Aspects of dosimetry and clinical practice of skin brachytherapy: The American Brachytherapy Society working group report

Single-Fraction Palliative High-Dose-Rate Brachytherapy for Symptom Management in a 97-Year-Old Patient With Dementia

Background: Delivering cancer treatment to elderly patients with dementia is often challenging. We describe performing palliative surface mold brachytherapy (SMBT) in an elderly patient with advanced dementia for pain control using music therapy to assist with agitation. Case Description: The patient was a 97-year-old Japanese woman with advanced dementia. Exudate was observed from her tumor, and she complained of Grade 2 severity pain using Support team assessment schedule (STAS), especially when undergoing would dressings. Given her advanced dementia, she was not considered a candidate for radical surgery or external beam radiotherapy. We instead treated her with high-dose-rate (HDR) SMBT. Due to her advanced dementia associated with agitation, she could not maintain her position. She was able to remain calm while listening to traditional Japanese enka music, which enables our team to complete her radiation without using anesthetics or sedating analgesics. Her localized pain severity decreased ≤21 days and the exudate fluid disappeared ≤63 days after HDR-SMBT. Her tumor was locally controlled until her death from intercurrent disease 1 year after HDR-SMBT. Discussion: Single fraction palliative HDR-SMBT was useful for successful treatment of skin cancer in an elderly patient. Traditional Japanese music helped reduce her agitation to complete HDR-SMBT. For elderly patients with agitation associated with dementia, we should consider using music and music therapy to facilitate radiation therapy.

Dosimetry of Large Field Valencia applicators for Cobalt-60-based brachytherapy

BACKGROUND

Non-melanoma skin cancer is one of the most common types of cancer and one of the main approaches is brachytherapy. For small lesions, the treatment of this cancer with brachytherapy can be done with two commercial applicators, one of these is the Large Field Valencia Applicators (LFVA).

PURPOSE

The aim of this study is to test the capabilities of the LFVA to use clinically 60Co sources instead of the 192Ir ones. This study was designed for the same dwell positions and weights for both sources.

METHODS

The Penelope Monte Carlo code was used to evaluate dose distribution in a water phantom when a 60Co source is considered. The LFVA design and the optimized dwell weights reported for the case of 192Ir are maintained with the only exception of the dwell weight of the central position, that was increased. 2D dose distributions, field flatness, symmetry and the leakage dose distribution around the applicator were calculated.

RESULTS

When comparing the dose distributions of both sources, field flatness and symmetry remain unchanged. The only evident difference is an increase of the penumbra regions for all depths when using the 60Co source. Regarding leakage, the maximum dose within the air volume surrounding the applicator is in the order of 20% of the prescription dose for the 60Co source, but it decreases to less than 5% at about 1 cm distance.

CONCLUSIONS

Flatness and symmetry remains unaltered as compared with 192Ir sources, while an increase in leakage has been observed. This proves the feasibility of using the LFVA in a larger range of clinical applications.

Realization of the absorbed dose to water for 70 kV electronic brachytherapy sources for surface applications

Objective.The purpose of this work is to establish a primary standard for the absorbed dose to water for surface applications with 70 kV electronic brachytherapy sources and thereby to investigate several reference conditions with respect to applicability in metrology institutes, calibration labs and clinics.Approach.A primary standard for the absorbed dose to water for LDR-Seeds (ipFAC) was utilized. For this, the method of evaluation was modified to account for the different geometries in interstitial and surface brachytherapy and for the different energy distributions of the radiation fields, respectively. The correction factors required to determine the absorbed dose to water were evaluated using Monte Carlo (MC) simulations. MC-calculations were also used to estimate the uncertainties of this method.Main results.It could be shown that determining the absorbed dose to water in 1 cm depth below the surface of a water phantomDw(1 cm) is feasible with the ipFAC. Thereby the method to determineDw(1 cm) when the source is placed at 50 cm distance and the beam is collimated turns out to be more robust to variations in the directional emittance of the source than placing the source applicator assembly directly on the phantom.Significance.The first method features significantly lower uncertainties, 1.4% compared to 3.7% (both fork= 2), for the second one. However, a calibration based on a transfer chamber calibrated with the second method is more practical and easier to implement in clinical routine.

Topical 188Re Ionizing Radiation Therapy Exerts High Efficacy in Curing Nonmelanoma Skin Cancer

PURPOSE OF THE REPORT

Nonmelanoma skin cancer (NMSC) is the most frequent malignancy. Surgical intervention is the common treatment but may lead to disappointing results; alternative treatment options are needed.

METHODS

In this monocentric pilot study, topical 188Re resin was investigated as a treatment for invasive NMSC up to 3-mm thickness. Twenty-two patients with 40 histologically confirmed NMSCs with a median size of 1.25 cm2 (range, 0.04-16.8 cm2) and a median tumor thickness of 0.35 mm (range, 0.1-2.1 mm) were included. Patients were treated once with 188Re resin with a targeted dose of 50 Gy. The median applied activity was 111.4 MBq (range, 21.0-168.0 MBq), and the median treatment time was 89 minutes (range, 38-175 minutes). The response rate, adverse events, and cosmetic outcome were assessed at 14 days, 4 months, and 12 months.

RESULTS

Response rate at 12 months was 97.5%, with 95% complete responses (clinically or histologically proven in case of clinical doubt). Most adverse events were reported at 14 days, with 20% itching and 12.5% mostly minor pain. Forty-nine percent of the lesions showed hypopigmentation only at 12 months. Forty-one percent of the lesions were graded as cosmetically superior to the expected result after surgery and 51.3% as comparable to successful surgery. The cosmetic outcome on the head and face was superior compared with the trunk and leg (P = 0.003).

CONCLUSION

188Re resin is a highly effective treatment for NMSC up to 3-mm thickness and a valid alternative to surgery, specifically for tumors located on sensitive areas such as nose or ear.

Quantitative study on dose distribution of Freiburg flap for keloid high-dose-rate brachytherapy based on MatriXX

PURPOSE

To quantify the dose distribution effect of insufficient scattering conditions in keloid HDR brachytherapy with Freiburg fFlap (FF) applicator.

MATERIALS AND METHODS

A phantom composed of FF applicator, MatriXX and solid water slices was designed and scanned for treatment planning. Bolus with different thicknesses were covered to offer different scatter conditions. Planar dose distributions were measured by MatriXX. The maximum value (Max), average value (Avg) and γ passing rate (3 mm/3%) were evaluated by the software MyQA Platform.

RESULTS

The maximum and average doses measured by MatriXX were lower than the calculated values. The difference increased as field size decreased. The Max value, found at 0.86 cm level in the two tube case, was -20.0%, and the avg value was -11.9%. All the γ values were less than 95%. This difference gradually decreased with increasing bolus thickness and the γ values were significantly improved.

CONCLUSION

MatriXX could be used for dose verification of HDR brachytherapy with an FF applicator. When the FF applicator was applied for keloid, insufficient scattering conditions would cause an insufficient target dose. This difference could be reduced by covering the bolus with different thicknesses on the applicator. The smaller the field, the thicker the bolus required.

Optimizing surface mould brachytherapy for treatment of nasal basal cell carcinoma using customized applicators

PURPOSE

Surface mould brachytherapy (SMBT) is ideal in treating superficial skin cancer over the curved surface of the nasal ala. We describe the process of initiating and optimizing SMBT treatment at our institution including clinical workflow, generation of three dimensional (3D) printed custom applicators, and clinical outcomes.

