Re-irradiation Cases Research Articles

Reirradiation Practice in Gynecological Cancer: Insights from a National Survey in Spain.

Given the lack of standardisation in gynecological cancer reirradiation, the Gyneacologial Radiation Oncology (GINECOR) working group on behalf of the Spanish Society of Radiation Oncology (SEOR), works towards to inquire the current state of reirradiation practices among the radiation oncology departments in Spain. An online 37-question survey was sent to all GINECOR members, representing most Spanish centers. The survey addressed general aspects of reirradiation, including experience, reirradiation sites, and techniques used. It included seven clinical case scenarios on reirradiation, and a final section on technical aspects of external beam radiotherapy (EBRT) and brachytherapy (BT) treatment. Descriptive statistics were used for data analysis. Out of 58 centers, 29 responded, with 51.7% performing ≥ 5 reirradiation cases annually. While most centers offer multiple techniques, only 16/29 have access to BT. For in-field local relapse with surgery contraindicated, 79.3% performed BT in endometrial cancer, but only 27.5% treated with BT in cervical cancer recurrence. In this case, 17.2% used SBRT. For endometrial and cervical cancer, 44.8% and 65.4% of centers prescribed doses based on organ-at-risk tolerance, respectively. For pelvic wall/parametrial in-field relapse, 46.4% of the centres reirradiated with stereotactic body radiotherapy (SBRT), and 32.1% with BT. In nodal reirradiation, SBRT was preferred by 90% of centers. Variability was observed in target volume definitions for EBRT and proton therapy. Reirradiation for gynecological cancer remains unstandardized, presenting significant challenges in clinical practice. To improve reirradiation protocols in gynecological cancer, the GINECOR working group is currently conducting a systematic review and formulating Delphi recommendations.

The Potential and Challenges of Proton FLASH in Head and Neck Cancer Reirradiation.

Ultrahigh-dose-rate therapy, also known as FLASH radiotherapy (RT), is an emerging technique that is garnering significant interest in cancer treatment due to its potential to revolutionize therapy. This method can achieve comparable tumor control to conventional-dose-rate RT while offering the enhanced protection of normal tissue through the FLASH-sparing effect. This innovative technique has demonstrated promising results in preclinical studies involving animals and cell lines. Particularly noteworthy is its potential application in treating head and neck (HN) cancers, especially in patients with challenging recurrent tumors and reirradiation cases, where the toxicity rates with conventional radiotherapy are high. Such applications aim to enhance tumor control while minimizing side effects and preserving patients' quality of life. In comparison to electron or photon FLASH modalities, proton therapy has demonstrated superior dosimetric and delivery characteristics and is a safe and effective FLASH treatment for human malignancies. Compared to the transmission proton FLASH, single-energy Bragg peak FLASH is a novel delivery method that allows highly conformal doses to targets and minimal radiation doses to crucial OARs. Proton Bragg peak FLASH for HN cancer has still not been well studied. This review highlights the significance of proton FLASH in enhancing cancer therapy by examining the advantages and challenges of using it for HN cancer reirradiation.

Does a peer review group consensus process for MR-Linac patients affect clinical care? Evaluation of impact and feasibility

Background and purposePeer review is an important component of quality assurance in radiotherapy. To our knowledge, there are no studies reporting on the feasibility and outcomes of the peer review process for magnetic resonance (MR) guided radiotherapy (MRgRT) on the MR linear accelerator (MR-Linac) despite the planning complexity involved and its evolving clinical indications. This study aimed to quantify the rate of change in treatment plans post-peer review and the time and resources required. Materials and methodsFifty-five cases presented at weekly MR-Linac peer review meetings across two centres from 8 June to 21September 2023 were prospectively collected. Cases were analysed to determine the rate and extent of plan changes based on the Peer Review Audit Tool for radiation oncology (PRAT) developed by the Royal Australian and New Zealand College of Radiologists (RANZCR). ResultsPeer review resulted in changes to 36.4 % of treatment plans (n = 20), with 3.6 % (n = 2) having major changes requiring deferment of treatment. The most frequent changes were to organs at risk (OAR) volumes involving both delineation and increased OAR sparing (16.4 %, n = 9), total dose and fractionation (10.9 %, n = 6) and target volume dose coverage (5.5 %, n = 3). Patients with SBRT plans (39.1 % cf 22.2 %), oligometastatic/oligoprogressive sites (38.1 % cf 30.7 %) and reirradiation cases (41.2 % cf 34.2 %) had higher rates of change. Cases took a mean of 7 min (range 2–15 minutes) to discuss. ConclusionThe high rates of plan changes support the value of peer review in MRgRT. We recommend, where possible that all MRgRT cases, particularly those involving SBRT plans, oligometastatic/oligoprogressive sites, and/or reirradiation, be subject to peer review.

