Ultrasound-guided intraoperative electron beam radiation therapy: A phantom study

PurposeTo develop the method for ultrasound (US)-guided intra-operative electron beam radiation therapy (IOERT).MethodsWe first established the simulation, planning, and delivery methods for US-guided IOERT and constructed appropriate hardware (the multi-function applicator, accessories, and US phantom). We tested our US-guided IOERT method using this hardware and the Monte Carlo simulation IOERT treatment planning system (TPS). The IOERT TPS used a compensator to build the conformal dose distribution. Then, we used the TPS to evaluate the effect of setup uncertainty on target coverage by introducing phantom setup error ranging from 0 mm to 10 mm to the plans with and without the compensator.ResultsThe simulation, planning, and delivery methods for US-guided IOERT were introduced and validated on a phantom. A complete technique for US-guided IOERT was established. Target coverage decreased by about 12% and 29% as the phantom setup error increased to 5 mm and 10 mm for the plans with compensator, respectively. Without compensator, the corresponding target coverage decreases were 2% and 13%, respectively.ConclusionIn our study, we developed the multi-function applicator, US Phantom, and TPS for IOERT. The procedures included not only dose distribution planning, but also intraoperative US imaging, which provided the information necessary during surgery to improve IOERT quality assurance. Target coverage was more sensitive to setup errors with compensator compared to no compensator. Further studies are needed to validate the clinical efficacy of this US-guided IOERT method.     

Assessment of clinically relevant dose distributions in pelvic IOERT using Gafchromic EBT3 films

PurposeIn IOERT a single dose of radiation is delivered to the tumour site during surgery. Manual dose calculations are used and the irradiation target volume, electron energy and applicator are decided on site by the radiation oncologist. This work assesses the effect that irregular and curved surfaces, typical of pelvic IOERT, may have on the expected dose distribution.MethodsThe feasibility of using Gafchromic EBT3 films and a slab phantom to obtain 2D dose distributions was investigated. Different set-ups were tested by comparison with water tank measurements, applying the gamma function analysis with 2% and 2 mm criteria. The validated set-up was then used to obtain reference dose distributions, which were converted to colour-coded graphical representations. Phantoms with step-like and curved surfaces were created to simulate typical pelvic IOERT irradiation surfaces, and the dose distributions were obtained and compared with the reference distributions.ResultsGood agreement with water tank measurements was obtained for all applicators below 2 mm, using the chosen setup in reference conditions. In non-reference conditions, the presence of a step-like surface creates an adjacent hotspot, followed by a quick reduction of the dose in depth. With curved surfaces, the dose distribution is shifted forward, becoming curved and deeper, but when the applicator is larger than the hole, hotspots are also observed.ConclusionsThe shape of the irradiation surfaces alters the dose distribution. Visualization of these effects is important to assess target coverage and interpret in vivo measurements in pelvic IOERT.     

Dosimetric evaluation of Gafchromic EBT2 film for breast intraoperative electron radiotherapy verification

PurposeQuality assurance (QA) is one of the most important issues that should be addressed for intraoperative electron radiotherapy (IOERT), which is not benefiting from image-based treatment planning system. The aim of this study is to evaluate the dosimetric characteristics of Gafchromic EBT2 film for breast IOERT QA procedure.MethodsDue to the fact that some dedicated accelerators are being used for IOERT, dependence of the film response to energy, field size, dose rate and incidence angle of electron beam from the LIAC IOERT accelerator was studied. Then, film response curve to breast IOERT doses was obtained and its accuracy was evaluated and justified through comparison to the results of ionometric dosimetry.ResultsThe results of this study indicated that there are no significant differences between the film responses at different energies of 6, 8, 10 and 12 MeV (P-value = 0.99). Similarly, no field size dependency was found when evaluating the response of the film to different field sizes ranging from 4 to 10 cm (P-value = 0.94). Film response was found to be independent of the dose rate of intraoperative electron beam (P-value = 0.12). Film response variations with changing the beam incidence angle were not significant (P-value > 0.8). Calibration curve at the dose range of 8–24 Gy had an acceptable accuracy. The difference between the results of film dosimetry and ionometric dosimetry was around 5% which was in agreement with the results of dose uncertainty estimation.ConclusionThe EBT2 film was found to be a potentially appropriate tool for breast IOERT verification.     

