Prescription Point Research Articles

Present clinical practices of stereotactic irradiation for metastatic brain tumors in Japan: results of questionnaire survey of the Japanese Radiation Oncology Study Group (JROSG) working subgroup for neurological tumors.

To determine the current practice of stereotactic irradiation (STI) for brain metastases in Japan by a questionnaire survey. A questionnaire was distributed to 313 institutions performing STI with one of the following machines: Gamma Knife (GK), CyberKnife (CK), Novalis (Nov), or other linear accelerator (LINAC)-based systems (OLS). The participation was voluntary. There were 163 responding institutions. The total number of STI treatments between April 2013 and March 2014 was 10,684. Stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (SRT) were performed in 8624 (80.7%) and 2060 (19.3%) cases, respectively. Whole-brain radiation therapy (WBRT) was performed for a total of 3515 cases. For a case model of a 1.5-cm solitary brain metastasis in a non-eloquent area, the most common GTV-PTV margin was 2mm (22 of 114 institutions), and an institutional standard fraction was 1 (75 of 114 institutions). The doses for the model case also varied from 13.0 to 26.0Gy (Median 20Gy) when converted to SRS (α/β = 10). A prescription point was at the PTV margin the most. The median dose constraints which were converted to SRS (α/β = 3) to organs at risk were 12.2, 12.7, and 13.7Gy for optic nerves, cavernous sinus, and brainstem, respectively. STI for brain metastases in current practice varied significantly among institutions. These different strategies relied mostly on the type of treatment machine used. It is thus necessary to establish a common guideline to express dose prescriptions and plan qualities for different STI machines.

Accuracy of Dose Calculation for Hemi-Body Treatment at Extended Distance using a Commercial Treatment Planning System

The objective of this study was to assess the accuracy of Monitor Unit (MU) calculation for extended distance hemi-body (HB) treatments in Pinnacle, a commercial treatment planning system. The agreement between planning and delivery of low dose radiation therapy (LD-RT) was assessed with direct comparison to expected doses and tabulated total body irradiation (TBI) calculations. Studies over the past decades indicate that LD-RT has strong potential to be an effective treatment modality for patients, particularly those with Non-Hodgkin’s Lymphoma (NHL), a cancer of the lymphocytes. Past studies also indicate that a LD-RT regime will present minimal toxicity and limited adverse side effects. LD-RT may directly trigger a systemic immune response. This physics-based study aims to provide sufficient conclusions required for prospective clinical studies involving HB irradiation regimes. Specifically, this study may provide reassurance of MU calculation in the Pinnacle system for an upcoming trial regarding non-targeted LD-RT for recurrent prostate cancer. Water Phantom: A plan was created in Pinnacle to deliver 100 cGy to a water phantom with an ion chamber (IC) mount. A percent depth dose (PDD) was obtained. Electrometer readings were recorded with each irradiation of 400 MU at varying IC depths at extended distance. A PDD was created from tabulated data. Anthropomorphic Phantom: A parallel opposed pair (POP) plan was created in Pinnacle to deliver 150 cGy over 10 fractions to the umbilicus of the phantom at 4 m extended source-to-surface distance (SSD). The MU required to deliver 150 cGy, as per Pinnacle were delivered to the phantom using 6 MV photons. Thermoluminescent dosimeters, used to measure exposure using light-emitting crystals, were placed along six reference locations on the phantom (lung, mid-T-spine, abdomen, mid-pelvis, thigh, and mid-abdomen). TLD measurements were then compared to the Pinnacle-derived ROI mean doses. For Experiment 2, TBI calculation factors were used to determine the required MU to deliver 150 cGy to the prescription (Rx) point. The calculated MUs were delivered and TLD readings were recorded to compare the level of agreement of using TBI calculations for HB treatments. Water Phantom: Pinnacle did not accurately estimate dmax at extended distance, however, it did accurately estimate the dose past dmax. Anthropomorphic Phantom: A 10% variation to expected dose was deemed significant. Lung dose did not present significant variation. The abdomen presented borderline significance. Remaining ROIs presented significant variation for both Pinnacle and TBI calculations. Both Pinnacle and TBI calculations were accurate methods of planning HB LD-RT treatment, with insignificant difference. Pinnacle accurately estimated dose to the Rx point but overestimated the dose to remaining ROIs. Overall average variation was borderline significant at 12.1%. At extended SSD, Pinnacle inaccurately estimated the entrance dose and dmax. PDD data supported Pinnacle’s ability to accurately estimate dose at depths greater than dmax. Anthropomorphic phantom studies indicated borderline significant variation, as per the implemented 10% limit. TBI calculations presented similar conclusions. For purposes of HB LD-RT, a borderline 10% variation will have insignificant impact to the patient’s ability to tolerate treatment. Trial eligible prostate cancer patients are currently being recruited for HB LD-RT at the Juravinski Cancer Centre.