METHODS AND MATERIALS

Planning CT scans were used to acquire images for delineating target volumes. The applicator was designed with customized catheter positioning (3-5mm from target) to cover target volume while sparing dose to organs at risk (OAR) such as adjacent skin and nasal mucosa. Applicators were 3D printed, with transparent resin to aid visualization of underlying skin. Dosimetric parameters evaluated included CTV D90, CTV D0.1cc, and D2cc to OARs. Clinical outcomes assessed were local control, acute and late toxicity (Common Terminology Criteria for Adverse Events v5.0 [CTCAEv5.0]), and cosmesis (Radiation Therapy Oncology Group [RTOG]).

RESULTS

Ten patients were treated with SMBT with a median followup of 17.8 months. Dose prescription was 40 Gy in 10 daily fractions. Mean CTV D90 was 38.5 Gy (range 34.7-40.6), mean CTV D0.1cc 49.2 Gy (range 45.6-53.5), which was <140% of the prescription dose in all patients. Treatment was well tolerated, with acceptable Grade 2 acute, Grade 0-1 late skin toxicity, and good-excellent cosmesis for all patients. Two patients experienced local failure, and both underwent surgical salvage.

CONCLUSIONS

SMBT was successfully planned and delivered for superficial nasal BCC using 3D printed custom applicators. Excellent target coverage was achieved while minimizing dose to OAR. Toxicity and cosmesis rates were good-excellent.

Use of Thermoluminescence Dosimetry for QA in High-Dose-Rate Skin Surface Brachytherapy with Custom-Flap Applicator

Surface brachytherapy (BT) lacks standard quality assurance (QA) protocols. Commercially available treatment planning systems (TPSs) are based on a dose calculation formalism that assumes the patient is made of water, resulting in potential deviations between planned and delivered doses. Here, a method for treatment plan verification for skin surface BT is reported. Chips of thermoluminescent dosimeters (TLDs) were used for dose point measurements. High-dose-rate treatments were simulated and delivered through a custom-flap applicator provided with four fixed catheters to guide the Iridium-192 (Ir-192) source by way of a remote afterloading system. A flat water-equivalent phantom was used to simulate patient skin. Elekta TPS Oncentra Brachy was used for planning. TLDs were calibrated to Ir-192 through an indirect method of linear interpolation between calibration factors (CFs) measured for 250 kV X-rays, Cesium-137, and Cobalt-60. Subsequently, plans were designed and delivered to test the reproducibility of the irradiation set-up and to make comparisons between planned and delivered dose. The obtained CF for Ir-192 was (4.96 ± 0.25) μC/Gy. Deviations between measured and TPS calculated doses for multi-catheter treatment configuration ranged from -8.4% to 13.3% with an average of 0.6%. TLDs could be included in clinical practice for QA in skin BT with a customized flap applicator.

Study of dose dependence on density in planar 3D-printed applicators for HDR Ir192 surface brachytherapy

PURPOSE

This paper describes a method to evaluate the influence of 3D printed plesiotherapy applicators densities in the most clinically relevant dosimetric planes of these brachytherapy treatments. Studied densities range goes from that of water to that of air including the intermediate applicators densities made of acrylonitrile butadiene styrene and polylactic acid, materials used as Fused Deposition Modelling (FDM) filaments.

METHODS AND MATERIALS

All applicators were manufactured by means of FDM 3D printing and a special empty applicator of ABS walls was designed to be filled with water or air. In each of these applicators, the values of the dose and gamma index at the surface and at the prescription depth were measured in clinical conditions, using EBT films.

RESULTS

Analysis of results allow us to conclude that the influence of the applicators density on the dose value in the studied materials depends on the distance at which the dose is measured. Thus, at the prescription depth no influence is observed, however this influence becomes noticeable near the surface of the applicators with dose differences of more than 10% for densities close to 0.4 g/cm³.

CONCLUSION

Therefore, the density of FDM manufactured applicators should be taken into account when calculating surface dose for low density applicators, as variations caused by density can have clinical implications because is the surface dose that is associated with the toxicity of brachytherapy skin treatments.

Advances in Skin Brachytherapy: Cosmesis and Function Preservation

Skin brachytherapy represents an excellent alternative treatment for patients with non-melanoma skin cancers. It offers superior conformity of dose distribution with rapid dose fall off, reducing the risk of radiotherapy-related treatment toxicity. A smaller treatment volume in brachytherapy, when compared with external beam radiotherapy, is conducive for hypofractionation, which is an attractive option for decreasing outpatient visits to the cancer centre, especially for elderly and frail patients. Skin brachytherapy is an excellent option to preserve function and cosmesis, especially in skin cancers located in the head and neck region. Electronic brachytherapy, image-guided superficial brachytherapy and 3D printed moulds are all emerging advances in skin brachytherapy.

HDR brachytherapy in keratinocyte skin carcinomas - Single center experience with analysis of clinical, dosimetric, and radiobiological factors in acute skin toxicity

PURPOSE

Radiotherapy techniques have been utilized to treat keratinocyte skin carcinoma (KSC). The objective of this study was to report the results of patients with KSC treated with HDR brachytherapy, with a variety of techniques and applicators. A statistical analysis of clinical, radiobiological, and technical factors has been made to analyze those factors related to skin acute toxicity, focused on acute epithelitis G3.

METHODS AND MATERIALS

Between February 2005 and August 2020, 93 patients with 120 histologically proven KSC have been treated in our Institution. BT treatment has been performed using superficial BT/plesiotherapy (Valencia applicator (22%), flaps (48%), customized molds (4%) or interstitial techniques (26%)). The indications of BT were primary/definitive in 38 treatments (32%) or adjuvant/postoperative in 82 (68%). In 14 (17%) of the 82 operated patients a skin graft. Mean comparison t tests were performed for quantitative variables, and percentage comparison Chi2 tests for qualitative. Multivariate binomial logistic regression models were done.

RESULTS

Median follow-up was 36.5 months (range 5-141). Local control was achieved in 110 treatments (92%). Acute toxicity, dermatitis, was G1 7%; G2, 57% and G3 38%. The main factors statistically associated to the appearance of dermatitis G3 were the total dose, the volume treated, and the use of manufactured flaps. The main protective factor against dermatitis G3 was implant of skin graft.

CONCLUSIONS

In KSC BT the use of manufactured flap is accompanied by greater EG3, only with a relationship with the volume of treatment and total dose.

Validation of an individualized home-made superficial brachytherapy mold applied for deep nonmelanoma skin cancer

Background

This study was conducted to evaluate the effect of brachytherapy (BT) customized mold [Condensation silicone elastomer (Protesil^TM)] and its thickness on the dose distribution pattern of deep nonmelanoma skin cancers (NMSC).

Materials and methods

Four blocks of mold material were constructed in 5, 10, 15, and 20 mm thickness and 100 × 100 mm² area by a plastic cast. The high dose rate (HDR) plus treatment planning system (TPS) (Version 3, Eckert & Ziegler BEBIG Gmbh, Berlin, Germany) with a ⁶⁰Co source (model: Co0.A86, EZAG BEBIG, Berlin, Germany) as an high dose rate brachytherapy (HDR-BT) source was used. Solid phantom and MOSFET^TM and GAFCHROMIC^TM EBT3 film dosimeters were used for experimental dosimetry of the different thicknesses (up to 20 mm) of BT customized mold. Skin dose and dose to different depths were evaluated.

Result

The TPS overestimated the calculated dose to the surface. Skin dose can be reduced from 250% to 150% of the prescription dose by increasing mold thickness from 5 mm to 20 mm. There was a 7.7% difference in the calculated dose by TPS and the measured dose by MOSFET. There was a good agreement between film dosimetry, MOSFET detector, and TPS' results in depths less than 5 mm.