Shielding disk position in intra-operative electron radiotherapy (IOERT): A Monte Carlo study

PurposeIn IOERT breast treatments, a shielding disk is frequently used to protect the underlying healthy structures. The disk is usually composed of two materials, a low-Z material intended to be oriented towards the beam and a high-Z material. As tissues are repositioned around the shield before treatment, the disk is no longer visible and its correct alignment with respect to the beam is guaranteed. This paper studies the dosimetric characteristics of four possible clinical positioning scenarios of the shielding disk. A new alignment method for the shielding disk in the beam is introduced. Finally, it suggests a new design for the shielding disk.MethodsAs the first step, the IOERT machine “Mobetron 1000” was modeled by using Monte Carlo simulation, tuning the MC model until an excellent match with the measured PDDs and profiles was achieved. Four possible shielding disk positioning scenarios were considered, determining the dosimetric impact. Furthermore, in our center, to prevent beam misalignment, we have developed a shielding disk equipped with guiding rods. Having ascertained a correct alignment between the disk and the beam, we can propose a new internal design of the shielding disk that can improve the dose distribution with a better coverage of the treated area.ResultsAll MC simulations were performed with a 12 MeV beam, the maximum energy of Mobetron 1000 and a 5.5 cm diameter flat tip applicator, this applicator being the most clinically used. The simulations were compared with measurements performed in a water phantom and showed good results within 2.2% of root mean square difference (RMSD). The misplacement positions of the shielding disk have dosimetric impacts in the treatment volume and a small translation could have a significant influence on healthy tissues. The D-scenario is the worst which could happens when the shielding disk is flipped upside down, giving up to 144% dose instead of 90% at the surface of the Pb/Al shielding disk. A new shielding design used, together with our alignment tool, is able to give a more homogeneous dose in the target area.ConclusionsThe accuracy of shielding disk position can still be problematic in IOERT dosimetry. Any method that can ascertain the good alignment between the shielding disk and the beam is beneficial for the dose distribution and is a prerequisite for an optimized shield internal design that could improve the coverage of the treated area and the protection of healthy tissues.     

Electron radiotherapy (IOERT) for applications outside of the breast: Dosimetry and influence of tissue inhomogeneities

PurposeThe purpose of study is to investigate the dosimetry of electron intraoperative radiotherapy (IOERT) of the Intraop Mobetron 2000 mobile LINAC in treatments outside of the breast. After commissioning and external validation of dosimetry, we report in vivo results of measurements for treatments outside the breast in a large patient cohort, and investigate if the presence of inhomogeneities can affect in vivo measurements.Methods and materialsApplicator factors and profile curves were measured with a stereotactic diode. The applicators factors of the 6 cm flat and beveled applicators were also confirmed with radiochromic films, parallel-plate ion chamber and by an external audit performed with ThermoLuminescent Dosimeters (TLDs). The influence of bone on dose was investigated by using radiochromic films attached to an insert equivalent to cortical bone, immersed in the water phantom. In vivo dosimetry was performed on 126 patients treated with IOERT using metal oxide-silicon semiconductor field effect transistors (MOSFETs) placed on the tumor bed.ResultsRelatively small differences were found among different detectors for measurements of applicator factors. In the external audit, the agreement with the TLD was mostly within ±0.2%. The largest increase of dose due to the presence of cortical bone insert was +6.0% with energy 12 MeV and 3 cm applicator. On average, in vivo dose was significantly (+3.1%) larger than prescribed dose.ConclusionIOERT in applications outside the breast results in low discrepancies between in vivo and prescribed doses, which can be also explained with the presence of tissue inhomogeneity.     

