Personalized organ dose assessment from CT imaging during proton therapy for classical Hodgkin lymphoma patients

Proton therapy (PT) improves treatment precision for classical Hodgkin lymphoma (cHL), with computed tomography (CT) being essential for treatment planning and verification. This study evaluates the individual organ doses from CT imaging in these patients treated with PT using free-breathing (FB) or deep inspirational breath hold (DIBH) techniques.

A cohort of 38 patients treated at the Skandion Clinic was studied. Organ doses from each planning and verification scan were estimated using VirtualDose software, based on CT parameters extracted from DICOM data. The impact of different imaging protocols (standard dose [SD], low dose [LD], and 4DCT) was assessed for patients with target in mediastinum, and neck and upper thorax.

Significant variations were observed in the number of CT scans (median 9, range 3-12) and the protocols used among patients. Organ doses were further influenced by the extent of the scanning volume and the scanning technique. SD protocols in the mediastinum set resulted in median dose per scan to the lungs around 21 mGy (males and females), while LD protocol reduced these doses by up to 87%. The most exposed organs can receive a total dose of several hundred mGy.

Large inter-patient variations highlight the need for personalized CT dose calculations. Although in-field and near-field organs may receive relatively high doses from imaging, these remain significantly lower than the prescribed dose, less than 2%. Nevertheless, organ doses and their associated risks for long-term survivors of cHL could be further minimized by implementing low-dose CT protocols whenever feasible.