ESTRO 2024 - Abstract Book

S5980

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

1. Owens R, Mukherjee S, Padmanaban S et al. Intensity-modulated radiotherapy with a simultaneous integrated boost in rectal cancer, Clinical oncology (Royal College of Radiologists (Great Britain)) . 2019; 32(1):35-42.

2. Appelt AL, Kerkhof EM, Nyvang L et al. STAR-TREC collaborative group. Robust dose planning objectives for mesorectal radiotherapy of early stage rectal cancer - A multicentre dose planning study. Tech Innov Patient Support Radiat Oncol. 2019 Oct 15;11:14-21.

1777

Mini-Oral

Hypofractionated proton therapy reduces beam on time in esophageal cancer patients

Petra Klinker, Jeffrey Free, Gabriel Guterres Marmitt, Margriet Dieters, Charlotte Ijsbrandy, Jannet C. Beukema, Erik W. Korevaar, Johannes A. Langendijk, Christina T. Muijs

University Medical Centre Groningen, Radiation Oncology, Groningen, Netherlands

Purpose/Objective:

Lymphocytes play a role in the immune response to (chemo)radiotherapy. Clinical data shows that radiation-induced lymphopenia (RIL) negatively affects tumour response and overall survival in several tumour sites, including in esophageal cancer (EC). Dai et al (2022) concluded in their meta-analyses that severe RIL was associated with lower pathologic complete response rates (OR = 0.44), worse OS (HR = 1.50), and worse progression-free survival (HR = 1.70). The risk of irradiating circulating lymphocytes seems related to the opportunity to hit the lymphocytes. This can be affected by reducing the organs at risk (OARs) dose, the number of fractions or the duration of the total beam-on time (BOT). This planning study aimed to evaluate the impact of hypofractionation (less fractions with higher fractionation dose) on dose to OARs and BOT.

Material/Methods:

We included 15 EC patients who were treated with neoadjuvant proton chemoradiotherapy (nPCRT). These patients were selected based on differences in NTCP between photon and proton treatment plans (model-based selection). The original clinical treatment plans for 23 fractions of 1.8 Gy RBE (CROSS) were replanned for 18 fractions of 2.2 Gy RBE (hypoCROSS) (Figure 1). All plans were robustly optimized using a three beam approach, including 5 times repainting to be robust against intrafraction motion. Logfiles were collected to register the BOT for these individual treatment plans. Differences in OARs dose and BOT between the standard CROSS and hypoCROSS were compared and tested using the Wilcoxon signed rank test. Amongst the hypoCROSS plans, we classified patients as high and low BOT patients, based on the median BOT. We evaluated differences between these patients, regarding clinical and patient factors using the Mann Whitney U test.

Results: