Three-dimensional motion analysis of an improved head immobilization system for simulation, CT, MRI, and PET imaging

Situational anxiety in head and neck cancer: Rates, patterns and clinical management interventions in a regional cancer setting

INTRODUCTION

Research indicates that the immobilisation mask required for radiation therapy (RT) for head and neck cancers can provoke intense anxiety. However, little is known about the rates of this anxiety, whether it changes over a course of treatment and how it is managed in clinical practice. This study aimed to describe the rates and patterns of situational anxiety in patients undergoing RT for head and neck cancer and the use of anxiety management interventions in current clinical practice in a major regional cancer setting in New South Wales, Australia.

METHODS

Situational anxiety rates and patterns were assessed at five time points using the State-Trait Anxiety Inventory prior to treatment planning (SIM), the first three treatment sessions (Tx 1, Tx 2 and Tx 3) and treatment 20 (Tx 20). Sessions were observed to record the use of general supportive interventions (music and support person) and anxiety-specific interventions (break from the mask, relaxation techniques and anxiolytic medication). Sociodemographic and clinical information was extracted from the medical record.

RESULTS

One hundred and one patients were recruited. One-third had clinically significant anxiety at any of the first three time points (33.3-40%), and a quarter at Tx 3 (26.4%) and Tx 20 (23.4%). Of the sample, 55.4% had available data for categorisation into one of four pattern groups: 'No Anxiety' (46.4%); 'Decreasing Anxiety' (35.7%); 'Increasing Anxiety' (7.1%); and 'Stable High Anxiety' (10.7%). Most participants had social support present at SIM (53.5%) and listened to music during treatment (86.7-92.9%). Few participants received relaxation techniques alone (1.2-2.3%). Anxiolytic medication was provided for 10% of patients at some stage during the treatment journey and 5% required a break from the mask at SIM, with frequency decreasing throughout the treatment course.

CONCLUSIONS

In this regional cancer setting, situational anxiety was common, but generally decreased throughout treatment. Some patients experience persistent or increasing anxiety, with up to 10% of patients receiving specific anxiety management interventions.

Single patient learning for adaptive radiotherapy dose prediction

BACKGROUND

Throughout a patient's course of radiation therapy, maintaining accuracy of their initial treatment plan over time is challenging due to anatomical changes-for example, stemming from patient weight loss or tumor shrinkage. Online adaptation of their RT plan to these changes is crucial, but hindered by manual and time-consuming processes. While deep learning (DL) based solutions have shown promise in streamlining adaptive radiation therapy (ART) workflows, they often require large and extensive datasets to train population-based models.

PURPOSE

This study extends our prior research by introducing a minimalist approach to patient-specific adaptive dose prediction. In contrast to our prior method, which involved fine-tuning a pre-trained population model, this new method trains a model from scratch using only a patient's initial treatment data. This patient-specific dose predictor aims to enhance clinical accessibility, thereby empowering physicians and treatment planners to make more informed, quantitative decisions in ART. We hypothesize that patient-specific DL models will provide more accurate adaptive dose predictions for their respective patients compared to a population-based DL model.

METHODS

We selected 33 patients to train an adaptive population-based (AP) model. Ten additional patients were selected, and their respective initial RT data served as single samples for training patient-specific (PS) models. These 10 patients contained an additional 26 ART plans that were withheld as the test dataset to evaluate AP versus PS model dose prediction performance. We assessed model performance using Mean Absolute Percent Error (MAPE) by comparing predicted doses to the originally delivered ground truth doses. We used the Wilcoxon signed-rank test to determine statistically significant differences in terms of MAPE between the AP and PS model results across the test dataset. Furthermore, we calculated differences between predicted and ground truth mean doses for segmented structures and determined statistical significance in the differences for each of them.

RESULTS

The average MAPE across AP and PS model dose predictions was 5.759% and 4.069%, respectively. The Wilcoxon signed-rank test yielded two-tailed p-value = 2.9802 × 10 - 8 $2.9802\ \times \ {10}^{ - 8}$ , indicating that the MAPE differences between the AP and PS model dose predictions are statistically significant, and 95% confidence interval = [-2.1610, -1.0130], indicating 95% confidence that the MAPE difference between the AP and PS models for a population lies in this range. Out of 24 total segmented structures, the comparison of mean dose differences for 12 structures indicated statistical significance with two-tailed p-values < 0.05.

CONCLUSION

Our study demonstrates the potential of patient-specific deep learning models in application to ART. Notably, our method streamlines the training process by minimizing the size of the required training dataset, as only a single patient's initial treatment data is required. External institutions considering the implementation of such a technology could package such a model so that it only requires the upload of a reference treatment plan for model training and deployment. Our single patient learning strategy demonstrates promise in ART due to its minimal dataset requirement and its utility in personalization of cancer treatment.

'Having the mask on didn't worry me until … they clamped my head down so I wouldn't move': A qualitative study exploring anxiety in patients with head and neck cancer during radiation therapy

INTRODUCTION

More than 20% of patients undergoing radiation therapy for head and neck cancer report anxiety specifically related to the immobilisation mask, a tight-fighting mask patients are required to wear for the duration of each treatment session. However, limited research has investigated this from the patient perspective. The aim of this study was to better understand patient experiences of mask anxiety during head and neck cancer radiation therapy and to explore patient attitudes toward potential strategies that may reduce mask anxiety during this treatment.

METHODS

Five patients with head and neck cancer, who had self-reported mask anxiety during radiation therapy, participated in semi-structured, qualitative interviews exploring their experiences of anxiety and suggestions for reducing anxiety. A codebook thematic analysis was conducted.

RESULTS

Six main themes were identified: (1) triggers of anxiety; (2) adjusting to radiation therapy; (3) education about the mask; (4) coping; (5) motivation and (6) improving the patient experience.

CONCLUSION

Findings from these interviews provide valuable insight into how and when healthcare providers may be able to assist patients to manage mask anxiety. Recommendations include increased communication from health care providers; delivery of visual information to improve patient preparedness; exposure/opportunities to interact with the masks prior to treatment commencing and increased control of music/soundtrack selection. However, a limitation of this study is the small sample size and further research is warranted.

Accuracy of MRI-CT registration in brain stereotactic radiotherapy: Impact of MRI acquisition setup and registration method

BACKGROUND

In MR-based radiotherapy (RT), MRI images are co-registered to the planning CT to leverage MR image information for RT planning. Especially in brain stereotactic RT, where typical CTV-PTV margins are 1-2 mm, high registration accuracy is critical. Several factors influence the registration accuracy, including the acquisition setup during MR simulation and the registration methods.

PURPOSE

In this work, the impact of the MRI acquisition setup and registration method was evaluated in the context of brain RT, both geometrically and dosimetrically.

METHODS AND MATERIALS

MRI of 20 brain radiotherapy patients was acquired in two MRI acquisition setups (RT and diagnostic). Three different automatic registration tools provided by three treatment planning systems were used to rigidly register both MRIs and CT in addition to the clinical registration. Segmentation-based evaluation using Hausdorff Distance (HD)/Dice Similarity Coefficient and landmark-based evaluation were used as evaluation metrics. Dose-volume-histograms were evaluated for target volumes and various organs at risks.

RESULTS

MRI acquisition in the RT setup provided a similar head extension as compared to the planning CT. The registration method had a more significant influence than the acquisition setup (Wilcoxon signed-rank test, p<0.05). When registering using a less optimal registration method, the RT setup improved the registration accuracy compared to the diagnostic setup (Difference: ΔMHD = 0.16 mm, ΔHD_P95 = 0.64 mm, mean Euclidean distance (ΔmEuD) = 2.65 mm). Different registration methods and acquisition setups lead to the variation of the clinical DVH. Acquiring MRI in the RT setup can improve PTV and GTV coverage compared to the diagnostic setup.

CONCLUSIONS

Both MRI acquisition setup and registration method influence the MRI-CT registration accuracy in brain RT patients geometrically and dosimetrically. MR-simulation in the RT setup assures optimal registration accuracy if automatic registration is impaired, and therefore recommended for brain RT.

Non-pharmacological approaches to procedural anxiety reduction for patients undergoing radiotherapy for cancer: systematic review protocol

INTRODUCTION

Procedural anxiety relates to an affective state of anxiety or fear in relation to a medical procedure. Various treatment-related factors may elicit anxiety among oncology patients, including fear of diagnostic imaging (such as MRI scans) and impending treatment and medical procedures (such as chemotherapy and radiotherapy). It is common in oncology settings to manage acute anxiety relating to medical procedures with anxiolytic medication. However, pharmacological approaches are not suitable for many patients. Despite this, non-pharmacological interventions are infrequently used. The aim of this systematic review is to determine whether non-pharmacological interventions delivered prior to, or during, radiotherapy are effective in reducing procedural anxiety.

