GEC-ESTRO survey of 106Ru eye applicator practice for ocular melanoma - Physicist survey.

AIM: 106Ru eye plaque brachytherapy (BT, interventional radiotherapy) is an eye-preserving treatment for uveal melanoma performed in about 100 clinics worldwide. Despite this relatively low number, there is a considerable variation in clinical practice. In 2022, the BRAPHYQS and Head & Neck and Skin GEC-ESTRO working groups conducted a survey to map the current clinical practice. The survey consisted of a physicist and a physician part. This paper describes the physicist results. However, three physician questions with overlapping interest are included here as well. MATERIALS AND METHODS: The survey questions pertained to commissioning and quality control (QC) of the plaques, treatment planning, radiobiological correction, as well as more general questions on practice improvement. The questions overlapping with the physician survey were related to dose prescription and margins. RESULTS: Sixty-five physicist responses were included. A majority of the centres do not perform an independent measurement of the absorbed dose at reference depth, percentage depth dose (PDD) and off-axis data. A lack of calibration services and suitable equipment are the main reasons. About one third of the centres indicated that they do image based treatment planning. The use of margins and dose prescription showed a large variability, despite the availability of guidelines [1]. Many respondents expressed a strong wish for improvement in a wide range of aspects of clinical practice. CONCLUSION: The physics survey showed a wide variability regarding quality control of the 106Ru sources and treatment planning practice.

Ring Versus Ovoids and Intracavitary Versus Intracavitary-Interstitial Applicators in Cervical Cancer Brachytherapy: Results From the EMBRACE I Study.

PURPOSE: The aim of this study was to investigate the influence of brachytherapy technique and applicator type on target dose, isodose surface volumes, and organ-at-risk (OAR) dose. METHODS AND MATERIALS: Nine hundred two patients treated with tandem/ovoids (T&O) (n = 299) and tandem/ring (T&R) (n = 603) applicators from 16 EMBRACE centers were analyzed. Patients received external beam radiation therapy and magnetic resonance imaging guided brachytherapy with dose prescription according to departmental practice. Centers were divided into 4 groups, according to applicator/technique: Ovoids and ring centers treating mainly with the intracavitary (IC) technique and ovoids and ring centers treating routinely with the intracavitary/interstitial (IC/IS) technique. V85Gy EQD210, CTVHR D90% (EQD210), and bladder, rectum, sigmoid, and vaginal 5-mm lateral-point doses (EQD23) were evaluated among center groups. Differences between T&O and T&R were tested with multivariable analysis. RESULTS: For similar point A doses, mean CTVHR D90% was 3.3 Gy higher and V85Gy was 23% lower for ring-IC compared with ovoids-IC centers (at median target volumes). Mean bladder/rectum doses (D2cm3 and ICRU-point) were 3.2 to 7.7 Gy smaller and vaginal 5-mm lateral-point was 19.6 Gy higher for ring-IC centers. Routine use of IC/IS technique resulted in increased target dose, whereas V85Gy was stable (T&R) or decreased (T&O); reduced bladder and rectum D2cm3 and bladder ICRU-point by 3.5 to 5.0 Gy for ovoids centers; and similar OAR doses for ring centers. CTVHR D90% was 2.8 Gy higher, bladder D2cm3 4.3 Gy lower, rectovaginal ICRU-point 4.8 Gy lower, and vagina 5-mm lateral-point 22.4 Gy higher for ring-IC/IS versus ovoids-IC/IS centers. The P values were <.002 for all comparisons. Equivalently, significant differences were derived from the multivariable analysis. CONCLUSIONS: T&R-IC applicators have better target dose and dose conformity than T&O-IC in this representative patient cohort. IC applicators fail to cover large target volumes, whereas routine application of IC/IS improves target and OAR dose considerably. Patients treated with T&R show a more favorable therapeutic ratio when evaluating target, bladder/rectum doses, and V85Gy. A comprehensive view on technique/applicators should furthermore include practical considerations and clinical outcome.

Image registration, contour propagation and dose accumulation of external beam and brachytherapy in gynecological radiotherapy.

