Eye Plaque Brachytherapy for Choroidal Malignant Melanoma: A Case Report on the Use of Innovative Technology to Expand Access, Improve Practice, and Enhance Outcomes

Our institute established an eye plaque interstitial brachytherapy (EPIBT) program in 2007 using the Collaborative Ocular Melanoma Study (COMS) eye plaque. In this case report, we demonstrated an eye plaque treatment planned and executed using Eye Physics Plaque (Los Alamitos, CA) for a 72-year-old male patient with an extra-large tumor with a maximum width of 18.6 mm and height of 13.7 mm. The use of a customized eye plaque, manufactured through three-dimensional (3D) printing, has empowered us to plan and administer treatment for this patient with uveal melanoma. Without this option, enucleation, an option declined by the patient, or proton beam therapy (PBT), which the patient was unwilling to pursue in another state, would have been the alternative course of action. We were able to use more than one activity of the I-125 seeds, which enabled us to shape and reduce the dose to normal surrounding structures at risk within the orbit and in the vicinity of the orbital cavity. Using the dose evaluation tools available with the modern treatment planning system, we reduced the prescription dose from 85 to 70 Gy, with D90 of 140 Gy, thereby providing effective treatment and limiting risk organ doses. In summary, we were able to dose-deescalate without compromising the chances of controlling retinal/scleral tumors. The patient is doing well from a recent follow-up visit 12 months after the eye plaque brachytherapy treatment. The tumor was 4.80 mm high, 1/3 of the original height, and vision is back to 20/60, demonstrating a successful treatment.

The Dosimetric Analysis of Duodenal and Intestinal Toxicity After a Curative Dose Re-irradiation Using the Intensity-Modulated Radiotherapy for Abdominopelvic Lymph Node Lesions

INTRODUCTION

This study aimed to examine the influence of dosimetric factors on gastrointestinal toxicity after radical re-irradiation for lymph node recurrence in the abdominopelvic region using a composite plan.

METHODS

Between January 2008 and March 2017, 33 patients underwent radical re-irradiation for lymph node recurrence in the abdominopelvic region with a complete overlap with previous radiation therapy (RT) with the median prescription dose of the second RT of 71.7 Gy10. Re-irradiation planning protocol for target volume and organs at risk (OARs) (duodenum, small and large intestines) was decided as follows: more than equal to 97% of the prescription dose was administered to the D95 (percentage of the minimum dose that covered 95% of the target volume) of planning target volume (PTV); minimal dose to the maximally irradiated doses delivered to 1cc [D1 cc] and 5cc [D5 cc] of OARs was set below 70 Gy3 and 50 Gy3, respectively; and D1 cc and D5 cc in the cumulative plans to OARs were 120 Gy3 and 100 Gy3. Kaplan-Meier analyses were performed to evaluate overall survival (OS) and univariate log-rank and multivariate Cox proportional hazards model analyses were performed to explore predictive factors. Using dose summation of the first and re-irradiation plans, we conducted a dosimetric analysis for grade ≥ 3 toxicities of the duodenum and intestine.

RESULTS

With a median follow-up of 18 months, the two-year OS rate was 45.5%. The number of RT fields (localized or multiple) was a significant predisposing factor for OS rate with a hazard ratio of 0.23 (95% confidence interval 0.07-0.73). The two-year OS of the patients with a localized RT field was 63.6% and 9.1% for multiple RT fields (p= 0.00007). Four patients experienced grade ≥3 gastrointestinal toxicity related to re-irradiation (4/33=12.1%). We could not find any predisposing dosimetric value in the comparisons with and without toxicity.

CONCLUSIONS

The dose constraints presented in this study are relatively low rates of toxicity, which may be useful when planning re-irradiation. Especially, for the patients who could be treated with localized RT field, radical re-irradiation with a high curative dose is a good option. No dosimetric predisposing factor was found for radical re-irradiation of abdominopelvic lesions in the composite plan.

Optimal Bladder Condition in Volumetric Modulated Arc Therapy for Prostate Cancer: The Role of Superior-Inferior Lengths of the Bladder and Dose Constraints

Background Optimal bladder conditions based on dose constraints in prostate cancer radiation therapy (RT) are important. In this study, the superior-inferior (SI) lengths of the bladder were assessed to define the ideal bladder state for RT. Materials and methods In this study, 50 prostate cancer cases treated with three-dimensional conformal radiation therapy between January and December 2021 were retrospectively analyzed. Using their CT data, a volumetric modulated arc therapy (VMAT) plan was simulated. Bladder dose constraints and dimensions, including SI, right-left (RL), and anterior-posterior (AP) lengths, were assessed. In total, 28 cases met the dose constraints and 22 cases did not meet the dose constraints.  Results Median bladder volumes (BVs) for compliant and non-compliant cases were 163.6 ml and 88.5 ml, respectively (p<0.0001). For compliant plans, median bladder dimensions were RL: 78 mm, AP: 89 mm, and SI: 51 mm. Non-compliant plans showed RL: 72 mm, AP: 84 mm, and SI: 42 mm, with significant differences (SI: p=0.0004, RL: p=0.0065, AP: p=0.037). Established thresholds were SI: 46 mm, RL: 92 mm, AP: 75 mm, and BV: 142.8 ml. SI showed the strongest correlation with BV (coefficient: 0.78). Conclusions This study analyzed the SI lengths of the bladder concerning dose constraints in VMAT for prostate cancer. It was concluded that smooth treatment planning could be achieved with proper consideration of the bladder's SI distance. Further case collection and prospective studies are warranted.

Averaging of absorbed doses: How matter matters

BACKGROUND

Dosimetry in radionuclide therapy often requires the calculation of average absorbed doses within and between spatial regions, for example, for voxel-based dosimetry methods, for paired organs, or across multiple tumors. Formation of such averages can be made in different ways, starting from different definitions.

PURPOSE

The aim of this study is to formally specify different averaging strategies for absorbed doses, and to compare their results when applied to absorbed dose distributions that are non-uniform within and between regions.

METHODS

For averaging within regions, two definitions of the average absorbed dose are considered: the simple average over the region (the region average) and the average when weighting by the mass density (density-weighted region average). The latter is shown to follow from the definition of mean absorbed dose according to the ICRU, and to be consistent with the MIRD formalism. For averaging between different spatial regions, three definitions follow: the volume-weighted, the mass-weighted, and the unweighted average. With respect to characterizing non-uniformity, the different average definitions lead to the use of dose-volume histograms (DVHs) (region average), dose-mass histograms (DMHs) (density-weighted region average), and unweighted histograms (unweighted average). Average absorbed doses are calculated for three worked examples, starting from the different definitions. The first, schematic, example concerns the calculation of the average absorbed dose between two regions with different volumes or mass densities. The second, stylized, example concerns voxel-based dosimetry, for which the average absorbed-dose rate within a region is calculated. The geometries studied include three 177 Lu-filled voxelized spheres, where the sphere masses are held constant while the material compositions, densities, and volumes are varied. For comparison, the mean absorbed-dose rates obtained using unit-density sphere S-values are also included. The third example concerns SPECT/CT-based tumor dosimetry for five patients undergoing therapy with 177 Lu-PSMA and six patients undergoing therapy with 177 Lu-DOTA-TATE, for which the average absorbed-dose rates across multiple tumors are calculated. For the second and third examples, analyses also include representations by histograms.

