Publications by authors named "Søren Kynde Nielsen"

15 Publications

  • Page 1 of 1

Characterization of combined intracavitary/interstitial brachytherapy including oblique needles in locally advanced cervix cancer.

Brachytherapy 2021 Jul-Aug;20(4):796-806. Epub 2021 May 14.

Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.

Purpose: To characterize and report on dosimetric outcomes of image guided adaptive brachytherapy (IGABT) using intracavitary and interstitial (IC/IS) applicators including oblique needles (O-needles) in locally advanced cervical cancer (LACC).

Methods And Materials: Twenty LACC patients treated with radio-chemotherapy and offered IC/IS-IGABT including O-needles were analyzed. An in-house 3D-printed vaginal template was used to steer the needles parallel and obliquely in relation to the tandem, supplemented with free-hand needles if needed. Implant characteristics and loading patterns were analyzed. Using the equivalent dose in 2Gy-fractions (EQD2) concept, cumulative (EBRT+BT) V85, V75, V60Gy, targets/OARs doses and high dose volumes (150%, 200% and 300% (100% = 85 Gy EQD2)) were evaluated.

Results: Median(range) tumor width at diagnosis was 5.5(3.6; 7.5)cm; CTV volume was 45(23; 136)cm with maximum distance from tandem to CTV border of 3.4(2.5; 4.8)cm. T-stage distribution was IIB/III/IVA in 6(30%)/9(45%)/5(25%) of patients. At BT, 13(65%) patients had distal parametrial/pelvic wall infiltration. Median(range) number of needles per patient was 11(8-18). Average distribution of intrauterine, vaginal and interstitial dwell times were 31%, 25% and 44%, respectively. Median(range) dwell-time per dwell position was 11(2-127)% of average point-A based standard loading. Median V/V/V/V were 85(38; 171)/41(21; 93)/22(12; 41)/7(4; 19) cm; CTV D was 93(83; 97)Gy EQD2; bladder/rectum/sigmoid/bowel D were 78(64; 104)/65(52; 76)/59(53; 69)/61(47; 76)Gy EQD2.

Conclusions: The use of O-needles in patients with large and/or unfavorable tumors resulted in excellent target coverage and OARs sparing. Intrauterine and vaginal loadings were reduced compared to standard loading and almost half of the loading was shifted into IS needles. This was achieved with gentle loading in the majority of dwell positions.
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http://dx.doi.org/10.1016/j.brachy.2021.03.019DOI Listing
October 2021

Clinical outcome of interstitial pulsed dose rate brachytherapy in multimodality treatment of locally advanced primary or recurrent rectal and sigmoid cancer with high risk of incomplete microscopic resection.

Acta Oncol 2016 Dec 18;55(12):1408-1413. Epub 2016 Aug 18.

c Department of Oncology , Aarhus University Hospital , Aarhus , Denmark.

Objective: To evaluate the role of interstitial pulsed dose rate brachytherapy (PDR-BT) in multimodality treatment of locally advanced primary or recurrent rectal and sigmoid cancer with high risk of microscopic incomplete resection (R1).

Methods And Material: A total of 73 consecutive patients (recurrent/primary: 40/33) were treated with PDR-BT between 2001 and 2010. Patients received preoperative external beam radiotherapy (EBRT) and concomitant chemotherapy. Following resection of the tumor and the involved pelvic organs, a median of four (3-8) catheters were sutured to the tumor bed with a distance of approximately 1 cm between the catheters. A target respecting the catheters with a margin of 5 mm was contoured on computed tomography (CT) and three-dimensional (3D) dose planning with a planning aim for BT of D90 > 30 Gy, (0.6 Gy/pulse, 1 pulse/h) was performed. Previously irradiated patients (27%) underwent surgery that was directly followed by PDR-BT. Postoperative EBRT was then applied to the tumor bed 3-5 weeks after PDR-BT.

Results: A total of 23 patients (31%) received a radical resection (R0) and 45 patients (62%) received an R1 resection. Five patients (7%) received a macroscopic incomplete resection (R2). The five-year overall survival was 33%. Local control at five years was 67% for patients who received a R0 resection and 32% for patients who received an R1 resection. The five-year actuarial risk of a grade 3-4 BT-related complication was 5%.

