The impact of virtual simulation in palliative radiotherapy for non-small-cell lung cancer

Pre-planning: a new approach to virtual simulation

Background

For palliative radiotherapy treatments, two types of simulation are available at our Centre: conventional (or 2D) and virtual. Each has its advantages: conventional simulation requires less preparation time whereas virtual simulation allows accurate visualisation and identification of target volumes in 3D. We propose a new approach where treatment field parameters are determined on diagnostic CT scans, and then reproduced with reference to a patient’s bony landmarks using conventional simulation. This combines the benefits of both methods. We argue that the slight differences in set-up between diagnostic and simulation CT scans will have little impact on the determination of the target volume in palliative treatment settings.

Methods

In total, 12 patients who had diagnostic scans done within a month before their virtual simulation were randomly selected. Both scans were retrieved retrospectively for the study. An independent radiation oncologist contoured the target volumes on both scans and their relative positions were compared by fusing the digitally reconstructed radiographs generated from the respective scans. A 2D Conformity Index (2DCI) was then calculated and tabulated for 0, 0.5, 1.0, 1.5 and 2 cm margins to evaluate the accuracy of this approach and determine the margins required to account for the inherent variability of this method. In addition, the deviation or offset of the centre of field (COF) was also measured and analysed.

Results

The median 2DCI (0 margin) was 0.85. For margins of 0.5, 1.0, 1.5 and 2.0 cm, the median 2DCIs were 0.97, 1, 1 and 1, respectively. The median displacement of the COF in the superior–inferior direction was 0.7 cm and that in the right–left direction was 0.2 cm.

Conclusion

Our pilot study suggests that our approach is feasible. We recommend adding an additional margin of up to 0.5 cm (to the usual treatment margins) to ensure good coverage of the target volume when using this method.

Increasing use of advanced radiation therapy technologies in the last 30 days of life among patients dying as a result of cancer in the United States

PURPOSE

We sought to analyze trends in radiation therapy (RT) technology use and costs in the last 30 days of life for patients dying as a result of cancer.

METHODS

We used the Surveillance, Epidemiology, and End Results (SEER) -Medicare and Texas Cancer Registry-Medicare databases to analyze claims data for 13,488 patients dying as a result of lung, breast, prostate, colorectal, melanoma, and pancreas cancers from 2000 to 2009. Logistic regression modeling was used to conduct adjusted analyses regarding influence of demographic, clinical, and health services variables on receipt of types of RT. Costs were calculated in 2009 US dollars.

RESULTS

The proportion of patients treated with two-dimensional RT decreased from 74.9% of those receiving RT in the last 30 days of life in 2000 to 32.7% in 2009 (P < .001). Those receiving three-dimensional RT increased from 27.2% in 2000 to 58.5% in 2009 (P < .001). The proportion of patients treated with intensity-modulated radiation therapy in the last 30 days of life increased from 0% in 2000 to 6.2% in 2009 (P < .001), and those undergoing stereotactic radiosurgery increased from 0% in 2000 to 5.0% in 2009 (P < .001). The adjusted mean costs of per-patient RT services delivered in the last 30 days of life were higher in the years 2007 to 2009.

CONCLUSION

Among patients receiving RT in the last month of life, there was a shift away from the simplest technique toward more advanced RT technologies. Studies are needed to ascertain whether these technology shifts improve palliative outcomes and quality of life for patients dying as a result of cancer who receive RT services.

Determination of internal target volume from a single positron emission tomography/computed tomography scan in lung cancer

PURPOSE

The use of four-dimensional computed tomography (4D-CT) to determine the tumor internal target volume (ITV) is usually characterized by high patient radiation exposure. The objective of this study was to propose and evaluate an approach that relies on a single static positron emission tomography (PET)/CT scan to determine the ITV, thereby eliminating the need for 4D-CT and thus reduce patient radiation dose.

METHODS AND MATERIALS

The proposed approach is based on the concept that the observed PET image is the result of a joint convolution of an ideal PET image (free from motion and partial volume effect) with a motion-blurring kernel (MBK) and partial volume effect. In this regard, the MBK and tumor ITV are then estimated from the deconvolution of this joint model. To test this technique, phantom and patient studies were performed using different sphere/tumor sizes and motion trajectories. In all studies, a 4D-CT and a PET/CT image of the sphere/tumor were acquired. The ITV from the proposed technique was then compared to the maximum intensity projection (MIP) volume of the 4D-CT images. A Dice coefficient of the two volumes was calculated to represent the similarity between the two ITVs.

