Outcomes in Patients Treated with Post-mastectomy Chest Wall Radiotherapy without the Routine Use of Bolus

American Radium Society Appropriate Use Criteria Postmastectomy Radiation Therapy: Executive Summary of Clinical Topics

PURPOSE

To conduct an appropriate use criteria expert panel update on clinical topics relevant to current clinical practice regarding postmastectomy radiation therapy (PMRT).

METHODS AND MATERIALS

An analysis of the medical literature from peer-reviewed journals was conducted from May 4, 2010 to May 4, 2022 using the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines to search the PubMed database to retrieve a comprehensive set of relevant articles. A well-established methodology (modified Delphi) was used by the expert panel to rate the appropriate use of procedures.

RESULTS

Evidence for key questions in PMRT regarding benefit in special populations and technical considerations for delivery was examined and described. Risk factors for local-regional recurrence in patients with intermediate-risk disease that indicate benefit of PMRT include molecular subtype, age, clinical stage, and pathologic response to neoadjuvant chemotherapy. Use of hypofractionated radiation in PMRT has been examined in several recent randomized trials and is under investigation for patients with breast reconstruction. The use of bolus varies significantly by practice region and has limited evidence for routine use. Adverse effects occurred with both PMRT preimplant and postimplant exchange in 2-staged breast reconstruction.

CONCLUSIONS

Most patients with even limited nodal involvement will likely benefit from PMRT with significant reduction in local-regional recurrence and potential survival. Patients with initial clinical stage III disease and/or any residual disease after neoadjuvant chemotherapy should be strongly considered for PMRT. Growing evidence supports the use of hypofractionated radiation for PMRT with equivalent efficacy and decreased acute side effects, but additional evidence is needed for special populations. There is limited evidence to support routine use of bolus in all patients. Timing of PMRT regarding completion of 2-staged breast reconstruction requires a discussion of increased risks with radiation postimplant exchange compared with increased risk of failure of reconstruction or surgical complications with radiation preimplant exchange.

Superficial Dosimetry Study of the Frequency of Bolus Using in Volumetric Modulated Arc Therapy after Modified Radical Mastectomy

OBJECTIVE

To investigate the effect of various frequencies of bolus use on the superficial dose of volumetric modulated arc therapy after modified radical mastectomy for breast cancer.

METHODS

Based on the computed tomography images of a female anthropomorphic breast phantom, a 0.5 cm silicone-based 3D-printed bolus was created. Nine points evenly distributed on the breast skin were selected for assessing the skin dose, and a volume of subcutaneous lymphatic drainage of the breast (noted as ROI2-3) was delineated for assessing the chest wall dose. The treatment plans with and without bolus (plan_wb and plan_nb) were separately designed using the prescription of 50 Gy in 25 fractions following the standard dose constraints of the adjacent organ at risk. To characterize the accuracy of treatment planning system (TPS) dose calculations, the doses of the nine points were measured five times by thermoluminescence dosimeters (TLDs) and then were compared with the TPS calculated dose.

RESULTS

Compared with Plan_nb (144.46 ± 10.32 cGy), the breast skin dose for plan_wb (208.75 ± 4.55 cGy) was significantly increased (t = -18.56, P < 0.001). The deviation of skin dose was smaller for Plan_wb, and the uniformity was significantly improved. The calculated value of TPS was in good agreement with the measured value of TLD, and the maximum deviation was within 5%. Skin and ROI2-3 doses were significantly increased with increasing frequencies of bolus applications. The mean dose of the breast skin and ROI2-3 for 15 and 23 times bolus applications were 45.33 Gy, 50.88 Gy and 50.36 Gy, 52.39 Gy, respectively.

CONCLUSION

3D printing bolus can improve the radiation dose and the accuracy of the planned dose. Setting Plan_wb to 15 times for T1-3N+ breast cancer patients and 23 times for T4N+ breast cancer patients can meet the clinical need. Quantitative analysis of the bolus application frequency for different tumor stages can provide a reference for clinical practice.

