Guidelines for primary radiotherapy of patients with prostate cancer

BACKGROUND AND PURPOSES

The appropriate application of 3-D conformal radiotherapy, intensity modulated radiotherapy or image guided radiotherapy for patients undergoing radiotherapy for prostate cancer requires a standardisation of target delineation as well as clinical quality assurance procedures.

PATIENTS AND METHODS

Pathological and imaging studies provide valuable information on tumour extension. In addition, clinical investigations on patient positioning and immobilisation as well as treatment verification data offer an abundance of information.

RESULTS

Target volume definitions for different risk groups of prostate cancer patients based on pathological and imaging studies are provided. Available imaging modalities, patient positioning and treatment preparation studies as well as verification procedures are collected from literature studies. These studies are summarised and recommendations are given where appropriate.

CONCLUSIONS

On behalf of the European Organisation for Research and Treatment of Cancer (EORTC) Radiation Oncology Group this article presents a common set of recommendations for external beam radiotherapy of patients with prostate cancer.

Involved-node radiotherapy (INRT) in patients with early Hodgkin lymphoma: Concepts and guidelines

BACKGROUND AND PURPOSE

To describe new concepts for radiation fields in patients with early stage Hodgkin lymphoma treated with a combined modality.

PATIENTS AND MATERIALS

Patients receiving combined modality therapy with at least 2 or 3 cycles of chemotherapy prior to radiotherapy. Pre- and postchemotherapy cervical and thoracic CT scans are mandatory and should be performed, whenever possible, in the treatment position with the use of image fusion capabilities. A pre-chemotherapy PET scan is strongly recommended to increase the detection of involved lymph nodes.

RESULTS

Radiation fields are designed to irradiate the initially involved lymph nodes exclusively and to encompass their initial volume. In some cases, radiation fields are slightly modified to avoid unnecessary irradiation of muscles or organs at risk.

CONCLUSIONS

The concept of involved-node radiotherapy (INRT) described here is the first attempt to reduce the size of radiation fields compared to the classic involved fields used in adult patients. Proper implementation of INRT requires adequate training and an efficient prospective or early retrospective quality assurance program.

Spanish patterns of care for 3D radiotherapy in non–small-cell lung cancer

PURPOSE

Curative radiotherapy for non-small-cell lung cancer is a difficult challenge, despite the use of conformal radiotherapy. Optimal three-dimensional delineation of treatment volumes is essential for improvement of local control and for limiting of tissue toxicity.

MATERIAL AND METHODS

A planning course on clinical practice of lung cancer was held in Barcelona. A questionnaire was given concerning (1) patient positioning, (2) planning-computed tomography scan, (3) accounting for tumor mobility, (4) investigative-procedure respiration-gated radiotherapy and breath-holding maneuvers, (5) generation of target volumes, (6) treatment planning, and (7) treatment delivery. This questionnaire was made to determine the Spanish application of European recommendations.

RESULTS

On the negative side, 1 hospital did not use three-dimensional tools, less than 50% used immobilization devices, and 55.6% used computed tomography slices of greater than 5 mm. On the positive side, 70.4% did not use standard margins for gross target volume derived from a computed tomography scan, 92.6% agreed with the inclusion of Naruke anatomic criteria of 1 cm or more in gross target volume planning, and 75% used V20 to estimate the risk of pneumonitis.

CONCLUSIONS

This study is the first validation of European recommendations for treatment planning and execution of radiotherapy in lung cancer. The main conclusion is the need to improve the negative aspects determined.

