Random deformations ranged from 0.5 to 3.6 mm. CONCLUSION: Head-and-neck cancer patients show considerable local setup variations, exceeding residual global patient setup uncertainty in an offline correction protocol. Current planning target volume margins may be inadequate to account for these uncertainties. We propose registration of multiple ROIs to drive correction protocols and adaptive radiotherapy to reduce the impact of local setup variations.

Evaluation of a single-isocenter technique for axillary radiotherapy in breast cancer.

The aim of this study was to develop a technique for axillary radiotherapy that minimizes the risk of radiation-induced damage to the surrounding normal tissue (i.e., arm, shoulder, lung, esophagus, and spinal cord) while keeping the risk of a nodal recurrence to a minimum. A planning study was performed in 20 breast cancer patients. The target volume of the axillary treatment encompassed the periclavicular and axillary lymph node areas. The 3-dimensional (3D) computed tomography (CT) information in this study was used to outline the lymph node areas and the organs at risk (i.e., the esophagus, spinal cord, brachial plexus, and lung). A conventional AP-PA technique (with a transmission plate placed in the AP beam) was evaluated. In addition, a new single-isocenter technique consisting of AP/PA fields using a gantry rotation of +/-20 degrees and a medial AP segment was developed. Both techniques were compared by evaluation of the calculated dose distributions and the dose-volume histograms of the target volume and surrounding organs at risk. The field borders and humeral shielding were redefined based on the 3D anatomical references. Adapting the humeral shielding reduced the irradiated volume by 19% and might contribute to a reduction of the incidence of arm edema and impairment of shoulder function. The maximum radiation dose in the esophagus and spinal cord was reduced by more than 50% using the single-isocenter technique. The difference between both techniques with respect to the mean doses in the target volume and lung, and the maximum dose in brachial plexus, was not statistically significant. Moreover, the single-isocenter technique allowed a fast and easy treatment preparation and reduced the execution time considerably (with approximately 10 minutes per fraction).