Surface dose and acute skin reactions in external beam breast radiotherapy

Dosimetric effect of silicone-based gel on skin surface during volumetric modulated arc therapy for breast cancer

PURPOSE

This study aims to quantify and compare the dosimetric effects of varying thicknesses of StrataXRT, a silicone-based gel, and other topical agents on the skin surface during volumetric modulated arc therapy (VMAT) for breast cancer.

METHODS

A VMAT plan was created for breast cancer treatment using a female RANDO phantom with a prescription dose of 50 Gy in 25 fractions. The planning target volume (PTV) encompassed the left breast and the regional lymph nodes. Irradiation was performed using a 6 MV photon beam. Three topical agents (StrataXRT, Hirudoid Soft Ointment, and RINDERON-Vs Ointment) having eight thicknesses (0.0-1.5 mm) were evaluated. Dosimetry was conducted using Gafchromic EBT4 films at three anatomical locations-subclavicular, medial, and lateral aspects of the left breast.

RESULTS

Mean dose enhancement ratios (DERs) of 102%-116% were observed in VMAT for topical agent thicknesses of 0.1-0.5 mm, increasing to 116%-126% at 1.0 and 1.5 mm. Among the evaluated agents, StrataXRT consistently exhibited the lowest DER, with a statistically significant difference (p < 0.05).

CONCLUSIONS

This study demonstrated that StrataXRT exhibited the lowest DER among the evaluated topical agents in VMAT for breast cancer. Thicknesses exceeding 0.5 mm potentially exceeded the threshold dose for acute skin reactions.

Visual Dose Monitoring for Whole Breast Radiation Therapy Treatments via Combined Cherenkov Imaging and Scintillation Dosimetry

PURPOSE

This study investigates scintillation dosimetry coupled with Cherenkov imaging for in vivo dose monitoring during whole breast radiation therapy (WBRT). Given recent observations of excess dose to the contralateral breast (CB), in vivo dosimetry (IVD) could help ensure accurate dose delivery and decrease risks of secondary cancer. This work presents a rapid, streamlined alternative to traditional IVD, providing direct visualization of measurement location relative to the treatment field on the patient.

METHODS AND MATERIALS

Ten WBRT patients consented under an institutional review board-approved protocol were monitored with scintillation dosimetry and always-on Cherenkov imaging, on both their treated and CB for 1 to 3 fractions. Scintillator dosimeters, small plastic discs 1 mm thick and 15 mm in diameter, were calibrated against optically stimulated luminescent dosimeters (OSLDs) to generate an integral output-to-dose conversion, where integral output is measured in postprocessing through a custom fitting algorithm. The discs have been extensively characterized in a previous study for various treatment conditions including beam energy and treatment geometry.

RESULTS

A total of 44 dosimetry measurements were evaluated, including 22 treated breast and 22 CB measurements. After integral output-to-dose calibration, in vivo scintillator dosimeters exhibited high linearity (R2 = 0.99) with paired OSLD readings across all patients. The difference between scintillation and OSLD dose measurements averaged 2.8% of the prescribed dose, or an absolute dose difference of approximately 7 cGy.

CONCLUSIONS

Integration of scintillation dosimetry with Cherenkov imaging offers an accurate, rapid alternative for in vivo dose verification in WBRT, circumventing the limitations of conventional point dosimeters. The additional benefit of visualizing measurement locations relative to the treatment field provides users an enhanced understanding of results and allows for detection of high dose gradients. Future work will explore the applicability of this technique across a broader range of radiation therapy treatments, aiming to streamline IVD practices.

Dosimetric Correlation of Acute Radiation Dermatitis in Patients With Breast Cancer Undergoing Hypofractionated Proton Beam Therapy Using Pencil Beam Scanning

PURPOSE

Pencil-beam scanning (PBS) is a modern delivery technique used in proton beam therapy (PBT) to reduce normal tissue reactions. No dosimetric correlation between dermatitis and PBS has been reported for breast cancer. The current study aimed to investigate the factors associated with grade 2 or higher dermatitis in patients with breast cancer undergoing PBT using PBS.

METHODS

The medical data of 42 patients with breast cancer who underwent adjuvant radiotherapy between December 2019 and September 2023 were reviewed. All patients received hypofractionated radiotherapy (HFRT), either 26 Gy (relative biological effectiveness [RBE])/five fractions or 40.05 or 43.5 Gy (RBE)/15 fractions, for the whole breast/chest wall with or without nodal irradiation. The duration of acute radiation dermatitis was defined as within 90 days from the start of radiotherapy. The Kaplan-Meier method and Cox proportional hazards model were used for univariate and multivariate analyses of the actuarial rates of grade 2-3 dermatitis.