This review provides an overview of the current status of image registration for image guided gynaecological brachytherapy including combination with external beam radiotherapy. Contour propagation between individual fractions and dose accumulation can be useful for cervix cancer radiotherapy. Contour mapping and applicator reconstruction with rigid registration based on the applicator geometry provide good accuracy. However, deformable image registration is particularly challenging in the pelvic region, due to the large and complex deformations caused by tumor shrinkage, bladder and rectum filling, insertion of a brachytherapy applicator and presence of packing material. This causes substantial limitations and uncertainties when using it in the clinical workflow so that the current generation of deformable image registration algorithms is not yet robust enough to handle complexities involving the dose accumulation of external beam and brachytherapy. The direct addition of doses provides a reasonable estimate of the total absorbed dose. However, in case of significant dose gradients from external beam boosts or midline-shielding adding dose contributions from the different radiotherapy modalities and fractions remains subject to large uncertainties.

Validation and IMRT/VMAT delivery quality of a preconfigured fast-rotating O-ring linac system.

PURPOSE: A fast-rotating O-ring dedicated intensity modulated radiotherapy (IMRT)/volumetric modulated arc therapy (VMAT) delivery system, the Halcyon, is delivered by default with a fully preconfigured photon beam model in the treatment planning system (TPS). This work reports on the validation and achieved IMRT/VMAT delivery quality on the system. METHODS: Acceptance testing followed the vendor's installation product acceptance and was supplemented with mechanical QA. The dosimetric calibration was performed according to the IAEA TRS-398 code-of-practice, delivering 600 cGy/min at 10 cm depth, a 90 cm source-surface distance, and a 10 × 10 cm² field size. The output factors, multileaf collimator (MLC) transmission and dosimetric leaf gap (DLG) were validated by comparing measurements with the modeled values in the TPS. Validation of IMRT/VMAT was conducted following AAPM reports (MPPG 5.a, TG-119). Next, dose measurements were performed for end-to-end (E2E) checks in heterogeneous anthropomorphic phantoms using radiochromic film in multiple planes and using ionization chambers (IC) point measurements. E2E checks were performed for VMAT (cranial, rectum, spine, and head and neck) and IMRT (lung). Additionally, IROC Houston mailed dosimetry audits were performed for the beam calibration and E2E measurements using a thorax phantom (IMRT) and a head and neck phantom (VMAT). Lastly, extensive patient-specific QA was performed for the first patients of each new indication, 26 in total (nrectum = 2, nspine = 5, nlung = 5, nesophagus = 2, nhead and neck = 7, ncranial = 5), treated on the fast-rotating O-ring linac. The patient-specific QA followed the AAPM TG-218 guidelines and comprised of portal dosimetry, ArcCHECK diode array, radiochromic film dosimetry in a MultiCube phantom, and IC point measurements. RESULTS: The measured output factors showed an agreement <1% for fields ≥3 × 3 cm². Field sizes ≤2 × 2 cm² had a difference of <2%. The measured single-layer MLC transmission was 0.42 ± 0.01% and the measured DLG was 0.27 ± 0.22 mm. The AAPM MPPG 5.a measurements were fully compliant with the guideline criteria. Dose differences larger than 2% were found for the PDD at large depths (>25 cm). TG-119's confidence limits were achieved for the VMAT point dose measurements and for both the IMRT and VMAT radiochromic film measurements. The TG-119 confidence limits were not achieved for IMRT point dose measurements in both the target (5.9%) and the avoidance structure (6.4%). All E2E tests had point differences below 2.3% and gamma agreement scores above 90.6%. The IROC beam calibration audit showed agreement of <1%. The IROC lung IMRT audit and head and neck VMAT audit had results compliant with the IROC Houston's credentialing criteria. All IMRT and VMAT plans selected for patient-specific QA were within the action limits suggested by TG-218. CONCLUSIONS: The fast-rotating O-ring linac and its preconfigured TPS are compliant with the international commissioning criteria of AAPM MPPG 5.a and AAPM TG-119. E2E measurements on heterogeneous anthropomorphic phantoms were within clinically acceptable tolerances. IROC Houston's audits satisfied the credentialing criteria. This work comprises the first extensive dataset reporting on the preconfigured fast-rotating O-ring linac.

Isodose surface volumes in cervix cancer brachytherapy: Change of practice from standard (Point A) to individualized image guided adaptive (EMBRACE I) brachytherapy.

