Optimization of skin dose using in-vivo MOSFET dose measurements in bolus/non-bolus fraction ratio: A VMAT and a 3DCRT study

Individualized 3D-printed bolus promotes precise postmastectomy radiotherapy in patients receiving breast reconstruction

Purpose

To evaluate the efficacy and safety of 3D-printed tissue compensations in breast cancer patients receiving breast reconstruction and postmastectomy radiotherapy (PMRT).

Methods and materials

We enrolled patients with breast cancer receiving breast reconstruction and PMRT. The dose distribution of target and skin, conformability, and dose limit of organs at risk (OARs) were collected to evaluate the efficacy of the 3D-printed bolus. Radiation Therapy Oncology Group (RTOG) radiation injury classification was used to evaluated the skin toxicities.

Results

A total of 30 patients diagnosed between October 2019 to July 2021 were included for analysis. Among all the patients, the 3D-printed bolus could ensure the dose coverage of planning target volume (PTV) [homogeneity index (HI) 0.12 (range: 0.08-0.18)], and the mean doses of D99%, D98%, D95%, D50%, D2% and Dmean were 4606.29cGy, 4797.04cGy, 4943.32cGy, 5216.07cGy, 5236.10cGy, 5440.28cGy and 5462.10cGy, respectively. The bolus demonstrated an excellent conformability, and the mean air gaps between the bolus and the chest wall in five quadrants were 0.04cm, 0.18cm, 0.04cm, 0.04cm and 0.07cm, respectively. In addition, the bolus had acceptable dosage limit of OARs [ipsilateral lung: Dmean 1198.68 cGy, V5 46.10%, V20 21.66%, V30 16.31%); heart: Dmean 395.40 cGy, V30 1.02%, V40 0.22%; spinal cord planning risk volume (PRV): Dmax 1634 cGy] and skin toxicity (grade 1, 76.0%; grade 2, 21.0%; grade 3, 3.3%).

Conclusion

The 3D-printed bolus offers advantages in terms of dose uniformity and controllable skin toxicities in patients receiving breast reconstruction and PMRT. Further research is needed to comprehensively evaluate the effectiveness of the 3Dprinted bolus in this patient subset.

A novel approach to predict acute radiation dermatitis in patients with head and neck cancer using a model based on Bayesian probability

PURPOSE

In this study, we aimed to establish a method for predicting the probability of each acute radiation dermatitis (ARD) grade during the head and neck Volumetric Modulated Arc Therapy (VMAT) radiotherapy planning phase based on Bayesian probability.

METHODS

The skin dose volume >50 Gy (V50), calculated using the treatment planning system, was used as a factor related to skin toxicity. The empirical distribution of each ARD grade relative to V50 was obtained from the ARD grades of 119 patients (55, 50, and 14 patients with G1, G2, and G3, respectively) determined by head and neck cancer specialists. Using Bayes' theorem, the Bayesian probabilities of G1, G2, and G3 for each value of V50 were calculated with an empirical distribution. Conversely, V50 was obtained based on the Bayesian probabilities of G1, G2, and G3.

RESULTS

The empirical distribution for each graded patient group demonstrated a normal distribution. The method predicted ARD grades with 92.4 % accuracy and provided a V50 value for each grade. For example, using the graph, we could predict that V50 should be ≤24.5 cm3 to achieve G1 with 70 % probability.

CONCLUSIONS

The Bayesian probability-based ARD prediction method could predict the ARD grade at the treatment planning stage using limited patient diagnostic data that demonstrated a normal distribution. If the probability of an ARD grade is high, skin care can be initiated in advance. Furthermore, the V50 value during treatment planning can provide radiation oncologists with data for strategies to reduce ARD.

Effect of 0.35 T and 1.5 T magnetic fields on superficial dose in MR-guided radiotherapy of laryngeal cancer

Background

Treatment of head and neck cancer on linear accelerators with on-board magnetic resonance imaging (MR-linac) might be beneficial to reduce side effects and increase accuracy. For many head and neck cancer patients, dose coverage of the often superficially located planning target volumes (PTVs) is required. This study examines the impact of the electron return effect (ERE) on the surface dose in MR-guided radiotherapy (MRgRT) compared to conventional radiotherapy.