METHODS AND ANALYSIS

Data sources will include the bibliographic databases CINAHL, MEDLINE, EMBASE, PsycINFO and Cochrane Central Register of Controlled trials (CENTRAL) (from inception onward). Eligible studies will include adult patients with cancer undergoing radiotherapy treatment. Included studies will be those which employ a non-pharmacological intervention, delivered within existing radiotherapy appointments, with the aim of reducing procedural anxiety related to radiotherapy. All research designs with a control or other comparison group will be included. The primary outcome will be change in levels of self-reported procedural anxiety. Secondary outcomes will be changes in scores on physiological measures of anxiety and/or changes in treatment completion and/or changes in treatment duration and/or changes in psychological distress. Two investigators will independently complete title and abstract screening, full-text screening, data extraction and assessment of methodological quality. If appropriate, a meta-analyses will be performed. Any important amendments to this protocol will be updated in the PROSPERO registration and documented in the resulting review publication.

ETHICS AND DISSEMINATION

No ethical issues are anticipated from this review. The findings will be disseminated through peer-reviewed publication and at conferences by presentation.

SYSTEMATIC REVIEW REGISTRATION

CRD42019112941.

Does an immobilization mask have added value during planning magnetic resonance imaging for stereotactic radiotherapy of brain tumours?

BACKGROUND AND PURPOSE

When using an immobilization mask, a magnetic resonance imaging (MRI) head receive coil cannot be used and patients may experience discomfort during the examination. We therefore wish to assess the added value of an immobilization mask during all MRI scans intended for cranial stereotactic radiotherapy (SRT) planning.

MATERIALS AND METHODS

An MRI was acquired with and without a thermoplastic immobilization mask in ten patients eligible for SRT. A planning computed tomography (CT) scan was also made, to which the two MRIs were independently registered. Additionally, the MRI without immobilization was registered to the MRI in mask. On each sequence, gross tumour volume (GTV), the right eye, brain stem and chiasm were delineated. The absolute differences in centre-of-gravity coordinates and Dice coefficients of the volumes of the delineated structures between the two MRIs were compared.

RESULTS

Differences in GTV volume between the two MRIs were low, with median Dice coefficients between 0.88 and 0.91. Similarly, the median absolute differences in centre-of-gravity coordinates between the GTVs, organs at risk and landmarks delineated on the two MRIs were within 0.5 mm. The 95% confidence intervals of the median absolute differences in the three GTV coordinates was within 1 mm, which corresponds to the target volume safety margin used to account for possible errors during the SRT treatment chain.

CONCLUSIONS

The effect of scanning a patient without the immobilization mask falls within acceptable bounds of error for the geometrical accuracy of the SRT treatment chain. Consequently, placing the head in treatment position during all MRI scans for patients undergoing radiotherapy of brain metastasis is deemed unnecessary.

Use dose bricks concept to implement nasopharyngeal carcinoma treatment planning

Purpose. A “dose bricks” concept has been used to implement nasopharyngeal carcinoma treatment plan; this method specializes particularly in the case with bell shape nasopharyngeal carcinoma case. Materials and Methods. Five noncoplanar fields were used to accomplish the dose bricks technique treatment plan. These five fields include (a) right superior anterior oblique (RSAO), (b) left superior anterior oblique (LSAO), (c) right anterior oblique (RAO), (d) left anterior oblique (LAO), and (e) superior inferior vertex (SIV). Nondivergence collimator central axis planes were used to create different abutting field edge while normal organs were blocked by multileaf collimators in this technique. Results. The resulting 92% isodose curves encompassed the CTV, while maximum dose was about 115%. Approximately 50% volume of parotid glands obtained 10–15% of total dose and 50% volume of brain obtained less than 20% of total dose. Spinal cord receives only 5% from the scatter dose. Conclusions. Compared with IMRT, the expenditure of planning time and costing, “dose bricks” may after all be accepted as an optional implementation in nasopharyngeal carcinoma conformal treatment plan; furthermore, this method also fits the need of other nonhead and neck lesions if organ sparing and noncoplanar technique can be executed.

Migration from full-head mask to "open-face" mask for immobilization of patients with head and neck cancer

To provide an alternative device for immobilization of the head while easing claustrophobia and improving comfort, an “open‐face” thermoplastic mask was evaluated using video‐based optical surface imaging (OSI) and kilovoltage (kV) X‐ray radiography. A three‐point thermoplastic head mask with a precut opening and reinforced strips was developed. After molding, it provided sufficient visible facial area as the region of interest for OSI. Using real‐time OSI, the head motion of ten volunteers in the new mask was evaluated during mask locking and 15 minutes lying on the treatment couch. Using a nose mark with reference to room lasers, forced head movement in open‐face and full‐head masks (with a nose hole) was compared. Five patients with claustrophobia were immobilized with open‐face masks, set up using OSI and kV, and treated in 121 fractions, in which 61 fractions were monitored during treatment using real‐time OSI. With the open‐face mask, head motion was found to be 1.0 ± 0.6 mm and 0.4° ± 0.2° in volunteers during the experiment, and 0.8 ± 0.3 mm and 0.4° ± 0.2° in patients during treatment. These agree with patient motion calculated from pre‐/post‐treatment OSI and kV data using different anatomical landmarks. In volunteers, the head shift induced by mask‐locking was 2.3 ± 1.7 mm and 1.8° ± 0.6°, and the range of forced movements in the open‐face and full‐head masks were found to be similar. Most (80%) of the volunteers preferred the open‐face mask to the full‐head mask, while claustrophobic patients could only tolerate the open‐face mask. The open‐face mask is characterized for its immobilization capability and can immobilize patients sufficiently (< 2 mm) during radiotherapy. It provides a clinical solution to the immobilization of patients with head and neck (HN) cancer undergoing radiotherapy, and is particularly beneficial for claustrophobic patients. This new open‐face mask is readily adopted in radiotherapy clinic as a superior alternative to the standard full‐head mask.

PACS numbers: 87.19.xj, 87.63.L‐, 87.59.‐e, 87.55.tg, 87.55.‐x

Technical note: 9-month repositioning accuracy for functional response assessment in head and neck chemoradiotherapy

The use of thermoplastic immobilisation masks in head and neck radiotherapy is now common practice. The accuracy of these systems has been widely studied, but always within the context and time frame of the radiation delivery-some 6-8 weeks. There is growing current interest in the use of functional imaging to assess the response to treatment, particularly in the head and neck. It is therefore of interest to determine the accuracy with which functional images can be registered to baseline CT over the extended periods of time used for functional response assessment: 3-6 months after radiotherapy. In this study, repeated contrast-enhanced diagnostic quality CT and mid-quality localisation CT from a positron emission tomography/CT scanner were available for five time points over a period of 9 months (before, during and up to 6 months after chemoradiotherapy) for a series of eight patients enrolled in a clinical pilot study. All images were acquired using thermoplastic immobilisation masks. The overall set-up accuracy obtained from this 9-month study of 5.5 ± 3.2 mm (1 standard deviation) and 1.9 ± 1.3° (1 standard deviation) is in agreement with published data acquired over 6-8 weeks. No statistically significant change in set-up error was seen with time. This work indicates that thermoplastic immobilisation masks can be used to accurately align multimodality functional image data for assessment of the response to treatment in head and neck patients over extended follow-up periods.

Cone Beam CT (CBCT) Evaluation of Inter- and Intra-Fraction Motion for Patients Undergoing Brain Radiotherapy Immobilized using a Commercial Thermoplastic Mask on a Robotic Couch

Patients receiving fractionated intensity-modulated radiation therapy (IMRT) for brain tumors are often immobilized with a thermoplastic mask; however, masks do not perfectly re-orient the patient due to factors including the maximum pressure which can be applied to the face, deformations of the mask assembly, patient compliance, etc. Consequently, ~3–5 mm PTV margins (beyond the CTV) are often recommended. We aimed to determine if smaller PTV margins are feasible using mask immobilization coupled with 1) a gantry mounted CBCT image guidance system and 2) position corrections provided by a full six-degree of freedom (6-DOF) robotic couch. A cohort of 34 brain tumor patients was treated with fractionated IMRT. After the mask set-up, an initial CBCT was obtained and registered to the planning CT. The robotic couch corrected the misalignments in all 6-DOF and a pre-treatment verification CBCT was then obtained. The results indicated a repositioning alignment within our threshold of 1.5 mm (3D). Treatment was subsequently delivered. A post-treatment CBCT was obtained to quantify intra-fraction motion. Initial, pre-treatment and post-treatment CBCT image data was analyzed. A total of 505 radiation fractions were delivered to the 34 patients resulting in ~1800 CBCT scans. The initial median 3D (magnitude) set-up positioning error was 2.60 mm. Robotic couch corrections reduced the 3D median error to 0.53 mm prior to treatment. Intra-fraction movement was responsible for increasing the median 3D positioning error to 0.86 mm, with 8% of fractions having a 3D positioning error greater than 2 mm. Clearly CBCT image guidance coupled with a robotic 6-DOF couch dramatically improved the positioning accuracy for patients immobilized in a thermoplastic mask system; however, such intra-fraction motion would be too large for single fraction radiosurgery.

