Dosimetric comparison of proton and photon three-dimensional, conformal, external beam accelerated partial breast irradiation techniques

Five-Year Outcomes of a Phase 1/2 Trial of Accelerated Partial Breast Irradiation Using Proton Therapy for Women With Stage 0-IIA Breast Cancer

Purpose

We report the results of a phase 1/2 trial of external beam partial breast radiation using proton therapy.

Methods and Materials

Eligible patients included stage 0-IIA breast cancer pTis-T2, N0, and size ≤3 cm. Proton beam radiation was used to deliver 3.85 Gy twice daily to 38.5 Gy. The phase 1 portion determined feasibility based on criteria of successful plan creation, treatment delivery, and acute toxicity grade ≥3 in ≤20% of patients. The phase 2 portion had efficacy goals of acute toxicity grade ≥3 in ≤20% of patients and observing physician-rated cosmesis of excellent or good >85% of patients at 2 years.

Results

From April 2013 to March 2015, there were 12 patients enrolled onto the phase 1 portion, and the preplanned analysis of feasibility was met in all 4 required criteria. From July 2015 through December 2019 there were 28 patients with 29 treated breasts (1 bilateral) enrolled onto the phase 2 portion of the trial out of 45 originally planned. The trial was closed to accrual because of the coronavirus pandemic and not reopened. Thirty-eight breasts were treated with double-scattering and 3 pencil-beam scanning protons. The median follow-up of the 40 patients is 5.4 years (range, 2.3-8.6 years). There was 1 local recurrence. There was no grade ≥3 acute or late toxicity. At baseline all patients had physician-rated cosmesis good or excellent but at 2 years was excellent in 56%, good in 19%, and fair in 25%.

Conclusions

Proton-accelerated partial breast irradiation delivered with a twice-daily fractionation was feasible and associated with very low acute and long-term toxicity. However, the trial did not meet goals for cosmesis outcomes and was closed prematurely. Future study is needed to determine whether pencil-beam scanning protons or different fractionation could improve these outcomes.

Outcomes and toxicities after proton partial breast radiotherapy for early stage, hormone receptor positive breast cancer: 3-Year results of a phase II multi-center trial

Purpose

Proton therapy (PT) for partial breast irradiation (PBI) in early-stage breast cancer can decrease morbidity versus photon PBI with superior organs-at-risk sparing. We report 3-year outcomes of the first prospective, multicenter, phase II trial of proton PBI.

Methods and Materials

This Proton Collaborative Group phase II trial (PCG BRE007-12) recruited women ≥ 50 years with node-negative, estrogen receptor (ER)-positive, ≤3cm, invasive ductal carcinoma (IDC) or ductal carcinoma in situ undergoing breast conserving surgery followed by proton PBI (40 Gy(RBE), 10 daily fractions). Primary endpoint was freedom from ipsilateral breast cancer recurrence. Adverse events were prospectively graded using CTCAEv4.0. Breast Cancer Treatment Outcome Scale (BCTOS) assessed patient-reported quality of life (PRQOL).

Results

Thirty-eight evaluable patients enrolled between 2/2013-11/2016. Median age was 67 years (range 50-79); 55 % had left-sided disease, and median tumor size was 0.9 cm. Treatment was delivered in ≥ 2 fields predominantly with uniform scanning PT (n = 37). At 35-month median follow-up (12-62), all patients were alive, and none had local, regional or distant disease progression. One patient developed an ER-negative contralateral IDC. Seven grade 2 adverse events occurred; no radiotherapy-related grade ≥ 3 toxicities occurred. Changes in BCTOS subdomain mean scores were maximum 0.36, indicating no meaningful change in PRQOL. Median heart volume receiving 5 Gy (V5Gy), lung V20Gy, and lung V10Gy were 0 %, 0 % and 0.19 %, respectively.

Conclusion

At 3 years, proton PBI provided 100 % cancer control for early-stage, ER-positive breast cancer. Toxicities are minimal, and PRQOL remains acceptable with continued follow-up. These findings support PT as a safe and effective PBI delivery option.

Hypofractionated proton therapy in breast cancer: where are we? A critical review of the literature

PURPOSE

To critically review available literature on hypofractionated (≥ 3 Gy/fraction) proton therapy (PT) for breast cancer (BCa).

METHODS

A systematic screening of the literature was performed in April 2021 in compliance with the preferred reporting items for systematic reviews and meta-analyses recommendations. All full-text publication written in English were considered eligible. Acute and late toxicities, oncological outcomes and dosimetric features were considered for the analysis.

RESULTS

Twelve publications met the inclusion criteria; all studies but one focused on accelerated partial breast irradiation (APBI). Eleven works considered post-operative patients, one referred to ABPI as a curative-intent modality. The dosimetric profile of PT compared favorably with both photon-based 3D conformal and intensity-modulated techniques, while a more extended follow-up is warranted to fully assess both the long-term toxicities and the non-inferiority of oncological outcomes.

CONCLUSION

Our work shows that results on PT for BCa are currently only available for APBI applications, with dosimetric analyses demonstrating a clear advantage over both 3D conformal and intensity modulated X-rays techniques, especially when ≥ 2 treatment fields were used. However, further evidence is needed to define whether such theoretical benefit translates into clinical improvements, especially in the long-term.