Materials and methods

For this bicentric dosimetric study, 14 cases of laryngeal carcinomas with PTVs reaching up to the skin surface were included. For each patient, five different plans were compared, two VMAT plans (with and without a 5 mm bolus) and three IMRT MRgRT plans (0.35 T, 1.5 T and 0 T, each without bolus). Dose distributions were also validated with film measurements.

Results

A similar coverage on the most superficial 3-5 mm of the PTV was achieved in the VMAT plans with bolus and the MRgRT plans for both 0.35 T and 1.5 T. However, coverage on this region was usually not achieved for VMAT without bolus and the 0 T plans. The film measurements on phantoms confirmed the results with the relative error never exceeding the calculated differences between the plans.

Conclusion

The present study could demonstrate that the ERE for both commercially available MR-linac variants provides sufficient coverage of the superficial tissue layers in MRgRT-plans for laryngeal carcinoma.

Colorectal liver metastases patients prognostic assessment: prospects and limits of radiomics and radiogenomics

In this narrative review, we reported un up-to-date on the role of radiomics to assess prognostic features, which can impact on the liver metastases patient treatment choice. In the liver metastases patients, the possibility to assess mutational status (RAS or MSI), the tumor growth pattern and the histological subtype (NOS or mucinous) allows a better treatment selection to avoid unnecessary therapies. However, today, the detection of these features require an invasive approach. Recently, radiomics analysis application has improved rapidly, with a consequent growing interest in the oncological field. Radiomics analysis allows the textural characteristics assessment, which are correlated to biological data. This approach is captivating since it should allow to extract biological data from the radiological images, without invasive approach, so that to reduce costs and time, avoiding any risk for the patients. Several studies showed the ability of Radiomics to identify mutational status, tumor growth pattern and histological type in colorectal liver metastases. Although, radiomics analysis in a non-invasive and repeatable way, however features as the poor standardization and generalization of clinical studies results limit the translation of this analysis into clinical practice. Clear limits are data-quality control, reproducibility, repeatability, generalizability of results, and issues related to model overfitting.

Clinical Application of a Customized 3D-Printed Bolus in Radiation Therapy for Distal Extremities

In radiation therapy (RT) for skin cancer, tissue-equivalent substances called boluses are widely used to ensure the delivery of an adequate dose to the skin surface and to provide a radioprotective effect for normal tissue. The aim of this study was to develop a new type of three-dimensional (3D) bolus for RT involving body parts with irregular geometries and to evaluate its clinical feasibility. Two 3D-printed boluses were designed for two patients with squamous cell carcinoma (SCC) of their distal extremities based on computed tomography (CT) images and printed with polylactic acid (PLA). The clinical feasibility of the boluses was evaluated by measuring the in vivo skin dose at the tumor site with optically stimulated luminescence detectors (OSLDs) and comparing the results with the prescribed and calculated doses from the Eclipse treatment planning system (TPS). The average measured dose distribution for the two patients was 94.75% of the prescribed dose and 98.8% of the calculated dose. In addition, the average measured dose during repeated treatments was 189.5 ± 3.7 cGy, thus demonstrating the excellent reproducibility of the proposed approach. Overall, the customized 3D-printed boluses for the RT of distal extremities accurately delivered doses to skin tumors with improved reproducibility.

Paraffin gauze bolus as tissue compensator in photon irradiation for mycosis fungoides – regarding a case study

Introduction:

Total skin electron beam therapy is a treatment option in patients with mycosis fungoides (MF) affecting a significant amount of the body surface. For patients with involvement of soles and interdigital folds, however, this approach is ineffective, requiring alternatives such as localised radiotherapy (RT). Although electron beams are well suited for superficial lesions, on irregular surfaces it provides inadequate tumour coverage and excess dose variance, requiring photon irradiation with tissue compensation.

Methods:

We present the case of a patient with extensive cutaneous MF with skin lesions spread over both lower limbs and treated on these affected areas with photon beam RT. Long sheets of paraffin gauze dressings were used to create a 0·5-cm-thick bolus. The patient received a single fraction of 8 Gy. In vivo dosimetry using Gafchromic films was performed.

