Oncology Daily Report: 01/14/2024

The Watchful Waiting 2 trial (NCT02438839) was a phase II study (1). The population under investigation comprised patients with low resectable rectal cancer. This study aimed to investigate the non-surgical management of this condition, primarily focusing on definitive chemoradiation as a treatment modality.

The intervention under investigation was a high-dose radiotherapy treatment plan. This plan was executed in accordance with a specific protocol, which mandated a dose of 50.4 Gy in 28 fractions to the elective volume (CTV-/PTV-E) and a concomitant boost of 62 Gy in 28 fractions to the primary target volume (CTV-/PTV-T).

The study involved 108 patients, although the analysis was conducted on 106 treatment plans. The results showed that the dose coverage planning goals for the main target structures were achieved for 94% of the treatment plans. However, there was a significant variation in doses to organs-at-risk (OARs) among the participating centers, particularly concerning the intestines and bladder. Specifically, five patients experienced a V60Gy greater than 10 cm(3) for the intestines, and two patients had the same for the bladder.

In conclusion, the study found that while the prescribed planning goals for target coverage were met in the majority of cases, there were notable intercenter differences in the doses and volumes of OARs. The study also indicated that the dose escalation to 62 Gy, applied as a concomitant boost to the primary tumor, did not result in substantial high dose volumes (>60 Gy) to the bladder and intestines. These findings suggest that the treatment planning goals established in this study could be utilized for future evaluations of high-dose radiotherapy in the context of organ preservation for low rectal cancer.

Reference

Arp DT, Appelt AL, Jensen LH, Havelund BM, Nissen HD, Risumlund SL, Sjölin MEE, Nielsen MS, Poulsen LØ. Treatment planning for patients with low rectal cancer in a multicenter prospective organ preservation study. Phys Med. 2024 Jan 14;118:103206. doi: 10.1016/j.ejmp.2023.103206. Epub ahead of print. PMID: 38224663.