The Special Medical Physics Consult Process for Reirradiation Patients

Radiobiologically equivalent deformable dose mapping for re-irradiation planning: Implementation, robustness, and dosimetric benefits

BACKGROUND

Re-irradiation in radiotherapy presents complexities that require dedicated tools to generate optimal re-treatment plans. This study presents a robust workflow that considers fractionation size, anatomical variations between treatments, and cumulative bias doses to improve the re-irradiation planning process.

METHODS

The workflow was automated in MIM® Software and the Elekta© Monaco® treatment planning system. Prior treatment doses are deformably mapped, converted to equivalent dose in 2 Gy fractions (EQD2), and accumulated onto the re-treatment planning CT. Two MIM extensions were developed to estimate voxel-wise dose mapping uncertainties and to convert the cumulative EQD2 into a physical dose distribution equivalent to the re-treatment fractionation size. This dose distribution is used in Monaco as bias to optimize the re-irradiation plan. The workflow was retrospectively tested with data from 14 patients, and the outcomes were compared to the manually optimized plans (MOPs) clinically utilized.

RESULTS

Bias-dose guided plans (BDGPs) demonstrated a median reduction of the critical organ at risk (OAR) cumulative EQD2 metrics of 240 cGy (range: 1909 cGy, -187 cGy, p = 0.002). BDGPs allowed higher target coverage in cases where the MOP approach implied dose de-escalation of the target. The dose mapping uncertainties resulted in OAR cumulative EQD2 metrics increments ranging from 10 cGy to 730 cGy.

CONCLUSIONS

We introduced a re-irradiation planning workflow using commercially available software that accounts for anatomic and fraction size variations and improves planning efficiency. Employing voxel-level bias dose guidance demonstrated OAR-sparing benefits while maximizing prescription dose coverage to targets. The workflow's robustness tools aid informed clinical decision-making.

Magnetic Resonance-Guided Stereotactic Body Radiotherapy (MRgSBRT) with Daily Online Plan Adaptation for Reirradiation in the Abdomen

PURPOSE

Reirradiation in the abdomen poses a challenge due to both interfraction and intrafraction motion of the target and nearby organs at risk (OARs). We hypothesized that magnetic resonance-guided stereotactic body radiotherapy (MRgSBRT) with daily online adaptation allows for safe and effective dose-escalated treatment by minimizing grade 3+ gastrointestinal (GI) toxicities.

MATERIALS/METHODS

We performed a single-institution retrospective review of 38 patients who received a total of 44 courses of MRgSBRT reirradiation within the abdomen. Clinical outcomes included local control, overall survival, and GI toxicities assessed using CTCAE v5. OAR metrics of original and adapted plans were compared to assess the added value of daily adaptation.

RESULTS

Fourteen different primary histologies were treated, with the most common including pancreatic (18.2%), renal (18.2%), and prostate (15.9%) cancers. The most common site for reirradiation was abdominal lymph nodes (61.3%). A majority (70.4%) of MRgSBRT courses were preceded by prior SBRT. The median and modal prescribed dose of MRgSBRT reirradiation was 40 Gy in 5 fractions (BED10=72); 87% of courses were treated to a BED10 of at least 59.5. Across 218 total fractions, daily adaptation improved PTV coverage by a mean of 4.1% (95% CI: 3.1 - 5.1%, p<0.0001) and met 100% of hard luminal GI OAR 0.03cc constraints that would have been exceeded without adaptation in 53.2% of fractions. The median follow-up after MRgSBRT reirradiation was 15.8 months. One-year local control and overall survival were 89.5% and 74.9%, respectively. Grade 3+ toxicity possibly related to MRgSBRT reirradiation was observed following two (4.5%) courses.

CONCLUSION

MRgSBRT allows for dose escalation and good local control in cases of abdominal reirradiation with acceptable toxicity. Daily adaptation provided substantial benefit in meeting safety goals and improving coverage. This retrospective study supports the development of a prospective clinical trial of MRgSBRT reirradiation in the abdomen.

RAdiotherapy Dose Accumulation Routine (RADAR)-A Novel Dose Accumulation Script With Built-In Uncertainty

PURPOSE

To incorporate uncertainty into dose accumulation for reirradiation.

METHODS AND MATERIALS

The RAdiotherapy Dose Accumulation Routine (RADAR) script for the Eclipse treatment planning system (Varian Medical Systems) is described, and the voxel-wise ellipsoid search algorithm is introduced as a means of incorporating uncertainty. RADAR is first demonstrated on a test patient reirradiated to the spine, illustrating the effect of the uncertainty algorithm. A summary of initial evaluation testing conducted by 11 users, each of whom ran a separate spine reirradiation case, follows. Finally, RADAR run times are reported for various conditions.

RESULTS

In the demonstration case in which a 3-mm ellipsoid search was used, the maximum RADAR 2-Gy equivalent (EQD2) accumulated spinal cord dose increased from 7244 to 12,689 cGy because the ellipsoid search pulled dose from closer to the adjacent target structure. When the ellipsoid search was restricted to voxels within the spinal cord, the maximum accumulated cord dose was reduced to 6523 cGy and did not exceed the sum of the maximum EQD2 spinal cord doses of the individual plans (6730 cGy). In the evaluation cases, the RADAR EQD2 maximum dose for the spinal cord increased by an average of 31.6% with uncertainty applied compared to a conventional dose accumulation and decreased by an average of 16.7% compared to a conventional dose accumulation when the uncertainty calculation was restricted to voxels within the spinal cord. RADAR run times vary depending on the number of plans added and the type of uncertainty used.

CONCLUSIONS

RADAR offers a novel way to directly account for uncertainty in dose accumulation through a voxel-wise ellipsoid search algorithm. EQD2 dose accumulation with and without dose discounts is also available.

Embracing the Future of Clinical Trials in Radiation Therapy: An NRG Oncology CIRO Technology Retreat Whitepaper on Pioneering Technologies and AI-Driven Solutions

This white paper examines the potential of pioneering technologies and artificial intelligence-driven solutions in advancing clinical trials involving radiation therapy. As the field of radiation therapy evolves, the integration of cutting-edge approaches such as radiopharmaceutical dosimetry, FLASH radiation therapy, image guided radiation therapy, and artificial intelligence promises to improve treatment planning, patient care, and outcomes. Additionally, recent advancements in quantum science, linear energy transfer/relative biological effect, and the combination of radiation therapy and immunotherapy create new avenues for innovation in clinical trials. The paper aims to provide an overview of these emerging technologies and discuss their challenges and opportunities in shaping the future of radiation oncology clinical trials. By synthesizing knowledge from experts across various disciplines, this white paper aims to present a foundation for the successful integration of these innovations into radiation therapy research and practice, ultimately enhancing patient outcomes and revolutionizing cancer care.

