3D-printed applicators for high dose rate brachytherapy: Dosimetric assessment at different infill percentage

PurposeDosimetric assessment of high dose rate (HDR) brachytherapy applicators, printed in 3D with acrylonitrile butadiene styrene (ABS) at different infill percentage.Materials and methodsA low-cost, desktop, 3D printer (Hamlet 3DX100, Hamlet, Dublin, IE) was used for manufacturing simple HDR applicators, reproducing typical geometries in brachytherapy: cylindrical (common in vaginal treatment) and flat configurations (generally used to treat superficial lesions). Printer accuracy was investigated through physical measurements. The dosimetric consequences of varying the applicator’s density by tuning the printing infill percentage were analysed experimentally by measuring depth dose profiles and superficial dose distribution with Gafchromic EBT3 films (International Specialty Products, Wayne, NJ). Dose distributions were compared to those obtained with a commercial superficial applicator.ResultsMeasured printing accuracy was within 0.5 mm. Dose attenuation was not sensitive to the density of the material. Surface dose distribution comparison of the 3D printed flat applicators with respect to the commercial superficial applicator showed an overall passing rate greater than 94% for gamma analysis with 3% dose difference criteria, 3 mm distance-to-agreement criteria and 10% dose threshold.ConclusionLow-cost 3D printers are a promising solution for the customization of the HDR brachytherapy applicators. However, further assessment of 3D printing techniques and regulatory materials approval are required for clinical application.     

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.     

End-to-end dosimetric audit: A novel procedure developed for Irish HDR brachytherapy centres

PurposeA dosimetric audit of Ir-192 high dose rate (HDR) brachytherapy remote after-loading units was carried out in 2019. All six brachytherapy departments on the island of Ireland participated in an end-to-end test and in a review of local HDR dosimetry procedures.Materials and methodsA 3D-printed customised phantom was created to position the following detectors at known distances from the HDR source: a Farmer ionization chamber, GafChromic film and thermoluminescent dosimeters (TLDs). Dedicated HDR applicator needles were used to position an Ir-192 source at 2 cm distance from these detectors. The end-to-end dosimetry audit pathway was performed at each host site and included the stages of imaging, applicator reconstruction, treatment planning and delivery. Deviations between planned and measured dose distributions were quantified using gamma analysis methods. Local procedures were also discussed between auditors and hosts.ResultsThe mean difference between Reference Air Kerma Rate (RAKR) measured during the audit and RAKR specified by the vendor source certificate was 1.3%. The results of end-to-end tests showed a mean difference between calculated and measured dose of 2.5% with TLDs and less than 0.5% with Farmer chamber measurements. GafChromic films showed a mean gamma passing rates of >95% for plastic and metal applicators with 2%/1 mm global tolerance criteria.ConclusionsThe results of this audit indicate dosimetric consistency between centres. The ‘end to end’ dosimetry audit methodology for HDR brachytherapy has been successfully implemented in a multicentre environment, which included different models of Ir-192 sources and different treatment planning systems.The ability to create a 3D-printed water-equivalent phantom customised to accurately position all three detector types simultaneously at controlled distances from the Ir-192 source under evaluation gives good reproducibility for end-to-end methodology.     

Dosimetric verification of a high dose rate brachytherapy treatment planning system in homogeneous and heterogeneous media

ObjectivesTo verify the dosimetric accuracy of treatment plans in high dose rate (HDR) brachytherapy by using Gafchromic EBT2 film and to demonstrate the adequacy of dose calculations of a commercial treatment planning system (TPS) in a heterogeneous medium.MethodsAbsorbed doses at chosen points in anatomically different tissue equivalent phantoms were measured using Gafchromic EBT2 film. In one case, tandem ovoid brachytherapy was performed in a homogeneous cervix phantom, whereas in the other, organ heterogeneities were introduced in a phantom to replicate the upper thorax for esophageal brachytherapy treatment. A commercially available TPS was used to perform treatment planning in each case and the EBT2 films were irradiated with the HDR Ir-192 brachytherapy source.ResultsFilm measurements in the cervix phantom were found to agree with the TPS calculated values within 3% in the clinically relevant volume. In the thorax phantom, the presence of surrounding heterogeneities was not seen to affect the dose distribution in the volume being treated, whereas, a little dose perturbation was observed at the lung surface. Doses to the spinal cord and to the sternum bone were overestimated and underestimated by 14.6% and 16.5% respectively by the TPS relative to the film measurements. At the trachea wall facing the esophagus, a dose reduction of 10% was noticed in the measurements.ConclusionsThe dose calculation accuracy of the TPS was confirmed in homogeneous medium, whereas, it was proved inadequate to produce correct dosimetric results in conditions of tissue heterogeneity.     