Intraoperative Radiotherapy With INTRABEAM: Technical and Dosimetric Considerations.

We evaluate dose characteristics and clinical applications of treatment accessories used in intraoperative radiotherapy (IORT) and make site-specific recommendations for their optimal use. Dose measurements were performed for a low energy (50 kV) X-ray INTRABEAM source. For spherical, flat, surface, and needle applicators, the following dosimetric parameters were measured: depth-dose (DD) profiles, surface dose (Ds), output factors (OF), and target dose homogeneity (DH). Optical density versus exposure calibration films were employed to obtain 2-dimensional dose distributions in planes parallel and perpendicular to beam direction. Film results were verified via repeat dose measurements with a parallel-plate ionization chamber in a custom water tank. The impact of applicator design on dose distributions was evaluated. Spherical applicators are commonly used for treating the inner-surface of breast lumpectomy cavity. Flat and surface applicators provide uniform planar dose for head and neck, abdomen, and pelvis targets. Needle applicators are designed for kypho-IORT of spinal metastasis. Typically, larger applicators produce a more homogeneous target dose region with lower surface dose, but require longer treatment times. For 4-cm diameter spherical, flat, and surface applicators, dose rates (DR) at their respective prescription points were found to be: 0.8, 0.3, and 2.2 Gy/min, respectively. The DR for a needle applicator was 7.04 Gy/min at 5 mm distance from the applicator surface. Overall, film results were in excellent agreement with ion-chamber data. IORT may be delivered with a variety of site-specific applicators. Appropriate applicator use is paramount for safe, effective, and efficient IORT delivery. Results of this study should help clinicians assure optimized target dose coverage and reduced normal tissue exposure.

Dose optimization of total or partial skin electron irradiation by thermoluminescent dosimetry.

Due to the complex surface of the human body, total or partial skin irradiation using large electron fields is challenging. The aim of the present study was to quantify the magnitude of dose optimization required after the application of standard fields. Total skin electron irradiation (TSEI) was applied using the Stanford technique with six dual-fields. Patients presenting with localized lesions were treated with partial skin electron irradiation (PSEI) using large electron fields, which were individually adapted. In order to verify and validate the dose distribution, in vivo dosimetry with thermoluminescent dosimeters (TLD) was performed during the first treatment fraction to detect potential dose heterogeneity and to allow for an individual dose optimization with adjustment of the monitor units (MU). Between 1984 and 2017, a total of 58patients were treated: 31patients received TSEI using 12treatment fields, while 27patients underwent PSEI and were treated with 4-8treatment fields. After evaluation of the dosimetric results, an individual dose optimization was necessary in 21patients. Of these, 7patients received TSEI (7/31). Monitor units (MU) needed to be corrected by amean value of 117 MU (±105, range 18-290) uniformly for all 12 treatment fields, corresponding to amean relative change of 12% of the prescribed MU. In comparison, the other 14patients received PSEI (14/27) and the mean adjustment of monitor units was 282 MU (±144, range 59-500) to single or multiple fields, corresponding to amean relative change of 22% of the prescribed MU. Asecond dose optimization to obtain asatisfying dose at the prescription point was need in 5patients. Thermoluminescent dosimetry allows an individual dose optimization in TSEI and PSEI to enable areliable adjustment of the MUs to obtain the prescription dose. Especially in PSEI in vivo dosimetry is of fundamental importance.

