Dosimetry Planning Research Articles

Contrast enhanced-magnetic resonance imaging as a surrogate to map verteporfin delivery in photodynamic therapy

The use of in vivo contrast-enhanced magnetic resonance (MR) imaging as a surrogate for photosensitizer (verteporfin) dosimetry in photodynamic therapy of pancreas cancer is demonstrated by correlating MR contrast uptake to ex vivo fluorescence images on excised tissue. An orthotopic pancreatic xenograft mouse model was used for the study. A strong correlation (r = 0.57) was found for bulk intensity measurements of T1-weighted gadolinium enhancement and verteporfin fluorescence in the tumor region of interest. The use of contrast-enhanced MR imaging shows promise as a method for treatment planning and photosensitizer dosimetry in human photodynamic therapy (PDT) of pancreas cancer.

In Vivo Dose Measurements in the Postmastectomy Irradiation of a Patient With a Gas-Based Tissue Expander

In Vivo Dose Measurements in the Postmastectomy Irradiation of a Patient With a Gas-Based Tissue Expander

Changes in the Lumpectomy Cavity From Initial Whole Breast Irradiation to Sequential Boost

In whole breast irradiation (WBI) with sequential boost for breast cancer, the dosimetry plans for both WBI and boost are usually generated together before WBI. It has been concerned that the lumpectomy cavity (LC) may change at the time of boost, resulting in deviation in the dose delivery. The purpose of this work is to quantitatively characterize these LC changes.

Peer Review Chart Rounds as a Component of the Automated Workflow in a New Department

Peer-review chart rounds (PRCRs) are a crucial part of a radiation oncology department's Quality Assurance (QA) program. Ideally, all patients should be reviewed before starting treatment or at least before completing a significant portion of it. To increase likelihood of this, we decided to include PRCR as part of an automated workflow process. The radiation oncology department of Centre de Santé et de Services Sociaux de Laval opened its doors on February 21st 2012 as a fully electronic clinic as all medical, clinical and administrative activities are carried out through an Oncology Electronic Medical Record. There are 175 comprehensive and standardized care plans currently in use consisting of pre-defined order sets starting from decision to treat and extending beyond treatment completion. They are used in conjunction with more than 500 quality checklists to customize and automate the workflow. The automation reinforces the standardized care plan by specifying a sequence. When a radiation oncologist approves a dosimetry plan, a Planning Task is completed. This automatically pushes a PRCR task to the PRCR location in the sequence, which automatically adds the case to the list of patients up for review at the next PRCR. These bi-weekly meetings are interdisciplinary and attended by radiation oncologists, physicists, dosimetrists, therapists and nurses. The intent is to present all cases to insure that diagnosis, indication for treatment, contouring of target volumes and dosimetry are up to standards. The review outcome is documented. Since the opening, the PRCR data have been prospectively collected in customized assessments with discrete data. Between February 21, 2012 and December 31, 2012, 644 plans were reviewed in 82 sessions (630 patients treated): 86.8% of all plans underwent review before 25% of the prescribed dose was delivered and 64.3% actually had review prior to treatment start. When stratified for the aim of treatment, 98.8% of curative cases were presented before completing 25% of treatment (79.6% before treatment started) and 65.7% of palliative cases were presented before completing 25% of treatment (37.3% before treatment started). After peer review, 26 (4%) charts/plans needed follow-up. Of these, 6 (0.9%) plans required changes. These results suggest that including PRCR within an automated workflow process may help to improve the amount of patients peer reviewed within an appropriate time and thus the quality of care. The difference between the proportion of curative cases reviewed before starting treatment compared to palliative cases may be explained by the fact that a significant part of palliative cases were single dose treatments very often treated the same day as planning which made it impossible for them to be presented before starting treatment.

