The risk for developing a secondary cancer after breast radiation therapy: Comparison of photon and proton techniques

A framework for in-field and out-of-field patient specific secondary cancer risk estimates from treatment plans using the TOPAS Monte Carlo system

Objective. To allow the estimation of secondary cancer risks from radiation therapy treatment plans in a comprehensive and user-friendly Monte Carlo (MC) framework.Method. Patient planning computed tomography scans were extended superior-inferior using the International Commission on Radiological Protection's Publication 145 computational mesh phantoms and skeletal matching. Dose distributions were calculated with the TOPAS MC system using novel mesh capabilities and the digital imaging and communications in medicine radiotherapy extension interface. Finally, in-field and out-of-field cancer risk was calculated using both sarcoma and carcinoma risk models with two alternative parameter sets.Result. The TOPAS MC framework was extended to facilitate epidemiological studies on radiation-induced cancer risk. The framework is efficient and allows automated analysis of large datasets. Out-of-field organ dose was small compared to in-field dose, but the risk estimates indicate a non-negligible contribution to the total radiation induced cancer risk.Significance. This work equips the TOPAS MC system with anatomical extension, mesh geometry, and cancer risk model capabilities that make state-of-the-art out-of-field dose calculation and risk estimation accessible to a large pool of users. Furthermore, these capabilities will facilitate further refinement of risk models and sensitivity analysis of patient specific treatment options.

A comprehensive overview of radiation therapy impacts of various cancer treatments and pivotal role in the immune system

The cancer treatment landscape is significantly evolving, focusing on advanced radiation therapy methods to maximize effectiveness and minimize the adverse effects. Recognized as a pivotal component in cancer and disease treatment, radiation therapy (RT) has drawn attention in recent research that delves into its intricate interplay with inflammation and the immune response. This exploration unveils the underlying processes that significantly influence treatment outcomes. In this context, the potential advantages of combining bronchoscopy with RT across diverse clinical scenarios, alongside the targeted impact of brachytherapy, are explored. Concurrently, radiation treatments serve multifaceted roles such as DNA repair, cell elimination, and generating immune stress signaling molecules known as damage-associated molecular patterns, elucidating their effectiveness in treating various diseases. External beam RT introduces versatility by utilizing particles such as photons, electrons, protons, or carbon ions, each offering distinct advantages. Advanced RT techniques contribute to the evolving landscape, with emerging technologies like FLASH, spatially fractionated RT, and others poised to revolutionize the field. The comprehension of RT, striving for improved treatment outcomes, reduced side effects, and facilitating personalized and innovative treatments for cancer and noncancer patients. After navigating these advancements, the goal is fixed to usher in a new era in which RT is a cornerstone of precision and effectiveness in medical interventions. In summarizing the myriad findings, the review underscores the significance of understanding the differential impacts of radiation approaches on inflammation and immune modulation, offering valuable insights for developing innovative therapeutic interventions that harness the immune system in conjunction with RT.

Secondary cancer risk in six anatomical sites when using PAT, IMPT, and VMAT/IMRT radiotherapy

BACKGROUND AND PURPOSE

Compared to intensity modulated proton therapy (IMPT), proton arc therapy (PAT) is expected to improve dose conformality, delivery efficiency, and provide a more favorable LET distribution. Alternatively, the low-dose bath is potentially spread over larger volumes, which could impact the likelihood of developing a radiation-induced, secondary cancer (SC). The goal of this study was to evaluate this risk in several anatomical sites using newly developed commercial tools.

MATERIALS AND METHODS

Treatment plans encompassing six anatomical sites, five patients per site, and three techniques per patient were created using RayStation. Techniques included PAT and IMPT for protons, and either volumetrically modulated radiotherapy (VMAT) or intensity modulated radiotherapy (IMRT) for photons. Risk estimates were based on the organ-equivalent dose (OED) concept using both Schneider's mechanistic dose-response model for carcinoma induction and a linear dose-response model.

RESULTS

With few exceptions, mean and integral dose were lowest with PAT. For protons, the factor OEDIMPT/OEDPAT ranged from 0.7 to 1.8 with both the mechanistic and linear model, while for photons OEDphoton/OEDPAT ranged from 1.5 to 10 using the mechanistic model and 1.3 to using the linear model. A strong correlation was found between mean dose and OED for organs with significant repopulation/repair (high R value) and less cell death from single hit interactions (low α value).

CONCLUSION

Based on results from both mechanistic and linear risk models, the transition from IMPT to PAT should not substantially affect SC risk in patients treated with proton therapy. Additionally, when using Schneider's model, the shapes of the dose-response curves can be used as a good predictor of how SC risk will respond to shifts from intermediate dose to low dose as anticipated when moving from IMPT to PAT.

Dosimetric analysis of six whole-breast irradiation techniques in supine and prone positions

In breast cancer radiation therapy, minimizing radiation-related risks and toxicity is vital for improving life expectancy. Tailoring radiotherapy techniques and treatment positions can reduce radiation doses to normal organs and mitigate treatment-related toxicity. This study entailed a dosimetric comparison of six different external beam whole-breast irradiation techniques in both supine and prone positions. We selected fourteen breast cancer patients, generating six treatment plans in both positions per patient. We assessed target coverage and organs at risk (OAR) doses to evaluate the impact of treatment techniques and positions. Excess absolute risk was calculated to estimate potential secondary cancer risk in the contralateral breast, ipsilateral lung, and contralateral lung. Additionally, we analyzed the distance between the target volume and OARs (heart and ipsilateral lung) while considering the treatment position. The results indicate that prone positioning lowers lung exposure in X-ray radiotherapy. However, particle beam therapies (PBTs) significantly reduce the dose to the heart and ipsilateral lung regardless of the patient's position. Notably, negligible differences were observed between arc-delivery and static-delivery PBTs in terms of target conformity and OAR sparing. This study provides critical dosimetric evidence to facilitate informed decision-making regarding treatment techniques and positions.