A practical Monte Carlo MU verification tool for IMRT quality assurance

Quality assurance (QA) for intensity-modulated radiation therapy (IMRT) treatment planning and beam delivery, using ionization chamber measurements and film dosimetry in a phantom, is time consuming. The Monte Carlo method is the most accurate method for radiotherapy dose calculation. However, a major drawback of Monte Carlo dose calculation as currently implemented is its slow speed. The goal of this work is to bring the efficiency of Monte Carlo into a practical range by developing a fast Monte Carlo monitor unit (MU) verification tool for IMRT. A special estimator for dose at a point called the point detector has been used in this research. The point detector uses the next event estimation (NEE) method to calculate the photon energy fluence at a point of interest and then converts it to collision kerma by the mass energy absorption coefficient assuming the presence of transient charged particle equilibrium. The MU verification tool has been validated by comparing the calculation results with measurements. It can be used for both patient dose verification and phantom QA calculation. The dynamic leaf-sequence log file is used to rebuild the actual MLC leaf sequence in order to predict the dose actually received by the patient. Dose calculations for 20 patient plans have been performed using the point detector method. Results were compared with direct Monte Carlo simulations using EGS4/MCSIM, which is a well-benchmarked Monte Carlo code. The results between the point detector and MCSIM agreed to within 2%. A factor of 20 speedup can be achieved with the point detector method compared with direct Monte Carlo simulations.

Evaluation of GafChromic EBT prototype B for external beam dose verification

The capability of the new GafChromic EBT prototype B for external beam dose verification is investigated in this paper. First the general characteristics of this film (dose response, postirradiation coloration, influence of calibration field size) were derived using a flat-bed scanner. In the dose range from 0.1 to 8 Gy, the sensitivity of the EBT prototype B film is ten times higher than the response of the GafChromic HS, which so far was the GafChromic film with the highest sensitivity. Compared with the Kodak EDR2 film, the response of the EBT is higher by a factor of 3 in the dose range from 0.1 to 8 Gy. The GafChromic EBT almost does not show a temporal growth of the optical density and there is no influence of the chosen calibration field size on the dose response curve obtained from this data. A MatLab program was written to evaluate the two-dimensional dose distributions from treatment planning systems and GafChromic EBT film measurements. Verification of external beam therapy (SRT, IMRT) using the above-mentioned approach resulted in very small differences between the planned and the applied dose. The GafChromic EBT prototype B together with the flat-bed scanner and MatLab is a successful approach for making the advantages of the GafChromic films applicable for verification of external beam therapy.

[A preliminary study of beam weight optimization of intensity-modulated radiation therapy with genetic algorithm]

To study the method for dose calculation and beam weight optimization of intensity-modulated radiation therapy (IMRT).

METHODS

The IMRT dose calculation model based on two-dimensional convolution was constructed, the program of dose calculation and beam weight optimization with genetic algorithm was written with Visual c#.Net, and the optimization results were analyzed.

RESULTS

Genetic algorithm optimization of beam weights can produce highly conformal dose distributions within a clinically acceptable computation time.

CONCLUSION

Genetic algorithm is valid and efficient in IMRT beam weight optimization, which may facilitate IMRT treatment planning.

Conformity index: a review

We present a critical analysis of the conformity indices described in the literature and an evaluation of their field of application. Three-dimensional conformal radiotherapy, with or without intensity modulation, is based on medical imaging techniques, three-dimensional dosimetry software, compression accessories, and verification procedures. It consists of delineating target volumes and critical healthy tissues to select the best combination of beams. This approach allows better adaptation of the isodose to the tumor volume, while limiting irradiation of healthy tissues. Tools must be developed to evaluate the quality of proposed treatment plans. Dosimetry software provides the dose distribution in each CT section and dose-volume histograms without really indicating the degree of conformity. The conformity index is a complementary tool that attributes a score to a treatment plan or that can compare several treatment plans for the same patient. The future of conformal index in everyday practice therefore remains unclear.

IMRT with compensators for head-and-neck cancers treatment technique, dosimetric accuracy, and practical experiences

BACKGROUND AND PURPOSE

With three-dimensional conformal intensity-modulated radiotherapy (3D-c-IMRT) a heterogeneous dose distribution can be achieved in both planning treatment volume and in adjacent normal tissues and organs to be spared. 3D-c-IMRT demands for modified photon fluence profiles which can be accomplished with different techniques. This report deals with the commissioning of metal compensators and the first experiences in clinical use. Dosimetric accuracy, dose coverage and practical experience like treatment delivery time, monitor units and dose outside the treated volume are evaluated.

PATIENTS AND METHODS

From January 2002 to April 2004, 24 patients with head-and-neck cancers were treated with 3D-c-IMRT using tin-wax compensators. The dose prescription included a simultaneously integrated boost (SIB). High-dose volume was irradiated with 60-70 Gy (median 66 Gy), low-dose volume with 48-54 Gy (median 52 Gy) administered by a standardized seven- portal coplanar beam arrangement. Dose at one parotid gland was aimed at 26 Gy. The compensators used consisted of tin granules embedded in wax; recalculation was performed with compensators made of the alloy MCP96 as well.