Feasibility and flexibility of a novel multi-dose level avoidance reirradiation technical methodology in recurrent head and neck cancer.

Reirradiation in recurrent head and neck cancer presents a considerable clinical challenge in radiation oncology. Though technically feasible due to advanced treatment delivery and planning techniques, confidence in delivering such treatments is not universal and patient selection is critical. Radiotherapy planning in reirradiation cases presents a complex technical challenge owing to the often-considerable overlap of dose from a patient's first treatment plan. This technical note describes three clinical case studies of recurrent head and neck cancer and the technical details of how their multidose level reirradiation was planned. Each patient had confirmed recurrence of squamous cell carcinoma and was referred for reirradiation to a previously irradiated area. The clinical details for each patient are provided before a detailed description of the treatment planning methodology is presented, which specifies how to approach such complex overlapping treatment volumes. The patient outcomes are described and a discussion is presented outlining the clinical challenges associated with these cases and the variables that must be accounted for when considering patients for potential reirradiation.

Classification of Patients With Painful Tumors to Predict Response to Palliative Radiation Therapy

PurposeThis study aimed to identify factors affecting pain response to develop a patient classification system for palliative radiotherapy. Methods and MaterialsOur prospective observational study (XXXXX) provided data on patients who received palliative radiotherapy for painful tumors. The eligibility criteria were that the numerical rating scale (NRS) was 2 or more before treatment, and palliative radiotherapy was performed between August 2021 and September 2022. Post-radiotherapy follow-up was scheduled prospectively at 2, 4, 12, 24, 36, and 52 weeks. Pain response was assessed using the International Consensus Pain Response Endpoints, with the primary outcome being the response rate within 12 weeks. Multivariable logistic regression was performed to identify factors affecting pain response and develop the classification system. Each class evaluated the differences in response rate, time to response, and progression. ResultsOf the 488 registered lesions, 366 from 261 patients met the criteria. Most patients had bone metastases (75%), with 72% using opioids and 22% were re-irradiation cases. Conventional radiotherapy (e.g., 8 Gy single fraction, 20 Gy in 5 fractions) was administered to 93% of patients. Over 6.8 months median follow-up, the average NRS decreased from 6.1 to 3.4 at 12 weeks for 273 evaluable lesions, with a 60% response rate. Opioid use and re-irradiation negatively impacted the response rate in multivariate analysis (P<0.01). Lesions were categorized into class 1 (no opioids, no re-irradiation, 89 lesions), class 2 (neither class 1 nor 3, 211 lesions), and class 3 (opioids and re-irradiation, 66 lesions), with respective response rates of 75%, 61%, and 36% (P<0.001). Time to response was similar across classes (P = 0.91), but progression rates at 24 weeks were different (11%, 27%, 63%, P<0.001). ConclusionsOpioid use and re-irradiation were identified as factors leading to significant variations in pain response rates and time to progression.

Multi-centre evaluation of variation in cumulative dose assessment in reirradiation scenarios

Background and PurposeSafe reirradiation relies on assessment of cumulative doses to organs at risk (OARs) across multiple treatments. Different clinical pathways can result in inconsistent estimates. Here, we quantified the consistency of cumulative dose to OARs across multi-centre clinical pathways. Material and MethodsWe provided DICOM planning CT, structures and doses for two reirradiation cases: head & neck (HN) and lung. Participants followed their standard pathway to assess the cumulative physical and EQD2 doses (with provided α/β values), and submitted DVH metrics and a description of their pathways. Participants could also submit physical dose distributions from Course 1 mapped onto the CT of Course 2 using their best available tools. To assess isolated impact of image registrations, a single observer accumulated each submitted spatially mapped physical dose for every participating centre. ResultsCumulative dose assessment was performed by 24 participants. Pathways included rigid (n = 15), or deformable (n = 5) image registration-based 3D dose summation, visual inspection of isodose line contours (n = 1), or summation of dose metrics extracted from each course (n = 3). Largest variations were observed in near-maximum cumulative doses (25.4 – 41.8 Gy for HN, 2.4 – 33.8 Gy for lung OARs), with lower variations in volume/dose metrics to large organs. A standardised process involving spatial mapping of the first course dose to the second course CT followed by summation improved consistency for most near-maximum dose metrics in both cases. ConclusionLarge variations highlight the uncertainty in reporting cumulative doses in reirradiation scenarios, with implications for outcome analysis and understanding of published doses. Using a standardised workflow potentially including spatially mapped doses improves consistency in determination of accumulated dose in reirradiation scenarios.

A Single Institution Experience of a Biweekly Head and Neck Contouring Peer Review.