Evidence-based clinical recommendations for hypofractionated radiotherapy: exploring efficacy and safety - Part 4: Liver and locally recurrent rectal cancer

In this paper, we review the use of hypofractionated radiotherapy for gastrointestinal malignancies, focusing on primary and metastatic liver cancer, and recurrent rectal cancer. Technological advancements in radiotherapy have facilitated the direct delivery of high-dose radiation to tumors, while limiting normal tissue exposure, supporting the use of hypofractionation. Hypofractionated radiotherapy is particularly effective for primary and metastatic liver cancer where high-dose irradiation is crucial to achieve effective local control. For recurrent rectal cancer, the use of stereotactic body radiotherapy offers a promising approach for re-irradiation, balancing efficacy and safety in patients who have been administered previous pelvic radiotherapy and in whom salvage surgery is not applicable. Nevertheless, the potential for radiation-induced liver disease and gastrointestinal complications presents challenges when applying hypofractionation to gastrointestinal organs. Given the lack of universal consensus on hypofractionation regimens and the dose constraints for primary and metastatic liver cancer, as well as for recurrent rectal cancer, this review aims to facilitate clinical decision-making by pointing to potential regimens and dose constraints, underpinned by a comprehensive review of existing clinical studies and guidelines.

Reirradiation - still navigating uncharted waters?

With the emergence of high-precision radiotherapy technologies such as stereotactic ablative radiotherapy (SABR), MR guided brachytherapy, image guided intensity modulated photon and proton radiotherapy and most recently daily adaptive radiotherapy, reirradiation is increasingly recognized as a viable treatment option for many patients. This includes those with recurrent, metastatic or new malignancies post initial radiotherapy. The primary challenge in reirradiation lies in balancing tumor control against the risk of severe toxicity from cumulative radiation doses to previously irradiated normal tissue. Although technology for precise delivery has advanced at a fast pace, clinical practice of reirradiation still mostly relies on individual expertise, as prospective evidence is scarce, the level of reporting in clinical studies is not standardized and of low quality - especially with respect to cumulative doses received by organs at risk. A recent ESTRO/EORTC initiative proposed a standardized definition of reirradiation and formulated general requirements for minimal reporting in clinical studies [1]. As a consequence we found it timely to convene for an international and interdisciplinary meeting with experts in the field to summarize the current evidence, identify knowledge gaps and explore which best practices can be derived for safe reirradiation. The meeting was held on 15.06.2023 in Zurich and was endorsed by the scientific societies SASRO, DEGRO and ESTRO. Here, we report on available evidence and research priorities in the field of reirradiation, as discussed during the meeting.

Thoracic reirradiation of recurrent non-small cell lung carcinoma: A comprehensive review

Due to the recent advances in the systemic treatment of non-small cell lung cancer, the management of locoregional recurrences, especially after initial radiotherapy (with or without concurrent chemotherapy), is of increasing significance. The potential alternatives in this setting include: a salvage local strategy (based on surgery, radiotherapy or thermoablative treatment), promising approach, but sometimes difficult to implement in often frail patients, and whose modalities remain under-researched; or alternatively, the initiation of systemic treatment, where the prognosis aligns with that of de novo metastatic patients. This comprehensive literature review focused on salvage radiotherapy treatment of recurrent non-small cell lung carcinomas, after initial radiotherapy, with or without associated systemic treatment. It aims to present the main findings on this area, from patient selection and preparation, to key characteristics, including dosimetric aspects, and the main limitations and uncertainties associated with this therapeutic modality.

Criteria for Re-Irradiation

BACKGROUND

The treatment options for patients with progressive malignant tumors despite primary radiotherapy are often limited. In selected cases, re-irradiation can be offered. This article concerns the selection criteria and results of re-irradiation for certain types of cancer.

METHODS

This review is based on pertinent publications retrieved by a selective search in PubMed, with particular attention to glio - blastoma, head and neck tumors, and prostatic carcinoma.

RESULTS

The published studies of re-irradiation are few in number and often of limited methodological quality. For glioblastoma, a randomized controlled trial (RCT) found that adding re-irradiation to treatment with bevacizumab yielded no significant improvement in either median progression-free survival or median overall survival (hazard ratio [HR] 0.73; p = 0.05 and HR 0.98; p = 0.46, respec - tively). Re-irradiation is a treatment option for locoregional recurrences of head and neck tumors after primary radiotherapy, but it carries a risk of serious side effects. For unresectable recurrences of nasopharyngeal carcinoma, an RCT has shown that hyperfractionated re-irradiation is more effective than normofractionated re-irradiation (overall survival: HR 0.54, p = 0.014). For locally recurrent prostatic carcinoma after radiotherapy, re-irradiation can yield good oncologic outcomes with an acceptable level of urogenital and gastrointestinal side effects (5-year recurrence-free survival: stereotactic body radiation therapy (SBRT), 58%; high dose rate (HDR) brachytherapy, 77%; versus salvage prostatectomy, 72%). RCTs on this topic are lacking.

CONCLUSION

Re-irradiation is a treatment option for selected cancer patients. As the available scientific evidence is limited, multidisciplinary collaboration and participatory decision-making are particularly important.

Salvage Reirradiation with Proton Beam Therapy for Locoregionally Recurrent Non-Small Cell Lung Cancer

BACKGROUND/OBJECTIVES

This retrospective study evaluates outcomes of 66 patients who underwent reirradiation (re-RT) with proton beam therapy (PBT) for recurrent non-small cell lung cancer.

METHODS

Toxicity was scored via the CTCAE v5.0, and outcomes estimated using the Kaplan-Meier method, with associations evaluated via Cox proportional hazards and logistic regression analyses.