RESULTS

In 21 of 24 patients 3D-c-IMRT with tin-wax compensators reduced the median dose to one parotid gland to < 30 Gy. Recalculation with compensators with higher density which allowed higher attenuation revealed better protection of the parotid gland. The treatment delivery time per fraction was between 6 and 12 min (plus time for patient positioning), approximately 300 MU per 2 Gy were applied. The dose outside the treated volume was increased with regard to open fields and comparable with a physical wedge of 15-30 degrees . Quality assurance and treatment of patient were fast and simple. It was shown, that calculated dose distribution corresponded to measured dose distribution with high accuracy.

CONCLUSION

The described method offers facilities for a good dose coverage of irregular target volumes with different prescribed doses and a considerable dose reduction in adjacent organs at risk. The dose sparing of organs at risk can be further improved, if a compensator material with higher density is used.

Margins between clinical target volume and planning target volume for electron beam therapy

When growing a clinical target volume (CTV) to a planning target volume (PTV), it is necessary to determine suitable margins, based on the systematic and random uncertainties. For electron therapy, where treatments are usually given with single fields, the factors affecting the margin are very different in the direction of the incident beam from those in the perpendicular directions, since set-up errors do not affect the depth of the 90% isodose. For a typical case, the perpendicular margins are three times the margin in the direction of the incident beam. This gives rise to problems with volume growing algorithms if the beam axis is not aligned with a cardinal axis.

CT image fusion as a tool for measuring in 3D the setup errors during conformal radiotherapy for prostate cancer

AIMS AND BACKGROUND

The importance of optimal daily patient positioning has been stressed in order to ensure treatment reproducibility and gain in accuracy and precision. We report our data on the 3D setup uncertainty during radiation therapy for prostate cancer using the CT image fusion technique.

METHODS

Ten consecutive patients scheduled for radiation therapy for prostate cancer underwent 5 prone position CT scans using an individualized immobilization cast. These different setups were analyzed using the image fusion module of the ERGO 3D-Line Medical System (Milan, Italy) treatment planning system. The isocenter and the body marker displacements were measured.

RESULTS

The 3D isocenter dislocations were quantified: systematic error was sigma(3D) = 3.9 mm, whereas random error was sigma(3D) = 1 mm. The mean of the minimum displacements was 0.2 +/- 1 mm showing that the immobilization device used allows an accurate setup to be obtained. Single direction errors were also measured showing systematic errors, sigma(AP), = 2.6 mm, sigma(LL) = 0.6 mm, SigmaSI = 3 mm in the anterior-posterior, latero-lateral, superior-inferior direction, respectively. Related random errors were sigma(AP), = 1 mm, sigma(LL) = 0.6 mm, sigma(SI) = 1.2 mm. In terms of accuracy, our uncertainties are similar to those reported in the literature.

CONCLUSIONS

By applying the CT image fusion technique, a 3D study on setup accuracy was performed. We demonstrated that the use of an individualized immobilization system for prostate treatment is adequate to obtain good setup accuracy, as long as a high-quality positioning control method, such as the stereoscopic X-ray-based positioning system, is used.

Commissioning and quality assurance of a commercial stereotactic treatment-planning system for extracranial IMRT