RESULTS

The average ITVs of the proposed technique were 97.2% ± 0.3% and 81.0% ± 16.7% similar to the MIP volume in the phantom and patient studies, respectively. The average dice coefficients were 0.87 ± 0.05 and 0.73 ± 0.16, respectively, for the two studies.

CONCLUSION

Using the proposed approach, a single static PET/CT scan has the potential to replace a 4D-CT to determine the tumor ITV. This approach has the added advantage of reducing patient radiation exposure and determining the tumor MBK compared to 4D-CT/MIP-CT.

The emerging role of IG-IMRT for palliative radiotherapy: a single-institution experience

Many modern radiotherapy centers now have image-guided intensity-modulated radiotherapy (ig-imrt) tools available for clinical use, and the technique offers many options for patients requiring palliative radiotherapy. We describe a single-institution experience with ig-imrt for short-course palliative radiotherapy, highlighting the unique situations in which the technique can be most effectively used.

Rapid palliative radiotherapy: comparing IG-IMRT with more conventional approaches

Purpose: To assess the efficiency of an integrated imaging, planning, and treatment delivery system to provide image-guided intensity-modulated radiotherapy (IG-IMRT) for patients requiring palliative radiotherapy (PRT).

Methods: Between December 2006 and May 2008, 28 patients requiring urgent PRT were selected to undergo single-session megavoltage computed tomography (MV-CT) simulation, IMRT treatment planning, position verification and delivery of the first faction of radiotherapy on a helical Tomotherapy® unit. The time required to complete each step was recorded and compared to our standard approach of using either fluoroscopic or CT-based simulation, simplified treatment planning and delivery on a megavoltage unit.

Results: Twenty-eight patients were treated with our integrated IG-IMRT protocol. The median age was 72 years, with 61% men and 39% women. The indications for PRT were: painful bone and soft tissue metastasis (75%); bleeding lesions (14%); and other reasons (11%). The areas treated included the following: hip and/or pelvis (42%); spine (36%); and other areas (21%). The most commonly used dose prescription was 20 Gy in five fractions. Average times for the integrated IG-IMRT processes were as follows: image acquisition, 15 minutes; target delineation, 16 minutes; IMRT treatment planning, 9 minutes; treatment position verification, 10 minutes; and treatment delivery, 12 minutes. The average total time was 62 minutes compared to 66 minutes and 81 minutes for fluoroscopic and CT-simulation-based approaches, respectively. The IMRT dose distributions were also superior to simpler plans.

Conclusions: PRT with an integrated IG-IMRT approach is efficient and convenient for patients, and has potential for future applications such as single-fraction radiotherapy.

Quantifying interobserver variation in target definition in palliative radiotherapy

PURPOSE

To describe the degree of interobserver and intraobserver variability in target and field definition when using three-dimensional (3D) volume- vs. two-dimensional (2D) field-based planning.

METHODS AND MATERIALS

Standardized case scenario and diagnostic imaging for 9 palliative cases (3 bone metastases, 3 palliative lung cancer, and 3 abdominal pelvis soft-tissue disease) were presented to 5 study radiation oncologists. After a decision on what the intended anatomic target should be, observers created two sets of treatment fields, first using a 2D field-based and then a 3D volume-based planning approach. Percent overlap, under-coverage, and over-coverage were used to describe interobserver and intraobserver variations in target definition.

RESULTS

The degree of interobserver variation for 2D and 3D planning was similar with a degree of overlap of 76% (range, 56%-85%) and 74% (range, 55%-88%), respectively. When comparing the treatment fields defined by the same observer using the two different planning methods, the mean degree of overlap was 78%; over-coverage, 22%; and under-coverage, 41%. There was statistically significantly more under-coverage when field-based planning was used for bone metastases (33%) vs. other anatomic sites (16%) (p = 0.02). In other words, 2D planning is more likely to result in geographic misses in bone metastases compared with other areas.

CONCLUSIONS

In palliative radiotherapy clinically significant interobserver and intraobserver variation existed when using both field- and volume-based planning approaches. Strategies that would reduce this variability deserve further investigation.

Optimising the use of virtual and conventional simulation: a clinical and economic analysis

Background and purpose: Currently, optimal use of virtual simulation for all treatment sites is not entirely clear. This study presents data to identify specific patient groups for whom conventional simulation may be completely eliminated and replaced by virtual simulation.