Incidence of Nonkeratinocyte Skin Cancer After Breast Cancer Radiation Therapy

Importance

Previous studies have suggested that radiation therapy may contribute to an increased risk of subsequent nonkeratinocyte (ie, not squamous and basal cell) skin cancers.

Objective

To test the hypothesis that radiation therapy for breast cancer increases the risk of subsequent nonkeratinocyte skin cancers, particularly when these cancers are localized to the skin of the breast or trunk.

Design, Setting, and Participants

This population-based cohort study used longitudinal data from the Surveillance, Epidemiology, and End Results (SEER) Program for January 1, 2000, to December 31, 2019. The SEER database includes population-based cohort data from 17 registries. Patients with newly diagnosed breast cancer were identified and were evaluated for subsequent nonkeratinocyte skin cancer development. Data analysis was performed from January to August 2023.

Exposures

Radiation therapy, chemotherapy, or surgery for breast cancer.

Main Outcomes and Measures

The primary outcomes were standardized incidence ratios (SIRs) for subsequent nonkeratinocyte skin cancer development from 2000 to 2019 based on treatment type (radiation therapy, chemotherapy, or surgery), skin cancer site on the body, and skin cancer subtype.

Results

Among the 875 880 patients with newly diagnosed breast cancer included in this study, 99.3% were women, 51.6% were aged older than 60 years, and 50.3% received radiation therapy. A total of 11.2% patients identified as Hispanic, 10.1% identified as non-Hispanic Black, and 69.5% identified as non-Hispanic White. From 2000 to 2019, there were 3839 patients with nonkeratinocyte skin cancer, including melanoma (3419 [89.1%]), Merkel cell carcinoma (121 [3.2%]), hemangiosarcoma (104 [2.7%]), and 32 other nonkeratinocyte skin cancers (195 [5.1%]), documented to occur after breast cancer treatment. The risk of nonkeratinocyte skin cancer diagnosis after breast cancer treatment with radiation was 57% higher (SIR, 1.57 [95% CI, 1.45-1.7]) than that of the general population when considering the most relevant site: the skin of the breast or trunk. When risk at this site was stratified by skin cancer subtype, the SIRs for melanoma and hemangiosarcoma were both statistically significant at 1.37 (95% CI, 1.25-1.49) and 27.11 (95% CI, 21.6-33.61), respectively. Receipt of radiation therapy was associated with a greater risk of nonkeratinocyte skin cancer compared with chemotherapy and surgical interventions.

Conclusions and Relevance

In this study of patients with breast cancer, an increased risk of melanoma and hemangiosarcoma after breast cancer treatment with radiation therapy was observed. Although occurrences of nonkeratinocyte skin cancers are rare, physicians should be aware of this elevated risk to help inform follow-up care.

Evaluation of conventional IMRT and VMAT strategies for postmastectomy radiation therapy after immediate implant-based reconstruction using the new ESTRO-ACROP contouring guidelines

This study evaluated the usability of conventional templates based on the new contour guidelines of the European Society of Radiation and Oncology and Advisory Committee in Radiation Oncology Practice (ESTRO-ACROP) for treatment plans of postmastectomy radiotherapy after immediate implant-based reconstruction. Intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans generated with two different treatment planning systems (TPSs, Eclipse and Monaco) were examined. Six computed tomography scans of patients aged 35-54 years were retrospectively analysed who had undergone mastectomy and breast reconstruction using silicone implants after being diagnosed with left breast cancer. Six radiation oncologists participated in this study, and each of them contoured the target volume of one left breast using conventional contour (CTV-CONV) and new contour (CTV-ESTRO) methods. This study showed that compared with CTV-CONV, using CTV-ESTRO with objectives and cost functions similar to those of TPSs worsened the target volume coverage and increased the total number of monitor units. Considering the organs at risk, CTV-ESTRO tended to increase the mean dose delivered to the contralateral lung. It is concluded that the approach used for the new ESTRO-ACROP contour method cannot be applied in a manner similar to that for the conventional breast contour method, implying that the new ESTRO-ACROP contour method may require more time for improving plans for a given treatment.

Radiation Therapy for Stage IIA/B Seminoma: Modeling Secondary Cancer Risk for Protons and VMAT versus 3D Photons

Radiation therapy (RT) is an effective treatment for stage IIA and select stage IIB seminomas. However, given the long life expectancy of seminoma patients, there are concerns about the risk of secondary cancers from RT. This study assessed differences in secondary cancer risk for stage II seminoma patients following proton pencil-beam scanning (PBS) and photon VMAT, compared to 3D conformal photon RT. Ten seminoma patients, five with a IIA staging who received 30 GyRBE and five with a IIB staging who received 36 GyRBE, had three RT plans generated. Doses to organs at risk (OAR) were evaluated, and secondary cancer risks were calculated as the Excess Absolute Risk (EAR) and Lifetime Attributable Risk (LAR). PBS reduced the mean OAR dose by 60% on average compared to 3D, and reduced the EAR and LAR for all OAR, with the greatest reductions seen for the bowel, liver, and stomach. VMAT reduced high doses but increased the low-dose bath, leading to an increased EAR and LAR for some OAR. PBS provided superior dosimetric sparing of OAR compared to 3D and VMAT in stage II seminoma cases, with models demonstrating that this may reduce secondary cancer risk. Therefore, proton therapy shows the potential to reduce acute and late side effects of RT for this population.

Postmastectomy radiotherapy in breast reconstruction: Current controversies and trends

Breast cancer is the most common cancer among women worldwide. Postmastectomy radiotherapy (PMRT) is an essential component of combined therapy for early-stage, high-risk breast cancer. Breast reconstruction (BR) is often considered for patients with breast cancer who have undergone mastectomy. There has been a considerable amount of discussion about the optimal approach to combining PMRT with BR in the treatment of breast cancer. PMRT may increase the risk of complications and prevent good aesthetic results after BR, while BR may increase the complexity of PMRT and the radiation dose to surrounding normal tissues. The purpose of this review is to give a broad overview and summary of the current controversies and trends in PMRT and BR in the context of the most recent literature available.