Due to the complexity of head and neck radiotherapy, a single weekly chart rounds session is insufficient to review contours. A dedicated biweekly review of all head and neck contours (prior to treatment planning) that can fully assess images and targets can lead to better patient outcomes. A full review of all head and neck contours also increases the number of contours that resident physicians can observe. In total, 38 consecutive patients treated between August 2022 and December 2022 were analyzed in a biweekly head and neck contouring peer review. Three head and neck faculty radiation oncologists and four resident physicians participated. An allotted 30-minute time was granted per review session. Changes were tracked and stratified by whether physician contours underwent no changes/minor changes/major changes. Other metrics including re-irradiation status and attendance were noted. An average of 1.65 patients were discussed per review. Given the allotted time, on average this allowed for up to 18 minutes of discussion per patient. In contrast, our departmental chart rounds session is allotted 1 hour for 40+ patients to be discussed (1.5 minutes per patient). Overall, 10/38 patients underwent minor changes (26.3%) to contour structures and 1 patient underwent a major change (2.6%). Four patients (10.5%) were re-irradiation cases CONCLUSION: A dedicated biweekly half hour review session is both feasible and practical. Additional discussion of head and neck contours helps to implement improvements into a patient's treatment plan. Additional discussion and debate for primary and re-irradiation also increases the number of cases that a training resident physician can observe.

Carbon-Ion Radiation Therapy for Unresectable Locally Recurrent Colorectal Cancer: A Promising Curative Treatment for Both Radiation Therapy: Naïve Cases and Reirradiation Cases

It is difficult to effectively cure patients with unresectable locally recurrent colorectal cancers (LRCRCs) using conventional chemotherapy or chemoradiation therapy. Furthermore, treatment options vary depending on the patient's history of radiation therapy. Carbon-ion radiation therapy (CIRT) is a potentially curative treatment for these patients. Here, we compare the treatment outcomes of radiation therapy-naïve cases (nRT) and re-irradiation cases (reRT). Patients with LRCRC treated with CIRT at QST Hospital between 2003 and 2019 were eligible. CIRT was administered daily 4 d/wk for 16 fractions. The total irradiated dose was set at 73.6 Gy (relative biologic effectiveness-weighted dose [RBE]) for nRT and 70.4 Gy (RBE) for reRT patients. We included 390 nRT cases and 83 reRT cases. The median follow-up period from the initiation of CIRT was 48 (5-208) months. The 3-year overall survival (OS) rates for nRT and reRT were 73% (95% CI, 68%-77%) and 76% (65%-84%), respectively. The 5-year OS rates were 50% (45%-55%) and 50% (38%-61%), respectively. These rates did not differ significantly (P=.55). The 3-year local control (LC) rates for nRT (73.6 Gy) and reRT (70.4 Gy) cases were 80% (75%-84%) and 80% (68%-88%), respectively. The 5-year LC rates were 72% (67%-78%) and 69% (55%-81%), respectively, without a significant difference (P=.56). Our results suggest that CIRT for LRCRC is a very effective and promising treatment for both nRT and reRT cases.

Rates of Radiosurgical Decompression for High Grade Epidural Spinal Disease Due to Solid Tumor Metastases

A recent phase 2 study reported a significant difference in Bilsky grading of treated lesions before and after SBRT. This study reports rates of epidural downgrading following spine SBRT in a larger cohort of patients with high grade epidural disease. Patients with high grade epidural disease from solid spinal metastases treated with SBRT from 2009-2021 were retrospectively reviewed. High grade epidural disease was defined as Bilsky grade 1c-3 for lesions above the conus. A modified Bilsky grading was developed and used for lesions below the conus; grade 0 is spinal bone involvement only; grade 1 is epidural involvement without contact of cauda equina; grade 2 is contact of cauda equina with visible cerebrospinal fluid (CSF); grade 3 is compression of cauda equina with no visible CSF. High grade epidural disease below the conus was defined as a modified Bilsky grade 1-3. Patients who received upfront surgery were included in the current study if post-surgical grading met inclusion criteria. The first post-SBRT MRI was compared to the SBRT simulation imaging to evaluate the extent of epidural downgrading. Epidural disease grading pre- and post-SBRT were compared using the Wilcoxon signed-rank test. A total of 460 vertebral segments from 201 patients were included. The most common histologies were GI (19.3%), breast (16.0%), renal cell carcinoma (13.9%), and prostate (12.6%). Metastases were most often in the T-spine (45.8%), L-spine (34.8%), C-spine (11.8%), and Sacrum (7.6%). Most cases were treated with 3 (37.4%) or 5 (44.5%) fractions with a median prescription dose of 27 Gy or 30 Gy, respectively. 43.3% of cases were treated in the postoperative setting, while 18.5% of cases had prior radiation therapy at the same vertebral level. Median time to first post-SBRT MRI was 3.0 months (IQR 1.8-3.6). Among those with disease above the conus, 98 of the 139 cases (70.5%) had a pre-SBRT Bilsky grade of 2. For those with disease below the conus, 70 of the 99 cases (70.7%) had a pre-SBRT modified Bilsky grade of 1. Epidural downgrading was seen in 32.3% of all cases, 24.3% of postoperative cases, and 25.0% of reirradiation cases. The change in epidural grading was statistically different between pre- and post-SBRT evaluation for all cases (p<0.001), postoperative cases (p<0.001), and reirradiation cases (p = 0.01). We report the largest study to date exploring epidural downgrading following spine SBRT. Although surgery is typically deemed essential for decompression of neural elements, this study suggests that SBRT results in epidural downgrading in as many as one quarter to one third of patients, depending on the clinical scenario.

