Skin surface brachytherapy: A survey of contemporary practice patterns

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.

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.

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.

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.

High-dose-rate surface brachytherapy as a treatment option for renal cell carcinoma cutaneous metastases

Purpose

The aim of this study was to present a case of complete clinical response of renal clear cell carcinoma cutaneous metastases after high-dose-rate surface brachytherapy (HDR sBT).

Material and methods

An 81-year-old female diagnosed with stage IV clear cell renal carcinoma reported to our center with painful relapse of two cutaneous metastases after a previous metastasectomy. The patient was disqualified from systemic therapy due to comorbidities, and qualified to attempt a treatment using HDR sBT. The unit equipped with an iridium-192 source was used to deliver 36 Gy/6 Gy in 6 fractions twice weekly. Overall treatment time was 18 days.

Results

Two weeks after HDR sBT, complete response was observed in one irradiated location, while the partial response was observed in the latter. EORTC grade 1 skin toxicity was reported in both irradiated fields. Three and five months after the treatment, the patient presented complete response and pain relief in both locations with no signs of relapse. The patient remained in palliative care and died seven months after the treatment due to sudden cardiac death.

Conclusions

HDR sBT can be a valuable treatment option for cutaneous metastatic renal cell carcinoma, especially for patients with significant comorbidities. The treatment provided was associated with low toxicity and excellent clinical outcome.

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.

High-Dose-Rate Brachytherapy for the Treatment of Basal and Squamous Cell Carcinomas on Sensitive Areas of the Face: A Report of Clinical Outcomes and Acute and Subacute Toxicities

Purpose

Basal cell and cutaneous squamous cell carcinoma are common malignancies (keratinocyte carcinomas [KCs]). Surgical resection is the standard of care. Radiation using high-dose rate brachytherapy (HDR-BT) may serve as a superior alternative where surgical scars may be of cosmetic concern or in elderly patients with significant comorbidity. We aim to describe the clinical and cosmetic outcomes as well as posttreatment radiation toxicities associated with HDR-BT in patients who were treated for KCs of the face.

Methods and Materials

Patients with KCs treated with HDR-BT from 2015 to 2018 were included in the study. Patient medical records and clinical photos were reviewed at multiple time points: start of treatment, end of treatment, short-term (2 week) follow-up, 3-month follow-up, and if needed at 6 months. Radiation toxicity was graded using the Radiation Therapy Oncology Grading (RTOG) acute toxicity scale. Median (range) toxicity grades at follow-up intervals were calculated. Clinical outcomes including local recurrence were evaluated for all patients.

Results

The study included 19 patients and 20 KCs. The median radiation dose was 42 Gy (39-42 Gy) over 6 fractions. The median toxicity at completion of treatment was RTOG grade 2 (85% of patients). At short-term follow-up, 50% of patients (n = 10) improved to RTOG grade 1 (0-2). At 3 months, 70% of patients (n = 14) had RTOG grade 0, and by 6 months, 100% of patients (n = 18) had RTOG grade 0. No RTOG grade 3 or higher skin toxicity was observed. With a median follow-up of 7.2 months (range, 1.3-54.4 months), the local recurrence-free survival was 95%.

Conclusions

We demonstrate that HDR-BT can be used as definitive treatment of KCs of the face with excellent cosmetic outcomes and local control. Acute and subacute skin toxicities were most commonly RTOG grade 2 or less with resolution of patient's skin toxicity by 3 months.

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.

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.

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.

Mould-based surface high-dose-rate brachytherapy for eyelid carcinoma

Purpose

To evaluate toxicity and clinical outcomes in patients with eyelid tumour treated with contact high-dose-rate brachytherapy (HDR-BT).

Material and methods

Between April 2010 and August 2017, 10 consecutive patients with tumour of the eyelid underwent contact HDR-BT and custom-made surface mould. Every applicator was manually built using conventional thermoplastic material and standard plastic catheters. The median dose prescribed was 42 Gy (range, 30-48) with a median dose per fraction of 3.5 Gy (range, 2-4.5). The dose was delivered in a median of 12 fractions (range, 10-17) over a median of 16 days. In all cases, an ocular shield was placed to reduce the dose to the eye. Acute and late toxicity was evaluated according to RTOG toxicity criteria.

Results

We analyzed data of 9 of 10 patients (one patient was excluded because he did not give consent for investigation). The median age was 68 years (range, 31-88). According to the TNM-UICC staging system, 4, 1 and 4 patients were stage IA, IB and IC, respectively. Basal cell and sebaceous gland carcinomas were reported in 5 and 2 patients, respectively; other histological types were non-Hodgkin lymphoma and plasmacytoma. After a median follow-up of 51 months (range, 16-90), there was no evidence of local or distant recurrence. The treatment was very well tolerated. Most commonly acute reactions consisted of low grade (G1-G2) conjunctivitis and skin erythema. Only one patient required a temporary interruption of the treatment due to acute G2 conjunctivitis and G3 lid erythema. Only one G2 late toxicity was reported (corneal ulceration), without resulting in functional impairment or blindness.