Conclusion

Each BT department should validate any individualized material chosen to construct the customized surface BT mold. Increasing the mold thickness can treat lesions without overexposing the skin surface. Superficial BT can be recommended as an appropriate treatment option for some deep NMSC lesions (up to 20 mm) with pre-planning considerations employing thicker molds.

Feasibility of using polytetrafluoroethylene flexible implant tube for interstitial brachytherapy patients

PURPOSE

To design the different Polytetrafluoroethylene (PTFE) based flexible implant tubes using an in-house developed device and to evaluate them for High dose rate (HDR) interstitial brachytherapy using computer tomography images.

METHODS AND MATERIALS

PTFE hollow tube having a 2 mm (6 French) outer diameter (OD) and 1.4 mm inner diameter (ID) was used to design in-house single and/or double leader flexible catheters for interstitial brachytherapy implant. An in-house Plastic Wire Drawing Plate (PWDP) machine was developed. Customization of PTFE hollow flexible implant tube (FIT) was done through PWDP. Different percentages of BaSO₄ (5%, 10%, & 15%) were added to Nylon 6 to make radiopaque button. Various quality assurance tests were performed with the PTFE tubes implanted in the brinjal (phantom) before using them on the patients. That is, coupling of brachytherapy machine transfer tube with flexible PTFE Tubes, CT scan artifacts, tube kinks, breast template, and free-hand compatibility.

RESULTS

With the help of the PWDP machine, plastic wires of different lengths were made for single leader and double leader tubes. The different plastic leader ends of 1 cm to 50 cm lengths having 1 mm diameter were created. The radiopaque button of Nylon 6 in circular shape having 1 cm diameter and 0.5 cm thick was created. Developed radiopaque buttons were visible on CT scan images as well as on radiograph images.

CONCLUSIONS

PTFE tubes of the desired length can be made depending upon the size of the brachytherapy implant and are inexpensive than commercially available flexible implant tubes.

Categorization of Common Pigmented Skin Lesions (CPSL) using Multi-Deep Features and Support Vector Machine

The skin is the main organ. It is approximately 8 pounds for the average adult. Our skin is a truly wonderful organ. It isolates us and shields our bodies from hazards. However, the skin is also vulnerable to damage and distracted from its original appearance: brown, black, or blue, or combinations of those colors, known as pigmented skin lesions. These common pigmented skin lesions (CPSL) are the leading factor of skin cancer, or can say these are the primary causes of skin cancer. In the healthcare sector, the categorization of CPSL is the main problem because of inaccurate outputs, overfitting, and higher computational costs. Hence, we proposed a classification model based on multi-deep feature and support vector machine (SVM) for the classification of CPSL. The proposed system comprises two phases: First, evaluate the 11 CNN model's performance in the deep feature extraction approach with SVM, and then, concatenate the top performed three CNN model's deep features and with the help of SVM to categorize the CPSL. In the second step, 8192 and 12,288 features are obtained by combining binary and triple networks of 4096 features from the top performed CNN model. These features are also given to the SVM classifiers. The SVM results are also evaluated with principal component analysis (PCA) algorithm to the combined feature of 8192 and 12,288. The highest results are obtained with 12,288 features. The experimentation results, the combination of the deep feature of Alexnet, VGG16 and VGG19, achieved the highest accuracy of 91.7% using SVM classifier. As a result, the results show that the proposed methods are a useful tool for CPSL classification.

H&N and Skin (HNS) GEC-ESTRO Working Group critical review of recommendations regarding prescription depth, bolus thickness and maximum dose in skin superficial brachytherapy with flaps and customized moulds

The aim of this publication is the assessment of the existing guidelines for non-melanoma skin cancer (NMSC) superficial brachytherapy (BT) and make a critical review based on the existing literature about the maximum dose prescription depth, bolus thickness and maximum skin surface dose (D_max) of the published clinical practice. A systematic review of NMSC superficial BT published articles was carried out by the GEC-ESTRO Head & Neck and Skin (HNS) Working Group (WG). 10 members and 2 external reviewers compared the published clinical procedures with the recommendations in the current guidelines and examined the grade of evidence. Our review verified that there is a large variation among centres with regards to clinical practice in superficial BT and identified studies where published parameters such as maximum dose prescription depth, bolus thickness and D_max exceed the constraints recommended in the guidelines, while showing excellent results in terms of local control, toxicity and cosmesis. This review confirmed that current recommendations on skin superficial BT do not include published experience on tumours treated with superficial BT that require dose prescription depth beyond the recommended 5mm under the skin surface and that the existing literature does not provide sufficient evidence to relate dosimetry of superficial BT to patient reported outcome measures. The GEC-ESTRO HNS WG considers acceptable to prescribe superficial BT dose at a depth above 5mm beyond the skin surface, and modify the bolus thickness to optimize the treatment plan and adjust the acceptable maximum dose on the skin surface, all pending clinical situation.

Impact of detector selection on commissioning of Leipzig surface applicators with improving immobilization in high-dose-rate brachytherapy

PURPOSE

Commission and treatment setup of Leipzig surface applicators, because of the steep dose gradient and lack of robust immobilization, is challenging. We aim to improve commissioning reliability by investigating the impact of detector choice on percentage depth dose (PDD) verifications, and to enhance accuracy and reproducibility in calibration/treatment setup through a simple and novel immobilization device.

METHODS AND MATERIALS

PDD distributions were measured with radiochromic films, optically stimulated luminescent dosimeters (OSLDs), a diode detector, and both cylindrical and parallel plate ionization chambers. The films were aligned to the applicators in parallel and transverse orientations. PDD data from a benchmarking Monte Carlo (MC) study were compared with the measured results, where surface doses were acquired from extrapolation. To improve setup accuracy and reproducibility, a custom-designed immobilization prototype device was made with cost-effective materials using a 3D printer.

RESULTS

The measured PDD data with different detectors had an overall good agreement (<±10%). The parallel plate ionization chamber reported unreliable doses for the smallest applicator. There was no remarkable dose difference between the two film setups. The two-in-one prototype device provided a rigid immobilization and a flexible positioning of the applicator. It enhanced accuracy and reproducibility in calibration and treatment setup.

CONCLUSION

We recommend using radiochromic films in the transverse orientation for a reliable and efficient PDD verification. The applicator's clinical applicability has been limited by a lack of robust immobilization. We expect this economical, easy-to-use prototype device can promote the use of Leipzig applicators in surface brachytherapy.

The State of the Art of Radiotherapy for Non-melanoma Skin Cancer: A Review of the Literature

Due to the general aging population and the fashion trend of sun exposure, non-melanoma skin cancer (NMSC) is rising. The management of NMSC is difficult and necessitates a multidisciplinary team (i.e., pathologists, dermatologists, medical oncologists, surgeons, and radiation oncologists). When surgery is not an option or will cause unacceptably functional morbidity, radiation therapy (RT) may be a preferable tissue-preserving option. Whether used alone or in conjunction with other treatments, RT has been shown to be quite effective in terms of cosmetic results and local control. Contact hypofractionated RT, brachytherapy, and electronic brachytherapy are all promising new treatments. However, rigorous, randomized trials are missing, explaining the disparity in dose, fractionation, and technique recommendations. Therefore, it is essential that interdisciplinary teams better understand RT modalities, benefits, and drawbacks. Our review will provide the role and indications for RT in patients with NMSC.

