Evaluation of Radiotherapy Dose and Survival Outcomes for Teenagers, and Young Adults with Nasopharyngeal Carcinoma in UK and Ireland

PURPOSE/OBJECTIVE(S)

Nasopharyngeal carcinoma (NPC) follows a bimodal distribution with a smaller incidence peak in teenagers and young adults (TYAs). In TYAs, an over-whelming proportion are associated with Epstein-Barr virus (EBV). We have evaluated the variation in TYA NPC practice patterns across the UK and Ireland, along with survival outcomes.

MATERIALS/METHODS

We performed a multicenter, observational cohort study, of patients aged 13-25 years, with histologically confirmed NPC, treated between the years 2002-2022. An initial expression of interest was sent to selected centers treating H&N patients in the UK and Ireland. For analysis, patients were assessed based on total prescribed dose, with a cut off for low dose (LD) (≤61.2Gy) versus a high dose (HD)(>61.2Gy).

RESULTS

Ninety-five patients, from 9 centers, were eligible for inclusion. Patient demographics are shown in table1. At a median follow up of 45 months (IQR 23-111), 3-year overall survival (OS) was 98% (95% CI 93%-100%) with LD versus 91% (95% CI 83%-99%) with HD (Hazard ratio (HR) = 3.0; 95% CI 0.3-27, p = 0.3). 3-year progression free survival (PFS) was 84% (95% CI 71%-97%) with LD versus 83% (95% CI 72%-94%) with HD (HR 1.3; 95% CI 0.4-4.0, p = 0.6), and 5-year PFS was 84% (95% CI 71%-97%) with LD versus 83% (95% CI 72%-94%) with HD (HR 1.3; 95% CI 0.4-4.0, p = 0.6). Incidence of distant metastasis (DM) was 9.9%. 2 patients (6%) with T3-T4 tumors, treated with LD, had locoregional failure (LRF) compared to 1 patient (3%) treated with HD.

CONCLUSION

We have demonstrated excellent survival outcomes for the UK & Ireland TYA NPC patients. As the majority of cases in this age group have EBV+ NPC, with survival similar between LD and HD protocols, we propose that pediatric protocols, with lower radiotherapy doses should be considered for all TYA NPC, with the aim of reducing late effects. Additional analysis to better understand the impact of heterogeneity between both groups, including choice of protocol, induction and adjuvant treatment will follow this study. Prospective evaluation, as part of an international collaboration, is required to optimize the management strategy for this rare cohort of patients.

Equity of Access to Proton Beam Therapy in England: A National NHS analysis

PURPOSE/OBJECTIVE(S)

Policies to improve population health have often focused on equitable access to health services. While new technologies have an enormous potential in improving health outcomes, they may not always be equally accessible across diverse geographical areas and socio-economic backgrounds. Between 2008 and 2018, 1352 patients with eligible indications for Proton Beam Therapy (PBT) were treated overseas within the NHS Proton Overseas Programme (POP) and 947 patients have been treated at the Christie since the National NHS PBT service started in December 2018. The 8 most common PBT cancer indications cover more than 80% of the referrals and referral rates depend on several factors. Aim of this study is to evaluate equity of access to PBT throughout the country and how this has changed since the national PBT service inception.

MATERIALS/METHODS

Incidence data were available for 7/8 of the most common PBT cancer indications. These data were provided by the National Disease Registration Service (NDRS) by diagnosis, age group and by the 7 NHS regions in England. The incidence data referred to the time period 2013-2019. The first national NHS PBT center started accepting referrals in October 2018, therefore this time period was split in pre-NHS PBT (1/1/13-30/9/18) and post-NHS PBT (1/10/18-31/12/19). Demographics and clinical characteristics of patients referred for PBT were extracted from the national NHS PBT registry for matching clinical diagnoses and time period. The ratio between the referred (observed) and newly diagnosed (expected) patients is the Proton Utilization Proportion (PUP), which tracks the proportion of eligible patients using the technology.

RESULTS

For the 7 common PBT indications examined, the total number of newly diagnosed patients was 2134 in the pre-NHS PBT period and 461 in the post-NHS PBT period. The (accepted) referrals were 587 and 300 in the pre-and post-NHS PBT period, respectively. An increase in the PUP between the pre-NHS PBT and the post-NHS PBT is noted for any diagnostic category, age group and NHS region. The most noticeable increase is noticed for Medulloblastoma, which became a commissioned indication for PBT only in 2016.The PUP in England increased post-NHS PBT by 137% overall. Of note, post-NHS PBT, 99% of the patients aged 0-15 with these 7 common indications for PBT were referred and treated with PBT.

CONCLUSION

Promoting equality of access to cutting-edge radiotherapy technologies is at the heart of NHS England's values. Throughout the development of the policies and processes related to PBT access in the UK, the NHS has given regard to the need to reduce geographical variation which may contribute to health inequalities. The PUP has increased since the opening of a National PBT service in England, which uses a central web-based Proton Referral Pathway managed by a National Proton Office. Further analysis will follow to examine whether socio-economic or geographical barriers exist within each region.

Dose Volume Thresholds Associated with Acute Skin Toxicities in Proton Beam Therapy

PURPOSE/OBJECTIVE(S)

The depth-dose characteristics of proton beam therapy (PBT) mean that the skin-sparing effect is reduced with PBT, potentially leading to an increased incidence and severity of acute radiotherapy induced skin toxicities (RIST). Predictive factors of acute RIST in patients treated with PBT remain largely undefined. In this study, we retrospectively reviewed the acute RIST of patients treated with pencil beam scanning (PBS) PBT to identify dose-volume thresholds which are predictive of acute RIST.

MATERIALS/METHODS

All patients treated with PBS-PBT at a single institution between December 2018-October 2022 were included in this study. Acute RIST were recorded as per RTOG grading scale and dichotomized to Grade (G) <2 vs ≥2. Anonymized demographics, clinical and dosimetric data were extracted from electronic patient records and a treatment planning system. Skin structure is defined as 5mm rind grown as an inner margin from the patient contour. The following skin dose-volume statistics were collected: Dmax (maximum dose to any pixel inside the skin contour) and dose to skin volumes in 5Gy increments (V5Gy, V10Gy etc.). Preliminary analyses of dosimetric data of patients with G0, G1 vs ≥G2 acute RIST are presented, with significance assessed at the 5% level using t-tests and univariate logistic regression models, and risk thresholds determined using receiver operating characteristic (ROC) curves.

RESULTS

We report the data for 582 patients with extracted dosimetric data. The pediatric, teenage and young adult (TYA) and adult populations were 38%, 19% and 43% respectively. The three most common indications for PBT were head and neck cancers (HNC) (23%), sarcoma (21%), and chordoma (15%). Increasing age, HNC and sarcoma were associated with an increased risk of grade 2+ acute RIST. For patients who developed acute RIST of G2+, the median volume receiving 10Gy, 20Gy, 30Gy, 40Gy and 50Gy were significantly higher (P<0.0001) than patients with G0 and G1. The dose volume effect of acute RIST is greater at 30Gy and above. Similarly, median Dmax was significantly higher in the G2+ acute RIST group compared to G0 and G1 (P<0.0001) for all age groups. Using the ROC curve, we observed threshold volumes (in cm3) for V10Gy, V20Gy, V30Gy, V40Gy and V50Gy (Table 1).

CONCLUSION

The volume of irradiated skin and Dmax are associated with the risk of developing acute RIST in patients treated with PBS PBT. Further work is being done to develop a model predictive of acute RIST in clinical setting.