Breast cancer is the most prevalent disease for women. With advances in breast cancer screening, most breast cancers are now diagnosed in the early stages. With knowledge of different subtypes and their behavior, breast cancer treatment has become more individualized. Radiation therapy as one of the mainstays of breast cancer treatment has also been evolving. This review attempts to provide a summary of the most influential clinical studies that have driven the technological advances in radiation therapy for early-stage breast cancer.

PurposeStudies on Lattice radiotherapy (LRT) for breast cancer have been largely lacking. This study investigates the dosimetric feasibility of using Gamma Pod, a stereotactic radiotherapy apparatus originally designed for breast SBRT, to deliver LRT to large, bulky breast tumor as a noninvasive treatment option.MethodsThe GammaPod‐based LRT was simulated using Geant4 Gate Monte Carlo software. The simulated GammaPod was equipped with 5 mm diameter non‐coplanar circular beams that span 28° latitudinally from 18° to 43° off the horizontal plane. Two degrees longitudinal intervals were used to simulate rotating sources. To simulate the treatments to different breast sizes, three water‐equivalent hemisphere volumes with diameters of 10, 15, and 20 cm were analyzed. The lattice was planned by spacing focal points 2 cm apart in the transverse and sagittal planes and 2.5 cm in the coronal plane. This resulted in 22‐172 shots for full breast treatment. The maximum dose for each individual shot was 20 Gy. The peak‐to‐valley dose differences and skin dose were analyzed. To verify the feasibility of delivering LRT, a test plan was created and delivered to a commercial diode array dose verification device using a clinical GammaPod system with 15 mm collimators.ResultsThe dose profiles showed the average peak‐to‐valley dose percent differences of 94.10% in the 10 cm hemispherical volume, 88.95% in the 15 cm hemispherical volume, and 83.60% in the 20 cm hemispherical volume. Average skin dose was 1.27, 1.72, and 2.13 Gy for the 10, 15, and 20 cm irradiation volumes, respectively. The LRT plan delivered using a clinical GammaPod system with larger collimators verified the feasibility of LRT plan delivery.ConclusionGammaPod‐based lattice radiotherapy is a viable treatment option and its application can be extended to treating large bulky breast tumors.

Radiation oncology is a technology-driven treatment modality in the management of cancer, and has evolved substantially over the past few decades. Particularly in recent years, there has been a boom in the introduction of innovative, and sometimes even almost disruptive, technologies in radiation oncology, such as Cyberknife, Tomotherapy, Proton therapy, and MRI-linac. Entrepreneurs have played an important role in turning ideas into products in many of these technological innovations. Some people, therefore, believe that entrepreneur-driven start-up companies are ideal environments to foster disruptive innovation in radiation oncology technology, while others argue that academic hospitals and universities are better suited for initiating disruptive innovations in radiation oncology. This is the premise debated in this month's Point/Counterpoint. This article is protected by copyright. All rights reserved.