Conclusions

Our results suggest that contact HDR-BT with a customized applicator is safe, effective and offers very good local control and can be considered for the treatment of eyelid tumours.

End-to-end test and MOSFET in vivo skin dosimetry for 192Ir high-dose-rate brachytherapy of chronic psoriasis

Purpose

This study was performed using end-to-end testing and real-time in vivo skin dose measurements, using metal oxide semiconductor field effect transistor (MOSFET) dosimeters on our first chronic psoriasis patient treated with iridium-192 (¹⁹²Ir) high-dose-rate (HDR) brachytherapy (BT).

Material and methods

Treatment delivery was planned with the prescription dose of 1.8 Gy to a 3 mm depth for 12 fractions, using our custom-fabricated surface mold and Varian soft catheters. The optimal technique to provide an adequate and acceptable skin dose as well as its feasibility were evaluated by an end-to-end exercise using a perspex finger phantom. The accuracy and reliability of MOSFET dose measurement was explored with a thermoluminescence dosimetry (TLD) before being used in vivo to monitor skin doses during treatment delivery for each BT fraction.

Results

Using custom-made surface mold (2.4 mm Med-Tec thermoplastic mask for hand fixation and 5 applicators attached to each finger for dose delivery), the optimal skin dose on the phantom was obtained without the need for additional bolus to increase thickness of applicator. We acquired mean skin doses at different skin depths from various dose-volume parameters of no-bolus and 3 mm-added bolus plans. They were 125% and 110% (1 mm), 120% and 108% (2 mm), and 114% and 106% (3 mm), respectively. There was excellent agreement between MOSFET and TLD for ¹⁹²Ir HDR-BT within ±3% (mean 2.65%, SD = 2.05%). With no energy correction, MOSFET overestimated the Acuros BV surface doses by up to 7% in the phantom study and in the clinical case.

Conclusions

We demonstrated achievable HDR-BT for our first case of nail bed psoriasis. The end-to-end exercise was an efficient methodology to evaluate new feasibility for this technique. Real-time dose monitoring using MOSFET was an effective and reliable tool to ensure treatment quality and patient safety.

Dosimetric comparison of surface mould HDR brachytherapy with VMAT

INTRODUCTION

The aim of this study was to investigate the dosimetric differences between surface mould high-dose-rate (HDR) brachytherapy and external beam volumetric-modulated arc therapy (VMAT) for two treatment sites.

METHODS

Previously treated HDR brachytherapy surface mould scalp (n = 4) and lower leg (n = 3) treatments were retrospectively analysed. The VMAT plans were optimised using an additional 3-mm setup margin on the clinical target volume (CTV) of the previously treated HDR plans. The HDR plans were calculated and normalised using the TG-43 formalism and recalculated with Acuros BV (AC).

RESULTS

On average, the mean brain and normal tissue doses were reduced by 44.8% and 27.4% for scalp and lower leg VMAT cases, respectively, when compared to AC calculated HDR plans. For VMAT plans, the average dose to a 1-mm thick skin structure deep to the target volume was not any lower than that in AC HDR plans. On average, the CTV coverage was 13.8% and 9.6% lower for scalp cases with AC dose calculation than with TG-43 and 8.3% and 5.3% lower for lower leg cases if 0- or 1-cm backscatter material was applied above the catheters, respectively.

CONCLUSIONS

VMAT is a feasible treatment option in the case of extensive skin malignancies of the scalp and lower leg. Uncertainties related to delivered dose with HDR brachytherapy when using the TG-43 dose calculation model or possible air gaps between the mould and skin favour the use of VMAT. The potential soft tissue deformation needs to be considered if VMAT is used.

Evaluation of effective treatment depth in skin cancer treatments with electronic brachytherapy

PURPOSE

To evaluate changes in the percent depth dose (PDD) and effective depth of treatment due to force applied by the applicator during treatments of nonmelanoma skin cancer with the Xoft electronic brachytherapy system.

METHODS

To simulate compressible tissue, a 5-mm tissue-equivalent bolus was used. A soft x-ray ion chamber was used for output measurements, which were performed for all Xoft surface applicators with plastic endcaps in place. Output was first measured at 5 mm depth with minimal pressure from the applicator on the bolus and then repeated after applying uniform pressure on the applicator to calculate the change in PDD and effective treatment depth.