A 3D treatment‐planning system (TPS) for stereotactic intensity‐modulated radiotherapy (IMRT) using a micro‐multileaf collimator has been made available by Radionics. In this work, we report our comprehensive quality assurance (QA) procedure for commissioning this TPS. First, the accuracy of stereotaxy established with a body frame was checked to ensure accurate determination of a target position within the planning system. Second, the CT‐to‐electron density conversion curve used in the TPS was fitted to our site‐specific measurement data to ensure the accuracy of dose calculation and measurement verification in a QA phantom. Using the QA phantom, the radiological path lengths were verified against known geometrical depths to ensure the accuracy of the ray‐tracing algorithm. We also checked inter‐ and intraleaf leakage/transmission for adequate jaw settings. Measurements for dose verification were performed in various head/neck and prostate IMRT treatment plans using the patient‐specific optimized fluence maps. Both ion chamber and film were used for point dose and isodose distribution verifications. To ensure that adjacent organs at risk receive dose within the expectation, we used the Monte Carlo method to calculate dose distributions and dose‐volume histograms (DVHs) for these organs at risk. The dosimetric accuracy satisfied the published acceptability criteria. The Monte Carlo calculations confirmed the measured dose distributions for target volumes. For organs located on the beam boundary or outside the beam, some differences in the DVHs were noticed. However, the plans calculated by both methods met our clinical criteria. We conclude that the accuracy of the XKnife™ RT2 treatment‐planning system is adequate for the clinical implementation of stereotactic IMRT.

PACS numbers: 87.53.Xd, 87.53.Ly, 87.53.Wz

A TL-based anthropomorphic benchmark for verifying 3-D dose distributions from external electron beams calculated by radiotherapy treatment planning systems

Initial results are reported of a Polish-Finnish project to verify electron dose distributions calculated by treatment planning systems (TPSs), CadPlan v.6.3.2 and Theraplan v.3.5, which use different electron beam dose distribution algorithms. Treatment of gross tumour volumes representing lung and parotid cancer was simulated in an Alderson anthropomorphic phantom with thermoluminescent detectors (TLDs) (Li(2)B(4)O(7):Mn,Si) placed at selected measurement points inside its volume. The observed discrepancy between relative values of dose calculated and measured by TLDs at each of the measurement points and those calculated by the different TPSs at the same points is discussed.

Evaluation of image-guided radiation therapy (IGRT) technologies and their impact on the outcomes of hypofractionated prostate cancer treatments: A radiobiologic analysis

PURPOSE

To quantify the mitigation of geometric uncertainties achieved with the application of various patient setup techniques during the delivery of hypofractionated prostate cancer treatments, using tumor control probability (TCP) and normal tissue complication probability.

METHODS AND MATERIALS

Five prostate cancer patients with approximately 16 treatment CT studies, taken during the course of their radiation therapy (77 total), were analyzed. All patients were planned twice with an 18 MV six-field conformal technique, with 10- and 5-mm margin sizes, with various hypofractionation schedules (5 to 35 fractions). Subsequently, four clinically relevant patient setup techniques (laser guided and image guided) were simulated to deliver such schedules.

RESULTS

As hypothesized, the impact of geometric uncertainties on clinical outcomes increased with more hypofractionated schedules. However, the absolute gain in TCP due to hypofractionation (up to 21.8% increase) was significantly higher compared with the losses due to geometric uncertainties (up to 8.6% decrease).

CONCLUSIONS

The results of this study suggest that, although the impact of geometric uncertainties on the treatment outcomes increases as the number of fractions decrease, the reduction in TCP due to the uncertainties does not significantly offset the expected theoretical gain in TCP by hypofractionation.

Improvement of radiotherapy treatment delivery accuracy using an electronic portal imaging device

Reliable application of advanced external beam techniques for the treatment of patients with cancer, such as intensity modulated radiotherapy, requires an adequate quality assurance programme for the verification of the dose delivery. Accurate patient positioning is mandatory because of the steep dose gradients outside the tumour volume. Owing to the increased complexity of the treatment planning and delivery techniques, verification of the dose delivery before and during the actual patient treatment is equally important. For this purpose, a quality assurance programme has been established in our clinic that is primarily based on measurements with electronic portal imaging devices. To minimise systematic set-up errors, the patient positioning is measured in the first few treatment fractions and a set-up correction is applied in the subsequent ones. Before the first treatment fraction, portal dose measurements are performed for each treatment field with the electronic portal imaging device to verify that the planned fluence distribution is correctly delivered at the treatment unit. Dosimetric measurements are also performed during patient treatment to derive the actually delivered fluence maps. By combining this information with knowledge on the patient set-up, the delivered 3-D dose distribution to both the tumour and sensitive organs may be assessed. However, for the highest accuracy, exact knowledge on the (internal) patient geometry during treatment, e.g. using a cone-beam CT, is required.