Exploring Helium Ions' Potential for Post-Mastectomy Left-Sided Breast Cancer Radiotherapy

Proton therapy presents a promising modality for treating left-sided breast cancer due to its unique dose distribution. Helium ions provide increased conformality thanks to a reduced lateral scattering. Consequently, the potential clinical benefit of both techniques was explored. An explorative treatment planning study involving ten patients, previously treated with VMAT (Volumetric Modulated Arc Therapy) for 50 Gy in 25 fractions for locally advanced, node-positive breast cancer, was carried out using proton pencil beam therapy with a fixed relative biological effectiveness (RBE) of 1.1 and helium therapy with a variable RBE described by the mMKM (modified microdosimetric kinetic model). Results indicated that target coverage was improved with particle therapy for both the clinical target volume and especially the internal mammary lymph nodes compared to VMAT. Median dose value analysis revealed that proton and helium plans provided lower dose on the left anterior descending artery (LAD), heart, lungs and right breast than VMAT. Notably, helium therapy exhibited improved ipsilateral lung sparing over protons. Employing NTCP models as available in the literature, helium therapy showed a lower probability of grade ≤ 2 radiation pneumonitis (22% for photons, 5% for protons and 2% for helium ions), while both proton and helium ions reduce the probability of major coronary events with respect to VMAT.

Proton Beam Therapy for Breast Cancer

Given the radiobiological and physical properties of the proton, proton beam therapy has the potential to be advantageous for many patients compared with conventional radiotherapy by limiting toxicity and improving patient outcomes in specific breast cancer scenarios.

Proton Therapy in Breast Cancer: A Review of Potential Approaches for Patient Selection

Proton radiotherapy may be a compelling technical option for the treatment of breast cancer due to its unique physical property known as the "Bragg peak." This feature offers distinct advantages, promising superior dose conformity within the tumor area and reduced radiation exposure to surrounding healthy tissues, enhancing the potential for better treatment outcomes. However, proton therapy is accompanied by inherent challenges, primarily higher costs and limited accessibility when compared to well-developed photon irradiation. Thus, in clinical practice, it is important for radiation oncologists to carefully select patients before recommendation of proton therapy to ensure the transformation of dosimetric benefits into tangible clinical benefits. Yet, the optimal indications for proton therapy in breast cancer patients remain uncertain. While there is no widely recognized methodology for patient selection, numerous attempts have been made in this direction. In this review, we intended to present an inspiring summarization and discussion about the current practices and exploration on the approaches of this treatment decision-making process in terms of treatment-related side-effects, tumor control, and cost-efficiency, including the normal tissue complication probability (NTCP) model, the tumor control probability (TCP) model, genomic biomarkers, cost-effectiveness analyses (CEAs), and so on. Additionally, we conducted an evaluation of the eligibility criteria in ongoing randomized controlled trials and analyzed their reference value in patient selection. We evaluated the pros and cons of various potential patient selection approaches and proposed possible directions for further optimization and exploration. In summary, while proton therapy holds significant promise in breast cancer treatment, its integration into clinical practice calls for a thoughtful, evidence-driven strategy. By continuously refining the patient selection criteria, we can harness the full potential of proton radiotherapy while ensuring maximum benefit for breast cancer patients.

Postmastectomy Intensity Modulated Proton Therapy: 5-Year Oncologic and Patient-Reported Outcomes

PURPOSE

To report oncologic, physician-assessed, and patient-reported outcomes (PROs) for a group of women homogeneously treated with modern, skin-sparing multifield optimized pencil-beam scanning proton (intensity modulated proton therapy [IMPT]) postmastectomy radiation therapy (PMRT).

METHODS AND MATERIALS

We reviewed consecutive patients who received unilateral, curative-intent, conventionally fractionated IMPT PMRT between 2015 and 2019. Strict constraints were applied to limit the dose to the skin and other organs at risk. Five-year oncologic outcomes were analyzed. Patient-reported outcomes were evaluated as part of a prospective registry at baseline, completion of PMRT, and 3 and 12 months after PMRT.

RESULTS

A total of 127 patients were included. One hundred nine (86%) received chemotherapy, among whom 82 (65%) received neoadjuvant chemotherapy. The median follow-up was 4.1 years. Five-year locoregional control was 98.4% (95% CI, 93.6-99.6), and overall survival was 87.9% (95% CI, 78.7-96.5). Acute grade 2 and 3 dermatitis was seen in 45% and 4% of patients, respectively. Three patients (2%) experienced acute grade 3 infection, all of whom had breast reconstruction. Three late grade 3 adverse events occurred: morphea (n = 1), infection (n = 1), and seroma (n = 1). There were no cardiac or pulmonary adverse events. Among the 73 patients at risk for PMRT-associated reconstruction complications, 7 (10%) experienced reconstruction failure. Ninety-five patients (75%) enrolled in the prospective PRO registry. The only metrics to increase by >1 point were skin color (mean change: 5) and itchiness (2) at treatment completion and tightness/pulling/stretching (2) and skin color (2) at 12 months. There was no significant change in the following PROs: bleeding/leaking fluid, blistering, telangiectasia, lifting, arm extension, or bending/straightening the arm.

CONCLUSIONS

With strict dose constraints to skin and organs at risk, postmastectomy IMPT was associated with excellent oncologic outcomes and PROs. Rates of skin, chest wall, and reconstruction complications compared favorably to previous proton and photon series. Postmastectomy IMPT warrants further investigation in a multi-institutional setting with careful attention to planning techniques.