Modification of Source Strength in Low-Dose-Rate Lung Brachytherapy with 125I and 103Pd Seeds.

A new treatment approach for most patients who have undergone early stage non-small-cell lung carcinoma (NSCLC) is wedge resection plus permanent implant brachytherapy. However, the specification of dose to medium at low energies especially in heterogeneous lung is unclear yet. The present study aims to modify source strength for different configurations of 125I and 103Pd seeds used in lung permanent implant brachytherapy. Different arrays of 125I and 103Pd seeds were simulated by MCNPX code in protocol-based water vs. actual 3D lung environments. Absorbed dose was, then, scored in both mediums. Dose differences between both environments were calculated and source strength was modified for the prescription point. In addition, lung-to-water absorbed dose ratio was obtained and presented by precise equations. Due to significant differences in prescription dose, source strength was modified 16%-19% and 37%-43% for different configurations of 125I and 103Pd seeds, respectively. In addition, depth-dependent dose differences were observed between the actual lung and protocol-based water mediums (dose difference as a function of depth). Modification of source strength is essential for different arrangements of 125I and 103Pd seeds in lung implantation. Modified source strength and presented equations are recommended to be considered in future studies based on lung brachytherapy.

A phantom study for in-vivo dosimetry of high dose rate brachytherapy applicators

Purpose: The aim of the current investigation was to calibrate the diode in-vivo dosimetry (IVD) system for high-dose-rate (HDR) brachytherapy and to design a phantom study for in-vivo dosimetry of HDR brachytherapy applicators. Methods: Gamma Med Plus with Abacus 3.1 treatment planning system (TPS), and diode dosimetry system has been used in this study. Calibration and different correction factors of diode have been measured in water phantom. Treatment simulation, planning of different applicators for esophagus, rectum/vagina and cervix (fletcher & ring), dose delivery and finally in-vivo verification at prescription point using diode in water phantom has been performed. Results: The mean calibration factor for diode for Ir-192 HDR source is 1.256 (N=15) with σ ± 0.0015. The overall average percentage difference between TPS dose and diode dose was 1.87% (σ ± 2.64) for all measurements, 1.86% (σ ± 2.73) for esophagus, 1.86% (σ± 2.94) for rectum/vagina and 1.67% (σ ±2.81) for fletcher and 2.07% (σ ± 2.26) for ring applicators, respectively. These results advocate that the dose calculated by TPS and dose measured using diode for the various clinical situations deliberated here are in good agreement (~2%) at the points of clinical importance. Conclusion: The in-vivo phantom dosimetry study gives both a confidence that the treatments are being delivered as prescribed and enhance the reliability of the HDR brachytherapy treatment. This may be used for acceptance testing/commissioning of new treatment planning system and to validate the new brachytherapy techniques in the clinics.

American Brachytherapy Society: Brachytherapy treatment recommendations for locally advanced cervix cancer for low-income and middle-income countries

PurposeMost cervix cancer cases occur in low-income and middle-income countries (LMIC), and outcomes are suboptimal, even for early stage disease. Brachytherapy plays a central role in the treatment paradigm, improving both local control and overall survival. The American Brachytherapy Society (ABS) aims to provide guidelines for brachytherapy delivery in resource-limited settings. Methods and MaterialsA panel of clinicians and physicists with expertise in brachytherapy administration in LMIC was convened. A survey was developed to identify practice patterns at the authors' institutions and was also extended to participants of the Cervix Cancer Research Network. The scientific literature was reviewed to identify consensus papers or review articles with a focus on treatment of locally advanced, unresected cervical cancer in LMIC. ResultsOf the 40 participants invited to respond to the survey, 32 responded (response rate 80%). Participants were practicing in 14 different countries including both high-income (China, Singapore, Taiwan, United Kingdom, and United States) and low-income or middle-income countries (Bangladesh, Botswana, Brazil, India, Malaysia, Pakistan, Philippines, Thailand, and Vietnam). Recommendations for modifications to existing ABS guidelines were reviewed by the panel members and are highlighted in this article. ConclusionsRecommendations for treatment of locally advanced, unresectable cervical cancer in LMIC are presented. The guidelines comment on staging, external beam radiotherapy, use of concurrent chemotherapy, overall treatment duration, use of anesthesia, applicator choice and placement verification, brachytherapy treatment planning including dose and prescription point, recommended reporting and documentation, physics support, and follow-up.