ORIFICE (Interventional Radiotherapy for Face Aesthetic Preservation) Study: Results of Interdisciplinary Assessment of Interstitial Interventional Radiotherapy (Brachytherapy) for Periorificial Face Cancer

(1) Background: Periorificial face cancer (PFC), defined as both squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) arising around the eyelids, the nose vestibule and the lips, has very high incidence rates worldwide. The aim of our retrospective analysis, focusing on local control (LC) and patients’ degree of satisfaction with the cosmetic outcome, is to present the results of a single institutional series of patients affected by PFC and treated by interventional radiotherapy (brachytherapy–IRT). (2) Methods: We retrospectively evaluated patients affected by PFC who were treated at our Interventional Oncology Center (IOC) with interstitial IRT from 2012 to 2021 with doses and volumes specific for each subsite considered. (3) Results: We report the results of 40 patients affected by PFC and treated by HDR interstitial IRT. The median follow-up was 24 months. The actuarial 3-year LC was 94%. Regarding patients’ satisfaction, we found that 93% of patients were satisfied and only 7% of patients were not completely satisfied with the final cosmetic result. (4) Conclusions: Interstitial HDR IRT could be an effective therapeutic option providing adequate disease control and preventing potentially disfiguring surgical approaches. More numerous and standardized studies are warranted to confirm the available evidence.

Versatile Detection and Monitoring of Ionizing Radiation Treatment Using Radiation-Responsive Gel Nanosensors

Modern radiation therapy workflow involves complex processes intended to maximize the radiation dose delivered to tumors while simultaneously minimizing excess radiation to normal tissues. Safe and accurate delivery of radiation doses is critical to the successful execution of these treatment plans and effective treatment outcomes. Given extensive differences in existing dosimeters, the choice of devices and technologies for detecting biologically relevant doses of radiation has to be made judiciously, taking into account anatomical considerations and modality of treatment (invasive, e.g., interstitial brachytherapy vs noninvasive, e.g., external-beam therapy radiotherapy). Rapid advances in versatile radiation delivery technologies necessitate new detection platforms and devices that are readily adaptable into a multitude of form factors in order to ensure precision and safety in dose delivery. Here, we demonstrate the adaptability of radiation-responsive gel nanosensors as a platform technology for detecting ionizing radiation using three different form factors with an eye toward versatile use in the clinic. In this approach, ionizing radiation results in the reduction of monovalent gold salts leading to the formation of gold nanoparticles within gels formulated in different morphologies including one-dimensional (1D) needles for interstitial brachytherapy, two-dimensional (2D) area inserts for skin brachytherapy, and three-dimensional (3D) volumetric dose distribution in tissue phantoms. The formation of gold nanoparticles can be detected using distinct but complementary modes of readout including optical (visual) and photothermal detection, which further enhances the versatility of this approach. A linear response in the readout was seen as a function of radiation dose, which enabled straightforward calibration of each of these devices for predicting unknown doses of therapeutic relevance. Taken together, these results indicate that the gel nanosensor technology can be used to detect ionizing radiation in different morphologies and using different detection methods for application in treatment planning, delivery, and verification in radiotherapy and in trauma care.

Radiotherapy in the Adjuvant and Advanced Setting of CSCC

Introduction

The use of radiotherapy for cutaneous squamous cell carcinoma (CSCC) has solid historical roots. It is used with patients who are not suitable for surgery, with patients with high-risk histological features in the adjuvant setting, and in palliative care.

Objectives

The aim of this article is to summarize and provide a radiation therapy overview on the indications, effectiveness, and potential adverse events of radiotherapy in the adjuvant and advanced setting of CSCC.

Methods

We performed a comprehensive literature review on PubMed, adopted as our biomedical literature database. Articles were selected based on their date of publication (in the last 30 years) and relevance.

Results

Radiotherapy (RT) can safely be used to manage non-surgical patients and high-risk patients in the advanced CSCC setting. The remarkable progress of delivery techniques has greatly improved the effectiveness and toxicity profile of RT treatments. From 2D techniques to intensity modulated radiation therapy (IMRT), and brachytherapy, all RT techniques have greatly advanced. To improve acute and chronic side effects, a deeper care has been used. As regards CSCC, several dose fractionations and schedules have been suggested, in line with the patient's age and medical conditions.

Conclusions

RT is a fundamental and constantly evolving therapeutic option in the treatment of CSCC, to minimize the risk of recurrence and metastases in the adjuvant setting and in the exclusive treatment for non-surgical patients. Patients' selection is crucial, together with and a collaborative team working approach among the specialists involved in disease management in the perspective of the best multidisciplinary assessment.

Electronic brachytherapy for treatment of non-melanoma skin cancers: clinical results and toxicities

Purpose

Although surgical approaches are standard for most non-melanomatous skin cancers, some patients are not candidates due to medical co-morbidities or functional or cosmetic or lesion location. High-dose-rate electronic brachytherapy (HDR-EBT) may be an alternative treatment modality.

Material and methods

A retrospective chart review was conducted from April 2011 to April 2013. All lesions were pathologically confirmed as malignant basal cell or squamous cell carcinoma. A HDR-EBT system delivered a median biological equivalent dose of 50 Gy total to a depth of 0.1-0.5 cm using various sizes of applicators. Treatment feasibility, acute and late toxicity, cosmetic outcomes, and local recurrence were assessed.

Results

Thirty-three patients with a mean age of 76 years with 50 cutaneous lesions were treated. Locations included 17 extremity lesions and 33 head and neck lesions. After treatments, acute grade 3 moist desquamation developed in 9 of the lesions (18%). Acute grade 4 ulceration developed in 3 lesions in the lower extremity (6%) and 1 upper lip lesion (2%). These toxicities were improved after a median of 20 days. Amongst the 4 lesions with grade 4 toxicities, a greater proportion were in lower extremity lesions compared to head and neck lesions (75% vs. 25%). There was no difference in the rate of grade 3 and 4 toxicities between patients aged ≤ 75 years and aged > 75 years (p = 0.082). With a mean long-term follow-up of 45.6 months, there was 1 local recurrence treated with surgery and no reported late toxicities.

Conclusions

Our experience with HDR-EBT for non-melanomatous skin cancers is encouraging in terms of efficacy and convenience for patients. Our long-term follow-up shows a good response in all treated sites. Caution should be used for extremity sites, and more fractionated regimens should be considered to avoid severe acute toxicities.

High-dose-rate plesiotherapy with customized molds in non-melanoma skin cancer: efficacy and safety at 10 years-single institution experience

Purpose

Our center adopted high-dose-rate brachytherapy with surface applicators (plesiotherapy) in 2008, creating custom molds to treat irregular areas. This study describes the efficacy and safety outcomes after extensive follow-up in the patients.

Methods/patients

We planned the treatment using two computed tomography (CT) scans: the first to delineate the lesion and the second after placing the thermoplastic mold. Fusing the two CT images enables planning of the target volume and pinpointing, where the catheters are in the mold.

Results

Seventy patients received plesiotherapy, either exclusively or following excision in patients with risk factors for recurrence. Those receiving plesiotherapy alone showed a complete response rate of 95.8%, and recurrences occurred in 5.7% at a mean follow-up of 96.2 months. Chronic toxicity appeared in 26.6% of patients, but severity was limited to grade 1 or 2.

Conclusions

High-dose-rate brachytherapy with customized molds yields a high rate of complete response, with long-term recurrence rates in line with similar studies and an acceptable toxicity rate.

Additive manufacturing (3D printing) in superficial brachytherapy

The aim of this work is to provide an overview of the current state of additive manufacturing (AM), commonly known as 3D printing, within superficial brachytherapy (BT). Several comprehensive database searches were performed to find publications linked to AM in superficial BT. Twenty-eight core publications were found, which can be grouped under general categories of clinical cases, physical and dosimetric evaluations, proof-of-concept cases, design process assessments, and economic feasibility studies. Each study demonstrated a success regarding AM implementation and collectively, they provided benefits over traditional applicator fabrication techniques. Publications of AM in superficial BT have increased significantly in the last 5 years. This is likely due to associated efficiency and consistency benefits; though, more evidences are needed to determine the true extent of these benefits.