PURPOSE: To investigate the isodose surface volumes (ISVs) for 85, 75 and 60 Gy EQD2 for locally advanced cervix cancer patients. MATERIALS AND METHODS: 1201 patients accrued in the EMBRACE I study were analysed. External beam radiotherapy (EBRT) with concomitant chemotherapy was followed by MR based image-guided adaptive brachytherapy (MR-IGABT). ISVs were calculated using a predictive model based on Total Reference Air Kerma and compared to Point A-standard loading systems. Influence of fractionation schemes and dose rates was evaluated through comparison of ISVs for α/ß 10 Gy and 3 Gy. RESULTS: Median V85 Gy, V75 Gy and V60 Gy EQD210 were 72 cm3, 100 cm3 and 233 cm3, respectively. Median V85 Gy EQD210 was 23% smaller than in standard 85 Gy prescription to Point A. For small (<25 cm3), intermediate (25-35 cm3) and large (>35 cm3) CTVHR volumes, the V85 Gy was 57 cm3, 70 cm3 and 89 cm3, respectively. In 38% of EMBRACE patients the V85 Gy was similar to standard plans with 75-85 Gy to Point A. 41% of patients had V85 Gy smaller than standard plans receiving 75 Gy at Point A, while 21% of patients had V85 Gy larger than standard plans receiving 85 Gy at Point A. CONCLUSIONS: MR-IGABT and individualized dose prescription during EMBRACE I resulted in improved target dose coverage and decreased ISVs compared to standard plans used with classical Point A based brachytherapy. The ISVs depended strongly on CTVHR volume which demonstrates that dose adaptation was performed per individual tumour size and response during EBRT.

GEC-ESTRO/ACROP recommendations for performing bladder-sparing treatment with brachytherapy for muscle-invasive bladder carcinoma.

The standard treatment for muscle-invasive bladder cancer (MIBC) is a radical cystectomy with pelvic lymph node dissection with or without neoadjuvant chemotherapy. In selected cases a bladder sparing approach is possible, for example a limited surgical excision combined with external beam radiotherapy and brachytherapy. To perform brachytherapy flexible catheters have to be implanted in the bladder wall. The implantation is done either by the open retropubic approach or the endoscopic surgical approach. The largest experience for brachytherapy is with low-dose rate and pulsed-dose rate, although some short-term experience with high-dose rate is also reported. The main advantage for this technique is the conservation of bladder function, with comparable local control rates as for cystectomy series in selected cases. The GEC-ESTRO/ACROP (Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology / Advisory Committee on Radiation Oncology Practice) recommendations to perform bladder implantations and brachytherapy as a treatment option for MIBC are described.

Long term experience with 3D image guided brachytherapy and clinical outcome in cervical cancer patients.

BACKGROUND AND PURPOSE: To report our 10years' experience and learning curve of the treatment of cervical cancer patients with chemo radiotherapy and MRI (or CT in 9 selected patients) guided brachytherapy using pulsed dose rate (PDR) brachytherapy (BT). METHODS AND MATERIALS: Hundred and seventy consecutive patients with cervical cancer FIGO stage IB-IVB (without metastases beyond the para-aortic nodal region) were treated in our institute between 2002 and 2012. Patients received external beam radiotherapy (nodal boost to the lymph nodes positive at diagnosis)±chemotherapy followed by a pulsed or low dose rate brachytherapy boost. MRI (or CT) images were taken with the applicator in situ. The first 16 patients were treated according to X-ray-based plans, optimized on MRI. High-risk CTV, intermediate-risk CTV, bladder, rectum and sigmoid were retrospectively contoured according to the GEC-ESTRO recommendations. In all other patients, treatment plans were optimized after delineation of the target volumes and organs at risk at MRI (or CT). Doses were converted to the equivalent dose in 2Gy (EQD2) by applying the linear quadratic model. The median age of the patients was 55years (range 16-88). 41% had stage III or IV disease. Of the 170 patients, 91 patients had on imaging metastatic lymph nodes at diagnosis (62 patients pelvic lymph node involvement and 29 para-aortic). In 27 (16%) patients the intracavitary technique was combined with interstitial brachytherapy. RESULTS: The mean D90 and D100 for the high-risk CTV were 84.8±8.36Gy and 67.5±6.29Gy for the entire patient group. Mean D90 and D100 values for the IR CTV were 68.7±5.5Gy and 56.5±6.25Gy. There was an important learning curve between both patient groups, with an increase in mean D90 of 75.8Gy for the first 16 patients compared to 85.8Gy for the second group. At the same time, the mean dose to 2cm3 of bladder and sigmoid decreased from 86.1Gy to 82.7Gy and from 70Gy to 61.7Gy, respectively. At a median follow-up of 37months (range 2-136months), local control rate for all patients was 96%, the regional control (pelvic and para-aortic) rate 81% and crude disease free survival rate 55%. The overall survival at 5years is 65%. The higher dose to the target volume resulted in an increase in local control from 88% in the first 16 patients compared to 97% in the second patient group. Regarding late toxicity, 21 patients (12%) presented grade 3-4 late morbidity. Rectal, urinary, sigmoid and vaginal morbidity was 5%, 6%, 2% and 5%, respectively. A correlation between rectal D2cm3 >65Gy and grade >3 late morbidity was found (p=0.006). CONCLUSION: Although the majority of the patients presented with locally advanced carcinoma, excellent local and regional control rates were achieved. Rectal, urinary, sigmoid and vaginal grade 3-4 morbidity was 5%, 6%, 2% and 5%, respectively. A correlation between rectal D2cm3 >65Gy and grade >3 late morbidity was found (p=0.006).

