Radiotherapy & Oncology

Editorial Board

2010-02-01

Vorsprung durch Technik: Evolution, implementation, QA and safety of new technology in radiotherapy

David I. Thwaites, Dirk Verellen — 2010-02-22

These are exciting times in radiotherapy. The challenge repeatedly presented to the radiotherapy team by each new patient is one of treatment optimisation i.e., of delivering high and effective doses to the required targets but minimising unwanted side-effects, and this has continued to drive research and the development of technology and techniques. This issue of Radiotherapy and Oncology contains mainly papers from presentations at the recent ESTRO 10th Biennial Conference on Physics and Radiation Technology for Clinical Radiotherapy (Maastricht, September 2009) . Each of these meetings presents the current state of the art and draws together developments over the interval since the last , as also reflected in publications in the journal over that period. Better insights into radiobiology and the increasing application of multi-modality imaging, both morphological and functional , provide enhanced information on targeting and on sub-targets . Intensity-modulated photon radiotherapy (IMRT) , including intensity-modulated arc therapy (both fan beam and cone beam ) can deliver multi-targeted dose-sculpted irradiation to these defined volumes, whilst improved dose distributions also drive the growing interest in proton therapy . Image-guided radiotherapy (IGRT), using various in-room imaging techniques , provides precise real-time monitoring of target position, enabling treatment verification and correction and also the basis for responsive adaptive techniques . Imaging information supports decisions on geometric uncertainties, margins and correction strategies . 4D techniques underpin strategies for dealing with organ motion . In vivo, in-phantom and associated dose verification techniques provide assurance for complex treatment delivery . Image-guided brachytherapy techniques are developing in parallel for specific applications. IT systems for radiotherapy, including Oncology Information Systems (OIS) and treatment planning systems (TPS), continue to expand and develop to handle the very significant amounts of information involved, to better model and optimise treatment, to move increasingly towards integration of all the necessary process functions, and to provide greater workflow efficiency .

The European Society of Therapeutic Radiology and Oncology–European Institute of Radiotherapy (ESTRO–EIR) report on 3D CT-based in-room image guidance systems: A practical and technical review and guide

2010-02-15

Abstract: The past decade has provided many technological advances in radiotherapy. The European Institute of Radiotherapy (EIR) was established by the European Society of Therapeutic Radiology and Oncology (ESTRO) to provide current consensus statement with evidence-based and pragmatic guidelines on topics of practical relevance for radiation oncology. This report focuses primarily on 3D CT-based in-room image guidance (3DCT-IGRT) systems. It will provide an overview and current standing of 3DCT-IGRT systems addressing the rationale, objectives, principles, applications, and process pathways, both clinical and technical for treatment delivery and quality assurance. These are reviewed for four categories of solutions; kV CT and kV CBCT (cone-beam CT) as well as MV CT and MV CBCT. It will also provide a framework and checklist to consider the capability and functionality of these systems as well as the resources needed for implementation. Two different but typical clinical cases (tonsillar and prostate cancer) using 3DCT-IGRT are illustrated with workflow processes via feedback questionnaires from several large clinical centres currently utilizing these systems. The feedback from these clinical centres demonstrates a wide variability based on local practices. This report whilst comprehensive is not exhaustive as this area of development remains a very active field for research and development. However, it should serve as a practical guide and framework for all professional groups within the field, focussed on clinicians, physicists and radiation therapy technologists interested in IGRT.

Validation of functional imaging with pathology for tumor delineation in the prostate

2010-02-01

Abstract: Introduction: A study was performed to validate magnetic resonance (MR) based prostate tumor delineations with pathology.Material and methods: Five patients with biopsy proven prostate cancer underwent a T2 weighted (T2w), diffusion weighted MRI (DW-MRI) and dynamic contrast-enhanced MRI (DCE-MRI) scan before prostatectomy. Suspicious regions were delineated based on all available MR information. After prostatectomy whole-mount hematoxylin–eosin stained (H&E) sections were made. Tumor tissue was delineated on the H&E stained sections and compared with the MR based delineations. The registration accuracy between the MR images and H&E stained sections was estimated.Results: A tumor coverage of 44–89% was reached by the MR based tumor delineations. The application of a margin of ∼5mm to the MR based tumor delineations yielded a tumor coverage of 85–100% in all patients. Errors created during the registration procedure were 2–3mm, which cannot completely explain the limited tumor coverage.Conclusions: An accurate tissue processing and registration method was presented (registration error 2–3mm), which enables the validation of MR based tumor delineations with pathology. Reasonable tumor coverage of about 85% and larger was found when applying a margin of ∼5 mm to the MR based tumor delineations.