Trends in Radiation Dose to the Contralateral Breast During Breast Cancer Radiation Therapy

Over 4 million survivors of breast cancer live in the United States, 35% of whom were treated before 2009. Approximately half of patients with breast cancer receive radiation therapy, which exposes the untreated contralateral breast to radiation and increases the risk of a subsequent contralateral breast cancer (CBC). Radiation oncology has strived to reduce unwanted radiation dose, but it is unknown whether a corresponding decline in actual dose received to the untreated contralateral breast has occurred. The purpose of this study was to evaluate trends in unwanted contralateral breast radiation dose to inform risk assessment of second primary cancer in the contralateral breast for long-term survivors of breast cancer. Individually estimated radiation absorbed doses to the four quadrants and areola central area of the contralateral breast were estimated for 2,132 women treated with radiation therapy for local/regional breast cancers at age <55 years diagnosed between 1985 and 2008. The two inner quadrant doses and two outer quadrant doses were averaged. Trends in dose to each of the three areas of the contralateral breast were evaluated in multivariable models. The population impact of reducing contralateral breast dose on the incidence of radiation-associated CBC was assessed by estimating population attributable risk fraction (PAR) in a multivariable model. The median dose to the inner quadrants of the contralateral breast was 1.70 Gy; to the areola, 1.20 Gy; and to the outer quadrants, 0.72 Gy. Ninety-two percent of patients received ≥1 Gy to the inner quadrants. For each calendar year of diagnosis, dose declined significantly for each location, most rapidly for the inner quadrants (0.04 Gy/year). Declines in dose were similar across subgroups defined by age at diagnosis and body mass index. The PAR for CBC due to radiation exposure >1 Gy for women <40 years of age was 17%. Radiation dose-reduction measures have reduced dose to the contralateral breast during breast radiation therapy. Reducing the dose to the contralateral breast to <1 Gy could prevent an estimated 17% of subsequent radiation-associated CBCs for women treated under 40 years of age. These dose estimates inform CBC surveillance for the growing number of breast cancer survivors who received radiation therapy as young women in recent decades. Continued reductions in dose to the contralateral breast could further reduce the incidence of radiation-associated CBC.

Proton Therapy in the Adolescent and Young Adult Population

BACKGROUND

Adolescent and young adult cancer patients are at high risk of developing radiation-associated side effects after treatment. Proton beam radiation therapy might reduce the risk of these side effects for this population without compromising treatment efficacy.

METHODS

We review the current literature describing the utility of proton beam radiation therapy in the treatment of central nervous system tumors, sarcomas, breast cancer and Hodgkin lymphoma for the adolescent and young adult cancer population.

RESULTS

Proton beam radiation therapy has utility for the treatment of certain cancers in the young adult population. Preliminary data suggest reduced radiation dose to normal tissues, which might reduce radiation-associated toxicities. Research is ongoing to further establish the role of proton therapy in this population.

CONCLUSION

This report highlights the potential utility of proton beam radiation for certain adolescent young adult cancers, especially with reducing radiation doses to organs at risk and thereby potentially lowering risks of certain treatment-associated toxicities.

Comparison of intraoperative radiotherapy as a boost vs. simultaneously integrated boosts after breast-conserving therapy for breast cancer

Background

Currently, there are no data from randomized trials on the use of intraoperative radiotherapy (IORT) as a tumor bed boost in women at high risk of local recurrence. The aim of this retrospective analysis was to compare the toxicity and oncological outcome of IORT or simultaneous integrated boost (SIB) with conventional external beam radiotherapy (WBI) after breast conserving surgery (BCS).

Methods

Between 2009 and 2019, patients were treated with a single dose of 20 Gy IORT with 50 kV photons, followed by WBI 50 Gy in 25 or 40.05 in 15 fractions or WBI 50 Gy with SIB up to 58.80-61.60 Gy in 25-28 fractions. Toxicity was compared after propensity score matching. Overall survival (OS) and progression-free survival (PFS) were calculated using the Kaplan-Meier method.

Results

A 1:1 propensity-score matching resulted in an IORT + WBI and SIB + WBI cohort of 60 patients, respectively. The median follow-up for IORT + WBI was 43.5 vs. 32 months in the SIB + WBI cohort. Most women had a pT1c tumor: IORT group 33 (55%) vs. 31 (51.7%) SIB group (p = 0.972). The luminal-B immunophenotype was most frequently diagnosed in the IORT group 43 (71.6%) vs. 35 (58.3%) in the SIB group (p = 0.283). The most reported acute adverse event in both groups was radiodermatitis. In the IORT cohort, radiodermatitis was grade 1: 23 (38.3%), grade 2: 26 (43.3%), and grade 3: 6 (10%) vs. SIB cohort grade 1: 3 (5.1%), grade 2: 21 (35%), and grade 3: 7 (11.6%) without a meaningful difference (p = 0.309). Fatigue occurred more frequently in the IORT group (grade 1: 21.7% vs. 6.7%; p = 0.041). In addition, intramammary lymphedema grade 1 occurred significantly more often in the IORT group (11.7% vs. 1.7%; p = 0.026). Both groups showed comparable late toxicity. The 3- and 5-year local control (LC) rates were each 98% in the SIB group vs. 98% and 93% in the IORT group (LS: log rank p = 0.717).

Conclusion

Tumor bed boost using IORT and SIB techniques after BCS shows excellent local control and comparable late toxicity, while IORT application exhibits a moderate increase in acute toxicity. These data should be validated by the expected publication of the prospective randomized TARGIT-B study.

Voluntary versus mechanically-induced deep inspiration breath-hold for left breast cancer: A randomized controlled trial

BACKGROUND AND PURPOSE

Deep inspiration breath-hold (DIBH) protects critical organs-at-risk (OARs) for adjuvant breast radiotherapy. Guidance systems e.g. surface guided radiation therapy (SGRT) improve the positional breast reproducibility and stability during DIBH. In parallel, OARs sparing with DIBH is enhanced through different techniques e.g. prone position, continuous positive airway pressure (CPAP). By inducing repeated DIBH with the same level of positive pressure, mechanically-assisted and non-invasive ventilation (MANIV) could potentially combine these DIBH optimizations.