RESULTS

Patients were treated to a median re-RT prescription of 66 Gy/33 fxs (BED10 = 79 Gy; IQR: 71-84 Gy) at an interval of 1.4 years from prior RT. Half (50%) received concurrent chemotherapy. At 14 months follow-up, the median OS and PFS were 5 months (95%CI: 13-17) and 12.5 months (95%CI: 10-15), respectively. On multivariable analysis, a higher RT dose (BED10 > 70 Gy) [HR0.37; 95%CI: 0.20-0.68, p = 0.001] and concurrent chemotherapy (HR0.48; 95%CI: 0.28-0.81, p = 0.007) were associated with improved PFS, while treatment site overlap was adversely associated (HR1.78; 95%CI: 1.05-3.02, p = 0.031). The median PFS for definitive RT with concurrent chemotherapy (n = 28), definitive RT alone (BED10 > 70 Gy) [n = 22], and lower prescription RT (BED10 < 70 Gy) [n = 16] was 15.5 months (95%CI: 7.3-23.7), 14.1 months (95%CI: 10.9-17.3), and 3.3 months (95%CI: 0-12.3), respectively (log-rank, p = 0.006), with corresponding 2-year estimates of 37% (±9), 18% (±8), and 12.5% (±8), respectively. The incidence of Grade 3+ toxicity was 10.5% (6% pulmonary; 3% esophageal; and 1.5% skin), including one Grade 4 bronchopulmonary hemorrhage but no Grade 5 events. Cases with central site overlap had higher composite Dmax to the esophagus (median 87 Gy [IQR:77-90]), great vessels (median 120 Gy [IQR:110-138]), and proximal bronchial tree (median 120 Gy [IQR:110-138]) as compared to other cases (p ≤ 0.001 for all). However, no significant associations were identified with Grade 3+ events.

CONCLUSIONS

Thoracic re-RT with PBT is an option for recurrent NSCLC with acceptable outcomes and toxicity for select patients. When feasible, higher prescription doses (BED10 > 70 Gy) should be delivered for definitive intent, and concurrent chemotherapy may benefit individual cases.

Stereotactic Body Radiation Therapy for Primary Lung Cancer and Metastases: A Case-Based Discussion on Challenging Cases

PURPOSE

Data informing the safety, efficacy, treatment logistics, and dosimetry of stereotactic body radiation therapy (SBRT) for lung tumors has primarily been derived from patients with favorably located solitary tumors. SBRT is now considered a standard-of-care treatment for inoperable early-stage non-small cell lung cancer and lung metastases, and therefore extrapolation beyond this limited foundational patient population remains an active source of interest.

METHODS AND MATERIALS

This case-based discussion provides a practical framework for delivering SBRT to challenging, yet frequently encountered, cases in radiation oncology. The cases highlighted herein include the use of SBRT for ultracentral tumors, multiple tumors, and reirradiation. Patient characteristics, fractionation, prescription dose, treatment technique, and dose constraints are discussed. Relevant literature to these cases is summarized to provide a framework for the treatment of similar patients.

RESULTS

Treatment of challenging cases with lung SBRT requires many considerations, including treatment intent, fractionation selection, tumor localization, and plan optimization. In such scenarios, patient selection is critical to understanding the risk-benefit profile of an SBRT approach despite significant advances in delivery techniques and safety.

CONCLUSIONS

A case-based discussion was developed by the Radiosurgery Society to provide a practical guide to the common challenging scenarios noted above affecting patients with lung tumors. A multidisciplinary approach should guide the treatment of such cases to maximize the therapeutic window.

Thoracic Re-irradiation With Definitive External Beam Radiation Therapy Using Intensity Modulated Radiation Therapy: A Case Report

Thoracic re-irradiation has a high risk of severe adverse events, and re-irradiation with curative intent has rarely been performed. However, in recent years, with the introduction of intensity-modulated radiation therapy (IMRT) and stereotactic body radiation therapy, it has become possible to deliver high doses to the target lesions while minimizing the doses to surrounding tissues. The patient in this case had a history of definitive radiation therapy for esophageal cancer. The patient developed new lung cancer, which was treated by re-irradiation. We created a radiation treatment plan using IMRT. This allowed us to reduce the dose to organs at risk and deliver a higher dose to the cancer, increasing the potential for cure. The patient has not experienced any severe late adverse events as of three years and six months after treatment. Additionally, the treatment has been sufficiently effective, and the patient remains recurrence-free. To confirm the feasibility of the IMRT plan, we also created a radiation treatment plan using three-dimensional conformal radiation therapy (3D-CRT) and compared it with the IMRT plan. Compared with 3D-CRT, the IMRT plan was able to reduce the dose to organs at risk and meet the dose constraints indicated in multiple studies. The possibility of adverse events such as bronchial hemorrhage, esophageal hemorrhage, bronchial fistula, radiation pneumonitis, esophageal fistula, and pericarditis was significantly reduced.

Tumor reirradiation: Issues, challenges and perspectives for radiobiology

The radiobiology of tumor reirradiation is poorly understood. It pertains to tumors and their sensitivity at the time of relapse, encompassing primary tumors, metastases, or secondary cancers developed in or proximal to previously irradiated tissues. The ability to control the pathology depends, in part, on understanding this sensitivity. To date, literature data remains limited regarding changes in the radiosensitivity of tissues after initial irradiation, and most proposals are based on conjecture. The response of healthy tissues at the site of irradiation raises concerns about radio-induced complications. Cumulative dose is likely a major factor in this risk, thus using equivalent dose calculations might help reduce the risk of complications. However, the correlation between mathematical equivalence formulas and clinical effects of radiobiological origin is weak, and the lack of knowledge of the alpha/beta (α/β) ratio of healthy tissues remains an obstacle to the extensive use of these formulas. However, tissues exposed to recovery dose may have a tolerance to irradiation much higher than assumed, thus further biological work remains to be developed. Also, the functionality of previously irradiated tissues could be useful in selecting the most suitable irradiation beams. Finally, research on the genomics of irradiated healthy tissues could improve the prediction of side effects and personalize radiotherapy.

Complex Multi-site Stereotactic Body Re-irradiation With CT-Guided Online Adaptive Radiotherapy

Online adaptive radiotherapy optimizes a patient's treatment plan to their daily anatomy to account for inter-fraction motion. Daily target and organ-at-risk (OAR) delineation allows for optimized treatments and has been shown to have favorable outcomes in the abdominal region. Adaptive radiotherapy also has the potential to support fine control of dose in re-irradiation to OARs. Herein, we describe a complex multi-site re-irradiation case utilizing CT-guided adaptive radiotherapy. A 46-year-old man with metastatic hepatocellular carcinoma presented for re-irradiation of four metastatic lesions to the right acetabulum, T11, S2, and a gastrosplenic lymph node (gsLN). The right acetabulum, T11, and S2 lesions previously received 20 Gy in five fractions. For the current course, he was prescribed 35 Gy (T11, right acetabulum, and gsLN) and 30 Gy (S2) in five fractions. An equivalent dose in 2 Gy fractions (EQD2) was employed to assess cumulative doses for critical OARs and guide planning. The re-irradiated lesions were treated with stereotactic body radiation therapy (SBRT), and the gsLN was treated with adaptive radiotherapy. An isotoxic approach was utilized to create the scheduled and adapted plans for the gsLN. Adapted plans were created on the patient's daily anatomy as visualized on kilovoltage cone beam computed tomography and compared against the scheduled plan. Dose-volume histogram objectives were used to compare the plans, and the superior plan was chosen for delivery. The adapted plan was used for all five fractions and met all critical OAR constraints while maintaining target coverage. The use of the scheduled plan would have resulted in stomach and/or esophagus constraint violations on all five fractions. This resulted in reduced EQD2 doses of 6.4 and 12.3 Gy for the esophagus and stomach, respectively. We report the successful treatment of a patient undergoing tri-site SBRT re-irradiation with concurrent CT-guided adaptive radiotherapy to a gsLN. The adaptive treatment allowed us to meet critical OAR constraints while maintaining target coverage. Few studies have described the use of CT-guided adaptive radiotherapy in re-irradiation cases, and the potential benefit for these complex cases is evident.