Conclusions: Meaningful disease control and survival can be obtained at an acceptable rate of late morbidity in selected patients with locally advanced primary and recurrent rectal or sigmoid cancer using (chemo) RT, extensive surgery and PDR-BT when a high risk of an R1 resection is expected.
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http://dx.doi.org/10.1080/0284186X.2016.1213416DOI Listing
December 2016

Individualised 3D printed vaginal template for MRI guided brachytherapy in locally advanced cervical cancer.

Radiother Oncol 2016 Jan 29;118(1):173-5. Epub 2015 Dec 29.

Department of Oncology, Aarhus University Hospital, Denmark.

Intracavitary-interstitial applicators for MRI guided brachytherapy are becoming increasingly important in locally advanced cervical cancer. The 3D printing technology enables a versatile method for obtaining a high degree of individualisation of the implant. Our clinical workflow is presented and exemplified by a stage IVA cervical cancer with superior dose distribution.
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http://dx.doi.org/10.1016/j.radonc.2015.12.012DOI Listing
January 2016

MRI-guided adaptive radiotherapy in locally advanced cervical cancer from a Nordic perspective.

Acta Oncol 2013 Oct 21;52(7):1510-9. Epub 2013 Aug 21.

Department of Oncology, Aarhus University Hospital , Aarhus , Denmark.

Background: The first Nordic protocol for three-dimensional (3D) planned radiotherapy in locally advanced cervical cancer was the prospective NOCECA study (1994-2000). NOCECA consisted of computed tomography (CT)-based 3D conformal external beam radiotherapy (EBRT) with a simultaneous integrated boost (SIB) to the primary tumour combined with brachytherapy (BT) based on x-ray imaging. In NOCECA the planning aim was to achieve 80 Gy at point A from EBRT and BT combined. However, the balance of dose between EBRT and BT was determined by tumour size at diagnosis with more EBRT dose given to point A and less by BT in more advanced stages. In 2005 image-guided adaptive brachytherapy (IGABT) based on magnetic resonance imaging (MRI) and optimisation of the BT dose distribution to the remaining tumour and cervix at time of BT (HR CTV) was introduced in Aarhus. EBRT remained like in NOCECA until 2008 when the SIB to the primary tumour was abandoned and IMRT was introduced as routine technique. In this study, we report outcome of our first five-year experience with IGABT using our NOCECA cohort as reference.

Material And Methods: The NOCECA cohort comprising 99 patients was compared with 140 consecutive patients treated by IGABT. Patients with para-aortic nodes were excluded in NOCECA but were present in 9% of the patients treated with IGABT. No patient in NOCECA received chemotherapy whereas concomitant cisplatin was given to 79% of the IGABT patients.

Results: With IGABT actuarial local control was 91% at three years. When comparing NOCECA with IGABT overall survival was significantly improved from 63% to 79% (p = 0.005). In parallel, both moderate and severe late morbidity were reduced by about 50% (p = 0.02).

Conclusion: Introduction of IGABT reduced morbidity and generated a very high rate of local control, which likely has improved survival by at least as much as concomitant chemotherapy.
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http://dx.doi.org/10.3109/0284186X.2013.818253DOI Listing
October 2013

Simple DVH parameter addition as compared to deformable registration for bladder dose accumulation in cervix cancer brachytherapy.

Radiother Oncol 2013 Apr 13;107(1):52-7. Epub 2013 Mar 13.

Department of Medical Physics, Aarhus University Hospital, Denmark.

Background And Purpose: Variations in organ position, shape, and volume cause uncertainties in dose assessment for brachytherapy (BT) in cervix cancer. The purpose of this study was to evaluate uncertainties associated with bladder dose accumulation based on DVH parameter addition (previously called "the worst case assumption") in fractionated BT.

Materials And Methods: Forty-seven patients treated for locally advanced cervical cancer were included. All patients received EBRT combined with two individually planned 3D image-guided adaptive BT fractions. D(2cm(3)) and D(0.1cm(3)) were estimated by DVH parameter addition and compared to dose accumulations based on an in-house developed biomechanical deformable image registration (DIR) algorithm.

Results: DIR-based DVH analysis was possible in 42/47 patients. DVH parameter addition resulted in mean dose deviations relative to DIR of 0.4±0.3 Gy(αβ3) (1.5±1.8%) and 1.9±1.6 Gy(αβ3) (5.2±4.2%) for D(2cm(3)) and D(0.1cm(3)), respectively. Dose deviations greater than 5% occurred in 2% and 38% of the patients for D(2cm(3)) and D(0.1cm(3)), respectively. Visual inspection of the dose distributions showed that hotspots were located in the same region of the bladder during both BT fractions for the majority of patients.