[Place of radiotherapy in the treatment of cutaneous carcinomas]

Basal cell carcinomas and cutaneous squamous cell carcinomas are among the most common cancerous tumors in the world. Their treatment is most often based on surgery. Adjuvant radiotherapy may be indicated in case of risk factors for recurrence or as an alternative to surgery if surgery is not feasible due to the patient's advanced age and/or co-morbidities or as an alternative to potentially mutilating surgery. Radiotherapy is also part of the therapeutic arsenal for rarer skin tumors such as Merkel cell carcinoma, cutaneous lymphomas, Kaposi's disease and cutaneous adnexal carcinomas.

Acute and late complications and toxicities of skin brachytherapy

Skin cancer is the most prevalent malignancy, and its incidence is rising. Surgery is the primary treatment, however, morbidity of surgical resection in certain parts of the body warrant alternate treatment options such as radiation therapy. Complex topology of the skin can pose a challenge for treatment with photon and electron external beam radiotherapy techniques. Brachytherapy can be an attractive radiotherapy technique for these regions. Furthermore, brachytherapy results in lower dose to the underlying deep organs. The goal of this manuscript is to provide a brief overview of the role of brachytherapy for skin malignancies and to outline potential acute and long-term toxicities.

Non-melanoma Skin Cancer Treated by Contact High-dose-rate Radiotherapy (Brachytherapy): A Mono-institutional Series and Literature Review

BACKGROUND/AIM

Non-melanoma skin cancers (NMSC) are the most common neoplasms worldwide and their incidence has been proven to increase in recent years and their treatment should aim at cancer cure as well as cosmetic and functional results. The aim of the study was to report the results of our mono-institutional series of high-dose-rate radiotherapy (cHDR-RT) in NMSC, based on a homogenous technique and two different treatment schedules.

PATIENTS AND METHODS

All patients affected by NMSC who were consecutively evaluated and treated at our Interventional Oncology Center from October 2018 to August 2020, were included. Patients underwent cHDR-RT using flap applicators and remotely afterloaded Ir-192 sources.

RESULTS

Overall, 51 patients were treated for a total of 67 lesions. Local control (LC) and disease-specific survival (DSS) were 94.0% and 100%, respectively. Grade 1, grade 2, grade 3 and grade 4 acute toxicity rates were 24.6%, 3.5%, 3.5%, and 0.0%, respectively. The cosmetic results were graded as excellent/good, fair, and poor in 73.7%, 19.3%, and 7.0%.

CONCLUSION

cHDR-RT of NMSC is an effective alternative to surgery due to excellent outcomes both in terms of local control and aesthetic results especially in the face.

Impact of GBBS algorithm on post-mastectomy scar boost irradiation of breast using catheter flap

Purpose

Post-mastectomy radiation therapy significantly reduces locoregional recurrence rates, which can be achieved with external beam radiotherapy delivered to chest wall, followed by scar irradiation either by electron or high-dose-rate (HDR) mould brachytherapy. The present study evaluates dosimetric advantage of Acuros^® BV, a TG-186 MBDCA, over TG-43 formalism using ¹⁹²Ir source for HDR brachytherapy in chest wall scar boost using catheter flap.

Material and methods

A total of 25 patients, free of cardiac and pulmonary co-morbidities, who met the inclusion criteria were involved in the study. Catheter flap made of silicon with 20 channels was used to deliver a total dose of 7.5 Gy/3 fx by HDR surface mould brachytherapy to delineated scar volume. Plan was optimized with iterative method to obtain desired results with TG-43 formalism, followed by Acuros^® BV (GBBS algorithm) without altering dwell positions or time. The two algorithm plans were analyzed qualitatively and quantitatively with dose-volume histograms.

Results

The mean D_98% CTV-HDR_evl coverage decreased by 1.16% compared to TG-43, and near-maximum dose decreased by 8.18% (p = 0.000), mean D_max dose to CTV-HDR_evl, and mean D_mean dose was lesser by 6.25% (p = 0.000) and 10.82% (p = 0.000), respectively, compared to TG-43. Heart D_2% showed significant results, whereas D_median (cGy) revealed very significant difference. A 5 mm thick skin contour showed statistically significant results (p = 0.000) for V_150% and V_200%.

Conclusions

The presented data showed how Acuros^® BV, algorithm-based calculation in scar boost irradiation of breast, accounting for a mass density of the medium and scatter condition, considered actual dose prediction in a medium.

A study of Type B uncertainties associated with the photoelectric effect in low-energy Monte Carlo simulations

Purpose.To estimate Type B uncertainties in absorbed-dose calculations arising from the different implementations in current state-of-the-art Monte Carlo (MC) codes of low-energy photon cross-sections (<200 keV).Methods.MC simulations are carried out using three codes widely used in the low-energy domain: PENELOPE-2018, EGSnrc, and MCNP. Three dosimetry-relevant quantities are considered: mass energy-absorption coefficients for water, air, graphite, and their respective ratios; absorbed dose; and photon-fluence spectra. The absorbed dose and the photon-fluence spectra are scored in a spherical water phantom of 15 cm radius. Benchmark simulations using similar cross-sections have been performed. The differences observed between these quantities when different cross-sections are considered are taken to be a good estimator for the corresponding Type B uncertainties.Results.A conservative Type B uncertainty for the absorbed dose (k = 2) of 1.2%-1.7% (<50 keV), 0.6%-1.2% (50-100 keV), and 0.3% (100-200 keV) is estimated. The photon-fluence spectrum does not present clinically relevant differences that merit considering additional Type B uncertainties except for energies below 25 keV, where a Type B uncertainty of 0.5% is obtained. Below 30 keV, mass energy-absorption coefficients show Type B uncertainties (k = 2) of about 1.5% (water and air), and 2% (graphite), diminishing in all materials for larger energies and reaching values about 1% (40-50 keV) and 0.5% (50-75 keV). With respect to their ratios, the only significant Type B uncertainties are observed in the case of the water-to-graphite ratio for energies below 30 keV, being about 0.7% (k = 2).Conclusions.In contrast with the intermediate (about 500 keV) or high (about 1 MeV) energy domains, Type B uncertainties due to the different cross-sections implementation cannot be considered subdominant with respect to Type A uncertainties or even to other sources of Type B uncertainties (tally volume averaging, manufacturing tolerances, etc). Therefore, the values reported here should be accommodated within the uncertainty budget in low-energy photon dosimetry studies.

Dosimetric comparison of volumetric modulated arc therapy (VMAT) and high-dose-rate brachytherapy (HDR-BT) for superficial skin irradiation with significant curvature in one or more planes

PURPOSE

This study compares the plan quality of high-dose-rate brachytherapy (HDR-BT) and volumetric modulated arc therapy (VMAT) for superficial irradiation of large areas of skin with significant curvature in one or more planes.

METHODS

A total of 14 patients from two centres previously treated with either HDR-BT or VMAT were retrospectively replanned using the alternative technique. Sites included scalp and lower limbs. Identical computed tomography (CT) scans, clinical target volume (CTV) and organs at risk (OARs) and prescription were used for both techniques. Conformity, skin surface dose and OAR doses were compared.