Analysis of couch position tolerance limits to detect mistakes in patient setup

This work investigates the use of the tolerance limits on the treatment couch position to detect mistakes in patient positioning and warn users of possible treatment errors. Computer controlled radiotherapy systems use the position of the treatment couch as a surrogate for patient position and a tolerance limit is applied against a planned position. When the couch is out of tolerance a warning is sent to a user to indicate a possible mistake in setup. A tight tolerance may catch all positioning mistakes while as the same time sending too many warnings; while a loose tolerance will not catch all mistakes. We develop a statistical model of the absolute position for the three translational axes of the couch. The couch position for any fraction is considered a random variable x(i). The ideal planned couch position x(p) is unknown before a patient starts treatment and must be estimated from the daily positions x(i). As such x(p) is also a random variable. The tolerance, tol, is applied to the difference between the daily and planned position, d(i) = x(i) - x(p). The di is a linear combination of random variables and therefore the density of di is the convolution of distributions of xi and xp. Tolerance limits are based on the standard deviation of d(i) such that couch positions that are more than 2 standard deviation away are considered out of tolerance. Using this framework we investigate two methods of setting x(p) and tolerance limits. The first, called first day acquire (FDA), is to take couch position on the first day as the planned position. The second is to use the cumulative average (CumA) over previous fractions as the planned position. The standard deviation of d(i) shrinks as more samples are used to determine x(p) and so the tolerance limit shrinks as a function of fraction number when a CumA technique is used. The metrics of sensitivity and specificity were used to characterize the performance of the two methods to correctly identify a couch position as in or out of tolerance. These two methods were tested using simulated and real patient data. Five clinical sites with different indexed immobilization were tested. These were whole brain, head and neck, breast, thorax and prostate. Analysis of the head and neck data shows that it is reasonable to model the daily couch position as a random variable in this treatment site. Using an average couch position for x(p) increased the sensitivity of the couch interlock and reduced the chances of acquiring a couch position that was a statistical outlier. Analysis of variation in couch position for different sites allowed the tolerance limit to be set specifically for a site and immobilization device. The CumA technique was able to increase the sensitivity of detecting out of tolerance positions while shrinking tolerance limits for a treatment course. Making better use of the software interlock on the couch positions could have a positive impact on patient safety and reduce mistakes in treatment delivery.

CHAINED LIGHTNING, PART II

THE FUNDAMENTAL PRINCIPLE in the radiosurgical treatment of neurological conditions is the delivery of energy to a lesion with minimal injury to surrounding structures. The development of radiosurgical techniques from Leksell's original design has focused on the refinement of various methodologies to achieve energy containment within a target. This article is the second in a series reviewing the evolution of radiosurgical instruments with respect to issues of energy beam generation and delivery for improved conformal therapy.

Continuing with concepts introduced in an earlier article, this article examines specific aspects of beam delivery and the emergence of stereotactic radiosurgery as a measure for focusing energy beams within a target volume. The application of stereotactic principles and devices to gamma ray and linear accelerator-based energy sources provides the methodology by which energy beams are generated and targeted precisely in a focal lesion. Advanced technological systems are reviewed, including fixed beams, dynamic radiosurgery, multileaf collimation, beam shaping, and robotics as various approaches for manipulating beam delivery. Radiosurgical instruments are also compared with regard to mechanics, geometry, and dosimetry. Finally, new radiosurgical designs currently on the horizon are introduced. In exploring the complex history of radiosurgery, it is evident that the discovery and rediscovery of ideas invariably leads to the development of innovative technology for the next generation.

Repositioning accuracy of two different mask systems—3D revisited: Comparison using true 3D/3D matching with cone-beam CT

PURPOSE

The repositioning accuracy of mask-based fixation systems has been assessed with two-dimensional/two-dimensional or two-dimensional/three-dimensional (3D) matching. We analyzed the accuracy of commercially available head mask systems, using true 3D/3D matching, with X-ray volume imaging and cone-beam CT.

METHODS AND MATERIALS

Twenty-one patients receiving radiotherapy (intracranial/head-and-neck tumors) were evaluated (14 patients with rigid and 7 with thermoplastic masks). X-ray volume imaging was analyzed online and offline separately for the skull and neck regions. Translation/rotation errors of the target isocenter were analyzed. Four patients were treated to neck sites. For these patients, repositioning was aided by additional body tattoos. A separate analysis of the setup error on the basis of the registration of the cervical vertebra was performed. The residual error after correction and intrafractional motility were calculated.

RESULTS

The mean length of the displacement vector for rigid masks was 0.312 +/- 0.152 cm (intracranial) and 0.586 +/- 0.294 cm (neck). For the thermoplastic masks, the value was 0.472 +/- 0.174 cm (intracranial) and 0.726 +/- 0.445 cm (neck). Rigid masks with body tattoos had a displacement vector length in the neck region of 0.35 +/- 0.197 cm. The intracranial residual error and intrafractional motility after X-ray volume imaging correction for rigid masks was 0.188 +/- 0.074 cm, and was 0.134 +/- 0.14 cm for thermoplastic masks.

CONCLUSIONS

The results of our study have demonstrated that rigid masks have a high intracranial repositioning accuracy per se. Given the small residual error and intrafractional movement, thermoplastic masks may also be used for high-precision treatments when combined with cone-beam CT. The neck region repositioning accuracy was worse than the intracranial accuracy in both cases. However, body tattoos and image guidance improved the accuracy. Finally, the combination of both mask systems with 3D image guidance has the potential to replace therapy simulation and intracranial stereotaxy.

2D/3D Image fusion for accurate target localization and evaluation of a mask based stereotactic system in fractionated stereotactic radiotherapy of cranial lesions

The purpose of this study was to evaluate the accuracy of a two-dimensional (2D) to three-dimensional (3D) image-fusion-guided target localization system and a mask based stereotactic system for fractionated stereotactic radiotherapy (FSRT) of cranial lesions. A commercial x-ray image guidance system originally developed for extracranial radiosurgery was used for FSRT of cranial lesions. The localization accuracy was quantitatively evaluated with an anthropomorphic head phantom implanted with eight small radiopaque markers (BBs) in different locations. The accuracy and its clinical reliability were also qualitatively evaluated for a total of 127 fractions in 12 patients with both kV x-ray images and MV portal films. The image-guided system was then used as a standard to evaluate the overall uncertainty and reproducibility of the head mask based stereotactic system in these patients. The phantom study demonstrated that the maximal random error of the image-guided target localization was +/-0.6 mm in each direction in terms of the 95% confidence interval (CI). The systematic error varied with measurement methods. It was approximately 0.4 mm, mainly in the longitudinal direction, for the kV x-ray method. There was a 0.5 mm systematic difference, primarily in the lateral direction, between the kV x-ray and the MV portal methods. The patient study suggested that the accuracy of the image-guided system in patients was comparable to that in the phantom. The overall uncertainty of the mask system was +/-4 mm, and the reproducibility was +/-2.9 mm in terms of 95% CI. The study demonstrated that the image guidance system provides accurate and precise target positioning.

Repeated positioning in accurate radiotherapy based on virtual net technique and contrary reconstruction scheme

This paper presents a new repeated positioning system for external radiotherapy. A new scheme is proposed to rebuild patient's body surface 3-D image based on simple stereo vision model and virtual net technique, which improves the reconstruction precision of the template. For the calculation of the positioning error, the contrary reconstruction scheme is adopted and the positioning speed is greatly improved. The 3-D reconstructed video image of the right position in the first positioning is used as the reference template for the next positioning, and the positioning error is evaluated by projecting the template image into the patient's real-time video images and calculating the correlation ratio in the areas limited by the triangle of the reference image.