SU‐E‐T‐500: 3D‐Personalized Monte Carlo Dosimetry in 90Y‐Microspheres Therapies of Primary and Secondary Hepatic Cancers: Absorbed Dose and Biological Effective Dose Considerations

Purpose: To develop and evaluate a 3D‐Personalized Monte Carlo Dosimetry (PMCD) for treatment planning in 90Y‐microspheres therapies of unresectable hepatic cancers. Methods: The PMCD method was evaluated from the 99mTc‐MAA distribution of 20 patients treated for hepatic metastases or hepatocellular carcinoma. Using the OEDIPE software, regions of interest outlines, drawn on CT images, were used to create patient‐specific voxel phantoms and 99mTc‐MAA SPECT data were used to generate 3D‐matrices of cumulated activity. Absorbed doses and BED at the voxel scale were calculated using the MCNPX Monte Carlo transport code. OEDIPE was used to determine the maximum injectable activity (MIA) for tolerance criteria on organs at risk (OARs), i.e. the lungs and non tumoral liver (NTL). Tolerance criteria based on mean absorbed doses, mean BED (Biological Effective Dose), Dose‐Volume Histograms (DVHs) or BED‐Volume Histograms (BVHs) were considered. Those MIAs were compared to the ones recommended by conventional Methods: the Body Surface Area (BSA) method and the Partition Model with tolerance criteria on mean absorbed doses. Results: Compared to Partition Model recommendations, performing dosimetry using the PMCD method enables to increase the activity prescription while ensuring OARs radiation protection. Moreover, considering tolerance criteria based on DVHs further enhances treatment planning efficiency by taking advantage of the parallel characteristic of the liver and the lungs whose functions are not impaired if the level of irradiation to a fraction of the organ is kept sufficiently low. Finally, tolerance criteria on mean BED and BVHs further improve treatment planning by taking into account biological considerations such as cell repair, radiosensibility or dose‐rate distribution. Conclusion: Besides its feasibility and applicability in clinical routine, the interest of a personalized Monte Carlo dosimetry for treatment planning in 90Y‐microspheres therapies was confirmed from those patient studies.

3D personalized Monte Carlo dosimetry for treatment planning in 90Y-microspheres therapies of hepatic cancers

Introduction For targeted radiation therapies, treatment planning is a real challenge. In fact, the activity that can be injected to the patient is limited by the dose to organs at risk (OARs) which has to be kept below the tolerance threshold. Therefore, a 3D dosimetric method (PMCD), based on Monte Carlo calculations, has been developed in order to personalize and optimize the activity prescription for Selective Internal Radiotherapy (SIRT) treatments. Methods The PMCD method was used with data from 10 patients treated for hepatic metastases. Using the OEDIPE software, regions of interest outlines, drawn on CT images, were used to create patient-specific voxel phantoms and 99mTc-MAA SPECT data were used to generate 3D-matrices of cumulated activity. The absorbed dose and biological effective dose (BED) were calculated at the voxel scale using the MCNPX Monte Carlo transport code and OEDIPE. The maximum injectable activity (MIA) was then calculated using OEDIPE depending on tolerance criteria on OARs based on mean absorbed doses, mean BED, Dose-Volume Histograms (DVHs) or BED-Volume Histograms (BVHs). Those MIAs were compared to the ones recommended by conventional methods: the Body Surface Area (BSA) method and the Partition Model with tolerance criteria on mean absorbed doses. Results Performing a personalized dosimetry using the PMCD method enables to increase the activity prescription while ensuring OARs’ radiation protection. Moreover, considering tolerance criteria based on DVHs further enhances treatment planning efficiency by taking advantage of the parallel characteristic of the liver and the lungs whose functions are not impaired if the level of irradiation to a fraction of the organ is kept below the tolerance threshold. Finally, tolerance criteria on mean BED and BVHs further improve treatment planning by taking into account biological considerations such as cell repair, radiosensibility or dose-rate distribution. Conclusion Besides its feasibility and applicability in clinical routine, the interest of a personalized Monte Carlo dosimetry for treatment planning in 90Y-microspheres therapies was confirmed from those patient studies.