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.

Future Perspectives of Proton Therapy in Minimizing the Toxicity of Breast Cancer Radiotherapy

The toxicity of radiotherapy is a key issue when analyzing the eligibility criteria for patients with breast cancer. In order to obtain better results, proton therapy is proposed because of the more favorable distribution of the dose in the patient’s body compared with photon radiotherapy. Scientific groups have conducted extensive research into the improved efficacy and lower toxicity of proton therapy for breast cancer. Unfortunately, there is no complete insight into the potential reasons and prospects for avoiding undesirable results. Cardiotoxicity is considered challenging; however, researchers have not presented any realistic prospects for preventing them. We compared the clinical evidence collected over the last 20 years, providing the rationale for the consideration of proton therapy as an effective solution to reduce cardiotoxicity. We analyzed the parameters of the dose distribution (mean dose, Dmax, V5, and V20) in organs at risk, such as the heart, blood vessels, and lungs, using the following two irradiation techniques: whole breast irradiation and accelerated partial breast irradiation. Moreover, we presented the possible causes of side effects, taking into account biological and technical issues. Finally, we collected potential improvements in higher quality predictions of toxic cardiac effects, like biomarkers, and model-based approaches to give the full background of this complex issue.

Proton Therapy for Partial Breast Irradiation: Rationale and Considerations

In an era of continued advancements in personalized medicine for the treatment of breast cancer, select patients with early stage breast cancer may be uniquely poised to benefit from partial breast irradiation (PBI) delivered with proton therapy. PBI presents an opportunity to improve quality of life during treatment with a significantly shorter treatment duration. By targeting less non-target breast tissue, excess radiation exposure and resulting toxicities are also reduced. Proton therapy represents a precision radiotherapy technology that builds on these advantages by further limiting the normal tissue exposure to unnecessary radiation dose not only to uninvolved breast tissue but also the underlying thoracic organs including the heart and lungs. Herein, we present a concise review of the rationale for the use of proton therapy for PBI, evidence available to date, and practical considerations in the implementation and use of proton therapy for this indication.

Reirradiation for Locoregional Recurrent Breast Cancer

Purpose

Reirradiation poses a distinct therapeutic challenge owing to risks associated with exceeding normal tissue tolerances and possibly more therapeutically resistant disease biology. We report our experience with reirradiation for locoregional recurrent or second primary breast cancer.

Methods and Materials

Between 1999 and 2019, all patients with breast cancer treated with repeat breast/chest wall radiation therapy (RT) at our institution were identified. Adverse events were assessed using the Common Terminology Criteria for Adverse Events v5.0. Fisher exact, Mann-Whitney rank-sum, and unpaired t tests were used for statistical analysis. Freedom from locoregional recurrence and distant metastasis as well as overall survival were calculated using the Kaplan-Meier method.

Results

Seventy-two patients underwent reirradiation. Median prior RT dose, reirradiation dose, and cumulative dose were 60 Gy (interquartile range [IQR], 50-60.4 Gy), 45 Gy (IQR, 40-50 Gy), and 103.54 Gy₂ (IQR, 95.04-109.62 Gy₂), respectively. Median time between RT courses was 73 months (IQR, 29-129 months). Thirty-four patients (47%) had gross residual disease at time of reirradiation. Course intent was described as curative in 44 patients (61%) and palliative in 28 (39%). Fifty-two patients (72%) were treated with photons ± electrons and 20 (28%) with protons. With a median follow-up of 22 months (IQR, 10-43 months), grade 3 adverse events were experienced by 13% of patients (10% acute skin toxicity and 3% late skin necrosis). Time between RT courses and reirradiation fields was significantly associated with the development of grade 3 toxicity at any point. Proton therapy conferred a dosimetric advantage without difference in toxicity. At 2 years, locoregional recurrence-free survival was 74.6% and overall survival was 65.5% among all patients, and 93.1% and 76.8%, respectively, among curative intent patients treated without gross disease. Distant metastasis-free survival was 59.0% among all curative intent patients.

Conclusions

Reirradiation for locoregional recurrent breast cancer is feasible with acceptable rates of toxicity. Disease control and survival are promising among curative intent reirradiation patients without gross disease.

Proton beam therapy reirradiation for breast cancer: Multi-institutional prospective PCG registry analysis

To investigate adverse events (AEs, CTCAE v4.0) and clinical outcomes for proton beam therapy (PBT) reirradiation (reRT) for breast cancer. From 2011 to 2016, 50 patients received PBT reRT for breast cancer in the prospective Proton Collaborative Group (PCG) registry. Acute AEs occurred within 180 days from start of reRT. Late AEs began or persisted beyond 180 days. Fisher's exact and Mann-Whitney rank-sum tests were utilized. Kaplan-Meier methods were used to estimate overall survival (OS) and local recurrence-free survival (LFRS). Median follow-up was 12.7 months (0-41.8). Median prior RT dose was 60 Gy (10-96.7). Median reRT dose was 55.1 Gy (45.1-76.3). Median cumulative dose was 110.6 Gy (70.6-156.8). Median interval between RT courses was 103.8 months (5.5-430.8). ReRT included regional nodes in 84% (66% internal mammary node [IMN]). Surgery included the following: 44% mastectomy, 22% wide local excision, 6% lumpectomy, 2% reduction mammoplasty, and 26% no surgery. Grade 3 AEs were experienced by 16% of patients (10% acute, 8% late) and were associated with body mass index (BMI) > 30 kg/m² (P = 0.04), bilateral recurrence (P = 0.02), and bilateral reRT (P = 0.004). All grade 3 AEs occurred in patients receiving IMN reRT (P = 0.08). At 1 year, LRFS was 93%, and OS was 97%. Patients with gross disease at time of PBT trended toward worse 1-year LRFS (100% without vs. 84% with, P = 0.06). PBT reRT is well tolerated with favorable local control. BMI > 30, bilateral disease, and IMN reRT were associated with grade 3 AEs. Toxicity was acceptable despite median cumulative dose > 110 Gy.