RESULTS

Conformity index was consistently better with VMAT than HDR-BT (p < 0.01). Maximum skin surface dose (D0.1cc) had a higher mean of 49.6 Gy with HDR-BT compared to 31.4 Gy for VMAT (p < 0.01). Significantly smaller volumes of healthy tissue were irradiated with VMAT than with HDR-BT. This can be seen in brain volumes receiving 10, 20 and 30 Gy EQD2 and in extremities receiving 5 and 10 Gy. When close to the volume, the lens received significantly lower doses with VMAT (p < 0.01).

CONCLUSION

In this small sample, VMAT gives equal coverage with lower OAR and skin surface doses than HDR-BT for both scalp and extremities. VMAT is a useful technique for treating large, superficial volumes with significant curvature in one or more planes.

Tumor control and cosmetic outcome of weekly iridium-192 high-dose-rate brachytherapy for nonmelanoma skin cancers in the elderly

PURPOSE

Radiotherapy with high-dose-rate (HDR) brachytherapy is used to treat nonmelanoma skin cancers. We retrospectively analyzed a hypofractionated regimen to assess its safety and efficacy in elderly patients ≥70 years.

METHODS AND MATERIALS

Forty-eight patients with 67 lesions treated since 2016 with catheter-based iridium-192 HDR brachytherapy using a custom mold or three-dimensional-printed applicator met inclusion criteria. Treatment was 36 Gy in six weekly fractions. Local and locoregional control were assessed with Kaplan-Meier curves. Acute and late toxicity were graded as per Common Terminology Criteria for Adverse Events, version 5. Cosmesis was defined as "excellent" (indistinguishable from untreated skin), "good" (minimal changes), or "poor" (extensive changes). Univariate analyses were performed.

RESULTS

Median age was 85.7 years, and 21 were female. Durable local control occurred in 63 lesions (94.0%), giving estimated local control of 100% at 6 months, 95.1% at 1 year, and 88.8% at 2 years. No factors were predictive of local control on univariate analysis. All experienced acute toxicity that ultimately resolved: 28.4% Grade 2 and 4.5% Grade 3. Larger treatment volume receiving ≥36 Gy was associated with increased Grade ≥2 acute toxicity. Patients experienced late Grade 2 and late Grade 4 toxicity after 6.5% treatments each. Younger age was associated with increased Grade ≥2 late toxicity. "Good" or better cosmesis occurred in 93.2%, and "poor" cosmesis was associated with lower extremities and larger lesions.

CONCLUSIONS

Hypofractionated HDR brachytherapy using 36 Gy in six weekly fractions is associated with satisfactory locoregional control and cosmesis with minimal risk of severe acute or late toxicities.

Novel method of combined photon beam radiotherapy and brachytherapy for treatment of extensive advanced scalp squamous cell carcinoma

Radiotherapy of extensive malignant scalp lesions has always been a challenge for radiation oncologists considering the proximity of critical structures. We treated a 39-year-old patient with extensive scalp squamous cell carcinoma with application of adjuvant concurrent chemoradiation and external beam radiation therapy (EBRT), followed by high-dose-rate (HDR) surface brachytherapy boost using an exclusively designed mould, and assessed the radiation dose reaching planning target volume, brain, and optic structures. Comparison between conventional planning with sole EBRT and combined treatment planning with EBRT and brachytherapy, assured the use of the latter treatment to avoid high radiation doses from reaching critical organs at risk without compromising the required dose for planning target volume.

Computed tomography-based flap brachytherapy for non-melanoma skin cancers of the face

PURPOSE

Non-melanoma skin cancers of the face are at high-risk for local recurrence and metastatic spread. While surgical interventions such as Mohs microsurgery are considered the standard of care, this modality has the potential for high rates of toxicity in sensitive areas of the face. Catheter flap high-dose-rate (HDR) brachytherapy has shown promising results, with high rates of local control and acceptable cosmetic outcomes.

MATERIAL AND METHODS

Patients with non-melanoma skin cancers (NMSC) located on the face were treated with 40 Gy in 8 fractions, given twice weekly via catheter flap HDR brachytherapy. Clinical target volume (CTV) included the visible tumor plus a margin of 5 mm in all directions, with no additional planning target volume (PTV) margin.

RESULTS

Fifty patients with 53 lesions on the face were included, with a median follow-up of 15 months. All were considered high-risk based on NCCN guidelines. Median tumor size and thickness were 18 mm and 5 mm, respectively. Median PTV volume and D90 were 1.7 cc and 92%, respectively. Estimated rate of local control at twelve months was 92%. Three patients (5%) experienced acute grade 2 toxicity. Two patients (4%) continued to suffer from chronic grade 1 skin toxicity at 12 months post-radiotherapy (RT), with an additional two patients (4%) experiencing chronic grade 2 skin toxicity. Forty-nine lesions (92%) were found to have a good or excellent cosmetic outcome with complete tumor remission.

CONCLUSIONS

CT-based flap applicator brachytherapy is a valid treatment option for patients with NMSC of the face. This modality offers high rates of local control with acceptable cosmetic outcomes and low rates of toxicity.

Depth-dose measurement corrections for the surface electronic brachytherapy beams of an Esteya® unit: a Monte Carlo study

Three different correction factors for measurements with the parallel-plate ionization chamber PTW T34013 on the Esteya electronic brachytherapy unit have been investigated. This chamber type is recommended by AAPM TG-253 for depth-dose measurements in the 69.5 kV x-ray beam generated by the Esteya unit.

Monte Carlo simulations using the PENELOPE-2018 system were performed to determine the absorbed dose deposited in water and in the chamber sensitive volume at different depths with a Type A uncertainty smaller than 0.1%. Chamber-to-chamber differences have been explored performing measurements using three different chambers. The range of conical applicators available, from 10 to 30 mm in diameter, has been explored.

Using a depth-independent global chamber perturbation correction factor without a shift of the effective point of measurement yielded differences between the absorbed dose to water and the corrected absorbed dose in the sensitive volume of the chamber of up to 1% and 0.6% for the 10 mm and 30 mm applicators, respectively. Calculations using a depth-dependent perturbation factor, including or excluding a shift of the effective point of measurement, resulted in depth-dose differences of about ± 0.5% or less for both applicators. The smallest depth-dose differences were obtained when a shift of the effective point of measurement was implemented, being displaced 0.4 mm towards the center of the sensitive volume of the chamber. The correction factors were obtained with combined uncertainties of 0.4% (k = 2). Uncertainties due to chamber-to-chamber differences are found to be lower than 2%.

The results emphasize the relevance of carrying out detailed Monte Carlo studies for each electronic brachytherapy device and ionization chamber used for its dosimetry.

Clinically-implementable template plans for multidwell treatments using Leipzig-style applicators in 192Ir surface brachytherapy

PURPOSE

Multiple dwell positions ("multidwell") within a Leipzig-style applicator can be used to increase dose uniformity and treatment area. Model-based dose calculation algorithms (MBDCAs) are necessary for accurate calculations involving these applicators because of their nonwater equivalency and complex geometry. The purpose of this work was to create template plans from MBDCA calculations and present their dwell times and positions for users of these applicators without access to MBDCAs.

METHODS AND MATERIALS

The Leipzig-style solid applicator model within our treatment planning system was used to design template plans. Five template plans, normalized to 0.3 cm depth within a water phantom, were optimized using the treatment planning system MBDCA. Each template plan contained unique dwell positions, times, and active lengths (0.5-1.5 cm). A single-dwell distribution was optimized for comparison. The stem of this applicator stops within the shell; therefore, one template plan contained an intrafraction rotation to determine the largest dose distribution achievable. Effects of imperfect applicator rotation were quantified by inserting rotational offsets and comparing the V_100%, D_95%, and minimum dose coverage for planning target volumes created from 80%/90% isodose lines.