RESULTS

Example 1 shows that the average absorbed doses, calculated using different definitions, can differ considerably if the masses and absorbed doses for two regions are markedly different. From example 2 it is seen that the density-weighted region average is stable under different activity and density distributions and is also in line with results using S-values. In contrast, the region average varies as function of the activity distribution. In example 3, the absorbed dose rates for individual tumors differ by (1.1 ± 4.3)% and (-0.1 ± 0.4)% with maximum deviations of +34.4% and -1.4% for 177 Lu-PSMA and 177 Lu-DOTA-TATE, respectively, when calculated as region averages or density-weighted region averages, with largest deviations obtained when the density is non-uniform. The average absorbed doses calculated across all tumors are similar when comparing mass-weighted and volume-weighted averages but these differ substantially from unweighted averages.

CONCLUSION

Different strategies for averaging of absorbed doses within and between regions can lead to substantially different absorbed-dose estimates. At reporting of radionuclide therapy dosimetry, it is important to specify the averaging strategy applied.

Dose-Volume Histogram Parameters and Quality of Life in Patients with Prostate Cancer Treated with Surgery and High-Dose Volumetric-Intensity-Modulated Arc Therapy to the Prostate Bed

INTRODUCTION

Prostate bed radiotherapy (RT) is a major affecter of patients' long-term quality of life (QoL). To ensure the best possible outcome of these patients, dose constraints are key for optimal RT planning and delivery. However, establishing refined dose constraints requires access to patient-level data. Therefore, we aimed to provide such data on the relationship between OAR and gastrointestinal (GI) as well as genitourinary (GU) QoL outcomes of a homogenous patient cohort who received dose-intensified post-operative RT to the prostate bed. Furthermore, we aimed to conduct an exploratory analysis of the resulting data.

METHODS

Patients who were treated with prostate bed RT between 2010 and 2020 were inquired about their QoL based on the Expanded Prostate Cancer Index Composite (EPIC). Those (n = 99) who received volumetric arc therapy (VMAT) of at least 70 Gy to the prostate bed were included. Dose-volume histogram (DVH) parameters were gathered and correlated with the EPIC scores.

RESULTS

The median age at the time of prostate bed RT was 68.9 years, and patients were inquired about their QoL in the median 2.3 years after RT. The median pre-RT prostate-specific antigen (PSA) serum level was 0.35 ng/mL. The median duration between surgery and RT was 1.5 years. The median prescribed dose to the prostate bed was 72 Gy. A total of 61.6% received prostate bed RT only. For the bladder, the highest level of statistical correlation (p < 0.01) was seen for V10-20Gy, Dmean and Dmedian with urinary QoL. For bladder wall, the highest level of statistically significant correlation (p < 0.01) was seen for V5-25Gy, Dmean and Dmedian with urinary QoL. Penile bulb V70Gy was statistically significantly correlated with sexual QoL (p < 0.05). A larger rectal volume was significantly correlated with improved bowel QoL (p < 0.05). Sigmoid and urethral DVH parameters as well as the surgical approach were not statistically significantly correlated with QoL.

CONCLUSION

Specific dose constraints for bladder volumes receiving low doses seem desirable for the further optimization of prostate bed RT. This may be particularly relevant in the context of the aspiration of establishing focal RT of prostate cancer and its local recurrences. Our comprehensive dataset may aid future researchers in achieving these goals.

Risk factors for primary site necrosis after definitive concurrent chemoradiotherapy in head and neck cancer

OBJECTIVE

To identify risk factors of primary site necrosis (PSN) after definitive concurrent chemoradiation therapy (CCRT) in patients with nonoral cavity head and neck cancer (HNC).

METHODS

We retrospectively reviewed the records of 256 patients treated with CCRT for HNC during 2010-2018. Patient-related (age, sex, history of smoking, hypertension, diabetes mellitus, serum hemoglobin and albumin), tumor-related (tumor site, American Joint Committee on Cancer stage), and treatment-related (induction chemotherapy, maximum point dose and mean dose of planning target volume [PTV] of primary site, absolute volumes of the PTV receiving >50-75 Gy [V₅₀-V₇₅]) variables were analyzed. Critical dosimetric parameters of PSN were identified using receiver operating characteristic (ROC) curve analysis. Univariate and multivariate Cox regression analyses were used to select the significant variables for PSN development.

RESULTS

After median follow-up of 44 months (range, 5-127), 7 patients (2.7%) developed PSN with a median time to event of 10 months (range, 3-12). V₇₀ ⩾79.8 mL was the most critical dosimetric parameter for PSN (area under the ROC curve 0.873, sensitivity 0.857, specificity 0.747). In univariate analyses, pretreatment serum hemoglobin <11.0 g/dL and V₇₀ ⩾79.8 mL were significantly associated with higher risk of PSN occurrence. V₇₀ ⩾79.8 mL (hazard ratio 5.960, 95% confidence interval 1.289-27.548; p = 0.022) remained significant predictors of PSN in multivariate analyses.

CONCLUSIONS

V₇₀ ⩾79.8 mL is significantly related to the risk of developing PSN. These findings offer valuable clues for clinicians to minimize PSN incidence in HNC treated with curative CCRT.

Efficient dose-volume histogram-based pretreatment patient-specific quality assurance methodology with combined deep learning and machine learning models for volumetric modulated arc radiotherapy

BACKGROUND

Weak correlation between gamma passing rates and dose differences in target volumes and organs at risk (OARs) has been reported in several studies. Evaluation on the differences between planned dose-volume histogram (DVH) and reconstructed DVH from measurement was adopted and incorporated into patient-specific quality assurance (PSQA). However, it is difficult to develop a methodology allowing the evaluation of errors on DVHs accurately and quickly.

PURPOSE

To develop a DVH-based pretreatment PSQA for volumetric modulated arc therapy (VMAT) with combined deep learning (DL) and machine learning models to overcome the limitation of conventional gamma index (GI) and improve the efficiency of DVH-based PSQA.

METHODS

A DL model with a three-dimensional squeeze-and-excitation residual blocks incorporated into a modified U-net was developed to predict the measured PSQA DVHs of 208 head-and-neck (H&N) cancer patients underwent VMAT between 2018 and 2021 from two hospitals, in which 162 cases was randomly selected for training, 18 for validation, and 28 for testing. After evaluating the differences between treatment planning system (TPS) and PSQA DVHs predicted by DL model with multiple metrics, a pass or fail (PoF) classification model was developed using XGBoost algorithm. Evaluation of domain experts on dose errors between TPS and reconstructed PSQA DVHs was taken as ground truth for PoF classification model training.