SU‐E‐T‐259: Dosimetric Comparison of Cs‐131 Vs. I‐125 Vs. Pd‐103 Intraoperative Brachytherapy in Patients with Resected Brain Metastasis

Purpose: Cs‐131, I‐125 and Pd‐103, have been used for permanent implant brachytherapy. Cs‐131 has shorter half‐life — 9.7 days as compared to I‐125 and Pd‐103 — 59.4 and 17.0 days, respectively. It is likely more biologically efficient for tumor cell kill as the initial dose rate from Cs‐131(23.9 cGy/h) is 4 times higher than that of I‐125(5.8 cGy/h) and twice of Pd‐103(13.62 cGy/h). These isotopes differ in their average gamma‐ray energies (30.4keV, 28.5keV and 20.8keV, respectively). This study examines the dosimetric differences amongst these isotopes when used as a permanent implant for patients with resected brain metastasis with regard to exposure of normal brain tissue and the potential for developing radiation necrosis (RN). Methods: 24 patients with a single newly diagnosed and resected brain metastasis were implanted with Cs‐131. Post‐op dosimetry plans were generated for Cs‐131, I‐125 model #6711 and Pd‐103 model #200. The prescription dose was 80 Gy to 5mm depth from the surface cavity. The mean air kerma strength for the Cs‐131, I‐125 and Pd‐103 seeds were 2.4U, 0.6985U and 2.11U respectively. The volume of brain tissue exposed to radiation at 100%, 80% and 50% isodose lines were compared for each isotope. Results: Significantly larger volume of brain tissue exposed to radiation, with the use of I‐125 when compared to both Cs‐131 (p less than 0.00005) and Pd‐103 (p less than 0.00004). There is no significant difference when comparing Cs‐131 to Pd‐103 (p=0.26605). Conclusion: In this analysis, we report that Cs‐131 and Pd‐103 expose less normal brain tissue to radiation when compared to I‐125, thus providing a dosimetric superiority and subjecting less tissue to RN. In addition, Cs‐131 has the shortest T1/2 and in our trial with a median follow up of 10 months, all 24 patients have 100% local control while experiencing 0% incidence of RN.

SU-E-T-481: Treatment Plans of Brain Metastasis with Cutting Edge Radiation Therapy Techniques: A Dosimetric Comparison Study of 3D Conformational Radiotherapy, Intensity Modulation Radiation Therapy, Dynamic Stereotactic Radiation Therapy and Contrast-En

Purpose: Contrast‐enhanced stereotactic synchrotron radiation therapy (SSRT) is an innovative technique based on localized dose‐enhancement effects obtained by reinforced photoelectric absorption in the target using medium energy monochromatic x‐rays (50–100 keV). The purpose of this study is to compare three cutting edge radiation therapy techniques with conventional 3D conformational radiotherapy: intensity modulated radiation therapy (IMRT), dynamic stereotactic arctherapy and contrast enhanced SSRT. Methods: A patient bearing a single parenchymal brain metastasis has received two helical 3D CT scans, the head being immobilized by a stereotactic frame. The fisrt scan is performed without contrast injection for high energy radiotherapy dosimetry. The second scan is performed 15 min after the injection of 200 mL of iodinated contrast agent contrast‐enhanced SSRT dosimetry. 3D conformational radiotherapy, IMRT, dynamic arctherapy contrast enhanced dosimetry plans have been performed on dedicated treatment planing softwares (Eclipse, IPlan and Isogray, respectively). The objective of each plans is such as the 100% of the prescribed dose is delivered at the beams isocentre and that the 70% isodose should contain all the target volume. The volume of the 70% isodose and the average and maximal dosed delivered to the organs at risk (brainstem, optical nerves, chiasma, eyes, skull bone and healthy brain parenchyma) are compared for each technique. Results: Among all high energy techniques, the stereotactic dynamic arctherapy gave the best results in terms of dose conformation and organs at risk sparing effect. However contrast enhanced SSRT provide a serious added value in terms of dosimetry by significantly reducing the dose delivered to the brainstem and the brain parenchyma. Conclusion: This study validates the dosimetric advantages of contrast enhanced SSRT for treating brain metastasis. This is another crucial step toward SSRT clinical trials.