New developments in radiochromic film dosimetry

NIST has been a pioneer in the use of radiochromic film for medical dosimetry applications. Beginning in 1988 with experiments with (90)Sr/Y ophthalmic applicators, this work has continued into the present. A review of the latest applications is presented, which include high activity low-energy photon source dosimetry and ultra-high resolution film densitometry for dose enhancement near stents and microbeam radiation therapy dosimetry. An exciting recent development is the availability of a new radiochromic emulsion which has been developed for IMRT dosimetry. This emulsion is an order of magnitude more sensitive than was previously available. Measurements of the sensitivity and uniformity of samples of this new film are reported, using a spectrophotometer and two scanning laser densitometers. A unique feature of the new emulsion is that the peak of the absorbance spectrum falls at the wavelength of the HeNe lasers used in the densitometer, maximising sensitivity. When read at a wavelength of 633 nm, sensitivities on the order of 900 mAU Gy(-1) were determined for this new film type, compared with about 40 mAU Gy(-1) for type HS film, 20 mAU Gy(-1) for type MD-55-2 film, and 3 mAU Gy(-1) for type HD-810. Film uniformities were found to be good, on the order of 6% peak to peak. However, there is a strong polarisation effect in the samples examined, requiring care in film orientation during readout.

The RBE issues in ion-beam therapy: conclusions of a joint IAEA/ICRU working group regarding quantities and units

This paper summarises the conclusions of a working group established jointly by the International Atomic Energy Agency (IAEA) and the International Commission on Radiation Units and Measurements (ICRU) to address some of the relative biological effectiveness (RBE) issues encountered in ion-beam therapy. Special emphasis is put on the selection and definition of the involved quantities and units. The isoeffective dose, as introduced here for radiation therapy applications, is the dose that delivered under reference conditions would produce the same clinical effects as the actual treatment in a given system, all other conditions being identical. It is expressed in Gy. The reference treatment conditions are: photon irradiation, 2 Gy per fraction, 5 daily fractions a week. The isoeffective dose D(IsoE) is the product of the physical quantity absorbed dose D and a weighting factor W(IsoE). W(IsoE) is an inclusive weighting factor that takes into account all factors that could influence the clinical effects like dose per fraction, overall time, radiation quality (RQ), biological system and effects. The numerical value of W(IsoE) is selected by the radiation-oncology team for a given patient (or treatment protocol). It is part of the treatment prescription. Evaluation of the influence of RQ on W(IsoE) raises complex problems because of the clinically significant RBE variations with biological effect (late vs. early) and position in depth in the tissues which is a problem specific to ion-beam therapy. Comparison of the isoeffective dose with the equivalent dose frequently used in proton- and ion-beam therapy is discussed.

Accuracy evaluation of image registration and segmentation tools used in conformal treatment planning of prostate cancer

Segmentation and registration tools are commonly used in radiotherapy for target and at risk organs localisation. In this work the performances of three different segmentation tools and of a surface matching registration technique, used on computed tomography (CT) and magnetic resonance (MR) images for the treatment planning of conformal prostate carcinoma, are studied. The accuracy of the segmentation and registration tools was evaluated by phantom experiment and on patient data, respectively. A preliminary estimate of MR image distortion was also performed.

An optimisation algorithm for determination of treatment margins around moving and deformable targets

PURPOSE

Determining treatment margins for inter-fractional motion of moving and deformable clinical target volumes (CTVs) remains a major challenge. This paper describes and applies an optimisation algorithm designed to derive such margins.

MATERIAL AND METHODS

The algorithm works by expanding the CTV, as determined from a pre-treatment or planning scan, to enclose the CTV positions observed during treatment. CTV positions during treatment may be obtained using, for example, repeat CT scanning and/or repeat electronic portal imaging (EPI). The algorithm can be applied to both individual patients and to a set of patients. The margins derived will minimise the excess volume outside the envelope that encloses all observed CTV positions (the CTV envelope). Initially, margins are set such that the envelope is more than adequately covered when the planning CTV is expanded. The algorithm uses an iterative method where the margins are sampled randomly and are then either increased or decreased randomly. The algorithm is tested on a set of 19 bladder cancer patients that underwent weekly repeat CT scanning and EPI throughout their treatment course.

