Gastric Radiotherapy in the UK - Current Practice and Opinion on Future Directions

PURPOSE/OBJECTIVE(S)

Gastric radiotherapy (RT) is more commonly practiced in the US compared to the UK, where postoperative chemoradiotherapy (CRT) is reserved for selected high-risk patients, and preoperative CRT is not standard of care pending the results of phase 3 trials, TOPGEAR and CRITICSII. CRT for inoperable, non-metastatic gastric cancer is also not recommended in the UK, despite being listed in NCCN guidelines. Recent systematic review of definitive gastric CRT (dCRT) conducted by the authors found median overall survival of 11-26.4 months, clinical complete response rates of 8-45% and acceptable rates of ≥G3 toxicity, supporting further research. Given these promising findings and perceived low uptake of gastric RT in the UK, we set out to establish current UK practice, opinion and RT technique to inform the development of a UK gastric RT protocol and future clinical trials.

MATERIALS/METHODS

A 19 question survey was developed. Following local ethical approval and pilot by 4 clinical oncologists, the final survey was distributed electronically on 13/12/22 to UK Consultant Clinical Oncologists specializing in esophago-gastric (OG) cancer. Responses were anonymous. Survey was closed 6/2/23 and data analyzed using JISC/spreadsheet software.

RESULTS

A total of 43 clinicians completed the survey. For gastric cancer, 28.6%, 7.1% and 9.5% would agree/strongly agree with use of postoperative (postopRT), preoperative (preopRT) or definitive RT (dRT) respectively, compared to 26.2%, 45.2% and 46.6% for type III gastro-esophageal junction tumors. 93% had prescribed palliative gastric RT in the last 3 years compared to 40.5% postopRT, 16.7% dRT and 9.5% preopRT. Main reasons for infrequent use were; rarely indicated within standard UK practice 88.4%, lack of UK gastric RT protocol 53.5%, toxicity concerns 44.2%. 45Gy/25# was most commonly used for preopRT (66%) and postopRT (86%), and 50Gy/25# for dRT (58%). 96% use IMRT/VMAT, 85% CT simulation with IV/oral contrast, 69% gastric filling protocol and 54% 4DCT. When ranked out of 10 (1 = low 10 = high), clinician confidence in accurately delineating gastric volumes mean rank was 4.33 for postopRT, with 9% rating ≥8/10, and 4.52 for dCRT/preopRT with 17% rating ≥8/10. However, 48.8% were experienced in outlining upper abdominal nodes and 62.8% duodenum. 93% would find a detailed outlining protocol useful, 81.4% wanted some form of peer review, 76.7% a nodal atlas, and 74.4% a workshop with an expert. 77.6% would be supportive of a future clinical trial of dCRT, with 23.4% needing more supporting evidence. No-one would not support a future trial in this setting.

CONCLUSION

Gastric RT is not often practiced in the UK, due to lacking evidence and toxicity concerns. Given the growing evidence and supportive OG community, it is time to consider a trial of dCRT in the UK, which must include detailed RT protocols, atlases and educational materials to improve clinician confidence and ensure good RT quality assurance.

Dose Escalation in Esophageal Cancer: Comparing Pre-Accrual and On-Trial Target Volume Delineation in the UK SCOPE2 Trial

PURPOSE/OBJECTIVE(S)

The ongoing UK SCOPE2 trial evaluates radiotherapy (RT) dose escalation and PET-guided systemic therapy in esophageal cancer, and has an accompanying RT trials quality assurance (RTTQA) program, evolved through the preceding SCOPE trials. We compare pre-accrual with on-trial individual case review (ICR) target volume delineation (TVD).

MATERIALS/METHODS

Prior to recruitment, centers were required to undertake TVD exercises using 3D/4D DICOM datasets with relevant clinical details and a RT planning guidance document (RPGD) provided. Contours were then compared against the RTTQA team-defined gold standard. Exceptions were those who had satisfied QA requirements for a previous esophageal RT trial (NeoSCOPE). For ICRs, prospective reviews (prior RT start, PRs) were undertaken for each center's first submission, plus high-dose cases submitted pending formal safety review. Additional PRs were undertaken at the RTTQA team's discretion. Timely retrospective reviews (within 2 weeks of RT start, TRR) were also undertaken for a random 10% sample. TVDs were assessed for compliance using predefined criteria and the RPGD. Resubmission was requested at reviewer's discretion, usually due to unacceptable variation (UV) from protocol. Clarification was sought before contour approval/resubmission request if appropriate. Review outcomes were then evaluated. PTV6000 was new to SCOPE2, along with a greater emphasis on use of 4DCT than in prior SCOPE trials.