Results:

After 3 months, a complete response was achieved. In this case, paraffin gauze bolus proved to be an inexpensive, convenient, effective and flexible method for irregular superficial cancer irradiations.

Conclusion:

Paraffin gauze bolus is a suitable option for irregular contours.

Contralateral breast radiation doses in breast cancer patients treated with helical tomotherapy

We aimed to evaluate contralateral breast doses calculated with a Treatment Planning System (TPS) and verified with metal oxide semiconductor field effect transistor (MOSFET) detectors in patients with early-stage breast cancer (BC) who received helical tomotherapy (HT) after breast-conserving surgery. The dosimetric data of 30 patients (15 left-sided and 15 right-sided) with BC treated with 50.4 Gy to the whole breast and 64.4 Gy to the tumor bed in 28 fractions were analyzed. TPS doses were calculated and MOSFET doses were measured in the contralateral breast (CB) at cranial, caudal, and midpoint and 2 cm lateral to the central point. TPS and MOSFET doses were compared in the entire cohort as well as by tumor location (inner vs outer quadrant) and planning target volume of the breast (<1200 cc vs ≥1200 cc). The average doses at superior, inferior, central, and lateral points calculated with the TPS were 0.26 ± 0.15 cGy, 0.21 ± 0.09 cGy, 0.65 ± 0.14 cGy, and 0.50 ± 0.11 cGy, respectively, and were 0.37 ± 0.16 cGy, 0.34 ± 0.12 cGy, 0.60 ± 0.18 cGy, and 0.34 ± 0.15 cGy, respectively in MOSFET readings. Except for the central point, TPS-calculated doses and MOSFET readings were differed. The doses to the CB in patients with inner and outer quadrant tumors were not significantly different. In patients with large breasts, MOSFET doses were higher at superior and lateral points than TPS doses, but TPS doses were greater at inferior points. MOSFET readings were higher than TPS calculated doses in patients with inner or outer quadrant tumors in small or large breast volumes. The dose calculated by the TPS and that measured by MOSFET differed by a very small amount. The maximum dose to the CB administered at the midpoint was 1.8 Gy, as calculated using the TPS and confirmed using MOSFET detectors, in patients with early-stage BC undergoing breast-only radiotherapy with HT.

Application of thermoplastic elastomer (TPE) bolus in postmastectomy radiotherapy

PURPOSE

To assess the planned dose, in vivo dosimetry, acute skin toxicity, pain, and distress using Thermoplastic Elastomer (TPE) bolus for postmastectomy radiotherapy (PMRT).

MATERIAL AND METHODS

Thirty-two PMRT patients with TPE bolus (17 patients for 25 fractions, 15 patients for the first 20 fractions) were selected for the study. The acute skin toxicity, pain, and psychological distress were assessed from the first treatment week to the fourth week after the end of treatment. At the first treatment, the MOSFET was used in vivo dosimetry measurement.

RESULTS

In vivo dosimetry with the bolus, the dose deviation ranged from -6.22% to -1.56% for 5 points. The presence of grade 1 and 2 skin toxicity reached its peak (70.0% and 13.3%) in the sixth week. Two patients (6.6%) with 25 fractions bolus experienced moist desquamation in the fifth and seventh week, with pain score 2 and 3, and interruptions of 3 and 5 days, respectively. The incidence of pain score 1, 2, and 3 peaked in the fifth (33.3%), fourth (33.3%), and seventh (10.0%) week. No patients experienced grade 3 skin toxicity and severe pain. One patient had significant anxiety, and two patients had significant depression.

CONCLUSION

The TPE bolus can accurately fit skin and improve the surface dose to more than 90%. Twenty fractions with TPE bolus had similar skin toxicity and pain to those without bolus and did not increase patients' distress and clinical workload, compared with the literature's data, which is an alternative to the 3D printing bolus for PMRT.