SU-E-T-472: Personalized 3D Dose Prediction for Intrabeam Treatments Based On Patient CT Imaging with Monte Carlo GATE Simulations

Purpose: The aim of partial breast irradiation is to reduce the risk of local recurrence into the tumor bed. After surgical resection of the tumor, the Intrabeam™ system delivers a single dose fraction of 20 Gy at the surface of the applicator, irradiating the tumor bed through a 50keV X‐ray beam. However, there is currently no latitude for personalized dose prescription which is in contrast to official recommendations for individual dose optimization in radiotherapy. In this context, the study aim was to perform personalized 3D dose prediction for Intrabeam™ treatments based on patient CT imaging using Monte Carlo (MC) simulations. Methods: A model of the Intrabeam™ system was developed with GATE taking into account the different parts of the device. A preoperative CT acquisition of the patient breast is performed and included in the simulation allowing accurate dose calculation. During intra‐operative radiotherapy, thermo‐luminescent dosimeters are placed on the skin at 1 and 3 cm around the spherical applicator. Comparison between simulation results and TLD measurements are performed to confirm the dose prediction at the TLD locations. This study was performed on 10 patients, including 3 who had an intra‐operative CT acquisition in order to validate the overall dosimetry evaluation protocol. Results: Patient results show good agreement between clinical experiments and simulations. Indeed the relative mean deviation between TLD dose measurements and GATE dose scoring is 0.09% ± 0.11% with a maximum of 0.334% and less than 1% of dose estimation uncertainty (min 0.41% max 0.95%). Conclusion: We propose the use of an accurate model of the Intrabeam system on the GATE platform based on Geant4 MC toolkit. The dosimetric evaluation of the proposed platform with patient datasets supports its use for patient specific dosimetry planning.

SU-E-T-349: An Optimized Dosimetric Study of a Multi-Channel Vaginal Cylindrical Applicator in Brachytherapy

Purpose: Toptimized dosimetry of a CT/MRI multi‐lumen brachytherapy applicator was planned to treat vaginal cancer after hysterectomy. Multichannel design of cylinder includes several peripheral channels isotropically placed 5mm inside cylinder from surface with a separate central channel to allow single lumen brachytherapy as an option. The optimized dosimetry plans were compared between single‐channel versus multi‐channel to determine the sufficient coverage to the vaginal apex and other potential dosimetric advantages. Methods: CT simulation for each treatment of vaginal brachytherapy of postoperative endometrial or vaginal cancer. Seventeen CT image data sets were collected in this study. Standard single channel treatment was planned. Prescribed dose was to the 5mm cuff from the cylinder surface. PTV of 5mm rind with prescribed length was constructed. Doses to PTV and ROIs such as bladder and rectum were documented in DVH. Dose point to the apex of 5mm rind which locates at 5mm from applicator tip was specified. A second brachytherapy plan was generated using a multi‐channel loading. DVH of 5mm rind coverage, doses to apex, bladder and rectum were optimized in Oncentra brachytherapy planning system. Results: Optimized 95% to V95 and lower dose to adjacent structures were reported in multi‐channel plan. Improvements to apex dose by 3‐5% and organ sparing by 7‐14% were achieved. At the apex, inverse planning was further optimized by adjusting unequal contribution selectively from multi‐channel end. It is difficult for single channel to eliminate the cold spot at apex and maintain the dose uniformity to the 5mm cuff simultaneously. Conclusion: Possible optimization of brachytherapy treatment planning of vagina is investigated in this study by using a new multi‐lumen vaginal cylinder. The new device can increase the therapeutic ratio by improving target coverage and at the apex region as well. A reduction in the potential toxicity to the adjacent critical organs is feasible.

A Monte Carlo tool for evaluating VMAT and DIMRT treatment deliveries including planar detectors