Dose-response relationship between volume base dose and tumor local control in definitive radiotherapy for vaginal cancer

OBJECTIVE

This study aimed to establish the dose-response relationship between volume base dose and tumor local control for vaginal cancer, including primary vaginal cancer and recurrent gynecologic malignancies in the vagina.

MATERIALS AND METHODS

We identified studies that reported volume base dose and local control by searching the PubMed, the Web of Science, and the Cochrane Library Database through August 12, 2023. The regression analyses were performed using probit model between volume based dose versus clinical outcomes. Subgroup analyses were performed according to stratification: publication year, country, inclusion time of patients, patients with prior radiotherapy, age, primaries or recurrent, tumor size, concurrent chemoradiotherapy proportion, dose rate, image modality for planning, and interstitial proportion.

RESULTS

A total of 879 patients with vaginal cancer were identified from 18 studies. Among them, 293 cases were primary vaginal cancer, 573 cases were recurrent cancer in the vagina, and 13 cases were unknown. The probit model showed a significant relationship between the HR-CTV (or CTV) D90 versus the 2-year and 3-year local control, P values were 0.013 and 0.014, respectively. The D90 corresponding to probabilities of 90% 2-year local control were 79.0 GyEQD2,10 (95% CI: 75.3-96.6 GyEQD2,10).

CONCLUSIONS

A significant dependence of 2-year or 3-year local control on HR-CTV (or CTV) D90 was found. Our research findings encourage further validation of the dose-response relationship of radical radiotherapy for vaginal cancer through protocol based multicenter clinical trials.

Lung cancer reirradiation: Exploring modifications to utilization, treatment modalities and factors associated with outcomes

BACKGROUND

Patients treated for lung cancer (LC) often experience locoregional failure after initial treatment. Due to technological advances, thoracic reirradiation (re-RT) has become a viable treatment option. We sought to investigate the use of thoracic re-RT in LC patients over a time period characterized by technological advances in a large, multi-center cohort.

METHODS AND MATERIALS

LC patients treated with thoracic re-RT in two University Hospitals from 2010-2020 were identified. Clinical variables and RT data were extracted from the medical records and treatment planning systems. Overall survival (OS) was calculated from the last day of re-RT until death or last follow up.

RESULTS

296 patients (small cell LC n=30, non-small cell LC n=266) were included. Three-dimensional conformal radiation therapy was the RT technique used most frequently (63%), and 86% of all patients were referred for re-RT with palliative treatment intent. During the second half of the study period, the use of thoracic re-RT increased in general, more patients received curative re-RT, and there was an increased use of stereotactic body radiation therapy (SBRT). Median time between initial RT and re-RT was 18 months (range 1-213 months). Only 83/296 patients had combined treatment plans that allowed for registration of combined doses to organs at risk (OAR). Most of the combined doses to OAR were below recommendations from guidelines. Multivariate analysis showed superior OS (p<0.05) in patients treated with curative intent, SBRT or intensity modulated radiation therapy or had excellent performance status prior to re-RT.

CONCLUSIONS

The use of re-RT increased in the second half of the study period, although 2020 did not follow the trend. The use of SBRT and IMRT became more frequent over the years, yet the majority received palliative re-RT. Combined dose plans were only created for one third of the patients.

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

BACKGROUND AND PURPOSE

Safe 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 METHODS

We 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.

RESULTS

Cumulative 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.

CONCLUSION

Large 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.

Automated planning of stereotactic spine re-irradiation using cumulative dose limits

Background and Purpose

The lack of dedicated tools in commercial planning systems currently restricts efficient review and planning for re-irradiation. The aim of this study was to develop an automated re-irradiation planning framework based on cumulative doses.

Materials and Methods

We performed a retrospective study of 14 patients who received spine SBRT re-irradiation near a previously irradiated treatment site. A fully-automated workflow, DART (Dose Accumulation-based Re-irradiation Tool), was implemented within Eclipse by leveraging a combination of a dose accumulation script and a proprietary automated optimization algorithm. First, we converted the prior treatment dose into equivalent dose in 2 Gy fractions (EQD2) and mapped it to the current anatomy, utilizing deformable image registration. Subsequently, the intersection of EQD2 isodose lines with relevant organs at risk defines a series of optimization structures. During plan optimization, the residual allowable dose at a specified tissue tolerance was treated as a hard constraint.

Results

All DART plans met institutional physical and cumulative constraints and passed plan checks by qualified medical physicists. DART demonstrated significant improvements in target coverage over clinical plans, with an average increase in PTV D99% and V100% of 2.3 Gy [range -0.3-7.7 Gy] and 3.4 % [range -0.4 %-7.6 %] (p < 0.01, paired t-test), respectively. Moreover, high-dose spillage (>105 %) outside the PTV was reduced by up to 7 cm3. The homogeneity index for DART plans was improved by 19 % (p < 0.001).

Conclusions

DART provides a powerful framework to achieve more tailored re-irradiation plans by accounting for dose distributions from the previous treatments. The superior plan quality could improve the therapeutic ratio for re-irradiation patients.

The Dosimetric Analysis of Duodenal and Intestinal Toxicity After a Curative Dose Re-irradiation Using the Intensity-Modulated Radiotherapy for Abdominopelvic Lymph Node Lesions

INTRODUCTION

This study aimed to examine the influence of dosimetric factors on gastrointestinal toxicity after radical re-irradiation for lymph node recurrence in the abdominopelvic region using a composite plan.