RESULTS

The prediction model was able to achieve a good agreement between predicted, measured, and TPS doses. Quantitative evaluation demonstrated no significant difference between predicted PSQA dose and measured dose for target and OARs, except for D_mean of PTV6900 (p = 0.001), D₅₀ of PTV6000 (p = 0.014), D₂ of PTV5400 (p = 0.009), D₅₀ of left parotid (p = 0.015), and D_max of left inner ear (p = 0.007). The XGBoost model achieved an area under curves, accuracy, sensitivity, and specificity of 0.89 versus 0.88, 0.89 versus 0.86, 0. 71 versus 0.71, and 0.95 versus 0.91 with measured and predicted PSQA doses, respectively. The agreement between domain experts and the classification model was 86% for 28 test cases.

CONCLUSIONS

The successful prediction of PSQA doses and classification of PoF for H&N VMAT PSQA indicating that this DVH-based PSQA method is promising to overcome the limitations of GI and to improve the efficiency and accuracy of VMAT delivery.

Assessment of Dose-Volume Histogram Precision for Five Clinical Systems

PURPOSE

To investigate the dependency of dose-volume histogram behavior (DVH) and precision on underlying DICOM discretization using shapes and dose distributions with known analytical DVHs for five commercial DVH calculators.

METHODS

DVHs and summary metrics were extracted from all five systems using synthetic DICOM cone and cylinder objects for which the true volume and DVH curves were known. Trends in the curves and metrics were explored by varying the underlying voxelization of the CT image, structure set, and dose grid as well by varying the geometry of the structure and direction of a linear dose gradient. Using synthetic structures allowed for comparison with ground-truth DVH curves to assess their accuracy while an algorithm was additionally developed to assess the precision of each system. The precision was calculated with a novel algorithm that treats any "stair step" behavior in a DVH curve as an uncertainty band and calculates the width, characterized as a percent difference, of the band for various DVH metrics. The underlying voxelization was additionally changed and DVHs were extracted for two clinical examples. The details of how each system calculated DVHs were also investigated and tendencies in the calculated curves, metrics, and precision were related to choices made in the calculation methodology.

RESULTS

Calculation methodology differences that had a noticeable impact on the DVH curves and summary metrics include supersampling beyond the input grids and interpretation of the superior and inferior ends of the structures. Amongst the systems studied, the median precision ranged from 0.902% to 3.22%, and interquartile ranges varied from 1.09% to 3.91%.

CONCLUSIONS

Commercial dose-evaluation solutions can calculate different DVH curves, structure volume measures, and dose statistics for the same input data due to differences in their calculation methodologies. This study highlights the importance of understanding and investigating the DVH calculation when considering a new clinical system and when using more than one system for data transfer. This article is protected by copyright. All rights reserved.

To evaluate the use of tandem and cylinder as an intracavitary brachytherapy device for carcinoma of the cervix with regard to local control and toxicities

Introduction

Brachytherapy always remains a keystone in the treatment of gynecological carcinoma for both definitive and adjuvant treatments. Due to the rapid fall-off nature of brachytherapy, the target gets a high dose with a low dose to the normal organs nearby and thereby increasing the tumor control probability.

Aims and Objectives

This study aims at the evaluation of local control and toxicities in the carcinoma of the cervix using tandem and cylinder as brachytherapy applicator.

Materials and Methods

The study was conducted between January 2014 and December 2018 in a tertiary care hospital. Thirty-one patients who fulfilled our set criterion of Clinical stage IB3-IVA, Performance status Eastern Cooperative Oncology Group 0-2 were selected. All patients were treated initially with external beam radiotherapy and later by high dose rate intracavitary brachytherapy after completion of external beam radiation therapy (EBRT). A dose of 18-21 Gy was delivered to the residual disease in three sessions with a 1-week interval between each session. The dose was optimized in such a way that the organs at risk (OAR), namely bladder and rectum received doses within their tolerance levels. The patients were continuously monitored using Common Terminology Criteria for Adverse Events version 5.0 for both acute and late toxicities and by imaging for local control. Statistical analysis using SPSS Version 20.0 (SPSS Inc., Chicago, Illinois, USA) was used to evaluate the results. Continuous variables were expressed as mean ± standard deviation, and categorical variables were summarized as frequencies and percentages.

Results

Out of the 31 patients, 5 (16.1%) experienced radiation-induced Grade 1 skin changes which were due to EBRT, 1 (3.2%) had Grade 1 G. I. T toxicity, 1 (3.2%) had Grade 1 radiation-induced vaginal mucositis after brachytherapy. At 6-8-week follow-up, all the patients showed no evidence of disease on radiological imaging. At 3 months of follow-up, 1 (3.2%) patient had radiation-induced proctitis of Grades 2 and 3 (9.7%) had radiation-induced cystitis of Grades 1 and 1 (3.2%) had Grade 2 cystitis. At 6 months of follow-up, 1 (3.2%) had Grade 1, 1 (3.2%) had Grade 2, and 1 (3.2%) had Grade 3 radiation-induced proctitis. At 3 months of follow-up, 29 (93.5%) patients had no evidence of disease, while 2 (6.5%) were having residual disease on imaging. At 6 months of follow-up, all the patients were disease-free. At 12 months of follow-up, 26 (83.9%) patients were disease-free, 1 (3.2%) had local recurrence, 2 (6.5%) had distant metastasis, and 2 (6.5%) had expired. At 24 months of follow-up, 26 patients were disease-free. Acute and late toxicities were similar to those used in the treatment of carcinoma cervix by standard brachytherapy applicators. Local control was achieved in 83.87% of cases. Two-year survival was 93.5%.

Conclusion

We observed that the tandem and cylinder applicator is an acceptable applicator to be used for intracavitary brachytherapy. It is safe and simple besides this; the toxicities and local control are similar to the other standard applicators used in brachytherapy in carcinoma cervix. However, the required dose prescription to point A was not possible in all the patients due to limitations of OARs. Furthermore, long-term follow-up is needed to see the patterns of failure, recurrence-free survival, overall survival, and long-term toxicities in the treated patients.

Role of non-absorbable oral antibiotics in bowel preparation for intracavitary brachytherapy: effects of rifaximin on rectal dosimetric parameters during vaginal cuff brachytherapy

Purpose

Brachytherapy is a major tool for dose escalation in gynecological cancer treatment. Control of rectal repletion is particularly challenging; it can impact dose received by this organ at risk and there are reported toxicities. The use of methods, such as enema and bowel preparation, to reduce rectal volume is a difficult process for patients, and its repeatability requires patients' cooperation. Due to the effect of antibiotics on reducing intestinal gases, this study was conducted to measure the effect of adding rifaximin to bowel preparation on rectal dose-volume histogram (DVH) parameters.

Material and methods

In this prospective interventional study, 24 patients with cervical and endometrial cancer were treated with adjuvant high-dose-rate (HDR) brachytherapy. Both first and second sessions of brachytherapy were performed with bowel preparation, before and after the administration of rifaximin, respectively. The rectum was contoured as an organ at risk, and DVH parameters were recorded and compared in both sessions using magnetic resonance imaging (MRI)-based 3D treatment planning system.

Results

Rifaximin consumption reduced the rectal volume (p = 0.01), but had no significant correlation with other DVH parameters, especially D_2cc (p = 0.599). Moreover, rectal volume had no significant correlation with DVH parameters (all p-values ≤ 0.05).