Analysis of Individualized Silicone Rubber Bolus Using Fan Beam Computed Tomography in Postmastectomy Radiotherapy: A Dosimetric Evaluation and Skin Acute Radiation Dermatitis Survey

Objective: To investigate the dosimetric effects of using individualized silicone rubber (SR) bolus on the target area and organs at risk (OARs) during postmastectomy radiotherapy (PMRT), as well as evaluate skin acute radiation dermatitis (ARD). Methods: A retrospective study was performed on 30 patients with breast cancer. Each patient was prepared with an individualized SR bolus of 3 mm thickness. Fan-beam computed tomography (FBCT) was performed at the first and second fractions, and then once a week for a total of 5 times. Dosimetric metrics such as homogeneity index (HI), conformity index (CI), skin dose (SD), and OARs including the heart, lungs, and spinal cord were compared between the original plan and the FBCTs. The acute side effects were recorded. Results: In targets' dosimetric metrics, there were no significant differences in Dmean and V105% between planning computed tomography (CT) and actual treatments (P > .05), while the differences in D95%, V95%, HI, and CI were statistically significant (P < .05). In OARs, there were no significant differences between the Dmean, V5, and V20 of the affected lung, V5 of the heart and Dmax of the spinal cord (P > .05) except the V30 of affected lung, which was slightly lower than the planning CT (P < .05). In SD, both Dmax and Dmean in actual treatments were increased than plan A, and the difference was statistically significant (P < .05), while the skin-V20 and skin-V30 has no difference. Among the 30 patients, only one patient had no skin ARD, and 5 patients developed ARD of grade 2, while the remaining 24 patients were grade 1. Conclusion: The OR bolus showed good anastomoses and high interfraction reproducibility with the chest wall, and did not cause deformation during irradiation. It ensured accurate dose delivery of the target and OARs during the treatment, which may increase SD by over 101%. In this study, no cases of grade 3 skin ARD were observed. However, the potential of using OR bolus to reduce grade 1 and 2 skin ARD warrants further investigation with a larger sample size.

Adjuvant Radiation Treatment of Breast Cancer After Mastectomy: Advanced Algorithms and Partial Bolus Improve the Dose Calculation Accuracy in the Case of Thin-Chest-Wall Irradiation

Purpose

The aim of this study was to examine measured and calculated dose distributions in a thin-chest-wall phantom and estimate the variations in the dose-volume histogram (DVH) parameters used in plan evaluation for patient geometries with chest-wall thicknesses <15 mm with and without bolus implementation.

Methods and Materials

Measurements were made using thermoluminescent dosimeters in a chest-wall phantom. The Monte Carlo method, anisotropic analytical algorithm, and Acuros XB Eclipse algorithms were used to calculate dose distributions for clinical plans. DVH parameters for clinical target volume tumor (CTVT) and planning target volume (PTV) and mean doses were evaluated for 15 patients with a chest-wall thickness of 8 to 15 mm with and without partial bolus and for 10 patients with a chest-wall thickness of 20 to 25 mm without bolus.

Results

Measurements showed that the dose at a depth of 2 to 12 mm at the beam entrance and laterally was within 90% of the dose at 8 mm depth. Monte Carlo and Acuros XB calculations were well aligned with the experimental data, whereas the anisotropic analytical algorithm underestimated the beam entrance and lateral doses. The DVH parameters for the patients with a thin chest wall were sensitive to calculation algorithm, resolution, body structure definition, and patient geometry. The parameters CTVT_V95%, CTVT_D98%, and PTV_D98% were much lower than the tolerance criteria. Partial bolus improved the values for all algorithms and decreased the variations due to patient geometry. Dose calculations for patients with a chest-wall thickness of 20 to 25 mm resulted in sufficient target coverage and low dependence on patient geometry and calculation algorithm without the use of bolus.

Conclusions

Dose calculations using advanced algorithms and resolution <2 mm are recommended for patients with a thin chest wall. Specific DVH criteria or the implementation of partial bolus was needed to facilitate plan development and evaluation for this patient group.