METHODS

Between January 2008 and March 2017, 33 patients underwent radical re-irradiation for lymph node recurrence in the abdominopelvic region with a complete overlap with previous radiation therapy (RT) with the median prescription dose of the second RT of 71.7 Gy10. Re-irradiation planning protocol for target volume and organs at risk (OARs) (duodenum, small and large intestines) was decided as follows: more than equal to 97% of the prescription dose was administered to the D95 (percentage of the minimum dose that covered 95% of the target volume) of planning target volume (PTV); minimal dose to the maximally irradiated doses delivered to 1cc [D1 cc] and 5cc [D5 cc] of OARs was set below 70 Gy3 and 50 Gy3, respectively; and D1 cc and D5 cc in the cumulative plans to OARs were 120 Gy3 and 100 Gy3. Kaplan-Meier analyses were performed to evaluate overall survival (OS) and univariate log-rank and multivariate Cox proportional hazards model analyses were performed to explore predictive factors. Using dose summation of the first and re-irradiation plans, we conducted a dosimetric analysis for grade ≥ 3 toxicities of the duodenum and intestine.

RESULTS

With a median follow-up of 18 months, the two-year OS rate was 45.5%. The number of RT fields (localized or multiple) was a significant predisposing factor for OS rate with a hazard ratio of 0.23 (95% confidence interval 0.07-0.73). The two-year OS of the patients with a localized RT field was 63.6% and 9.1% for multiple RT fields (p= 0.00007). Four patients experienced grade ≥3 gastrointestinal toxicity related to re-irradiation (4/33=12.1%). We could not find any predisposing dosimetric value in the comparisons with and without toxicity.

CONCLUSIONS

The dose constraints presented in this study are relatively low rates of toxicity, which may be useful when planning re-irradiation. Especially, for the patients who could be treated with localized RT field, radical re-irradiation with a high curative dose is a good option. No dosimetric predisposing factor was found for radical re-irradiation of abdominopelvic lesions in the composite plan.

Re-irradiation in clinical practice: Results of an international patterns of care survey within the framework of the ESTRO-EORTC E2-RADIatE platform

BACKGROUND

Re-irradiation is an increasingly utilized treatment for recurrent, metastatic or new malignancies after previous radiotherapy. It is unclear how re-irradiation is applied in clinical practice. We aimed to investigate the patterns of care of re-irradiation internationally.

MATERIAL/METHODS

A cross-sectional survey conducted between March and September 2022. The survey was structured into six sections, each corresponding to a specific anatomical region. Participants were instructed to complete the sections of their clinical expertise. A total of 15 multiple-choice questions were included in each section, addressing various aspects of the re-irradiation process. The online survey targeted radiation and clinical oncologists and was endorsed by the European Society for Radiotherapy and Oncology (ESTRO) and the European Organisation for Research and Treatment of Cancer (EORTC).

RESULTS

371 physicians from 55 countries across six continents participated. Participants had a median professional experience of 16 years, and the majority (60%) were affiliated with an academic hospital. The brain region was the most common site for re-irradiation (77%), followed by the pelvis (65%) and head and neck (63%). Prolonging local control was the most common goal (90-96% across anatomical regions). The most common minimum interval between previous radiotherapy and re-irradiation was 6-12 months (45-55%). Persistent grade 3 or greater radiation-induced toxicity (77-80%) was the leading contraindication. Variability in organs at risk dose constraints for re-irradiation was observed. Advanced imaging modalities and conformal radiotherapy techniques were predominantly used. A scarcity of institutional guidelines for re-irradiation was reported (16-19%). Participants from European centers more frequently applied thoracic and abdominal re-irradiation. Indications did not differ between academic and non-academic hospitals.

CONCLUSION

This study highlights the heterogeneity in re-irradiation practices across anatomical regions and emphasizes the need for high-quality evidence from prospective studies to guide treatment decisions and derive safe cumulative dose constraints.

Advancements of radiotherapy for recurrent head and neck cancer in modern era

Head and neck cancer is a kind of cancer which can be eradicated from radical radiation therapy. However, with best efforts, nearly 40% patients will experience locoregional recurrence. Locoregional recurrence is the main cause of cancer-related death in head and neck cancers, so local treatments play a key role in improving progression free survival. In the last decades, radiation techniques have been tremendously developed, highly conformal radiation techniques such as intensity-modulated radiotherapy, stereotactic body radiation therapy, brachytherapy and proton or heavy ion radiation therapy have their unique radiobiological advances. Although reirradiation is widely used in clinical practice, but little is known when comparing the different techniques. In this review, we will provide a comprehensive overview of the role of reirradiation in recurrent head and neck cancers including radiation techniques, patient selection, overall clinical benefits, and toxicities.

Resource Allocations for Common Radiation Oncology Procedures

PURPOSE

Radiation Oncology is a complex, resource-intensive discipline. The complexity of the radiation oncology treatment process has increased significantly in recent years with the introduction of more advanced imaging, planning, and treatment delivery technology and enhanced use of multidisciplinary care paths. We conducted a multi-institutional study to estimate the average time by functional unit for a wide range of modern radiation oncology treatment regimens.

METHODS AND MATERIALS

Structured process mapping was performed for 24 treatment categories, and average time estimates for 6 functional groups were obtained for each process step through consultation with the full clinical team at each institution. Six geographically dispersed institutions participated in the study. Significant effort was invested in aggregate data analysis and clarification of assumptions.

RESULTS

The findings show significant variability in the resources expended for many treatment categories as well as the distribution of workload between functional units. Major factors in the variability include the rate of adoption of hypofractionation in external beam therapy, adoption of automation tools and standardization, and the transition to multimodality image-based planning in brachytherapy.

CONCLUSIONS

The data obtained from this study may be useful in designing institution-specific staffing models appropriate to the scope of radiation therapy services provided at each institution.

Treatment plan optimisation for reirradiation

BACKGROUND

The STRIDeR (Support Tool for Re-Irradiation Decisions guided by Radiobiology) project aims to create a clinically viable re-irradiation planning pathway within a commercial treatment planning system (TPS). Such a pathway should account for previously delivered dose, voxel-by-voxel, taking fractionation effects, tissue recovery and anatomical changes into account. This work presents the workflow and technical solutions in the STRIDeR pathway.

METHODS

The pathway was implemented in RayStation (version 9B DTK) to allow an original dose distribution to be used as background dose to guide optimisation of re-irradiation plans. Organ at risk (OAR) planning objectives in equivalent dose in 2 Gy fractions (EQD2) were applied cumulatively across the original and re-irradiation treatments, with optimisation of the re-irradiation plan performed voxel-by-voxel in EQD2. Different approaches to image registration were employed to account for anatomical change. Data from 21 patients who received pelvic Stereotactic Ablative Radiotherapy (SABR) re-irradiation were used to illustrate the use of the STRIDeR workflow. STRIDeR plans were compared to those produced using a standard manual method.