Dosimetric verification of dose optimisation algorithm during endovascular brachytherapy of the peripheral vessels

AimDosimetric verification of the dose optimisation model used in endovascular brachytherapy, evaluation of the optimised dose distributions using elaborated indices.BackgroundThe equipment used for standard radiotherapy is used in vascular brachytherapy for prevention of restenosis after angioplasty.Material and MethodA paraffin-wax phantom, thermoluminescent detectors and MD-55 Gafchromic® films were used for dose measurements. The edge dose index (EDI), central dose index (CDI) and treatment length index (TLI) were introduced to compare dose distributions calculated and measured.ResultsObtained values (p>0.05) show no statistically significant differences between calculated doses and measured doses. EDI values showed improvement in dose homogeneity on the edges of the application after optimisation. After optimisation CDI values from 0.9% to 1.6% for calculated and from ?1.8% to 3.1% for measured showed improvement in dose homogeneity in the central part of the application. Observed values of TLI from 3% to 21% for calculated doses and from 7% to 24% for doses measured by Gafchromic® films showed increase of RIL for optimised treatment plans.Conclusions1/ The designed phantom allowed repeatable dosimetric verification of dose distributions in endovascular brachytherapy. 2/ Measurements with thermoluminescent detectors and Gafchromic films proved the accuracy of the calculation algorithm in endovascular brachytherapy conditions. 3/ Elaborated indices were found to be a useful tool in describing dose homogeneity. They allowed the process of optimisation to be controlled and thus an increase in dose homogeneity by 30% at the edges and by 7% in the middle of the treated volume to be achieved.     

Fetal dose measurements and shielding efficiency assessment in a custom setup of 192Ir brachytherapy for a pregnant woman with breast cancer

PurposeTo assess the radiation dose to the fetus of a pregnant patient undergoing high-dose-rate (HDR) ¹⁹²Ir interstitial breast brachytherapy, and to design a new patient setup and lead shielding technique that minimizes the fetal dose.MethodsRadiochromic films were placed between the slices of an anthropomorphic phantom modeling the patient. The pregnant woman was seated in a chair with the breast over a table and inside a leaded box. Dose variation as a function of distance from the implant volume as well as dose homogeneity within a representative slice of the fetal position was evaluated without and with shielding.ResultsWith shielding, the peripheral dose after a complete treatment ranged from 50 cGy at 5 cm from the caudal edge of the breast to <0.1 cGy at 30 cm. The shielding reduces absorbed dose by a factor of two near the breast and more than an order of magnitude beyond 20 cm. The dose is heterogeneous within a given axial plane, with variations from the central region within 50%. Interstitial HDR ¹⁹²Ir brachytherapy with breast shielding can be more advantageous than external-beam radiotherapy (EBRT) from a radiation protection point of view, as long as the distance to the uterine fundus is higher than about 10 cm. Furthermore, the weight of the shielding here proposed is notably lower than that needed in EBRT.ConclusionsShielded breast brachytherapy may benefit pregnant patients needing localized radiotherapy, especially during the early gestational ages when the fetus is more sensitive to ionizing radiation.     

Comprehensive methodology for commissioning modern 3D-image-based treatment planning systems for high dose rate gynaecological brachytherapy: A review

PurposeCorrect commissioning of treatment planning systems (TPSs) is important for reducing treatment failure events. There is currently no comprehensive and robust methodology available for TPS commissioning in modern brachytherapy. This review aimed to develop a comprehensive template for commissioning modern 3D-image-based brachytherapy TPSs for high dose rate (HDR) gynaecological applications.MethodsThe literature relevant to TPS commissioning, including both external beam radiation therapy (EBRT) and brachytherapy, as well as guidelines by the International Atomic Energy Agency (IAEA), the American Association of Physicists in Medicine (AAPM), and the European Society for Radiotherapy and Oncology (ESTRO) were searched, studied and appraised. The applied relevant EBRT TPS commissioning tests were applied to brachytherapy. The developed template aimed to cover all dosimetric and non-dosimetric issues.ResultsThe essential commissioning items could be categorized into six parts: geometry, dose calculation, plan evaluation tools, plan optimization, TPS output, and end-to-end verification. The final template consists of 43 items. This paper presents the purpose and role of each test, as well as tolerance limits, to facilitate the use of the template.ConclusionThe information and recommendations available in a collection of publications over many years have been reviewed in order to develop a comprehensive template for commissioning complex modern 3D-image-based brachytherapy TPSs for HDR gynaecological applications. The up-to-date and concise information contained in the template can aid brachytherapy physicists during TPS commissioning as well as devising a regular quality assurance program and allocation of time and resources.     