The aim of this work is to describe and validate a new general research tool that performs Monte Carlo (MC) simulations for volumetric modulated arc therapy (VMAT) and dynamic intensity modulated radiation therapy (DIMRT), simultaneously tracking dose deposition in both the patient CT geometry and an arbitrary planar detector system. The tool is generalized to handle either entrance or exit detectors and provides the simulated dose for the individual control-points of the time-dependent VMAT and DIMRT deliveries. The MC simulation tool was developed with the EGSnrc radiation transport. For the individual control point simulation, we rotate the patient/phantom volume only (i.e. independent of the gantry and planar detector geometries) using the gantry angle in the treatment planning system (TPS) DICOM RP file such that each control point has its own unique phantom file. After MC simulation, we obtained the total dose to the phantom by summing dose contributions for all control points. Scored dose to the sensitive layer of the planar detector is available for each control point. To validate the tool, three clinical treatment plans were used including VMAT plans for a prostate case and a head-and-neck case, and a DIMRT plan for a head-and-neck case. An electronic portal imaging device operated in ‘movie’ mode was used with the VMAT plans delivered to cylindrical and anthropomorphic phantoms to validate the code using an exit detector. The DIMRT plan was delivered to a novel transmission detector, to validate the code using an entrance detector. The total MC 3D absolute doses in patient/phantom were compared with the TPS doses, while 2D MC doses were compared with planar detector doses for all individual control points, using the gamma evaluation test with 3%/3 mm criteria. The MC 3D absolute doses demonstrated excellent agreement with the TPS doses for all the tested plans, with about 95% of voxels having γ <1 for the plans. For planar dosimetry image comparisons, we defined an acceptable pass rate of >90% of percentage pixels with γ <1. We found that over 90% of control points in the plans passed this criterion. In general, our results indicate that the simulation tool is suitable for accurately calculating both patient/phantom doses and planar doses for VMAT dose delivery. The tool will be valuable to check performance and advance the development of in vivo planar detectors for use in measurement-based VMAT dose verification. In addition, the tool can be useful as an independent research tool for VMAT commissioning of the TPS and delivery system.

Commissioning of intensity modulated neutron radiotherapy (IMNRT)

Intensity modulated neutron radiotherapy (IMNRT) has been developed using inhouse treatment planning and delivery systems at the Karmanos Cancer Center∕Wayne State University Fast Neutron Therapy facility. The process of commissioning IMNRT for clinical use is presented here. Results of commissioning tests are provided including validation measurements using representative patient plans as well as those from the TG-119 test suite. IMNRT plans were created using the Varian Eclipse optimization algorithm and an inhouse planning system for calculation of neutron dose distributions. Tissue equivalent ionization chambers and an ionization chamber array were used for point dose and planar dose distribution comparisons with calculated values. Validation plans were delivered to water and virtual water phantoms using TG-119 measurement points and evaluation techniques. Photon and neutron doses were evaluated both inside and outside the target volume for a typical IMNRT plan to determine effects of intensity modulation on the photon dose component. Monitor unit linearity and effects of beam current and gantry angle on output were investigated, and an independent validation of neutron dosimetry was obtained. While IMNRT plan quality is superior to conventional fast neutron therapy plans for clinical sites such as prostate and head and neck, it is inferior to photon IMRT for most TG-119 planning goals, particularly for complex cases. This results significantly from current limitations on the number of segments. Measured and calculated doses for 11 representative plans (six prostate∕five head and neck) agreed to within -0.8 ± 1.4% and 5.0 ± 6.0% within and outside the target, respectively. Nearly all (22∕24) ion chamber point measurements in the two phantom arrangements were within the respective confidence intervals for the quantity [(measured-planned)∕prescription dose] derived in TG-119. Mean differences for all measurements were 0.5% (max = 7.0%) and 1.4% (max = 4.1%) in water and virtual water, respectively. The mean gamma pass rate for all cases was 92.8% (min = 88.6%). These pass rates are lower than typically achieved with photon IMRT, warranting development of a planar dosimetry system designed specifically for IMNRT and∕or the improvement of neutron beam modeling in the penumbral region. The fractional photon dose component did not change significantly in a typical IMNRT plan versus a conventional fast neutron therapy plan, and IMNRT delivery is not expected to significantly alter the RBE. All other commissioning results were considered satisfactory for clinical implementation of IMNRT, including the external neutron dose validation, which agreed with the predicted neutron dose to within 1%. IMNRT has been successfully commissioned for clinical use. While current plan quality is inferior to photon IMRT, it is superior to conventional fast neutron therapy. Ion chamber validation results for IMNRT commissioning are also comparable to those typically achieved with photon IMRT. Gamma pass rates for planar dose distributions are lower than typically observed for photon IMRT but may be improved with improved planar dosimetry equipment and beam modeling techniques. In the meantime, patient-specific quality assurance measurements should rely more heavily on point dose measurements with tissue equivalent ionization chambers. No significant technical impediments are anticipated in the clinical implementation of IMNRT as described here.