Conclusion: DVH parameter addition provides a good estimate for D(2cm(3)), whereas D(0.1cm(3)) is less robust to this approximation.
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http://dx.doi.org/10.1016/j.radonc.2013.01.013DOI Listing
April 2013

Clinical feasibility of combined intracavitary/interstitial brachytherapy in locally advanced cervical cancer employing MRI with a tandem/ring applicator in situ and virtual preplanning of the interstitial component.

Radiother Oncol 2013 Apr 26;107(1):63-8. Epub 2013 Feb 26.

Department of Oncology, Aarhus University Hospital, Denmark.

Purpose: To investigate the reproducibility of virtually planned needles, changes in DVH parameters and clinical feasibility of combined intracavitary/interstitial (IC/IS) pulsed dose rate brachytherapy (PDR-BT) for locally advanced cervical cancer based on 3D MRI preplanning.

Material And Methods: Fifty-eight consecutively patients accrued in the EMBRACE study were included. Treatment was initiated with external beam radiotherapy and cisplatin. Three BT implants and MRI with the applicator in situ were performed in all patients, i.e. week 5 (BT0), week 6 (BT1) and week 7 (BT2) of the treatment. BT0 was only used for preplanning of subsequent implantations, whereas BT1 and BT2 comprised 2 equal sized fractions of PDR BT.

Results: Based on BT0, 24 patients (41%) were selected for a combined IC/IS implant at BT1 and BT2. Patients treated with IC/IS BT had significantly larger tumours compared with patients treated with IC BT only (p<0.03). Additional time in general anaesthesia for the IC/IS component was on average 16 min. The number of preplanned virtual needles was 5.3±2.7 compared to 5.3±2.9 and 5.4±3.0 needles implanted at BT1 and BT2, respectively (p=0.72). Planned needle implantation depth was 33±15 mm compared to 30±10 mm at BT1 and 29±11 mm at BT2 (p=0.04). In the 24 patients selected for IC/IS BT both the virtual IC/IS plan (BT0) and the actually delivered plan (BT1+BT2) significantly increased D90 and D100 for HR CTV (p<0.01) and reduced D2cc for sigmoid (p<0.01) and bowel (p=0.04) compared to the optimised IC preplan (BT0). IC/IS BT was only associated with minor morbidity, which was resolved at a 3-month follow up.

Conclusion: Combined IC/IS BT based on full 3D MRI preplanning is clinically feasible. The virtual preplanned needle positions are reproducible at subsequent BT applications leading to significantly improved DVH parameters and a clinically feasible and fast implant procedure.
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http://dx.doi.org/10.1016/j.radonc.2013.01.010DOI Listing
April 2013

Identifying afterloading PDR and HDR brachytherapy errors using real-time fiber-coupled Al(2)O(3):C dosimetry and a novel statistical error decision criterion.

Radiother Oncol 2011 Sep 29;100(3):456-62. Epub 2011 Sep 29.

Radiation Research Division, Technical University of Denmark, Roskilde, Denmark.

Background And Purpose: The feasibility of a real-time in vivo dosimeter to detect errors has previously been demonstrated. The purpose of this study was to: (1) quantify the sensitivity of the dosimeter to detect imposed treatment errors under well controlled and clinically relevant experimental conditions, and (2) test a new statistical error decision concept based on full uncertainty analysis.

Materials And Methods: Phantom studies of two gynecological cancer PDR and one prostate cancer HDR patient treatment plans were performed using tandem ring applicators or interstitial needles. Imposed treatment errors, including interchanged pairs of afterloader guide tubes and 2-20mm source displacements, were monitored using a real-time fiber-coupled carbon doped aluminum oxide (Al(2)O(3):C) crystal dosimeter that was positioned in the reconstructed tumor region. The error detection capacity was evaluated at three dose levels: dwell position, source channel, and fraction. The error criterion incorporated the correlated source position uncertainties and other sources of uncertainty, and it was applied both for the specific phantom patient plans and for a general case (source-detector distance 5-90 mm and position uncertainty 1-4mm).

Results: Out of 20 interchanged guide tube errors, time-resolved analysis identified 17 while fraction level analysis identified two. Channel and fraction level comparisons could leave 10mm dosimeter displacement errors unidentified. Dwell position dose rate comparisons correctly identified displacements ≥ 5mm.