Sampling and method: Two hundred and sixty patients were recruited from four treatment sites (head and neck, breast, pelvis, and thorax). Patients were randomly assigned to be treated using the usual treatment process involving conventional simulation, or a treatment process differing only in the replacement of conventional plan verification with virtual verification. Data were collected on set-up accuracy at verification, and the number of unsatisfactory verifications requiring a return to the conventional simulator. A micro-economic costing analysis was also undertaken, whereby data for each treatment process episode were also collected: number and grade of staff present, and the time for each treatment episode.

Results: The study shows no statistically significant difference in the number of returns to the conventional simulator for each site and study arm. Image registration data show similar quality of verification for each study arm. The micro-costing data show no statistical difference between the virtual and conventional simulation processes.

Conclusions: At our institution, virtual simulation including virtual verification for the sites investigated presents no disadvantage compared to conventional simulation.

Localization: conventional and CT simulation

Recent developments in imaging and computer power have led to the ability to acquire large three dimensional data sets for target localization and complex treatment planning for radiation therapy. Conventional simulation implies the use of a machine capable of the same mechanical movements as treatment units. Images obtained from these machines are essentially two dimensional with the facility to acquire a limited number of axial slices to provide patient contours and tissue density information. The recent implementation of cone beam imaging on simulators has transformed them into three dimensional imaging devices able to produce the data required for complex treatment planning. The introduction of computed axial tomography (CT) in the 1970s was a step-change in imaging and its potential use in radiotherapy was quickly realised. However, it remained a predominantly diagnostic tool until modifications were introduced to meet the needs of radiotherapy and software was developed to perform the simulation function. The comparability of conventional and virtual simulation has been the subject of a number of studies at different disease sites. The development of different cross sectional imaging modalities such as MRI and positron emission tomography has provided additional information that can be incorporated into the simulation software by image fusion and has been shown to aid in the delineation of tumours. Challenges still remain, particularly in localizing moving structures. Fast multislice scanning protocols freeze patient and organ motion in time and space, which may lead to inaccuracy in both target delineation and the choice of margins in three dimensions. Breath holding and gated respiration techniques have been demonstrated to produce four-dimensional data sets that can be used to reduce margins or to minimize dose to normal tissue or organs at risk. Image guided radiotherapy is being developed to address the interfraction movement of both target volumes and critical normal structures. Whichever method of localization and simulation is adopted, the role of quality control is important for the overall accuracy of the patient's treatment and must be adapted to reflect the networked nature of the process.

Computerized tomographic simulation compared with clinical mark-up in palliative radiotherapy: A prospective study

PURPOSE

To evaluate the impact of computed tomographic (CT) planning in comparison to clinical mark-up (CM) for palliative radiation of chest wall metastases.

METHODS AND MATERIALS

In patients treated with CM for chest wall bone metastases (without conventional simulation/fluoroscopy), two consecutive planning CT scans were acquired with and without an external marker to delineate the CM treatment field. The two sets of scans were fused for evaluation of clinical tumor volume (CTV) coverage by the CM technique. Under-coverage was defined as the proportion of CTV not covered by the CM 80% isodose.

RESULTS

Twenty-one treatments (ribs 17, sternum 2, and scapula 2) formed the basis of our study. Due to technical reasons, comparable data between CM and CT plans were available for 19 treatments only. CM resulted in a mean CTV under-coverage of 36%. Eleven sites (58%) had an under-coverage of >20%. Mean volume of normal tissues receiving >/=80% of the dose was 5.4% in CM and 9.3% in CT plans (p = 0.017). Based on dose-volume histogram comparisons, CT planning resulted in a change of treatment technique from direct apposition to a tangential pair in 7 of 19 cases.

CONCLUSIONS

CT planning demonstrated a 36% under-coverage of CTV with CM of ribs and chest wall metastases.

Palliative chest irradiation in sitting position in patients with bulky advanced lung cancer

Some patients with bulky advanced lung cancer are not able to lie down because of dyspnea. We therefore designed a technique for irradiation in a sitting position by using a dedicated chair. The reproducibility of the sitting position was high and all ten patients preferred this position over lying down. In selected patients who are unable to lie down, palliative irradiation in a sitting position may be an option.

