Dosimetric evaluation of integrated IMRT treatment of the chest wall and supraclavicular region for breast cancer after modified radical mastectomy

Executive Summary of the American Radium Society Appropriate Use Criteria: Regional Nodal Irradiation for Breast Cancer

OBJECTIVES

Recent literature has provided additional data to further individualize treatment recommendations on regional nodal irradiation (RNI) patient selection and delivery techniques, but controversies surrounding optimal RNI utilization remain, including radiation technique, modality selection, and internal mammary lymph node (IMN) inclusion. The American Radium Society (ARS) Breast Appropriate Use Criteria (AUC) Committee performed a systematic review and developed a consensus guideline to summarize recent data and provide evidence-based recommendations.

METHODS

A multidisciplinary panel comprised of 15 members representing radiation oncologists, medical oncologists, and surgical oncologists specializing in the treatment of breast cancer conducted an analysis of the medical literature from January 1, 2011 to April 1, 2024. Modified Delphi methodology was used to rate the appropriateness of treatments for variants across 3 key questions.

RESULTS

Patients with intermediate-risk breast cancer, such as limited nodal involvement or large primary tumor size, are reasonable candidates for RNI, although a subset of patients with overall favorable clinicopathologic features may be considered for treatment de-escalation. Data on the use of advanced radiation techniques for RNI were limited in scope and strength, and the panel agreed that careful patient selection is needed when using these tools. Evidence suggests that the IMN should be included when delivering RNI given the absolute benefit demonstrated in multiple randomized trials.

CONCLUSION

A systematic review and evidence-based summary of recommendations are provided in these consensus guidelines from the ARS Breast AUC Committee to provide current comprehensive guidance on the optimal management of non-metastatic breast cancer patients being considered for RNI.

A robust treatment planning approach for chest motion in postmastectomy chest wall intensity modulated radiation therapy

PURPOSE

Chest wall postmastectomy radiation therapy (PMRT) should consider the effects of chest wall respiratory motion. The purpose of this study is to evaluate the effectiveness of robustness planning intensity modulated radiation therapy (IMRT) for respiratory movement, considering respiratory motion as a setup error.

MATERIAL AND METHODS

This study analyzed 20 patients who underwent PMRT (10 left and 10 right chest walls). The following three treatment plans were created for each case and compared. The treatment plans are a planning target volume (PTV) plan (PP) that covers the PTV within the body contour with the prescribed dose, a virtual bolus plan (VP) that sets a virtual bolus in contact with the body surface and prescribing the dose that includes the PTV outside the body contour, and a robust plan (RP) that considers respiratory movement as a setup uncertainty and performs robust optimization. The isocenter was shifted to reproduce the chest wall motion pattern and the doses were recalculated for comparison for each treatment plan.

RESULT

No significant difference was found between the PP and the RP in terms of the tumor dose in the treatment plan. In contrast, VP had 3.5% higher PTV Dmax and 5.5% lower PTV V95% than RP (p < 0.001). The RP demonstrated significantly higher lung V20Gy and Dmean by 1.4% and 0.4 Gy, respectively, than the PP. The RP showed smaller changes in dose distribution affected by chest wall motion and significantly higher tumor dose coverage than the PP and VP.

CONCLUSION

We revealed that the RP demonstrated comparable tumor doses to the PP in treatment planning and was robust for respiratory motion compared to both the PP and the VP. However, the organ at risk dose in the RP was slightly higher; therefore, its clinical use should be carefully considered.

Systematic quantitative evaluation of Plan-IQ for intensity-modulated radiation therapy after modified radical mastectomy