Experimental determination of breast skin dose using volumetric modulated arc therapy and field-in-field treatment techniques

Introduction:

The use of volumetric modulated arc therapy (VMAT) on the breast has several dosimetric advantages but its impact on skin dose should be evaluated and compared to well-established treatment techniques using tangential fields. The aim of this work is to contrast the skin dose for VMAT and field-in-field (FIF) and to estimate the magnitude of the skin dose involved.

Method:

The skin dose was measured, without build-up, using thermoluminescent dosimeter (TLD) and optically stimulated luminescence dosimeter (OSLD) in breast radiotherapy by an in-house anthropomorphic phantom. Two different treatment techniques were used: FIF and VMAT, based on the planning strategy proposed by Nicolini et al. The dose levels were 4300 cGy, 4600 cGy and 5600 cGy in 20 fractions. In vivo dosimetry with TLD for VMAT was performed for different breast sizes in the same locations as phantom measurements.

Results:

The ipsilateral phantom breast skin dose using both treatment techniques was equivalent. TLD measured doses by the VMAT technique were up to 5% higher than OSLD, although they agree if we consider the geometry uncertainty of the TLD. In accordance with in vivo dosimetry, the mean dose of the ipsilateral breast skin was 62 ± 6% (51%, 75%) relative to the prescribed dose, regardless of the breast size for the volumes considered with this small population (n = 9) as shown by Mann–Whitney U-test (Z = 1·9, 95% confidence). The uncertainty expected in this region due to geometry (volume) changes is up to 9% higher for volumes from 225·9 cc to 968·8 cc. According to the treatment techniques and in vivo dosimetry, the contralateral breast skin dose was 1·0% in FIF and 2·5% in VMAT concerning the prescribed dose.

Conclusion:

There is no difference in skin dosimetry between VMAT and FIF techniques on the ipsilateral breast. It provides useful support for the use of VMAT as a planning technique for breast irradiation. The work describes the importance of quantifying potential differences in skin dosimetry.

The Clinical Application of 3D-Printed Boluses in Superficial Tumor Radiotherapy

During the procedure of radiotherapy for superficial tumors, the key to treatment is to ensure that the skin surface receives an adequate radiation dose. However, due to the presence of the built-up effect of high-energy rays, equivalent tissue compensators (boluses) with appropriate thickness should be placed on the skin surface to increase the target radiation dose. Traditional boluses do not usually fit the skin perfectly. Wet gauze is variable in thickness day to day which results in air gaps between the skin and the bolus. These unwanted but avoidable air gaps lead to a decrease of the radiation dose in the target area and can have a poor effect on the outcome. Three-dimensional (3D) printing, a new rising technology named “additive manufacturing” (AM), could create physical models with specific shapes from digital information by using special materials. It has been favored in many fields because of its advantages, including less waste, low-cost, and individualized design. It is not an exception in the field of radiotherapy, personalized boluses made through 3D printing technology also make up for a number of shortcomings of the traditional commercial bolus. Therefore, an increasing number of researchers have tried to use 3D-printed boluses for clinical applications rather than commercial boluses. Here, we review the 3D-printed bolus’s material selection and production process, its clinical applications, and potential radioactive dermatitis. Finally, we discuss some of the challenges that still need to be addressed with the 3D-printed boluses.

Evaluation of monoxide film-based dosimeters for surface dose detection in electron therapy

Generally, electron therapy is applied to tumors on or close to the skin surface. However, this causes a variety of skin-related side effects. To alleviate the risk of these side effects, clinical treatment uses skin dosimeters to verify the therapeutic dose. However, dosimeters suffer from poor accuracy, because their attachment sites are approximated with the help of naked eyes. Therefore, a dosimeter based on a flexible material that can adjust to the contours of the human body is required. In this study, the reproducibility, linearity, dose-rate dependence, and percentage depth ionization (PDI) of PbO and HgO film-based dosimeters are evaluated to explore their potential as large-scale flexible dosimeters. The results demonstrate that both dosimeters deliver impressive reproducibility (within 1.5%) and linearity (≥ 0.9990). The relative standard deviations of the dose-rate dependence of the PbO and HgO dosimeters were 0.94% and 1.16% at 6 MeV, respectively, and 1.08% and 1.25% at 9 MeV, respectively, with the PbO dosimeter outperforming the 1.1% of existing diodes. The PDI analysis of the PbO and HgO dosimeters returned values of 0.014 cm (-0.074 cm) and 0.051 cm (-0.016 cm), respectively at 6 MeV (9 MeV) compared to the thimble chamber and R50. Therefore, the maximum error of each dosimeter is within the allowable range of 0.1 cm. In short, the analysis reveals that the PbO dosimeter delivers a superior performance relative to its HgO counterpart and has strong potential for use as a surface dosimeter. Thus, flexible monoxide materials have the necessary qualities to be used for dosimeters that meet the requisite quality assurance standards and can satisfy a variety of radiation-related applications as flexible functional materials.