RESULTS

From repeated runs on individual patients, the algorithm produces margins within a range of +/-2 mm that lie among the best results found with an exhaustive search approach, and that agree within 3mm with margins determined by a manual approach on the same data. The algorithm could be used to determine margins to cover any specified geometrical uncertainty, and allows for the determination of reduced margins by relaxing the coverage criteria, for example disregarding extreme CTV positions, or an arbitrarily selected volume fraction of the CTV envelope, and/or patients with extreme geometrical uncertainties.

CONCLUSION

An optimisation approach to margin determination is found to give reproducible results within the accuracy required. The major advantage with this algorithm is that it is completely empirical, and it is therefore particularly useful for CTVs where the geometrical uncertainties are difficult to model, such as the bladder.

Use of CD-ROM–based tool for analyzing contouring variations in involved-field radiotherapy for Stage III NSCLC

BACKGROUND

Interclinician variability in defining target volumes is a problem in conformal radiotherapy. A CD-ROM-based contouring tool was used to conduct a dummy run in an international trial of involved-field chemoradiotherapy for Stage III non-small-cell lung cancer.

METHODS AND MATERIALS

The CT scan of an eligible patient was installed on an "auto-run" CD-ROM incorporating a contouring program based on ImageJ for Windows, which runs on any personal computer equipped with a CD-ROM drive. This tool was initially piloted at four academic centers and was subsequently mailed, together with all relevant clinical, radiologic, and positron emission tomography findings, to all participating centers in the international trial. Clinicians were instructed to contour separate gross tumor volumes (GTVs) for the tumor and two enlarged nodes and a clinical target volume for the hilus. A reference "consensus" target volume for each target was jointly generated by three other clinicians.

RESULTS

The data received from the four academic centers and 16 study participants were suitable for analysis. Data from one center was unsuitable for detailed analysis because the target volumes were contoured at 1.2-cm intervals. GTVs were available for a total of 21 tumors and 19 nodes, and 15 hilar clinical target volumes were available. The mean GTV of the primary tumor was 13.6 cm(3) (SD, 5.2; median, 12.3; range, 8.3-26.9). The variation in the center of the mass relative to the mean center of the mass in the left-right, ventrodorsal, and craniocaudal axes was 1.5, 0.4, and 1.0 mm, respectively. The largest volume variation was observed for the right hilar clinical target volume (mean, 33.7 cm(3); SD, 31.2; median, 20.3; range, 4.8-109.9). Smaller variations were observed for the subcarinal node (mean, GTV, 1.9 cm(3); SD, 1.2; median, 1.7; range, 0.5-5.3), except caudally where the node was difficult to distinguish from the pericardium. The "consensus" volumes for all targets were generally close to the median of the contoured values.

CONCLUSION

Most clinicians were able to use this CD-ROM tool to contour target volumes in compliance with the study protocol. The rapid completion of the dummy run indicated the suitability of this approach for quality assurance in multicenter clinical trials. Routine use of similar tools will reduce the risk that new techniques (or study objectives) are misunderstood and/or misapplied in clinical trials.

Dose–volume based ranking of incident beam direction and its utility in facilitating IMRT beam placement

PURPOSE

Beam orientation optimization in intensity-modulated radiation therapy (IMRT) is computationally intensive, and various single beam ranking techniques have been proposed to reduce the search space. Up to this point, none of the existing ranking techniques considers the clinically important dose-volume effects of the involved structures, which may lead to clinically irrelevant angular ranking. The purpose of this work is to develop a clinically sensible angular ranking model with incorporation of dose-volume effects and to show its utility for IMRT beam placement.

METHODS AND MATERIALS

The general consideration in constructing this angular ranking function is that a beamlet/beam is preferable if it can deliver a higher dose to the target without exceeding the tolerance of the sensitive structures located on the path of the beamlet/beam. In the previously proposed dose-based approach, the beamlets are treated independently and, to compute the maximally deliverable dose to the target volume, the intensity of each beamlet is pushed to its maximum intensity without considering the values of other beamlets. When volumetric structures are involved, the complication arises from the fact that there are numerous dose distributions corresponding to the same dose-volume tolerance. In this situation, the beamlets are not independent and an optimization algorithm is required to find the intensity profile that delivers the maximum target dose while satisfying the volumetric constraints. In this study, the behavior of a volumetric organ was modeled by using the equivalent uniform dose (EUD). A constrained sequential quadratic programming algorithm (CFSQP) was used to find the beam profile that delivers the maximum dose to the target volume without violating the EUD constraint or constraints. To assess the utility of the proposed technique, we planned a head-and-neck and abdominal case with and without the guidance of the angular ranking information. The qualities of the two types of IMRT plans were compared quantitatively.