Dual application of Polyvinyl Alcohol Glutaraldehyde Methylthymol Blue Fricke hydrogel in clinical practice: Surface dosimeter and bolus

An essential issue is an accurate evaluation of surface dose distribution for such sensitive treatments. This work aimed to feasibility of the dual application of the Ferrous Polyvinyl Alcohol Glutaraldehyde Methylthymol Blue (PVA-GTA-MTB) gel as a bolus compensator and surface dosimeter in breast radiotherapy. The differences between the surface dose measured using PVA-GTA-MTB gel and film dosimetry in the medial and lateral parts of the breast were 3.74% and 4.18%, respectively. A qualitative comparison of the isodose curves showed that the PVA-GTA-MTB bolus creates a uniform dose distribution similar to the superflab bolus in the target volume.

The transition in practice to reduce bolus use in post-mastectomy radiotherapy: A dosimetric study of skin and subcutaneous tissue

To inform clinical practice for women receiving post-mastectomy radiotherapy (PMRT), this study demonstrates the dosimetric impact of removing daily bolus on skin and subcutaneous tissue. Two planning strategies were used: clinical field-based (n = 30) and volume-based planning (n = 10). The clinical field-based plans were created with bolus and recalculated without bolus for comparison. The volume-based plans were created with bolus to ensure a minimum target coverage of the chest wall PTV and recalculated without bolus. In each scenario, the dose to superficial structures, including skin (3 mm and 5 mm) and subcutaneous tissue (a 2 mm layer, 3 mm deep from surface) were reported. Additionally, the difference in the clinically evaluated dosimetry to skin and subcutaneous tissue in volume-based plans were recalculated using Acuros (AXB) and compared to the Anisotropic Analytical Algorithm (AAA) algorithm. For all treatment planning strategies, chest wall coverage (V90%) was maintained. As expected, superficial structures demonstrate significant loss in coverage. The largest difference observed in the most superficial 3 mm where V90% coverage is reduced from a mean (± standard deviation) of 95.1% (± 2.8) to 18.9% (± 5.6) for clinical field-based treatments with and without bolus, respectively. For volume-based planning, the subcutaneous tissue maintains a V90% of 90.5% (± 7.0) compared to the clinical field-based planning coverage of 84.4% (± 8.0). In all skin and subcutaneous tissue, the AAA algorithm underestimates the volume of the 90% isodose. Removing bolus results in minimal dosimetric differences in the chest wall and significantly lower skin dose while dose to the subcutaneous tissue is maintained. Unless the skin has disease involvement, the most superficial 3 mm is not considered part of the target volume. The continued use of the AAA algorithm is supported for the PMRT setting.

Randomized clinical trial of tissue equivalent bolus prescription in postmastectomy radiotherapy stratified by skin involvement status

Purpose

To assess the impact and optimize the prescription of tissue-equivalent bolus in postmastectomy radiotherapy (PMRT), we compared the use of different bolus regimens tailored by skin involvement status.

Methods

Patients with breast cancer who required PMRT were recruited (NCT01925651) and classified into two groups: standard-risk (SR, without skin involvement) and high-risk (HR, with skin involvement). SR was randomized between no bolus or 5 mm-bolus on alternate days and HR between 5 mm-bolus on alternate days or daily. Conventional fractionation (50.4 Gy; 1.8 Gy/daily) was used. Acute skin toxicity was evaluated blindly and the radiodermatitis-specific toxicity index [rads-TI] calculated. Subsequently, patients were followed up to assess oncologic outcomes, focusing on chest wall (CW) local control.

Results

Fifty-eight patients were enrolled (34 SR and 24 HR). Baseline characteristics were similar between arms within the same risk group. Overall, maximal radiodermatitis rates were 29.4 % (G2) and 15.7 % (G3). In the SR group, no difference existed in G2 radiodermatitis incidence between the subgroups (p = 0.70) and no G3 events occurred. In the HR group, incidences of G2 (100 % vs 44.5 %, p = 0.01) and G3 radiodermatitis (70 % vs 11.1 %, p = 0.02) were higher with daily bolus. After adjusting for confounders, the daily bolus had a higher incidence of G2 (p = 0.03), G3 radiodermatitis (p = 0.04), and worse rads-TI (p < 0.01). After a median follow-up of 6.2 years, the 5-year local control was 95.8 % (95 %CI: 88.2 %-100 %) in the SR and 91.7 % (95 %CI: 77.3 %-100 %) in the HR groups. Per risk group, there was no difference in local control between the SR (p = 0.90) or the HR bolus regimens (p = 0.70).