Conclusion: This phantom study demonstrates that Al(2)O(3):C real-time dosimetry can identify applicator displacements ≥ 5mm and interchanged guide tube errors during PDR and HDR brachytherapy. The study demonstrates the shortcoming of a constant error criterion and the advantage of a statistical error criterion.
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http://dx.doi.org/10.1016/j.radonc.2011.09.009DOI Listing
September 2011

Image and laparoscopic guided interstitial brachytherapy for locally advanced primary or recurrent gynaecological cancer using the adaptive GEC ESTRO target concept.

Radiother Oncol 2011 Sep 15;100(3):473-9. Epub 2011 Sep 15.

Department of Oncology, Aarhus University Hospital, Denmark.

Purpose: To retrospectively assess treatment outcome of image and laparoscopic guided interstitial pulsed dose rate brachytherapy (PDR-BT) for locally advanced gynaecological cancer using the adaptive GEC ESTRO target concept.

Materials And Methods: Between June 2005 and December 2010, 28 consecutive patients were treated for locally advanced primary vaginal (nine), recurrent endometrial (12) or recurrent cervical cancer (seven) with combined external beam radiotherapy (EBRT) and interstitial PDR-BT. Treatment was initiated with whole pelvic EBRT to a median dose of 45 Gy followed by PDR-BT using the Martinez Universal Perineal Interstitial Template (MUPIT). All implants were virtually preplanned using MRI of the pelvis with a dummy MUPIT in situ. The GEC ESTRO high risk clinical target volume (HR CTV), intermediate risk clinical target volume (IR CTV) and the organs at risk (OAR) were contoured and a preplan for implantation was generated (BrachyVision, Varian). The subsequent implantation was performed under laparoscopic visualisation. Final contouring and treatment planning were done using a post-implant CT. Planning aim of PDR-BT was to deliver 30 Gy in 50 hourly pulses to HR CTV. Manual dose optimisation was performed with the aim of reaching a D90>80 Gy in the HR CTV calculated as the total biologically equivalent to 2 Gy fractions of EBRT and BT (EQD2). Dose to the OAR were evaluated using dose volume constraints for D(2cc) of 90 Gy for bladder and 70 Gy for rectum and sigmoid.

Results: For HR CTV the median volume was 26 cm(3) (7-91 cm(3)). Coverage of the HR CTV was 97% (90-100%) and D90 was 82 Gy (77-88 Gy). The D(2cc) for bladder, rectum, and sigmoid were 65 Gy (47-81 Gy), 61 Gy (50-77 Gy), and 52 Gy (44-68 Gy), respectively. Median follow up was 18 months (6-61 months). The actuarial 2 years local control rate was 92% (SE 5), while disease-free survival and overall survival were 59% (SE 11) and 74%, respectively (SE 10). No complications to the laparoscopic guided implantation were encountered. Late grade 2 (CTC v 3.0) complications were recorded in nine (32%) patients. One patient had a grade 3 vaginal complication. No grade 4-5 complications have been recorded so far.

Conclusion: Image and laparoscopic guided interstitial PDR-BT using the GEC ESTRO target concept is applicable for locally advanced primary vaginal or recurrent endometrial and cervical cancer resulting in an excellent local control rate and limited morbidity.
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http://dx.doi.org/10.1016/j.radonc.2011.08.016DOI Listing
September 2011

Parametrial boost using midline shielding results in an unpredictable dose to tumor and organs at risk in combined external beam radiotherapy and brachytherapy for locally advanced cervical cancer.

Int J Radiat Oncol Biol Phys 2011 Apr 26;79(5):1572-9. Epub 2010 Aug 26.

Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.

Purpose: Midline-blocked boost (MBB) fields are frequently used in the treatment of locally advanced cervical cancer. The purpose of this study was to evaluate the dose contribution from MBBs to tumor and organs at risk.