Conclusions

Even though the addition of rifaximin to bowel preparation significantly reduced rectal volume, no significant difference was observed in DVH parameters. Therefore, it is recommended that adjuvant vaginal cuff HDR brachytherapy should be performed without the use of rifaximin, until further researches' validate its effects.

Impact of pre-brachytherapy magnetic resonance imaging on dose-volume histogram of locally advanced cervical cancer patients treated with radiotherapy including high-dose-rate brachytherapy

Purpose

This study investigated the suitability of brachytherapy technique selection based on pre-brachytherapy magnetic resonance imaging (MRI) findings in cervical cancer by evaluating dose-volume histogram parameters.

Material and methods

We retrospectively evaluated data from 61 patients with cervical cancer who underwent pre-brachytherapy MRI within 7 days before their first high-dose-rate brachytherapy treatment, selected according to pre-brachytherapy MRI findings. Combined intracavitary brachytherapy with interstitial techniques (IC/ISBT) or interstitial brachytherapy (ISBT) were favored treatments for poor-responding tumors after concurrent chemoradiotherapy, asymmetrical tumors, bulky parametrial extensions, bulky primary disease, and extensive paravaginal or distal vaginal involvement. Intracavitary brachytherapy (ICBT) was the preferred treatment for small tumors without extensive involvement of the vagina and parametrium.

Results

The median tumor size was 58 mm on pre-treatment MRI and 38 mm on pre-brachytherapy MRI. On pre-brachytherapy MRI, 13 patients had a tumor with severe vaginal invasion, 15 patients presented with an asymmetrical bulky tumor, and 4 patients had bulky residual tumors. IC/ISBT or ISBT were administered to 26 patients (43%). Median equivalent dose in 2 Gy fractions of clinical target volume D₉₀ was 70.8 Gy for all patients. Median clinical target volume D₉₀ in each brachytherapy session exceeded the prescribed dose in both patients treated with ICBT and IC/ISBT or ISBT. Median equivalent dose in 2 Gy fractions of D_2cc to the bladder, sigmoid colon, and rectum was 69.5, 52.0, and 58.4 Gy, respectively. All cases remained within the doses recommended for organs at risk.

Conclusions

Pre-brachytherapy MRI may be helpful in selecting suitable candidates for each type of brachytherapy and deliver the recommended doses to the tumor and organs at risk, particularly in cases with large tumors, poor response to concurrent chemoradiotherapy, asymmetrical tumors, severe vaginal invasion, extensive parametrial invasion, and/or corpus invasion.

Implementation of a DVH Registry to provide constraints and continuous quality monitoring for pediatric CSI treatment planning

Craniospinal irradiation (CSI) is a complex radiation therapy technique that is used for patients, often children and teenagers/young adults, with tumors that have a propensity to spread throughout the central nervous system such as medulloblastoma. CSI is associated with important long‐term side effects, the risk of which may be affected by numerous factors including radiation modality and technique. Lack of standardization for a technique that is used even in larger radiation oncology departments only a few times each year may be one such factor and the current ad hoc manner of planning new CSI patients may be greatly improved by implementing a dose–volume histogram registry (DVHR) to use previous patient data to facilitate prospective constraint guidance for organs at risk. In this work, we implemented a DVHR and used it to provide standardized constraints for CSI planning. Mann–Whitney U tests and mean differences at 95% confidence intervals were used to compare two cohorts (pre‐ and post‐DVHR intervention) at specific dosimetric points to determine if observed improvements in standardization were statistically significant. Through this approach, we have shown that the implementation of dosimetric constraints based on DVHR‐derived data helped improve the standardization of pediatric CSI planning at our center. The DVHR also provided guidance for a change in CSI technique, helping to achieve practice standardization across TomoTherapy and IMRT.

Associating dose-volume characteristics with theoretical radiobiological metrics for rapid Gamma Knife stereotactic radiosurgery plan evaluation

Purpose

To examine general dose–volume characteristics in Gamma Knife (GK) plans which may be associated with higher tumor control probability (TCP) and equivalent uniform dose (EUD) using characteristic curve sets.

Methods

Two sets of dose–volume histograms (DVHs) were exported alongside an analytical purpose‐generated DVH: (a) single‐shot large collimator (8 or 16 mm) emulated with multiple shots of 4 mm collimator. (b) shot‐within‐shot (SWS) technique with isodose lines (IDLs) of 40–75%. TCP, average dose, EUD in single‐fraction (EUD_T) and 2 Gy fractionated regimens (EUD_R) were examined for trends with cumulative DVH (cDVH) shape as calculated using a linear‐quadratic cell survival model (α/β = 10.0 Gy, N₀ = 1 × 10⁶) with both α = 0.20 Gy⁻¹ and α = 0.23 Gy⁻¹.

Results

Using α = 0.20 Gy⁻¹ (α = 0.23 Gy⁻¹), plans in the analytical set with higher shoulder regions had TCP, EUD_T, EUD_R increased by 180%, 5.9%, 10.7% (11.2%, 6.3%, 10.0%), respectively. With α = 0.20 Gy⁻¹ (α = 0.23 Gy⁻¹), plans with higher heels had TCP, EUD_T, EUD_R increased by 4.0%, <1%, <1% (0.6%, <1%, <1%), respectively. In emulating a 16 (8) mm collimator, 64 (12) shots of the small collimators were used. Plans based on small collimators had higher shoulder regions and, with α = 0.20 Gy⁻¹ (α = 0.23 Gy⁻¹), TCP, EUD_T, EUD_R was increased up to 351.4%, 5.0%, 8.8% (270.4%, 5.0%, 6.8%) compared with the single‐shot large collimator. Delivery times ranged from 10.2 to 130.3 min. The SWS technique used 16:8 mm collimator weightings ranging from 1:2 to 9.2:1 for 40–75% IDL. With α = 0.20 Gy⁻¹ (α = 0.23 Gy⁻¹), the 40% IDL plan had the highest shoulder with increased TCP, EUD_T, EUD_R by 130.7%, 9.6%, 17.1% (12.9%, 9.1%, 16.4%) over the 75% IDL plan. Delivery times ranged 6.9–13.8 min.

Conclusions

The magnitude of the shoulder region characteristic to GK cDVHs may be used to rapidly identify superior plan among candidates. Practical issues such as delivery time may require further consideration.

Coverage of the external prostatic region by the hybrid method compared with the conventional method of prostate low-dose-rate brachytherapy: A randomized controlled study

OBJECTIVES

To compare the dose evaluation parameters between conventional (using loose seed alone) and hybrid (using loose seeds in combination with stranded seeds) low-dose rate brachytherapy for prostate cancer.

METHODS

Between 2014 and July 2016, a total of 219 patients who underwent low-dose rate brachytherapy were enrolled in a randomized controlled trial (trial number: UMIN 000012780). Patients were randomized and allocated to two groups (conventional method vs hybrid method). Post-dosimetric parameters (%D90, minimal percentage of the dose received by 90% of the prostate gland; V100, percentage of the prostate volume receiving 100% of the prescribed minimal peripheral dose; V150, percentage of the prostate volume receiving 150% of the prescribed minimal peripheral dose; %UD30, minimal percentage of the dose received by 30% of the urethra; R100, rectal volume [mL] receiving 100% of the prescribed dose) calculated at 1 month after seed implantation by computed tomography scan were compared between the two groups, as well as the post-dosimetric parameters using the planning target volume of the prostate + 5-mm margin.