Conclusion

Daily 5 mm bolus prescription significantly increased the overall toxicity burden. In this preliminary study, within the same risk group, no detriment in CW local control was detected with less intense bolus regimens (SR: no bolus; HR: alternate-days bolus). Additionally, the rads-TI was able to distinguish overall radiodermatitis burden.

Evaluation of brass alloy density as tissue equivalence bolus using electron density phantom and optical density method

The brass mesh bolus alloy has been shown to be a promising substitute for tissue-equivalent bolus to increase the surface dose during breast cancer radiotherapy treatment. This study is aimed to evaluate the brass alloy density in order to better understand the brass qualities as a bolus in radiotherapy. The mass density of brass alloy determined in this work are using solid approaches, i) traditional density method, ii) Computed Tomography (CT) number using electron density phantom and CT scan and iii) mean pixel value via ImageJ software. According to ANOVA F (2,6) 2.982, p0.126, there was no statistically significant difference between the groups. As a result, all methods for calculating the density of brass alloy are valid. The X² test of CT number of brass plug to breast substitute in electron density phantom indicates no association. Density analysis using computed tomography and an electron density phantom, as well as the traditional density method and Image J analysis, were all shown to be acceptable methods for estimating the density of the brass alloy. Considering this, brass alloy can be considered as a potential substitute for tissue-equivalent bolus with further extensive of research in conjunction to CT number.

Risk Factors Related to Acute Radiation Dermatitis in Breast Cancer Patients After Radiotherapy: A Systematic Review and Meta-Analysis

Background

Acute radiation dermatitis (ARD) is the most common acute response after adjuvant radiotherapy in breast cancer patients and negatively affects patients’ quality of life. Some studies have reported several risk factors that can predict breast cancer patients who are at a high risk of ARD. This study aimed to identify patient- and treatment-related risk factors associated with ARD.

Methods

PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure, and WanFang literature databases were searched for studies exploring the risk factors in breast cancer patients. The pooled effect sizes, relative risks (RRs), and 95% CIs were calculated using the random-effects model. Potential heterogeneity and sensitivity analyses by study design, ARD evaluation scale, and regions were also performed.

Results

A total of 38 studies composed of 15,623 breast cancer patients were included in the analysis. Of the seven available patient-related risk factors, four factors were significantly associated with ARD: body mass index (BMI) ≥25 kg/m² (RR = 1.11, 95% CI = 1.06–1.16, I² = 57.1%), large breast volume (RR = 1.02, 95% CI = 1.01–1.03, I² = 93.2%), smoking habits (RR = 1.70, 95% CI = 1.24–2.34, I² = 50.7%), and diabetes (RR = 2.24, 95% CI = 1.53–3.27, I² = 0%). Of the seven treatment-related risk factors, we found that hypofractionated radiotherapy reduced the risk of ARD in patients with breast cancer compared with that in conventional fractionated radiotherapy (RR = 0.28, 95% CI = 0.19–0.43, I² = 84.5%). Sequential boost and bolus use was significantly associated with ARD (boost, RR = 1.91, 95% CI = 1.34–2.72, I² = 92.5%; bolus, RR = 1.94, 95% CI = 1.82–4.76, I² = 23.8%). However, chemotherapy regimen (RR = 1.17, 95% CI = 0.95–1.45, I² = 57.2%), hormone therapy (RR = 1.35, 95% CI = 0.94–1.93, I² = 77.1%), trastuzumab therapy (RR = 1.56, 95% CI = 0.18–1.76, I² = 91.9%), and nodal irradiation (RR = 1.57, 95% CI = 0.98–2.53, I² = 72.5%) were not correlated with ARD. Sensitivity analysis results showed that BMI was consistently associated with ARD, while smoking, breast volume, and boost administration were associated with ARD depending on study design, country of study, and toxicity evaluation scale used. Hypofractionation was consistently shown as protective. The differences between study design, toxicity evaluation scale, and regions might explain a little of the sources of heterogeneity.