Preliminary clinical outcomes of patients treated with vaginal brachytherapy alone using multi-channel vaginal brachytherapy applicator in operated early-stage endometrial cancer

BackgroundRecommendations for adjuvant treatment for postoperative, early-stage endometrial cancer varies from observation through vaginal brachytherapy alone to pelvic radiation. While observation alone can lead to recurrence, external radiotherapy has increased morbidity. The aim of this study is to show our results with vaginal brachytherapy alone using a multichannel applicator for treatment of early-stage endometrial cancer.Materials and methodsConsecutive patients undergoing vaginal brachytherapy alone following surgery for early-stage endometrial cancer were examined. A Miami multichannel vaginal brachytherapy applicator was used to deliver HDR brachytherapy in 62 patients from May 2013 to June 2018. CT scan-based images guided planning. A dose of 5.5–6.5 Gy × 4 fractions was prescribed 5 mm from the surface of the applicator.ResultsAt a median follow up of 19 months (6–48 months), 93% of patients treated were alive with no recurrence. Two patients had only local recurrence, and 1 was salvaged with external radiotherapy and chemotherapy. There was only one nodal failure and 2 distant failures. There was no grade 2 or higher vaginal, gastrointestinal or genitourinary toxicity.ConclusionVaginal brachytherapy alone using a multichannel applicator can be considered for early-stage endometrial cancers without compromising outcomes.     

Optimizing MRI sequences and images for MRI-based stereotactic radiosurgery treatment planning

AimDevelopment of MRI sequences and processing methods for the production of images appropriate for direct use in stereotactic radiosurgery (SRS) treatment planning.BackgroundMRI is useful in SRS treatment planning, especially for patients with brain lesions or anatomical targets that are poorly distinguished by CT, but its use requires further refinement. This methodology seeks to optimize MRI sequences to generate distortion-free and clinically relevant MR images for MRI-only SRS treatment planning.Materials and methodsWe used commercially available SRS MRI-guided radiotherapy phantoms and eight patients to optimize sequences for patient imaging. Workflow involved the choice of correct MRI sequence(s), optimization of the sequence parameters, evaluation of image quality (artifact free and clinically relevant), measurement of geometrical distortion, and evaluation of the accuracy of our offline correction algorithm.ResultsCT images showed a maximum deviation of 1.3 mm and minimum deviation of 0.4 mm from true fiducial position for SRS coordinate definition. Interestingly, uncorrected MR images showed maximum deviation of 1.2 mm and minimum of 0.4 mm, comparable to CT images used for SRS coordinate definition. After geometrical correction, we observed a maximum deviation of 1.1 mm and minimum deviation of only 0.3 mm.ConclusionOur optimized MRI pulse sequences and image correction technique show promising results; MR images produced under these conditions are appropriate for direct use in SRS treatment planning.     

Evaluation of a commercial automatic treatment planning system for liver stereotactic body radiation therapy treatments

PurposeAutomated treatment planning is a new frontier in radiotherapy. The Auto-Planning module of the Pinnacle³ treatment planning system (TPS) was evaluated for liver stereotactic body radiation therapy treatments.MethodsTen cases were included in the study. Six plans were generated for each case by four medical physics experts. The first two planned with Pinnacle TPS, both with manual module (MP) and Auto-Planning one (AP). The other two physicists generated two plans with Monaco TPS (VM). Treatment plan comparisons were then carried on the various dosimetric parameters of target and organs at risk, monitor units, number of segments, plan complexity metrics and human resource planning time. The user dependency of Auto-Planning was also tested and the plans were evaluated by a trained physician.ResultsStatistically significant differences (Anova test) were observed for spinal cord doses, plan average beam irregularity, number of segments, monitor units and human planning time. The Fisher-Hayter test applied to these parameters showed significant statistical differences between AP e MP for spinal cord doses and human planning time; between MP and VM for monitor units, number of segments and plan irregularity; for all those between AP and VM. The two plans created by different planners with AP were similar to each other.ConclusionsThe plans created with Auto-Planning were comparable to the manually generated plans. The time saved in planning enables the planner to commit more resources to more complex cases. The independence of the planner enables to standardize plan quality.     