Dosimetric Impact of Radiolucent Carbon Fiber Hardware for Post-Operative Spine Stereotactic Body Radiation Therapy

The spine is the most common site of osseous metastases. In the non-operative setting, there is growing support for stereotactic body radiation therapy (SBRT) over conventional radiation therapy for improved pain relief and local control. Hybrid therapy consisting of separation surgery and post-operative SBRT is considered in patients with biomechanical instability and epidural cord compression. Surgery traditionally requires titanium (Ti) implants, which introduce artifacts on post-operative imaging in addition to increased uncertainty and beam attenuation. Use of radiolucent carbon fiber reinforced polyetheretherketone (CFR-PEEK) hardware has been shown to provide safe and comparable surgical outcomes as compared to Ti. Our primary objective is to assess the dosimetric impact of Ti versus carbon fiber implants in spine SBRT. Single institution retrospective series of post-operative spine SBRT from 2019-2020. Re-irradiation cases were excluded. The electronic medical record and treatment planning systems (TPS) were queried. Dosimetric analyses compared original Ti plans with reoptimized plans, replacing Ti hardware electronic density with carbon fiber. Maintaining clinical goals, dose calculations were performed in a treatment planning system using a collapsed cone algorithm. All treatments used step and shoot intensity modulated radiation therapy to avoid beam angles with significant metal along the beam path. Metallic artifacts were contoured and assigned the appropriate tissue density. A D'Agostino-Pearson test was used to assess data for normality. We used paired Student's t-tests to compare three dosimetric outcomes in the setting of Ti and carbon fiber implants. Planning target volume (PTV) coverage was represented by the volume receiving at least the prescribed dose (%), the maximum point dose (dmax, cGy) to the spinal cord planning risk volume (PRV, 2 mm margin), and the overall hot spot intensity (plan dmax). A series of 14 consecutive SBRT cases were evaluated (dose 27-30 Gy in 3-5 fractions). All dosimetric outcomes were normally distributed (p>0.05). We found a statistically significant difference in PTV coverage between the original SBRT treatment plans with Ti hardware (mean 85.1 ± 7.9%) and reoptimized carbon fiber hardware (87.3 ± 6.6%; p = 0.002). There was no significant difference in mean spinal cord PRV dmax between Ti and carbon fiber plans (1846 ± 483 cGy vs. 1842 ± 495 cGy; p>0.05). We observed a nonsignificant increase in mean overall dmax from 3932 ± 416 cGy in the Ti cohort to 4111 ± 906 cGy in the carbon fiber cohort (p>0.05). Carbon fiber implants provide a significant increase in SBRT target coverage, without impacting the overall plan and spinal cord PRV dmax in this retrospective series. In addition to improved post-operative imaging and reduced uncertainty, carbon fiber hardware may offer dosimetric advantages as compared to traditional Ti spinal implants, and warrants further investigation in a larger cohort.

Low Tesla MR Imaging for Spine with Hardware

Acquiring MR images with minimized susceptibility artifacts is essential for spines with medical hardware to delineate clinical target volumes (CTVs) in radiation therapy for chordomas, chondrosarcomas, and other sarcomas. Since it can be more challenging to visualize the primary structures in high-tesla MR images due to metal-induced artifacts, we optimized imaging parameters to acquire high-quality, low-tesla MR images for clinical use. OptimalMR imaging parameters were investigated under general guidelines for artifact reduction techniques by testing several 3D spin echo and gradient echo sequences in a 0.23-T MR scanner. A customized spine phantom was developed to acquire MR images for bony materials which included, 4-6 industrial titanium screws, an aluminum plate, and a superflab bolus. While the 3D b-FFE sequence was used to acquire MR images with a high signal-to-noise ratio, the other 3D T1-FFE, THRIVE, and DTSE sequences were applied to reduce susceptible artifacts to the medical hardware. The optimized parameters determined in the phantom test were applied to the 15 clinical cases, including patients with residual spinal tumors and fusion hardware. The low-tesla MR imaging technique was also used to scan sarcomas of the extremities and re-irradiation cases of spinal metastases. The optimized low-tesla MR images in the spine were noticeably useful to guide CTV delineations for patients with medical hardware, especially for residual or recurrent tumors. The imaging technique to minimize susceptibility artifacts enabled a more defined separation of each hardware component from the spinal cord and CTVs. In spine metastasis cases, pre-irradiated target volumes were determined, reflecting property changes in the bone marrow. The MR images acquired using the optimized parameters showed minimal artifacts to scan spine patients with hardware. By using the low-tesla MR images, spinal chordoma and chondrosarcoma patients could be treated to improve tumor control probabilities with minimized complications.