RESULTS

Twenty-two (52.4%) and 20 (47.6%) patients were diagnosed with grade 1 and 2 dermatitis, respectively. Multivariate analysis revealed a clinical target volume (CTV) ≥ of 320 cc (p = 0.035) and a skin dose of D10cc ≥ 38.3 Gy (RBE) (p = 0.009) as independent factors of grade 2 dermatitis. The 10-week cumulative grade 2 dermatitis rates were 88.2%, 39.4%, and 8.3% (p < 0.001) for patients with both high, either high, and neither high CTV and D10cc, respectively.

CONCLUSION

To the best of our knowledge, this is the first study on dosimetric correlations for dermatitis in patients with breast cancer who underwent hypofractionated PBT using PBS. In the era of HFRT, skin dose modulation using PBS may reduce the incidence of dermatitis.

Effectiveness of glutamine for the treatment of radiodermatitis in cancer patients: a meta-analysis of randomized controlled trials

BACKGROUND

After receiving radiation therapy, 60%-95% of patients with cancer develop radiodermatitis, which causes pain, wound infection, and poor quality of life. Glutamine is a popular nutritional supplement for patients with cancer. Several studies examined the usefulness of glutamine for reducing radiodermatitis. However, there is still no consolidated evidence for clinical use.

METHODS

We searched PubMed, Embase, Cochrane Library, CINAHL PLUS, and the China Knowledge Resource Integrated Database for the relevant literature published up to March 2023, without language restrictions. Two reviewers screened, filtered, and appraised these articles independently, and their data were pooled using a random-effects model.

RESULTS

Five randomized controlled trials (RCTs) with 218 participants were analyzed. The incidence of radiodermatitis in the glutamine group (89/110) was significantly lower than in the placebo group (99/108; risk ratio [RR], 0.90; 95% CI, 0.81-1.00; p = 0.05; I2 = 7%). The incidence of moderate to severe radiodermatitis was significantly lower in the glutamine group than in the placebo group (RR, 0.49; 95% CI, 0.32-0.76; p = 0.001; I2 = 52%). Moreover, subgroup analysis demonstrated heterogeneity (I2 = 52%) for moderate to severe radiodermatitis, the risk of which might be significantly reduced by a glutamine dose of 20-30 g/day (RR, 0.60; 95% CI, 0.41-0.87; I2 = 0%).

CONCLUSION

The meta-analysis indicate that glutamine might lead to a lower incidence of radiodermatitis, and that a glutamine dose of 20-30 g/day might decrease the incidence of moderate to severe dermatitis. Thus, the serious impact of radiodermatitis on treatment follow-up makes the clinical use of glutamine even more important. PROSPERO number: CRD42021254394.

Toward a Skin Dose-Area Metric Predictive of Moist Desquamation Using In Vivo Skin Dosimetry and Skin Assessments

Purpose

Moist desquamation (MD) is a concerning acute side effect of radiation therapy for breast cancer, often seen in skin folds for patients having large or pendulous breasts. In vivo skin dosimetry, clinical assessments, and patient-reported skin reactions were used to determine a relationship between dose-area metrics and the development of MD, to lend insight into skin tolerances and possibly guide future treatment planning dose constraints.

Methods and Materials

Skin dose was measured using GafChromic film on the inner surface of an early prototype carbon-fiber accessory for breast support to remove the inframammary fold in 20 patients at high risk of developing MD undergoing adjuvant whole breast radiation therapy. Prescribed doses were 42.5 Gray (Gy) in 16 fractions or 50 Gy in 25 fractions using 6 to 15 MV x-rays. To account for fraction size differences, analysis was performed using the equivalent dose in 2 Gy fractions using α/β = 11 (EQD211). MD was assessed out to 2 weeks post radiation therapy by trained therapists and by a patient-reported outcome questionnaire.

Results

Statistically significant differences in areas receiving 30 to 48 Gy (EQD211) were observed between patients who did and did not develop MD in the inframammary area. Patients receiving EQD211 maximum dose ≤ 46 Gy and ≥ 38 Gy to ≤ 50 cm2 of their breast skin did not develop MD.

Conclusions

The findings of this study offer insight into the relationship between skin toxicity and areas of skin irradiated to doses up to 50 Gy. Potential skin dose constraints to test in future studies to prevent MD are suggested.

Near-Surface Dose Correlates With Moist Desquamation and Unplanned Reconstructive Surgery in Patients With Implant-Based Reconstruction Receiving Postmastectomy Radiation Therapy

Purpose

Postmastectomy radiation therapy (PMRT) reduces disease recurrence in appropriately selected patients but may compromise implant-based reconstruction. We investigated whether near-surface dose correlates with radiation-related toxic effects in these patients.