Verification of Balloon Integrity by Ultrasound Imaging in Accelerated Partial Breast Irradiation

<p class="cco-body"><em><span lang="EN-GB">Purpose</span></em><span lang="EN-GB">: An overview of the ultrasound imaging artifacts encountered in Mammosite balloon APBI is presented. Analysis of ultrasound measurement errors and the dosimetric impact of balloon leakage were used to determine whether clinically relevant changes in balloon size can be reliably detected. <em>Methods</em>: Ultrasound imaging of a Mammosite balloon phantom was performed to better understand measurement errors and accuracy. The dose to the prescription point as a function of balloon diameter was computed for different sized balloons. The results were compared to phantom measurements of balloon diameter versus filling volume to assess the dose change that would result from tissue moving inward with a shrinking balloon boundary. In APBI patients undergoing a course of 10 treatment fractions, the accuracy and variability of balloon size measured with ultrasound imaging was compared to CT. <em>Results</em>: Ultrasound artifacts combine to form a false image of the distal balloon boundary. Proper US probe orientation and choice of measurement point locations improved distance measurement accuracy. A 1 mm change in balloon diameter is measurable with ±0.1 mm error and corresponds to <4% change in dose 1 cm from the balloon. Measurement errors relative to CT averaged less than 1.4 mm and variability (standard deviation) over the course of treatment averaged 1.9 mm. <em>Conclusions</em>: Properly performed ultrasound image acquisition and analysis can detect dosimetrically relevant changes in the size of a leaking balloon. This study confirms that US imaging is a valid method of verifying APBI balloon integrity over the course of treatment.</span></p>

Electron depth dose curves in inhomogeneous medium for radiation therapy: A simulation approach

Introduction MeV energy electron beam is used very often for skin cancers treatment. Most of the time the percentage depth dose (PDD) and depth of maximum dose deposited (Dmax) is to be calculated based on homogenous medium. But the dose distribution can be significantly altered in the presence of tissue inhomogeneity such as bone, lung, and air cavities. Purpose It is difficult to determine dose distribution within or around small inhomogeneity because of enhanced electron scattering effects, therefore, accurate knowledge of dose distribution in homogeneous and inhomogeneous medium is very important for the delivery of accurate dose and treatment. Materials and methods In present work, EGSnrc Monte Carlo code has been used for the calculation of PDD curves in homogeneous and inhomogeneous medium. The bone of varying thickness is considered in water phantom to study effect of tissue inhomogeneity. Electron beam of energies 4–20 MeV have been used for the simulation purpose. Results The PDD has been estimated for the case of homogenous medium of water and bone and also for the case of bone of different thicknesses inserted before and after the build-up region in water phantom. It has been observed that the values of R90, R50, Rp have been decreased linearly with the bone thickness for all electron energies. Also it has been found that below the depth of inhomogeneity, PDD has increased by 10% for 0.8 cm of bone at 12 MeV. Conclusion It is concluded that because of inhomogeneity, PDD beyond inhomogeneity increases and after Dmax it decreases. This data could be useful for the clinicians to define dose prescription point during electron beam therapy and can achieve the perfection of treatment.