Carbon Ion Radiotherapy in the Treatment of Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is a highly lethal cancer with limited treatment options and poor prognosis. Carbon ion radiotherapy (CIRT) has emerged as a promising treatment modality for HCC due to its unique physical and biological properties. CIRT uses carbon ions to target and destroy cancer cells with a high precision and efficacy. The Bragg Peak phenomenon allows precise dose delivery to the tumor while minimizing damage to healthy tissues. In addition, the high relative biological effectiveness of carbon ions can be shown against radioresistant and hypoxic tumor areas. CIRT also offers a shorter treatment schedule than conventional radiotherapy, which increases patient convenience and compliance. The clinical outcomes of CIRT for HCC have shown excellent local control rates with minimal side effects. Considering its physical and biological properties, CIRT may be a viable option for complex clinical scenarios such as patients with poor liver function, large tumors, re-irradiation cases, and tumors close to critical organs. Further research and larger studies are needed to establish definitive indications for CIRT and to compare its efficacy with that of other treatment modalities. Nevertheless, CIRT offers a potential breakthrough in HCC management, providing hope for improved therapeutic outcomes and reduced treatment-related toxicities.

Management of reirradiations: A clinical and technical overview based on a French survey

IntroductionThe reirradiation number increased due to systemic therapies and patient survival. Few guidelines regarding acceptable cumulative doses to organs at risk (OARs) and appropriate dose accumulation tools need, made reirradiation challenging. The survey objective was to present the French current technical and clinical practices in reirradiations. MethodsA group of physician and physicists developed a survey gathering major issues of the topic. The questionnaire consisted in 4 parts: data collection, demographic, clinical and technical aspects. It was delivered through the SFRO and the SFPM. Data collection lasted 2 months and were gathered to compute statistical analysis. Results48 institutions answered the survey. Difficulties about patient data collection were related to patient safety, administrative and technical limitations. Half of the institutions discussed reirradiation cases during a multidisciplinary meeting. It mainly aimed at discussing the indication and the new treatment total dose (92%). 79% of the respondents used various references but only 6% of them were specific to reirradiations. Patients with pain and clinical deficit were ranked as best inclusion criteria. 54.2% of the institutions considered OARs recovery, especially for spinal cord and brainstem. A commercial software was used for dose accumulation for 52% of respondents. Almost all institutions performed equivalent dose conversion (94%). A quarter of the institutions estimated not to have the appropriate equipment for reirradiation. ConclusionThis survey showed the various approaches and tools used in reirradiation management. It highlighted issues in collecting data, and the guidelines necessity for safe practices, to increase clinicians confidence in retreating patients.

MSS02 Presentation Time: 3:50 PM: Feasibility of 3D-Printed Endorectal High Dose Rate Brachytherapy Applicator: A Single Patient Case Report

<h3>Purpose</h3> Endorectal brachytherapy is an effective treatment for select patients with rectal cancer, particularly in re-irradiation cases. In the United States, this technique is underutilized. Herein we describe, to our knowledge, the first report of a previously irradiated rectal cancer patient treated with a 3D-printed Endorectal High Dose Rate Brachytherapy Applicator. <h3>Materials and Methods</h3> A 64 year old morbidly obese female who was previously irradiated for endometrial cancer in 2009 presented with newly diagnosed uT3N0, MRI T2N0 rectal adenocarcinoma. Previous radiation records were no longer available other than a treatment summary identifying a total dose of 50.4 Gy in 28 fractions was delivered to the pelvis. Total neoadjuvant therapy was recommended with a watch and wait approach given surgical difficulties in a morbidly obese woman previously irradiated. The mass began 3 cm from the anal verge, extended nearly 5 cm superiorly, and circumferentially involved less than 50% of the rectal lumen. Fiducial markers were placed in the 4 cardinal directions. A 2.5 cm diameter, 18 cm length, 13 multichannel applicator (1 central channel, and 12 outer channels 5mm from cylinder surface) design was designed in <i>Autodesk Fusion 360</i> to ensure adequate coverage (see figure 1). 3D printing was achieved with a FormLabs 3 printer using Surgical Guide V1 resin. [JF1] The applicator was placed on the first day of treatment at CT simulation. The patient was placed in the prone position with the applicator inserted in the rectum. Treatment was delivered in 4 consecutive daily fractions of 6.5 Gy for a total of 26 Gy. <h3>Results</h3> The CTV volume was 19.8 cc and maximum tumor depth was 13 mm. Tumor coverage was excellent with a V200 of 6%, V150 of 23%, V100 of 70%, D90 of 83%. Target coverage was sacrificed to reduce the V200, given unknown previous radiation fields. The bladder D2cc dose was 5.4 Gy[JD2] [MS3] . The patient had complete resolution of rectal bleeding by the 4^th fraction. She reported no acute toxicities. At the time of this report, the patient is 1 month post brachytherapy with no reported toxicities with significantly easier bowel movements and continues to have no bleeding. <h3>Conclusion</h3> To our knowledge, this is the first reported 3D printed Endorectal High Dose Rate Brachytherapy Applicator used in clinical practice. In this case, the patient had early response with no adverse events. We believe 3D printing is a useful tool for Brachytherapists, and a feasible treatment option for rectal cancer patients.