RESULTS

The STRIDeR pathway resulted in clinically acceptable plans in 20/21 cases. Compared to plans produced using the laborious manual method, less constraint relaxation was required or higher re-irradiation doses could be prescribed in 3/21.

CONCLUSION

The STRIDeR pathway used background dose to guide radiobiologically meaningful, anatomically-appropriate re-irradiation treatment planning within a commercial TPS. This provides a standardised and transparent approach, offering more informed re-irradiation and improved cumulative OAR dose evaluation.

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

INTRODUCTION

The 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.

METHODS

A 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.

RESULTS

48 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.

CONCLUSION

This 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.

Bevacizumab combined with re-irradiation in recurrent glioblastoma

Background

Glioblastoma is characterized by rich vasculature and abnormal vascular structure and function. Currently, there is no standard treatment for recurrent glioblastoma (rGBM). Bevacizumab (BEV) has established role of inhibiting neovascularization, alleviating hypoxia in the tumor area and activating the immune microenvironment. BEV may exert synergistic effects with re-irradiation (re-RT) to improve the tumor microenvironment for rGBM.

Purpose

The purpose of this study was to evaluate the safety, tolerability, and efficacy of a combination of BEV and re-RT for rGBM treatment.

Methods

In this retrospective study, a total of 26 rGBM patients with surgical pathologically confirmed glioblastoma and at least one event of recurrence were enrolled. All patients were treated with re-RT in combination with BEV. BEV was administered until progression or serious adverse events.

Results

Median follow-up was 21.9 months for all patients, whereas median progression-free survival (PFS) was 8.0 months (95% confidence interval [CI]: 6.5–9.5 months). In addition, the 6-month and 1-year PFS rates were 65.4% and 28.2%, respectively. The median overall survival (OS), 6-month OS rate, and 1-year OS rate were 13.6 months (95% CI: 10.2–17.0 months), 92.3%, and 67.5%, respectively. The patient showed good tolerance during the treatment with no grade > 3 grade side event and radiation necrosis occurrence rate of 0%. Combined treatment of gross total resection (GTR) before re-RT and concurrent temozolomide during re-RT was an independent prognostic factor that affected both OS and PFS in the whole cohort (OS: 0.067, 95% CI: 0.009–0.521, p = 0.010; PFS: 0.238, 95% CI: 0.076–0.744, p = 0.038).

Conclusion

In this study, re-RT combined with concurrent and maintenance BEV treatment was safe, tolerable, and effective in rGBM patients. Moreover, GTR before re-RT and selective concurrent temozolomide could further improve patient PFS and OS.

Retreatment of Recurrent or Second Primary Head and Neck Cancer After Prior Radiation: Executive Summary of the American Radium Society® (ARS) Appropriate Use Criteria (AUC): Expert Panel on Radiation Oncology - Head and Neck Cancer

BACKGROUND

Re-treatment of recurrent or second primary head and neck cancers occurring in a previously irradiated field is complex. Few guidelines exist to support practice.

METHODS

We performed an updated literature search of peer-reviewed journals in a systematic fashion. Search terms, key questions, and associated clinical case variants were formed by panel consensus. The literature search informed the committee during a blinded vote on the appropriateness of treatment options via the modified Delphi method.

RESULTS

The final number of citations retained for review was 274. These informed five key questions, which focused on patient selection, adjuvant re-irradiation, definitive re-irradiation, stereotactic body radiation (SBRT), and re-irradiation to treat non-squamous cancer. Results of the consensus voting are presented along with discussion of the most current evidence.

CONCLUSIONS

This provides updated evidence-based recommendations and guidelines for the re-treatment of recurrent or second primary cancer of the head and neck.

Clinical and technical challenges of cancer reirradiation: Words of wisdom

Since the development of new radiotherapy techniques that have improved healthy tissue sparing, reirradiation (reRT) has become possible. The selection of patients eligible for reRT is complex given that it can induce severe or even fatal side effects. The first step should therefore be to assess, in the context of multidisciplinary staff meeting, the patient's physical status, the presence of sequelae resulting from the first irradiation and the best treatment option available. ReRT can be performed either curatively or palliatively to treat a cancer-related symptom that is detrimental to the patient's quality of life. The selected techniques for reRT should provide the best protection of healthy tissue. The construction of target volumes and the evaluation of constraints regarding the doses that can be used in this context have not yet been fully codified. These points raised in the literature suggest that randomized studies should be undertaken to answer pending questions.

A Safe and Practical Cycle for Team-Based Development and Implementation of In-House Clinical Software

Purpose

Due to a gap in published guidance, we describe our robust cycle of in-house clinical software development and implementation, which has been used for years to facilitate the safe treatment of all patients in our clinics.

Methods and Materials

Our software development and implementation cycle requires clarity in communication, clearly defined roles, thorough commissioning, and regular feedback. Cycle phases include design requirements and use cases, development, physics evaluation testing, clinical evaluation testing, and full clinical release. Software requirements, release notes, test suites, and a commissioning report are created and independently reviewed before clinical use. Software deemed to be high-risk, such as those that are writable to a database, incorporate the use of a formal, team-based hazard analysis. Incident learning is used to both guide initial development and improvements as well as to monitor the safe use of the software.

Results

Our standard process builds in transparency and establishes high expectations in the development and use of custom software to support patient care. Since moving to a commercial planning system platform in 2013, we have applied our team-based software release process to 16 programs related to scripting in the treatment planning system for the clinic.

Conclusions

The principles and methodology described here can be implemented in a range of practice settings regardless of whether or not dedicated resources are available for software development. In addition to teamwork with defined roles, documentation, and use of incident learning, we strongly recommend having a written policy on the process, using phased testing, and incorporating independent oversight and approval before use for patient care. This rigorous process ensures continuous monitoring for and mitigatation of any high risk hazards.

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

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.

An international Delphi consensus for pelvic stereotactic ablative radiotherapy re-irradiation

INTRODUCTION

Stereotactic Ablative Radiotherapy (SABR) is increasingly used to treat metastatic oligorecurrence and locoregional recurrences but limited evidence/guidance exists in the setting of pelvic re-irradiation. An international Delphi study was performed to develop statements to guide practice regarding patient selection, pre-treatment investigations, treatment planning, delivery and cumulative organs at risk (OARs) constraints.

MATERIALS AND METHODS

Forty-one radiation oncologists were invited to participate in three online surveys. In Round 1, information and opinion was sought regarding participants' practice. Guidance statements were developed using this information and in Round 2 participants were asked to indicate their level of agreement with each statement. Consensus was defined as ≥75% agreement. In Round 3, any statements without consensus were re-presented unmodified, alongside a summary of comments from Round 2.