Methods and Materials

Patients receiving PMRT at a single institution from 2016 to 2019 were retrospectively reviewed. Patient demographics and treatment information were collected. Three near-surface structures were retrospectively generated, bound by the chest wall tangent beam as well as the skin surface and the skin-3 mm contour (SR3), skin surface and skin-5 mm contour (SR5), or skin-5 and skin-10 mm contours. Dosimetric analysis of these near-surface contours was performed in 2 Gy intervals. Univariate and multivariate analyses were used to identify predictors of moist desquamation, grade 2+ chest wall pain, use of opiate pain medication, unplanned reconstructive surgery, and implant failure. Logistic regression for each outcome and near-surface contour was performed for receiver-operator area under the curve (AUC) analysis and the Youden J Statistic was used to determine the optimal threshold for each dosimetric parameter.

Results

Of 126 patients reviewed, 109 met the study's eligibility criteria. Median follow-up was 2.3 years. Twenty-five patients (23%) underwent unplanned reconstructive surgery, and 10 (9.2%) experienced implant failure. Among clinical variables, low body mass index and history of smoking predicted unplanned surgery on univariate and multivariate analyses, and moist desquamation predicted grade 2+ chest wall pain. The top dosimetric parameters by AUC for moist desquamation, grade 2+ chest wall pain, use of opiates, unplanned reconstructive surgery, and implant failure were SR5 D10 cc (AUC = 0.701, optimal threshold 57.8 Gy, P < .001), SR3 D10 cc (AUC = 0.600, optimal threshold 56.8 Gy, P = .079), SR5 D10 cc (AUC = 0.642, optimal threshold 57.3 Gy, P = .041), SR3 V44 Gy (AUC = 0.711, optimal threshold 81%, P = .001), and SR3 V44 Gy (AUC = 0.688, optimal threshold 82%, P = .052), respectively.

Conclusions

Near-surface dose correlates with moist desquamation and unplanned reconstructive surgery after PMRT. Further evaluation of prospective optimization of dosimetric parameters related to SR3 and SR5 should be considered.

Estimation of the Surface Dose in Breast Irradiation by the Beam Incident Angle and the 1 cm Depth Dose

To develop a method of estimating surface dose in whole breast irradiation, we used an anthropomorphic phantom with accessories for the simulation of different breast sizes. The surface points, which are measured by TLDs, are set along with two main directions, superior-inferior and medial-lateral. The incident angle between the photon beam and the surface and the doses at 1 cm beneath the surface at every point are assessed by a computerized treatment planning system (cTPS). With the prescription dose of 200 cGy, the average surface doses under tangential irradiation are 97.73 (±14.96) cGy, 99.90 (±10.73) cGy, and 105.26 (±9.21) cGy for large, medium, and small breast volumes, respectively. The surface dose increased in the model of small breast volume without significance (p = 0.39). The linear analysis between surface dose and the incident angle is y = 0.5258x + 69.648, R² = 0.7131 (x: incident angle and y: surface dose). We develop the percentage of skin surface dose with reference to a depth of 1 cm (PSDR1cm) to normalize the inhomogeneous dose. The relationship between incident angle and PSDR1cm is y = 0.1894x + 36.021, R² = 0.6536 (x: incident angle and y: PSDR1cm) by linear analysis. In conclusion, the surface dose in whole breast irradiation could be estimated from this linear relationship between PSDR1cm and incident angle in daily clinical practice by cTPS. Further in vivo data should be studied to verify this formula.

Out-of-field scattering from the Integral Quality Monitor® in megavolt photon beams

PURPOSE

To investigate out-of-field scattered doses from the Integral Quality Monitor (IQM) transmission detector in megavoltage photon beams.

MATERIALS AND METHODS

We measured out-of-field point doses for 20 × 20 cm² 6-15 MV photon beams using 10 × 2 cm² Gafchromic EBT3 film strips placed across the surfaces of 5-cm thick water-equivalent RW3 slabs. The films were placed at 10 cm intervals from the central axis (CAX) of each beam, up to 1.0 m away on opposite sides of the CAX. The measurements were conducted at 80 cm and 100 cm source-to-surface distances (SSD) without the IQM, and were repeated with the IQM in the paths of the beams. Measurements were also performed at 90 cm SSD for 20 × 20 and 30 × 30 cm² 15 MV fields. Surface dose profiles were then constructed from the measurements for each beam setup with and without the IQM to examine the differences in scattered dose off-axis. The dose profile for each beam setup was normalised to dose maximum measured on the CAX.

RESULTS

Overall, surface dose profiles acquired with the IQM in the paths of the beams were higher than the corresponding profiles without the IQM. The out-of-field dose increased with increase in photon energy, field size, and shorter SSDs, and decreased with off-axis distance. At 80 cm SSD for the 20 × 20 cm² field, the IQM-induced surface dose ranged from -0.6% ÷ 1.9%, -0.3% ÷ 3.0%, and 0.3% ÷ 6.8% for 6, 10, and 15 MV beams, respectively.

CONCLUSION

The higher surface dose profiles measured with the IQM attached to the linac compared to the profiles without the IQM indicates that the device is acting as an additional source of scattered radiation.