Radiotherapy (RT) is one of the main treatment strategies of breast cancer. It is challenging to design RT plans that can completely cover the target area while protecting organs at risk (OAR). The Plan-IQ feasibility tool can estimate the best sparing dose of OAR before optimizing the Plan. A systematic quantitative evaluation of the quality change of intensity-modulated radiation therapy (IMRT) using the Plan-IQ feasibility tool was performed for modified radical mastectomy in this study. We selected 50 patients with breast cancer treated with IMRT. All patients received the same dose in the planning target volume (PTV). The plans are categorized into two groups, with each patient having one plan in each group: the clinically accepted normal plan group (NP group) and the repeat plan group (RP group). An automated planning strategy was generated using a Plan-IQ feasibility dose volume histogram (FDVH) in RP group. These plans were assessed according to the dosimetry parameters. A detailed scoring strategy was based on the RTOG9804 report and 2018 National Comprehensive Cancer Network guidelines, combined with clinical experience. PTV coverage in both groups was achieved at 100% of the prescribed dose. Except for the thyroid coverage, the dose limit of organs at risk (OAR) in RP group was significantly better than that in NP group. In the scoring analysis, the total scores of RP group decreased compared to that of NP group (P < 0.05), and the individual scores of PTV and OAR significantly changed. PTV scores in RP group decreased (P < 0.01); however, OAR scores improved (P < 0.01). The Plan-IQ FDVH was useful for evaluating a class solution for IMRT planning. Plan-IQ can automatically help physicians design the best OAR protection plan, which sacrifices part of PTV, but still meets clinical requirements.

Challenges in lung and heart avoidance for postmastectomy breast cancer radiotherapy: Is automated planning the answer?

Postmastectomy radiotherapy (PMRT) has been shown to improve the overall survival for invasive breast cancer patients. However, it represents a challenging treatment geometry and individualized planning strategies with complex field arrangements are usually adopted to decrease radiotoxicity to heart and lungs. Automated treatment planning has the potential to improve plan quality consistency and planning efficiency. Herein, we describe the application of the Pinnacle³ Autoplanning engine as a valuable technological resource able to allow the treatment of challenging patients theoretically unfit for radiotherapy for major cardiac and pulmonary comorbidities. Treatment was planned for three left-sided chest wall and regional lymph-nodes postmastectomy breast cancer patients. A deep inspiration breath-hold (DIBH) technique was used aiming to reduce the OARs irradiation. Three manually generated plans (hybrid-IMRT (HMRT), hybrid-VMAT (HVMAT) and full VMAT (MP-VMAT) and a fully automated plan created by the Autoplanning engine (AP-VMAT) were optimized in order to ensure a safe radiation therapy to the patients. The plans were evaluated based on planning target volumes (PTVs) coverage, dose homogeneity index (HI), conformity index (CN), dose to organs at risk (OARs) and normal tissue complication probabilities (NTCPs) of pericarditis, long term mortality and pneumonitis. Despite the use of deep moderated breath-hold, all human-driven plans failed to reach the stringent dose objectives for OARs. All plans provided an optimal coverage for chest wall and lymph-nodal area. AP-VMAT delivered the lowest mean dose to the heart (3.4 to 4.9 Gy) and ipsilateral lung (7.5 to 12.5 Gy) reporting the lowest NTCP for pneumonitis (<1%), confirming the only chance to comply the dose objectives. Moreover, AP-VMAT reported a decrease of the integral dose, which was lower by about 4-8% with respect to manual plans. AP-VMAT plan resulted in up to 58% increase of MUs with respect to manual plans, suggesting a more pronounced fluence modulation and plan complexity. A major difference was found for the planning time which was reduced to less than 30 minutes by using the Auto-Planning module. With improved planning quality and efficiency, Auto-planning is an effective tool to enable high-quality plans in challenging postmastectomy breast cancer radiotherapy.

[Concomitant radiotherapy and trastuzumab: Rational and clinical implications]

The HER2 receptor (Human Epidermal Growth Receptor 2) is a transmembrane receptor with tyrosine kinase activity that is over-expressed in 25-30 % of breast carcinomas. Its activation is associated with an exaggeration of cell proliferation with an increase in repair capacity resulting in increased radioresistance. On cardiac tissues, HER2 receptor activation plays a cardio-protective role. Trastuzumab, the first anti-HER2 drug used to treat patients with breast cancer overexpressing HER2 receptor , inhibits the cascade of reactions resulting in the proliferation of tumor cells, thus restoring cellular radiosensitivity. However, the combination of Trastuzumab with radiation therapy also removes HER2 receptor cardio-protective role on myocardial cells which increases the risk of cardiotoxicity. Thus, the concomitant association of these two modalities has long been a subject of controversy. Recent advances in radiation therapy technology and early detection of cardiac injury may limit the cardiotoxicity of this combination. Through this review, we developed the biological basis and the benefit-risk of concomitant combination of radiotherapy and Trastuzumab in adjuvant treatment of breast cancers overexpressing HER2 and we discuss the modalities of its optimization.