Standardizing dose prescriptions: An ASTRO white paper

This white paper recommends the standardization (content and presentation order) of several “key components” of the radiation therapy prescription to facilitate accurate communication between radiation therapy care providers. The rationale, other similar efforts, and detailed considerations are described. In brief, the Task Force recommends that the prescription’s “elements” include: treatment site, method of delivery, dose per fraction, total number of fractions, total dose (eg, right breast, tangent photons, 267 cGy * 16 = 4272 cGy). A similar formalism is recommended for brachytherapy (eg, cervix, Ir-192 brachytherapy, 600cGy * 5 = 3000 cGy) and other modalities. The white paper also considers future directions for other items such as the simulation order, treatment planning objectives, prescription point or volume, treatment schedule, localization imaging, laboratory monitoring, concurrent chemotherapy, patient instructions for treatment, etc. The intent of this white paper is to facilitate accurate communication among providers to support safe practice as well as to guide vendors in product development that is consistent with this standard prescription.

Low dose-rate brachytherapy for the treatment of cervix cancer is outdated and should be discontinued.

Low dose-rate brachytherapy for the treatment of cervix cancer is outdated and should be discontinued.

SU‐F‐T‐65: AutomaticTreatment Planning for High‐Dose Rate (HDR) Brachytherapy with a VaginalCylinder Applicator

Purpose:High dose rate (HDR) brachytherapy treatment planning is conventionally performed in a manual fashion. Yet it is highly desirable to perform computerized automated planning to improve treatment planning efficiency, eliminate human errors, and reduce plan quality variation. The goal of this research is to develop an automatic treatment planning tool for HDR brachytherapy with a cylinder applicator for vaginal cancer.Methods:After inserting the cylinder applicator into the patient, a CT scan was acquired and was loaded to an in‐house developed treatment planning software. The cylinder applicator was automatically segmented using image‐processing techniques. CTV was generated based on user‐specified treatment depth and length. Locations of relevant points (apex point, prescription point, and vaginal surface point), central applicator channel coordinates, and dwell positions were determined according to their geometric relations with the applicator. Dwell time was computed through an inverse optimization process. The planning information was written into DICOM‐RT plan and structure files to transfer the automatically generated plan to a commercial treatment planning system for plan verification and delivery.Results:We have tested the system retrospectively in nine patients treated with vaginal cylinder applicator. These cases were selected with different treatment prescriptions, lengths, depths, and cylinder diameters to represent a large patient population. Our system was able to generate treatment plans for these cases with clinically acceptable quality. Computation time varied from 3–6 min.Conclusion:We have developed a system to perform automated treatment planning for HDR brachytherapy with a cylinder applicator. Such a novel system has greatly improved treatment planning efficiency and reduced plan quality variation. It also served as a testbed to demonstrate the feasibility of automatic HDR treatment planning for more complicated cases.

WE‐DE‐201‐02: A Statistical Analysis Tool for Plan Quality Verification in HDR Brachytherapy Forward Planning for Cervix Cancer

Purpose:High Dose Rate (HDR) brachytherapy forward planning is principally an iterative process; hence, plan quality is affected by planners’ experiences and limited planning time. Thus, this may lead to sporadic errors and inconsistencies in planning. A statistical tool based on previous approved clinical treatment plans would help to maintain the consistency of planning quality and improve the efficiency of second checking.Methods:An independent dose calculation tool was developed from commercial software. Thirty‐three previously approved cervical HDR plans with the same prescription dose (550cGy), applicator type, and treatment protocol were examined, and ICRU defined reference point doses (bladder, vaginal mucosa, rectum, and points A/B) along with dwell times were collected. Dose calculation tool then calculated appropriate range with a 95% confidence interval for each parameter obtained, which would be used as the benchmark for evaluation of those parameters in future HDR treatment plans. Model quality was verified using five randomly selected approved plans from the same dataset.Results:Dose variations appears to be larger at the reference point of bladder and mucosa as compared with rectum. Most reference point doses from verification plans fell between the predicted range, except the doses of two points of rectum and two points of reference position A (owing to rectal anatomical variations & clinical adjustment in prescription points, respectively). Similar results were obtained for tandem and ring dwell times despite relatively larger uncertainties.Conclusion:This statistical tool provides an insight into clinically acceptable range of cervical HDR plans, which could be useful in plan checking and identifying potential planning errors, thus improving the consistency of plan quality.