Establishment and validation of a method for multi-dose irradiation of cells in 96-well microplates

Microplates are useful tools in chemistry, biotechnology and molecular biology. In radiobiology research, these can be also applied to assess the effect of a certain radiation dose delivered to the whole microplate, to test radio-sensitivity, radio-sensitization or radio-protection. Whether different radiation doses can be accurately applied to a single 96-well plate to further facilitate and accelerated research by one hand and spare funds on the other, is a question dealt in the current paper. Following repeated ion-chamber, TLD and radiotherapy planning dosimetry we established a method for multi-dose irradiation of cell cultures within a 96-well plate, which allows an accurate delivery of desired doses in sequential columns of the microplate. Up to eight different dose levels can be tested in one microplate. This method results in fast and reliable estimation of radiation dose–response curves.

Integration method of 3D MR spectroscopy into treatment planning system for glioblastoma IMRT dose painting with integrated simultaneous boost

BackgroundTo integrate 3D MR spectroscopy imaging (MRSI) in the treatment planning system (TPS) for glioblastoma dose painting to guide simultaneous integrated boost (SIB) in intensity-modulated radiation therapy (IMRT).MethodsFor sixteen glioblastoma patients, we have simulated three types of dosimetry plans, one conventional plan of 60-Gy in 3D conformational radiotherapy (3D-CRT), one 60-Gy plan in IMRT and one 72-Gy plan in SIB-IMRT. All sixteen MRSI metabolic maps were integrated into TPS, using normalization with color-space conversion and threshold-based segmentation. The fusion between the metabolic maps and the planning CT scans were assessed. Dosimetry comparisons were performed between the different plans of 60-Gy 3D-CRT, 60-Gy IMRT and 72-Gy SIB-IMRT, the last plan was targeted on MRSI abnormalities and contrast enhancement (CE).ResultsFusion assessment was performed for 160 transformations. It resulted in maximum differences <1.00 mm for translation parameters and ≤1.15° for rotation. Dosimetry plans of 72-Gy SIB-IMRT and 60-Gy IMRT showed a significantly decreased maximum dose to the brainstem (44.00 and 44.30 vs. 57.01 Gy) and decreased high dose-volumes to normal brain (19 and 20 vs. 23% and 7 and 7 vs. 12%) compared to 60-Gy 3D-CRT (p < 0.05).ConclusionsDelivering standard doses to conventional target and higher doses to new target volumes characterized by MRSI and CE is now possible and does not increase dose to organs at risk. MRSI and CE abnormalities are now integrated for glioblastoma SIB-IMRT, concomitant with temozolomide, in an ongoing multi-institutional phase-III clinical trial. Our method of MR spectroscopy maps integration to TPS is robust and reliable; integration to neuronavigation systems with this method could also improve glioblastoma resection or guide biopsies.

Early prediction of tumour response to PRRT

Summary[177Lu-DOTA0, Tyr3]-octreotate (177Lu-octreotate) in peptide receptor radionuclide therapy (PRRT) offers direct intra-therapeutic dosimetry. The aim of this study was to compare tumour and non-tumour parameters and assess intra-individual variations. Patients, methods: Retrospective analysis of 53 consecutive PRRT treatment cycles (mean activity of 7.53 ± 0.46 GBq 177Lu-octreotate, intended four cycles at intervals of 10–14 weeks, standard nephroprotection) in 27 GEP NET patients. Extended planar dosimetry with serial wholebody imaging on selected, non-superimposed tumour and non-tumour regions; liver (LM), bone (BM), and other (OM) metastases. The per-cycle variation was compared with posttreatment response (CT/MRI three months post-treatment, modified SWOG criteria). Results: Residence time in tumor lesions (133–147 h) exceeded that in kidneys (93 h). Tumour-to-kidney absorbed dose ratios ranged from 14 to 28 (LM, BM, OM). Intra-individual per-cycle dose variation was insignificant for kidneys, but significant for metastases (LM, BM, and OM; p &lt; 0.05). The mean per-cycle decrease of tumour absorbed dose (_D/A0[%]) was linked to morphologic response after PRRT. A mean decrease of &gt;20% was predictive of a partial or minor remission in all 11 evaluable patients, while absent significant dose reduction indicated stable or progressive disease in 4/5 patients. The dose decrease was unrelated to volume effects and also observed for BM. Conclusion: Besides confirmation of a favourable tumour-to-kidney parameter relation for 177Lu-octreotate, stepwise intra-lesional comparison seems to imply a prognostic impact of tumor dosimetry: The early per-cycle change _D/A0 between treatment cycles may predict the outcome after PRRT. Larger studies are needed to confirm this finding.