Evaluation of Repeated Lung Stereotactic Body Radiotherapy Using a Radiotherapy Dose Accumulation Routine

<h3>Purpose/Objective(s)</h3> Repeated lung SBRT has been used for recurrent or metachronous non-small-cell lung cancer. Comprehensive evaluation of cumulative dose is essential for safe reirradiation to minimize the risk of pneumonitis and esophageal toxicity. We evaluated an in-house script named RADAR (Radiotherapy Dose Accumulation Routine) designed to provide accurate dose assessment that accounts for registration uncertainties, and improve the efficiency of clinical workflow. <h3>Materials/Methods</h3> In this pilot study, we analyzed a cohort of 20 patients who underwent 2-5 courses of repeated lung SBRT. Lung volume changed 8±8% between courses. Planning CT images from earlier treatment courses were registered onto the final course in two steps: first, a rigid registration based on alignment of spine and rib cage, then a deformable image registration (DIR) using a ‘demons' algorithm in a planning system. The resulting deformable vector fields were used by RADAR to transform voxels for automated dose accumulation. User can choose to output either physical dose or equivalent dose in 2Gy fractions (EQD2, α/β=3) with a discount factor (Paradis, ARO 2019). RADAR provides three approaches for dose accumulation: 1) direct sum that outputs voxel level dose summation; 2) unrestricted search that incorporates DIR uncertainty by conservatively assigning the maximum dose within a search radius (3mm) to the voxel of interest for dose accumulation; 3) restricted search, which performs the same dose accumulation as in 2) but imposes structure label matching in the search radius, therefore including only voxels within the same structure. Accumulated dose distribution was written back to the planning system for evaluation. We extracted mean lung dose (MLD) and esophagus D5cc (EsoD5cc) with respect to various accumulation approaches for comparison. <h3>Results</h3> MLD and EsoD5cc were significantly higher when accounting for DIR uncertainties (<i>p</i><0.001 two-tailed t-test). MLD has less uncertainty than EsoD5cc due to its averaging nature. For radiotherapy with >2 courses, RADAR considerably shortened the processing time by auto-accumulating dose from multiple courses simultaneously, as opposed to the cumbersome manual approach of creating plan sums iteratively. Typical time for dose accumulation and evaluation using RADAR is < 10 mins. <h3>Conclusion</h3> RADAR is a convenient and efficient tool to calculate and evaluate cumulative dose for lung reirradiation cases. It identifies higher OAR doses due to dose accumulation uncertainties, for example coming from the registration. Our study provides initial data to establish clinical guidance for design and optimization of repeated lung SBRT.

Assessing the Clinical Impact of the Special Physics Consult (SPC)

<h3>Purpose/Objective(s)</h3> Progress in cancer care has improved the survival rates of treated cancer patients. With patients living longer, radiation oncologists are more likely to manage patients who have had prior courses of adjacent or overlapping radiation. To facilitate and improve the safety of re-irradiation, the special physics consult (SPC) was adopted in certain clinics. SPCs are ordered by physicians and performed by physicists to address complex planning and physics considerations (including physics evaluation of patients with implantable devices, anatomical changes during treatment, and monitoring surface dose). Results are used to inform clinical decision-making in patients who may be at an increased risk of complications. This study aims to evaluate the clinical impact of using SPCs by evaluating the extent to which results can alter management. <h3>Materials/Methods</h3> We evaluated 100 consecutive SPC orders entered over a 5-month period. The purpose for ordering the SPC and its impact on management were recorded for all cases. For re-irradiation SPCs, the dose from prior treatments was applied onto the current CT dataset using rigid or deformable registration, then all dose was scaled to equivalent dose in 2-Gy fractions (EQD₂) and summed. Patients with implantable devices were evaluated following the recommendations of AAPM TG 203. When in-vivo dosimetry was ordered, it was performed on patients using an optically stimulated luminescence dosimeter system. In the case of anatomical changes to a patient throughout the course of treatment, an adaptive plan was created using the daily imaging CBCT and the dose was compared to the originally planned dose. The results of all SPCs were reviewed with the ordering physician prior to final clinical decision-making. <h3>Results</h3> The majority of SPCs were ordered for re-irradiation cases (88.0%). SPCs were otherwise ordered to evaluate implantable devices (8.0%), adaptive replanning (3.0%) and in-vivo dosimetry (1.0%) as shown in table 1. Across all SPCs, 37.0% yielded one or more adjustments to the treatment plan. For re-irradiation cases, the SPC results produced one or more planning changes in 38.6% of cases. These changes include re-optimization (29.5%), target contour revisions (9.1%), replanning (5.7%), modality change (4.5%), OAR contour revisions (2.3%), and fractionation changes (1.1%). <h3>Conclusion</h3> Our data shows that SPC results can impact management in more than a third of evaluated cases. Re-irradiation is the most common reason for ordering an SPC, highlighting it as a valuable tool for ensuring patient safety and quality of care. Future studies are needed to further evaluate the benefits of SPCs.