Evaluation of early metabolic responses in rectal cancer during combined radiochemotherapy or radiotherapy alone: Sequential FDG-PET-CT findings

2010-02-01

Abstract: Background and purpose: The purpose of this study was to prospectively investigate metabolic changes of rectal tumors after 1week of treatment of either radiochemotherapy (28×1.8Gy+Capecitabine) (RCT) or hypofractionated radiotherapy (5×5Gy) alone (RT).Materials and methods: Fourty-six rectal cancer patients, 25 RCT- and 21 RT-patients, were included in this study. Sequential FDG-PET-CT scans were performed for each of the included patients both prior to treatment and after the first week of treatment. Consecutively, the metabolic treatment response of the tumor was evaluated.Results: For the patients referred for pre-operative RCT, significant reductions of SUVmean (p<0.001) and SUVmax (p<0.001) within the tumor were found already after the first week of treatment (8Gy biological equivalent dose (BED). In contrast, 1week of treatment with RT alone did not result in significant changes in the metabolic activity of the tumor (p=0.767, p=0.434), despite the higher applied RT dose of 38.7Gy BED.Conclusions: Radiochemotherapy of rectal cancer leads to significant early changes in the metabolic activity of the tumor, which was not the case early after hypofractionated radiotherapy alone, despite the higher radiotherapy dose given. Thus, the chemotherapeutic agent Capecitabine might be responsible for the early metabolic treatment responses during radiochemotherapy in rectal cancer.

Tumor perfusion increases during hypofractionated short-course radiotherapy in rectal cancer: Sequential perfusion-CT findings

2010-01-18

Abstract: Purpose: The purpose of this study was to investigate perfusion of rectal tumors and to determine early responses to short-course hypofractionated radiotherapy (RT).Material and methods: Twenty-three rectal cancer patients were included, which underwent perfusion-CT imaging before (pre-scan) and after treatment (post-scan). Contrast-enhancement was measured in tumor and muscle tissues and in the external iliac artery. Perfusion was quantified with three pharmacokinetic parameters: Ktrans, ve and vp. Perfusion differences between tumor and normal tissue and changes of the pharmacokinetic parameters between both scans were evaluated.Results: The median tumors Ktrans values increased significantly from the pre-scan (0.36±0.11 (min−1)) to the post-scan (0.44±0.13 (min−1)) (p<0.001). Also, histogram analysis showed a shift of tumor voxels from lower Ktrans values towards higher Ktrans values. Furthermore, the median Ktrans values were significantly higher for tumor than for muscle tissue on both the pre-scan (0.10±0.05 (min−1), p<0.001) and the post-scan (0.10±0.04 (min−1), p<0.001). In contrast, no differences between tumor and muscle tissues were found for ve and vp. Also, no significant differences were observed for ve and vp between the two pCT-imaging time-points.Conclusions: Hypofractionated radiotherapy of rectal cancer leads to an increased tumor perfusion as reflected by an elevated Ktrans, possibly improving the bioavailability of cytotoxic agents in rectal tumors, often administered early after radiotherapy treatment.

The value of magnetic resonance imaging in target volume delineation of base of tongue tumours – A study using flexible surface coils

2010-01-25

Abstract: Introduction: Magnetic resonance imaging (MRI) provides superior diagnostic accuracy over computed tomography (CT) in oropharyngeal tumours. Precise delineation of the gross tumour volume (GTV) is mandatory in radiotherapy planning when a GTV boost is required. CT volume definition in this regard is poor. We studied the feasibility of using flexible surface (flex-L) coils to obtain MR images for MR–CT fusion to assess the benefit of MRI over CT alone in planning base of tongue tumours.Methods: Eight patients underwent CT and MRI radiotherapy planning scans with an immobilisation device. Distortion-corrected T1-weighted post-contrast MR scans were fused to contrast-enhanced planning CT scans. GTV, clinical target and planning target volumes (CTV, PTV) and organs at risk (OAR) were delineated on CT, then on MRI with blinding to the CT images. The volumetric and spatial differences between MRI and CT volumes for GTV, CTV, PTV and OAR were compared. MR image distortions due to field inhomogeneity and non-linear gradients were corrected and the need for such correction was evaluated.Results: The mean primary GTV was larger on MRI (22.2 vs. 9.5cm3, p=0.05) than CT. The mean primary and nodal GTV (i.e. BOT and macroscopic nodes) was significantly larger on MRI (27.2 vs. 14.4cm3, p=0.05). The volume overlap index (VOI) between MRI and CT for the primary was 0.34 suggesting that MRI depicts parts of the primary tumour not detected by CT. There was no significant difference in volume delineation between MR and CT for CTV, PTV, nodal CTV and nodal PTV. MRI volumes for brainstem and spinal cord were significantly smaller due to improved organ definition (p=0.002). Susceptibility and gradient-related distortions were not found to be clinically significant.Conclusion: MRI improves the definition of tongue base tumours and neurological structures. The use of MRI is recommended for GTV dose-escalation techniques to provide precise depiction of GTV and improved sparing of spinal cord and brainstem.