Review of clinical brachytherapy uncertainties: analysis guidelines of GEC-ESTRO and the AAPM.

BACKGROUND AND PURPOSE: A substantial reduction of uncertainties in clinical brachytherapy should result in improved outcome in terms of increased local control and reduced side effects. Types of uncertainties have to be identified, grouped, and quantified. METHODS: A detailed literature review was performed to identify uncertainty components and their relative importance to the combined overall uncertainty. RESULTS: Very few components (e.g., source strength and afterloader timer) are independent of clinical disease site and location of administered dose. While the influence of medium on dose calculation can be substantial for low energy sources or non-deeply seated implants, the influence of medium is of minor importance for high-energy sources in the pelvic region. The level of uncertainties due to target, organ, applicator, and/or source movement in relation to the geometry assumed for treatment planning is highly dependent on fractionation and the level of image guided adaptive treatment. Most studies to date report the results in a manner that allows no direct reproduction and further comparison with other studies. Often, no distinction is made between variations, uncertainties, and errors or mistakes. The literature review facilitated the drafting of recommendations for uniform uncertainty reporting in clinical BT, which are also provided. The recommended comprehensive uncertainty investigations are key to obtain a general impression of uncertainties, and may help to identify elements of the brachytherapy treatment process that need improvement in terms of diminishing their dosimetric uncertainties. It is recommended to present data on the analyzed parameters (distance shifts, volume changes, source or applicator position, etc.), and also their influence on absorbed dose for clinically-relevant dose parameters (e.g., target parameters such as D90 or OAR doses). Publications on brachytherapy should include a statement of total dose uncertainty for the entire treatment course, taking into account the fractionation schedule and level of image guidance for adaptation. CONCLUSIONS: This report on brachytherapy clinical uncertainties represents a working project developed by the Brachytherapy Physics Quality Assurances System (BRAPHYQS) subcommittee to the Physics Committee within GEC-ESTRO. Further, this report has been reviewed and approved by the American Association of Physicists in Medicine.

CT- and MRI-based seed localization in postimplant evaluation after prostate brachytherapy.

PURPOSE: To compare the uncertainties in CT- and MRI-based seed reconstruction in postimplant evaluation after prostate seed brachytherapy in terms of interobserver variability and quantify the impact of seed detection variability on a selection of dosimetric parameters for three postplan techniques: (1) CT, (2) MRI-T1 weighted fused with MRI-T2 weighted, and (3) CT fused with MRI-T2 weighted. METHODS AND MATERIALS: Seven physicists reconstructed the seed positions on postimplant CT and MRI-T1 images of three patients. For each patient and imaging modality, the interobserver variability was calculated with respect to a reference seed set. The effect of this variability on dosimetry was calculated for CT and CT + MRI-T2 (CT-based seed reconstruction), as well as for MRI-T1 + MRI-T2 (MRI-T1-based seed reconstruction), using fixed CT and MRI-T2 prostate contours. RESULTS: Averaged over three patients, the interobserver variability in CT-based seed reconstruction was 1.1 mm (1 SDref, i.e., standard deviation with respect to the reference value). The D90 (dose delivered to 90% of the target) variability was 1.5% and 1.3% (1 SDref) for CT and CT + MRI-T2, respectively. The mean interobserver variability in MRI-based seed reconstruction was 3.0 mm (1 SDref), and the impact of this variability on D90 was 6.6% for MRI-T1 + MRI-T2. CONCLUSIONS: Seed reconstruction on MRI-T1-weighted images was less accurate than on CT. This difference in uncertainties should be weighted against uncertainties due to contouring and image fusion when comparing the overall reliability of postplan techniques.