Performance evaluation of a dedicated computed tomography scanner used for virtual simulation using in-house fabricated CT phantoms

Comprehensive tests on single slice CT scanner was carried out using in-house fabricated phantoms/test tools following AAPM recommended methods to independently validate the auto-performance test (APT) results. Test results of all the electromechanical parameters were found within the specified limits. Radiation and sensitivity profile widths were within ± 0.05 cm of the set slice thickness. Effective energy corresponding to nominal kVp of 80, 110 and 130 were 49.99, 55.08 and 59.48 keV, respectively. Percentage noise obtained by APT was 1.32% while the independently measured value was 0.38%. Observed contrast resolutions by independent method at 0.78% and 12% contrast difference were 4 mm and 1.25 mm (= 4 lp/cm) respectively. However, high contrast resolution (limiting spatial resolution) by APT at 50, 10 and 2% MTF levels were 9, 12.5 and 14.1 lp/cm respectively. Difference in calculated and measured CT numbers of water, air, teflon, acrylic, polystyrene and polypropylene were in the range of 0 to 24 HU, while this difference was 46 and 94 HU in case of nylon and bakelite respectively. The contrast scale determined using CT linearity phantom was 1.998×10⁻⁴ cm⁻¹/CT number. CT dose index (CTDI) and weighted CTDI (CTDI_w) measured at different kVp for standard head and body phantoms were smaller than manufacturer-specified and system-calculated values and were found within the manufacturer-specified limit of ± 20%. Measured CTDIs on surface (head: 3.6 cGy and body: 2.6 cGy) and at the center (3.3 cGy, head; and 1.2 cGy, body) were comparable to reported values of other similar CT scanners and were also within the industry-quoted CTDI range. Comprehensive QA and independent validation of APT results are necessary to obtain baseline data for CT virtual simulation.

Improvements in radiotherapy practice: the impact of new imaging technologies

Improvements in imaging technology are impacting on every stage of the radiotherapy treatment process. Fundamental to this is the move towards computed tomography (CT) simulation as the basis of all radiotherapy planning. Whilst for many treatments, the definition of three-dimensional (3D) tumour volumes is necessary, for geometrically simple treatments virtual simulation may be more speedily performed by utilising the reconstruction of data in multiple imaging planes. These multi-planar reconstructions may be used to define both the treatment volumes (e.g. for palliative lung treatments) and the organs at risk to be avoided (e.g. for para-aortic strip irradiation). For complex treatments such as conformal radiotherapy (CFRT) and intensity-modulated radiotherapy (IMRT) where 3D volumes are defined, improvements in imaging technologies have specific roles to play in defining the gross tumour volume (GTV) and the planning target volume (PTV). Image registration technologies allow the incorporation of functional imaging, such as positron emission tomography and functional magnetic resonance imaging, into the definition of the GTV to result in a biological target volume. Crucial to the successful irradiation of these volumes is the definition of appropriate PTV margins. Again improvements in imaging are revolutionising this process by reducing the necessary margin (active breathing control, treatment gating) and by incorporating patient motion into the planning process (slow CT scans, CT/fluoroscopy units). CFRT and IMRT are leading to far closer conformance of the treated volume to the defined tumour volume. To ensure that this is reliably achieved on a daily basis, new imaging technologies are being incorporated into the verification process. Portal imaging has been transformed by the introduction of electronic portal imaging devices and a move is underway from two-dimensional (2D) to 3D treatment verification (cone beam CT, optical video systems). A parallel development is underway from off-line analysis of portal images to the incorporation of imaging at the time of treatment using image-guided radiotherapy. By impacting on the whole process of radiotherapy (tumour definition, simulation, treatment verification), these new imaging technologies offer improvements in radiotherapy delivery with the potential for greater cure rates and a minimum level of treatment side effects.

Virtual simulation in palliative lung radiotherapy

AIMS

To study the accuracy of tumour-volume localisation in a comparison of conventional and virtual simulation for palliative lung radiotherapy. To assess if three-dimensional tumour outlining is necessary for the virtual simulation process.