RESULTS

A total of 85 pre-accrual cases from 33 UK centers were reviewed, of which 20 (24%) were resubmissions, and 50 (59%) were accepted. 99 TVD UVs were observed in 49 cases, most commonly in CTVB (42/99, 42%), which included editing for normal structures and elective lymph node regions, followed by ITV (4D cases only, 14/52, 27%) and PTV6000 (13/99, 13%). 121 ICRs from 31 UK centers were available for review. 87 (72%) were PRs and 34 (28%) TRRs. 43 (36%) completed the relevant SCOPE2 exercise. 19 (16%) were resubmissions, and 82 (68%) were accepted. 72 UVs were observed in 45 ICRs; again, most commonly in CTVB (34/72, 48%), PTV6000 (high dose arm only, 11/46, 24%) and ITV (4D only, 5/26, 19%). Of the 45 cases where a UV was recorded, 16 (36%) had completed the relevant SCOPE2 pre-accrual. Comparing area of UV on SCOPE2 pre-accrual cases and ICRs, 3 (19%) contours contained the same (2 = CTVB, 1 = PTV6000), 5 (31%) contained different and 8 (50%) had no UVs at pre-accrual. The rate of UV was significantly lower for ICR than for pre-accrual submissions (0.60 and 1.16 respectively, p = 0.001).

CONCLUSION

Significantly fewer UVs in ICR compared with pre-accrual supports a robust, educational RTTQA program through national collaboration and evolving trial series. CTVB, along with newer volumes of ITV and PTV6000, were recurring UV domains and should inform RPGD development and RTTQA for ongoing recruitment and future trials.

The Promise of Proton Beam Therapy for Oesophageal Cancer: A Systematic Review of Dosimetric and Clinical Outcomes

AIMS

Due to its physical advantages over photon radiotherapy, proton beam therapy (PBT) has the potential to improve outcomes from oesophageal cancer. However, for many tumour sites, high-quality evidence supporting PBT use is limited. We carried out a systematic review of published literature of PBT in oesophageal cancer to ascertain potential benefits of this technology and to gauge the current state-of-the-art. We considered if further evaluation of this technology in oesophageal cancer is desirable.

MATERIALS AND METHODS

A systematic literature search of Medline, Embase, Cochrane Library and Web of Science using structured search terms was carried out. Inclusion criteria included non-metastatic cancer, full articles and English language studies only. Articles deliberating technical aspects of PBT planning or delivery were excluded to maintain a clinical focus. Studies were divided into two sections: dosimetric and clinical studies; qualitatively synthesised.

RESULTS

In total, 467 records were screened, with 32 included for final qualitative synthesis. This included two prospective studies with the rest based on retrospective data. There was heterogeneity in treatment protocols, including treatment intent (neoadjuvant or definitive), dose, fractionation and chemotherapy used. Compared with photon radiotherapy, PBT seemed to reduce dose to organs at risk, especially lung and heart, although not for all reported parameters. Toxicity outcomes, including postoperative complications, were reduced compared with photon radiotherapy. Survival outcomes were reported to be at least comparable with photon radiotherapy.

CONCLUSION

There is a paucity of high-quality evidence supporting PBT use in oesophageal cancer. Wide variation in intent and treatment protocols means that the role and 'gold-standard' treatment protocol are yet to be defined. Current literature suggests significant benefit in terms of toxicity reduction, especially in the postoperative period, with comparable survival outcomes. PBT in oesophageal cancer holds significant promise for improving patient outcomes but requires robust systematic evaluation in prospective studies.

Comparing Proton to Photon Radiotherapy Plans: UK Consensus Guidance for Reporting Under Uncertainty for Clinical Trials

In the UK, the recent introduction of high-energy proton beam therapy into national clinical practice provides an opportunity for new clinical trials, particularly those comparing proton and photon treatments. However, comparing these different modalities can present many challenges. Although protons may confer an advantage in terms of reduced normal tissue dose, they can also be more sensitive to uncertainty. Uncertainty analysis is fundamental in ensuring that proton plans are both safe and effective in the event of unavoidable discrepancies, such as variations in patient setup and proton beam range. Methods of evaluating and mitigating the effect of these uncertainties can differ from those approaches established for photon therapy treatments, such as the use of expansion margins to assure safety. These differences should be considered when comparing protons and photons. An overview of the effect of uncertainties on proton plans is presented together with an introduction to some of the concepts and terms that should become familiar to those involved in proton therapy trials. This report aims to provide guidance for those engaged in UK clinical trials comparing protons and photons. This guidance is intended to take a pragmatic approach considering the tools that are available to practising centres and represents a consensus across multidisciplinary groups involved in proton therapy in the UK.