Monitoring photodynamic therapy of head and neck malignancies with optical spectroscopies

In recent years there has been significant developments in photosensitizers (PSs), light sources and light delivery systems that have allowed decreasing the treatment time and skin phototoxicity resulting in more frequent use of photodynamic therapy (PDT) in the clinical settings. Compared to standard treatment approaches such as chemo-radiation and surgery, PDT has much reduced morbidity for head and neck malignancies and is becoming an alternative treatment option. It can be used as an adjunct therapy to other treatment modalities without any additive cumulative side effects. Surface illumination can be an option for pre-malignant and early-stage malignancies while interstitial treatment is for debulking of thick tumors in the head and neck region. PDT can achieve equivalent or greater efficacy in treating head and neck malignancies, suggesting that it may be considered as a first line therapy in the future. Despite progressive development, clinical PDT needs improvement in several topics for wider acceptance including standardization of protocols that involve the same administrated light and PS doses and establishing quantitative tools for PDT dosimetry planning and response monitoring. Quantitative measures such as optical parameters, PS concentration, tissue oxygenation and blood flow are essential for accurate PDT dosimetry as well as PDT response monitoring and assessing therapy outcome. Unlike conventional imaging modalities like magnetic resonance imaging, novel optical imaging techniques can quantify PDT-related parameters without any contrast agent administration and enable real-time assessment during PDT for providing fast feedback to clinicians. Ongoing developments in optical imaging offer the promise of optimization of PDT protocols with improved outcomes.

Laser interstitial thermotherapy of small breast fibroadenomas: Numerical simulations

Laser interstitial thermotherapy (LITT) is potentially a novel method to treat small breast fibroadenoma, without the need for surgical removal. Dosimetry planning and conformation of the treated area of tumor remain major issues, especially for a moving organ such as the breast. Pre-treatment simulation planning of this therapy is an effective method to predict the final thermal damage. In this study, a mathematical model is elaborated to simulate the heat distribution and the thermal damage. The mathematical model was based on finite element method (FEM) to solve the light distribution, bioheat, and thermal damage equations. Six simulations were performed with the following powers: 5, 6, 7, 8, 9, and 10 W (λ = 980 nm), and for an irradiation time of 125 seconds, with a 50 °C iso-damage temperature. To validate these simulations, six turkey breast samples were irradiated with parameters used for simulations. Volumes of thermal damage were calculated by using formulas: spherical, Elliptical, and Carlsson volumes and compared to the simulated volumes. Differences between volumes were from 0.01 to 1 cm3. Interpolations between volumes from ex vivo experiments with corresponding powers were established. The relationship between the volume of the thermal damage and the laser power was described by a polynomial equation (R2 = 0.99). The power estimated by the interpolation to obtain 1 cm3 of thermal damage was 7.4 W (922 J) and the maximum corresponding temperature was 90 °C. In this study, a good correlation was established between simulation and ex vivo experiments of LITT for fibroadenoma breast cancer.