Prognosis and Prophylactic Regional Nodal Irradiation in Breast Cancer Patients With the First Isolated Chest Wall Recurrence After Mastectomy

Background and Purpose

Optimal radiation target volumes for breast cancer patients with their first isolated chest wall recurrence (ICWR) after mastectomy are controversial. We aimed to analyze the regional failure patterns and to investigate the role of prophylactic regional nodal irradiation (RNI) for ICWR.

Materials and Methods

Altogether 205 patients with ICWR after mastectomy were retrospectively analyzed. Post-recurrence progression-free survival (PFS) and overall survival (OS) rates were calculated by Kaplan-Meier method and the differences were compared with Log-rank test. Competing risk model was used to estimate the subsequent regional recurrence (sRR) and locoregional recurrence (sLRR) rates, and the differences were compared with Gray test.

Results

The 5-year sRR rate was 25.2% with median follow-up of 88.6 months. Of the 52 patients with sRR, 30 (57.7%) recurred in the axilla, 29 (55.8%) in supraclavicular fossa (SC), and five (9.6%) in internal mammary nodes. Surgery plus radiotherapy was independently associated with better sLRR and PFS rates (p<0.001). The ICWR interval of ≤ 4 years was associated with unfavorable sRR (p=0.062), sLRR (p=0.014), PFS (p=0.001), and OS (p=0.005). Among the 157 patients who received radiotherapy after ICWR, chest wall plus RNI significantly improved PFS (p=0.004) and OS (p=0.021) compared with chest wall irradiation alone. In the 166 patients whose ICWR interval was ≤ 4 years, chest wall plus RNI provided the best PFS (p<0.001) and OS (p=0.022) compared with chest wall irradiation alone or no radiotherapy.

Conclusion

Patients with ICWR have a high-risk of sRR in SC and axilla. Chest wall plus RNI is recommended.

Verification of the junctional dose for irradiation of the chest wall and supraclavicular regions under the circumstances of advanced technologies

A single-isocenter half-beam technique is commonly used when irradiating the chest wall and supraclavicular regions in patients with high-risk breast cancer. However, several studies have reported that underdosage can occur at the junction of the chest wall and supraclavicular regions due to a "tongue-and-groove" effect. This study verified the efficacy of an open leaf technique (OL-tech) that involves placing a multileaf collimator 5 mm outside from the beam central axis to remove the effect of the multileaf collimator in a single-isocenter half-beam technique. We compared the junction doses of the OL-tech with those of a conventional technique (C-tech) in square and clinical plans, using 4 and 10 MV x-rays in the Clinac iX and 6 and 10 MV x-rays in the Trilogy accelerators (Varian Medical Systems, Palo Alto, CA). EBT3 radiochromic films were used for measurements. Measurements were performed at a depth of 3 cm when verifying field matching. The EBT3 films in the square plan indicated junction doses for the C-tech of 78.3% with the Clinac iX accelerator and 73.6% with the Trilogy accelerator. By contrast, the corresponding doses for the OL-tech were 107.2% and 99.8%, respectively. In the clinical plan, the junction doses for the C-tech were 76.5% with the Clinac iX accelerator and 72.6% with the Trilogy accelerator; the corresponding doses for the OL-tech were 108.3% and 101.7%, respectively. As with the square plan, variations in the junction dose were much smaller using the OL-tech than using the C-tech. Our results suggest that the OL-tech can be useful for improving dose homogeneity at the junction of the chest wall and supraclavicular regions.

Integrated IMRT vs segmented 3D-CRT of the chest wall and supraclavicular region for Breast Cancer after modified Radical Mastectomy: An 8-year follow-up

Objective: The purpose of this study was to evaluate the efficacy of two radiotherapy techniques for breast cancer patients with post-mastectomy. The intensity-modulated radiotherapy for treating the chest wall and regional nodes contoured as a whole planning target volume was compared with the conventional segmented 3-dimensional conformal radiotherapy undergoing modified radical mastectomy.