Is Proton Therapy a "Pro" for Breast Cancer? A Comparison of Proton vs. Non-proton Radiotherapy Using the National Cancer Database

Background: Limited data exists demonstrating the clinical benefit of proton radiotherapy (PRT) in breast cancer. Using the National Cancer Database, we evaluated predictors associated with PRT use for patients with breast cancer. An exploratory analysis also investigates the impact of PRT on overall survival (OS).

Methods: Patients with non-metastatic breast cancer treated with adjuvant radiotherapy from 2004 to 2014 were identified. Patients were stratified based on receipt of PRT or non-PRT (i.e., photons ± electrons). A logistic regression model was used to determine predictors for PRT utilization. For OS, Multivariable analysis (MVA) was performed using Cox proportional hazard model.

Results: A total of 724,492 patients were identified: 871 received PRT and 723,621 received non-PRT. 58.3% of the PRT patients were group stage 0–1. Median follow-up time was 62.2 months. On multivariate logistic analysis, the following factors were found to be significant for receipt of PRT (all p < 0.05): academic facility (odds ratio [OR] = 2.50), South (OR = 2.01) and West location (OR = 12.43), left-sided (OR = 1.21), ER-positive (OR = 1.59), and mastectomy (OR = 1.47); pT2-T4 disease predicted for decrease use (OR = 0.79). PRT was not associated with OS on MVA for all patients: Hazard Ratio: 0.85, p = 0.168. PRT remained not significant on MVA after stratifying for subsets likely associated with higher heart radiation doses, including: left-sided (p = 0.140), inner-quadrant (p = 0.173), mastectomy (p = 0.095), node positivity (p = 0.680), N2-N3 disease (p = 0.880), and lymph node irradiation (LNI) (p = 0.767).

Conclusions: Receipt of PRT was associated with left-sided, ER+ tumors, mastectomy, South and West location, and academic facilities, but not higher group stages or LNI. PRT was not associated with OS, including in subsets likely at risk for higher heart doses. Further studies are required to determine non-OS benefits of PRT. In the interim, given the high cost of protons, only well-selected patients should receive PRT unless enrolled on a clinical trial.

Proton therapy for breast cancer: progress & pitfalls

As the number of patients cured from breast cancer increases with improvements in multidisciplinary care, emphasis on reducing late toxicities of treatment has increased, in order to improve long-term quality of life. Proton beam therapy (PBT) is a form of radiotherapy that uses particles with unique physical properties that enable treatment delivery with minimal dose deposition beyond the treatment target. Therefore, PBT has emerged as an exciting radiotherapy modality for breast cancer due to the ability to minimize exposure to the heart, lungs, muscle, and bone. Herein, we review the rationale for PBT in breast cancer, potential clinical applications, and the available clinical data supporting its use. We also address some of the technical and logistical challenges and areas of ongoing research that will ultimately establish the role for PBT for breast cancer in the years ahead.

The evolution of proton beam therapy: Current and future status

Proton beam therapy (PBT) has been increasingly used in a variety of cancers due to its excellent physical properties and superior dosimetric parameters. PBT may improve patient survival by improving the local tumor treatment rate while reducing injury to normal organs, which may result in fewer radiation-induced adverse effects. However, the significant cost of establishing and maintaining proton facilities cannot be overlooked. In addition, there has been significant controversy regarding routine application of this treatment in certain types of cancer. The challenges of PBT in the future mainly include the lack of basic clinical trials, unclear biological effects, immature imaging technology and miniaturization of imaging guidance. Overcoming these limitations may promote the rapid development of PBT. We herein provide an overview of the existing literature on the efficacy and toxicity of common oncological applications of proton beam therapy.

Proton beam radiotherapy as part of comprehensive regional nodal irradiation for locally advanced breast cancer

PURPOSE

This study evaluates acute toxicity outcomes in breast cancer patients treated with adjuvant proton beam therapy (PBT).

METHODS

From 2011 to 2016, 91 patients (93 cancers) were treated with adjuvant PBT targeting the intact breast/chest wall and comprehensive regional nodes including the axilla, supraclavicular fossa, and internal mammary lymph nodes. Toxicity was recorded weekly during treatment, one month following treatment, and then every 6months according to the Common Terminology Criteria for Adverse Events (CTCAE) v4.0. Charts were retrospectively reviewed to verify toxicities, patient parameters, disease and treatment characteristics, and disease-related outcomes.