Multicentre treatment planning study of MRI-guided brachytherapy for cervical cancer: comparison between tandem-ovoid applicator users.

BACKGROUND AND PURPOSE: To compare MRI-guided treatment planning approaches between four centres that use tandem-ovoid applicators. MATERIAL AND METHODS: Four centres generated three treatment plans for four patients: standard, optimised intracavitary, and optimised intracavitary/interstitial. Prescribed D90 High-Risk CTV (HR-CTV) was 85 Gy EQD2 (external-beam radiotherapy and brachytherapy), while the D(2cc) OAR limit was 90 Gy EQD2 for bladder and 75 Gy EQD2 for rectum, sigmoid, and bowel, respectively. DVH-parameters, source loading patterns and spatial dose distributions of the three treatment plans were compared. RESULTS: The standard plans of the different centres were comparable with respect to the D90 HR-CTV, but differed in OAR doses. MRI-guided intracavitary optimisation resulted in organ sparing and smaller variation in DVH parameters between the centres. Adding interstitial needles led to target dose escalation while respecting the OAR constraints. However, substantial differences in relative weights of the applicator parts resulted in an increased variation in DVH parameters and locations of high dose regions. CONCLUSIONS: MRI-guided brachytherapy treatment planning optimisation provides the possibility to increase the dose to the HR-CTV and spare the OARs. Depending on the degree of conformity the centres make different choices in relative weighting of applicator parts, leading to different dose distributions.

Prostate post-implant dosimetry: interobserver variability in seed localisation, contouring and fusion.

AIM: Reliable post-implant evaluation of prostate seed implants requires optimal seed identification and accurate delineation of anatomical structures. In this study the GEC-ESTRO groups BRAPHYQS and PROBATE investigated the interobserver variability in post-implant prostate contouring, seed reconstruction and image fusion and its impact on the dose-volume parameters. MATERIALS: Post-implant T2-TSE, T1-GE and CT images were acquired for three patients, in order to evaluate four post-plan techniques: (a) CT, (b) T1+T2, (c) CT+T2, (d) CT+T1(int)+T2. Three interobserver studies were set up. (1) Contouring: the CTV-prostate was delineated on CT and T2 by eight physicians. Additionally one reference contour was defined on both image modalities for each patient. (2) Seed reconstruction: seven physicists localised the seeds on T1 and CT, manually and with CT seed finder tools. A reference seed geometry was defined on CT and T1. (3) Fusion: six physicists registered the image sets for technique (b)-(d), using seeds (if visible) and anatomical landmarks. A reference fusion was determined for each combined technique. RESULTS: (1) The SD(ref) for contouring (1 SD with respect to the reference volume) was largest for CT (23%), but also surprisingly large for MRI (17%). This resulted in large SD(ref) values for D90 for all techniques (17-23%). The surprisingly large SD(ref) for MRI was partly due to variations in interpretation of what to include in the prostate contour. (2) The SD(ref) in D90 for seed reconstruction was small (2%) for all techniques, except for T1+T2 (7%). (3) The SD(ref) in D90 due to image fusion was quite large, especially for direct fusion of CT+T2 (16%) where clearly corresponding landmarks were missing (seeds hardly visible on T2). In general, we observed large differences in D90 depending on the technique used. CONCLUSIONS: The dosimetric parameters for prostate post-implant evaluation showed large technique-dependent interobserver variabilities. Contouring and image fusion are the 'weak links' in the procedure. Guidelines and training in contouring together with incorporation of automated fusion software need to be implemented.

Recommendations from Gynaecological (GYN) GEC-ESTRO Working Group: considerations and pitfalls in commissioning and applicator reconstruction in 3D image-based treatment planning of cervix cancer brachytherapy.