RESULTS

Regarding dose evaluation parameters, the prostate dose (%D90, V100, V150) and the urethral dose (%UD30) were not significantly different between the two groups, whereas V100 (+5-mm margin) and %D90 (+5-mm margin) were significantly higher in the hybrid method group compared with the conventional method group (P < 0.001).

CONCLUSION

The present randomized study shows that the hybrid method of low-dose rate brachytherapy can achieve a higher coverage of the periprostatic region compared with the conventional method while maintaining an acceptable level of urethral and rectal doses.

Risk factors of radiation pneumonitis in patients with NSCLC treated with concomitant chemoradiotherapy--Are we underestimating diabetes?--Turkish oncology group (TOG)/Lung cancer study group

INTRODUCTION

To evaluate the clinical and dosimetric parameters that increase the risk of radiation pneumonitis (RP) in locally advanced non-small cell lung cancer (NSCLC) patients treated with concomitant chemoradiotherapy of nationwide multicentric data analysis.

METHODS

All data of 268 patients who underwent definitive chemoradiotherapy were retrospectively collected from eight institutes participating in this study. Patient, tumor and treatment-related factors and dosimetric parameters were analyzed for grade ≥2 RP. The toxicity scoring system of The Radiation Therapy Oncology Group used for grading the severity of pneumonitis. A relationship with the risk of RP with potential predictive factors were evaluated by univariate and multivariate analyses. A recursive partition analysis (RPA) was applied to stratify patients according to the risk of developing RP.

RESULTS

There were 90 (33.6%) patients who had grade ≥2 RP. The median time to pneumonitis after treatment was 4 months (range:1-6 months). In univariate analysis, diabetes mellitus (DM), use of cisplatin/etoposide, total and daily radiotherapy (RT) fraction dose, the planning target volume (PTV) size, mean lung dose, V5, V10 and RT technique were associated with the development of pneumonitis. In multivariate analysis, only DM (P = 0.008) was found to be independent risk factors for RP. According to RPA, the risk of developing RP was highest in patients with DM.

CONCLUSIONS

In our study, besides the known dosimetric factors, DM was found to be the most important risk factor causing RP development in multivariate analysis and RPA. The risk is tripled compared to patients without DM.

Radiation pneumonitis after definitive concurrent chemoradiotherapy with cisplatin/docetaxel for non-small cell lung cancer: Analysis of dose-volume parameters

Background

Radiation pneumonitis (RP) is a major pulmonary adverse event of chest radiotherapy. The PACIFIC trial that identified durvalumab as an effective subsequent‐line therapy after concurrent chemoradiotherapy (CCRT) found that patients with grade 2 or higher RP may have to be excluded from treatment under certain criteria. The purpose of this study was to investigate the relationship between grade ≥2 RP and the parameters of dose‐volume histograms after CCRT with cisplatin/docetaxel for stage III non‐small cell lung cancer and conduct a subset analysis of severe RP that can lead to the permanent discontinuation of treatment per the PACIFIC trial criteria to help determine treatment strategy.

Methods

We calculated the percentage of the lung volume received at least 5 Gy (V5) and 20 Gy (V20), the mean lung dose (MLD), and the lung volume spared from a 5 Gy dose (VS5) to the total lung volume. Factors affecting the incidence of grade ≥2 RP were identified; severe RP was defined as grade ≥3 as well as grade 2 RP that required ≥10 mg prednisolone for at least 12 weeks.

Results

This study included 45 patients. On univariate analysis, all parameters and total lung volume were found to be significant predictors of grade ≥2 RP (P = .001, .003, .03, .004, and .02, respectively). On multivariate analysis, V20 was a significant predictive factor of grade ≥2 RP (P = .007). Severe RP developed in 6 of 37 patients (16.2%) whose V20 values were 35% or lower. On univariate analysis, only V20 was a significant predictor of severe RP in these patients (P = .01).

Conclusions

The best approach to reduce the rate of grade ≥2 RP is to maintain the V5, V20, MLD, and VS5 as low as possible during radiotherapy planning in patients receiving definitive CCRT with cisplatin/docetaxel.

Dose-volume Histogram-based Predictors for Hematuria and Rectal Hemorrhage in Patients Receiving Radiotherapy After Radical Prostatectomy

AIM

The aim of this study was to evaluate the dose-volume histogram parameters for late hematuria and rectal hemorrhage in patients receiving radiotherapy after radical prostatectomy.

PATIENTS AND METHODS

Data of 86 patients treated between January 2006 and June 2019 were retrospectively evaluated. The median radiation dose was 64 Gy in 32 fractions. Receiver operating characteristic (ROC) curves were used to identify optimal cut-off values for late adverse events.

RESULTS

Eleven patients experienced hematuria, and the 5-year cumulative rate was 18%. Four patients experienced rectal hemorrhage, and the 5-year cumulative rate was 7%. ROC curve analysis demonstrated the following significant cut-off values: bladder V50 Gy: 43% (p=0.02) and V40 Gy: 50% (p=0.03) for hematuria, and rectum V60 Gy: 13% (p=0.04) and V50 Gy: 33% (p=0.03) for rectal hemorrhage.

CONCLUSION

This is the first study to identify dose constraints that may reduce hematuria and rectal hemorrhage in patients receiving radiotherapy in the postoperative setting.

Outcome of postoperative radiation therapy for cholangiocarcinoma and analysis of dose-volume histogram of remnant liver

The aim of this study was to analyze dose-volume histogram (DVH) of the remnant liver for postoperative cholangiocarcinoma (CCA) patients, to find toxicity rates, and to confirm efficacy of postoperative radiation therapy (RT).Thirty-two postoperative CCA patients received partial liver resection and postoperative RT with curative intent. The "liver reduction rate" was calculated by contouring liver volume at computed tomography (CT) just before the surgery and at CT for planning the RT. To evaluate late toxicity, the radiation-induced hepatic toxicity (RIHT) was determined by the common terminology criteria for adverse events toxicity grade of bilirubin, aspartate transaminase, alanine transaminase, alkaline phosphatase, and albumin, and was defined from 3 months after RT until liver metastasis was revealed. The radiation-induced liver disease (RILD) was also evaluated.Tumor stages were distributed as follows: I: 1, II: 8, IIIA: 1, IIIB: 6, IIIC: 14, IVA: 2. Median prescribed total dose was 50 Gy. Median follow-up time was 27 months. Two-year overall survival (OS): 72.4%, disease-free survival: 47.7%, local control: 65.3%, and the median survival time was 40 months. The median "liver reduction rate" was 21%. The OS had statistically significant difference in nodal status (P = .032) and "liver reduction rate" >30% (P = .016). In the association between the ≥grade 2 RIHT and DVH, there were significantly differences in V30 and V40 (P = .041, P = .034), respectively. The grade ≥2 RIHT rates differ also significantly by sex (P = .008). Two patients (6.2%) were suspected of RILD.We suggest that RT for remnant liver should be considered the liver V30, V40 to prevent radiation-induced liver dysfunction.