RESULTS

Twenty-three radiation oncologists participated in Round 1 and, of these, 21 (91%) and 22 (96%) completed Rounds 2 and 3 respectively. Twenty-nine of 44 statements (66%) achieved consensus in Round 2. The remaining 15 statements (34%) did not achieve further consensus in Round 3. Consensus was achieved for 10 of 17 statements (59%) regarding patient selection/pre-treatment investigations; 12 of 13 statements (92%) concerning treatment planning and delivery; and 7 of 14 statements (50%) relating to OARs. Lack of agreement remained regarding the minimum time interval between irradiation courses, the number/size of pelvic lesions that can be treated and the most appropriate cumulative OAR constraints.

CONCLUSIONS

This study has established consensus, where possible, in areas of patient selection, pre-treatment investigations, treatment planning and delivery for pelvic SABR re-irradiation for metastatic oligorecurrence and locoregional recurrences. Further research into this technique is required, especially regarding aspects of practice where consensus was not achieved.

Re-irradiation of multiple brain metastases using CyberKnife stereotactic radiotherapy: Case report

INTRODUCTION

Brain metastasis (BM) is the commonest adult intracranial malignancy and many patients with brain metastases require two course radiotherapy. Re-irradiation is frequently performed in Radiotherapy (RT) departments for multiple brain metastases.

PATIENT CONCERNS

We present a case of a 55-year-old male patient suffering from brain metastases, who had previously received whole-brain radiotherapy (WBRT) and first CyberKnife Stereotactic Radiotherapy (CKSRT) for metastases, presented with a recurrence of metastasis and new lesions in the brain.

DIAGNOSES

An enhanced computed tomography (CT) scan of the brain revealed abnormalities with double-dosing of intravenous contrast that identified >10 lesions scattered in the whole brain.

INTERVENTIONS

Re-irradiation was performed using CKSRT. The patient was treated with 30 Gy in 5 fractions for new lesions and 25 Gy in 5 fractions for lesion that were locally recurrent and close to brainstem lesions.

OUTCOME

The lesions were well-controlled, and the headache of the patient was significantly relieved one month after radiotherapy. The total survival time of the patients was 17 months from the beginning of the Cyberknife treatment.

CONCLUSION

The present case report demonstrates that CyberKnife therapy plays a significant role in the repeated radiotherapy for multiple metastatic brain tumors. CKSRT can be used as a salvage method in recurrent multiple brain metastases.

Ultra hypofractionated extended nodal irradiation using volumetric modulated arc therapy for oligorecurrent pelvic nodal prostate cancer

Prostate cancer (PCa) may recur after primary treatment but no standard of care exists for patients with pelvic nodal relapse. Based on obervational data, Extended Nodal Irradiation (ENI) might be associated with fewer treatment failures than Stereotactic Ablative Radiotherapy (SABR) to the involved node(s) alone. Ultra hypofractionated ENI is yet to be evaluated in this setting, but it could provide a therapeutic advantage if PCa has a low α/β ratio in addition to patient convenience/resource benefits. This volumetric modulated arc therapy (VMAT) planning study developed a class solution for 5-fraction Extended Nodal Irradiation (ENI) plus a simultaneous integrated boost (SIB) to involved node(s). Ten patients with oligorecurrent nodal disease after radical prostatectomy/post-operative prostate bed radiotherapy were selected. Three plans were produced for each dataset to deliver 25 Gy in 5 fractions ENI plus SIBs of 40, 35 and 30 Gy. The biologically effective dose (BED) formula was used to determine the remaining dose in 5 fractions that could be delivered to re-irradiated segments of organs at risk (OARs). Tumour control probability (TCP) and normal tissue complication probability (NTCP) were calculated using the LQ-Poisson Marsden and Lyman-Kutcher-Burman models respectively. Six patients had an OAR positioned within planning target volume node (PTVn), which resulted in reduced target coverage to PTV node in six, five and four instances for 40, 35 and 30 Gy SIB plans respectively. In these instances, only 30 Gy SIB plans had a median PTV coverage >90% (inter-quartile range 90-95). No OAR constraint was exceeded for 30 Gy SIB plans, including where segments of OARs were re-irradiated. Gross tumour volume node (GTVn) median TCP was 95.7% (94.4-96), 90.7% (87.1-91.2) and 78.6% (75.8-81.1) for 40, 35 and 30 Gy SIB plans respectively, where an α/β ratio of 1.5 was assumed. SacralPlex median NTCP was 43.2% (0.7-61.2), 12.1% (0.6-29.7) and 2.5% (0.5-5.1) for 40, 35 and 30 Gy SIB plans respectively. NTCP for Bowel_Small was <0.3% and zero for other OARs for all three plan types. Ultra hypofractionated ENI planning for pelvic nodal relapsed PCa appears feasible with encouraging estimates of nodal TCP and low estimates of NTCP, especially where a low α/β ratio is assumed and a 30 Gy SIB is delivered. This solution should be further evaluated within a clinical trial and compared against SABR to involved node(s) alone.

Treatment planning system and beam data validation for the ZAP-X: A novel self-shielded stereotactic radiosurgery system

PURPOSE

To evaluate the treatment planning system (TPS) performance of the ZAP-X stereotactic radiosurgery (SRS) system through nondosimetric, dosimetric, and end-to-end (E2E) tests.

METHODS

A comprehensive set of TPS commissioning and validation tests was developed using published guidelines. Nondosimetric validation tests included information transfer, computed tomography-magnetic resonance (CT-MR) image registration, structure/contouring, geometry, dose tools, and CT density. Dosimetric validation included comparisons between TPS and water tank/Solid Water measurements for various geometries and beam arrangements and end-to-end (E2E) tests. Patient-specific quality assurance was performed with an ion chamber in the Lucy phantom and with Gafchromic EBT3 film in the CyberKnife head phantom. RadCalc was used for independent verification of monitor units. Additional E2E tests were performed using the RPC Gamma Knife thermoluminescent dosimeter (TLD) phantom, MD Anderson SRS head phantom, and PseudoPatient gel phantom for independent absolute dose verification.

