Intensity-modulated radiotherapy reduces lung irradiation in patients with carcinoma of the oesophagus.

The 2-year survival rate after conventional radiotherapy for carcinoma of the oesophagus is around 10–20% [8]. Concomitant chemoradiation schedules have produced survival figures of 25–30% at 5 years, and this is now considered standard treatment [1]. Conformal radiotherapy techniques offer the potential to deliver higher doses of radiation to oesophageal tumours [5], and this may improve local tumour control. However, concerns regarding late normal tissue damage to the lung parenchyma and spinal cord remain a concern. Intensitymodulated radiotherapy (IMRT) allows complex dose distributions to be produced, and can reduce the dose to radiosensitive organs close to the tumour [2]. The present study was designed to investigate the impact of beam intensity modulation on treatment planning for carcinoma of the oesophagus, by comparing a standard three-dimensional conformal radiotherapy (3DCRT) technique to an IMRT technique using the same number and orientation of treatment fields.

A comparison of conformal and intensity-modulated techniques for oesophageal radiotherapy.

Background and purpose: To investigate the potential of intensity-modulated radiotherapy (IMRT) to reduce lung irradiation in the treatment of oesophageal carcinoma with radical radiotherapy.Materials and methods: A treatment planning study was performed to compare two-phase conformal radiotherapy (CFRT) with IMRT in five patients. The CFRT plans consisted of anterior, posterior and bilateral posterior oblique fields, while the IMRT plans consisted of either nine equispaced fields (9F), or four fields (4F) with orientations equal to the CFRT plans. IMRT plans with seven, five or three equispaced fields were also investigated in one patient. Treatment plans were compared using dose-volume histograms and normal tissue complication probabilities.Results: The 9F IMRT plan was unable to improve on the homogeneity of dose to the planning target volume (PTV), compared with the CFRT plan (dose range, 16.9+/-4.5 (1 SD) vs. 12.4+/-3.9%; P=0.06). Similarly, the 9F IMRT plan was unable to reduce the mean lung dose (11.7+/-3.2 vs. 11.0+/-2.9 Gy; P=0.2). Similar results were obtained for seven, five and three equispaced fields in the single patient studied. The 4F IMRT plan provided comparable PTV dose homogeneity with the CFRT plan (11.8+/-3.3 vs. 12.4+/-3.9%; P=0.6), with reduced mean lung dose (9.5+/-2.3 vs 11.0+/-2.9 Gy; P=0.001).Conclusions: IMRT using nine equispaced fields provided no improvement over CFRT. This was because the larger number of fields in the IMRT plan distributed a low dose over the entire lung. In contrast, IMRT using four fields equal to the CFRT fields offered an improvement in lung sparing. Thus, IMRT with a few carefully chosen field directions may lead to a modest reduction in pneumonitis, or allow tumour dose escalation within the currently accepted lung toxicity.

Potential role of intensity-modulated radiotherapy in the treatment of tumors of the maxillary sinus.

To assess 3-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) techniques to see whether doses to critical structures could be reduced while maintaining planning target volume (PTV) coverage in patients receiving conventional radiotherapy (RT) for carcinoma of the maxillary sinus because of the risk of radiation-induced complications, particularly visual loss. Six patients who had recently received conventional RT for carcinoma of the maxillary sinus were studied. Conventional RT, 3D-CRT, and step-and-shoot IMRT plans were prepared using the same 2-field arrangement. The effect of reducing the number of segments in the IMRT beams was investigated. 3D-CRT and IMRT reduced the brain and ipsilateral parotid gland doses compared with the conventional plans. IMRT reduced doses to both optic nerves; for the contralateral optic nerve, 15-segment IMRT plans delivered an average maximal dose of 56.4 Gy (range 53.9–59.3) compared with 65.7 Gy (range 65.3–65.9) and 64.2 Gy (range 61.4–65.6) for conventional RT and 3D-CRT, respectively. IMRT also gave improved PTV homogeneity and improved coverage, with an average of 8.5% (range 7.0–11.7%) of the volume receiving

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

Background and purpose: Radiotherapy is widely used to palliate local symptoms in non-small-cell lung cancer. Using conventional X-ray simulation, it is often difficult to accurately localize the extent of the tumour. We report a randomized, double blind trial comparing target localization with conventional and virtual simulation.Methods: Eighty-six patients underwent both conventional and virtual simulation. The conventional simulator films were compared with digitally reconstructed radiographs (DRRs) produced from the computed tomography (CT) data. The treatment fields defined by the clinicians using each modality were compared in terms of field area, position and the implications for target coverage.Results: Comparing fields defined by each study arm, there was a major mis-match in coverage between fields in 66.2% of cases, and a complete match in only 5.2% of cases. In 82.4% of cases, conventional simulator fields were larger (mean 24.5+/-5.1% (95% confidence interval)) than CT-localized fields, potentially contributing to a mean target under-coverage of 16.4+/-3.5% and normal tissue over-coverage of 25.4+/-4.2%.Conclusions: CT localization and virtual simulation allow more accurate definition of the target volume. This could enable a reduction in geographical misses, while also reducing treatment-related toxicity.