RESULTS

Median follow-up was 15.5months. Median PBT dose was 50.4 Gray relative biological effectiveness (GyRBE), with subsequent boost as clinically indicated (N=61, median 10 GyRBE). Chemotherapy, when administered, was given adjuvantly (N=42) or neoadjuvantly (N=46). Grades 1, 2, and 3 dermatitis occurred in 23%, 72%, and 5%, respectively. Eight percent required treatment breaks owing to dermatitis. Median time to resolution of dermatitis was 32days. Grades 1, 2, and 3 esophagitis developed in 31%, 33%, and 0%, respectively.

CONCLUSIONS

PBT displays acceptable toxicity in the setting of comprehensive regional nodal irradiation.

Medical factors influencing decision making regarding radiation therapy for breast cancer

Radiation therapy is an important and effective adjuvant therapy for breast cancer. Numerous health conditions may affect medical decisions regarding tolerance of breast radiation therapy. These factors must be considered during the decision-making process after breast-conserving surgery or mastectomy for breast cancer. Here, we review currently available evidence focusing on medical conditions that may affect the patient-provider decision-making process regarding the use of radiation therapy.

Promise and pitfalls of heavy-particle therapy

Proton beam therapy, the most common form of heavy-particle radiation therapy, is not a new invention, but it has gained considerable public attention because of the high cost of installing and operating the rapidly increasing number of treatment centers. This article reviews the physical properties of proton beam therapy and focuses on the up-to-date clinical evidence comparing proton beam therapy with the more standard and widely available radiation therapy treatment alternatives. In a cost-conscious era of health care, the hypothetical benefits of proton beam therapy will have to be supported by demonstrable clinical gains. Proton beam therapy represents, through its scale and its cost, a battleground for the policy debate around managing expensive technology in modern medicine.

Partial breast radiation therapy with proton beam: 5-year results with cosmetic outcomes

PURPOSE

We updated our previous report of a phase 2 trial using proton beam radiation therapy to deliver partial breast irradiation (PBI) in patients with early stage breast cancer.

METHODS AND MATERIALS

Eligible subjects had invasive nonlobular carcinoma with a maximal dimension of 3 cm. Patients underwent partial mastectomy with negative margins; axillary lymph nodes were negative on sampling. Subjects received postoperative proton beam radiation therapy to the surgical bed. The dose delivered was 40 Gy in 10 fractions, once daily over 2 weeks. Multiple fields were treated daily, and skin-sparing techniques were used. Following treatment, patients were evaluated with clinical assessments and annual mammograms to monitor toxicity, tumor recurrence, and cosmesis.

RESULTS

One hundred subjects were enrolled and treated. All patients completed the assigned treatment and were available for post-treatment analysis. The median follow-up was 60 months. Patients had a mean age of 63 years; 90% had ductal histology; the average tumor size was 1.3 cm. Actuarial data at 5 years included ipsilateral breast tumor recurrence-free survival of 97% (95% confidence interval: 100%-93%); disease-free survival of 94%; and overall survival of 95%. There were no cases of grade 3 or higher acute skin reactions, and late skin reactions included 7 cases of grade 1 telangiectasia. Patient- and physician-reported cosmesis was good to excellent in 90% of responses, was not changed from baseline measurements, and was well maintained throughout the entire 5-year follow-up period.

CONCLUSIONS

Proton beam radiation therapy for PBI produced excellent ipsilateral breast recurrence-free survival with minimal toxicity. The treatment proved to be adaptable to all breast sizes and lumpectomy cavity configurations. Cosmetic results appear to be excellent and unchanged from baseline out to 5 years following treatment. Cosmetic results may be improved over those reported with photon-based techniques due to reduced breast tissue exposure with proton beam, skin-sparing techniques, and the dose fractionation schedule used in this trial.

Long-term cosmetic outcomes and toxicities of proton beam therapy compared with photon-based 3-dimensional conformal accelerated partial-breast irradiation: a phase 1 trial

PURPOSE

To present long-term outcomes of a prospective feasibility trial using either protons or 3-dimensional conformal photon-based (accelerated partial-breast irradiation [APBI]) techniques.

METHODS AND MATERIALS

From October 2003 to April 2006, 98 evaluable patients with stage I breast cancer were treated with APBI (32 Gy in 8 fractions given twice daily) on a prospective clinical trial: 19 with proton beam therapy (PBT) and 79 with photons or mixed photons/electrons. Median follow-up was 82.5 months (range, 2-104 months). Toxicity and patient satisfaction evaluations were performed at each visit.

RESULTS

At 7 years, the physician rating of overall cosmesis was good or excellent for 62% of PBT patients, compared with 94% for photon patients (P=.03). Skin toxicities were more common for the PBT group: telangiectasia, 69% and 16% (P=.0013); pigmentation changes, 54% and 22% (P=.02); and other late skin toxicities, 62% and 18% (P=.029) for PBT and photons, respectively. There were no significant differences between the groups in the incidences of breast pain, edema, fibrosis, fat necrosis, skin desquamation, and rib pain or fracture. Patient-reported cosmetic outcomes at 7 years were good or excellent for 92% and 96% of PBT and photon patients, respectively (P=.95). Overall patient satisfaction was 93% for the entire cohort. The 7-year local failure rate for all patients was 6%, with 3 local recurrences in the PBT group (7-year rate, 11%) and 2 in photon-treated patients (4%) (P=.22).