Treatment planning systems dosimetry auditing project in Portugal

Background and purposeThe Medical Physics Division of the Portuguese Physics Society (DFM_SPF) in collaboration with the IAEA, carried out a national auditing project in radiotherapy, between September 2011 and April 2012. The objective of this audit was to ensure the optimal usage of treatment planning systems. The national results are presented in this paper.Material and methodsThe audit methodology simulated all steps of external beam radiotherapy workflow, from image acquisition to treatment planning and dose delivery. A thorax CIRS phantom lend by IAEA was used in 8 planning test-cases for photon beams corresponding to 15 measuring points (33 point dose results, including individual fields in multi-field test cases and 5 sum results) in different phantom materials covering a set of typical clinical delivery techniques in 3D Conformal Radiotherapy.ResultsAll 24 radiotherapy centers in Portugal have participated. 50 photon beams with energies 4–18 MV have been audited using 25 linear accelerators and 32 calculation algorithms.In general a very good consistency was observed for the same type of algorithm in all centres and for each beam quality.ConclusionsThe overall results confirmed that the national status of TPS calculations and dose delivery for 3D conformal radiotherapy is generally acceptable with no major causes for concern. This project contributed to the strengthening of the cooperation between the centres and professionals, paving the way to further national collaborations.     

Determination of an inflection point for a dosimetric analysis of unflattened beam using the first principle of derivatives by python code programming

BackgroundPractice of Unflattened or Flattening filter free (FFF) beam has become the high dose standard in radiotherapy (RT), such as stereotactic radio-surgery (SRS) and stereotactic radiotherapy (SRT). The removal of a flattening filter (FF) from the path of a photon beam alters the characteristics of FFF beam. Since the conventional route for dosimetric analysis of FF beam cannot be applied to FFF beam, the procedure of analyzing beam characteristics for FFF beam based on inflection points (IPs) is used. IP is a point where the concavity change observed corresponds to its change in sign (±) of the second derivative.AimThe objective of the study is to determine IPs for dosimetric analysis of the FFF beam profile.Methods and materialsIn this study, IPs are determined through the python code programming based on the mathematical first principle of the derivative. They are compared with IPs estimated by the conventional graphical manual method using Microsoft Excel (MS). IPs and their dependent dosimetric parameters determined by both mathematical and graphical manual methods are compared.ResultPercentage differences between the IPs determined by both methods, for 6MVFFF inline and crossline beam profile are found to be 2.7% and 0.8% respectively. Similarly, the average penumbra differences for 6MVFFF inline and crossline beam profile are found to be 0.15 mm and 0.9 mm, respectively. However, differences in the field width between both methods are found insignificant.ConclusionGraphical manual method is very time-consuming, tedious and user dependent. However, the mathematical method through python code programming is more precise, faster and independent of individual users.     

Phantom development for daily checks in electron intraoperative radiotherapy with a mobile linac

PurposeIORT with mobile linear accelerators is a well-established modality where the dose rate and, therefore, the dose per pulse are very high. The constancy of the dosimetric parameters of the accelerator has to be checked daily. The aim of this work is to develop a phantom with embedded detectors to improve both accuracy and efficiency in the daily test of an IORT linac at the surgery room.MethodsThe developed phantom is manufactured with transparent polymethyl methacrylate (PMMA), allocating 6 parallel-plate chambers: a central one to evaluate the on-axis beam output, another on-axis one placed at a fixed depth under the previous one to evaluate the energy constancy and four off-axis chambers to evaluate the flatness and symmetry. To analyse the readings a specific application has been developed.ResultsFor all chambers and energies, the mean saturation and polarization corrections were smaller than 0.7%. The beam is monitored at different levels of the clinical beam. Output, energy constancy and flatness correlate very well with the correspondent values with the complete applicator. During the first six months of clinical use the beam dosimetric parameters showed excellent stability.ConclusionsA phantom has been developed with embedded parallel plate chambers attached to the upper applicator part of an IORT linac. The phantom allows a very efficient setup reducing the time to check the parameters. It provides complete dosimetric information (output, energy and flatness) with just one shot and using ionization chambers with minimum saturation effect, as this highly pulsed beam requires.     