Conclusion

The results of this systematic review and meta-analysis indicated that BMI ≥ 25 kg/m² was a significant predictor of ARD and that hypofractionation was consistently protective. Depending on country of study, study design, and toxicity scale used, breast volume, smoking habit, diabetes, and sequential boost and bolus use were also predictive of ARD.

A Delphi study and International Consensus Recommendations: The use of bolus in the setting of postmastectomy radiation therapy for early breast cancer

Bolus serves as a tissue equivalent material that shifts the 95-100% isodose line towards the skin and subcutaneous tissue. The need for bolus for all breast cancer patients planned for postmastectomy radiation therapy (PMRT) has been questioned. The work was initiated by the faculty of the European SocieTy for Radiotherapy & Oncology (ESTRO) breast cancer courses and represents a multidisciplinary international breast cancer expert collaboration to optimize PMRT. Due to the lack of randomised trials evaluating the benefits of bolus, we designed a stepwise project to evaluate the existing evidence about the use of bolus in the setting of PMRT to achieve an international consensus for the indications of bolus in PMRT, based on the Delphi method.

Surface Dose Measurements in Chest Wall Postmastectomy Radiotherapy to Achieve Optimal Dose Delivery with 6 MV Photon Beam

Aim

A tissue-equivalent bolus of sufficient thickness is used to overcome build up effect to the chest wall region of postmastectomy radiotherapy (PMRT) patients with tangential technique till Radiation Therapy Oncology Group (RTOG) Grade 2 (dry desquamation) skin reaction is observed. The aim of this study is to optimize surface dose delivered to chest wall in three-dimensional radiotherapy using EBT3 film.

Materials and Methods

Measurements were conducted with calibrated EBT3 films with thorax phantom under "open beam, Superflab gel (0.5 cm) and brass bolus conditions to check correlation against TPS planned doses. Eighty-two patients who received 50 Gy in 25# were randomly assigned to Group A (Superflab 0.5 cm gel bolus for first 15 fractions followed by no bolus in remaining 10 fractions), Group B or Group C (Superflab 0.5 cm gel or single layer brass bolus, respectively, till reaching RTOG Grade 2 skin toxicity).

Results

Phantom measured and TPS calculated surface doses were within - 5.5%, 4.7%, and 8.6% under open beam, 0.5 cm gel, and single layer of brass bolus applications, respectively. The overall surface doses (OSD) were 80.1% ±2.9% (n = 28), 92.6% ±4.6% (n = 28), and 87.4% ±4.7% (n = 26) in Group A, B, and C, respectively. At the end of treatment, 7 out of 28; 13 out of 28; and 9 out of 26 patients developed Grade 2 skin toxicity having the OSD value of 83.0% ±1.6% (n = 7); 93.7% ±3.2% (n = 13); and 89.9% ±5.6% (n = 9) in Groups A, B, and C, respectively. At the 20^th-23^rd fraction, 2 out of 7; 6 out of 13; and 4 out of 9 patients in Groups A, B, and C developed a Grade 2 skin toxicity, while the remaining patients in each group developed at the end of treatment.

Conclusions

Our objective to estimate the occurrence of optimal dose limit for bolus applications in PMRT could be achieved using clinical EBT3 film dosimetry. This study ensured correct dose to scar area to protect cosmetic effects. This may also serve as quality assurance on optimal dose delivery for expected local control in these patients.

The use of bolus in postmastectomy radiation therapy for breast cancer: A systematic review

PURPOSE

Post mastectomy radiation therapy (PMRT) reduces locoregional recurrence (LRR) and breast cancer mortality for selected patients. Bolus overcomes the skin-sparing effect of external-beam radiotherapy, ensuring adequate dose to superficial regions at risk of local recurrence (LR). This systematic review summarizes the current evidence regarding the impact of bolus on LR and acute toxicity in the setting of PMRT.

RESULTS

27 studies were included. The use of bolus led to higher rates of acute grade 3 radiation dermatitis (pooled rates of 9.6% with bolus vs. 1.2% without). Pooled crude LR rates from thirteen studies (n = 3756) were similar with (3.5%) and without (3.6%) bolus.