The use of probability maps to deal with the uncertainties in prostate cancer delineation

2010-01-20

Abstract: Background and purpose: The use of dynamic contrast-enhanced (DCE) imaging for delineation of prostate tumors requires that decisions are made on a voxel wise basis about the presence of tumor. While the sensitivity and specificity of this technique is high, we propose a probabilistic approach to deal with the intrinsic imaging uncertainty.Material and methods: Twenty-nine patients with biopsy-proven prostate cancer underwent a DCE-CT exam prior to radiotherapy. From a logistic regression on Ktrans values from healthy and diseased appearing prostate regions we obtained a probability function for the presence of tumor. Ktrans parameter maps were converted into probability maps and a stratification was applied at the 5% and 95% probability level, to identify low-, intermediate-, and high-risk areas for the presence of tumor.Results: In all patients, regions with high-, intermediate-, and low-risk were identified, with median volume percentages of 7.6%, 40.0%, and 52.1%, respectively. The contiguous areas that resulted from the voxel wise stratification can be interpreted as GTV, high-risk CTV, and CTV.Conclusions: Ktrans parameter maps from a DCE-CT exam can be converted into probability maps for the presence of tumor. In this way, the intrinsic uncertainty that a voxel contains tumor can be incorporated into the treatment planning process.

From point A to the sculpted pear: MR image guidance significantly improves tumour dose and sparing of organs at risk in brachytherapy of cervical cancer

2010-02-08

Abstract: Background and purpose: Brachytherapy in locally advanced cervical cancer is still widely based on 2D standard dose planning, although 3D image guidance is available. The purpose of this study was to compare point doses to 3D dose volume parameters for tumour and organs at risk (OARs), and to evaluate the improvement of dose parameters with MR image guided adaptive brachytherapy (IGABT).Material and methods: MRI-based IGABT was performed in 72 consecutive patients. HR-CTV, IR-CTV, bladder, rectum and sigmoid were contoured according to GEC-ESTRO recommendations. BT standard dose planning was compared to MRI-based dose optimisation.Results: HR-CTV dose (D90) was highly variable in standard plans with point A dose prescription. In small tumours (<31cc) HR-CTV was well covered by standard plans in 94% of patients, while OAR constraints were exceeded in 72% of patients. Optimisation decreased violation of OAR constraints to only 6% of patients while maintaining excellent target coverage. In large tumours (>31cc) the dose optimisation improved the HR-CTV D90 by a mean of 7Gy resulting in full coverage in 72% of patients as compared to 25% for standard plans, even while reducing violation of OAR constraints.Conclusion: Point A dose is a poor surrogate of HR-CTV dose, and the use of 3D image-based dose planning is encouraged. MRI-based IGABT significantly improves target coverage and OAR dose.

3D Dosimetric verification of volumetric-modulated arc therapy by portal dosimetry

2010-01-20

Abstract: Background and purpose: To demonstrate the feasibility of back-projection portal dosimetry for accurate 3D dosimetric verification of volumetric-modulated arc therapy (VMAT), pre-treatment as well as in vivo.Materials and methods: Several modifications to our existing approach were implemented to make the method applicable to VMAT: (i) gantry angle-resolved data acquisition, (ii) calculation of the patient transmission, (iii) compensation for detector ‘flex’ and (iv) 3D dose reconstruction and evaluation.Results: Planned and EPID-(Electronic Portal Image Detector)-reconstructed dose distributions show good agreement for pre-treatment verification of two prostate, a stereotactic lung and a head-and-neck VMAT plan and for in vivo verification of VMAT treatments of prostate and lung cancer. Averaged over pre-treatment verifications, planned and measured isocentre dose ratios were −1.2% (range [−4.7%,1.8%]). 3D gamma analysis (3% maximum dose, 3mm) revealed mean γ 〈γmean〉=0.37 [0.34,0.39], maximum 1% γ 〈γ1%〉=0.72 [0.66,0.81] and percentage of points with γ⩽1 〈Pγ⩽1〉=99% [97%,100%]. For in vivo verification, the average isocentre dose ratio was −1.2% [−0.8%,−1.7%], 〈γmean〉=0.52 [0.40,0.64], 〈γ1%〉=0.92 [0.76,1.08] and 〈Pγ⩽1〉=96% [93%,100%].Conclusions: Our portal dosimetry method was successfully adapted for verification of VMAT treatments, pre-treatment as well as in vivo.