Image-guided brachytherapy in cervical cancer is increasingly replacing X-ray based dose planning. In image-guided brachytherapy the geometry of the applicator is extracted from the patient 3D images and introduced into the treatment planning system; a process referred to as applicator reconstruction. Due to the steep brachytherapy dose gradients, reconstruction errors can lead to major dose deviations in target and organs at risk. Appropriate applicator commissioning and reconstruction methods must be implemented in order to minimise uncertainties and to avoid accidental errors. Applicator commissioning verifies the location of source positions in relation to the applicator by using auto-radiography and imaging. Sectional imaging can be utilised in the process, with CT imaging being the optimal modality. The results from the commissioning process can be stored as library applicators. The importance of proper commissioning is underlined by the fact that errors in library files result in systematic errors for clinical treatment plans. While the source channel is well visualised in CT images, applicator reconstruction is more challenging when using MR images. Availability of commercial dummy sources for MRI is limited, and image artifacts may occur with titanium applicators. The choice of MR sequence is essential for optimal visualisation of the applicator. Para-transverse imaging (oriented according to the applicator) with small slice thickness (< or =5 mm) is recommended or alternatively 3D MR sequences with isotropic voxel sizes. Preferably, contouring and reconstruction should be performed in the same image series in order to avoid fusion uncertainties. Clear and correct strategies for the applicator reconstruction will ensure that reconstruction uncertainties have limited impact on the delivered dose. Under well-controlled circumstances the reconstruction uncertainties are in general smaller than other brachytherapy uncertainties such as contouring and organ movement.

Potential of dose optimisation in MRI-based PDR brachytherapy of cervix carcinoma.

BACKGROUND AND PURPOSE: In this study on PDR treatment planning of utero-vaginal carcinoma, we analysed the dosimetry of traditional X-ray based plans as it presents on MR images. The potential gain of MRI-based dose optimisation was assessed. PATIENTS AND METHODS: Sixteen patients boosted with PDR brachytherapy after external beam therapy were included. The clinical X-ray based plans were projected on MR images. The GTV, HR-CTV and IR-CTV were retrospectively contoured, as well as the bladder, rectum and sigmoid colon. The dose in the critical organs and target coverage was investigated. In a second phase, the plans were manually optimised using the MR information. The objectives were to lower the dose in the critical organs (or= 85 Gy(alphabeta10). RESULTS: In the X-ray based plans, D(2cc) in bladder and sigmoid colon exceeded the tolerance doses in 10/16 and 7/16 patients, respectively. Coverage of the IR-CTV with the 60 Gy(alphabeta10) was acceptable. D90 of the HR-CTV was below 85 Gy(alphabeta10) in 13 out of 16 patients. After optimisation, the dose constraints in the OAR were not exceeded anymore in any patient. The average D(2cc) dose reduction was 7+/-6 Gy(alphabeta3) in the bladder and 7+/-4 Gy(alphabeta3) in the sigmoid colon for those patients in which the dose constraint was initially exceeded. In addition, an average dose increase of 3 Gy(alphabeta10) was accomplished in the HR-CTV. CONCLUSIONS: MRI-based dose optimisation can play an important role to reduce the dose delivered to the critical organs and to improve target coverage.

Phantom investigations on CT seed imaging for interstitial brachytherapy.

BACKGROUND AND PURPOSE: The Braphyqs group (BRAchytherapy PHYsics Quality System, the brachytherapy physicist's task group of GEC-ESTRO) investigated the quality of CT- and X-ray based seed reconstruction procedures using the Kiel-phantom. In this study systematic phantom investigations on CT post-planning and the results of a mailed multi-centre inter-comparison are presented. MATERIALS AND METHODS: The phantom was equipped with a test configuration composed of 17 non-radioactive seeds. To investigate the quality of seed reconstruction CT measurements with varying CT parameters and different seed models were carried out. In a mailed multi-centre approach the phantom was sent to six European seed centres. The centres performed a typical CT- or X-ray based post-planning. The coordinates of the reconstructed sources were compared with the known positions in the phantom. RESULTS: In the systematic study it was found for the used CT scanner and seed models that when the slice thickness or the table index (respectively, an appropriate pitch for helical scans) reaches 4 or 5mm the accuracy of the CT seed reconstruction decreases in longitudinal direction. No influences of scanned field of view, tube current, kV(p), or scan type (axial or spiral) on seed reconstruction accuracy were detected. This finding was confirmed by the multi-centre evaluation. It was demonstrated that the Kiel-phantom is a suitable quality assurance (QA) tool for the assessment of the seed reconstruction accuracy in post-implant procedures and that it is a feasible QA test tool for a mailed multi-centre approach. CONCLUSIONS: QA of seed post-planning is necessary. A trend was observed that when the slice thickness and table index is 4 or 5mm the standard deviation of the reconstructed seeds increases for CT-based post-planning. Individual optimizations can be performed with dedicated phantoms.

Accuracy of volume and DVH parameters determined with different brachytherapy treatment planning systems.