Case report of a dose-volume histogram analysis of rib fracture after accelerated partial breast irradiation: interim analysis of a Japanese prospective multi-institutional feasibility study

We initiated the first multi-institutional prospective study of accelerated partial breast irradiation for early breast cancer in Japan. Our early clinical results showed that the treatment methods were technically reproducible between institutions and showed excellent disease control at a median follow-up of 26 months in our previous report. At present, total 46 patients from six institutions underwent the treatment regimen from October 2009 to December 2011, and the median follow-up time was 60 months (range, 57-67 months). In 46 patients, we experienced one patient who had rib fracture as a late complication. The dose-volume histogram (DVH) result of this patient was analyzed. The D_0.01cc, D_0.1cc, and D_1cc values of the patient were 913, 817, and 664 cGy per fraction, respectively. These values were the highest values in 46 patients. The average D_0.01cc, D_0.1cc, and D_1cc values of the other 45 patients were 546, 500, and 419, respectively, cGy per fraction. From this result, DVH values showing high-dose irradiated volume (D_0.01cc, D_0.1cc, and D_1cc) seem to be a good predictive factor of rib fracture for accelerated partial breast irradiation. However, further investigation is necessary because of the small number of patients investigated.

The Efficacy and Late Toxicities of Computed Tomography-based Brachytherapy with Intracavitary and Interstitial Technique in Advanced Cervical Cancer

Purpose: To report the efficacy and late side effects(LSEs) of CT-based image-guided brachytherapy for the treatment of cervical cancer.

Materials: Between 2008 and 2014, 100 patients with FIGO stage IIB-IVA cervical carcinoma were analyzed. The patients received pelvic irradiation (45-50 Gy in 25 fractions) with concurrent chemotherapy, whereas the mean prescribed EBRT dose, including initial and boost doses to positive lymph nodes, ranged from 54 to 64 Gy. Afterwards, intracavitary(IC) or combined intracavitary/interstitial(IC/IS) brachytherapy was performed using a CT-based procedure with prescribed doses of 6 or 8 Gy in 3-7 fractions.

Results: The median follow-up time was 46 months. The 5-year local control, distant metastasis-free survival, and overall survival rates were 88.9%, 81.8%, 77.9%, respectively. IC/IS brachytherapy improved the HR-CTV D90 compared with IC (p<0.01). Seven patients (7.0%) had grade 2 bladder LSEs and none had grade 3/4 bladder LSEs. There was no significant relationship between bladder LSEs and the dose-volume histogram (p>0.05 for all). Thirty-seven patients (37%) had grade 2 rectal LSEs, 3(3%) had grade 3 rectal LSE. The rectum D_1cc, D_2cc, and D_5cc values were significantly higher in patients with grades 2/3 rectal toxicity than in those with grades 0/1 (p<0.05 for all). There was no grade 2 and above small bowel LSEs.

Conclusions: CT-based brachytherapy planning can achieve excellent local control with acceptable morbidity. HR-CTV D90 can increase in the IC/IS group compared with the IC group. The D_1cc, D_2cc, and D_5cc all showed excellent predictive values for rectal LSEs.

Dosimetric Comparison of Treatment Plans Using Physical Wedge and Enhanced Dynamic Wedge for the Planning of Breast Radiotherapy

The aim of this study is to compare the physical wedge (PW) with enhanced dynamic wedge (EDW) to determine the difference in the dose distribution affecting the treated breast and the contralateral breast, lungs, heart, esophagus, spine, and surrounding skin in the radiotherapy of breast cancer. Computed tomography (CT) data sets of 30 breast cancer patients were selected from the database for the study. The treatment plans which were executed with PW were re-planned with EDW without changing the beam parameters. Keeping the wedge angles same, the analytic anisotropic algorithm (AAA) with heterogeneity correction was used for dose calculation in all plans. The prescription was 50 Gy in 25 fractions. The dose- volume histogram (DVH) of the planning target volume (PTV) and critical structures of both PW and EDW plans were analyzed. The analysis showed that the maximum dose within the target volume is higher in EDW plan compared to PW plan. However the PTV conformity index (CI) remained the same in both plans. For all the critical structures, the EDW technique offered less dose compared to PW technique. The effect of volume of the contralateral breast on the dose to contralateral breast and the effect of volume of PTV breast for patients with carcinoma left breast on the dose to heart were studied and analyzed for the two wedges. No correlation between volumes and dose parameters was found for the two techniques. The number of monitor units to deliver a particular dose with EDW field is less than that of PW field due to change in wedge factor. As EDW produces less scattered dose to structures outside the treatment field, the risk of a second malignancy can be reduced with this technique.

Outlier identification in radiation therapy knowledge-based planning: A study of pelvic cases

PURPOSE

The purpose of this study was to apply statistical metrics to identify outliers and to investigate the impact of outliers on knowledge-based planning in radiation therapy of pelvic cases. We also aimed to develop a systematic workflow for identifying and analyzing geometric and dosimetric outliers.

METHODS

Four groups (G1-G4) of pelvic plans were sampled in this study. These include the following three groups of clinical IMRT cases: G1 (37 prostate cases), G2 (37 prostate plus lymph node cases) and G3 (37 prostate bed cases). Cases in G4 were planned in accordance with dynamic-arc radiation therapy procedure and include 10 prostate cases in addition to those from G1. The workflow was separated into two parts: 1. identifying geometric outliers, assessing outlier impact, and outlier cleaning; 2. identifying dosimetric outliers, assessing outlier impact, and outlier cleaning. G2 and G3 were used to analyze the effects of geometric outliers (first experiment outlined below) while G1 and G4 were used to analyze the effects of dosimetric outliers (second experiment outlined below). A baseline model was trained by regarding all G2 cases as inliers. G3 cases were then individually added to the baseline model as geometric outliers. The impact on the model was assessed by comparing leverages of inliers (G2) and outliers (G3). A receiver-operating-characteristic (ROC) analysis was performed to determine the optimal threshold. The experiment was repeated by training the baseline model with all G3 cases as inliers and perturbing the model with G2 cases as outliers. A separate baseline model was trained with 32 G1 cases. Each G4 case (dosimetric outlier) was subsequently added to perturb the model. Predictions of dose-volume histograms (DVHs) were made using these perturbed models for the remaining 5 G1 cases. A Weighted Sum of Absolute Residuals (WSAR) was used to evaluate the impact of the dosimetric outliers.

RESULTS

The leverage of inliers and outliers was significantly different. The Area-Under-Curve (AUC) for differentiating G2 (outliers) from G3 (inliers) was 0.98 (threshold: 0.27) for the bladder and 0.81 (threshold: 0.11) for the rectum. For differentiating G3 (outlier) from G2 (inlier), the AUC (threshold) was 0.86 (0.11) for the bladder and 0.71 (0.11) for the rectum. Significant increase in WSAR was observed in the model with 3 dosimetric outliers for the bladder (P < 0.005 with Bonferroni correction), and in the model with only 1 dosimetric outlier for the rectum (P < 0.005).