OBJECTIVES: High-dose radiotherapy has merits in treating bulky human tumors. Three different approaches were evaluated by using an animal model. METHODS: The dorsal skin of C3H/HeJ mice was shaved, lifted, and sutured on a titanium holder to fix the skin for a known geometry. The holder has an oblique open window (16x14 mm), where pluripotent mouse NE cells were injected into the skin. Tumor growth was monitored by using a caliper. RESULTS: To simulate stereotactic body radiation therapy (SBRT), tumors grown to 5-10 mm in diameter were irradiated with 13 Gy daily for 4 days for a total of 52 Gy of 250 Kv X-rays (2.2 Gy/min). Among 14 tumors exposed, 13 of them were not regrown during 36 days of observation period. The cure rate for SBRT was 13/14 (93%). A miniature version of existing MLC grid was milled with copper blocks to make 25 holes of 2.0 mm squares (1:3 open-to-closed ratio), which was converged from the source of the X-rays. This grid allows 1⁄4 of target area (oblique window) to be exposed. The 52 Gy (SBRT dose) was delivered to each quarter daily for 4 consecutive days to cover the whole 4 quarters of target area exposed, which is called quadruple grid radiotherapy (QGRT). The cure rate for QGRT was 9/12 (75%). When skin fur regrowth in irradiated area was quantified as a sign of recovery, a Student's t-test showed that the regrowth for QGRT was much greater (p=0.0003) than that for SBRT. In QGRT trials, some low-dose pockets were noted, so that the grid opening was widened from 2.0 to 2.4 mm squares, in which beam overlap was inevitable. To compensate the dose (9.7%) caused by overlaps, a priming dose (8-12 Gy) was adopted prior to quadruple grid exposures. This modified treatment plan is named as wQGRT. The cure rate for wQGRT was 13/15 (87%). Chi-squared test shows that tumor cure rates among SBRT, QGRT and wQGRT are not different (p=0.431). CONCLUSIONS: Our mouse model appears to be useful in evaluating that wQGRT offers tumor cure rates equivalent to SBRT, and with reduced normal tissue damage. Open Access Abstract

Abstract Background: The lumpectomy cavity (LPC) boost has been shown in 2 randomized studies to improve local control in breast cancer. Hypofraction is now being used for delivery of the LPC boost in some early-stage patients. This trial delivers the LPC boost in a single fraction using a novel breast immobilization device/treatment delivery system. Trial design: Patients are enrolled in this trial after standard resection with lumpectomy/sentinel lymph node biopsy (as appropriate) and chemotherapy (as indicated per standard of care). At the time of CT simulation for whole-breast radiation therapy (RT), the radiation oncologist evaluates breast size and LPC position. If consented for treatment, the patient receives a single fraction “boost” treatment of 8 Gy in 1 fraction followed by standard whole-breast RT to start within 7 days of completion of the boost. Whole-breast radiation is delivered in the supine or prone position with the following fractionation schemes: 4005 cGy in 15 fractions or 5000 cGy in 25 fractions. On the day of the boost treatment, the patient is fitted with the breast immobilization device, with a plastic inner cup that is fitted so that the breast fills all or most of the cup. A rigid outer cup with a built-in stereotactic fiducial system is attached. Moderate negative pressure is applied to immobilize the breast within the cup system. Patients then undergo CT simulation in the prone position. Clip placement and LPC cavity location must meet eligibility criteria before proceeding with treatment planning and delivery. Eligibility criteria: Eligibility criteria: age >60 yo; female only; dx of invasive ductal or lobular carcinoma or ductal carcinoma in situ; estrogen receptor positive; successful completion of lumpectomy ± sentinel lymph node biopsy with negative margins for invasive or noninvasive cancer; greatest tumor dimension <4 cm before surgery; weight <330 lb; height <76 inches; nonlactating and nonpregnant. Various additional dosimetric factors must be met prior to treatment. If these are unable to be met, the patient will become ineligible for treatment. Specific aims: The aim of this study is to demonstrate the feasibility and safety of delivering the LPC boost RT using a single fraction with a novel immobilization device/treatment delivery system while ensuring coverage of the target volume with appropriate dose homogeneity and conformity. Secondary aims are evaluation of patient comfort, acute toxicity (1 month), and late toxicity (1 year). Statistical methods: A Simon 2-stage design is utilized for this trial. After evaluating the device and treatment on 8 patients in the first stage, the trial was designed to be terminated and device rejected if the dose distribution was acceptable for ≤5 patients. The first stage was completed in spring 2017 and progressed to the second stage, designed to include a total of 17 patients. Accrual and target accrual: Target accrual for this study is 14 patients successfully treated while meeting all protocol constraints. As of 6/2017, 16 patients have been enrolled, of whom 13 have been successfully treated while meeting all protocol constraints. Citation Format: Nichols EM, Becker S, Hong J, Cohen RJ, Mishra MV, Citron W, Cheston SB, Niu Y, Mutaf Y, Yu CX, Feigenberg SJ. Delivery of a single fraction lumpectomy cavity boost using a novel immobilization device and treatment delivery system [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT2-03-03.

To compare the performance of five prognostic models [RTOG recursive partitioning analysis (RPA), Score Index for Radiosurgery in Brain Metastases (SIR), Barnholtz-Sloan–Kattan nomogram (BSKN), diagnosis-specific Graded Prognostic Assessment (dsGPA), and Graded Prognostic Assessment for Lung Cancer Using Molecular Markers (Lung-molGPA)] against actual survival in patients with brain metastases treated with SRS +/− WBRT.