PURPOSE: To determine the uncertainties in dose volume histogram (DVH) analysis used in modern brachytherapy treatment planning systems (TPSs). MATERIALS AND METHODS: A phantom with three different volumes was scanned with CT and MRI. An inter-observer analysis was based on contouring performed by 5 persons. The volume of a standard contour set was calculated using seven different TPSs. For five systems a typical brachytherapy dose distribution was used to compare DVH determination. RESULTS: The inter-observer variability (1SD) was 13% for a small cylindrical volume, 5% for a large cylinder and 3% for a conical shape. A standardized volume for a 4mm CT scan contoured on seven different TPS varied by 7%, 2%, and 5% (1SD). Use of smaller slice thickness reduced the variations. A treatment plan with the sources between the large cylindrical shape and the cone showed variations for D(2cc) of 1% and 5% (1SD), respectively. Deviations larger than 10% were observed for a smaller source to cylinder surface distance of 5mm. CONCLUSIONS: Modern TPSs minimize the volumetric and dosimetric calculation uncertainties. These are comparable to inter-observer contouring variations. However, differences in volume result from the methods of calculation in the first and last slice of a contoured structure. For this situation and in case of high dose gradients inside analyzed volumes, high uncertainties were observed. The use of DVH parameters in clinical practice should take into account the method of calculation and the possible uncertainties.

Accuracy of seed reconstruction in prostate postplanning studied with a CT- and MRI-compatible phantom.

BACKGROUND AND PURPOSE: Postimplant dosimetry of prostate seed implants is usually performed by seed localisation on transversal CT or MR images. In order to obtain reliable dosimetric evaluation data, it is important that seeds are reconstructed accurately. Currently, there is no comparative data available on seed localisation accuracy of CT-and MRI-based reconstructions, mainly due to the lack of a suitable QA tool. In this study, we developed a CT-and MRI compatible prostate phantom to investigate the intrinsic accuracy of seed detection for both imaging modalities. PATIENTS AND METHODS: A 60 seed geometry was created according to a clinically meaningful plan, including rotated and shifted seeds. After implantation of the seeds in the phantom, CT and MRI scans with 3, 4 and 5mm slice thickness were performed. The seed locations were reconstructed in the treatment planning system and compared with the known reference positions. RESULTS: Due to the comparable density and relaxation times of the phantom material to prostate tissue, the seeds are visualised similarly as on real patient images. The observed mean reconstruction uncertainties were in general smaller for CT (0.9+/-0.6, 0.9+/-0.6, 2.1+/-0.8 mm on 3, 4 and 5mm scans, respectively), than for MRI (Philips 1.5 T: 2.1+/-1.4, 1.6+/-1.2, 1.9+/-0.9 mm on 3, 4 and 5 mm scans, respectively, and Siemens 1.5 T: 2.3+/-0.8, 2.0+/-1.6, 1.6+/-0.8 mm on 3, 4 and 5mm scans, respectively). CONCLUSIONS: For our clinical sequences of both CT and MRI, the mean deviation of the reconstructed seed positions were all within acceptable limits for clinical use (<2.3 mm). The phantom was found to be a suitable quality assurance tool to assess the reliability and accuracy of the seed reconstruction procedure. Moreover, as the phantom material has the same imaging characteristics as real prostate tissue, it is a useful device to define proper MRI sequences.

Intercomparison of treatment concepts for MR image assisted brachytherapy of cervical carcinoma based on GYN GEC-ESTRO recommendations.

PURPOSE: To perform a multicentre intercomparison study of treatment concepts for MRI assisted brachytherapy of cervix cancer based on recommendations of the Gynaecological GEC-ESTRO Working Group. METHODS: Each participating centre (IGR Paris, University Hospital Leuven, Medical University of Vienna) contributed data of one patient with comparable clinical features. GTV, High Risk CTV (HR CTV), Intermediate Risk CTV (IR CTV) and organ walls of bladder, rectum and sigmoid colon were delineated at the time of each brachytherapy fraction on axial MR images with the applicator in place. Dose-volume histograms were calculated to evaluate doses to tumour, target volumes and organs at risk. Dose values were biologically normalised to equivalent doses in 2 Gy fractions (EQD(2), equivalent to 50 cGy/h low dose rate) applying the linear-quadratic model. RESULTS: Total doses to point A from external beam therapy plus brachytherapy ranged from 85 to 91 Gy and were close to the dose covering 90% of HR CTV (D90=85-87 Gy). D90 of IR CTV was within 69-73 Gy. Doses to organs at risk were comparable. CONCLUSIONS: This study indicates the feasibility of the GEC-ESTRO recommendations. Despite different treatment concepts, biologically normalised total doses to tumour, target volumes and organs at risk were comparable.