MATERIALS AND METHODS

We conducted a randomized, open-label, multicenter and single-institution non-inferiority trial. Sixty-six patients eligible for adjuvant left whole-breast radiotherapy in supine position were equally assigned between mechanically-induced DIBH (MANIV-DIBH) and voluntary DIBH guided by SGRT (sDIBH). The co-primary endpoints were positional breast stability and reproducibility with a non-inferiority margin of 1 mm. Secondary endpoints were tolerance assessed daily via validated scales, treatment time, dose to OARs and their inter-fraction positional reproducibility.

RESULTS

Differences between both arms for positional breast reproducibility and stability occurred at a sub-millimetric level (p < 0.001 for non-inferiority). The left anterior descending artery near-max dose (14,6 ± 12,0 Gy vs. 7,7 ± 7,1 Gy, p = 0,018) and mean dose (5,0 ± 3,5 Gy vs. 3,0 ± 2,0 Gy, p = 0,009) were improved with MANIV-DIBH. The same applied for the V_5Gy of the left ventricle (2,4 ± 4,1 % vs. 0,8 ± 1,6 %, p = 0,001) as well as for the left lung V_20Gy (11,4 ± 2,8 % vs. 9,7 ± 2,7 %, p = 0,019) and V_30Gy (8,0 ± 2,6 % vs. 6,5 ± 2,3 %, p = 0,0018). Better heart's inter-fraction positional reproducibility was observed with MANIV-DIBH. Tolerance and treatment time were similar.

CONCLUSION

Mechanical ventilation provides the same target irradiation accuracy as with SGRT while better protecting and repositioning OARs.

A dose planning study for cardiac and lung dose sparing techniques in left breast cancer radiotherapy: Can free breathing helical tomotherapy be considered as an alternative for deep inspiration breath hold?

Purpose

To investigate the possibility to be able to offer left sided breast cancer patients, not suitable for DIBH, an organ at risk saving treatment.

Materials and Methods

Twenty patients receiving radiotherapy for left breast cancer in DIBH were enrolled in the study. Planning CT scans were acquired in the same supine treatment position in FB and DIBH. 3DCRT_DIBH plans were designed and optimized using two parallel opposed tangent beams (with some additional segments) for the breast and chest wall and anterior-posterior fields for regional lymph nodes irradiation. Additionally, FB helical tomotherapy plans were optimized to minimize heart and lung dose. All forty plans were optimized with at least 95% of the total CTV covered by the 95% of prescribed dose of 50 Gy in 25 fractions.

Results

HT_FB plans showed significantly better dose homogeneity and conformity compared to the 3DCRT_DIBH specially for regional nodal irradiation. The heart mean dose was almost comparable in 3DCRT_DIBH and HT_FB while the volume (%) of the heart receiving 25 Gy had a statistically significant reduction from 7.90 ± 3.33 in 3DCRT_DIBH to 0.88 ± 0.66 in HT_FB. HT_FB was also more effective in left descending artery (LAD) mean dose reduction about 100% from 30.83 ± 9.2 Gy to 9.7 ± 3.1. The ipsilateral lung volume receiving 20 Gy has a further reduction of 43 % in HT_FB compared with 3DCRT_DIBH. For low dose comparison, 3DCRT_DIBH was superior for contralateral organ sparing compared to the HT_FB due to the limited angle for dose delivery.

Conclusion

For patients who cannot be a candidate for DIBH for any reason, HT in free breathing may be a good alternative and provides heart and ipsilateral lung dose sparing, however with the cost of increased dose to contralateral breast and lung.

Critical Evaluation of Secondary Cancer Risk After Breast Radiation Therapy with Hybrid Radiotherapy Techniques

Background

As hybrid radiotherapy technique can effectively balance dose distribution between targets and organs, it is necessary to evaluate the late effects related to radiotherapy. The aim of the study was to calculate and provide individual estimates of the risks for hybrid radiotherapy techniques in breast cancer patients.

Methods

Whole-breast irradiation was performed in 43 breast cancer patients by using 3D conformal, intensity-modulated and hybrid techniques. The excess absolute risk (EAR), lifetime attributable risk (LAR) and normal tissue complication probability (NTCP) were calculated to estimate risks in organs. The risk variability in contralateral breast was assessed by using the patient's anatomic parameters.

Results

Compared with IMRT and FinF, hybrid techniques achieved satisfactory dose distribution and comparable or lower estimated risks in organs. The LAR was estimated to be up to 0.549% for contralateral lung with advantages of tangential techniques over H-VMAT. For ipsilateral lung, the LAR was estimated to be up to 9.021%, but lower in H-VMAT and FinF without significant difference. The risk of thyroid was negligible in overall estimation. For contralateral breast, the LAR was estimated to be up to 0.865% with advantages of MH-IMRT and H-VMAT over TF-IMRT. The fraction of individual variability could be explained by using anatomic parameters of minimum breast distance (MBD) and minimum target concave angle (θ_MTCA). NTCP for all analyzed endpoints was significantly higher in TF-IMRT relative to FinF and hybrid techniques, while TH-IMRT and H-VMAT were presenting lower toxicity risk. However, MH-IMRT presented a higher probability of toxicity in lung. For most cases, H-VMAT demonstrated a benefit for contralateral breast, heart and lung sparing.

Conclusion

The optimal treatment should be performed individually according to anatomic parameters and balances between EAR and NTCP. Individual assessment may assist in achieving optimal balances between targets and organs as well as supporting clinical decision-making processes.

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.

Particle Therapy: Clinical Applications and Biological Effects

Particle therapy is a developing area of radiotherapy, mostly involving the use of protons, neutrons and carbon ions for cancer treatment. The reduction of side effects on healthy tissues in the peritumoral area is an important advantage of particle therapy. In this review, we analyze state-of-the-art particle therapy, as compared to conventional photon therapy, to identify clinical benefits and specify the mechanisms of action on tumor cells. Systematization of published data on particle therapy confirms its successful application in a wide range of cancers and reveals a variety of biological effects which manifest at the molecular level and produce the particle therapy-specific molecular signatures. Given the rapid progress in the field, the use of particle therapy holds great promise for the near future.