Intracranial stereotactic positioning systems: Report of the American Association of Physicists in Medicine Radiation Therapy Committee Task Group No. 68

Intracranial stereotactic positioning systems (ISPSs) are used to position patients prior to precise radiation treatment of localized lesions of the brain. Often, the lesion is located in close proximity to critical anatomic features whose functions should be maintained. Many types of ISPSs have been described in the literature and are commercially available. These are briefly reviewed. ISPS systems provide two critical functions. The first is to establish a coordinate system upon which a guided therapy can be applied. The second is to provide a method to reapply the coordinate system to the patient such that the coordinates assigned to the patient's anatomy are identical from application to application. Without limiting this study to any particular approach to ISPSs, this report introduces nomenclature and suggests performance tests to quantify both the stability of the ISPS to map diagnostic data to a coordinate system, as well as the ISPS's ability to be realigned to the patient's anatomy. For users who desire to develop a new ISPS system, it may be necessary for the clinical team to establish the accuracy and precision of each of these functions. For commercially available systems that have demonstrated an acceptable level of accuracy and precision, the clinical team may need to demonstrate local ability to apply the system in a manner consistent with that employed during the published testing. The level of accuracy and precision required of an individual ISPS system is dependent upon the clinical protocol (e.g., fractionation, margin, pathology, etc.). Each clinical team should provide routine quality assurance procedures that are sufficient to support the assumptions of accuracy and precision used during the planning process. The testing of ISPS systems can be grouped into two broad categories, type testing, which occurs prior to general commercialization, and site testing, performed when a commercial system is installed at a clinic. Guidelines to help select the appropriate tests as well as recommendations to help establish the required frequency of testing are provided. Because of the broad scope of different systems, it is important that both the manufacturer and user rigorously critique the system and set QA tests appropriate to the particular device and its possible weaknesses. Major recommendations of the Task Group include: introduction of a new nomenclature for reporting repositioning accuracy; comprehensive analysis of patient characteristics that might adversely affect positioning accuracy; performance of testing immediately before each treatment to establish that there are no gross positioning errors; a general request to the Medical Physics community for improved QA tools; implementation of weekly portal imaging (perhaps cone beam CT in the future) as a method of tracking fractionated patients (as per TG 40); and periodic routine reviews of positioning accuracy.

Quantification and Clinical Relevance of Head Motion During Computed Tomography

OBJECTIVE

To quantify the 3-dimensional translation and rotation components of head motion during computed tomography and to analyze the influence of such motion on perceptible artifacts and distortion of volume image data sets.

METHODS

Using high-precision optoelectronic motion-capture technology, changes in patient head position during axial CT scanning were registered in 20 cases and 2 phantoms with a spatial relative resolution better than 0.003 cm. Statistical analysis was performed on a base of 6-dimensional measurement-vectors, each with 3 translation and 3 rotation values. Because of the recording frequency of the tracking system, more than 80000 values were included in a statistical analysis.

RESULTS

All 20 patients had head motion during the CT scanning, with only 4 of 20 patients showing perceptible motion artifacts. The frequency, the extent, and the direction of the movements did not correlate with either the observations made by the radiologic staff or with the patient's subjective estimation of comfort. Translation movements of the head during CT accounted for a maximum of 0.5 cm and rotations of more than 2 degrees without perceptible motion artifacts. The extent of positional changes of the head was found to correlate with the duration of scanning (Pearson's correlation coefficient: 0.647 for translation shifts, 0.453 for rotation shifts). The mean direction of head motion could be characterized predominantly as a rotation around the longitudinal axis of the body (xy plane) at a significance level of 0.01.

CONCLUSION

Computed tomography evaluations of the head performed without rigid fixation suffer a spatial distortion of the volume image data sets, caused by interimage motion. The absence of motion artifacts is not correlated with the absence of motion.

Intensity-modulated radiation therapy for head-and-neck cancer: the UCSF experience focusing on target volume delineation

PURPOSE

To review the University of California-San Francisco (UCSF) experience of using intensity-modulated radiation therapy (IMRT) to treat head-and-neck cancer focusing on the importance of target volume delineation and adequate target volume coverage.

METHODS AND MATERIALS

Between April 1995 and January 2002, 150 histologically confirmed patients underwent IMRT for their head-and-neck cancer at our institution. Sites included were nasopharynx 86, oropharynx 22, paranasal sinus 22, thyroid 6, oral tongue 3, nasal cavity 2, salivary 2, larynx 2, hypopharynx 1, lacrimal gland 1, skin 1, temporal bone 1, and trachea 1. One hundred seven patients were treated definitively with IMRT +/- concurrent platinum chemotherapy (92/107), whereas 43 patients underwent gross surgical resection followed by postoperative IMRT +/- concurrent platinum chemotherapy (15/43). IMRT was delivered using three different techniques: 1) manually cut partial transmission blocks, 2) computer-controlled auto-sequencing segmental multileaf collimator, and 3) sequential tomotherapy using dynamic multivane intensity-modulating collimator. Forty-two patients were treated with a forward plan, 102 patients with an inverse plan, and 6 patients with both forward and inverse plans. The gross target volume (GTV) was defined as tumor detected on physical examination or imaging studies. In postoperative cases, the GTV was defined as the preoperative gross tumor volume. The clinical target volume (CTV) included all potential areas at risk for microscopic tumor involvement by either direct extension or nodal spread including a margin for patient motion and setup errors. The average prescription doses to the GTV were 70 Gy and 66 Gy for the primary and the postoperative cases, respectively. The site of recurrence was determined by the diagnostic neuroradiologist to be either within the GTV or the CTV volume by comparison of the treatment planning computed tomography with posttreatment imaging studies.

RESULTS

For the primary definitive cases with a median follow-up of 25 months (range 6 to 78 months), 4 patients failed in the GTV. The 2- and 3-year local freedom from progression (LFFP) rates were 97% and 95%. With a median follow-up of 17 months (range 8 to 56 months), 7 patients failed in the postoperative setting. The 2-year LFFP rate was 83%. For the primary group, the average maximum, mean, and minimum doses delivered were 80 Gy, 74 Gy, 56 Gy to the GTV, and 80 Gy, 69 Gy, 33 Gy to the CTV. An average of only 3% of the GTV and 3% of the CTV received less than 95% of the prescribed dose. For the postoperative group, the average maximum, mean, and minimum doses delivered were 79 Gy, 71 Gy, 37 Gy to the GTV and 79 Gy, 66 Gy, 21 Gy to the CTV. An average of only 6% of the GTV and 6% of the CTV received less than 95% of the prescribed dose.

CONCLUSION

Accurate target volume delineation in IMRT treatment for head-and-neck cancer is essential. Our multidisciplinary approach in target volume definition resulted in few recurrences with excellent LFFP rates and no marginal failures. Higher treatment failure rates were noted in the postoperative setting in which lower doses were prescribed. Potential dose escalation studies may further improve the local control rates in the postoperative setting.

Is one head and neck immobilization system as good as another? One center's experience

The William Buckland Radiotherapy Center has used 2 different immobilization systems for patients requiring radiotherapy to the head-and-neck region. A polycarbonate mask was manufactured for radical treatments and a thermoplastic mask for palliative treatments. This study evaluated field placement accuracy, staff opinion, and production costs of both systems. The manual matching program of Varian PortalVision Electronic Portal Imaging (EPI) System was used to assess field placement accuracy on a daily basis. Radiation therapists (RTs) were surveyed before and after the study to determine their opinions of each system. Production time and required materials were recorded to assess cost. Nineteen patients from each system had daily EPI results compiled with no statistically significant difference observed in field placement accuracy. The thermoplastic system was found to be more cost efficient due to a combination of the reduced production time and reuseability of the masks. User acceptability of the thermoplastic system has increased so that it is now the preferred system. In conclusion, the thermoplastic system is a viable alternative to the polycarbonate system in terms of treatment accuracy and cost. It is recommended that the thermoplastic system be used for all radical and palliative treatments. In addition, RTs prefer the thermoplastic system.

Assessment of a radiotherapy patient immobilization device using single plane port radiographs and a remote computed tomography scanner

Radiation treatment requires a precise procedure for interfraction repositioning of the patient. The purpose of this study was to determine the accuracy of our fixation device in treatment position and to evaluate the setup accuracy with two different methods. The positioning data of 19 canine patients with tumors in the head region (oral, nasal, cerebral) treated with photon or proton irradiation were included in this study. The patients were immobilized by means of an individualized fixation device. Focus was set upon interfraction displacement with systematic and random components. In one method, treatment position was evaluated using single plane port radiographs and megavoltage x-rays. In the other method, two orthogonal CT-topograms were acquired to evaluate the precision of positioning of the patient in the immobilization device. Systematic and random displacements were calculated and presented as mean values with corresponding 95% confidence intervals. In spite of a difference between both methods, the positioning seemed to be accurate within the expected range. It seems that a safety margin of 3.7 mm would be enough for both methods to take into account systematic and random position variability in the fixation device, thereby preventing geometric inaccuracies of treatment delivery. The reported immobilization protocol provides accurate patient immobilization for photon and conformal proton radiation therapy.

Intensity-modulated radiotherapy in the treatment of nasopharyngeal carcinoma: an update of the UCSF experience

PURPOSE

To update our experience with intensity-modulated radiotherapy (IMRT) in the treatment of nasopharyngeal carcinoma (NPC).