Methods And Materials: Six patients with locally advanced cervical cancer (IIB-IIIB) treated with definitive chemoradiotherapy and magnetic resonance imaging (MRI)-guided brachytherapy were analyzed. A three-phase plan was modeled: 45 Gy (1.8 Gy per fraction) four-field box, 9 Gy (1.8 Gy per fraction) MBB (midline-shielded anteroposterior/posteroanterior fields), and intracavitary MRI-guided brachytherapy boost of 28 Gy (7 Gy per fraction). Midline shields 3, 4, and 5 cm wide were simulated for each patient. Brachytherapy and MBB plans were volumetrically summed. The rectum, sigmoid, and bladder minimum dose in the most exposed 2 cm(3) of an organ at risk (D(2 cc)) and high-risk clinical target volume (HR-CTV) and intermediate-risk clinical target volume (IR-CTV) D90 and D100 were evaluated. The intended HR-CTV D90 was 85 Gy or greater, and the intended IR-CTV D90 was greater than 60 Gy.

Results: After a 4-cm MBB, HR-CTV D90 remained lower than 85 Gy in all cases (mean, 74 Gy; range, 64-82 Gy). High-risk clinical target volume (85 Gy) coverage increased slightly from 73% (range, 64-82%) to 78% (range, 69-88%). Mean IR-CTV D90 increased from 56 Gy (range, 53-64 Gy) to 62 Gy (range, 59-67 Gy). Intermediate-risk clinical target volume 60-Gy dose coverage increased from 81% (range, 72-96%) to 96% (range, 90-100%). The mean volume irradiated to 85 Gy increased by 14 cm(3) (range, 10-22 cm(3)), whereas the volume irradiated to 60 Gy increased from 276 cm(3) (range, 185-417 cm(3)) to 592 cm(3) (range, 385-807 cm(3)). Bladder, rectum, or sigmoid D(2 cc) increased by more than 50% of the boost dose in 4 of 6 patients.

Conclusions: Midline-blocked boosts contribute substantial dose to rectum, sigmoid, and bladder D(2 cc). HR-CTV dose and 85-Gy coverage remain compromised in large tumors despite MBB. IR-CTV 60-Gy coverage improved at the expense of a considerable increase in volume of normal tissue irradiated to 60 Gy.
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http://dx.doi.org/10.1016/j.ijrobp.2010.05.031DOI Listing
April 2011

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.

Radiother Oncol 2010 Feb;94(2):173-80

Department of Oncology, Aarhus University Hospital, Noerrebrogade, Aarhus, Denmark.

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 (<31 cc) 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 (>31 cc) the dose optimisation improved the HR-CTV D90 by a mean of 7 Gy 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.
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http://dx.doi.org/10.1016/j.radonc.2010.01.001DOI Listing
February 2010

Time-resolved in vivo luminescence dosimetry for online error detection in pulsed dose-rate brachytherapy.

Med Phys 2009 Nov;36(11):5033-43

Radiation Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark.

Purpose: The purpose of this study is to present and evaluate a dose-verification protocol for pulsed dose-rate (PDR) brachytherapy based on in vivo time-resolved (1 s time resolution) fiber-coupled luminescence dosimetry.

Methods: Five cervix cancer patients undergoing PDR brachytherapy (Varian GammaMed Plus with 192Ir) were monitored. The treatments comprised from 10 to 50 pulses (1 pulse/h) delivered by intracavitary/interstitial applicators (tandem-ring systems and/or needles). For each patient, one or two dosimetry probes were placed directly in or close to the tumor region using stainless steel or titanium needles. Each dosimeter probe consisted of a small aluminum oxide crystal attached to an optical fiber cable (1 mm outer diameter) that could guide radioluminescence (RL) and optically stimulated luminescence (OSL) from the crystal to special readout instrumentation. Positioning uncertainty and hypothetical dose-delivery errors (interchanged guide tubes or applicator movements from +/-5 to +/-15 mm) were simulated in software in order to assess the ability of the system to detect errors.

Results: For three of the patients, the authors found no significant differences (P>0.01) for comparisons between in vivo measurements and calculated reference values at the level of dose per dwell position, dose per applicator, or total dose per pulse. The standard deviations of the dose per pulse were less than 3%, indicating a stable dose delivery and a highly stable geometry of applicators and dosimeter probes during the treatments. For the two other patients, the authors noted significant deviations for three individual pulses and for one dosimeter probe. These deviations could have been due to applicator movement during the treatment and one incorrectly positioned dosimeter probe, respectively. Computer simulations showed that the likelihood of detecting a pair of interchanged guide tubes increased by a factor of 10 or more for the considered patients when going from integrating to time-resolved dose verification. The likelihood of detecting a +/-15 mm displacement error increased by a factor of 1.5 or more.