Materials and methods: Patients who received the two post-mastectomy radiation therapies were retrospectively analyzed. The chest wall and supra/infraclavicular region +/- internal mammary nodes were contoured as a whole planning target volume on the planning computed tomography. We evaluated differences in survival, recurrence, and late side effects between the integrated intensity-modulated radiotherapy group and the conventional segmented group.

Results: A total of 223 patients were recruited. The mean follow-up was 104.3 months. Of these patients, 129 received integrated radiotherapy and 94 patients received segmented radiotherapy. The 8-year disease-free survival rates were 86.0% and 73.4% for patients treated with integrated radiotherapy and traditional segmented radiotherapy, respectively (P = 0.022). The 8-year overall survival rates were 91.4% and 86.2% for patients treated with integrated radiotherapy and traditional segmented radiotherapy, respectively (P = 0.530). Multivariate analysis demonstrated that radiotherapy was an independent prognostic factor for disease-free survival. No significant difference was observed in late side-effects between the two groups.

Conclusion: Intensity-modulated radiotherapy for treating the chest wall and regional nodes contoured as a whole planning target volume reduces the recurrence rate for post-mastectomy breast cancer patients with tolerable toxicities.

Dosimetric Comparison of Three Radiotherapy Techniques in Irradiation of Left-Sided Breast Cancer Patients after Radical Mastectomy

Results

The VMAT plans showed superior to PTV dose conformity index (CI), homogeneity index (HI), protection of the ipsilateral lung, monitor units (MUs), and maximum dose (D_max) to the contralateral breast compared with TSP and 9FIMRT plans. The TSP provided better protection for D_mean of the heart and left ventricle (p < 0.05). A dose for left anterior descending artery from the three techniques had no significant difference. Compared with the 9FIMRT plans, the V_5Gy (%) and V_10Gy (%) for the ipsilateral lung were significantly reduced with TSP and VMAT (p < 0.05). The V_5Gy (%) and V_10Gy (%) for the ipsilateral lung turned out to be similar between VMAT and TSP techniques.

Conclusions

Our study indicates that VMAT should be a better choice of radiotherapy for left-sided breast cancer patients after radical mastectomy. If VMAT is unavailable, 9FIMRT can achieve better CI and HI values and be more MU-efficient compared with TSP; however, TSP can effectively reduce the low dose volume of the ipsilateral lungs and heart.

Dosimetric comparison between volumetric-modulated arc therapy and a hybrid volumetric-modulated arc therapy and segmented field-in-field technique for postmastectomy chest wall and regional lymph node irradiation

Decreasing radiotoxicity to the heart, lungs, and contralateral breast has proven to lower the risk of secondary malignancy and improve overall outcomes when treating chest wall (CW) and regional lymph nodes in postmastectomy breast cancer patients. In this retrospective study, 11 postmastectomy patients were selected and planned with a novel hybrid treatment method and a traditional volumetric arc therapy (VMAT) approach for comparison. This hybrid technique was able to optimize tangential beams to minimize heart dose and the VMAT contribution to improve dose conformity around the planning target volume (PTV). Overall, this hybrid technique produced more homogenous target dose coverage and demonstrated a decrease of integral dose to organs at risk (OAR), while the VMAT technique demonstrated a higher affinity for maintaining dose conformity. Further observation of dose distributions also revealed that the hybrid plans were more effective in sparing low-dose spread to healthy tissue in both right- and left-sided cases. This observation was made evident by the reduction in heart V5 and D_mean, decreases in all parameters regarding the contralateral lung, as well as all values other than the V20 of the ipsilateral lung. This unique hybrid planning technique could present an alternative to standard intensity-modulated radiation therapy (IMRT) planning when treating postmastectomy CW and regional lymph nodes, as it has shown the capacity to decrease cardiac, lung, and contralateral breast toxicity while maintaining quality PTV coverage.