MATERIALS AND METHODS

Ten consecutive patients with non-small cell lung cancer underwent target localisation for palliative lung radiotherapy using conventional and virtual simulation. The treatment fields were initially marked with a conventional simulator using fluoroscopy, plain X-ray film and available diagnostic imaging. Each patient then had a computed tomography (CT), and these simulated treatment fields were reproduced within the virtual simulation planning system. Two clinicians then independently defined treatment fields using virtual simulation alone. The virtual simulation was achieved without outlining the tumour in three dimensions. The coverage of an 'ideal' CT-defined planning-target volume (PTV) was then calculated for each of the virtually and conventionally simulated fields. In addition, the amount of irradiated normal lung was measured using dose-volume histograms (DVH). Field sizes and differences in tumour volume coverage were compared.

RESULTS

There was significantly greater tumour volume coverage using virtual simulation compared with conventional simulation (P < 0.03). This advantage was more pronounced in tumours that were larger and those that were closer to the patient's midline. There was no statistically significant difference in the volume of uninvolved lung irradiated between the two methods.

CONCLUSION

In this small sample of patients, we have demonstrated improved tumour volume coverage using virtual simulation, without increasing the volume of uninvolved lung treated. A simple but consistent method of virtual simulation for this patient group is offered as an alternative to both PTV-defined CT simulation and fluoroscopy-based conventional simulation.

Computed tomographic simulation in palliative radiotherapy: the Princess Margaret Hospital experience

AIM

To examine the pattern of palliative radiation planning and the use of computed tomographic simulation (CTSIM) for this purpose.

MATERIALS AND METHODS

We reviewed our department's external radiotherapy database for all courses of treatment with a palliative intent during the period of April to June 2002. Patient characteristics and treatment details were compared based on whether CTSIM had been used or not.

RESULTS

During the above period, 593 courses of external radiation treatment were delivered with palliative intent in our department. Of these, 100 treatments (17%) were planned with the help of CTSIM. The mean age of patients with CTSIM (62.9 years) was not significantly different with the patients planned without CTSIM (63.6 years). CTSIM use varied by treatment location, being highest in mediastinum/oesophagus (48%) and pancreas/stomach (47%) treatments, and lowest in spine (6%), lung (3%) and long bones (4%) (P < 0.01). Only 3% of palliative treatments without CTSIM were prescribed using multiple/complex fields (all field arrangements more complex than a single field or two opposed parallel fields). Although significantly higher (P < 0.001), this proportion was also only 24% in the cases planned with CTSIM. Only 12% of treatments without CTSIM were prescribed with more than 5 fractions, whereas 32% of CT-simulated treatments included more than 5 fractions (P < 0.001).

CONCLUSION

CTSIM was used much less frequently in our department's palliative radiotherapy compared with its use in radical treatments. The relatively low rate of multiple/complex fields planned in CT-simulated cases suggested that CTSIM was mostly used to improve tumour localisation. The optimal role of CTSIM in palliative radiotherapy will most probably evolve, based on an enhanced understanding of the implications from improved localisation and optimal planning techniques on clinical outcomes, patient convenience and resource accessibility.

Thoracic radiotherapy for limited-stage small cell lung cancer: issues of timing, volumes, dose, and fractionation

Although meta-analysis of randomized trials comparing chemotherapy alone versus chemotherapy plus thoracic irradiation demonstrated that thoracic radiotherapy reduced mortality by 14%, this analysis probably underestimates the effect of optimally delivered thoracic irradiation integrated with appropriate chemotherapy. However, there remains much debate as to the optimal timing of the radiotherapy and the radiotherapy volume, dose, and fractionation. Theoretically, early use of radiotherapy should reduce the probability of chemotherapy and radiation resistance, accelerated repopulation, and metastatic events. Deferred or sequential radiotherapy potentially allows smaller radiotherapy fields. Of the seven randomized controlled trials examining timing, only those with early chemoradiation have 5-year survival rates in excess of 20%. The "chemoradiation package" can be defined as the time from the start of chemotherapy until the completion of radiotherapy. The best median survival and long-term survival rates have been observed in trials with a chemoradiation package time of less than 6 weeks. Protocols combining chemotherapy and radiotherapy must respect radiobiologic principles concerning the time factor derived from radiotherapy fractionation studies.

CT simulation for radiotherapy treatment planning

The present status of CT simulation (CT sim) hardware, software and practice is reviewed, particularly with regard to the changes that have taken place over the last 5 years. The latest technology is discussed together with some recently developed techniques. The article concludes with a discussion of virtual simulation vs physical (conventional) simulation; in particular there is a review of the changes that have been made to the "Disadvantages table" presented by Conway and Robinson [1], which now make CT sim an attractive system for any radiotherapy department.