Image guidance improves freedom from recurrence in superficial radiation therapy for non-melanoma skin cancer
Authors: McClure Erin , Sedor Geoffrey , Moloney Mairead , Jin Yuxuan , Kattan Michael W. , Yu Lio 
Published: September 2022

Importance

This is the first study to quantify the 2-year recurrence rate of non-melanoma skin cancers (NMSCs) treated with image-guided superficial radiation therapy (IGSRT) and compare it to existing data on SRT, which is key to demonstrating the efficacy of IGSRT.

Objective

To quantify the 2-year recurrence rate for individuals with basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and squamous carcinoma in-situ (SCCIS) treated with IGSRT versus SRT without image guidance.

Design

A retrospective cohort study that collected data from a standardized electronic medical record (Modernizing Medicine – EMA), written radiation treatment records, and record/verify system (Sensus Healthcare – Sentinel) to evaluate the 2-year recurrence rate of NMSCs treated by IGSRT (March 2016 to January 2022) and compare it to existing data on NMSCs treated by SRT via one sample proportion tests.

Setting

Multi-institution outpatient dermatology practices.

Participants

Individuals > 18 years old with biopsy-proven SCC, SCCIS, and/or BCC treated with IGSRT. 1602 patients with a total of 2,880 treated lesions were followed until 1/14/2022. As of that date, 22 lesions had recurred, and 2858 lesions were still at risk for recurrence. An 18-month cutoff for recency of assessment was utilized, resulting in 1204 lesions (41.8%) that were lost to follow-up.

Exposure

Treatment with IGSRT or SRT.

Main Outcomes

The overall 2-year recurrence probability of 2880 NMSCs treated by IGSRT was 0.7%, which is statistically significantly lower than two previously reported SRT studies (p < 0.001).

Results

All NMSCs (SCC, SCCIS, BCC) treated by IGSRT in this cohort had an aggregate 2-year freedom from recurrence of 99.23%. When stratified by NMSC histologic type, the recurrence rate for BCC was 1.1%(N=1382), for SCC 0.8% (N=904) and for SCC 0.0% (N=594). These rates of recurrence are significantly improved compared to a pooled study that evaluated NMSCs across histology (Cognetta) and BCCs alone (Silverman) treated without image guidance (standard SRT) (p < 0.001).

Conclusions and relevance

Image-guided superficial radiation (IGSRT) therapy offers a paradigm-shifting treatment option for patients with NMSCs – offering statistically significantly improved outcomes compared to standard SRT, and a more desirable toxicity profile to surgical options. This study demonstrates that this treatment modality is associated with remarkably low recurrence rates, which are statistically significantly improved from the previous generation of SRT, and in line with modern outcomes for Mohs micrographic surgery, though a head-to-head comparison has yet to be performed.

Key Points

Question

Does treatment by new generation image-guided superficial radiation therapy (IGSRT) improve the rates of recurrence of nonmelanoma skin cancers (NMSCs) compared to non-image-guided SRT?

Findings

This cohort study evaluated the recurrence rates of 2880 NMSCs treated with IGSRT. In this dataset, the 2-year rate of recurrence for IGSRT-treated NMSCs collectively was 0.7%. This is statistically significantly lower than the recurrence rates of NMSC treated by SRT without image guidance (1.9% Cognetta; 6.3% Silverman).

Meaning

Recurrence rates in NMSCs when treated with IGSRT are statistically significantly improved from SRT without image guidance, supporting the use of this new technology in clinical practice.