CONCLUSIONS

Bolus may be indicated in cases with a high risk of LR in the skin, but seems not to be necessary for all patients. Further work is needed to define the role of bolus in PMRT.

A multidisciplinary approach for autologous breast reconstruction: A narrative (re)view for better management

Breast reconstruction and oncoplastic surgery have become an important part of breast cancer care. The use of autologous breast reconstruction (ABR) has evolved significantly with advances in microsurgery, aiming to reduce donor site complications and improve cosmesis. For years, immediate-ABR was considered a contraindication if postmastectomy irradiation (PMRT) was planned. As a result of de-escalation of axillary surgery the indication of PMRT are increasing along-side with observations that PMRT in the setting of ABR is not contraindicated. Surgical techniques may result in different amount and areas of breast residual glandular tissue and patient selection is important to reduce potential residual disease. Meticulus radiation planning is important to potentially reduce complications without compromising oncologic outcomes. Surgical techniques change constantly in aim to improve aesthetic results but should most importantly maintain priority to the oncological indications. By multidisciplinary team work with a comprehensive understanding of each discipline, we can preserve the accomplishments of breast surgery in the setting of PMRT, without compromising disease control.

A multidisciplinary view of mastectomy and breast reconstruction: Understanding the challenges

The current review paper was written in collaboration with breast cancer surgeons from the European Breast Cancer Research Association of Surgical Trialists (EUBREAST), a breast pathologist from the Danish Breast Cancer Group (DBCG), and representatives from the European SocieTy for Radiotherapy & Oncology (ESTRO) breast cancer course. Herein we summarize the different mastectomies and reconstruction procedures and define high-risk anatomical areas for breast cancer recurrences, to further specify the challenges in the surgical procedure, histopathological evaluation, and target volumes in case of postmastectomy irradiation, as recommended by the ESTRO guidelines according to the surgical procedure. The paper has original figures and illustrations for all disciplines for in-depth understanding of the differences between the procedures.

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Mastectomy techniques and reconstruction evolved to improve cosmetic outcomes.

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Different techniques maybe associated with different amount of residual breast tissue.

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More data is needed to estimate who are the patients at risk for residual disease or recurrence.

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Multidisciplinary work needed to individualise treatment for optimal oncological outcomes while maintaining the significant improvements in achieving better cosmesis for these patients.

Loco-regional adjuvant radiation therapy in breast cancer patients with positive axillary lymph-nodes at diagnosis (CN2) undergoing preoperative chemotherapy and with complete pathological lymph-nodes response. Development of GRADE (Grades of recommendation, assessment, Development and Evaluation) recommendation by the Italian Association of radiation therapy and Clinical Oncology (AIRO)

OBJECTIVE

To perform a meta-analysis to determine the effect of loco-regional radiation therapy (RT) compared to no loco-regional RT for operated patients in clinical stage cN2 breast cancer at diagnosis and ypN0 after preoperative chemotherapy (PST).

MATERIAL AND METHODS

Eligible studies were identified through a systematic search of the medical literature performed independently by two researchers using a validated search strategy. An electronic search of Medline via PubMed and Embase (Breast cancer AND preoperative chemotherapy AND radiation therapy) was conducted with no language or publication status restrictions. The effect of loco-regional RT on overall (OS), disease free (DFS), loco-regional recurrence-free (LRRFS) survival and local recurrence was evaluated. An electronic search of Medline via PubMed and Embase (Toxicity AND radiation therapy breast cancer AND preoperative therapy; toxicity AND breast surgery AND preoperative chemotherapy) was conducted for outcomes of harm: major acute and late skin toxicity, lymphedema and cardiac events.

RESULTS

Of 333 studies identified, 4 retrospective studies reporting on a total of 1107 patients were included in the meta-analysis. Six and 3 reported data of acute and late skin toxicity, while 2 studies provided information on cardiac events. Pooled results showed no difference in terms of hazard ratio for loco-regional RT versus no loco-regional RT [hazard ratio (HR) = 0.82, 95% confidence interval (CI) 0.63-1.68]. Loco-regional RT was associated with an OS benefit in the subgroup analysis: IIIB-C (loco-regional RT 79.3% vs no loco-regional RT 71.2%, p = 0.027) and T3-T4 (loco-regional RT 82.6% vs no loco-regional RT 76.6%, p = 0.025). No difference was shown in terms of 5-year DFS (loco-regional RT 91.2% vs no loco-regional RT 83%, p = 0.441) and LRRFS (loco-regional RT 98.1% vs no loco-regional RT 92.3%, p = 0.148). There was no significant difference between the groups in terms of acute and late skin toxicities, lymphedema and cardiac events.