CONCLUSIONS

Local failure rates of 3-dimensional APBI and PBT were similar in this study. However, PBT, as delivered in this study, led to higher rates of long-term telangiectasia, skin color changes, and skin toxicities. We recommend the use of multiple fields and treatment of all fields per treatment session or the use of scanning techniques to minimize skin toxicity.

Cardiac dose sparing and avoidance techniques in breast cancer radiotherapy

Breast cancer radiotherapy represents an essential component in the overall management of both early stage and locally advanced breast cancer. As the number of breast cancer survivors has increased, chronic sequelae of breast cancer radiotherapy become more important. While recently published data suggest a potential for an increase in cardiac events with radiotherapy, these studies do not consider the impact of newer radiotherapy techniques commonly utilized. Therefore, the purpose of this review is to evaluate cardiac dose sparing techniques in breast cancer radiotherapy. Current options for cardiac protection/avoidance include (1) maneuvers that displace the heart from the field such as coordinating the breathing cycle or through prone patient positioning, (2) technological advances such as intensity modulated radiation therapy (IMRT) or proton beam therapy (PBT), and (3) techniques that treat a smaller volume around the lumpectomy cavity such as accelerated partial breast irradiation (APBI), or intraoperative radiotherapy (IORT). While these techniques have shown promise dosimetrically, limited data on late cardiac events exist due to the difficulties of long-term follow up. Future studies are required to validate the efficacy of cardiac dose sparing techniques and may use surrogates for cardiac events such as biomarkers or perfusion imaging.

Phase II trial of proton beam accelerated partial breast irradiation in breast cancer

BACKGROUND AND PURPOSE

Here, we report the results of our phase II, prospective study of proton beam accelerated partial breast irradiation (PB-APBI) in patients with breast cancer after breast conserving surgery (BCS).

MATERIALS AND METHODS

Thirty patients diagnosed with breast cancer were treated with PB-APBI using a single-field proton beam or two fields after BCS. The treatment dose was 30 cobalt gray equivalent (CGE) in six CGE fractions delivered once daily over five consecutive working days.

RESULTS

All patients completed PB-APBI. The median follow-up time was 59 months (range: 43-70 months). Of the 30 patients, none had ipsilateral breast recurrence or regional or distant metastasis, and all were alive at the last follow-up. Physician-evaluated toxicities were mild to moderate, except in one patient who had severe wet desquamation at 2 months that was not observed beyond 6 months. Qualitative physician cosmetic assessments of good or excellent were noted in 83% and 80% of the patients at the end of PB-APBI and at 2 months, respectively, and decreased to 69% at 3 years. A good or excellent cosmetic outcome was noted in all patients treated with a two-field proton beam at any follow-up time point except for one. For all patients, the mean percentage breast retraction assessment (pBRA) value increased significantly during the follow-up period (p=0.02); however, it did not increase in patients treated with two-field PB-APBI (p=0.3).

CONCLUSIONS

PB-APBI consisting of 30 CGE in six CGE fractions once daily for five consecutive days can be delivered with excellent disease control and tolerable skin toxicity to properly selected patients with early-stage breast cancer. Multiple-field PB-APBI may achieve a high rate of good-to-excellent cosmetic outcomes. Additional clinical trials with larger patient groups are needed.

The clinical case for proton beam therapy

Over the past 20 years, several proton beam treatment programs have been implemented throughout the United States. Increasingly, the number of new programs under development is growing. Proton beam therapy has the potential for improving tumor control and survival through dose escalation. It also has potential for reducing harm to normal organs through dose reduction. However, proton beam therapy is more costly than conventional x-ray therapy. This increased cost may be offset by improved function, improved quality of life, and reduced costs related to treating the late effects of therapy. Clinical research opportunities are abundant to determine which patients will gain the most benefit from proton beam therapy. We review the clinical case for proton beam therapy. SUMMARY SENTENCE: Proton beam therapy is a technically advanced and promising form of radiation therapy.

Cost comparison of radiation treatment options after lumpectomy for breast cancer

BACKGROUND

Radiation therapy (RT) after lumpectomy for breast cancer can be delivered with several different regimens. We evaluated a cost-minimization strategy to select among RT options.

METHODS

An institutional review board (IRB)-approved retrospective review identified a sample of 100 women who underwent lumpectomy for invasive or in situ breast cancer during 2009. Post lumpectomy RT options included: no radiation in women ≥70 years [T1N0, estrogen receptor (ER)+] per Cancer and Leukemia Group B (CALGB) 9343 (no-RT), accelerated external-beam partial-breast irradiation (APBI), and Canadian fractionation (C-RT), as alternatives to standard whole-breast radiation therapy (WBRT). Eligibility for RT regimens was based on published criteria. RT costs were estimated using the 2011 US Medicare Physician Fee Schedule and average Current Procedural Terminology (CPT) codes billed per regimen at our institution. Costs were modeled in a 1,000-patient theoretical cohort.