Evaluation of LiF:Mg,Ti (TLD-100) for Intraoperative Electron Radiation Therapy Quality Assurance

Background

Purpose of the present work was to investigate thermoluminescent dosimeters (TLDs) response to intraoperative electron radiation therapy (IOERT) beams. In an IOERT treatment, a large single radiation dose is delivered with a high dose-per-pulse electron beam (2–12 cGy/pulse) during surgery. To verify and to record the delivered dose, in vivo dosimetry is a mandatory procedure for quality assurance. The TLDs feature many advantages such as a small detector size and close tissue equivalence that make them attractive for IOERT as in vivo dosimeters.

Methods

LiF:Mg,Ti dosimeters (TLD-100) were irradiated with different IOERT electron beam energies (5, 7 and 9 MeV) and with a 6 MV conventional photon beam. For each energy, the TLDs were irradiated in the dose range of 0–10 Gy in step of 2Gy. Regression analysis was performed to establish the response variation of thermoluminescent signals with dose and energy.

Results

The TLD-100 dose-response curves were obtained. In the dose range of 0–10 Gy, the calibration curve was confirmed to be linear for the conventional photon beam. In the same dose region, the quadratic model performs better than the linear model when high dose-per-pulse electron beams were used (F test; p<0.05).

Conclusions

This study demonstrates that the TLD dose response, for doses ≤10Gy, has a parabolic behavior in high dose-per-pulse electron beams. TLD-100 can be useful detectors for IOERT patient dosimetry if a proper calibration is provided.     

Effects of shielding on pelvic and abdominal IORT dose distributions

PurposeTo study the impact of shielding elements in the proximity of Intra-Operative Radiation Therapy (IORT) irradiation fields, and to generate graphical and quantitative information to assist radiation oncologists in the design of optimal shielding during pelvic and abdominal IORT.MethodAn IORT system was modeled with BEAMnrc and EGS++ Monte Carlo codes. The model was validated in reference conditions by gamma index analysis against an experimental data set of different beam energies, applicator diameters, and bevel angles. The reliability of the IORT model was further tested considering shielding layers inserted in the radiation beam. Further simulations were performed introducing a bone-like layer embedded in the water phantom. The dose distributions were calculated as 3D dose maps.ResultsThe analysis of the resulting 2D dose maps parallel to the clinical axis shows that the bevel angle of the applicator and its position relative to the shielding have a major influence on the dose distribution. When insufficient shielding is used, a hotspot nearby the shield appears near the surface. At greater depths, lateral scatter limits the dose reduction attainable with shielding, although the presence of bone-like structures in the phantom reduces the impact of this effect.ConclusionsDose distributions in shielded IORT procedures are affected by distinct contributions when considering the regions near the shielding and deeper in tissue: insufficient shielding may lead to residual dose and hotspots, and the scattering effects may enlarge the beam in depth. These effects must be carefully considered when planning an IORT treatment with shielding.     

Automatic VMAT technique to treat glioblastoma: A two years’ experience

PurposeThe present work aims to guide the physicist in order to start automated planning for the VMAT treatment of glioblastoma multiforme (GBM) by giving a recipe that was set up and tested during a long-term (two years) evaluation.MethodsAn automatic technique in AutoPlanning module of the Pinnacle3 (Philips Medical Systems, Fitchburg, WI) treatment planning system was created and validated by comparing dose distributions of automatic plans (APs) and manual plans (MPs) and by performing a blind AP-MP comparison on a cohort of 20 patients. Automatic technique was then applied to 145 patients and failures were recorded i.e. the number of times for which dose distributions produced by the automatic module were not suitable for treatment.ResultsEach of the 20 APs considered in the validation step was clinically acceptable and proved to be better (15 cases) or equal (5 cases) respect to MPs. A statistically significant improvement in brain stem, optic pathways, cochleae, pituitary gland and scalp sparing was observed for APs, while no statistically significant differences were recorded in target coverage or plan parameters. For only 5 cases out of the 145 plans the operator intervention was needed in order to obtain a clinical acceptable plan, while for the remaining 140 plans the automatic created solution was suitable.ConclusionsA straightforward automatic procedure has been created and tested in our clinic. The AutoPlanning technique proposed represents a reliable tool to improve treatment planning efficiency and the recipe, here presented, could be simply imported to every radiotherapy center.     