SU‐F‐T‐17: A Feasibility Study for the Transit Dosimetry with a Glass Dosimeter in Brachytherapy

Purpose:Confirming the dose delivered to a patient is important to make sure the treatment quality and safety of the radiotherapy. Measuring a transit dose of the patient during the radiotherapy could be an interesting way to confirm the patient dose. In this study, we evaluated the feasibility of the transit dosimetry with a glass dosimeter in brachytherapy.Methods:We made a phantom that inserted the glass dosimeters and placed under patient lying on a couch for cervix cancer brachytherapy. The 18 glass dosimeters were placed in the phantom arranged 6 per row. A point putting 1cm vertically from the source was prescribed as 500.00 cGy. Solid phantoms of 0, 2, 4, 6, 8, 10 cm were placed between the source and the glass dosimeter. The transit dose was measured each thickness using the glass dosimeters and compared with a treatment planning system (TPS).Results:When the transit dose was smaller than 10 cGy, the average of the differences between measured values and calculated values by TPS was 0.50 cGy and the standard deviation was 0.69 cGy. If the transit dose was smaller than 100 cGy, the average of the error was 1.67 ± 4.01 cGy. The error to a point near the prescription point was −14.02 cGy per 500.00 cGy of the prescription dose.Conclusion:The distances from the sources to skin of the patient generally are within 10 cm for cervix cancer cases in brachytherapy. The results of this preliminary study showed the probability of the glass dosimeter as the transit dosimeter in brachytherapy.

SU‐F‐T‐48: Clinical Implementation of Brachytherapy Planning System for COMS Eye Plaques

Purpose:To commission the Brachytherapy Planning (BP) system (Varian, Palo Alto, CA) for the Collaborative Ocular Melanoma Study (COMS) eye plaques by evaluating dose differences against original plans from Nucletron Planning System (NPS).Methods:NPS system is the primary planning software for COMS‐plaques at our facility; however, Brachytherapy Planning 11.0.47 (Varian Medical Systems) is used for secondary check and for seed placement configurations not originally commissioned. Dose comparisons of BP and NPS plans were performed for prescription of 8500 cGy at 5 mm depth and doses to normal structures: opposite retina, inner sclera, macula, optic disk and lens. Plans were calculated for Iodine‐125 seeds (OncoSeeds, Model 6711) using COMS‐plaques of 10, 12, 14, 16, 18 and 20 mm diameters. An in‐house program based on inverse‐square was utilized to calculate point doses for comparison as well.Results:The highest dose difference between BP and NPS was 3.7% for the prescription point for all plaques. Doses for BP were higher than doses reported by NPS for all points. The largest percent differences for apex, opposite retina, inner sclera, macula, optic disk, and lens were 3.2%, 0.9%, 13.5%, 20.5%, 15.7% and 2.2%, respectively. The dose calculated by the in‐house program was 1.3% higher at the prescription point, and were as high as 42.1%, for points away from the plaque (i.e. opposite retina) when compared to NPS.Conclusion:Doses to the tumor, lens, retina, and optic nerve are paramount for a successful treatment and vision preservation. Both systems are based on TG‐43 calculations and assume water medium tissue homogeneity (ρe=1, water medium). Variations seen may result from the different task group versions and/or mathematical algorithms of the software. BP was commissioned to serve as a backup system and it also enables dose calculation in cases where seeds don't follow conventional placement configuration.