RESULTS

Median patient age was 56.5 years (range 32-93 years). Tumor histology included invasive ductal cancer (78 %), ductal carcinoma in situ (DCIS) (15 %), invasive lobular cancer (6 %), and mixed histology (1 %). Median tumor size was 1 cm (range 0.2-5 cm). Estimated per-patient cost of radiation was US$5,341.81 for APBI, US$9,121.98 for C-RT, and US$13,358.37 for WBRT. When patients received the least expensive radiation regimen for which they were eligible, 14 % received no-RT, 44 % received APBI, 7 % received C-RT, and 35 % defaulted to WBRT. Using a cost-minimization strategy, estimated RT costs were US$7.67 million, versus US$13.36 million had all patients received WBRT, representing cost savings of US$5.69 million per 1,000 patients treated.

CONCLUSIONS

A cost-minimization strategy results in a 43 % reduction in estimated radiation costs among women undergoing breast conservation.

Impact of residual and intrafractional errors on strategy of correction for image-guided accelerated partial breast irradiation

BACKGROUND

The cone beam CT (CBCT) guided radiation can reduce the systematic and random setup errors as compared to the skin-mark setup. However, the residual and intrafractional (RAIF) errors are still unknown. The purpose of this paper is to investigate the magnitude of RAIF errors and correction action levels needed in cone beam computed tomography (CBCT) guided accelerated partial breast irradiation (APBI).

METHODS

Ten patients were enrolled in the prospective study of CBCT guided APBI. The postoperative tumor bed was irradiated with 38.5 Gy in 10 fractions over 5 days. Two cone-beam CT data sets were obtained with one before and one after the treatment delivery. The CBCT images were registered online to the planning CT images using the automatic algorithm followed by a fine manual adjustment. An action level of 3 mm, meaning that corrections were performed for translations exceeding 3 mm, was implemented in clinical treatments. Based on the acquired data, different correction action levels were simulated, and random RAIF errors, systematic RAIF errors and related margins before and after the treatments were determined for varying correction action levels.

RESULTS

A total of 75 pairs of CBCT data sets were analyzed. The systematic and random setup errors based on skin-mark setup prior to treatment delivery were 2.1 mm and 1.8 mm in the lateral (LR), 3.1 mm and 2.3 mm in the superior-inferior (SI), and 2.3 mm and 2.0 mm in the anterior-posterior (AP) directions. With the 3 mm correction action level, the systematic and random RAIF errors were 2.5 mm and 2.3 mm in the LR direction, 2.3 mm and 2.3 mm in the SI direction, and 2.3 mm and 2.2 mm in the AP direction after treatments delivery. Accordingly, the margins for correction action levels of 3 mm, 4 mm, 5 mm, 6 mm and no correction were 7.9 mm, 8.0 mm, 8.0 mm, 7.9 mm and 8.0 mm in the LR direction; 6.4 mm, 7.1 mm, 7.9 mm, 9.2 mm and 10.5 mm in the SI direction; 7.6 mm, 7.9 mm, 9.4 mm, 10.1 mm and 12.7 mm in the AP direction, respectively.

CONCLUSIONS

Residual and intrafractional errors can significantly affect the accuracy of image-guided APBI with nonplanar 3DCRT techniques. If a 10-mm CTV-PTV margin is applied, a correction action level of 5 mm or less is necessary so as to maintain the RAIF errors within 10 mm for more than 95% of fractions. Pre-treatment CBCT guidance is not a guarantee for safe delivery of the treatment despite its known benefits of reducing the initial setup errors. A patient position verification and correction during the treatment may be a method for the safe delivery.

External-beam accelerated partial breast irradiation using multiple proton beam configurations

PURPOSE

To explore multiple proton beam configurations for optimizing dosimetry and minimizing uncertainties for accelerated partial breast irradiation (APBI) and to compare the dosimetry of proton with that of photon radiotherapy for treatment of the same clinical volumes.

METHODS AND MATERIALS

Proton treatment plans were created for 11 sequential patients treated with three-dimensional radiotherapy (3DCRT) photon APBI using passive scattering proton beams (PSPB) and were compared with clinically treated 3DCRT photon plans. Monte Carlo calculations were used to verify the accuracy of the proton dose calculation from the treatment planning system. The impact of range, motion, and setup uncertainty was evaluated with tangential vs. en face beams.

RESULTS

Compared with 3DCRT photons, the absolute reduction of the mean of V100 (the volume receiving 100% of prescription dose), V90, V75, V50, and V20 for normal breast using protons are 3.4%, 8.6%, 11.8%, 17.9%, and 23.6%, respectively. For breast skin, with the similar V90 as 3DCRT photons, the proton plan significantly reduced V75, V50, V30, and V10. The proton plan also significantly reduced the dose to the lung and heart. Dose distributions from Monte Carlo simulations demonstrated minimal deviation from the treatment planning system. The tangential beam configuration showed significantly less dose fluctuation in the chest wall region but was more vulnerable to respiratory motion than that for the en face beams. Worst-case analysis demonstrated the robustness of designed proton beams with range and patient setup uncertainties.

CONCLUSIONS

APBI using multiple proton beams spares significantly more normal tissue, including nontarget breast and breast skin, than 3DCRT using photons. It is robust, considering the range and patient setup uncertainties.