Dosimetric comparison of three intensity-modulated radiation therapies for left breast cancer after breast-conserving surgery

PURPOSE

This study aimed to evaluate dosimetric differences of intensity-modulated radiation therapy (IMRT) in target and normal tissues after breast-conserving surgery.

METHODS

IMRT five-field plan I, IMRT six-field plan II, and field-in-field-direct machine parameter optimization-IMRT plan III were designed for each of the 50 patients. One-way analysis of variance was performed to compare differences, and P < 0.05 was considered statistically significant.

RESULTS

Homogeneity index of plan III is lower than those of plans I and II. No difference was identified in conformity index of targets. Plan I exhibited difference in mean dose (D_mean ) for the heart (P < 0.05). Plan I featured smaller irradiation dose volumes in V₅ , V₂₀ (P < 0.05) of the left lung than II. Plan I exhibited significantly higher V₅ in the right lung than plans II and III (P < 0.05). Under plan I, irradiation dose at V₅ in the right breast is higher than that in plans II and III. Patients in plan III presented less total monitor unit and total treatment time than those in plans I and II (P < 0.05).

CONCLUSION

IMRT six-field plans II, and field-in-field-direct machine parameter optimization-IMRT plans III can reduce doses and volumes to the lungs and heart better while maintaining satisfying conformity index and homogeneity index of target. Nevertheless, plan II neglects target movements caused by respiration. In the same manner, plan III can substantially reduce MU and shorten patient treatment time. Therefore, plan III, which considers target movement caused by respiration, is a more practical radiation mode.

An in silico comparative dosimetric study of postmastectomy locoregional irradiation using intensity-modulated vs 3-dimensional conventional radiotherapy

An in silico dosimetric evaluation of intensity-modulated radiation therapy (IMRT) vs 3-dimensional conventional radiation therapy (3D-CRT) treatment plans in postmastectomy radiation therapy (PMRT) to the chest wall and regional lymphatics was conducted. Twenty-five consecutive patients with breast cancer referred for locoregional PMRT, stages T_2-4 with N_1-3, were planned to receive 50 Gy in 25 fractions with IMRT. Additionally, a 3D-CRT plan was generated using identical contours for the clinical target volumes (CTV), planning target volumes (PTV), and organs at risk (OAR). Treatment plans were assessed using dose-volume histogram (DVH) parameters of D₉₈, D₉₅, D₅₀, D₂, and homogeneity index for individual CTVs and PTVs. OARs evaluated were ipsilateral and contralateral lungs, heart, spinal cord, and opposite breast. Most DVH parameters pertaining to CTVs and PTVs significantly favored IMRT. V₂₀ for ipsilateral and contralateral lungs, D₃₃ of heart and maximum dose to spinal cord favored IMRT (all p < 0.001). The mean dose to the opposite breast was significantly lesser with 3D-CRT (5.8 ± 1.8 Gy vs 2.0 ± 1.0 Gy, p < 0.001). Thus, except for the mean dose to the opposite breast, the compliance to DVH constraints applied to PTV and OARs were significantly better with IMRT. At a median follow-up of 76 months (7-91), none had locoregional failure or pulmonary or cardiac morbidity. For PMRT, requiring comprehensive irradiation to both chest wall and regional lymphatics, IMRT offers superior dosimetric advantages over 3D-CRT. This was also corroborated by long-term outcomes in these patients treated with IMRT.

Prevalence of hypothyroidism among patients with breast cancer treated with radiation to the supraclavicular field: a single-centre survey

Purpose

We investigated the prevalence of hypothyroidism (HT) in patients with breast cancer who received radiation therapy to the supraclavicular (SC) field to evaluate the effect of radiation on thyroid.

Methods

Between April 2007 and May 2016, consecutive patients with invasive breast cancer who received SC radiation were recruited. Thyroid-stimulating hormone (TSH) and free thyroxine (fT4) were measured between April and August 2016. On the basis of the radiation-planning CT images, thyroid volume was calculated and dose–volume parameters were estimated. The endpoints were the prevalence of HT as determined by high levels of TSH and low levels of fT4 in serum, and the prevalence of subclinical HT, determined by high-serum TSH and normal fT4.