RESULTS

For the 10-mm cone, a moderate force of 5 N changed the PDD by more than 20%. The effect was also pronounced for the 20-mm cone, while minimal for the 35- and 50-mm cones. Even when only a moderate force was applied, the effective prescription depth changed by several millimeters, on the order of a typical prescription depth.

CONCLUSION

Based on the results of this simulation, excessive pressure applied on the skin by the applicator can drastically alter the PDD and effective treatment depth. The effect is most pronounced for the 10- and 20-mm cones, which tend to be used most frequently. Inappropriate applicator placement may therefore result in significant consequences such as excessive dose to the target, severe skin reaction, permanent discoloration, skin indentation, and poor overall cosmesis upon completion of treatment.

Efficacy of hypofractionated radiotherapy in patients with non-melanoma skin cancer: Results of a systematic review

Radiation oncologists are increasingly tasked with the management of elderly patients with non-melanoma skin cancer, unsuitable for surgical intervention due to inoperable lesions and/or poor performance status. In this cohort, hypofractionated radiotherapy, delivered either daily, alternative daily or once weekly is highly effective. A systematic literature search was conducted of PUBMED, MEDLINE and EMBASE databases using the algorithm ('radiotherapy' OR 'radiation therapy' OR 'brachytherapy') AND ('hypofraction' OR 'hypofractionated' OR 'hypofractionation') AND ('skin neoplasms' OR 'carcinoma' OR 'malignancy') AND ('skin' OR 'epidermis' OR 'epidermal' OR 'cutaneous'). Forty relevant publications (1983-2017) encompassing 12,337 irradiated lesions were retrieved. Studies documented a mean age of 71.73 years and male predilection (54.5%). Both external beam radiotherapy and brachytherapy were utilized. Tumour subtype was squamous cell carcinoma (23.5%), basal cell carcinoma (75.2%) or others (1.3%). Irradiated lesions were primary (or denovo) (92.6%), located on the head and neck (95.7%) and received definitive therapy (96.5%). Analysis demonstrated a mean weighted total radiotherapy dose (38.15 Gy), dose per fraction (7.95 Gy) and treatments per week (2.98). Despite significant heterogeneity in the study population, the radiotherapy delivered and follow-up, local recurrence rate (crude or Kaplan-Meier analysis) did not exceed 7.9% in all but three of the 36 publications providing these data. Twenty-nine publications documented local control exceeding 90%. There is a body of evidence documenting the efficacy of hypofractionated radiotherapy as an option that confers no obvious disadvantage in local control when compared to traditional more protracted radiotherapy schedules.

GEC-ESTRO ACROP recommendations in skin brachytherapy

PURPOSE

The aim of this publication is to compile available literature data and expert experience regarding skin brachytherapy (BT) in order to produce general recommendations on behalf of the GEC-ESTRO Group.

METHODS

We have done an exhaustive review of published articles to look for general recommendations.

RESULTS

Randomized controlled trials, systemic reviews and meta-analysis are lacking in literature and there is wide variety of prescription techniques successfully used across the radiotherapy centers. BT can be delivered as superficial application (also called contact BT or plesiotherapy) or as interstitial for tumours thicker than 5 mm within any surface, including very irregular. In selected cases, particularly in tumours located within curved surfaces, BT can be advantageous modality from dosimetric and planning point of view when compared to external beam radiotherapy. The general rule in skin BT is that the smaller the target volume, the highest dose per fraction and the shortest overall length of treatment can be used.

CONCLUSION

Skin cancer incidence is rising worldwide. BT offers an effective non-invasive or minimally invasive and relative short treatment that particularly appeals to elder and frail population.

Custom mold applicator high-dose-rate brachytherapy for nonmelanoma skin cancer-An analysis of 273 lesions

PURPOSE

Nonmelanoma skin cancer is the most commonly diagnosed malignancy in the United States. A modern version of surface brachytherapy, "topographic applicator brachytherapy" (TAB), can be used to treat early-stage nonmelanoma skin cancer (ES-NMSC). The purpose of this study was to evaluate the acute toxicity, chronic toxicity, and recurrence rates of patients with ES-NMSC treated with TAB.

METHODS AND MATERIALS

From 2010 to 2013, 172 patients with 273 ES-NMSC tumors were consecutively treated with TAB. A custom applicator was created using a thermoplastic mold with Harrison Anderson Mick applicators. Dose fractionation schemes included 40 Gy in eight fractions delivered twice per week or 48 Gy in 16 fractions delivered four times per week.