METHODS AND MATERIALS

Between April 1995 and October 2000, 67 patients underwent IMRT for NPC at the University of California-San Francisco (UCSF). There were 20 females and 47 males, with a mean age of 49 (range 17-82). The disease was Stage I in 8 (12%), Stage II in 12 (18%), Stage III in 22 (33%), and Stage IV in 25 (37%). IMRT was delivered using three different techniques: 1) manually cut partial transmission blocks, 2) computer-controlled auto-sequencing segmental multileaf collimator (SMLC), and 3) sequential tomotherapy using a dynamic multivane intensity modulating collimator (MIMiC). Fifty patients received concomitant cisplatinum and adjuvant cisplatinum and 5-FU chemotherapy according to the Intergroup 0099 trial. Twenty-six patients had fractionated high-dose-rate intracavitary brachytherapy boost and 1 patient had gamma knife radiosurgery boost after external beam radiotherapy. The prescribed dose was 65-70 Gy to the gross tumor volume (GTV) and positive neck nodes, 60 Gy to the clinical target volume (CTV), 50-60 Gy to the clinically negative neck, and 5-7 Gy in 2 fractions for the intracavitary brachytherapy boost. Acute and late normal tissue effects were graded according to the Radiation Therapy Oncology Group (RTOG) radiation morbidity scoring criteria. The local progression-free, local-regional progression-free, distant metastasis-free rates, and the overall survival were calculated using the Kaplan-Meier method.

RESULTS

With a median follow-up of 31 months (range 7 to 72 months), there has been one local recurrence at the primary site. One patient failed in the neck. Seventeen patients developed distant metastases; 5 of these patients have died. The 4-year estimates of local progression-free, local-regional progression-free, and distant metastases-free rates were 97%, 98%, and 66% respectively. The 4-year estimate of overall survival was 88%. The worst acute toxicity documented was as follows: Grade 1 or 2 in 51 patients, Grade 3 in 15 patients, and Grade 4 in 1 patient. The worst late toxicity was Grade 1 in 20 patients, Grade 2 in 15 patients, Grade 3 in 7 patients, and Grade 4 in 1 patient. At 3 months after IMRT, 64% of the patients had Grade 2, 28% had Grade 1, and 8% had Grade 0 xerostomia. Xerostomia decreased with time. At 24 months, only one of the 41 evaluable patients had Grade 2, 32% had Grade 1, and 66% had Grade 0 or no xerostomia. Analysis of the dose-volume histograms (DVHs) showed that the average maximum, mean, and minimum dose delivered were 79.3 Gy, 74.5 Gy, and 49.4 Gy to the GTV, and 78.9 Gy, 68.7 Gy, and 36.8 Gy to the CTV. An average of only 3% of the GTV and 3% of the CTV received less than 95% of the prescribed dose.

CONCLUSION

Excellent local-regional control for NPC was achieved with IMRT. IMRT provided excellent tumor target coverage and allowed the delivery of a high dose to the target with significant sparing of the salivary glands and other nearby critical normal tissues.

Three-dimensional intensity-modulated radiotherapy in the treatment of nasopharyngeal carcinoma: the University of California-San Francisco experience

PURPOSE

To review our experience with three-dimensional intensity-modulated radiotherapy (IMRT) in the treatment of nasopharyngeal carcinoma.

METHODS AND MATERIALS

We reviewed the records of 35 patients who underwent 3D IMRT for nasopharyngeal carcinoma at the University of California-San Francisco between April 1995 and March 1998. According to the 1997 American Joint Committee on Cancer staging classification, 4 (12%) patients had Stage I disease, 6 (17%) had Stage II, 11 (32%) had Stage III, and 14 (40%) had Stage IV disease. IMRT of the primary tumor was delivered using one of the following three techniques: (1) manually cut partial transmission blocks, (2) computer-controlled autosequencing static multileaf collimator (MLC), and (3) Peacock system using a dynamic multivane intensity-modulating collimator (MIMiC). A forward 3D treatment-planning system was used for the first two methods, and an inverse treatment planning system was used for the third method. The neck was irradiated with a conventional technique using lateral opposed fields to the upper neck and an anterior field to the lower neck and supraclavicular fossae. The prescribed dose was 65-70 Gy to the gross tumor volume (GTV) and positive neck nodes, 60 Gy to the clinical target volume (CTV), and 50-60 Gy to the clinically negative neck. Eleven (32%) patients had fractionated high-dose-rate intracavitary brachytherapy boost to the primary tumor 1-2 weeks following external beam radiotherapy. Thirty-two (91%) patients also received cisplatin during, and cisplatin and 5-fluorouracil after, radiotherapy. Acute and late normal tissue effects were graded according to the Radiation Therapy Oncology Group (RTOG) radiation morbidity scoring criteria. Local-regional progression-free, distant metastasis-free survival and overall survival were estimated using the Kaplan-Meier method.

RESULTS

With a median follow-up of 21.8 months (range, 5-49 months), the local-regional progression-free rate was 100%. The 4-year overall survival was 94%, and the distant metastasis-free rate was 57%. The worst acute toxicity was Grade 2 in 16 (46%) patients, Grade 3 in 18 (51%) patients and Grade 4 in 1 (3%) patient. The worst late toxicity was Grade 1 in 15 (43%), Grade 2 in 13 (37%), and Grade 3 in 5 (14%) patients. Only 1 patient had a transient Grade 4 soft-tissue necrosis. At 24 months after treatment, 50% of the evaluated patients had Grade 0, 50% had Grade 1, and none had Grade 2 xerostomia. Analysis of the dose-volume histograms (DVHs) showed that the average maximum, mean, and minimum dose delivered were 79.5 Gy, 75.8 Gy, and 56.5 Gy to the GTV, and 78.9 Gy, 71.2 Gy, and 45.4 Gy to the CTV, respectively. An average of only 3% of the GTV and 2% of the CTV received less than 95% of the prescribed dose. The average dose to 5% of the brain stem, optic chiasm, and right and left optic nerves was 48.3 Gy, 23.9 Gy, 15.0 Gy, and 14.9 Gy, respectively. The average dose to 1 cc of the cervical spinal cord was 41.7 Gy. The doses delivered were within the tolerance of these critical normal structures. The average dose to 50% of the right and left parotids, pituitary, right and left T-M joints, and ears was 43. 2 Gy, 41.0 Gy, 46.3 Gy, 60.5 Gy, 58.3 Gy, 52.0 Gy, and 52.2 Gy, respectively.

CONCLUSION

3D intensity-modulated radiotherapy provided improved target volume coverage and increased dose to the gross tumor with significant sparing of the salivary glands and other critical normal structures. Local-regional control rate with combined IMRT and chemotherapy was excellent, although distant metastasis remained unabated.

Comparison of the accuracy of positioning devices for radiation therapy of canine and feline head tumors

The purpose of this retrospective study was to evaluate the repositioning accuracy of different positioning devices in order to determine their applicability for potential use in conformal radiation therapy for animals. Forty-four animals with spontaneous tumors of the head were included. The animals were divided into 3 groups determined according to the positioning device used. Group 1 animals were positioned using a thermoplastic mask. Group 2 animals were positioned using a head holder. Group 3 animals were positioned using the head holder and an inflatable pillow. The time of presentation determined which position device was used. Port films of the 44 patients were reviewed retrospectively, and the repositioning precision was recorded by measurements in three orthogonal planes. Groups 2 and 3 had significantly better repositioning accuracy (P < or = 0.05) compared to Group 1. The position variation was not significantly different (P < or = 0.05) between Groups 2 and 3 in the lateral and longitudinal direction. Group 3 had a median reposition variation of 0.5 to 1.0 mm, with a standard deviation of 1.0 to 1.5 mm.

A non-invasive immobilization system and related quality assurance for dynamic intensity modulated radiation therapy of intracranial and head and neck disease

PURPOSE

To develop and implement a non-invasive immobilization system guided by a dedicated quality assurance (QA) program for dynamic intensity-modulated radiotherapy (IMRT) of intracranial and head and neck disease, with IMRT delivered using the NOMOS Corporation's Peacock System and MIMiC collimator.

METHODS AND MATERIALS

Thermoplastic face masks are combined with cradle-shaped polyurethane foaming agents and a dedicated quality assurance program to create a customized headholder system (CHS). Plastic shrinkage was studied to understand its effect on immobilization. Fiducial points for computerized tomography (CT) are obtained by placing multiple dabs of barium paste on mask surfaces at intersections of laser projections used for patient positioning. Fiducial lines are drawn on the cradle along laser projections aligned with nasal surfaces. Lateral CT topograms are annotated with a crosshair indicating the origin of the treatment planning and delivery coordinate system, and with lines delineating the projections of superior-inferior field borders of the linear accelerator's secondary collimators, or with those of the fully open MIMiC. Port films exposed with and without the MIMIC are compared to annotated topograms to measure positional variance (PV) in superior-inferior (SI), right-left (RL), and anterior posterior (AP) directions. MIMiC vane patterns superposed on port films are applied to verify planned patterns. A 12-patient study of PV was performed by analyzing positions of 10 anatomic points on repeat CT topograms, plotting histograms of PV, and determining average PV.