CONCLUSIONS

We established a systematic workflow for identifying and analyzing geometric and dosimetric outliers, and investigated statistical metrics for outlier detection. Results validated the necessity for outlier detection and clean-up to enhance model quality in clinical practice.

The usefulness of fleet rectal enemas on high-dose-rate intracavitary cervical cancer brachytherapy. A prospective trial

Purpose

To evaluate the effects of rectal enemas on rectal doses during radical high-dose-rate (HDR) intracavitary cervical brachytherapy (BT).

Material and methods

Twenty patients suffering from cervical cancer and treated with external beam radiotherapy and HDR-BT were included in a prospective trial. The first brachytherapy fraction was considered the basal status, and patients were instructed to self-administer two rectal cleansing enemas before the second fraction. Dose-volume histogram (DVH) values were generated for the rectum and correlated with rectal volume variation. Brachytherapy was carried out with a Fletcher or Utrecht applicator.

Results

No significant rectal volume differences were observed between fractions with or without rectal enemas (without, 52.64 ± 15.92 cc; with, 53.16 ± 19.28 cc). There was a significant correlation between both rectal volumes (r = 0.722, p = 0.001). No significant differences were observed in analyzed DVH parameters (median values: ΔD_0.1cc, 4.17 vs. 3.61 Gy; ΔD_1cc, 3.23 vs. 2.87 Gy; ΔD_2cc, 2.9 vs. 2.54 Gy; ΔD_5cc, 2.35 vs. 2.05 Gy, for no enema and enema fraction, respectively). No significant rectal volume differences nor DVH parameter differences were observed according the applicator type.

Conclusions

Our rectal enemas protocol prior to HDR-BT was ineffective in significantly modifying rectal DVH parameters. No differences were observed according to the type of applicator used.

Radiation-induced Parotid Gland Atrophy in Patients with Head and Neck Cancer After Carbon-ion Radiotherapy

BACKGROUND/AIM

This study aimed to clarify the relationship between dosimetric factors and parotid gland (PG) atrophy after carbon ion radiotherapy (C-ion RT).

PATIENTS AND METHODS

Fifty-four patients with head and neck tumours were enrolled and 93 irradiated PGs were analyzed. Thirty and 24 patients were treated with total doses [relative biological effectiveness (RBE)] of 57.6 Gy and 64.0 Gy, respectively, in 16 fractions. PG volumes were measured using computed tomographic images obtained before C-ion RT and every 3-6 months thereafter.

RESULTS

The median follow-up period was 46.4 months (range=24.0-123.0 months). Univariate analysis showed that PG volumes receiving more than 5, 10, 15, and 20 Gy RBE (V5, V10, V15 and V20, respectively), mean dose, and maximum dose were significantly associated with PG atrophy. Multivariate analysis indicated that only V5 was significantly associated with atrophy.

CONCLUSION

Increasing V5 was a significant risk factor for PG atrophy after C-ion RT.

Predictors of Mastoiditis after Intensity-Modulated Radiotherapy in Nasopharyngeal Carcinoma: A Dose-Volume Analysis

Background: To identify predictors for development of mastoiditis after intensity-modulated radiation therapy (IMRT) in nasopharyngeal carcinoma (NPC).

Methods: Data for 146 NPC patients treated with IMRT was retrospectively reviewed under institutional ethics committee approval. Clinical factors associated with mastoiditis were analyzed. Dose-volume histogram analysis was performed for the Eustachian tube, tympanic cavity, mastoid air cells, cochlea, internal auditory canal and vestibular apparatus to relate doses to radiographic changes in the mastoid. Mastoiditis was assessed using magnetic resonance imaging and was classified as Grade 0 (none), 1 (mild), 2 (moderate) or 3 (severe); Grade 3 mastoiditis was the study end-point.

Results: Eighty-eight ears (36%) had radiation-induced mastoiditis: 38/244 (15.6%) mastoid complexes had Grade 1-2 mastoiditis and 50/244 (20.5%) mastoid complexes had Grade 3 mastoiditis. Multivariate analysis revealed a mastoid mean dose > 35.93 Gy (odds ratio [OR]=4.22, P=.003), Eustachian tube mean dose > 53.43 Gy (OR=2.16, P=.034) and advanced T category (T3 and T4; OR=10.33, P=.032) were negative prognostic factors for Grade 3 mastoiditis.

Conclusions: Radiation-induced mastoiditis remains a common late toxicity in NPC after radiotherapy. The mean dose to the mastoid air cells and Eustachian tube should be limited to reduce the risk of radiation-induced mastoiditis.

Risk factors for pericardial effusion in patients with stage I esophageal cancer treated with chemoradiotherapy

AIM

We investigated clinical and dosimetric factors influencing the risk of developing pericardial effusion (PCE) in patients with Stage I esophageal cancer undergoing definitive chemoradiotherapy.

PATIENTS AND METHODS

Sixty-nine patients with Stage I esophageal cancer who underwent definitive chemoradiotherapy were retrospectively analyzed. Treatment comprised of three-dimensional conformal radiotherapy (60 Gy in 30 fractions) with concurrent chemotherapy. Clinical and dosimetric factors associated with PCE development were analyzed.

RESULTS

The median follow-up was 37 months (range=8-111 months); the crude PCE incidence rate was 52.2%. Grade 2 and 3 incidence rate was 47.8% and 4.3%, respectively. The median time to PCE onset was 5.7 months after radiotherapy. In multivariate analysis, pericardial V30 ≥ 41.6%, age ≥ 66 years, body mass index (BMI) ≥ 19 and diabetes mellitus (DM) were significant predictors of developing PCE.

CONCLUSION

The present study suggests that higher pericardial V30, advanced age, high BMI and DM are risk factors for developing PCE.

Dose-volume analysis for respiratory toxicity in intrathoracic esophageal cancer patients treated with definitive chemoradiotherapy using extended fields

PURPOSE

We evaluated the relationship between dosimetric parameters (DPs) and the incidence of radiation pneumonitis (RP) and investigated the feasibility of a proposed treatment planning technique with the potential of reducing RP in esophageal cancer patients treated with definitive chemoradiotherapy using extended fields.

PATIENTS AND METHODS

A total of 149 patients with locally advanced esophageal cancer were prospectively enrolled for extended-field radiotherapy (EFRT) to three-field regional lymphatics between September 2004 and June 2009. We retrospectively reviewed 86 consecutive patients who were treated with a total dose of 50.4 Gy (plus an optional 9 Gy boost) and were available for dose-volume analysis. Lung DPs of patients in the Grade 0-1 RP (RPG≤1) group and the Grade 2-5 RP (RPG≥2) group were compared. We compared the proposed plan with the conventional plan to 50.4 Gy on DPs for each case.