RESULTS

The 90% (80%) isodose line dimensions at 0.3 cm depth for single-dwell increased from 0.94 × 0.97 (1.53 × 1.57) cm² to 2.09 × 1.24 (2.75 × 1.88) cm² in the largest template plan. Manually inserted angular offsets up to ±10° for the template plan requiring rotation preserved V_100%, D_95%, and minimum dose within 2.0%, 1.9%, and 8.0%, respectively.

CONCLUSION

A set of template plans was created to provide accessibility to the multidwell methodology, even for users without access to MBDCAs. Each template plan should be reviewed before clinical implementation.

High dose brachytherapy with non sealed 188Re (rhenium) resin in patients with non-melanoma skin cancers (NMSCs): single center preliminary results

Background and aim

High dose brachytherapy using a non sealed ¹⁸⁸Re-resin (Rhenium-SCT®, Oncobeta® GmbH, Munich, Germany) is a treatment option for non-melanoma skin cancer (NMSC). The aim of this prospective study was to assess the efficacy and the safety of a single application of Rhenium-SCT® in NMSC.

Materials and method

Fifty consecutive patients (15F, 35 M, range of age 56–97, mean 81) showing 60 histologically proven NMSCs were enrolled and treated with the Rhenium-SCT® between October 2017 and January 2020. Lesions were located on the face, ears, nose or scalp (n = 46), extremities (n = 9), and trunk (n = 5). Mean surface areas were 7.0 cm² (1–36 cm²), mean thickness invasion was 1.1 mm (0.2–2.5 mm), and mean treatment time was 79 min (21–85 min). Superficial, mean, and target absorbed dose were 185 Gy, 63 Gy, and 31 Gy respectively. Patients were followed-up at 14, 30, 60, 90, and 180 days posttreatment, when dermoscopy and biopsy were performed. Mean follow-up was 20 months (range 3–33 months). Early skin toxicity was classified according to Common Terminology Criteria for Adverse Events (CTCAE). Cosmetic results were evaluated after at least 12 months according to Radiation Therapy Oncology Group (RTOG) scale.

Results

At 6 months follow-up, histology and dermoscopy were available for 54/60 lesions, of which 53/54 (98%) completely responded. One patient showed a 1-cm² residual lesion that was subsequently surgically excised. Twelve months after treatment, 41/41 evaluable lesions were free from relapse. Twenty four months after treatment, 23/24 evaluable lesions were free of relapse. In 56/60 lesions early side effects, resolving within 32 days were classified as grades 1–2 (CTCAE). In the remaining 4/60 lesions, these findings were classified as grade 3 (CTCAE) and lasted up to 8–12 weeks but all resolved within 90 days. After at least 12 months (12–33 months), cosmetic results were excellent (30 lesions) or good (11 lesions).

Conclusion

High dose brachytherapy with Rhenium-SCT® is a noninvasive, reasonably safe, easy to perform, effective and well-tolerated approach to treat NMSCs, and it seems to be a useful alternative option when surgery or radiation therapy are difficult to perform or not recommended. In our population 98% of the treated lesions resolved completely after a single application and only one relapsed after 2 years. Larger patients’ population and longer follow-up are needed to confirm these preliminary data and to find the optimal dose to administer in order to achieve complete response without significant side effects.

The American Brachytherapy society consensus statement for skin brachytherapy

PURPOSE

Keratinocyte carcinoma (KC, previously nonmelanoma skin cancer) represents the most common cancer worldwide. While surgical treatment is commonly utilized, various radiation therapy techniques are available including external beam and brachytherapy. As such, the American Brachytherapy Society has created an updated consensus statement regarding the use of brachytherapy in the treatment of KCs.

METHODS

Physicians and physicists with expertise in skin cancer and brachytherapy created a consensus statement for appropriate patient selection, data, dosimetry, and utilization of skin brachytherapy and techniques based on a literature search and clinical experience.

RESULTS

Guidelines for patient selection, evaluation, and dose/fractionation schedules to optimize outcomes for patients with KC undergoing brachytherapy are presented. Studies of electronic brachytherapy are emerging, although limited long-term data or comparative data are available. Radionuclide-based brachytherapy represents an appropriate option for patients with small KCs with multiple techniques available.

CONCLUSIONS

Skin brachytherapy represents a standard of care option for appropriately selected patients with KC. Radionuclide-based brachytherapy represents a well-established technique; however, the current recommendation is that electronic brachytherapy be used for KC on prospective clinical trial or registry because of a paucity of mature data.

Feasibility of using multiple-dwell positions in 192Ir Leipzig-style brachytherapy surface applicators to expand target coverage and clinical application

PURPOSE

Leipzig-style applicators for surface brachytherapy are traditionally used with a single-source dwell position. This study explores the feasibility of using multiple-source dwell positions ("multidwell") to improve the dose coverage and applicability of Leipzig-style applicators.

METHODS AND MATERIALS

A virtual model of the Leipzig-style applicator was commissioned for a model-based dose calculation algorithm (MBDCA) and compared against American Association of Physicists in Medicine working group 186 benchmarking data sets and ionization chamber point measurements. An absolute dosimetry technique based on radiochromic film was used to validate both single-dwell and multidwell plans.

RESULTS

Dose distributions generated from the MBDCA-based virtual model were consistent with working group data sets, ion chamber measurements, and radiochromic film analysis. In one multidwell configuration, at 3 mm prescription depth, the 80% isodose width was increased to 25 mm, compared with 15 mm in the same dimension for a single-dwell delivery. In the same multidwell configuration, the flatness, measured as >98% isodose line, was more than doubled to 8 mm, compared with 3 mm in the same dimension. For multidwell plans, 2-D planar agreement between radiochromic film and MBDCA exceeded 93% in gamma analysis (3%/1 mm criteria). Submillimeter positional agreement was found, with a total dosimetric uncertainty of 4.5% estimated for the entire system.

CONCLUSIONS

Leipzig-style surface applicators with multiple-source dwell positions have been benchmarked against radiochromic film dosimetry. Results show that the clinically viable coverage area can be increased significantly.

Combined interstitial and surface high-dose-rate brachytherapy treatment of squamous cell carcinoma of the hand

Purpose

We present a case report of treatment using interstitial and surface high-dose-rate (HDR) brachytherapy for cutaneous squamous cell carcinoma (SCC) involving the interspace of the third and fourth digits. The patient refused two-ray amputation and the lesion was not amenable for external beam radiation therapy (EBRT). This is the first report detailing combined interstitial and surface HDR brachytherapy for a hand SCC.

Material and methods

The patient received 4050 cGy in 9 fractions, twice daily using 6 interstitial catheters and 8 Freiburg flap catheters. The clinical target was defined by MRI and ultrasound as a dorsal mass to the interspace between the heads of the third and fourth metacarpals measuring approximately 7 mm transverse × 5 mm volar-dorsal × 16 mm proximal-distal.

Results

The treatment resulted in radiographic and clinical tumor control. The patient retained functional use of her hand. However, there were both acute and late treatment-related side effects. Acutely, inpatient admission for pain control with a nerve block was needed. Long-term toxicity was notable for grade 2 skin necrosis treated with hyperbaric oxygen.

Conclusions

The first interstitial and surface HDR brachytherapy for cutaneous squamous cell carcinoma of a finger interspace for hand function preservation is presented. The initial experience revealed that brachytherapy was tolerated but with notable acute and late side effects. Treatment did result in tumor shrinkage with organ preservation and function of two rays. A larger cohort of patients will be required for additional conclusions related to long-term clinical benefits in patients who refuse ray amputation.