A novel breast specific stereotactic radiosurgery device (BSRD) was invented at our institution. Over the last several years the device has been systematically evaluated demonstrating the stereotactic accuracy of its patented breast immobilization system and dosimetric benefits in comparison to external beam radiotherapy, proton beam radiotherapy and brachytherapy. Based on these evaluations, an Investigator Device Exemption (IDE) was obtained through the FDA and a study was developed and approved to test its feasibility. This report is the 1st clinical experience of this device on this pre-FDA approved feasibility study. This protocol was approved through the Institutional Review Board. Eligible patients were > 60 years, recommended to undergo whole breast radiation(WBRT) without nodal radiation, had a tumor bed(TB) well visualized on CT simulation and the TB volume was < 25% of the WB. Once deemed eligible, patients received a single fraction of 8 Gy using the BSRD to the TB + 1cm prior to WBRT (40 Gy in 15 fx or 50 Gy in 25 fx). The primary objective of this trial was to ensure the adequacy of the radiation dose distribution(DD) with a secondary endpoint of acute toxcity. Dosimetric parameters evaluated in the protocol included planning tumor volume(PTV) coverage, PTV max dose, PTV min dose, and maximum dose to the skin, chest wall, rib, lung and heart. In order to meet the primary endpoint of feasibility, the two stage design by Simon was utilized. This tests the null hypothesis that the true proportion of patients for whom BSRD treatment planning is able to generate an acceptable DD is < 60%. Seventeen patients will be accrued, with a planned interim analysis in the 1st stage after 8 patients, where the DD needs to be acceptable in 6 or more in order to move forward to stage 2. Between 3/18/16 and 12/21/16, 9 patients signed consent for treatment and 8 patients underwent successful treatment. One patient, who was found not to eligible after simulation, was treated with conventional WBRT off study. The TB volume ranged from 2.86 to 20.38cc, while the PTV ranged from 21.69 to 89.56cc. The median(range) skinmax, lungmax, heartmax, and PTVmax dose were 2.04Gy(1.13-2.87), 1.40(0.1-1.98), 1.01(0.1-2.2) and 8.71 Gy(8.35-9.26), respectively. One patient with a deep seeded TB had a minor deviation and received a dose over the prescription dose to the chest wall, while a second patient had inadequate coverage of the PTV(major deviation). Acute toxicity related to the device has been minimal with one patient developing small blisters related to the immobilization device that was seen immediately following removal of the device. Based on an adequate dose distribution seen in 7 of the 1st 8 patients, stage 2 was initiated. The plan is to complete accrual this spring and submit the results for FDA approval.

This study introduces a practical four-dimensional (4D) planning scheme of IMAT using 4D computed tomography (4D CT) for planning tumor tracking with dynamic multileaf beam collimation. We assume that patients can breathe regularly, i.e., the same way as during 4D CT with an unchanged period and amplitude, and that the start of 4D-IMAT delivery can be synchronized with a designated respiratory phase. Each control point of the IMAT-delivery process can be associated with an image set of 4D CT at a specified respiratory phase. Target is contoured at each respiratory phase without a motion-induced margin. A 3D-IMAT plan is first optimized on a reference-phase image set of 4D CT. Then, based on the projections of the planning target volume (PTV) in the beam’s eye view (BEV) at different respiratory phases, a 4D-IMAT plan is generated by transforming the segments of the optimized 3D plan by using a direct aperture deformation (DAD) method. Compensation for both translational and deformable tumor motion is accomplished, and the smooth delivery of the transformed plan is ensured by forcing connectivity between adjacent angles (control points). It is envisioned that the resultant plans can be delivered accurately using the dose rate regulated tracking (DRRT) method which handles breathing irregularities (Yi et al 2008). This planning process is straightforward and only adds a small step to current clinical 3D planning practice. Our 4D planning scheme was tested on three cases to evaluate dosimetric benefits. The created 4D-IMAT plans showed similar dose distributions as compared with the 3D-IMAT plans on a single static phase, indicating that our method is capable of eliminating the dosimetric effects of breathing induced target motion. Compared to the 3D-IMAT plans with large treatment margins encompassing respiratory motion, our 4D-IMAT plans reduced radiation doses to surrounding normal organs and tissues.