Failure to Achieve PSA Level ≤I ng/ml Following Neo-Adjuvant LHRHa Therapy Predicts for a Lower Biochemical Control Rate and Overall Survival in Localized Prostate Cancer Treated with Radiotherapy

PURPOSE: To investigate whether failure to suppress the prostate-specific antigen (PSA) level to /=2 months of neoadjuvant luteinizing hormone-releasing hormone agonist therapy in patients scheduled to undergo external beam radiotherapy for localized prostate carcinoma is associated with reduced biochemical failure-free survival. METHODS AND MATERIALS: A retrospective case note review of consecutive patients with intermediate- or high-risk localized prostate cancer treated between January 2001 and December 2002 with neoadjuvant hormonal deprivation therapy, followed by concurrent hormonal therapy and radiotherapy was performed. Patient data were divided for analysis according to whether the PSA level in Week 1 of radiotherapy was 1 ng/mL in 52. At a median follow-up of 49 months, the 4-year actuarial biochemical failure-free survival rate was 84% vs. 60% (p = 0.0016) in favor of the patients with a PSA level after neoadjuvant hormonal deprivation therapy of 1 ng/mL at the beginning of external beam radiotherapy after >/=2 months of neoadjuvant luteinizing hormone-releasing hormone agonist therapy have a significantly greater rate of biochemical failure and lower survival rate compared with those with a PSA level of

Optimisation of radiotherapy for carcinoma of the parotid gland: a comparison of conventional, three-dimensional conformal, and intensity-modulated techniques

Background and purpose: To compare external beam radiotherapy techniques for parotid gland tumours using conventional radiotherapy (RT), three-dimensional conformal radiotherapy (3DCRT), and intensity-modulated radiotherapy (IMRT). To optimise the IMRT techniques, and to produce an IMRT class solution.Materials and methods: The planning target volume (PTV), contra-lateral parotid gland, oral cavity, brain-stem, brain and cochlea were outlined on CT planning scans of six patients with parotid gland tumours. Optimised conventional RT and 3DCRT plans were created and compared with inverse-planned IMRT dose distributions using dose-volume histograms. The aim was to reduce the radiation dose to organs at risk and improve the PTV dose distribution. A beam-direction optimisation algorithm was used to improve the dose distribution of the IMRT plans, and a class solution for parotid gland IMRT was investigated.Results: 3DCRT plans produced an equivalent PTV irradiation and reduced the dose to the cochlea, oral cavity, brain, and other normal tissues compared with conventional RT. IMRT further reduced the radiation dose to the cochlea and oral cavity compared with 3DCRT. For nine- and seven-field IMRT techniques, there was an increase in low-dose radiation to non-target tissue and the contra-lateral parotid gland. IMRT plans produced using three to five optimised intensity-modulated beam directions maintained the advantages of the more complex IMRT plans, and reduced the contra-lateral parotid gland dose to acceptable levels. Three- and four-field non-coplanar beam arrangements increased the volume of brain irradiated, and increased PTV dose inhomogeneity. A four-field class solution consisting of paired ipsilateral coplanar anterior and posterior oblique beams (15, 45, 145 and 170o from the anterior plane) was developed which maintained the benefits without the complexity of individual patient optimisation.Conclusions: For patients with parotid gland tumours, reduction in the radiation dose to critical normal tissues was demonstrated with 3DCRT compared with conventional RT. IMRT produced a further reduction in the dose to the cochlea and oral cavity. With nine and seven fields, the dose to the contra-lateral parotid gland was increased, but this was avoided by optimisation of the beam directions. The benefits of IMRT were maintained with three or four fields when the beam angles were optimised, but were also achieved using a four-field class solution. Clinical trials are required to confirm the clinical benefits of these improved dose distributions.

Investigation of various growth mechanisms of solid tumour growth within the linear-quadratic model for radiotherapy

The standard linear-quadratic survival model for radiotherapy is used to investigate different schedules of radiation treatment planning to study how these may be affected by different tumour repopulation kinetics between treatments.

Linear quadratic and tumour control probability modelling in external beam radiotherapy

The standard linear-quadratic (LQ) survival model for external beam radiotherapy is reviewed with particular emphasis on studying how different schedules of radiation treatment planning may be affected by different tumour repopulation kinetics. The LQ model is further examined in the context of tumour control probability (TCP) models. The application of the Zaider and Minerbo non-Poissonian TCP model incorporating the effect of cellular repopulation is reviewed. In particular the recent development of a cell cycle model within the original Zaider and Minerbo TCP formalism is highlighted. Application of this TCP cell-cycle model in clinical treatment plans is explored and analysed.