Knowledge-based DVH estimation and optimization for breast VMAT plans with and without avoidance sectors

BACKGROUND

To analyze RapidPlan knowledge-based models for DVH estimation of organs at risk from breast cancer VMAT plans presenting arc sectors en-face to the breast with zero dose rate, feature imposed during the optimization phase (avoidance sectors AS).

METHODS

CT datasets of twenty left breast patients in deep-inspiration breath-hold were selected. Two VMAT plans, PartArc and AvoidArc, were manually generated with double arcs from ~ 300 to ~ 160°, with the second having an AS en-face to the breast to avoid contralateral breast and lung direct irradiation. Two RapidPlan models were generated from the two plan sets. The two models were evaluated in a closed loop to assess the model performance on plans where the AS were selected or not in the optimization.

RESULTS

The PartArc plans model estimated DVHs comparable with the original plans. The AvoidArc plans model estimated a DVH pattern with two steps for the contralateral structures when the plan does not contain the AS selected in the optimization phase. This feature produced mean doses of the contralateral breast, averaged over all patients, of 0.4 ± 0.1 Gy, 0.6 ± 0.2 Gy, and 1.1 ± 0.2 Gy for the AvoidArc plan, AvoidArc model estimation, RapidPlan generated plan, respectively. The same figures for the contralateral lung were 0.3 ± 0.1 Gy, 1.6 ± 0.6 Gy, and 1.2 ± 0.5 Gy. The reason was found in the possible incorrect information extracted from the model training plans due to the lack of knowledge about the AS. Conversely, in the case of plans with AS set in the optimization generated with the same AvoidArc model, the estimated and resulting DVHs were comparable. Whenever the AvoidArc model was used to generate DVH estimation for a plan with AS, while the optimization was made on the plan without the AS, the optimizer evidentiated the limitation of a minimum dose rate of 0.2 MU/°, resulting in an increased dose to the contralateral structures respect to the estimation.

CONCLUSIONS

The RapidPlan models for breast planning with VMAT can properly estimate organ at risk DVH. Attention has to be paid to the plan selection and usage for model training in the presence of avoidance sectors.

[Risk Factors and Pathogenic Mechanism for Secondary Primary Lung Cancer in Breast Cancer Patients: A Review]

Breast cancer and lung cancer are the two most common malignancies in China. With the continuous improvement of breast cancer diagnosis and treatment technology, the survival time of breast cancer patients has been prolonged, and the number of breast cancer patients with second primary lung cancer (SPLC) has increased. In addition, breast cancer is the most common primary cancer in female patients with SPLC, and SPLC is the main cause of death in this population. More and more physicians pay attention to this clinical phenomenon. This paper summarized the risk and risk factors of SPLC in breast cancer patients, and elaborated its pathogenesis, in order to provide a theoretical basis for the clinical management of breast cancer patients and achieve accurate early intervention as soon as possible.
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Non-Oncological Radiotherapy: A Review of Modern Approaches

Despite being usually delivered in oncological patients, radiotherapy can be used as a successful treatment for several non-malignant disorders. Even though this use of radiotherapy has been scarcely investigated since the 1950s, more recent interest has actually shed the light on this approach. Thus, the aim of this narrative review is to analyze the applications of non-oncological radiotherapy in different disorders. Key references were derived from a PubMed query. Hand searching and clinicaltrials.gov were also used. This review contains a narrative report and a critical discussion of non-oncological radiotherapy approaches. In conclusion, non-oncological radiotherapy is a safe and efficacious approach to treat several disorders that needs to be further investigated and used in clinical practice.

Modelling the HPRT-gene mutation induction of particle beams: systematic in vitro data collection, analysis and microdosimetric kinetic model implementation

Objective. Since the early years, particle therapy treatments have been associated with concerns for late toxicities, especially secondary cancer risk (SCR). Nowadays, this concern is related to patients for whom long-term survival is expected (e.g. breast cancer, lymphoma, paediatrics). In the aim to contribute to this research, we present a dedicated statistical and modelling analysis aiming at improving our understanding of the RBE for mutation induction ( RBE M ˜ ) for different particle species. Approach. We built a new database based on a systematic collection of RBE data for mutation assays of the gene encoding for the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase from literature (105 entries, distributed among 3 cell lines and 16 particle species). The data were employed to perform statistical and modelling analysis. For the latter, we adapted the microdosimetric kinetic model (MKM) to describe the mutagenesis in analogy to lethal lesion induction. Main results. Correlation analysis between RBE for survival (RBES) and RBE M ˜ reveals significant correlation between these two quantities (ρ = 0.86, p < 0.05). The correlation gets stronger when looking at subsets of data based on cell line and particle species. We also show that the MKM can be successfully employed to describe RBE M ˜ , obtaining comparably good agreement with the experimental data. Remarkably, to improve the agreement with experimental data the MKM requires, consistently in all the analysed cases, a reduced domain size for the description of mutation induction compared to that adopted for survival. Significance. We were able to show that RBES and RBE M ˜ are strongly related quantities. We also showed for the first time that the MKM could be successfully applied to the description of mutation induction, representing an endpoint different from the more traditional cell killing. In analogy to the RBES, RBE M ˜ can be implemented into treatment planning system evaluations.

Particle Therapy for Breast Cancer

Particle therapy has received increasing attention in the treatment of breast cancer due to its unique physical properties that may enhance patient quality of life and reduce the late effects of therapy. In this review, we will examine the rationale for the use of proton and carbon therapy in the treatment of breast cancer and highlight their potential for sparing normal tissue injury. We will discuss the early dosimetric and clinical studies that have been pursued to date in this domain before focusing on the remaining open questions limiting the widespread adoption of particle therapy.

Hadrontherapy techniques for breast cancer

Radiotherapy plays a key role in breast cancer treatment, and recent technical advances have been made to improve the therapeutic window by limiting the risk of radiation-induced toxicity or by increasing tumor control. Hadrontherapy is a form a radiotherapy relying on particle beams; compared with photon beams, particle beams have specific physical, radiobiological and immunological properties, which can be valuable in diverse clinical situations. To date, available hadrontherapy techniques for breast cancer irradiation include proton therapy, carbon ion radiation therapy, fast neutron therapy and boron neutron capture therapy. This review analyzes the current rationale and level of evidence for each hadrontherapy technique for breast cancer.