RESULTS

CT-MR image registrations with known translational and rotational offsets were within tolerance (<0.5 × maximum voxel dimension). Slice thickness and distance accuracy were within 0.1 mm, and volume accuracy was within 0 to 0.11 cm³ . Treatment planning system volume measurement uncertainty was within 0.1 to 0.4 cm³ . Ion chamber point-dose measurements for a single beam in a water phantom agreed to TPS-calculated values within ±4% for collimator diameters 10 to 25 mm, and ±6% for 7.5 mm, for all measured depths (7, 50, 100, 150, and 200 mm). In homogeneous Solid Water, point-dose measurements agreed to within ±4% for cones sizes 7.5 to 25 mm. With 1-cm high/low density inserts, measurements were within ±4.2% for cone sizes 10 to 25 mm. Film-based E2E using 4/5-mm cones resulted in a gamma passing rate (%GP) of 99.8% (2%/1.5 mm). Point-dose measurements in a Lucy phantom with an ion chamber using 36 beams distributed along three noncoplanar arcs agreed to within ±4% for cone sizes 10 to 25 mm. The RPC Gamma Knife TLD phantom yielded passing results with a measured-to-expected TLD dose ratio of 1.02. The MD Anderson SRS head phantom yielded passing results, with 4% TLD agreement and %GP of 95%/93% (5%/3 mm) for coronal/sagittal film planes. The RTsafe gel phantom gave %GP of >95% (5%/2 mm) for all four targets. For our first 58 patients, film-based patient-specific quality assurance has resulted in an average %GP of 98.7% (range, 94-100%) at 2%/2 mm.

CONCLUSIONS

Core ZAP-X features were found to be functional. On the basis of our results, point-dose and planar measurements were in agreement with TPS calculations using multiple phantoms and setup geometries, validating the ZAP-X TPS beam model for clinical use.

A surveillance study of patterns of reirradiation practice using external beam radiotherapy in Japan

The aim of this study was to survey the present status and patterns of reirradiation (Re-RT) practice using external beam radiotherapy in Japan. We distributed an e-mail questionnaire to the Japanese Society for Radiation Oncology partner institutions, which consisted of part 1 (number of Re-RT cases in 2008-2012 and 2013-2018) and part 2 (indications and treatment planning for Re-RT and eight case scenarios). Of the 85 institutions that replied to part 1, 75 (88%) performed Re-RTs. However, 59 of these 75 institutions (79%) reported difficulty in obtaining Re-RT case information from their databases. The responses from 37 institutions included the number of Re-RT cases, which totaled 508 in the period from 2009 to 2013 (institution median 3; 0-235), and an increase to 762 cases in the period from 2014 to 2018 (12.5; 0-295). A total of 47 physicians responded to part 2 of the survey. Important indications for Re-RT that were considered were age, performance status, life expectancy, absence of distant metastases and time interval since previous radiotherapy. In addition to clinical decision-making factors, previous total radiation dose, volume of irradiated tissue and the biologically equivalent dose were considered during Re-RT planning. From the eight site-specific scenarios presented to the respondents, >60% of radiation oncologists agreed to perform Re-RT. Re-RT cases have increased in number, and interest in Re-RT among radiation oncologists has increased recently due to advances in technology. However, several problems exist that emphasize the need for consensus building and the establishment of guidelines for practice and prospective evaluation.

An International Expert Survey on the Indications and Practice of Radical Thoracic Reirradiation for Non-Small Cell Lung Cancer

Purpose

Thoracic reirradiation for non-small cell lung cancer with curative intent is potentially associated with severe toxicity. There are limited prospective data on the best method to deliver this treatment. We sought to develop expert consensus guidance on the safe practice of treating non-small cell lung cancer with radiation therapy in the setting of prior thoracic irradiation.

Methods and Materials

Twenty-one thoracic radiation oncologists were invited to participate in an international Delphi consensus process. Guideline statements were developed and refined during 4 rounds on the definition of reirradiation, selection of appropriate patients, pretreatment assessments, planning of radiation therapy, and cumulative dose constraints. Consensus was achieved once ≥75% of respondents agreed with a statement. Statements that did not reach consensus in the initial survey rounds were revised based on respondents’ comments and re-presented in subsequent rounds.

Results

Fifteen radiation oncologists participated in the 4 surveys between September 2019 and March 2020. The first 3 rounds had a 100% response rate, and the final round was completed by 93% of participants. Thirty-three out of 77 statements across all rounds achieved consensus. Key recommendations are as follows: (1) appropriate patients should have a good performance status and can have locally relapsed disease or second primary cancers, and there are no absolute lung function values that preclude reirradiation; (2) a full diagnostic workup should be performed in patients with suspected local recurrence and; (3) any reirradiation should be delivered using optimal image guidance and highly conformal techniques. In addition, consensus cumulative dose for the organs at risk in the thorax are described.

Conclusions

These consensus statements provide practical guidance on appropriate patient selection for reirradiation, appropriate radiation therapy techniques, and cumulative dose constraints.

Practical Clinical Implementation of the Special Physics Consultation Process in the Re-irradiation Environment

Purpose

The purpose of this work is to present a practical, structured process allowing for consistent, safe radiation therapy delivery in the re-treatment environment.

Methods and materials

A process for reirradiation is described with documentation in the form of a special physics consultation. Data acquisition associated with previous treatment is described from highest to lowest quality. Methods are presented for conversion to equieffective dose, as well as our departmental assumptions for tissue repair. The generation of organ-at-risk available physical dose for use in treatment planning is discussed. Results using our methods are compared with published values after conversion to biologically effective dose. Utilization of pulsed-low-dose-rate delivery is described, and data for reirradiation using these methods over the previous 5 years are presented.

Results

Between 2015 and 2019, the number of patients in our department requiring equieffective dose calculation has doubled. We have developed guidelines for estimation of sublethal damage repair as a function of time between treatment courses ranging from 0% for <6 months to 50% for >1 year. These guidelines were developed based on available spinal cord data because we found that 84% of organs at risk involved nerve-like tissues. The average percent repair used increased from 32% to 37% over this time period. When comparing the results obtained using our methods with published values, 99% of patients had a cumulative biologically effective dose below the limits established for acceptable myelopathy rates. Pulsed-low-dose-rate use over this period tripled with an average prescription dose of 49 Gy.

Conclusions

The methods described result in safe, effective treatment in the reirradiation setting. Further correlation with patient outcomes and side effects is warranted.

The Medical Physics Management of Reirradiation Patients

Medical physics consultation is critical to the safe and appropriate management of patients undergoing reirradiation. A rigorous and efficient workflow in radiation oncology departments is crucial to ensure the safety and quality of treatment. The need for this service is steadily increasing year after year with the increasing complexity of treatment. This article provides an overview of how the Retreatment Special Medical Physics Consult is performed at the University of Michigan, along with a detailed patient-specific example, the results of a survey of how other institutions approach this workflow, and recommendations for future work to improve this process.