This study introduces a practical four-dimensional (4D) planning scheme of IMAT using 4D computed tomography (4D CT) for planning tumor tracking with dynamic multileaf beam collimation. We assume that patients can breathe regularly, i.e. the same way as during 4D CT with an unchanged period and amplitude, and that the start of 4D-IMAT delivery can be synchronized with a designated respiratory phase. Each control point of the IMAT-delivery process can be associated with an image set of 4D CT at a specified respiratory phase. Target is contoured at each respiratory phase without a motion-induced margin. A 3D-IMAT plan is first optimized on a reference-phase image set of 4D CT. Then, based on the projections of the planning target volume in the beam's eye view at different respiratory phases, a 4D-IMAT plan is generated by transforming the segments of the optimized 3D plan by using a direct aperture deformation method. Compensation for both translational and deformable tumor motion is accomplished, and the smooth delivery of the transformed plan is ensured by forcing connectivity between adjacent angles (control points). It is envisioned that the resultant plans can be delivered accurately using the dose rate regulated tracking method which handles breathing irregularities (Yi et al 2008 Med. Phys. 35 3955-62).This planning process is straightforward and only adds a small step to current clinical 3D planning practice. Our 4D planning scheme was tested on three cases to evaluate dosimetric benefits. The created 4D-IMAT plans showed similar dose distributions as compared with the 3D-IMAT plans on a single static phase, indicating that our method is capable of eliminating the dosimetric effects of breathing induced target motion. Compared to the 3D-IMAT plans with large treatment margins encompassing respiratory motion, our 4D-IMAT plans reduced radiation doses to surrounding normal organs and tissues.

A dedicated stereotactic breast specific radiation therapy device was developed as a novel partial breast delivery unit. The first clinical unit was installed at our institution and commissioned to treat the first patient in the spring of 2016 using an FDA-approved study. A commissioning protocol was developed for the clinical implementation of this technology, reporting on the performance of the GammaPod system. The GammaPod treatment unit is comprised of a rotating hemispherical source carrier containing 36 Co-60 sources and a concentric rotating tungsten collimator providing beam diameters of 15 and 25 mm. Commissioning tests were developed to include safety, mechanical, geometric, and dosimetric performance of the treatment unit, control system, and treatment planning systems. Several dosimetric systems were utilized that included area survey meters, stereotactic size ion chambers, radiochromic film, and OSL detectors. Dosimetric measurements were performed using acrylic as well as polyethylene phantoms and also performed directly in patient breast cups filled with water and using a manually controlled 3-dimensional chamber positioning system. A commissioning protocol is provided with lists of performance tests for safety systems, mechanical, geometric, and dosimetric accuracy of GammaPod. Using this procedure, mechanical accuracy of the couch positioning system was measured over a 40-mm range using both mechanical methods (<0.2 mm) as well as the location of the radiation isocenter (<0.5 mm). The couch sag from the presence of varying weights was measured and modelled to be 0.1 mm per 10 kg of patient weight. The congruence of the radiation profile and mechanical positioning system was measured through several treatment table loading and unloading procedures over a period of 1 month and determined to be −0.1±0.1, 0.2±0.1, and 0.2±0.2 mm in x, y, and z directions, respectively. Single isocenter dose profiles were also measured in all 3 cardinal directions using radiochromic film. Dose profile widths were found to be within 0.2 mm of corresponding MC simulations for single isocenter 15- and 25-mm shots. Overall dosimetric and spatial accuracy of the system was also determined through a variety of plan dosimetric verifications as well as end-to-end tests. The first GammaPod treatment unit for breast-specific stereotactic radiation therapy was successfully installed and commissioned for commencement of patient treatments in 2016. A clinical commissioning protocol was devised to verify the integrity of the GammaPod system and characterize its performance in terms of safety profiles as well as its mechanical and dosimetric accuracy. We report our commissioning experience with the first clinical GammaPod unit in the world.