3D dose delivery verification using repeated cone-beam imaging and EPID dosimetry for stereotactic body radiotherapy of non-small cell lung cancer

Wouter van Elmpt, Steven Petit, Dirk De Ruysscher, Philippe Lambin, André Dekker — 2010-01-18

Abstract: Purpose: To implement a 3D dose verification procedure, based on in-room cone-beam CT imaging and portal dosimetry, for lung cancer patients treated with stereotactic body radiotherapy (SBRT).Materials and methods: MV cone-beam CT scans were made for patient positioning and calibrated for dose calculation purposes. Prior to treatment, the treatment fields were captured using a calibrated electronic portal imaging device (EPID). A Monte Carlo dose reconstruction model was used to estimate the 3D dose delivered to the patient inside the cone-beam CT images. The planned and delivered dose distributions were compared for 4 patients and 10 treatment fractions using dose–volume histograms and gamma analysis.Results: The gamma analysis showed a good agreement between the planned and delivered dose distributions for patients without changes in anatomy. The delivered mean dose per fraction inside the target volume deviated on average 1.1±1.4% from the planned dose. For the critical organs, only minor differences were observed between the reconstructed and planned dose.Conclusions: A method was presented that allows verification of the dose delivered in 3D for lung cancer patients treated with SBRT. The procedure is independent of the treatment planning system and uses in-room MV cone-beam CT imaging and portal dosimetry.

Automated analysis of images acquired with electronic portal imaging device during delivery of quality assurance plans for inversely optimized arc therapy

Anna Fredh, Stine Korreman, Per Munck af Rosenschöld — 2010-02-01

Abstract: This work presents an automated method for comprehensively analyzing EPID images acquired for quality assurance of RapidArc® treatment delivery. In-house-developed software has been used for the analysis and long-term results from measurements on three linacs are presented.

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

2010-01-18

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

A two-variable linear model of parotid shrinkage during IMRT for head and neck cancer

2010-02-01

Abstract: Purpose: To assess anatomical, clinical and dosimetric pre-treatment parameters, possibly predictors of parotid shrinkage during radiotherapy of head and neck cancer (HNC).Materials: Data of 174 parotids from four institutions were analysed; patients were treated with IMRT, with radical and adjuvant intent. Parotid shrinkage was evaluated by the volumetric difference (ΔV) between parotid volumes at the end and those at the start of the therapy, as assessed by CT images (MVCT for 40 patients, KVCT for 47 patients). Correlation between ΔVcc/% and a number of dosimetric, clinical and geometrical parameters was assessed. Univariate as well as stepwise logistic multivariate (MVA) analyses were performed by considering as an end-point a ΔVcc/% larger than the median value. Linear models of ΔV (continuous variable) based on the most predictive variables found at the MVA were developed.Results: Median ΔVcc/% were 6.95cc and 26%, respectively. The most predictive independent variables of ΔVcc at MVA were the initial parotid volume (IPV, OR: 1.100; p=0.0002) and Dmean (OR: 1.059; p=0.038). The main independent predictors of ΔV% at MVA were age (OR: 0.968; p=0.041) and V40 (OR: 1.0338; p=0.013). ΔVcc and ΔV% may be well described by the equations: ΔVcc=−2.44+0.076 Dmean (Gy)+0.279 IPV (cc) and ΔV%=34.23+0.192 V40 (%)−0.2203 age (year). The predictive power of the ΔVcc model is higher than that of the ΔV% model.Conclusions: IPV/age and Dmean/V40 are the major dosimetric and clinical/anatomic predictors of ΔVcc and ΔV%. ΔVcc and ΔV% may be well described by bi-linear models including the above-mentioned variables.