RESULTS AND DISCUSSION

A 1.5+/-0.3 mm SD shrinkage per 70 cm of thermoplastic was observed over 24 h. Average PV of 1.0+/-0.8, 1.2+/-1.1, and 1.3+/-0.8 mm were measured in SI, AP, and RL directions, respectively. Lateral port films exposed with and without the MIMiC showed PV of 0.2+/-1.3 and 0.8+/-2.2 mm in AP and SI directions. Vane patterns superimposed on port films consistently verified the planned patterns.

CONCLUSION

The CHS provided adequately reproducible immobilization for dynamic IMRT, and may be applicable to decrease PV for other cranial and head and neck external beam radiation therapy.

Patterns of failure following high-dose 3-D conformal radiotherapy for high-grade astrocytomas: a quantitative dosimetric study

PURPOSE

To analyze the failure patterns for patients with high-grade astrocytomas treated with high-dose conformal radiotherapy (CRT) using a quantitative technique to calculate the dose received by the CT- or MR-defined recurrence volume and to assess whether the final target volume margin used in the present dose escalation study requires redefinition before further escalation.

METHODS AND MATERIALS

Between 4/89 and 10/95, 71 patients with high-grade supratentorial astrocytomas were entered in a phase I/II dose escalation study using 3-D treatment planning and conformal radiotherapy. All patients were treated to either 70 or 80 Gy in conventional daily fractions of 1.8-2.0 Gy. The clinical and planning target volumes (CTV, PTV) consisted of successively smaller volumes with the final PTV defined as the enhancing lesion plus 0.5 cm margin. As of 10/95, 47 patients have CT or MR evidence of disease recurrence/progression. Of the 47 patients, 36 scans obtained at the time of recurrence were entered into the 3-D radiation therapy treatment planning system. After definition of the recurrent tumor volumes, the recurrence scan dataset was registered with the pretreatment CT dataset so that the actual dose received by the recurrent tumor volumes during treatment could be accurately calculated and then analyzed dosimetrically using dose-volume histograms. Recurrences were divided into several categories: 1) "central," in which 95% or more of the recurrent tumor volume (Vrecur) was within D95, the region treated to high dose (95% of the prescription dose); 2) "in-field," in which 80% or more of Vrecur was within the D95 isodose surface; 3) "marginal," when between 20 and 80% of Vrecur was inside the D95 surface; 4) "outside," in which less than 20% of Vrecur was inside the D95 surface.

RESULTS

In 29 of 36 patients, a solitary lesion was seen on recurrence scans. Of the 29 solitary recurrences, 26 were central, 3 were marginal, and none were outside. Multiple recurrent lesions were seen in seven patients: three patients had multiple central and/or in-field lesions only, three patients had central and/or in-field lesions with additional small marginal or outside lesions, and one patent had 6 outside and one central lesion. Since total recurrence volume was used in the final analysis, 6 of the 7 patients with multiple recurrent lesions were classified into centra/in-field category.

CONCLUSION

Analysis of the 36 evaluable patients has shown that 32 of 36 patients (89%) failed with central or in-field recurrences, 3/36 (8%) had a significant marginal component to the recurrence, whereas only 1/36 (3%) could be clearly labeled as failing mainly outside the high-dose region. Seven patients had multiple recurrences, but only 1 of 7 had large-volume recurrences outside the high-dose region. This study shows that the great majority of patient recurrences that occur after high-dose (70 or 80 Gy) conformal irradiation are centrally located: only 1/36 patients (with 7 recurrent lesions) had more than 50% of the recurrence volume outside the region previously treated to high dose. Further dose escalation to 90 Gy (and beyond) thus seems reasonable, based on the same target volume definition criteria

Fractionated stereotactic radiotherapy: rationale and methods

Stereotactic radiosurgery (SRS) has become a widely accepted technique for the treatment intracranial neoplasms. Combined with modern imaging modalities, SRS has established its efficacy in a variety of indications. From the outset, however, it was recognized that the delivery of a single large dose of radiation was essentially "bad biology made better by good physics." To achieve the accuracy required to compensate for this biological shortcoming, the application of SRS has required that a neurosurgical head frame of some sort be rigidly attached to the patients head. Historically, this prerequisite has, primarily for practical reasons, precluded the delivery of multiple fractions over multiple days. With recent improvements in immobilization and repeat fixation, the good biology of fractionated delivery has been realized. This technique, which has come to be known as stereotactic radiotherapy (SRT), has significantly expanded the efficacy of the technique through the use of accurate physical targeting coupled with the basic radiobiological principles gleaned from decades of clinical experience.

Use of a simulator with CT option in radiotherapy of macular degeneration

PURPOSE

To assess the accuracy of a conventional simulation procedure in radiotherapy of age-related macular degeneration.

METHODS AND MATERIALS

A computed tomographic (CT) extension attached to the treatment simulator was used to acquire CT images immediately after conventional simulation in 18 patients referred for treatment of age-related macular degeneration. Analysis was performed on 16 one-sided treatment cases for whom images were obtained. Error was estimated by the displacement between the observed treatment isocenter and the intended isocenter based on reconstructed eye geometry.

RESULTS

Based on single slice measurements, the mean error amplitude was 2.3 mm (range 0.2-5.6). Based on three-dimensional eye globe reconstruction, the mean error amplitude was 2.8 mm (range 0.8-5.3). An incidental finding previously unreported was the lower image quality at the center of the simulator-CT image acquisition field.

CONCLUSIONS

Small but significant errors from conventional simulation were noted. The integrated simulation-CT procedure may help correct the errors to improve the accuracy of simulation setup. The lower image quality at the center of image acquisition field requires adaptation of the simulation-CT procedure.

Simulation by a diagnostic CT for the early vocal cord carcinoma

The CT-based simulation with a 3D planning system permits the optimization of radiotherapy treatments. The goal is to obtain an increase in the local control and survival with a reduction of the treatment related toxicity. In our hospital, we do not have a CT simulator and our 3D planning system is not yet working, therefore, we have developed a system to simulate radiotherapy treatments using a diagnostic CT. We began by simulating an early vocal cord carcinoma. The rules of this simulation are presented using a clinical case as an example.

Parotid gland sparing in patients undergoing bilateral head and neck irradiation: techniques and early results

PURPOSE

To minimize xerostomia in patients receiving bilateral head and neck irradiation (RT) by using conformal RT planning to spare a significant volume of one parotid gland from radiation.

METHODS AND MATERIALS

The study involved 15 patients with head and neck tumors in whom bilateral neck radiation was indicated. The major salivary glands and the targets (tumor, surgical bed, metastases to lymph nodes, and the locations of lymph nodes at risk for metastases) were outlined on axial computed tomography images. Beam's-eye view (BEV) displays were used to construct conformal beams that delivered the prescribed doses to the targets while sparing from direct radiation most of one parotid gland. The gland that was planned to be spared resided in the neck side that was judged in each patient to be at a lesser risk of metastatic disease. Major salivary gland flow rates and the responses to a subjective xerostomia questionnaire were assessed before, during, and after radiation.

RESULTS

Radiation planning for patients with central oropharyngeal tumors required the generation of multiple axial nonopposed beams. The resulting isodoses encompassed the targets, including the retropharyngeal nodes and the jugular nodes up to the base of skull bilaterally, while limiting the dose to the oral cavity, spinal cord, and one parotid gland. For patients with lateralized tumors, the ipsilateral neck side was treated up to the base of the skull; in the contralateral neck side, the treatment included the subdigastric nodes but excluded the jugular nodes at the base of the skull and most of the parotid gland. This was accomplished by a moderate gantry angle that was chosen using the BEV displays. Three months following the completion of radiation, the spared parotid glands retained on average 50% of their unstimulated and stimulated flows. In contrast, no saliva flow was measured from the unspared glands in any of the patients. Subjective xerostomia was absent, mild, or not different from that reported before radiation in 10 of 15 patients (67%).

CONCLUSION

Partial parotid gland sparing is feasible by using three-dimensional planning in patients undergoing bilateral head and neck radiation. Approximately 50% of the saliva flow from the spared glands may be retained, and most patients thus treated have no or mild xerostomia in the early period after the completion of radiation. Whether tumor control and late complications are comparable to standard radiation will be assessed as more experience is gained.

Interactive three dimensional inspection of patient setup in radiation therapy using digital portal images and computed tomography data

PURPOSE

Presently, the majority of clinical tools to quantify deviations in patient setup during external beam radiotherapy is based on two-dimensional (2D) analysis of portal images. The purpose of this study is to develop a tool for the inspection of the patient setup in three dimensions (3D) and to validate its clinical advantage over methods based on 2D analysis in the presence of out-of-plane rotations.