Assessing the need for adaptive radiotherapy in head and neck cancer patients using an automatic planning tool

BackgroundUnbiased analysis of the impact of adaptive radiotherapy (ART) is necessary to evaluate dosimetric benefit and optimize clinics’ workflows. The aim of the study was to assess the need for adaptive radiotherapy (ART) in head and neck (H&N) cancer patients using an automatic planning tool in a retrospective planning study.Materials and methodsThirty H&N patients treated with adaptive radiotherapy were analysed. Patients had a CT scan for treatment planning and a verification CT during treatment according to the clinic’s protocol. Considering these images, three plans were retrospectively generated using the iCycle tool to simulate the scenarios with and without adaptation: 1) the optimized plan based on the planning CT; 2) the optimized plan based on the verification CT (ART-plan); 3) the plan obtained by considering treatment plan 1 re-calculated in the verification CT (non-ART plan). The dosimetric endpoints for both target volumes and OAR were compared between scenarios 2 and 3 and the SPIDERplan used to evaluate plan quality.ResultsThe most significant impact of ART was found for the PTVs, which demonstrated decreased D98% in the non-ART plan. A general increase in the dose was observed for the OAR but only the spinal cord showed a statistical significance. The SPIDERplan analysis indicated an overall loss of plan quality in the absence of ART.ConclusionThese results confirm the advantages of ART in H&N patients, especially for the coverage of target volumes. The usage of an automatic planning tool reduces planner-induced bias in the results, guaranteeing that the observed changes derive from the application of ART.     

Influence of different Fletcher–Suit applicator geometries on sagittal dose distribution

IntroductionOne of the brachytherapy treatment modality of cervix carcinomas is insertion with Fletcher–Suit (FS) applicator. Depending on the patient anatomy and pathology and on the construction of the FS applicator different geometrical arrangements in ovoid separation, in ovoids' sagittal level with respect to the tandem were experienced. The multiple insertions show minor differences in applicator geometries. The aim of the study is to evaluate the influence of main geometrical parameters: the ovoid separation, symmetry and the ovoids' sagittal shift on dose distribution in different FS applicator arrangements. We tested the effect of dwell time settings in improvement of dose distribution of less adequate insertions. We also investigated the effect of inter-fractional variation of applicator geometry.Materials and methodsWe considered 73 treatment fractions of 22 patients. All insertions were performed by the same gynaecologist with the same type of FS applicator, while the treatment plans were generated by the same physicist using the same treatment planning method. We compared the sagittal dose distribution of different FS applicator geometries with dose levels at two applicator points, defined 2 cm apart from the tandem towards the bladder and rectum. We computed the Pearson correlation coefficients between the dose levels at the applicator points and the ovoid separation, symmetry and the ovoids' sagittal shift. We also investigated the effect of dwell time settings in ovoids in order to decrease the dose to organs at risk. The inter-fractional variation of the FS applicator geometries and the influence on the dose levels at the two applicator points were also tested.Results and conclusionsStrong correlation was found between the ovoid separation and dose values to applicator points defined in sagittal direction of FS applicator arrangements. Also strong correlation was between the ovoids' sagittal position with respect to the tandem and the applicator point defined towards the rectum, while the ovoid symmetry had no influence on the sagittal dose distribution. The standard deviations of inter-fractional variation of the ovoid separation and the ovoids' sagittal position were within ±5.2 mm and ±10.2 mm respectively. The inter-fractional variations in FS applicator geometry resulted in variation in dose levels at the applicator points ±0.8 Gy typically, while the largest value was ±1.6 Gy.     