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

2010-01-18

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

Real-time dynamic MLC tracking for inversely optimized arc radiotherapy

2010-01-20

Abstract: Background and purpose: Motion compensation with MLC tracking was tested for inversely optimized arc radiotherapy with special attention to the impact of the size of the target displacements and the angle of the leaf trajectory.Materials and methods: An MLC-tracking algorithm was used to adjust the MLC positions according to the target movements using information from an optical real-time positioning management system. Two plans with collimator angles of 45° and 90°, respectively, were delivered and measured using the Delta4® dosimetric device moving in the superior–inferior direction with peak-to-peak displacements of 5, 10, 15, 20 and 25mm and a cycle time of 6s.Results: Gamma index evaluation for plan delivery with MLC tracking gave a pass rate higher than 98% for criteria 3% and 3mm for both plans and for all sizes of the target displacement. With no motion compensation, the average pass rate was 75% for plan 1 and 70% for plan 2 for 25mm peak-to-peak displacement.Conclusion: MLC tracking improves the accuracy of inversely optimized arc delivery for the cases studied. With MLC tracking, the dosimetric accuracy was independent of the magnitude of the peak-to-peak displacement of the target and not significantly affected by the angle between the leaf trajectory and the target movements.

Volumetric modulated arc therapy versus conventional intensity modulated radiation therapy for stereotactic spine radiotherapy: A planning study and early clinical data

Ingrid T. Kuijper, Max Dahele, Suresh Senan, Wilko F.A.R. Verbakel — 2010-02-01

Abstract: Background and purpose: Outcomes for selected patients with spinal metastases may be improved by dose escalation using stereotactic body radiation therapy (SBRT). As target geometry is complex, we compared SBRT plans using volumetric modulated arc radiotherapy (RapidArc®, RA) and conventional intensity-modulated radiotherapy (IMRT).Materials and methods: RA and IMRT plans to deliver a fraction of 16Gy to at least 90% of planning target volume (PTV) were compared for PTV coverage, normal organ sparing and estimated delivery times. Group 1 consisted of PTVs to only vertebral body (n=3), while group 2 had PTVs encompassing the entire vertebra (n=4). Finally, RA delivery parameters in four patients were assessed.Results: Both techniques delivered 16Gy to a mean of 95% and 85% of the PTV in groups 1 and 2, respectively. Spinal cord sparing was comparable; mean V10-partial cord for RA and IMRT in group 1 was 3.6%, and was 9.4% versus 11.5%, respectively, in group 2. Estimated mean treatment times for RA with 2–3 arcs and IMRT were comparable. Clinical RA beam-on times ranged from 11 to 15.4min.Conclusions: Both RA and conventional IMRT plans deliver high quality vertebral SBRT, but plan quality was poorer when the PTV consisted of the entire vertebra.

Monte Carlo-based analytical model for small and variable fields delivered by TomoTherapy

2010-01-21

Abstract: Background and purpose: Extend to very small fields the validity of a Monte Carlo (MC) based model of TomoTherapy called TomoPen for future implementation of the dynamic jaws feature for helical TomoTherapy.Materials and methods: First, the modelling of the electron source was revisited using a new method to measure source obscuration for very small fields (<1cm). The method consisted in MC simulations simulations and measurements of the central dose in a water phantom for a 10cm×FW field scanned to deliver a 10×10cm2 fluence. FW, the longitudinal field width, was varied from 0.4 to 5cm. The second part of the work consisted of adapting TomoPen to account for any configuration of the jaws in a fast and efficient way by using routinely only the phase-space file of the largest field (5cm) and interpolated analytical information of phase-space files of smaller field widths.Results: For the electron source fine tuning, it was shown that the best results were obtained for a 1.1mm wide spot. Our single phase-space method showed no significant differences compared to MC simulations of various field widths even though only longitudinal intensity and angular analytical functions were applied to the 5cm phase-space.Conclusion: The designed model is able to simulate all jaw openings from the 5cm field phase-space file by applying a bi-dimensional analytical function accounting for the fluence and the angular distribution in the longitudinal direction.