Radiotherapy in the presence of contrast agents: a general figure of merit and its application to gold nanoparticles

Delivering sufficient dose to tumours while sparing surrounding tissue is one of the primary challenges of radiotherapy, and in common practice this is typically achieved by using highly penetrating MV photon beams and spatially shaping dose. However, there has been a recent increase in interest in the possibility of using contrast agents with high atomic number to enhance the dose deposited in tumours when used in conjunction with kV x-rays, which see a significant increase in absorption due to the heavy element's high-photoelectric cross-section at such energies. Unfortunately, the introduction of such contrast agents significantly complicates the comparison of different source types for treatment efficacy, as the dose deposited now depends very strongly on the exact composition of the spectrum, making traditional metrics such as beam quality less valuable. To address this, a 'figure of merit' is proposed, which yields a value which enables the direct comparison of different source types for tumours at different depths inside a patient. This figure of merit is evaluated for a 15 MV LINAC source and two 150 kVp sources (both of which make use of a tungsten target, one with conventional aluminium filtration, while the other uses a more aggressive thorium filter) through analytical methods as well as numerical models, considering tissue treated with a realistic concentration and uptake ratio of gold nanoparticle contrast agents (10 mg ml(-1) concentration in 'tumour' volume, 10: 1 uptake ratio). Finally, a test case of human neck phantom is considered with a similar contrast agent to compare the abstract figure to a more realistic treatment situation. Good agreement was found both between the different approaches to calculate the figure of merit, and between the figure of merit and the effectiveness in a more realistic patient scenario. Together, these observations suggest that there is the potential for contrast-enhanced kilovoltage radiation to be a useful therapeutic tool for a number of classes of tumour on dosimetric considerations alone, and they point to the need for further research in this area.

An analysis of geometric uncertainty calculations for prostate radiotherapy in clinical practice.

Margins are used in radiotherapy to assist in the calculation of planning target volumes. These margins can be determined by analysing the geometric uncertainties inherent to the radiotherapy planning and delivery process. An important part of this process is the study of electronic portal images collected throughout the course of treatment. Set-up uncertainties were determined for prostate radiotherapy treatments at our previous site and the new purpose-built centre, with margins determined using a number of different methods. In addition, the potential effect of reducing the action level from 5 mm to 3 mm for changing a patient set-up, based on off-line bony anatomy-based portal image analysis, was studied. Margins generated using different methodologies were comparable. It was found that set-up errors were reduced following relocation to the new centre. Although a significant increase in the number of corrections to a patient's set-up was predicted if the action level was reduced from 5 mm to 3 mm, minimal reduction in patient set-up uncertainties would be seen as a consequence. Prescriptive geometric uncertainty analysis not only supports calculation and justification of the margins used clinically to generate planning target volumes, but may also best be used to monitor trends in clinical practice or audit changes introduced by new equipment, technology or practice. Simulations on existing data showed that a 3 mm rather than a 5 mm action level during off-line, bony anatomy-based portal imaging would have had a minimal benefit for the patients studied in this work.

Personnel radiation dose considerations in the use of an integrated PET–CT scanner for radiotherapy treatment planning of an integrated PET-CT scanner for radiotherapy treatment planning

The acquisition of radiotherapy planning scans on positron emission tomography (PET)-CT scanners requires the involvement of radiotherapy radiographers. This study assessed the radiation dose received by these radiographers during this process. Radiotherapy planning F- fluorodeoxyglucose (F-FDG) PET-CT scans were acquired for 28 non-small cell lung cancer patients. In order to minimise the radiation dose received, a two-stage process was used in which the most time-consuming part of the set-up was performed before the patient received their F-FDG injection. Throughout this process, the radiographers wore electronic personal dosemeters and recorded the doses received at different stages of the process. The mean total radiation dose received by a radiotherapy radiographer was 5.1±2.6 mSv per patient. The use of the two-stage process reduced the time spent in close proximity to the patient by approximately a factor of four. The two-stage process was effective in keeping radiation dose to a minimum. The use of a pre-injection set-up session reduces the radiation dose to the radiotherapy radiographers because of their involvement in PET-CT radiotherapy treatment planning scans by approximately a factor of three.

The role of PET/CT scanning in radiotherapy planning

The introduction of functional data into the radiotherapy treatment planning process is currently the focus of significant commercial, technical, scientific and clinical development. The potential of such data from positron emission tomography (PET) was recognized at an early stage and was integrated into the radiotherapy treatment planning process through the use of image fusion software. The combination of PET and CT in a single system (PET/CT) to form an inherently fused anatomical and functional dataset has provided an imaging modality which could be used as the prime tool in the delineation of tumour volumes and the preparation of patient treatment plans, especially when integrated with virtual simulation. PET imaging typically using F-Fluorodeoxyglucose (F-FDG) can provide data on metabolically active tumour volumes. These functional data have the potential to modify treatment volumes and to guide treatment delivery to cells with particular metabolic characteristics. This paper reviews the current status of the integration of PET and PET/CT data into the radiotherapy treatment process. Consideration is given to the requirements of PET/CT data acquisition with reference to patient positioning aids and the limitations imposed by the PET/CT system. It also reviews the approaches being taken to the definition of functional/ tumour volumes and the mechanisms available to measure and include physiological motion into the imaging process. The use of PET data must be based upon a clear understanding of the interpretation and limitations of the functional signal. Protocols for the implementation of this development remain to be defined, and outcomes data based upon clinical trials are still awaited. © 2006 The British Institute of Radiology.