An algorithm for thoracic re-irradiation using biologically effective dose: a common language on how to treat in a \u201cno-treat zone\u201d

BackgroundRe-irradiation (re-RT) is a technically challenging task for which few standardized approaches exist. This is in part due to the lack of a common platform to assess dose tolerance in relation to toxicity in the re-RT setting. To better address this knowledge gap and provide new tools for studying and developing thresholds for re-RT, we developed a novel algorithm that allows for anatomically accurate three-dimensional mapping of composite biological effective dose (BED) distributions from nominal doses (Gy).MethodsThe algorithm was designed to automatically convert nominal dose from prior treatment plans to corresponding BED value maps (voxel size 2.5 mm3 and α/β of 3 for normal tissue, BED3). Following the conversion of each plan to a BED3 dose distribution, deformable registration was used to create a summed composite re-irradiation BED3 plan for each patient who received two treatments. A proof-of-principle analysis was performed on 38 re-irradiation cases of initial stereotactic ablative radiotherapy (SABR) followed by either re-SABR or chemoradiation for isolated locoregional recurrence of early-stage non-small cell lung cancer.ResultsEvaluation of the algorithm-generated maps revealed appropriate conversion of physical dose to BED at each voxel. Of 14 patients receiving repeat SABR, there was one case each of grade 3 chest wall pain (7%), pneumonitis (7%), and dyspnea (7%). Of 24 patients undergoing repeat fractionated radiotherapy, grade 3 events were limited to two cases each of pneumonitis and dyspnea (8%). Composite BED3 dosimetry for each patient who experienced grade 2–3 events is provided and may help guide development of precise cumulative dose thresholds for organs at risk in the re-RT setting.ConclusionsThis novel algorithm successfully created a voxel-by-voxel composite treatment plan using BED values. This approach may be used to more precisely examine dosimetric predictors of toxicities and to establish more accurate normal tissue constraints for re-irradiation.

Reirradiation for Nasal Cavity or Paranasal Sinus Tumor-A Multi-Institutional Study.

Simple SummaryNasal cavity or paranasal sinus tumors are rare, with treatment outcomes reported as a small subgroup of all head and neck tumors. However, due to their unique anatomical characteristics (proximity to the optic pathway and skull base), treatment efficacy and toxicity in should be focused on those areas. After curative treatment involving radiotherapy, local recurrence is common and treated mainly through surgery. Unfortunately, surgery is difficult in almost all cases due to the critical organs involved. Systemic chemotherapy plays a central role in managing recurrent tumors; however, its efficacy is insufficient to extend longevity. Reirradiation is challenging, as it leads to higher toxicity, but it potentially offers long-lasting tumor control, including cure and symptom palliation in patients with no other remaining therapeutic options. We examined this subgroup using multi-institutional data and found that reirradiation is feasible for treating nasal cavity or paranasal sinus tumors. A relatively high distant metastasis ratio was found after reirradiation, especially in patients with lymph node metastasis.We evaluated the efficacy and toxicity of reirradiation of nasal cavity or paranasal sinus tumors. We collected and analyzed multi-institutional data of reirradiation cases. Seventy-eight patients with nasal or paranasal sinus tumors underwent reirradiation. The median survival time was 20 months with a medial follow-up of 10.7 months. The 2-year local control and overall survival rates were 43% and 44%, respectively. Tumor volume (≤25 cm3), duration between previous radiotherapy and reirradiation (≤12 months), histology (squamous cell carcinoma), male sex, and lymph node involvement were predisposing factors for poor survival. Distant metastasis was observed in 20 patients (25.6%). Grade ≥ 3 adverse events were observed in 22% of the patients, including five grade 4 (8.6%) cases and one grade 5 (1.2%) case. Tumor location adjacent to the optic pathway was a significant predisposing factor for grade ≥3 visual toxicity. Reirradiation of nasal and paranasal sinus tumors is feasible and effective. However, adverse events, including disease-related toxicities, were significant. Prognostic factors emerge from this study to guide multidisciplinary approaches and clinical trial designs.