The Dosimetric Impact of Air in Vaginal Vault Brachytherapy

Vaginal vault brachytherapy is an adjuvant treatment option to reduce risk of local recurrence for intermediate and high risk endometrial cancer. The aim of this planning study is to examine the dosimetric effect of air gaps between the surface of a cylindrical vaginal stump applicator and mucosal wall with dose prescribed to a depth of 5mm from the mucosal surface. The applicability of the TG 43 formalism in the presence of air was also assessed. The planning CT scans for a retrospective sample of 82 patients treated between January 2014 and October 2015 were examined for the presence of air gaps. These were quantified in terms of the radial and longitudinal aspect with reference to the applicator, frequency per patient and location along the applicator. The effect of the geometric displacement of the target tissue was calculated on the planning system. Ionisation chamber measurements were also made in a phantom to estimate the uncertainty of the TG43 algorithm resulting from the impact of air on the dosimetry. 75 of the 82 patients that were analysed had at least one air gap. The overall incidence of air gaps was 91.4%. Of the total gaps observed, 23.7% were located above the tip of the applicator. The most common radial size was between 2 and 3mm (43.0%) which resulted in an average dose reduction using the TG43 formalism of 14.8%. Only 4.3% of the gaps were above 5mm in radial size. There is a strong correlation between radial dimension and TG43 calculated dose reduction, showing a Pearson’s correlation coefficient of 0.92. Phantom measurements indicated that the inhomogeneity introduced by air resulted in a maximum of 2.3% deviation from doses calculated using TG43 (Figure 1). It has been established that the TG43 formalism is not significantly compromised by the presence of air. The error in dose calculation using TG43 will shift the prescription isodose by at most 0.5 mm towards the mucosal surface with an air gap diameter of 10mm. However the presence of the air does produce a displacement of the mucosal surface away from the applicator and this causes a clinically significant dose reduction of 33.7% for 5mm of air. An approximately linear relationship is seen between increasing radial diameter of air and percentage dose reduction caused by the displacement by air of the tissue at the prescription point.

Implementation and validation of a combined MRI-CT–based cervical cancer brachytherapy program using existing infrastructure

PurposeTo describe the implementation of an MRI-CT–based cervical cancer brachytherapy (BT) program using existing infrastructure. To evaluate its impact on treatment planning. Methods and MaterialsA step-wise method was used to design and implement three-dimensional–based planning. Prospective risk analysis was used to create a process map and planning protocol. To evaluate the program, charts of cervical cancer patients treated curatively between January 2013 and December 2014, with at least one MRI during BT planning, were reviewed. Dosimetric comparisons were made between prescription point used and that of the traditional Point A and between MRI-planned treatments and CT-planned treatments. They were evaluated for differences between plans as well as adherence to Groupe Européen de Curiethérapie–European Society for Radiotherapy & Oncology (GEC-ESTRO) recommendations for high-risk clinical target volume coverage and organs-at-risk constraints. ResultsImplementation of the MRI-CT planning program occurred using existing infrastructure. Key to the implementation was communication between departments and the use of a process map to document the workflow. Eighty percent of treatments were prescribed to a point other than Point A, there were no major differences between the MRI-planned and CT-planned (with MRI guidance) treatments, and GEC-ESTRO recommendations were met for target coverage and organs at risk dose constraints. ConclusionsIt was feasible to implement an MRI-CT–based cervical cancer BT planning program using existing infrastructure and that resulting plans meet GEC-ESTRO recommendations.

Dosimetric evaluation of tandem-based cervical high-dose-rate brachytherapy treatment planning using American Brachytherapy Society 2011 recommendations

AbstractPurposeThis study evaluated dosimetric parameters for cervical high-dose-rate (HDR) brachytherapy treatment using varying dose prescription methods.MethodsThis study includes 125 tandem-based cervical HDR brachytherapy treatment plans of 25 patients who received HDR brachytherapy. Delineation of high-risk clinical target volumes (HR-CTVs) and organ at risk were done on original computed tomographic images. The dose prescription point was defined as per International Commission in Radiation Units and Measurements Report Number 38 (ICRU-38), also redefined using American Brachytherapy Society (ABS) 2011 criteria. The coverage index (V100) for each HR-CTV was calculated using dose volume histogram parameters. A plot between HR-CTV and V100was plotted using the best-fit linear regression line (least-square fit analysis).ResultsMean prescribed dose to ICRU-38 Point A was 590·47±28·65 cGy, and to ABS Point A was 593·35±30·42 cGy. There was no statistically significant difference between planned ICRU-38 and calculated ABS Point A doses (p=0·23). The plot between HR-CTV and V100is well defined by the best-fit linear regression line with a correlation coefficient of 0·9519.ConclusionFor cervical HDR brachytherapy, dose prescription to an arbitrarily defined point (e.g., Point A) does not provide consistent coverage of HR-CTV. The difference in coverage between two dose prescription approaches increases with increasing CTV. Our ongoing work evaluates the dosimetric consequences of volumetric dose prescription approaches for these patients.