Results

Among the 68 consecutive patients, 26 were excluded from evaluation (10 patients died, 6 had a history of previous thyroid disease and 10 were lost to follow-up). One (2.4%) and six (14.3%) of these patients had HT and subclinical HT, respectively, with a mean TSH level of 8.27 µU/mL. By univariate analysis, a predictive factor of HT and subclinical HT was a thyroid volume <8 cm³ (OR 6.44, 95% CI 1.14 to 36.6; p=0.043). Multivariate analysis also showed an association between thyroid volume <8 cm³ and HT or subclinical HT (OR 18.48, 95% CI 1.48 to 230.86; p=0.024).

Conclusions

The prevalence of HT in patients with breast cancer studied was relatively low. Although thyroid volume appeared to be a predictive marker of HT in this cohort, further prospective evaluation is needed.

Dosimetric analysis of intensity-modulated radiotherapy and three-dimensional conformal radiotherapy for chest wall irradiation in breast cancer patients

Background

For chest wall irradiation in breast cancer patients, three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) have made tremendous changes in treatment delivery.

Purpose

The purpose of this study is to compare the dosimetric parameters in IMRT and 3DCRT plans.

Materials and methods

IMRT and 3DCRT plans were generated for 25 randomly selected postmastectomy breast cancer patients. The prescribed dose (PD) was 50 Gray (Gy) in 25 fractions (#) at the rate of 2 Gy/# with 5#/week. Dose volume histogram was evaluated for planning target volume (PTV) coverage and dose to organs at risk (OARs). All the dosimetric parameters were compared using unpaired student’s t-test.

Results

PTV coverage was significantly better in IMRT, although the 90% of PTV was well covered by 90% of PD in all plans by both the techniques. Homogeneity index and conformity index were better in IMRT. V5 Gy and Dmean of contralateral lung, contralateral breast and heart (right side chest wall cases) were found to be lesser in 3DCRT compared with that in IMRT. However, there was no significant difference in V20 Gy of ipsilateral lung and V25 Gy of heart (left side chest wall cases) in all the plans by both the techniques.

Conclusion

Adequate target coverage was achieved by both the techniques, however, dose to OARs were lesser in 3DCRT plans as compared with that in IMRT plans. Thus, it can be concluded that 3DCRT is as efficient as IMRT for the chest wall irradiation.

Dosimetric Comparison and Evaluation of Three Radiotherapy Techniques for Use after Modified Radical Mastectomy for Locally Advanced Left-sided Breast Cancer

This study aimed to compare the post-modified radical mastectomy radiotherapy (PMRMRT) for left-sided breast cancer utilizing 3-dimensional conformal radiotherapy with field-in-field technique (3DCRT-FinF), 5-field intensity-modulated radiation therapy (5F-IMRT) and 2- partial arc volumetric modulated arc therapy (2P-VMAT). We created the 3 different PMRMRT plans for each of the ten consecutive patients. We performed Kruskal-Wallis analysis of variance (ANOVA) followed by the Dunn's-type multiple comparisons to establish a hierarchy in terms of plan quality and dosimetric benefits. P < 0.05 was considered statistically significant. Both 5F-IMRT and 2P-VMAT plans exhibited similar PTV coverage (V95%), hotspot areas (V110%) and conformity (all p > 0.05), and significantly higher PTV coverage compared with 3DCRT-FinF (both p < 0.001). In addition, 5F-IMRT plans provided significantly less heart and left lung radiation exposure than 2P-VMAT (all p < 0.05). The 3DCRT-FinF plans with accurately estimated CTV displacement exhibited enhanced target coverage but worse organs at risk (OARs) sparing compared with those plans with underestimated displacements. Our results indicate that 5F-IMRT has dosimetrical advantages compared with the other two techniques in PMRMRT for left-sided breast cancer given its optimal balance between PTV coverage and OAR sparing (especially heart sparing). Individually quantifying and minimizing CTV displacement can significantly improve dosage distribution.

Dosimetric comparison for volumetric modulated arc therapy and intensity-modulated radiotherapy on the left-sided chest wall and internal mammary nodes irradiation in treating post-mastectomy breast cancer

Background

The aim of the study was to evaluate the dosimetric benefit of applying volumetric modulated arc therapy (VMAT) on the post-mastectomy left-sided breast cancer patients, with the involvement of internal mammary nodes (IMN).