Continuous arc rotation of the couch therapy for the delivery of accelerated partial breast irradiation: a treatment planning analysis

PURPOSE

We present a novel form of arc therapy: continuous arc rotation of the couch (C-ARC) and compare its dosimetry with three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and volumetric-modulated arc therapy (VMAT) for accelerated partial breast irradiation (APBI). C-ARC, like VMAT, uses a modulated beam aperture and dose rate, but with the couch, not the gantry, rotating.

METHODS AND MATERIALS

Twelve patients previously treated with APBI using 3D-CRT were replanned with (1) C-ARC, (2) IMRT, and (3) VMAT. C-ARC plans were designed with one medial and one lateral arc through which the couch rotated while the gantry was held stationary at a tangent angle. Target dose coverage was normalized to the 3D-CRT plan. Comparative endpoints were dose to normal breast tissue, lungs, and heart and monitor units prescribed.

RESULTS

Compared with 3D-CRT, C-ARC, IMRT, and VMAT all significantly reduced the ipsilateral breast V50% by the same amount (mean, 7.8%). Only C-ARC and IMRT plans significantly reduced the contralateral breast maximum dose, the ipsilateral lung V5Gy, and the heart V5%. C-ARC used on average 40%, 30%, and 10% fewer monitor units compared with 3D-CRT, IMRT, and VMAT, respectively.

CONCLUSIONS

C-ARC provides improved dosimetry and treatment efficiency, which should reduce the risks of toxicity and secondary malignancy. Its tangent geometry avoids irradiation of critical structures that is unavoidable using the en face geometry of VMAT.

Unacceptable cosmesis in a protocol investigating intensity-modulated radiotherapy with active breathing control for accelerated partial-breast irradiation

PURPOSE

To report interim cosmetic results and toxicity from a prospective study evaluating accelerated partial-breast irradiation (APBI) administered using a highly conformal external beam approach.

METHODS AND MATERIALS

We enrolled breast cancer patients in an institutional review board-approved prospective study of APBI using beamlet intensity-modulated radiotherapy (IMRT) at deep-inspiration breath-hold. Patients received 38.5 Gy in 3.85 Gy fractions twice daily. Dosimetric parameters in patients who maintained acceptable cosmesis were compared with those in patients developing unacceptable cosmesis in follow-up, using t-tests.

RESULTS

Thirty-four patients were enrolled; 2 were excluded from analysis because of fair baseline cosmesis. With a median follow-up of 2.5 years, new unacceptable cosmesis developed in 7 patients, leading to early study closure. We compared patients with new unacceptable cosmesis with those with consistently acceptable cosmesis. Retrospective analysis demonstrated that all but one plan adhered to the dosimetric requirements of the national APBI trial. The mean proportion of a whole-breast reference volume receiving 19.25 Gy (V50) was lower in patients with acceptable cosmesis than in those with unacceptable cosmesis (34.6% vs. 46.1%; p = 0.02). The mean percentage of this reference volume receiving 38.5 Gy (V100) was also lower in patients with acceptable cosmesis (15.5% vs. 23.0%; p = 0.02).

CONCLUSIONS

The hypofractionated schedule and parameters commonly used for external beam APBI and prescribed by the ongoing national trial may be suboptimal, at least when highly conformal techniques such as IMRT with management of breathing motion are used. The V50 and V100 of the breast reference volume seem correlated with cosmetic outcome, and stricter limits may be appropriate in this setting.

Technical considerations for noncoplanar proton-beam therapy of patients with tumors proximal to the optic nerve

PURPOSE

To investigate technical feasibilities of noncoplanar proton-beam therapy (PBT) on dose reduction to critical organs.

MATERIAL AND METHODS

The degree of mechanical precision, rotational limitations of the gantry and the treatment couch were evaluated, and dose-volume histograms were compared for noncoplanar and coplanar PBT. Following these studies, three patients with tumors proximal to the optic nerve underwent noncoplanar PBT.

RESULTS

Noncoplanar PBT offered advantage in dose reduction to the optic nerve when compared to coplanar therapy. This advantage was more significant if the tumor reduced in size during treatment. None experienced radiation injury to the optic nerve during a short follow-up time of 7-12 months.

CONCLUSION

Noncoplanar PBT appears to reduce doses to organs at risk.

Accelerated partial breast irradiation consensus statement from the American Society for Radiation Oncology (ASTRO)

PURPOSE

To present guidance for patients and physicians regarding the use of accelerated partial-breast irradiation (APBI), based on current published evidence complemented by expert opinion.

METHODS AND MATERIALS

A systematic search of the National Library of Medicine's PubMed database yielded 645 candidate original research articles potentially applicable to APBI. Of these, 4 randomized trials and 38 prospective single-arm studies were identified. A Task Force composed of all authors synthesized the published evidence and, through a series of meetings, reached consensus regarding the recommendations contained herein.

RESULTS

The Task Force proposed three patient groups: (1) a "suitable" group, for whom APBI outside of a clinical trial is acceptable, (2) a "cautionary" group, for whom caution and concern should be applied when considering APBI outside of a clinical trial, and (3) an "unsuitable" group, for whom APBI outside of a clinical trial is not generally considered warranted. Patients who choose treatment with APBI should be informed that whole-breast irradiation (WBI) is an established treatment with a much longer track record that has documented long-term effectiveness and safety.