Recommendations from gynaecological (GYN) GEC ESTRO working group (II): concepts and terms in 3D image-based treatment planning in cervix cancer brachytherapy-3D dose volume parameters and aspects of 3D image-based anatomy, radiation physics, radiobiology.

The second part of the GYN GEC ESTRO working group recommendations is focused on 3D dose-volume parameters for brachytherapy of cervical carcinoma. Methods and parameters have been developed and validated from dosimetric, imaging and clinical experience from different institutions (University of Vienna, IGR Paris, University of Leuven). Cumulative dose volume histograms (DVH) are recommended for evaluation of the complex dose heterogeneity. DVH parameters for GTV, HR CTV and IR CTV are the minimum dose delivered to 90 and 100% of the respective volume: D90, D100. The volume, which is enclosed by 150 or 200% of the prescribed dose (V150, V200), is recommended for overall assessment of high dose volumes. V100 is recommended for quality assessment only within a given treatment schedule. For Organs at Risk (OAR) the minimum dose in the most irradiated tissue volume is recommended for reporting: 0.1, 1, and 2 cm3; optional 5 and 10 cm3. Underlying assumptions are: full dose of external beam therapy in the volume of interest, identical location during fractionated brachytherapy, contiguous volumes and contouring of organ walls for >2 cm3. Dose values are reported as absorbed dose and also taking into account different dose rates. The linear-quadratic radiobiological model-equivalent dose (EQD2)-is applied for brachytherapy and is also used for calculating dose from external beam therapy. This formalism allows systematic assessment within one patient, one centre and comparison between different centres with analysis of dose volume relations for GTV, CTV, and OAR. Recommendations for the transition period from traditional to 3D image-based cervix cancer brachytherapy are formulated. Supplementary data (available in the electronic version of this paper) deals with aspects of 3D imaging, radiation physics, radiation biology, dose at reference points and dimensions and volumes for the GTV and CTV (adding to [Haie-Meder C, Pötter R, Van Limbergen E et al. Recommendations from Gynaecological (GYN) GEC ESTRO Working Group (I): concepts and terms in 3D image-based 3D treatment planning in cervix cancer brachytherapy with emphasis on MRI assessment of GTV and CTV. Radiother Oncol 2005;74:235-245]). It is expected that the therapeutic ratio including target coverage and sparing of organs at risk can be significantly improved, if radiation dose is prescribed to a 3D image-based CTV taking into account dose volume constraints for OAR. However, prospective use of these recommendations in the clinical context is warranted, to further explore and develop the potential of 3D image-based cervix cancer brachytherapy.

Recommendations from Gynaecological (GYN) GEC-ESTRO Working Group (I): concepts and terms in 3D image based 3D treatment planning in cervix cancer brachytherapy with emphasis on MRI assessment of GTV and CTV.

BACKGROUND AND PURPOSE: Brachytherapy (BT) plays a crucial role in the management of invasive cervix cancer from stage I to IV. Intracavitary techniques are based on afterloading devices, with different types of applicators. CT and/or MRI compatible applicators allow a sectional image based approach with a better assessment of gross tumour volume (GTV) and definition and delineation of target volume (CTV) compared to traditional approaches. Accurate and reproducible delineation of GTV, CTV and PTV, as well as of critical organs has a direct impact on BT treatment planning, especially if it is possible to adapt the pear-shape isodose by optimisation using DVH analysis. When introducing a 3D image based approach for GTV and CTV assessment, there is a need for a common language to describe the concepts and to define the terms which are to be used. METHODS: In 2000, GEC-ESTRO decided to support 3D imaging based 3D treatment planning approach in cervix cancer BT with the creation of a Working Group. The task was to describe basic concepts and terms and to work out a terminology enabling various groups working in this advanced field to use a common language. The recommendations described in this report were proposed based on clinical experience and dosimetric concepts of different institutions (IGR, Leuven, Vienna) and were stepwise validated against the background of different clinical experience. CONCLUSIONS: As GTV and CTV for BT change significantly during treatment, time frame for assessment of GTV and CTV for BT is specified in this report: at time of diagnosis GTV(D), CTV(D) and at time of BT GTV(B), CTV(B). Furthermore, CTV for BT is defined related to risk for recurrence: high risk CTV and intermediate risk CTV. Beside verbal descriptions detailed examples are given, partly in form of schematic drawings.