Geometric inaccuracy and co-registration errors for CT,DynaCT and MRI images used in robotic stereotactic radiosurgery treatment planning

PurposeTo measure the combined errors due to geometric inaccuracy and image co-registration on secondary images (dynamic CT angiography (dCTA), 3D DynaCT angiography (DynaCTA), and magnetic resonance images (MRI)) that are routinely used to aid in target delineation and planning for stereotactic radiosurgery (SRS).MethodsThree phantoms (one commercial and two in-house built) and two different analysis approaches (commercial and MATLAB based) were used to quantify the magnitude of geometric image distortion and co-registration errors for different imaging modalities within CyberKnife’s MultiPlan treatment planning software. For each phantom, the combined errors were reported as a mean target registration error (TRE). The mean TRE’s for different intramodality imaging parameters (e.g., mAs, kVp, and phantom set-ups) and for dCTA, DynaCTA, and MRI systems were measured.ResultsOnly X-ray based imaging can be performed with the commercial phantom, and the mean TRE ± standard deviation values were large compared to the in-house analysis using MATLAB. With the 3D printed phantom, even drastic changes in treatment planning CT imaging protocols did not greatly influence the mean TRE (<0.5 mm for a 1 mm slice thickness CT). For all imaging modalities, the largest mean TRE was found on DynaCT, followed by T2-weighted MR images (albeit all <1 mm).ConclusionsThe user may overestimate the mean TRE if the commercial phantom and MultiPlan were used solely. The 3D printed phantom design is a sensitive and suitable quality assurance tool for measuring 3D geometric inaccuracy and co-registration errors across all imaging modalities.     

Precision IORT – Image guided intraoperative radiation therapy (igIORT) using online treatment planning including tissue heterogeneity correction

BackgroundTo the present date, IORT has been eye and hand guided without treatment planning and tissue heterogeneity correction. This limits the precision of the application and the precise documentation of the location and the deposited dose in the tissue. Here we present a set-up where we use image guidance by intraoperative cone beam computed tomography (CBCT) for precise online Monte Carlo treatment planning including tissue heterogeneity correction.Materials and methodsAn IORT was performed during balloon kyphoplasty using a dedicated Needle Applicator. An intraoperative CBCT was registered with a pre-op CT. Treatment planning was performed in Radiance using a hybrid Monte Carlo algorithm simulating dose in homogeneous (MCwater) and heterogeneous medium (MChet). Dose distributions on CBCT and pre-op CT were compared with each other. Spinal cord and the metastasis doses were evaluated.ResultsThe MCwater calculations showed a spherical dose distribution as expected. The minimum target dose for the MChet simulations on pre-op CT was increased by 40% while the maximum spinal cord dose was decreased by 35%. Due to the artefacts on the CBCT the comparison between MChet simulations on CBCT and pre-op CT showed differences up to 50% in dose.ConclusionsigIORT and online treatment planning improves the accuracy of IORT. However, the current set-up is limited by CT artefacts. Fusing an intraoperative CBCT with a pre-op CT allows the combination of an accurate dose calculation with the knowledge of the correct source/applicator position. This method can be also used for pre-operative treatment planning followed by image guided surgery.     

Comparison of manual and inverse optimisation techniques in high dose rate intracavitary brachytherapy of cervical cancer: A dosimetric study

Aims and objectivesTo compare dosimetrically the manual optimisation with IPSA using dose volume histograms (DVH) among patients treated for carcinoma of cervix with intracavitary brachytherapy.BackgroundWith the advent of advanced imaging modalities, there has been a shift from conventional X-ray based planning to three-dimensional planning. Manual optimisation is widely used across various institutions but it is time consuming and operator dependant. Inverse planning simulated annealing (IPSA) is now available in various brachytherapy planning systems. But there is a paucity of studies comparing manual optimisation and IPSA in treatment of carcinoma cervix with intracavitary brachytherapy and hence this study.Materials and methodsFifteen consecutive patients treated between December 2013 and March 2014 with intracavitary brachytherapy for carcinoma of cervix were selected for this study. All patients were initially treated with external beam radiotherapy followed by intracavitary brachytherapy. The DVH was evaluated and compared between manually optimised plans and IPSA in the same set of patients.ResultsThere was a significant improvement in the HRCTV coverage, mean V100 of 87.75% and 82.37% (p = 0.001) and conformity index 0.67 and 0.6 (p = 0.007) for plans generated using IPSA and manual optimisation, respectively. Homogeneity index and dose to the OARs remained similar between the two groups.ConclusionThe use of inverse planning in intracavitary brachytherapy of cervix has shown a significant improvement in the target volume coverage when compared with manual planning.