RESULTS

An effective angular ranking model with consideration of volumetric effect has been developed. It is shown that the previously reported dose-based angular ranking represents a special case of the general formalism proposed here. Application of the technique to a abdominal and a head-and-neck IMRT case indicated that the proposed technique is capable of producing clinically sensible angular ranking. In both cases, we found that the IMRT plans obtained under the guidance of EUD-based angular ranking were improved in comparison with that obtained using the conventional uniformly spaced beams.

CONCLUSIONS

The EUD-based function is a general approach for angular ranking and allows us to identify the potentially good and bad angles for clinically complicated cases. The ranking can be used either as a guidance to facilitate the manual beam placement or as prior information to speed up the computer search for the optimal beam configuration. Thus the proposed technique should have positive clinical impact in facilitating the IMRT planning process.

Esophagus sparing with IMRT in lung tumor irradiation: An EUD-based optimization technique

PURPOSE

The aim of this study was to evaluate (1) the use of generalized equivalent uniform dose (gEUD) to optimize dose escalation of lung tumors when the esophagus overlaps the planning target volume (PTV) and (2) the potential benefit of further dose escalation in only the part of the PTV that does not overlap the esophagus.

METHODS AND MATERIALS

The treatment-planning computed tomography (CT) scans of patients with primary lung tumors located in different regions of the left and right lung were used for the optimization of beamlet intensity modulated radiation therapy (IMRT) plans. In all cases, the PTV overlapped part of the esophagus. The dose in the PTV was maximized according to 7 different primary cost functions: 2 plans that made use of mean dose (MD) (the reference plan, in which the 95% isodose surface covered the PTV and a second plan that had no constraint on the minimum isodose), 3 plans based on maximizing gEUD for the whole PTV with ever increasing assumptions for tumor aggressiveness, and 2 plans that used different gEUD values in 2 simultaneous, overlapping target volumes (the whole PTV and the PTV minus esophagus). Beam arrangements and NTCP-based costlets for the organs at risk (OARs) were kept identical to the original conformal plan for each case. Regardless of optimization method, the relative ranking of the resulting plans was evaluated in terms of the absence of cold spots within the PTV and the final gEUD computed for the whole PTV.

RESULTS

Because the MD-optimized plans lacked a constraint on minimum PTV coverage, they resulted in cold spots that affected approximately 5% of the PTV volume. When optimizing over the whole PTV volume, gEUD-optimized plans resulted in higher equivalent uniform PTV doses than did the reference plan while still maintaining normal-tissue constraints. However, only under the assumption of extremely aggressive tumors could cold spots in the PTV be avoided. Generally, high-level overall results are obtained when optimization in the whole PTV is also associated with a second simultaneous optimization in the PTV minus overlapping portions of the esophagus.

CONCLUSIONS

Intensity modulated radiation therapy optimizations that utilize gEUD-based cost functions for the PTV and NTCP-based constraints for the OARs result in increased doses to large portions of the PTV in cases where the PTV overlaps the esophagus, while still maintaining (and confining to the overlap region) minimum dose coverage equivalent to the homogeneous PTV optimization cases.

Definition of elective lymphatic target volume in ductal carcinoma of the pancreatic head based on histopathologic analysis

PURPOSE

In chemoradiation for pancreatic carcinoma three-dimensional target volume definitions could maximize tolerability and therapeutic effect at the same time because toxicity correlates with treatment volume. We aimed to define guidelines for elective treatment of nodal areas based on pathologic nodal involvement to optimize treatment volume for this tumor.