CONCLUSION

Accelerated partial-breast irradiation is a new technology that may ultimately demonstrate long-term effectiveness and safety comparable to that of WBI for selected patients with early breast cancer. This consensus statement is intended to provide guidance regarding the use of APBI outside of a clinical trial and to serve as a framework to promote additional clinical investigations into the optimal role of APBI in the treatment of breast cancer.

Cardiac dose evaluation for 3-dimensional conformal partial breast irradiation compared with whole breast irradiation

To compare the radiation dose to normal cardiac tissue for 3Dimensional (3D) conformal external beam partial breast irradiation (PBI) and standard whole breast irradiation (WBI), and examine the effect of tumor bed location. For 14 patients with left breast tumors randomized on the National Surgical Adjuvant Breast and Bowel Project B-39 protocol, computer-generated radiotherapy treatment plans were devised for WBI and PBI. Tumor bed location was designated according to whether more than 50% of the excision cavity was medial or lateral to the nipple line. The volume of heart receiving doses of 2.5, 5, 10, and 20 Gy was calculated for all PBI and WBI plans. Dose to 5% of the heart volume (D5) and mean heart dose were also calculated. The biologically-equivalent dose (BED) was calculated to account for the different fractionation used in PBI and WBI. Of the 14 patients, 8 had lateral tumor beds, and 6 had medial tumor beds. The volumes of heart receiving 2.5, 5, 10, and 20 Gy were significantly lower for lateral PBI compared with WBI. For medial PBI, significant cardiac sparing was only seen at a dose of 20 Gy. The difference of D5 values was significant for lateral PBI compared with WBI (p=0.008), but not for medial PBI compared with WBI (p=0.84). The mean dose was also significantly lower for lateral PBI compared with WBI (p=0.008), but not for medial PBI (p=0.16). The results from BED calculations did not change this outcome. Both 3D conformal PBI and standard WBI can deliver relatively low doses to the heart. For patients with lateralized tumor beds, PBI offers significant cardiac sparing compared with WBI. Patients with medial lesions have relatively similar heart dosimetry with PBI and WBI. 3D conformal PBI is an emerging treatment modality and continued participation on clinical trials is encouraged. Patients with left-sided lesions and lateralized tumor beds warrant special consideration for PBI, given the significant cardiac dose sparing.

Dosimetric comparison of four different external beam partial breast irradiation techniques: three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, helical tomotherapy, and proton beam therapy

BACKGROUND AND PURPOSE

As an alternative to whole breast irradiation in early breast cancer, a variety of accelerated partial breast irradiation (APBI) techniques have been investigated. The purpose of our study is to compare the dosimetry of four different external beam APBI (EB-APBI) plans: three-dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), helical tomotherapy (TOMO), and proton beam therapy (PBT).

METHODS AND MATERIALS

Thirty patients were included in the study, and plans for four techniques were developed for each patient. A total dose of 30Gy in 6Gy fractions once daily was prescribed in all treatment plans.

RESULTS

In the analysis of the non-PTV breast volume that was delivered 50% of the prescribed dose (PD), PBT (mean: 16.5%) was superior to TOMO (mean: 22.8%), IMRT (mean: 33.3%), and 3D-CRT (mean: 40.9%) (p<0.001). The average ipsilateral lung volume percentage receiving 20% of the PD was significantly lower in PBT (0.4%) and IMRT (2.3%) compared with 3D-CRT (6.0%) and TOMO (14.2%) (p<0.001). The average heart volume percentage receiving 20% and 10% of the PD in left-sided breast cancer (N=19) was significantly larger with TOMO (8.0%, 19.4%) compared to 3D-CRT (1.5%, 3.1%), IMRT (1.2%, 4.0%), and PBT (0%, 0%) (p<0.001).

CONCLUSIONS

All four EB-APBI techniques showed acceptable coverage of the PTV. However, effective non-PTV breast sparing was achieved at the cost of considerable dose exposure to the lung and heart in TOMO.

Current status of accelerated partial breast irradiation

Accelerated partial breast irradiation (APBI) is a radiotherapy method used in breast-conserving therapy. In APBI, the tumor bed is topically irradiated over a short period after breast-conserving surgery. The fundamental concept underlying APBI is that more than 70% of ipsilateral breast tumor recurrence occurs in the neighborhood of the original tumor, and that hypofractionated radiotherapy can be applied safely when the irradiated volume is small enough. It is expected to reduce the time and cost required for conventional whole breast irradiation while maintaining equivalent local control. Several techniques including multicatheter interstitial brachytherapy, intracavitary brachytherapy, intraoperative radiation therapy, and 3D conformal external beam radiation therapy have been proposed, and each of them has its own advantages and drawbacks. Although APBI is increasingly used in the United States and Europe, and the short-term results are promising, its equivalence with whole breast radiation therapy is not fully established. In addition, because the average breast size in Japan is considerably smaller than in the West world, the application of APBI to Japanese patients is technically more challenging. At this point, APBI is still an investigational treatment in Japan, and the optimal method of radiation delivery as well as its long-term efficacy and safety should be clarified in clinical trials.