Conclusions: In vivo fiber-coupled RL/OSL dosimetry based on detectors placed in standard brachytherapy needles was demonstrated. The time-resolved dose-rate measurements were found to provide a good way to visualize the progression and stability of PDR brachytherapy dose delivery, and time-resolved dose-rate measurements provided an increased sensitivity for detection of dose-delivery errors compared with time-integrated dosimetry.
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http://dx.doi.org/10.1118/1.3238102DOI Listing
November 2009

Characterization of a fiber-coupled Al2O3:C luminescence dosimetry system for online in vivo dose verification during 192Ir brachytherapy.

Med Phys 2009 Mar;36(3):708-18

Department of Radiation Research, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark.

A prototype of a new dose-verification system has been developed to facilitate prevention and identification of dose delivery errors in remotely afterloaded brachytherapy. The system allows for automatic online in vivo dosimetry directly in the tumor region using small passive detector probes that fit into applicators such as standard needles or catheters. The system measures the absorbed dose rate (0.1 s time resolution) and total absorbed dose on the basis of radioluminescence (RL) and optically stimulated luminescence (OSL) from aluminum oxide crystals attached to optical fiber cables (1 mm outer diameter). The system was tested in the range from 0 to 4 Gy using a solid-water phantom, a Varian GammaMed Plus 192Ir PDR afterloader, and dosimetry probes inserted into stainless-steel brachytherapy needles. The calibrated system was found to be linear in the tested dose range. The reproducibility (one standard deviation) for RL and OSL measurements was 1.3%. The measured depth-dose profiles agreed well with the theoretical expectations computed with the EGSNRC Monte Carlo code, suggesting that the energy dependence for the dosimeter probes (relative to water) is less than 6% for source-to-probe distances in the range of 2-50 mm. Under certain conditions, the RL signal could be greatly disturbed by the so-called stem signal (i.e., unwanted light generated in the fiber cable upon irradiation). The OSL signal is not subject to this source of error. The tested system appears to be adequate for in vivo brachytherapy dosimetry.
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http://dx.doi.org/10.1118/1.3063006DOI Listing
March 2009

Applicator reconstruction in MRI 3D image-based dose planning of brachytherapy for cervical cancer.

Radiother Oncol 2009 May 30;91(2):187-93. Epub 2008 Oct 30.

Department of Biomedical Engineering, Aarhus University Hospital, Aarhus, Denmark.

Background And Purpose: To elaborate a method for applicator reconstruction for MRI-based brachytherapy for cervical cancer.

Materials And Methods: Custom-made plastic catheters with a copper sulphate solution were made for insertion in the source channels of MR-CT compatible applicators: plastic and titanium tandem ring applicators, and titanium needles. The applicators were CT and MR scanned in a phantom for accurate 3D assessment of applicator visibility and geometry. A reconstruction method was developed and evaluated in 19 patient MR examinations with ring applicator (plastic: 14, titanium: 5). MR applicator reconstruction uncertainties related to inter-observer variation were evaluated.

Results: The catheters were visible in the plastic applicator on T1-weighted images in phantom and in 14/14 clinical applications. On T2-weighted images, the catheters appeared weaker but still visible in phantom and in 13/14 MR clinical applications. In the titanium applicator, the catheters could not be separated from the artifacts from the applicator itself. However, these artifacts could be used to localize both titanium ring applicator (5/5 clinical applications) and needles (6/6 clinical applications). Standard deviations of inter-observer differences were below 2 mm in all directions.

Conclusion: 3D applicator reconstruction based on MR imaging could be performed for plastic and titanium applicators. Plastic applicators proved well to be suited for MRI-based reconstruction. For improved practicability of titanium applicator reconstruction, development of MR applicator markers is essential. Reconstruction of titanium applicator and needles at 1.5 T MR requires geometric evaluations in phantoms before using the applicator in patients.
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http://dx.doi.org/10.1016/j.radonc.2008.09.002DOI Listing
May 2009

MRI-guided 3D optimization significantly improves DVH parameters of pulsed-dose-rate brachytherapy in locally advanced cervical cancer.

Int J Radiat Oncol Biol Phys 2008 Jul 11;71(3):756-64. Epub 2008 Jan 11.

Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.

Purpose: To compare dose-volume histogram parameters of standard Point A and magnetic resonance imaging-based three-dimensional optimized dose plans in 21 consecutive patients who underwent pulsed-dose-rate brachytherapy (PDR-BT) for locally advanced cervical cancer.