Purpose: A dedicated stereotactic breast radiotherapy device, GammaPod, was developed to treat early stage breast cancer. The first clinical unit was installed and commissioned at University of Maryland. We report our methodology of absolute dosimetry in multiple calibration conditions and dosimetric verifications of treatment plans produced by the system. Methods: GammaPod unit is comprised of a rotating hemi-spherical source carrier containing 36 Co-60 sources and a concentric tungsten collimator providing beams of 15 and 25 mm. Absolute dose calibration formalism was developed with modifications to AAPM protocols for unique geometry and different calibration medium (acrylic, polyethylene or liquid water). Breast cup-size specific and collimator output factors were measured and verified with respect to Monte-Carlo simulations for single isocenter plans. Multiple isocenter plans were generated for various target size, location and cup-sizes in phantoms and 20 breast cancer patients images. Stereotactic mini-farmer chamber, OSL and TLD detectors as well as radio-chromic films were used for dosimetric measurements. Results: At the time of calibration (1/14/2016), absolute dose rate of the GammaPod was established to be 2.10 Gy/min in acrylic for 25 mm for sources installed in March 2011. Output factor for 15 mm collimator was measured to be 0.950. Absolute dose calibration was independently verified by IROC-Houston with a TLD/Institution ratio of 0.99. Cup size specific output measurements in liquid water for single isocenter were found to be within 3.0% of MC simulations. Point-dose measurements of multiple isocenter treatment plans were found to be within −1.0 ± 1.2 % of treatment planning system while 2-dimensional gamma analysis yielded a pass rate of 97.9 ± 2.2 % using gamma criteria of 3% and 2mm. Conclusion: The first GammaPod treatment unit for breast stereotactic radiotherapy was successfully installed, calibrated and commissioned for patient treatments. An absolute dosimetry and dosimetric verification protocols were successfully created.

Arguing against the Proposition is Cedric X. Yu, D.Sc. Dr. Yu received his M.S. and D.Sc. degrees from Washington University, St. Louis and, after working in industry for three years, moved to William Beaumont Hospital, Royal Oak, MI, as a medical physicist and Assistant Professor at Oakland University. In 1997 he moved to the Department of Radiation Oncology, University of Maryland as Director of Medical Physics and became the endowed Carl M. Mansfield, M.D. Professor. Dr. Yu has served on many task groups and committees of the AAPM, including the Board of Directors, as well as President of the Mid-Atlantic Chapter. His major research interest is conformal radiotherapy such as intensity modulated photon therapy (IMRT) and intensity modulated arc therapy, which he invented in 1995. He holds 20 patents and has published over 100 peer-reviewed papers, and is certified in Radiation Oncology Physics by the ABMP. Dr. Yu is the founder and CEO of Xcision Medical Systems, LLC, and declares that he is a shareholder in the company. We see an increase in multimodality treatments such as combinations of radiation with targeted therapies or immunotherapy. These strategies will benefit from advanced control of the dose to organs at risk, tumor dose escalation, or dose painting. While a prescribed target dose can be often achieved with protons as well as photons, proton therapy will always deliver a factor of 2–7 less overall dose to critical structures, independent of photon delivery or optimization techniques.5 This adds leverage when optimizing multimodality treatment strategies. Most proton therapy patients are still treated with passive scattering. In the next few years, the majority of patients will be treated with proton beam scanning allowing treatment optimization with protons that is far superior to what is achievable with photons. Intensity modulated proton therapy (IMPT, which due to energy modulation offers one additional degree of freedom compared to IMRT) and robust optimization offer unprecedented dose shaping capabilities.6 Proton therapy is expected to catch up with photon therapy as far as in-room imaging is concerned. Even proton-MR systems are being designed. Most importantly though, there are novel imaging techniques for adaptive radiation therapy and dose delivery verification that are unique to proton beams (such as prompt gamma imaging) thus offering proton specific advancements in dose confirmation and image-guidance.7 Compared to these, further improvements in photon therapy are either marginal or can be utilized on the proton side as well. In summary, both photon as well as proton therapy technology will continue to improve but the ceiling for proton therapy is significantly higher. Consequently, in the future we will see an even bigger dosimetric advantage for protons. Although clinical significance has to be shown in clinical trials, it is likely that this will have a profound impact on treatment outcomes. In the two decades since the advent of IMRT, we have seen tremendous