Tolerance of the vaginal vault to high-dose rate brachytherapy and concomitant chemo-pelvic irradiation: Long-term perspective

Aim/background

We sought to determine the tolerance level and complication rates of the vaginal vault to combined high-dose-rate intra-cavitary brachytherapy with concomitant chemo-radiotherapy.

Patients and methods

A retrospective review of medical records of all the patients who received definitive chemo-radiotherapy for cervical cancer between 1998 and 2002 was undertaken. The records were reviewed for doses and for radiation-associated early and late sequelae of the vagina, rectum and bladder. Cumulative biological effective dose was calculated for two reference vaginal surface points.

Results

Fifty patients were included. Average age at diagnosis was 54 years. Median follow-up was 59 months. There were no recorded instances of acute grade IV toxicity. Maximal high-dose-rate vaginal surface dose (upper central point) was 103 Gy, and maximal brachytherapy lateral surface dose was 70 Gy. Maximal cumulative biological effective dose for the lateral surface reference point was 465.5 Gy₃, and the maximal cumulative biological effective dose for the superior reference point was 878.6 Gy₃. There were no cases of vaginal necrosis or fistulas, and no cases of grade IV late vaginal, rectal or bladder toxicity. No correlation was found between the maximal vaginal surface dose and vaginal, rectal or bladder toxicity.

Conclusions

The maximal surface HDR brachytherapy dose of 103 Gy and the maximal cBED of 878.6 Gy₃ were not associated with fistula or necrosis or other grade 3–4 vaginal complications. Concomitant chemo-radiotherapy, including pelvic radiotherapy and high-dose-rate intracavitary brachytherapy, is relatively safe for cervical cancer patients.     

Clinical application of MOSkin dosimeters to rectal wall in vivo dosimetry in gynecological HDR brachytherapy

PurposeThree MOSkins dosimeters were assembled over a rectal probe and used to perform in vivo dosimetry during HDR brachytherapy treatments of vaginal cancer. The purpose of this study was to verify the applicability of the developed tool to evaluate discrepancies between planned and measured doses to the rectal wall.Materials and methodsMOSkin dosimeters from the Centre for Medical Radiation Physics are particularly suitable for brachytherapy procedures for their ability to be easily incorporated into treatment instrumentation. In this study, 26 treatment sessions of HDR vaginal brachytherapy were monitored using three MOSkin mounted on a rectal probe. A total of 78 measurements were collected and compared to doses determined by the treatment planning system.ResultsMean dose discrepancy was determined as 2.2 ± 6.9%, with 44.6% of the measurements within ±5%, 89.2% within ±10% and 10.8% higher than ±10%. When dose discrepancies were grouped according to the time elapsed between imaging and treatment (i.e., group 1: ≤90 min; group 2: >90 min), mean discrepancies resulted in 4.7 ± 3.6% and 7.1 ± 5.0% for groups 1 and 2, respectively. Furthermore, the position of the dosimeter on the rectal catheter was found to affect uncertainty, where highest uncertainties were observed for the dosimeter furthest inside the rectum.ConclusionsThis study has verified MOSkin applicability to in-patient dose monitoring in gynecological brachytherapy procedures, demonstrating the dosimetric rectal probe setup as an accurate and convenient IVD instrument for rectal wall dose verification. Furthermore, the study demonstrates that the delivered dose discrepancy may be affected by the duration of treatment planning.     

Optimization of dose distributions in intraoperative HDR brachytherapy

The authors present their initial experience in physical aspects of treatment planning in HDR intraoperative brachytherapy. The examples are given of implantations in various tumour localizations: head and neck, pancreas, soft tissue sarcomas in the abdomen. The technical and dosimetric problems which may occur in such situations are discussed. The capabilities of dose distribution optimization by the Abacus HDR treatment planning system are presented.     