METHODS AND MATERIALS

We developed an interactive procedure to quantify the setup deviation of the patient in 3D. The procedure is based on fast computation of digitally reconstructed radiographs (DRRs) in two beam directions and comparison of these DRRs with corresponding portal images. The potential of the tool is demonstrated on three selected cases of prostate and parotid gland treatment where conventional 2D analysis produced inconsistent results. The measurements from 3D analysis are compared with those obtained from the 2D analysis.

RESULTS

Despite application of an immobilization cast, two investigated parotid gland setups showed rotational deviations in 3D up to 3 degrees. Two-dimensional analysis of these deviations produced inconsistent results. Analysis of the selected prostate setup in 3D showed a rotational deviation of 7 degrees around the left-right axis, possibly causing displacement of the seminal vesicles toward the borders of the conformal boost fields. Using 2D analysis, this out-of-plane rotation was misinterpreted as a translation resulting in the failure to trigger the decision protocol to correct the setup after the first fraction. Using the 3D patient setup analysis procedure, an accuracy of the order of 1 mm and 1 degree (SD) could be obtained. The computation time of the interactive DRRs is of the order of 1 s on a 60 MHz PC. The complete interactive 3D analysis requires about 10 min.

CONCLUSIONS

Quantification of the patient setup in 3D provides essential additional information in cases where conventional 2D analysis is inconsistent, e.g., in the presence of out-of-plane rotations or geometrical degeneracies. The speed and accuracy of the interactive 3D patient setup inspection are acceptable for use in offline clinical studies and analysis of problem cases.

A precision cranial immobilization system for conformal stereotactic fractionated radiation therapy

PURPOSE

Conformal radiotherapy has been shown to benefit from precision alignment of patient target to therapy beam (1, 6, 13). This work describes an optimized immobilization system for the fractionated treatment of intracranial targets. A study of patient motion demonstrates the high degree of immobilization which is available.

METHODS AND MATERIALS

A system using dental fixation and a thermoplastic mask that relocates on a rigid frame is described. The design permits scanning studies using computed tomography (CT) and magnetic resonance imaging (MR), conventional photon radiotherapy, and high precision stereotactic proton radiotherapy to be performed with minimal repositioning variation. Studies of both intratreatment motion and daily setup reliability are performed on patients under treatment for paranasal sinus carcinoma. Multiple radiographs taken during single treatments provide the basis for a three-dimensional (3D) motion analysis. Additionally, studies of orthogonal radiographs used to setup for proton treatments and verification port films from photon treatments are used to establish day to day patient position variation in routine use.

RESULTS

Net 3D patient motion during any treatment is measured to be 0.9 +/- 0.4 mm [mean +/- standard deviation (SD)] and rotation about any body axis is 0.14 +/- 0.67 degrees (mean +/- SD). Day-to-day setup accuracy to laser marks is limited to 2.3 mm (mean) systematic error and 1.6 mm (mean) random error.

CONCLUSION

We conclude that the most stringent immobilization requirements of 3D conformal radiotherapy adjacent to critical normal structures can be met with a high precision system such as the one described here. Without the use of pretreatment verification, additional developments in machine and couch design are needed to assure that patient repositioning accuracy is comparable to the best level of patient immobility achievable.

Comparison of plastic and Orfit masks for patient head fixation during radiotherapy: precision and costs

PURPOSE

Two widely used immobilization systems for head fixation during radiotherapy treatment for ear-nose-throat (ENT) tumors are evaluated.

METHODS AND MATERIALS

Masks made of poly vinyl-chloride (plastic) are compared to thermoplastic masks (Orfit) with respect to the accuracy of the treatment setup and the costs. For both types of material, a cut-out (windows corresponding to treatment fields) and a full mask (not cut out) are considered. Forty-three patients treated for ENT tumors were randomized into four groups, to be fixed by one of the following modalities: cut-out plastic mask (12 patients), full plastic mask (11 patients), cut-out Orfit mask (10 patients), and full Orfit mask (10 patients).

RESULTS

Reproducibility of the treatment setup was assessed by calculating the deviations from the mean value for each individual patient and was demonstrated to be identical for all subgroups: no differences were demonstrated between the plastic (s = 2.1 mm) and the Orfit (s = 2.1 mm) group nor between the cut-out (s = 2.0 mm) and not cut-out (s = 2.1 mm) group. The transfer chain from similar to treatment unit was checked by comparing portal images to their respective simulation image, and no differences between the four subgroups (s = +/- 3.5 mm) could be detected. A methodology was described to compare the costs of both types of masks, and illustrated with the data for a department. It was found that Orfit masks are a cheaper alternative than plastic masks; they require much less investment expenses and the workload and material cost of the first mask for each patient is also lower. Cut-out masks are more expensive than full masks, because of the higher workload and the additional material required for second and third masks that are required in case of field modifications.

CONCLUSIONS

No substantial difference in patient setup accuracy between both types of masks was detected, and cutting out the masks had no impact on the fixing capabilities. A first Orfit mask will typically be a cheaper alternative than a plastic mask for most departments (lower fixed and variable costs). The higher material cost of the subsequent Orfit masks, compared to the plastic masks, offset the lower investment expenses.

Simulation accuracy in radiotherapy for maxillary sinus tumors

PURPOSE

To evaluate the accuracy and clinical importance of beam positioning during simulation of radiation treatment for tumors in the maxillary sinus.

METHODS AND MATERIALS

Five patients were prepared as if they were to be treated for a maxillary sinus tumor. A three-beam computed tomography (CT) scan-based computer plan was made for each patient. The location of the central beam axis of each beam was measured, relative to bony anatomical structures. A simulation was performed using the bony references to position the radiation beams during simulation. After this, the simulation procedure was repeated by the use of a noninvasive external localization frame with a known accuracy and reproducibility within 2 mm margins.

RESULTS

When defining the clinical target volume as the known tumor with a 1 cm margin, three out of five patients would suffer a partial geographical miss throughout the entire radiation treatment due to erroneous beam positioning at the simulation stage when using bony structures as a guide for beam positioning. The influence of these errors is analyzed as normal tissue complication and tumor control probabilities.

CONCLUSION

When defining a planning target volume, one should consider a margin to correct for possible simulation errors. We advise the use of objective, external (and thus nonanatomical) landmarks as a reference during simulation to reduce this extra margin to a minimum. In case of simulation, using bony structures as a reference, an additional margin should be entered, depending on the simulation accuracy that can be obtained.

A CT-based simulation for head and neck tumors in centers without CT-simulator and 3D-planning system

We present a special CT-based simulation technique to optimize the radiotherapy treatments in head and neck tumors. On an immobilization device, some CT hyperdense markers are placed. Real-size CT slices are performed every 5 mm with the patient in the treatment position with the immobilization system. This study permits a more accurate knowledge of the gross tumoral volume and an optimization of the planning treatment.

Results of primary and adjuvant CT-based 3-dimensional radiotherapy for malignant tumors of the paranasal sinuses

PURPOSE

This study reports our clinical experience supporting the normal tissue-sparing capability of 3-dimensional (3-D) treatment planning when applied to advanced neoplasms of the paranasal sinuses.

METHODS AND MATERIALS

Between 1986 and 1992, computed tomography (CT)-based 3-D radiotherapy was used to treat 39 patients with advanced stage malignant tumors of the paranasal sinuses as all or part of initial treatment. Fifteen unresectable patients were treated with primary radiotherapy to a median prescribed total dose of 68.4 Gy. Twenty-four patients were treated with postoperative adjuvant radiotherapy for close margins (< 5 mm), microscopic or gross residual disease. The median prescribed total doses were 55.8 Gy, 59.4 Gy and 67.8 Gy, respectively. Globe-sparing fields were used in the primary treatment plans of 37 patients (95%). The median follow-up is 4.5 years (range, 19-86 months).

RESULTS

For the unresectable patients who were treated with radiotherapy alone, the local control rate at 3 years is 32%. The actuarial overall survivals at 3 and 4 years are 32%. For the patients who received postoperative adjuvant radiotherapy, none of the five patients irradiated for close surgical margins recurred locally. Three of the 14 with microscopic residual (21%) recurred locally at 26, 63, and 74 months from the start of irradiation. Four of the five with gross residual (80%) recurred locally with a median time to recurrence of 2 years. The local control rates at 3 and 5 years for the adjuvant group are 75% and 65%, respectively. The actuarial overall survival at 3 and 5 years are 65% and 60%, respectively. None of the first sites of local disease progression were judged to have occurred outside the high-dose region. There was one case of mild osteoradionecrosis successfully treated with conservative treatment, one case of limited optic neuropathy and one case of possible radiation-induced cataract. There was no blindness related to irradiation.

CONCLUSION

This study indicates that computed tomography-based 3-D radiotherapy can preserve critical structures unaffected by tumor invasion and achieve the generally expected local control rates when it is used as all or part of initial treatment for extensive malignant tumors of the paranasal sinus. The presence of gross disease was a major adverse prognostic factor in this study. Additional therapeutic maneuvers are essential to improve the local control and survival rate in patients with advanced paranasal sinus carcinomas.