Minimising contralateral breast dose in post-mastectomy intensity-modulated radiotherapy by incorporating conformal electron irradiation

2010-01-18

Abstract: Purpose: To assess the potential benefit of incorporating conformal electron irradiation in intensity-modulated radiotherapy (IMRT) for loco-regional post-mastectomy RT.Patients and methods: Ten consecutive patients that underwent left-sided mastectomy were selected for this comparative planning study. Three-dimensional conformal radiotherapy (3D-CRT) photon–electron dose plans were compared to photon-only IMRT (IMRTp) and photon IMRT with conformal electron irradiation (IMRTp/e). The planning target volume (PTV) was prescribed 50Gy and included the chest wall and the internal mammary and supra-clavicular lymph node regions. It was attempted to minimise dose delivered to heart, lungs and contralateral breast (CB), while maintaining adequate PTV coverage.Results: All plans complied with objectives for PTV coverage. IMRTp/e eliminated volumes receiving ⩾70Gy (V70) that were present in 3D-CRT at the junction of photon and electron beams. Both IMRT strategies reduced heart V30 significantly below 3D-CRT levels. Mean heart dose with IMRTp/e was the lowest and was equal to that with 3D-CRT. Minimising heart dose with IMRTp resulted in irradiated CB volumes much larger than that with 3D-CRT. With IMRTp/e, CB dose was only slightly increased when compared to 3D-CRT. Mean lung dose values were similar for IMRT and 3D-CRT. With IMRT, lung V20 was smaller, whereas V5 values for heart, lung and CB were higher than those with 3D-CRT.Conclusions: Incorporation of conformal electron irradiation in post-mastectomy IMRTp/e enables a heart dose reduction which can only be obtained with IMRTp when allowing large irradiated volumes in the contralateral breast.

A comparison of dose–volume constraints derived using peak and longitudinal definitions of late rectal toxicity

2010-01-25

Abstract: Background and purpose: Accurate reporting of complications following radiotherapy is an important part of the feedback loop to improve radiotherapy techniques. The definition of toxicity is normally regarded as the maximum or peak (P) grade of toxicity reported over the follow-up period. An alternative definition (integrated longitudinal toxicity (ILT)) is proposed which takes into account both the severity and the duration of the complication.Methods and materials: In this work, both definitions of toxicity were used to derive dose–volume constraints for six specific endpoints of late rectal toxicity from a cohort of patients who received prostate radiotherapy in the MRC RT01 trial. The dose–volume constraints were derived using ROC analysis for 30, 40, 50, 60, 65 and 70Gy.Results: Statistically significant dose–volume constraints were not derived for all dose levels tested for each endpoint and toxicity definition. However, where both definitions produced constraints, there was generally good agreement. Variation in the derived dose–volume constraints was observed to be larger between endpoints than between the two definitions of toxicity. For one endpoint (stool frequency (LENT/SOM)) statistically significant dose–volume constraints were only derived using ILT.Conclusions: The longitudinal definition of toxicity (ILT) produced results consistent with those derived using peak toxicity and in some cases provided additional information which was not seen by analysing peak toxicity alone.

Determining DVH parameters for combined external beam and brachytherapy treatment: 3D biological dose adding for patients with cervical cancer

2010-01-18

Abstract: Purpose: To compare two methods of DVH parameter determination for combined external beam and brachytherapy treatment of cervical cancer.Materials and methods: Clinical treatment plans from five patients were used in this study. We simulated two applications given with PDR (32×60cGy per application, given hourly) or HDR (4×7Gy in two applications; each application of two fractions of 7Gy, given within 17h) standard and optimised treatment plans, all combined with IMRT (25×1.8Gy). Additionally, we simulated an external beam (EBRT) boost to pathological lymph nodes or the parametrium (7×2Gy).We determined D90 of the high-risk CTV (HR-CTV) and D2cc of bladder and rectum in EQD2 in two ways. (1) ‘Parameter adding’: assuming a uniform contribution of the EBRT dose distribution and adding the values of DVH parameters for the two brachytherapy insertions, and (2) ‘distributions adding’: summing 3D biological dose distributions of IMRT and brachytherapy plans and subsequently determining the values of the DVH parameters. We took α/β=10Gy for HR-CTV, α/β=3Gy otherwise and half-time of repair 1.5h.Results: Without EBRT boost, ‘parameter adding’ yielded a good approximation. With an EBRT boost to lymph nodes, the total D90 HR-CTV was underestimated by 2.6 (SD 1.3)% for PDR and 2.8 (SD 1.4)% for HDR. This was even worse with a parametrium boost: 9.1 (SD 6.2)% for PDR and 9.9 (SD 6.2)% for HDR.Conclusion: Without an EBRT boost ‘parameter adding’, as proposed by the GEC-ESTRO, yielded accurate results for the values for DVH parameters. If an EBRT boost is given ‘distributions adding’ should be considered.

Important ESTRO dates

2010-02-01