Methods And Materials: All patients received external beam radiotherapy (elective target dose, 45 Gy in 25-30 fractions; tumor target dose, 50-60 Gy in 25-30 fractions). PDR-BT was applied with a tandem-ring applicator. Additional ring-guided titanium needles were used in 4 patients and a multichannel vaginal cylinder in 2 patients. Dose planning was done using 1.5 Tesla T(1)-weighted and T(2)-weighted paratransversal magnetic resonance imaging scans. T(1)-weighted visible oil-containing tubes were used for applicator reconstruction. The prescribed standard dose for PDR-BT was 10 Gy (1 Gy/pulse, 1 pulse/h) for two to three fractions to reach a physical dose of 80 Gy to Point A. The total dose (external beam radiotherapy plus brachytherapy) was normalized to an equivalent dose in 2-Gy fractions using alpha/beta = 10 Gy for tumor, alpha/beta = 3 Gy for normal tissue, and a repair half-time of 1.5 h. The goal of optimization was dose received by 90% of the target volume (D(90)) of > or =85 Gy(alpha/beta10) in the high-risk clinical target volume (cervix and remaining tumor at brachytherapy), but keeping the minimal dose to 2 cm(3) of the bladder and rectum/sigmoid at <90 and <75 Gy(alpha/beta3), respectively.

Results: Using three-dimensional optimization, all dose-volume histogram constraints were met in 16 of 21 patients compared with 3 of 21 patients with two-dimensional library plans (p < 0.001). Optimization increased the minimal target dose (D(100)) of the high-risk clinical target volume (p < 0.007) and decreased the minimal dose to 2 cm(3) for the sigmoid significantly (p = 0.03). For the high-risk clinical target volume, D(90) was 91 +/- 8 Gy(alpha/beta10) and D(100) was 76 +/- 5 Gy(alpha/beta10). The minimal dose to 2 cm(3) for the bladder, rectum, and sigmoid was 73 +/- 6, 67 +/- 6, and 69 +/- 6 Gy(alpha/beta3), respectively.

Conclusion: The results of our study have shown that magnetic resonance imaging-guided optimization of PDR-BT for locally advanced cervical cancer significantly improved the dose-volume histogram parameters.
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http://dx.doi.org/10.1016/j.ijrobp.2007.10.032DOI Listing
July 2008

Dose optimisation in single plane interstitial brachytherapy.

Radiother Oncol 2006 Oct 26;81(1):105-11. Epub 2006 Sep 26.

Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.

Background And Purpose: Brachytherapy dose distributions can be optimised by modulation of source dwell times. In this study dose optimisation in single planar interstitial implants was evaluated in order to quantify the potential benefit in patients.

Material And Methods: In 14 patients, treated for recurrent rectal and cervical cancer, flexible catheters were sutured intra-operatively to the tumour bed in areas with compromised surgical margin. Both non-optimised, geometrically and graphically optimised CT -based dose plans were made. The overdose index (OI), homogeneity index (HI), conformal index (COIN), minimum target dose, and high dose volumes were evaluated. The dependence of OI, HI, and COIN on target volume and implant regularity was evaluated. In addition, 12 theoretical implant configurations were analyzed.

Results: Geometrical and graphical optimisation improved the dose plans significantly with graphical optimisation being superior. Graphically optimised dose plans showed a significant decrease of 18%+/-9% in high dose volume (p<0.001). HI, COIN, and OI were significantly improved from 0.50+/-0.05 to 0.60+/-0.05, from 0.65+/-0.04 to 0.71+/-0.04, and from 0.19+/-0.03 to 0.15+/-0.03, respectively (p<0.001 for all). Moreover, minimum target dose increased significantly from 71%+/-5% to 80%+/-5% (p<0.001). The improvement in OI and HI obtained by optimisation depended on the regularity of the implant, such that the benefit of optimisation was larger for irregular implants. OI and HI correlated strongly with target volume limiting the usability of these parameters for comparison of dose plans between patients.

Conclusions: Dwell time optimisation significantly improved the dose distribution regarding homogeneity, conformity, minimum target dose, and size of high dose volumes. Graphical optimisation is fast, reproducible and superior to geometric optimisation.
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http://dx.doi.org/10.1016/j.radonc.2006.08.021DOI Listing
October 2006
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