Development of a transparent and flexible patient-specific bolus for total scalp irradiation

A commercially available flat bolus (commercial bolus) would not fully fit the irregular surfaces of the scalp. We developed a transparent and flexible material with good fitting properties, analyzed its physical characteristics, and evaluated the clinical feasibility of the bolus fabricated using a three-dimensional (3D) printer (3D bolus). To evaluate the physical characteristics of the new material, treatment plans with virtual, 3D, and commercial boluses were created for water-equivalent phantoms using a radiation treatment planning system (RTPS). Using a head phantom and the dose volume histogram calculated with RTPS, dose distributions for total scalp irradiation were compared between the three treatment plans. To evaluate the clinical feasibility, the fitness and reproducibility of the 3D bolus were compared with the head phantom and clinical cases using dice similarity coefficient (DSC) measurements. A good agreement was observed between the percentage depth dose (PDD) curves for the virtual, 3D, and commercial boluses. The homogeneity indexes of the planning target volume (PTV) for the 3D and commercial boluses were 0.083 and 0.153, respectively, proving that the former achieved a better dose uniformity of PTV than the latter. Good fitness and reproducibility with the 3D bolus were observed in both the head phantom and two clinical cases, with mean DSC values of 0.854, 0.829, and 0.843, respectively. These results successfully demonstrated and verified the utility of the 3D bolus for total scalp irradiation.

Hypofractionated Whole Breast Irradiation and Simultaneous Integrated Boost in Large-breasted Patients: Long-term Toxicity and Cosmesis

INTRODUCTION

The purpose of this study was to evaluate the impact of breast size on long-term toxicity and cosmesis in patients with breast cancer treated with hypofractionated simultaneous integrated boost (SIB) using volumetric modulated arc therapy (VMAT).

PATIENTS AND METHODS

Patients with early stage breast cancer were treated with 3-week hypofractionated SIB-VMAT to the whole breast (40.5 Gy) and tumor bed (48 Gy). Two cohorts were identified: small/medium- (< 1000 cm³) and large- (> 1000 cm³) breasted patients. Acute and late (at 2 and 5 years) skin toxicity and cosmetic data were analyzed. Univariate and multivariate analysis evaluated associations between toxicity and dosimetric/anatomical variables.

RESULTS

From August 2010 to March 2017, a total of 1160 patients were treated; 831 had at least 2 years of follow-up and were analyzed. Treated skin area (TSA) receiving at least 20 Gy > 400 cm² and V_{105% of Boost} > 5 cm³ were significant predictors for acute skin toxicity. Multivariate analysis at 2 years was significant for boost volume > 70 cm³, TSA > 400 cm², and breast size > 1500 cm³. At 5 year analysis (352 patients), none of the analyzed variables was significant. For cosmetic outcome, only the breast size (> 1000 cm³) and the boost size > 70 cm³ at 2 and 5 years, respectively, confirmed significance.

CONCLUSIONS

The TSA > 400 cm² resulted as a significant predictor of both acute and late skin toxicity at 2 years; however, at 5 years, no breast size or dosimetric parameter suggested indications for increased toxicity. A worse cosmetic outcome was recorded at the 2-year follow up for large breasts, but was not confirmed at the 5-year follow-up. These long-term data suggest that hypofractionated SIB-VMAT is a viable modality also in large-breasted patients.