improvements in delivery efficiency with rotational IMRT and in targeting accuracy with on-line and on-board image guidance. However, the dose distributions have not shown much improvement in spite of the intense efforts spent on optimization methods. This fact has misled many in the field to think that photon radiotherapy has reached its limits set by the physics of dose deposition and the future of radiotherapy is in protons and heavy ions. In a review paper on IMRT published eight years ago,8 the authors concluded the following: “Based on 10 years of experience with IMRT, we have learned that the opportunities in improving plan quality are limited within the constraint of present linac/MLC delivery.” It is important to note that these conclusions were based on the (then) current designs of the linear accelerator (linac) and multileaf collimator (MLC) and current delivery methods. If a new system design or new treatment method injects new degrees of freedom into plan optimization, better treatment plans can be realized. An example of exploring additional freedom is the 4πRT proposed by Ke Sheng and his colleagues. They have demonstrated that significant improvements in dose distribution can be achieved for liver,9 lung,10 head and neck,11 and prostate12 by extensive use of noncoplanar IMRT fields. Photons should also include gamma rays emitted from radionuclides. The small source sizes allow design of less compromising, site-specific solutions. A prime example is the Gamma Knife for intracranial radiosurgery. With the possibility of focusing hundreds of beams to a single spot, convenient and effective treatments can be delivered. The relative smaller sizes of teletherapy machines and linacs also allow simpler integration with imaging. The MRIdian system developed by ViewRay and the Atlantic system developed by Elekta exemplify the advantages of smaller photon machines. While the dosimetric characteristics of protons have certain advantages over those of photons, we must also recognize their disadvantages. In addition to high cost, some of these disadvantages include broader penumbra, proton beam range uncertainties, dose calculation uncertainties (e.g., CT artifacts), distal-end RBE uncertainties, high dosimetric sensitivity to anatomical changes (e.g., nasal cavity filling), and the limitations in spot size. The argument that proton therapy is still in its infancy and, therefore, it will have more room to advance is both untrue and invalid. Generally, the more complex the technology, the more restricted and difficult it is to advance. For example, intensity modulated proton arcs would be harder, if not impossible, to achieve with the current spot scanning technology. While the available freedom given by the current photon machine design and treatment methods has largely been exhausted, new designs and treatment techniques can inject new freedom and drastically improve the quality of plans. These dosimetry improvements can be achieved without losing the benefits of efficiency and image guidance. It would be shortsighted to think that radiotherapy with photons has reached its limits. Photon therapy has advanced leading to improved dose conformity. But these advances, instead of reducing the integral dose, mainly re-distribute the dose. This certainly has clinical merits. New techniques (e.g. 4π-RT) will increase dose conformity further. Yet, except at depths greater than about 15 cm (e.g., for lateral prostate fields), where scattering of protons causes the penumbra to be worse than with photons, the dose conformity can never reach that of a proton plan (which can be proven mathematically). Clinical significance is another matter. This is not the argument we are trying to settle. This debate is whether the gap between photons and protons is likely to narrow or to widen. Protons offer more potential in improvements compared to photons as outlined in my opening statement. Range and RBE uncertainties as well as sensitivity to anatomical changes are indeed proton-specific obstacles. Range uncertainties are currently reduced by advanced dose calculation and imaging, while RBE uncertainties are currently being assessed experimentally and clinically. This research will increase the current dosimetric gap between protons and photons, not decrease it. Anatomical changes are addressed with on-board imaging and adaptive therapy (for both photon and proton therapy). The lack of intensity modulated proton arcs is not a limitation because the technique is not even necessary for protons given the advanced dose shaping capabilities and small spot sizes. Photon machines are significantly smaller than proton machines (even single-room solutions). Whether efforts to make proton delivery systems more compact will result in machines with the same size as a photon system is debatable. But size is related to cost, not to treatment quality. I find my opponents’ statement that “new designs and treatment techniques can inject new freedom and drastically improve the quality of plans” unconvincing. While I agree that photon radiation therapy can be improved, it does have a