The dosimetric effect of variations in source position on treatments using Leipzig-style brachytherapy skin applicators

Leipzig-style skin brachytherapy applicators are an excellent choice for the treatment of small surface lesions, since they can be used with a high dose rate source to produce a tightly constrained treatment field on the desired area of the skin. The dosimetry of these applicators is challenging to independently verify due to their small dimensions, complex energy spectrum and steep dose gradients. In particular the close proximity of the brachytherapy source to the treatment region is cause for concern, since small variations in the position of the radioactive source may significantly affect the resulting dose distribution. The aim of this work was to assess the dosimetry of these applicators using three independently techniques and use these results to examine the effect of variation in source position on the dose distribution. Simulation of different sized applicators in conjunction with a Gammamed + Ir¹⁹² source was performed using the EGSnrc Monte Carlo code. Dose distributions at the prescription depth and at the surface generated by Monte Carlo were compared to the outputs of a commercially available treatment planning system and measurements using radiochromic film. Source displacements of up to 0.5 mm in the vertical direction, 0.65 mm in the horizontal direction, and rotations of the source by up to 5° were all simulated. Changes in dose of over 6% at the prescription point and reductions in coverage at the 100% isodose level of several millimetres were observed even for small shifts of the source from its intended position. This work demonstrates that variation in the position of the radiation source is the dominant source of uncertainty in the use of these types of applicators. Centres wishing to perform treatments using these applicators are advised to take steps to control the uncertainty and ensure it remains at an acceptable level.

Development and clinical implementation of semi-automated treatment planning including 3D printable applicator holders in complex skin brachytherapy

PURPOSE

High-dose-rate brachytherapy (HDR-BT) is a treatment option for malignant skin diseases compared to external beam radiation therapy, HDR-BT provides improved target coverage, better organ sparing, and has comparable treatment times. This is especially true for large clinical targets with complex topologies. To standardize and improve the quality and efficacy of the treatments, a novel streamlined treatment approach in complex skin HDR-BT was developed and implemented. This approach consists of auto generated treatment plans and a 3D printable applicator holder (3D-AH).

MATERIALS AND METHODS

The in-house developed planning system automatically segments computed tomography simulation images (a), optimizes a treatment plan (b), and generates a model of the 3D-AH (c). The 3D-AH is used as an immobilization device for the flexible Freiburg flap applicator used to deliver treatment. The developed, automated planning is compared against the standard clinical plan generation process for a flat 10 × 10 cm² field, curved fields with radii of 4, 6, and 8 cm, and a representative clinical case. The quality of the 3D print is verified via an additional CT of the flap applicator latched into the holder, followed by an automated rigid registration with the original planning CT. Finally, the methodology is implemented and tested clinically under an IRB approval.

RESULTS

All automatically generated plans were reviewed and accepted for clinical use. For the clinical workflow, the coverage achieved at a prescription depth for the flat 4, 6, and 8 cm applicator was (100.0 ± 4.9)%, (100.0 ± 4.9)%, (96.0 ± 0.3)%, and (98.4 ± 0.3)%, respectively. For auto planning, the coverage was (99.9 ± 0.3)%, (100.0 ± 0.2)%, (100.0 ± 0.3)%, and (100.1 ± 0.2)%. For the clinical test case, the D90 for the clinical workflow and auto planning was found to be 93.5% and 100.29% of the prescribed dose, respectively. Processing of the patient's CT to generate trajectories and positions as well as the 3D model of the applicator took <5 min.

CONCLUSION

This workflow automates time intensive catheter digitizing and treatment planning. Compared to printing full applicators, the use of 3D-AH reduces the complexity of the 3D prints, the amount of the material to be used, the time of 3D printing, and amount of quality assurance required. The proposed methodology improves the overall treatment plan quality in complex HDR-BT and impact patient treatment outcomes potentially.

Surface Mould Brachytherapy for Skin Cancers: The British Columbia Cancer Experience

Purpose To report on skin tumor treatment with surface mould brachytherapy at our institution. Methods This was a retrospective review for all patients with skin tumors treated using Ir-192 high dose rate (HDR) surface mould brachytherapy from January 1, 2010 to December 31, 2017 in British Columbia. We identified 65 lesions (59 patients). Median age at diagnosis was 83 (range = 45-97). The majority were basal cell (54%, n = 35) or squamous cell carcinomas (31%, n = 20). Most lesions were located in the head and neck region. The most commonly used RT dose was 40 Gy/10 fractions; all patients had individualized CT-based planning. Results The two-year overall survival (OS) was 77.6% and two-year progression-free survival (PFS) was 71.5%. Most deaths were from unrelated causes. Response was assessed in clinic 2-4 months post-treatment. Our complete response (CR) rate was 96.8%, with partial response in two patients; two patients could not be assessed for response. We report a two-year local control (LC) rate of 84.9%, and local recurrence in five patients. The procedure was well tolerated, with no grade 3-5 acute or late toxicities. There was one case of grade 2 radionecrosis (Common Terminology Criteria for Adverse Events (CTCAE) v. 4.03). The 100% isodose line median depth was 0.5 cm, and median surface dose = 126.5%. The median V90 = 92.3%. Conclusion Surface mould brachytherapy for skin tumors is a safe and effective modality, with excellent response rates. It is well-tolerated and a non-invasive option for elderly patients with comorbidities.

A dosimetric study of electron beam therapy vs. high-dose-rate mould brachytherapy in adjuvant treatment of non-melanoma skin carcinomas of the head and neck region

Purpose

Radiation for superficial tumours of the head and neck region can be given either by brachytherapy or electrons. Brachytherapy (BT), due to rapid dose fall-off and minor set-up errors, should be superior to external beam radiotherapy (EBRT) for treatment of lesions in difficult locations such as the nose and earlobe. The present study is a dosimetric comparison of computed tomography (CT)-based mould brachytherapy treatment plans with 3D conformal electron beam therapy in the treatment of non-melanoma skin cancers (NMSC).

Material and methods

From December 2017 to November 2018 10 patients with NMSC of the head and neck region (forehead, nose, cheek) who underwent adjuvant radiation with HDR brachytherapy (BT) with a surface mould individual applicator were enrolled for analysis. We evaluated dose coverage by minimal dose to 90% of planning target volume (PTV, D₉₀), volumes of PTV receiving 90-150% of prescribed dose (PD) (VPTV_90-150), conformal index for 90% and 100% of PD (COIN₉₀, COIN₁₀₀), dose homogeneity index (DHI), dose nonuniformity ratio (DNR), and exposure of organs at risk (OARs) (eyes, lens, underlying bone and skin). Prospectively, we created CT-based treatment plans for electron beam therapy. We compared conformity (COIN₉₀, COIN₁₀₀), dose coverage of PTV (D₉₀, VPTV₉₀, VPTV₁₀₀), volumes of body receiving 10-90% of PD (V₁₀-V₉₀), doses to OARs (D_0.1cc and D_2cc) of BT and electron plans.

Results

We obtained mean BT-DHI 0.81, BT-DNR 0.608, Electron-DHI 1.25. We observed no significant differences in VPTV_90,100 and D₉₀ between BT and electron beam. Mean BT-VPTV_125,150 were significantly higher than Electron-VPTV_100,125. COIN₉₀ was superior for BT plans.

Conclusions

CT-based surface mould brachytherapy results in better conformity of superficial lesions on small, irregular surfaces such as the nose and inner canthus than electrons with a slightly higher skin dose.

Contemporary Topics in Radiation Medicine: Skin Cancer

Radiation plays an important role in the management of a variety of skin cancers. This article discusses the role of radiation in the treatment of cutaneous squamous cell carcinoma, basal cell carcinoma, Merkel cell carcinoma, cutaneous T-cell lymphoma, and B-cell lymphomas.