Repeated CT examinations in limited volume irradiation of brain tumors: quantitative analysis of individualized (CT-based) treatment plans

Deviations of the position of the isocenter were quantitatively assessed for CT-based limited volume irradiation of brain tumors. Of the linear deviations, 95% were within 10 mm and 3 mm during treatment planning and delivery, respectively. The application of face masks before CT planning improved the accuracy of field alignment. Repeated CT examinations seemed to be more important after simulation than during treatment delivery.

Larynx motion associated with swallowing during radiation therapy

PURPOSE

A basis is presented for predicting the reduction in radiation dose to the larynx attributable to swallowing during radiation therapy treatment.

METHODS AND MATERIALS

Laryngeal movement associated with swallowing can occur during radiation therapy even when the patient's head is immobilized. Data on the extent and timing of laryngeal motions and the frequency of swallowing were used to predict the effect such motion would have on accuracy of radiation dose to the larynx.

RESULTS

In a nontracheostomized adult the larynx elevates approximately 2 cm during a swallow and moves anteriorly less than 1 cm. The normal frequency of swallowing in the supine position is once every 1-2 min. During therapy, the likelihood of a swallow occurring during an irradiation interval depended on the duration of the interval. For irradiation intervals less than 2 min long the ratio of number of swallows to number of intervals was 0.27. For irradiation intervals between 2-3 min long the ratio was 1.76. Based on conservative estimates of radiation field dimensions, larynx motion, and incidence of swallowing, the reduction in radiation dose attributable to swallowing during treatment would be approximately 0.5%.

CONCLUSION

With small fields the total dose is only decreased by 0.5% with swallowing, so the change in the total dose is insignificant.

Total scalp treatment of mycosis fungoides: the 4 x 4 technique

PURPOSE

A technique for treating mycosis fungoides confined to the scalp using a method known as the 4 x 4 technique is presented.

METHODS AND MATERIALS

Uniform dose distribution on the scalp and acceptable "hot spots" along five match lines is accomplished by using four sets of four fields (i.e., 4 x 4) on the patient. Precise and reproducible patient and field alignment was accomplished with a solid thermoplastic mask, which is the surface on which match lines are drawn. In-vivo dosimetry (thermoluminescent dosimeters and film) are easily attached to the mask which also provides a portion of the 7 mm bolus used to shift the characteristic 6 MeV electron depth dose toward the skin surface.

RESULTS

In-vivo dosimetry demonstrated that single fraction match line doses are within 25% to 30% of central axis dose. Shifting these match lines to four locations reduces these "hot spots" to satisfactory levels (less than 120%). Three patients have been treated with this technique and each patient continues to have a complete clinical response at 14 to 21 months post treatment. In addition, each patient has excellent cosmetic results with no evidence of acute or chronic side effects at the match lines.

CONCLUSION

The 4 x 4 technique has proven to be useful in the treatment of mycosis fungoides confined to the scalp.

Preservation of parotid function after external beam irradiation in head and neck cancer patients: a feasibility study using 3-dimensional treatment planning

PURPOSE

Radiation-induced xerostomia is a frequent complication and major cause of morbidity in head and neck cancer patients. The severity of xerostomia is related to radiation dose and the amount of parotid tissue included in the irradiated volume. To reduce this side-effect and preserve salivary function, we have evaluated the use of 3-dimensional (3-D) treatment planning to spare the contralateral parotid gland in twelve patients undergoing radiation therapy for head and neck cancers.

METHODS AND MATERIALS

In each case, beam's eye view displays were used to design beam and blocking arrangements that excluded the contralateral parotid. Ten patients were treated with 2 nonopposing oblique fields in the axial and non-axial plane while two patients required a non-axial, non-coplanar 3-field arrangement. These 3-D treatment plans were also compared with conventional 2-dimensional (2-D) plans. The 2-dimensional plans were designed independently of the 3-D treatment planning information using the orthogonal radiographs and hard copies of the computed tomography scans.

RESULTS

An average of 1.8% (range, 0-7%) of the target volume was underdosed with the 95% isodose level for the 3-D plans compared with 18.8% (range, 2.0-36.6%) for the 2-D plans. This was due to improved identification of the target volumes and better design of blocked fields with beam's eye view treatment planning. Furthermore, the mean dose to the opposite parotid was 3.9 Gy for the 3-D plans vs 28.9 Gy for the conventional plans. With a minimum follow-up of 4 months, only 2 of 12 patients have complained of a dry mouth.

CONCLUSION

These encouraging results suggest that this approach is feasible in many cases. 3-D treatment planning may allow the use of parotid sparing techniques in patients who otherwise would not have been considered candidates using conventional radiotherapy techniques.

Determining locations of intracerebral lesions for proton radiotherapy

Using an external view of the head, the ability to direct a proton radiotherapy beam at an intracerebral lesion is described, using a biostereometric (BSM) technique. The positions of markers, recognizable on computed tomography (CT) or magnetic resonance (MR) images, at known locations on the skin of a patient's head are related to the site of the lesion seen on the images. The markers' positions are determined by a BSM device, incorporating six video cameras coupled to a computer. A transformation from a coordinate system, defined by the CT or MR images, to another coordinate system, that of the BSM device, allows the proton beam to be directed towards the lesion. Markers used in this work were solid steel spheres for CT and plastic spheres containing oil for MR images.

A quantitative assessment of the addition of MRI to CT-based, 3-D treatment planning of brain tumors

Quantitative 3-D volumetric comparisons were made of composite CT-MRI macroscopic and microscopic tumor and target volumes to their independently defined constituents. Volumetric comparisons were also made between volumes derived from coronal and axial MRI data sets, and between CT and MRI volumes redefined at a repeat session in comparison to their original definitions. The degree of 3-D dose coverage obtained from use of CT data only or MRI data only in terms of coverage of composite CT-MRI volumes was also analyzed. On average, MRI defined larger volumes as well as a greater share of composite CT-MRI volumes. On average, increases in block margin on the order of 0.5 cm would have ensured coverage of volumes derived from use of both imaging modalities had only MRI data been used. However, the degree of inter-observer variation in volume definition is on the order of the magnitude of differences in volume definition seen between the modalities, and the question of which imaging modality best describes tumor volumes remains unanswered until detailed histologic studies are performed. Given that tumor volumes independently apparent on CT and MRI have equal validity, composite CT-MRI input should be considered for planning to ensure precise dose coverage for conformal treatments.

The clinical utility of magnetic resonance imaging in 3-dimensional treatment planning of brain neoplasms

Results of the clinical experience gained since 1986 in the treatment planning of patients with brain neoplasms through integration of magnetic resonance imaging (MRI) into computerized tomography (CT)-based, three-dimensional treatment planning are presented. Data from MRI can now be fully registered with CT data using appropriate three-dimensional coordinate transformations allowing: (a) display of MRI defined structures on CT images; (b) treatment planning of composite CT-MRI volumes; (c) dose display on either CT or MRI images. Treatment planning with non-coplanar beam arrangements is also facilitated by MRI because of direct acquisition of information in multiple, orthogonal planes. The advantages of this integration of information are especially evident in certain situations, for example, low grade astrocytomas with indistinct CT margins, tumors with margins obscured by bone artifact on CT scan. Target definitions have repeatedly been altered based on MRI detected abnormalities not visualized on CT scans. Regions of gadolinium enhancement on MRI T1-weighted scans can be compared to the contrast-enhancing CT tumor volumes, while abnormalities detected on MRI T2-weighted scans are the counterpart of CT-defined edema. Generally, MRI markedly increased the apparent macroscopic tumor volume from that seen on contrast-CT alone. However, CT tumor information was also necessary as it defined abnormalities not always perceptible with MRI (on average, 19% of composite CT-MRI volume seen on CT only). In all, the integration of MRI data with CT information has been found to be practical, and often necessary, for the three-dimensional treatment of brain neoplasms.

A head immobilization system for radiation simulation, CT, MRI, and PET imaging

An aquaplast mask/marker immobilization system for the routine radiation therapy treatment of head and neck disease is described. The system utilizes a commercially available thermoplastic mesh indexed and mounted to a rigid frame attached to the therapy couch. The apparatus is designed to permit CT, MRI, and PET diagnostic scans of the patient to be performed in the simulation and treatment position utilizing the same mask, thereby facilitating image correlation. Studies employing weekly simulation indicate that patient treatment position movement can be restricted to 3 mm over the course of treatment. This easily constructed system permits rapid mask formation to be performed on the treatment simulator, resulting in an immobilization device comparable to masks produced with vacuum-forming techniques. Details of construction, verification, and central axis CT, MRI, PET markers are offered.