Target coverage and cardiopulmonary sparing with the updated ESTRO-ACROP contouring guidelines for postmastectomy radiation therapy after breast reconstruction: a treatment planning study using VMAT and proton PBS techniques

BACKGROUND

The European Society for Therapeutic Radiology and Oncology Advisory Committee in Radiation Oncology Practice (ESTRO-ACROP) recently released new contouring guidelines for postmastectomy radiation therapy (PMRT) after implant-based reconstruction (IBR). As compared to prior ESTRO guidelines, the new guidelines primarily redefined the chest wall (CW) target to exclude the breast prosthesis. In this study, we assessed the impact of these changes on treatment planning and dosimetric outcomes using volumetric-modulated arc therapy (VMAT) and proton pencil-beam scanning (PBS) therapy.

METHODS

We performed a treatment planning study of 10 women with left-sided breast cancer who underwent PMRT after IBR. All target structures were delineated first using standard (ESTRO) breast contouring guidelines and then separately using the new (ESTRO-ACROP) guidelines. Standard organs-at-risk (OARs) and cardiac substructures were contoured. Four sets of plans were generated: (1) VMAT using standard ESTRO contours, (2) VMAT using new ESTRO-ACROP contours, (3) PBS using standard contours, and (4) PBS using new contours.

RESULTS

VMAT plans using the new ESTRO-ACROP guidelines resulted in modest sparing of the left anterior descending coronary artery (LAD) (mean dose: 6.99 Gy standard ESTRO vs. 6.08 Gy new ESTRO-ACROP, p = 0.010) and ipsilateral lung (V₂₀: 21.66% vs 19.45%, p = 0.017), but similar exposure to the heart (mean dose: 4.6 Gy vs. 4.3 Gy, p = 0.513), with a trend toward higher contralateral lung (V₅: 31.0% vs 35.3%, p = 0.331) and CW doses (V₅: 31.9% vs 35.4%, p = 0.599). PBS plans using the new guidelines resulted in further sparing of the heart (mean dose: 1.05 Gy(RBE) vs. 0.54 Gy(RBE), p < 0.001), nearly all cardiac substructures (LAD mean dose: 2.01 Gy(RBE) vs. 0.66 Gy(RBE), p < 0.001), and ipsilateral lung (V₂₀: 16.22% vs 6.02%, p < 0.001).

CONCLUSIONS

PMRT after IBR using the new ESTRO-ACROP contouring guidelines with both VMAT and PBS therapy is associated with significant changes in exposure to several cardiopulmonary structures.

Proton Therapy for Breast Cancer: A Consensus Statement From the Particle Therapy Cooperative Group Breast Cancer Subcommittee

Radiation therapy plays an important role in the multidisciplinary management of breast cancer. Recent years have seen improvements in breast cancer survival and a greater appreciation of potential long-term morbidity associated with the dose and volume of irradiated organs. Proton therapy reduces the dose to nontarget structures while optimizing target coverage. However, there remain additional financial costs associated with proton therapy, despite reductions over time, and studies have yet to demonstrate that protons improve upon the treatment outcomes achieved with photon radiation therapy. There remains considerable heterogeneity in proton patient selection and techniques, and the rapid technological advances in the field have the potential to affect evidence evaluation, given the long latency period for breast cancer radiation therapy recurrence and late effects. In this consensus statement, we assess the data available to the radiation oncology community of proton therapy for breast cancer, provide expert consensus recommendations on indications and technique, and highlight ongoing trials' cost-effectiveness analyses and key areas for future research.

Dosimetric Comparison of Radiation Techniques for Comprehensive Regional Nodal Radiation Therapy for Left-Sided Breast Cancer: A Treatment Planning Study

Purpose

How modern cardiac sparing techniques and beam delivery systems using advanced x-ray and proton beam therapy (PBT) can reduce incidental radiation exposure doses to cardiac and pulmonary organs individually or in any combination is poorly investigated.

Methods

Among 15 patients with left-sided breast cancer, partial wide tangential 3D-conformal radiotherapy (3DCRT) delivered in conventional fractionation (CF) or hypofractionated (HF) schedules; PBT delivered in a CF schedule; and volumetric modulated arc therapy (VMAT) delivered in an HF schedule, each under continuous positive airway pressure (CPAP) and free-breathing (FB) conditions, were examined. Target volume coverage and doses to organs-at-risk (OARs) were calculated for each technique. Outcomes were compared with one-way analysis of variance and the Bonferroni test, with p-values <0.05 considered significant.

Results

Target volume coverage was within acceptable levels in all interventions, except for the internal mammary lymph node D95 (99% in PBT, 90% in VMAT-CPAP, 84% in VMAT-FB, and 74% in 3DCRT). The mean heart dose (MHD) was the lowest in PBT (<1 Gy) and VMAT-CPAP (2.2 Gy) and the highest in 3DCRT with CF/FB (7.8 Gy), respectively. The mean lung dose (MLD) was the highest in 3DCRT-CF-FB (20 Gy) and the lowest in both VMAT-HF-CPAP and PBT (approximately 5-6 Gy). VMAT-HF-CPAP and PBT delivered a comparable maximum dose to the left ascending artery (7.2 and 6.13 Gy, respectively).

Conclusions

Both proton and VMAT in combination with CPAP can minimize the radiation exposure to heart and lung with optimal target coverage in regional RT for left-sided breast cancer. The clinical relevance of these differences is yet to be elucidated. Continued efforts are needed to minimize radiation exposures during RT treatment to maximize its therapeutic index.