Dose summation and image registration strategies for radiobiologically and anatomically corrected dose accumulation in pelvic re-irradiation

Background Re-irradiation (reRT) is a promising technique for patients with localized recurrence in a previously irradiated area but presents major challenges. These include how to deal with anatomical change between two courses of radiotherapy and integration of radiobiology when summating original and re-irradiation doses. The Support Tool for Re-Irradiation Decisions guided by Radiobiology (STRIDeR) project aims to develop a software tool for use in a commercial treatment planning system to facilitate more informed reRT by accounting for anatomical changes and incorporating radiobiology. We evaluated three approaches to dose summation, incorporating anatomical change and radiobiology to differing extents. Methods In a cohort of 21 patients who previously received pelvic re-irradiation the following dose summation strategies were compared: (1) Rigid registration (RIR) and physical dose summation, to reflect the current clinical approach, (2) RIR and radiobiological dose summation in equivalent dose in 2 Gy fractions (EQD2), and (3) Patient-specific deformable image registration (DIR) with EQD2 dose summation. Results RIR and physical dose summation (Strategy 1) resulted in high cumulative organ at risk (OAR) doses being ‘missed’ in 14% of cases, which were highlighted by EQD2 dose summation (Strategy 2). DIR (with EQD2 dose summation; Strategy 3) resulted in improved OAR overlap and distance to agreement metrics compared to RIR (with EQD2 dose summation; Strategy 2) and was consistently preferred in terms of clinical utility. DIR was considered to have a clinically important impact on dose summation in 38% of cases. Conclusion Re-irradiation cases require individualized assessment when considering dose summation with the previous treatment plan. Fractionation correction is necessary to meaningfully assess cumulative doses and reduce the risk of unintentional OAR overdose. DIR can add clinically relevant information in selected cases, especially for significant anatomical change. Robust solutions for cumulative dose assessment offer the potential for future improved understanding of cumulative OAR tolerances.

Patterns of Failure After SBRT Reirradiation for Recurrent Head and Neck Cancer

Stereotactic body radiotherapy (SBRT) is an emerging modality for the reirradiation of head and neck cancers (HNC). The need to use smaller reirradiation volumes to limit severe toxicity concerns represents a challenge in determining optimal target coverage. Herein, we investigate the associated patterns of failure after SBRT using previously defined spatial and dosimetric analysis (Mohamed et al, Radiat Oncol. 2017).SBRT reirradiation HNC cases treated between 2014-2019 and surveilled by CT, PET/CT, and/or MRI were reviewed retrospectively in this IRB approved study. Patients with radiographic evidence of recurrence within the head and neck region after SBRT were identified. Multifocal disease was defined as any non-contiguous FDG-avid or biopsy positive disease seen on imaging. Diagnostic scans were co-registered with planning CT scans (pCT) for manual segmentation of recurrent gross volumes (rGTV). rGTVs were then deformed to co-registered pCTs for failure classification. The classification followed a granular typology of 5 failure categories: central high-dose (type A or "in-field"), peripheral high-dose (type B), central low-dose (type C), peripheral low-dose (type D or "marginal"), and extraneous-dose (type E or "out of field"). Each type was determined based on the centroid location of rGTV relative to the planning target volumes plus the dose received by 95% of rGTV volume.A total of 106 SBRT cases were reviewed out of which 34 patients (32%) recurred after SBRT; 27 (79%) patients had squamous cell carcinomas, 7 (21%) received postoperative SBRT, and 24 (71%) received concurrent systemic therapy. Twenty-three (68%) patients received 42.5-45 Gy in 5 fractions (Fx) and 7 (21%) patients received 36 Gy in 6 Fx. Median time to failure was 5.5 months (range, 1-22 months). Twenty-two recurrences (65%) were out-of-field type E failures, 6 (18%) type A, 3 (9%) type C, and 3 (9%) type D. Fourteen of 16 (88%) multifocal SBRT reirradiation cases had Type E failures compared to 8 of 18 (44%) unifocal SBRT cases. Among the 6 in-field failures, 3 received 36 Gy in 6 Fx and 3 received 42.5-45 Gy in 5 Fx.Post SBRT reirradiation recurrences were seen in one-third of cases with the majority of failures being Type E (outside the treatment field), particularly in patients who were treated for multifocal disease. The use of 42.5-45 Gy in 5 Fx appears to be an effective biological dose for local tumor control. Marginal (Type C and D) failures may be reduced with larger margins, but limit feasibility of SBRT. Therefore, future reirradiation strategies should aim to improve patient selection, multimodal therapy, and margin definition in the HNC SBRT reirradiation setting.