Implementation of a dose gradient method into optimization of dose distribution in prostate cancer 3D-CRT plans

AimThe aim of this work is to present a method of beam weight and wedge angle optimization for patients with prostate cancer.Background3D-CRT is usually realized with forward planning based on a trial and error method. Several authors have published a few methods of beam weight optimization applicable to the 3D-CRT. Still, none on these methods is in common use.Materials and methodsOptimization is based on the assumption that the best plan is achieved if dose gradient at ICRU point is equal to zero. Our optimization algorithm requires beam quality index, depth of maximum dose, profiles of wedged fields and maximum dose to femoral heads. The method was tested for 10 patients with prostate cancer, treated with the 3-field technique. Optimized plans were compared with plans prepared by 12 experienced planners. Dose standard deviation in target volume, and minimum and maximum doses were analyzed.ResultsThe quality of plans obtained with the proposed optimization algorithms was comparable to that prepared by experienced planners. Mean difference in target dose standard deviation was 0.1% in favor of the plans prepared by planners for optimization of beam weights and wedge angles. Introducing a correction factor for patient body outline for dose gradient at ICRU point improved dose distribution homogeneity. On average, a 0.1% lower standard deviation was achieved with the optimization algorithm. No significant difference in mean dose–volume histogram for the rectum was observed.ConclusionsOptimization shortens very much time planning. The average planning time was 5 min and less than a minute for forward and computer optimization, respectively.     

Can the Day 0 CT-scan predict the post-implant scanning? Results from 136 prostate cancer patients

PurposePost-implant CT-scanning is an essential part of permanent prostate brachytherapy. However, the evaluation of post-implant CT dosimetry is not straightforward due to the edema that can modify the dose to the prostate and to the organs at risk. The aim of this study is to evaluate the impact of the timing of the post-implant CT-scan on the dosimetric results and to verify if the Day 0 scan findings can predict Day 50 scanning.Methods136 consecutive patients who received monotherapy with I-125 implants were selected for this study. Two sets of 8 dosimetric quality parameters corresponding to 2 different CT-scans (Day 0 and Day 50) were calculated and compared. The dosimetric parameters included are the percentage volume of the post-implant prostate receiving 80%, 100% and 150% of the prescribed dose, the doses covering 80% and 90% of the prostate volume and the Dose Homogeneity Index. The values of the dose covering 1 cm³ of the rectum and urethra were assessed.ResultsAll the dosimetric parameters of the Day 50 were higher than those of the Day 0 scan. Linear functions were obtained that calculate D₉₀ and V₁₀₀ values at Day 50 based on the Day 0 findings. Rectal and urethral parameters tended to be underestimated on Day 0 CT-scan relative to Day 50 based dosimetry.ConclusionsPredicting the Day 50 dosimetry from the Day 0 scan could be a possible alternative to a Day 50 scan only in specific situations, but with a degree of uncertainty in the predicted values.     

Dosimetric characterization of INTRABEAM® miniature accelerator flat and surface applicators for dermatologic applications

PurposeThis study aims at characterizing the dosimetric behavior of an INTRABEAM^® miniature accelerator equipped with flat and surface applicators, converting the spherical dose distribution into a flat one.MethodsDosimetric characterization was carried out in two steps. Firstly characterization was made in standard conditions for dermatologic applications, which is with the applicator directly on contact with the skin. Secondly, characterization was made in more clinical conditions, such as obliquities and heterogeneities.ResultsBehaviors of flat and surface applicators are different. Dose distribution for surface applicators is uniform at surface, whereas for flat applicator the maximum homogeneity is shown at a particular depth in water. Some results are different from previously published studies due to differences in the X-ray source design. The study showed that in the absence of a perfect contact between the applicator and the skin of the patient, there is a dose distribution spread on the edge of the irradiation field where the contact is not made. Dose loss due to lack of backscatter radiations is significant. By contrast, influence of a denser material behind the measurement point has no significant influence on the dose at this point. Thickness of tissue treated with flat and surface applicators is only a few millimeters, depending on the applicator's size, making these applicators ideal for superficial lesions, compared to high energy electrons and iridium brachytherapy.ConclusionsThe INTRABEAM^® miniature accelerator equipped with surface applicators is a reliable way of treating superficial cutaneous malignancies.     

Characterization of commercial MOSFET detectors and their feasibility for in-vivo HDR brachytherapy

AimThe present study was to investigate the use of MOSFET as an vivo dosimeter for the application of Ir-192 HDR brachytherapy treatments.Material and methodsMOSFET was characterized for dose linearity in the range of 50–1000 cGy, depth dose dependence from 2 to 7 cm, angular dependence. Signal fading was checked for two weeks.Result and discussionDose linearity was found to be within 2% in the dose range (50–1000 cGy). The response varied within 8.07% for detector-source distance of 2–7 cm. The response of MOSFET with the epoxy side facing the source (0 degree) is the highest and the lowest response was observed at 90 and 270 degrees. Signal was stable during the study period.ConclusionThe detector showed high dose linearity and insignificant fading. But due to angular and depth dependence, care should be taken and corrections must be applied for clinical dosimetry.     