lower ceiling than proton therapy. There is a consensus that the utmost goal in radiotherapy is delivering the best possible dose distribution to achieve the highest therapeutic ratio. The disagreement is which radiation type, photon and proton, will have a better long-term prospect to reliably deliver a more conformal dose distribution to the target while providing better sparing of the surrounding structures? Photon radiotherapy will more likely be the long-term winner based on the following facts. Most of the known drawbacks of proton beams as listed in my Opening Statement are rooted in the physics of particle transport in the medium and, therefore, are not easily overcome with technology. These drawbacks, coupled with the complexity and size of proton accelerators, will set the ceiling on the quality of plans and on the reliability in realizing such plans in the patient. There are many advanced treatment delivery and image guidance techniques being practiced today or emerging in practice for photons that will be hard for protons to follow. These include tracking tumor motion, rotational intensity modulation, and MRI imaging during treatment delivery. Prompt gamma imaging is unique to protons, but it merely overcomes one of the dosimetric uncertainties unique to proton beam delivery. Therefore, it should not be viewed as an advantage but rather an additional, required, imaging procedure that may further reduce patient throughput. Although proton beam therapy produces better dose distributions than photon beams today, it would be premature to assume that photon beam radiotherapy will not catch up or even surpass protons in dosimetric conformity. For example, 4π radiotherapy has shown dose distributions that rival IMPT for many sites.10,11 There is no reason that “the ceiling for proton therapy is significantly higher” than photons. It is often true that the more complex and cumbersome the technology, the harder it is to advance. Economic reasons aside, the relative reliability associated with photon beam treatment delivery and the associated treatment efficiency make advancing photon beam radiotherapy a better investment.

The first stereotactic radiation therapy system dedicated for breast cancer, the GammaPod™, has been installed and commissioned at our institution and expected to treat its first patient in March 2016. We describe our institutional design of the clinical processes and protocols as well as the quality control systems put in place for its safe and effective use. The GammaPod™ system is comprised of the treatment unit, the vacuum-assisted stereotactic breast cup immobilization device (BCID), an automatic patient loader for treatment planning imaging, and the dedicated treatment planning system. A multidisciplinary team of radiation oncologists, medical physicists, radiation therapists, and nurses designed and reviewed various sub-processes and generated process maps for different stages of GammaPod™ treatment to aid in the seamless execution of treatments. In the first single-institution clinical trial, which will test both the feasibility of delivering a high focal dose of radiation and the safety of the system, patients who receive whole-breast radiotherapy (WBRT) as part of their breast conservation therapy (BCT) will be given a single-fraction 8 Gy boost treatment using GammaPod™ prior to WBRT. Preliminary procedures were studied for 24 previously imaged volunteers used to test the reproducibility of the BCID through an IRB-approved protocol. The duration and adequacy of the procedure as well as the time spent for each of the processes were recorded throughout the experimentation period. A comprehensive clinical process map was developed for safe and efficient execution of this novel stereotactic technology. The use of a BCID for the stereotactic localization and immobilization of the breast requires a fast-paced but well-defined process. The single day image-and-treat workflow starts with selection and installation of the appropriate breast cup by the clinical team. In the preliminary testing, the average time for the initial BCID setup was 27±11 minutes. Out of 24 patients enrolled in the study, we had difficulty mounting the BCID due to patient comfort and body hiatus for 4 patients and were not able to find an appropriate breast cup size for 1 patient. For the remaining patients, CT imaging was performed in prone position with the help of the automated patient loader and images were then transferred to the treatment planning system. Patient plans were ready for treatment execution in 33±3 minutes after the completion of imaging. Throughout the entire process, several quality checklists and safety measures were also implemented to further improve the accuracy and efficiency of treatments. A clinical workflow was developed for the first installation of GammaPod™ stereotactic radiotherapy technology. Process mapping and identification of the causes and effects of potential failures relating to the workflow improves the quality of GammaPod™ treatments and increases safety and efficiency for the use of this technology.