METHODS AND MATERIALS

Pathologic patterns of regional nodal spread in 175 patients who underwent primary pancreatoduodenectomy with > or =10 assessed nodes and literature data on para-aortic spread were the base of the definition of the target volume. Significant correlations between spread to lymphatic areas and tumor characteristics were determined using Fisher's exact test. Computed tomography scans and a Pinnacle3 (Philips, Best, The Netherlands) system were used for treatment planning.

RESULTS

Among 175 resected tumors without pretreatment, 76% had regional nodal metastasis and 22% had spread to distant nodes. High-risk lymphatic areas were identified and selected for elective treatment. A standardized planning procedure was derived and tested under treatment conditions.

CONCLUSIONS

Histopathologic data allowed us to develop recommendations for standardized treatment planning for ductal carcinoma of the pancreatic head. These are proposed for quality assurance in multicenter studies and routine use.

Quality assurance: fundamental reproducibility tests for 3-D treatment-planning systems

The use of image-based 3D treatment planning has significantly increased the complexity of commercially available treatment-planning systems (TPSs). Medical physicists have traditionally focused their efforts on understanding the calculation algorithm; this is no longer possible. A quality assurance (QA) program for our 3D treatment-planning system (ADAC Pinnacle3) is presented. The program is consistent with the American Association of Physicists in Medicine Task Group 53 guidelines and balances the cost-versus-benefit equation confronted by the clinical physicist in a community cancer center environment. Fundamental reproducibility tests are presented as required for a community cancer center environment using conventional and 3D treatment planning. A series of nondosimetric tests, including digitizer accuracy, image acquisition and display, and hardcopy output, is presented. Dosimetric tests include verification of monitor units (MUs), standard isodoses, and clinical cases. The tests are outlined for the Pinnacle3 TPS but can be generalized to any TPS currently in use. The program tested accuracy and constancy through several hardware and software upgrades to our TPS. This paper gives valuable guidance and insight to other physicists attempting to approach TPS QA at fundamental and practical levels.

Intensity-modulated radiation therapy for mesothelioma: Impact of multileaf collimator leaf width and pencil beam size on planning quality and delivery efficiency

PURPOSE

To compare treatment plans for multileaf collimators (MLCs) with different leaf widths and different finite pencil beam (FPB) sizes, to determine the planning quality and delivery efficiency of segmented MLC (SMLC) delivery of intensity-modulated radiation therapy (IMRT) for malignant pleural mesothelioma (MPM).

METHODS AND MATERIALS

Computerized tomography images of 10 right-side MPM patients were used for this planning study on a CORVUS treatment-planning system (NOMOS Corporation, Sewickley, PA) for a Varian Millennium 120-MLC (Varian Medical Systems, Palo Alto, CA). Three beam models were used. The first model forced two 0.5-cm MLC leaves to move in tandem to simulate a 1-cm leaf-width MLC and a FPB size of 1 x 1 cm2. The second model used 0.5-cm leaves with a FPB size of 0.5 x 1 cm2 (1 cm in the direction of leaf movement). The third model used 0.5-cm leaves, with a FPB size of 0.5 x 0.5 cm2. For optimization, the same dose constraints and beam parameters were used for each data set. Tissue heterogeneity corrections were used during optimization and dose calculation. Plans were optimized such that the clinical target volume received 50 Gy in 25 fractions. Dose distributions to the target and normal structures were evaluated. The number of monitor units, the number of segments, and delivery times were used to evaluate delivery efficiency.

RESULTS

All three beam models could be used for IMRT planning for MPM. The doses to clinical target volume, spinal cord, lung, liver, heart, and contralateral kidney were acceptable with all three beam models. The 0.5 x 0.5-cm2 beam model used the most monitor units (6883 +/- 974 vs. 3332 +/- 406 and 3407 +/- 443 for the 1 x 1-cm2 and 0.5 x 1-cm2 models, respectively) and treated the most segments (4297 +/- 802 vs. 1357 +/- 156 and 1767 +/- 212 for the 1 x 1-cm2 and 0.5 x 1-cm2 models, respectively). The plan generated with the 1 x 1-cm2 model required the least amount of time to deliver.

CONCLUSIONS

The quality of the MPM IMRT plans generated with the three beam models presented here was similar; however, the 1 x 1-cm2 model provided the most efficient delivery of MPM IMRT with the CORVUS planning system.