RESULTS

Of these 86 patients, 10 (12%) developed RPG≥2 (Grade 2, n = 2 patients; Grade 3, n = 3; Grade 4, n = 3; Grade 5, n = 2). The patients in the RPG≤1 group showed significantly lower (P < 0.05) V5 and V10 values for the whole lung compared with those in the RPG≥2 group. There were two advantages gained from the proposed plan for V5 (<55%) and V10 (< 37%) values and the conformity of the PTV.

CONCLUSION

The increase in the volume of the lung exposed to low doses of EFRT was found to be associated with the incidence of RP. Our proposed plan is likely to reduce the incidence of RP.

Quantitative dosimetry for yttrium-90 radionuclide therapy: tumor dose predicts fluorodeoxyglucose positron emission tomography response in hepatic metastatic melanoma

PURPOSE

To assess a new method for generating patient-specific volumetric dose calculations and analyze the relationship between tumor dose and positron emission tomography (PET) response after radioembolization of hepatic melanoma metastases.

METHODS AND MATERIALS

Yttrium-90 ((90)Y) bremsstrahlung single photon emission computed tomography (SPECT)/computed tomography (CT) acquired after (90)Y radioembolization was convolved with published (90)Y Monte Carlo estimated dose deposition kernels to create a three-dimensional dose distribution. Dose-volume histograms were calculated for tumor volumes manually defined from magnetic resonance imaging or PET/CT imaging. Tumor response was assessed by absolute reduction in maximum standardized uptake value (SUV(max)) and total lesion glycolysis (TLG).

RESULTS

Seven patients with 30 tumors treated with (90)Y for hepatic metastatic melanoma with available (90)Y SPECT/CT and PET/CT before and after treatment were identified for analysis. The median (range) for minimum, mean, and maximum dose per tumor volume was 16.9 Gy (5.7-43.5 Gy), 28.6 Gy (13.8-65.6 Gy) and 36.6 Gy (20-124 Gy), respectively. Response was assessed by fluorodeoxyglucose PET/CT at a median time after treatment of 2.8 months (range, 1.2-7.9 months). Mean tumor dose (P = .03) and the percentage of tumor volume receiving ≥ 50 Gy (P < .01) significantly predicted for decrease in tumor SUV(max), whereas maximum tumor dose predicted for decrease in tumor TLG (P < .01).

CONCLUSIONS

Volumetric dose calculations showed a statistically significant association with metabolic tumor response. The significant dose-response relationship points to the clinical utility of patient-specific absorbed dose calculations for radionuclide therapy.

Emerging understanding of dosimetric factors impacting on dysphagia and nutrition following radiotherapy for oropharyngeal cancer

BACKGROUND

Research has reported relationships between 3-dimensional (3D) radiation dose to head and neck structures and consequential swallowing/nutritional outcomes. However, this evidence is preliminary. The current study aimed to identify which reported dose constraints identified functional impairment at 6 months posttreatment.

METHODS

Dose constraints with reported relationships to swallowing and nutrition were identified through a systematic literature review. Dose-volume histograms for 12 patients with T1-T3 oropharyngeal cancer treated with 3D conformal radiotherapy determined dosages delivered to specific structures. Doses were examined in relation to published dose constraints and the swallowing and nutritional outcomes at 6 months posttreatment.

RESULTS

In all, 66% of the reported mean, maximum, and partial doses to 8 structures correctly identified swallowing and nutrition outcomes at 6 months.

CONCLUSION

The relationships observed between known dosimetric constraints and functional outcomes highlight the potential for dosimetric data to assist in prognosis and treatment. Systematic research is required to refine dosimetric parameters and the impact on functional outcomes.

Assessment of dose homogeneity in conformal interstitial breast brachytherapy with special respect to ICRU recommendations

Purpose

To present the results of dose homogeneity analysis for breast cancer patients treated with image-based conformal interstitial brachytherapy, and to investigate the usefulness of the ICRU recommendations.

Material and methods

Treatment plans of forty-nine patients who underwent partial breast irradiation with interstitial brachytherapy were analyzed. Quantitative parameters were used to characterize dose homogeneity. Dose non-uniformity ratio (DNR), dose homogeneity index (DHI), uniformity index (UI) and quality index (QI) were calculated. Furthermore, parameters recommended by the ICRU 58 such as minimum target dose (MTD), mean central dose (MCD), high dose volume, low dose volume and the spread between local minimum doses were determined. Correlations between the calculated homogeneity parameters and usefulness of the ICRU parameters in image-based brachytherapy were investigated.

Results

Catheters with mean number of 15 (range: 6-25) were implanted in median 4 (range: 3-6) planes. The volume of the PTV ranged from 15.5 cm³ to 176 cm³. The mean DNR was 0.32, the DHI 0.66, the UI 1.49 and the QI 1.94. Related to the prescribed dose, the MTD was 69% and the MCD 135%. The mean high dose volume was 8.1 cm³ (10%), while the low dose volume was 63.8 cm³ (96%). The spread between minimum doses in central plane ranged from −14% to +20%. Good correlation was found between the DNR and the DHI (R²=0.7874), and the DNR correlated well with the UI (R²=0.7615) also. No correlation was found between the ICRU parameters and any other volumetric parameters.

Conclusions

To characterize the dose uniformity in high-dose rate breast implants, DVH-related homogeneity parameters representing the full 3D dose distributions are mandatory to be used. In many respects the current recommendations of the ICRU Report 58 are already outdated, and it is well-timed to set up new recommendations, which are more feasible for image-guided conformal interstitial brachytherapy.

Late rectal toxicity on RTOG 94-06: analysis using a mixture Lyman model

PURPOSE

To estimate the parameters of the Lyman normal-tissue complication probability model using censored time-to-event data for Grade ≥2 late rectal toxicity among patients treated on Radiation Therapy Oncology Group 94-06, a dose-escalation trial designed to determine the maximum tolerated dose for three-dimensional conformal radiotherapy of prostate cancer.

METHODS AND MATERIALS

The Lyman normal-tissue complication probability model was fitted to data from 1,010 of the 1,084 patients accrued on Radiation Therapy Oncology Group 94-06 using an approach that accounts for censored observations. Separate fits were obtained using dose-volume histograms for whole rectum and dose-wall histograms for rectal wall.

RESULTS

With a median follow-up of 7.2 years, the crude incidence of Grade ≥2 late rectal toxicity was 15% (n = 148). The parameters of the Lyman model fitted to dose-volume histograms data, with 95% profile-likelihood confidence intervals, were TD(50) = 79.1 Gy (75.3 Gy, 84.3 Gy), m = 0.146 (0.107, 0.225), and n = 0.077 (0.041, 0.156). The fit based on dose-wall histogram data was not significantly different. Patients with cardiovascular disease had a significantly higher incidence of late rectal toxicity (p = 0.015), corresponding to a dose-modifying factor of 5.3%. No significant association with late rectal toxicity was found for diabetes, hypertension, rectal volume, rectal length, neoadjuvant hormone therapy, or prescribed dose per fraction (1.8 Gy vs. 2 Gy).

CONCLUSIONS

These results, based on a large cohort of patients from a multi-institutional trial, are expected to be widely representative of the ability of the Lyman model to describe the long-term risk of Grade ≥2 late rectal toxicity after three-dimensional conformal radiotherapy of prostate cancer.