Application of Monte Carlo calculations for validation of a treatment planning system in high dose rate brachytherapy

AimThe accuracy of treatment planning systems is of vital importance in treatment outcomes in brachytherapy. In the current study the accuracy of dose calculations of a high dose rate (HDR) brachytherapy treatment planning system (TPS) was validated using the Monte Carlo method.Materials and methodsThree ⁶⁰Co sources of the GZP6 afterloading brachytherapy system were modelled using MCNP4C Monte Carlo (MC) code. The dose distribution around all the sources was calculated by MC and a dedicated treatment planning system. The results of both methods were compared.ResultsThere was good agreement (<2%) between TPS and MC calculated dose distributions except at a point near the sources (<1 cm) and beyond the tip of the sources.ConclusionsOur study confirmed the accuracy of TPS calculated dose distributions for clinical use in HDR brachytherapy.     

Dosimetric analysis of Tomotherapy-based intracranial stereotactic radiosurgery of brain metastasis

PurposeThis paper analyzes Tomotherapy-based intracranial stereotactic radiosurgery (HTSRS) of brain metastasis targeting two end-points: 1) evaluation of dose homogeneity, conformity and gradient scores for single and multiple lesions and 2) assay of dosimetric criticality of completion of HTSRS procedures.Methods42 treatment plans of 33 patients (53 brain lesions) treated with HTSRS were analyzed. Dose to healthy brain, homogeneity, conformity and gradient indexes were evaluated for each lesion. Influence of Field Length and multiple lesions cross-talk effect were assessed. Treatment interruption and completion was investigated using radiochromic films in order to examine the delivered dose and its robustness to patient intrafraction movement.ResultsThe average dose homogeneity index was 1.04 ± 0.02 (SD). Average dose conformity and gradient score indexes were 1.4 ± 0.2 and 50 ± 14 respectively. We found a strong correlation of the dose to healthy brain and conformity and gradient indexes with target(s) volume for which analytical functions were obtained. Field Length and cross-talk effect were significantly correlated with poor gradient scores, but were found not to affect dose conformity.ConclusionsHomogeneity and conformity of HTSRS plans achieved excellent scores, while dose falloff and dose to healthy brain were slightly larger when compared with non-coplanar SRS techniques. Care should be given if treating large (>3 cc) or multiple near in-plane lesions in order to reduce dose to healthy brain. Analysis of interrupted treatments suggests splitting HTSRS treatments in two consecutive fractions in order to prevent target miss and overdosage due to patient intrafraction movement.     

Evaluation of rectal dose discrepancies between planned and in vivo dosimetry using MOSkin detector and PTW 9112 semiconductor probe during 60Co HDR CT-based intracavitary cervix brachytherapy

PurposeDose to the rectum during brachytherapy treatment may differ from an approved treatment plan which can be quantified with in vivo dosimetry (IVD). This study compares the planned with in vivo doses measured with MOSkin and PTW 9112 rectal probe in patients undergoing CT based HDR cervical brachytherapy with Co-60 source.MethodsDose measurement of a standard pear-shaped plan carried out in phantom to verify the MOSkin dose measurement accuracy. With MOSkin attached to the third diode, RP3 of the PTW 9112, both detectors were inserted into patients’ rectum. The RP3 and MOSkin measured doses in 18 sessions as well as the maximum measured doses from PTW 9112, RP_max in 48 sessions were compared to the planned doses.ResultsPercentage dose differences ΔD (%) in phantom study for two MOSkin found to be 2.22 ± 0.07% and 2.5 ± 0.07%. IVD of 18 sessions resulted in ΔD(%) of −16.3% to 14.9% with MOSkin and ΔD(%) of −35.7% to −2.1% with RP3. In 48 sessions, RP_max recorded ΔD(%) of −37.1% to 11.0%. MOSkin_measured doses were higher in 44.4% (8/18) sessions, while RP3_measured were lower than planned doses in all sessions. RP_max_measured were lower in 87.5% of applications (42/47).ConclusionsThe delivered doses proven to deviate from planned doses due to unavoidable shift between imaging and treatment as measured with MOSkin and PTW 9112 detectors. The integration of MOSkin on commercial PTW 9112 surface found to be feasible for rectal dose IVD during cervical HDR ICBT.