Patients and methods

The prescription dose was 50 Gy delivered in 25 fractions, and the clinical target volume included the left chest wall (CW) and IMN. VMAT plans were created and compared with intensity-modulated radiotherapy (IMRT) plans on Pinnacle treatment planning system. Comparative endpoints were dose homogeneity within planning target volume (PTV), target dose coverage, doses to the critical structures including heart, lungs and the contralateral breast, number of monitor units and treatment delivery time.

Results

VMAT and IMRT plans showed similar PTV dose homogeneity, but, VMAT provided a better dose coverage for IMN than IMRT (p = 0.017). The mean dose (Gy), V₃₀ (%) and V₁₀ (%) for the heart were 13.5 ± 5.0 Gy, 9.9% ± 5.9% and 50.2% ± 29.0% by VMAT, and 14.0 ± 5.4 Gy, 10.6% ± 5.8% and 55.7% ± 29.6% by IMRT, respectively. The left lung mean dose (Gy), V₂₀ (%), V₁₀ (%) and the right lung V₅ (%) were significantly reduced from 14.1 ± 2.3 Gy, 24.2% ± 5.9%, 42.4% ± 11.9% and 41.2% ± 12.3% with IMRT to 12.8 ± 1.9 Gy, 21.0% ± 3.8%, 37.1% ± 8.4% and 32.1% ± 18.2% with VMAT, respectively. The mean dose to the contralateral breast was 1.7 ± 1.2 Gy with VMAT and 2.3 ± 1.6 Gy with IMRT. Finally, VMAT reduced the number of monitor units by 24% and the treatment time by 53%, as compared to IMRT.

Conclusions

Compared to 5-be am step-and-shot IMRT, VMAT achieves similar or superior target coverage and a better normal tissue sparing, with fewer monitor units and shorter delivery time.

Dosimetric analysis of the brachial plexus among patients with breast cancer treated with post-mastectomy radiotherapy to the ipsilateral supraclavicular area: report of 3 cases of radiation-induced brachial plexus neuropathy

Background

The purpose of this study was to evaluate the brachial plexus (BP) dose of postmastectomy radiotherapy (PMRT) to the ipsilateral supraclavicular (ISCL) area, and report the characteristics of radiation-induced brachial plexus neuropathy (RIBPN).

Methods

The BP dose of 31 patients who received adjuvant PMRT to the ISCL area and chest wall using three-dimensional conformal radiotherapy (3DCRT) and the records of 3 patients with RIBPN were retrospectively analyzed based on the standardized Radiation Therapy Oncology Group-endorsed guidelines. The total dose to the ISCL area and chest wall was 50 Gy in 25 fractions.

Results

Patients with a higher number of removed lymph nodes (RLNs) had a higher risk of RIBPN (hazard ratio [HR]: 1.189, 95% confidence interval [CI]: 1.005-1.406, p = 0.044). In 31 patients treated with 3DCRT, the mean dose to the BP without irradiation to the ISCL area was significantly less than that with irradiation to the ISCL area (0.97 ± 0.20 vs. 44.39 ± 4.13 Gy, t = 136.75, p <0.001). In the 3DCRT plans with irradiation to the ISCL area and chest wall, the maximum dose to the BP was negatively correlated with age (r = −0.40, p = 0.026), body mass index (BMI) (r = −0.44, p = 0.014), and body weight (r = −0.45, p = 0.011). Symptoms of the 3 patients with RIBPN occurred 37–65 months after radiotherapy, and included progressive upper extremity numbness, pain, and motor disturbance. After treatment, 1 patient was stable, and the other 2 patients’ symptoms worsened.

Conclusions

The incidence of RIBPN was higher in patients with a higher number of RLNs after PMRT. The dose to the BP is primarily from irradiation of the ISCL area, and is higher in slim and young patients. Prevention should be the main focus of managing RIBPN, and the BP should be considered an organ-at-risk when designing a radiotherapy plan for the ISCL area.