Assessment of image quality and dose calculation accuracy on kV CBCT, MV CBCT, and MV CT images for urgent palliative radiotherapy treatments.

A clinical workflow was developed for urgent palliative radiotherapy treatments that integrates patient simulation, planning, quality assurance, and treatment in one 30‐minute session. This has been successfully tested and implemented clinically on a linac with MV CBCT capabilities. To make this approach available to all clinics equipped with common imaging systems, dose calculation accuracy based on treatment sites was assessed for other imaging units. We evaluated the feasibility of palliative treatment planning using on‐board imaging with respect to image quality and technical challenges. The purpose was to test multiple systems using their commercial setup, disregarding any additional in‐house development. kV CT, kV CBCT, MV CBCT, and MV CT images of water and anthropomorphic phantoms were acquired on five different imaging units (Philips MX8000 CT Scanner, and Varian TrueBeam, Elekta VersaHD, Siemens Artiste, and Accuray Tomotherapy linacs). Image quality (noise, contrast, uniformity, spatial resolution) was evaluated and compared across all machines. Using individual image value to density calibrations, dose calculation accuracies for simple treatment plans were assessed for the same phantom images. Finally, image artifacts on clinical patient images were evaluated and compared among the machines. Image contrast to visualize bony anatomy was sufficient on all machines. Despite a high noise level and low contrast, MV CT images provided the most accurate treatment plans relative to kV CT‐based planning. Spatial resolution was poorest for MV CBCT, but did not limit the visualization of small anatomical structures. A comparison of treatment plans showed that monitor units calculated based on a prescription point were within 5% difference relative to kV CT‐based plans for all machines and all studied treatment sites (brain, neck, and pelvis). Local dose differences >5% were found near the phantom edges. The gamma index for 3%/3 mm criteria was ≥95% in most cases. Best dose calculation results were obtained when the treatment isocenter was near the image isocenter for all machines. A large field of view and immediate image export to the treatment planning system were essential for a smooth workflow and were not provided on all devices. Based on this phantom study, image quality of the studied kV CBCT, MV CBCT, and MV CT on‐board imaging devices was sufficient for treatment planning in all tested cases. Treatment plans provided dose calculation accuracies within an acceptable range for simple, urgently planned palliative treatments. However, dose calculation accuracy was compromised towards the edges of an image. Feasibility for clinical implementation should be assessed separately and may be complicated by machine specific features. Image artifacts in patient images and the effect on dose calculation accuracy should be assessed in a separate, machine‐specific study.PACS number(s): 87.55.D‐, 87.57.C‐, 87.57.Q‐

Verification of Oncentra brachytherapy planning using independent calculation

This study was done to investigate the verification technique of treatment plan quality assurance for brachytherapy. It is aimed to verify the point doses in 192Ir high dose rate (HDR) brachytherapy between Oncentra Masterplan brachytherapy treatment planning system and independent calculation software at a region of rectum, bladder and prescription points for both pair ovoids and full catheter set ups. The Oncentra TPS output text files were automatically loaded into the verification programme that has been developed based on spreadsheets. The output consists of source coordinates, desired calculation point coordinates and the dwell time of a patient plan. The source strength and reference dates were entered into the programme and then dose point calculations were independently performed. The programme shows its results in a comparison of its calculated point doses with the corresponding Oncentra TPS outcome. From the total of 40 clinical cases that consisted of two fractions for 20 patients, the results that were given in term of percentage difference, it shows an agreement between TPS and independent calculation are in the range of 2%. This programme only takes a few minutes to be used is preferably recommended to be implemented as the verification technique in clinical brachytherapy dosimetry.