The impact of continuously‐variable dose rate VMAT on beam stability, MLC positioning, and overall plan dosimetry

A recent control system update for Elekta linear accelerators includes the ability to deliver volumetric‐modulated arc therapy (VMAT) with continuously variable dose rate (CVDR), rather than a number of fixed binned dose rates (BDR). The capacity to select from a larger range of dose rates allows the linac to maintain higher gantry speeds, resulting in faster, smoother deliveries. The purpose of this study is to investigate two components of CVDR delivery — the increase in average dose rate and gantry speed, and a determination of their effects on beam stability, MLC positioning, and overall plan dosimetry. Initially, ten VMAT plans (5 prostate, 5 head and neck) were delivered to a Delta4 dosimetric phantom using both the BDR and CVDR systems. The plans were found to be dosimetrically robust using both delivery methods, although CVDR was observed to give higher gamma pass rates at the 2%/2 mm gamma level for prostates (p < 0.01). For the dual arc head‐and‐neck plans, CVDR delivery resulted in improved pass rates at all gamma levels (2%/2 mm to 4%/4 mm) for individual arc verifications (p < 0.01), but gave similar results to BDR when both arcs were combined. To investigate the impact of increased gantry speed on MLC positioning, a dynamic leaf‐tracking tool was developed using the electronic portal imaging device (EPID). Comparing the detected MLC positions to those expected from the plan, CVDR was observed to result in a larger mean error compared to BDR (0.13 cm and 0.06 cm, respectively, p < 0.01). The EPID images were also used to monitor beam stability during delivery. It was found that the CVDR deliveries had a lower standard deviation of the gun‐target (GT) and transverse (AB) profiles (p < 0.01). This study has determined that CVDR may offer a dosimetric advantage for VMAT plans. While the higher gantry speed of CVDR appears to increase deviations in MLC positioning, the relative effect on dosimetry is lower than the positive impact of a flatter and more stable beam profile.PACS numbers: 87.56.bd; 87.55.km; 87.55.Qr

An Optimization Study and Comparison of a Multichannel Vaginal Cylinder Versus Single Channel Cylinder Applicator in High-dose-rate Brachytherapy

A new CT/MRI multi-lumen brachytherapy applicator to optimize dosimetry and treatment of vaginal targets. The design includes several peripheral channels isotropically placed 5mm inside cylinder surface with a separate central channel allowing single lumen brachytherapy as an option. We compared optimized dosimetry plans between single channel versus multi-channel to determine potential dosimetric advantages in vaginal cancer treatment after hysterectomy.

American Society for Radiation Oncology's Performance Assessment for the Advancement of Radiation Oncology Treatment: A practical approach for informing practice improvement

PurposePerformance Assessment for the Advancement of Radiation Oncology Treatment (PAAROT) is a practice quality improvement program. This study seeks to determine baseline performance rates and practice variation from PAAROT data. Methods and MaterialsThe cohort includes all physicians from academic, hospital, and free-standing settings who completed at least 10 consecutive self-audited medical records in the PAAROT program (version 2.5) from 2010 to 2011 (n = 519 medical records). Mean performance rates were analyzed at the physician and medical record levels and, where appropriate, were stratified by the physician's practice setting. ResultsForty-nine physicians were included in the study; 22 (45%), 17 (35%), and 10 (20%) physicians practiced in a hospital, academic, or a free-standing setting, respectively. The measures with a high adoption rate (more than 80%) include the following: documentation of history and physical; review of physics and dosimetry plan by radiation oncologist; patient informed risks of therapy; evaluation of acute symptoms during therapy; pathology in consultation note; communication of treatment summary within 30 days of treatment completion; documentation of intent of treatment, use of clinical guidelines or published data; and documentation of American Joint Committee on Cancer staging. Lower rates of adoption were noted (mean, 65%; range, 0-100%) when these measures were converted to a composite measure. Low adherence was noted for screening of a pain using a standard scale (mean, 58%; range, 0-100%). Physicians from an academic setting scored higher on the composite measure (40%) compared with those from a hospital setting (36%) and from a free-standing setting (24%); (P < .001). Physicians from a hospital setting scored higher on the quality indicator of screening for pain (54%) compared with physicians from an academic setting (35%) and free-standing setting (11%) (P < .001). ConclusionsThis first assessment of PAAROT (version 2.5) data provides an initial snapshot on the use of quality indicators and practice patterns for radiation oncology. Self-reported practice data and the use of quality indicators will become important for the purpose of continuous, prospective evidence-based learning on an individual basis. Despite the small sample size, the data from this study will help address potential improvement opportunities for the next iteration of the PAAROT program.