CONCLUSIONS

Because of the limitations due to the small number of studies and heterogeneity in the analysis, the present study does not allow to draw any definitive conclusion, highlighting the need for well-controlled trials to determine the effect of loco-regional RT in patients with cN2 having a pathological complete response in the axillary nodes after preoperative chemotherapy.

In search of a one plan solution for VMAT post-mastectomy chest wall irradiation

PURPOSE

This study was designed to evaluate skin dose in both VMAT and tangent treatment deliveries for the purpose of identifying suitable bolus use protocols that should produce similar superficial doses.

METHODS

Phantom measurements were used to investigate skin dose in chest wall radiotherapy with and without bolus for 3D and rotational treatment techniques. Optically stimulated luminescence dosimeters (OSLDs) with and without housing and EBT3 film were used. Superflab (3, 5, and 10 mm) and brass mesh were considered. Measured doses were compared with predictions by the Eclipse treatment planning system. Patient measurements were also performed and the bolusing effect of hospital gowns and blankets were highlighted. The effect of flash for VMAT plans was considered experimentally by using 2 mm couch shifts.

RESULTS

For tangents, average skin doses without bolus were 0.64 (EBT3), 0.62 (bare OSLD), 0.77 (jacketed OSLD), and 0.68 (Eclipse) as a fraction of prescription. For VMAT, doses without bolus were 0.53 (EBT3), 0.53 (bare OSLD), 0.64 (jacketed OSLD), and 0.60 (Eclipse). For tangents, the average doses with different boluses as measured by EBT3 were 0.99 (brass mesh), 1.02 (3 mm), 1.03 (5 mm), and 1.07 (10 mm). For VMAT with bolus, average doses as measured by EBT3 were 0.83 (brass), 0.96 (3 mm), 1.03 (5 mm), and 1.04 (10 mm). Eclipse doses agreed with measurements to within 5% of measurements for all Superflab thicknesses and within 15% of measurements for no bolus. The presence of a hospital gown and blanket had a bolusing effect that increased the surface dose by approximately 10%.

CONCLUSIONS

Results of this work allow for consideration of different bolus thicknesses, materials, and usage schedules based on desired skin dose and choice of either tangents or an arc beam techniques.

Quantitative Effect of Bolus on Skin Dose in Postmastectomy Radiation Therapy

BACKGROUND

In postmastectomy radiation therapy (PMRT), some centres prescribe the use of a tissue-equivalent bolus to the skin to reduce the risk of chest wall recurrence. The addition of bolus causes an increase in the skin dose, which may lead to increased risk of radiodermatitis. Radiodermatitis can decrease patients' overall quality of life, bringing into question the benefit of using the bolus. The purpose of this retrospective chart review was to quantify the increase in skin dose associated with the use of bolus in the PMRT setting.

MATERIALS AND METHODS

We evaluated 70 patients who underwent PMRT at our institution during 2012-2018. Two similar treatment plans were generated for each patient: one with bolus and one without. Skin dose-volume histogram values were evaluated, and statistical analysis was performed using MATLAB R2015b.

RESULTS

There was no significant difference in the maximum skin dose within a depth of 5 mm for bolus versus nonbolus plans (P = 0.4). However, within a depth of 3 mm, bolus plans had a maximum skin dose 7% ± 2.5% higher than the nonbolus plans (P < .00001). Mean skin dose within depths of 3 and 5 mm were both significantly higher (P < .00001) for bolus plans. The photon beam energy and chest wall separation showed minimal or no effect on skin dose.

CONCLUSION

Given the differing opinions in the literature regarding the role for bolus in PMRT, there is still uncertainty of the optimal treatment method. This retrospective study demonstrates a 20%-30% reduction in mean skin dose when bolus is not used.