Estimating the second primary cancer risk due to proton therapy compared to hybrid IMRT for left sided breast cancer

BACKGROUND AND PURPOSE

Proton therapy has been proposed as a technique to improve the long-term quality of life of breast cancer patients. This is due to its ability to reduce the dose to healthy tissue compared to conventional X-ray therapy. The aim of this study was to investigate the risk of secondary carcinogenesis due to proton therapy compared to hybrid IMRT for breast treatments.

MATERIAL AND METHODS

In this study, the Pinnacle treatment planning system was used to simulate treatment plans for 15 female left-sided whole breast cancer patients with deep inspiration breath hold scans. Two treatment plans were generated for each patient: hybrid intensity modulated radiotherapy (h-IMRT) and intensity modulated proton therapy (IMPT). Using the dose-volume histograms (DVHs) from these plans, the mean lifetime attributed risk (LAR) for both lungs and the contralateral breast were evaluated using the BEIR VII and Schneider full risk models.

RESULTS

The results from both risk models show lower LAR estimates for the IMPT treatment plan compared to the h-IMRT treatment plan. This result was observed for all organs of interest and was consistent amongst the two separate risk models. For both treatment plans, the organs from most to least at risk were: ipsilateral lung, contralateral breast, and contralateral lung. In all cases, the risk estimated via the BEIR VII model was higher that the Schneider full risk model.

CONCLUSION

The use of proton therapy for breast treatments leads to reduced risk estimates for secondary carcinogenesis. Therefore, proton therapy shows promise in improving the long term treatment outcome of breast patients.

The impact of variable relative biological effectiveness in proton therapy for left-sided breast cancer when estimating normal tissue complications in the heart and lung

The aim of this study was to evaluate the clinical impact of relative biological effectiveness (RBE) variations in proton beam scanning treatment (PBS) for left-sided breast cancer versus the assumption of a fixed RBE of 1.1, particularly in the context of comparisons with photon-based three-dimensional conformal radiotherapy (3DCRT) and volumetric modulated arc therapy (VMAT). Ten patients receiving radiation treatment to the whole breast/chest wall and regional lymph nodes were selected for each modality. For PBS, the dose distributions were re-calculated with both a fixed RBE and a variable RBE using an empirical RBE model. Dosimetric indices based on dose-volume histogram analysis were calculated for the entire heart wall, left anterior descending artery (LAD) and left lung. Furthermore, normal tissue toxicity probabilities for different endpoints were evaluated. The results show that applying a variable RBE significantly increases the RBE-weighted dose and consequently the calculated dosimetric indices increases for all organs compared to a fixed RBE. The mean dose to the heart and the maximum dose to the LAD and the left lung are significantly lower for PBS assuming a fixed RBE compared to 3DCRT. However, no statistically significant difference is seen when a variable RBE is applied. For a fixed RBE, lung toxicities are significantly lower compared to 3DCRT but when applying a variable RBE, no statistically significant differences are noted. A disadvantage is seen for VMAT over both PBS and 3DCRT. One-to-one plan comparison on 8 patients between PBS and 3DCRT shows similar results. We conclude that dosimetric analysis for all organs and toxicity estimation for the left lung might be underestimated when applying a fixed RBE for protons. Potential RBE variations should therefore be considered as uncertainty bands in outcome analysis.

Clinical commissioning of intensity-modulated proton therapy systems: Report of AAPM Task Group 185

Proton therapy is an expanding radiotherapy modality in the United States and worldwide. With the number of proton therapy centers treating patients increasing, so does the need for consistent, high-quality clinical commissioning practices. Clinical commissioning encompasses the entire proton therapy system's multiple components, including the treatment delivery system, the patient positioning system, and the image-guided radiotherapy components. Also included in the commissioning process are the x-ray computed tomography scanner calibration for proton stopping power, the radiotherapy treatment planning system, and corresponding portions of the treatment management system. This commissioning report focuses exclusively on intensity-modulated scanning systems, presenting details of how to perform the commissioning of the proton therapy and ancillary systems, including the required proton beam measurements, treatment planning system dose modeling, and the equipment needed.

Proton pencil beam scanning reduces secondary cancer risk in breast cancer patients with internal mammary chain involvement compared to photon radiotherapy

Purpose

Proton pencil beam scanning (PBS) represents an interesting option for the treatment of breast cancer (BC) patients with nodal involvement. Here we compare tangential 3D-CRT and VMAT to PBS proton therapy (PT) in terms of secondary cancer risk (SCR) for the lungs and for contralateral breast.

Methods

Five BC patients including supraclavicular (SVC) nodes in the target (Group 1) and five including SVC plus internal-mammary-nodes (IMNs, Group 2) were considered. The Group 1 patients were planned by PT versus tangential 3D-CRT in free-breathing (FB). The Group 2 patients were planned by PT versus VMAT considering both FB and deep-inspiration breath hold (DIBH) irradiation. The prescription dose to the target volume was 50 Gy (2 Gy/fraction). A constant RBE = 1.1 was assumed for PT. The SCR was evaluated with the excess absolute risk (EAR) formalism, considering also the age dependence. A cumulative EAR was finally computed.

Results

According to the linear, linear-exponential and linear-plateau dose response model, the cumulative EAR for Group 1 patients after PT was equal to 45 ± 10, 17 ± 3 and 15 ± 3, respectively. The corresponding relative increase for tangential 3D-CRT was equal to a factor 2.1 ± 0.5, 2.1 ± 0.4 and 2.3 ± 0.4. Group 2 patients showed a cumulative EAR after PT in FB equal to 65 ± 3, 21 ± 1 and 20 ± 1, according to the different models; the relative risk obtained with VMAT increased by a factor 3.5 ± 0.2, 5.2 ± 0.3 and 5.1 ± 0.3. Similar values emerge from DIBH plans. Contrary to photon radiotherapy, PT appears to be not sensitive to the age dependence due to the very low delivered dose.

Conclusions

PBS PT is associated to significant SCR reduction in BC patients compared to photon radiotherapy. The benefits are maximized for young patients with both SVC and IMNs involvement. When combined with the improved sparing of the heart, this might contribute to the establishment of effective patient-selection criteria for proton BC treatments.