RESULTS

Of the 273 tumors treated, 23.8% were located on the nose, 54.2% were basal cell carcinoma, 76.2% were Stage I, 89.3% were treated definitively, 98.9% completed treatment, and 75.5% received 40 Gy in eight fractions. Median followup was 25.0 months (0.5-71.0 months). Maximum acute toxicity was G0, 0.4%; G1, 33.3%; G2, 48.7%; G3, 12.1%; and G4, 5.1%. Local recurrence was 4.8% at 25 months, with median time to recurrence being 9 months. There was no regional or distant metastasis documented during the followup. Chronic toxicities included erythema (4.4%), chronic ulceration (4.0%), telangiectasia (2.6%), and pigmentation changes (2.2%).

CONCLUSIONS

TAB was able to provide excellent local control (95.2%) with low rates of Grades 3 and 4 toxicities for treatment of ES-NMSC. TAB is a reasonable alternative to surgical resection when there is concern of poor cosmesis/wound healing.

Updates on the Management of Non-Melanoma Skin Cancer (NMSC)

Non-melanoma skin cancers (NMSCs) are the most common malignancy worldwide, of which 99% are basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) of skin. NMSCs are generally considered a curable diseases, yet they currently pose an increasing global healthcare problem due to rising incidence. This has led to a shift in emphasis on prevention of NMSCs with development of various skin cancer prevention programs worldwide. This article aims to summarize the most recent changes and advances made in NMSC management with a focus on prevention, screening, diagnosis, and staging.

The validity of Acuros BV and TG-43 for high-dose-rate brachytherapy superficial mold treatments

PURPOSE

The purpose of this work is to validate the Acuros BV dose calculation algorithm for high-dose-rate (HDR) brachytherapy superficial mold treatments in the absence of full scatter conditions and compare this with TG-43 dose calculations. We also investigate the impact of additional back scatter material (bolus) applied above surface molds to the dose distributions under the mold.

METHODS AND MATERIALS

The absorbed dose at various depths was compared for simulations performed using either TG-43 or Acuros BV dose calculations. Parameter variations included treatment area, thickness of the bolus, and surface shape (flat or spherical). Film measurements were carried out in a flat phantom.

RESULTS

Acuros BV calculations and film measurements agreed within 1.5% but were up to 15% lower than TG-43 dose calculations when no bolus was applied above the treatment catheters. The difference in dose at the prescription depth (1 cm below the central catheter) increased with increasing treatment area: 3.3% difference for a 3 × 3.5 cm² source loading area, 7.4% for 8 × 9 cm², and 13.4% for 18 × 19 cm². The dose overestimation of the TG-43 model decreased when bolus was added above the treatment catheters.

CONCLUSIONS

The TG-43 dosimetry formalism cannot model surface mold treatments in the absence of full scatter conditions within 5% for loading areas larger than approximately 5 × 5 cm². The TG-43 model results in an overestimation of the delivered dose, which increases with treatment area. This confirms the need for model-based dose calculation algorithms as discussed in TG-186.

Comparison of electronic brachytherapy and Mohs micrographic surgery for the treatment of early-stage non-melanoma skin cancer: a matched pair cohort study

Purpose

High-dose-rate electronic brachytherapy (EBT) provides a non-surgical treatment option for non-melanoma skin cancer (NMSC). This matched-pair cohort study compared the outcomes of treatment with EBT to those of Mohs micrographic surgery (MMS) in patients with NMSC.

Material and methods

At four treatment centers, patients treated with EBT were case matched to patients treated with MMS based on retrospectively-collected patient age, lesion size, location and type, and year of treatment. Follow-up data were prospectively collected and included local recurrence, toxicities, cosmesis, and patient-reported outcomes.

Results

The 369 patients (188 in the EBT treatment group and 181 in the MMS treatment group) had 416 lesions (208 in the EBT group and 208 in the MMS group), including 226 basal cell carcinomas (BCC) and 190 squamous cell carcinomas (SCC). Most patients were Caucasian (98.9% and 99.5%) and male (65.4% and 66.3%) of median age 80.7 (range: 61-98) (EBT) and 76.8 (range: 51-98) years (MMS). Most lesions were size > 1 cm and ≤ 2 cm, and located on the head. At mean 3.4 years post-treatment, 99.5% of EBT, and 100.0% of MMS-treated lesions were free of recurrence (p = ns). One recurrence was noted in the EBT group. Physicians rated cosmesis as “excellent” or “good” in 97.6% of EBT-treated lesions, and 95.7% of MMS-treated lesions.

Conclusions

This matched-pair cohort study supports the use of EBT as an effective non-surgical treatment option for NMSC with equivalent recurrence rates and cosmetic outcomes to MMS in appropriately-selected patients with early stage NMSC at extended follow-up.