2149 - Effectiveness and Safety of Definitive Radiation Therapy in Oldest Old Patients (=90 years): A Matched Pair Analysis

H. Tanaka, K. Ueda, C. Nakabe, A. Hironaka, M. Karita, T. Ono, Y. Manabe, M. Kajima, K. Fujimoto, and T. Shiinoki; Yamaguchi University Graduate School of Medicine, Department of Radiation Oncology, Ube, Japan

Purpose/Objective(s): Radiation therapy is less invasive and plays an important role in cancer treatment in older populations. However, for oldest old patients (=90 years), it is often difficult to decide on the radiation therapy approach due to concerns regarding the tolerability and consequences of irradiation. Here, we tested our hypothesis by evaluating the effectiveness and safety of definitive radiation therapy in oldest old patients using a matched pair analysis. Materials/

Methods: Patients =90 years who underwent definitive radiation therapy at our hospital between 2013 and 2022 were enrolled. A control cohort was constructed manually using pairwise matching from the remaining pool of patients aged =89 years who received definitive radiation therapy in same period. Patients were matched using the following criteria in order of priority: (i) cancer type (primary site), (ii) TNM classification, (iii) pathology, (iv) biological effective dose (BED), (v) presence or absence of concurrent chemotherapy, (vi) performance status (PS), and (vii) sex. Local control (LC) and overall survival (OS) rates were calculated using the Kaplan-Meier method. Adverse events were evaluated using CTCAE v5.
Results: Sixty-three oldest old patients received radiation therapy. Of these, 34 were irradiated with curative intent. Two oldest old patients, one with malignant melanoma and one with Merkel cell carcinoma, had no matched controls; therefore, comparisons were made with 32 cases each (Table). There was no significant difference in the completion rate of radiation therapy between the two groups. There was no significant difference in the LC rate or OS rate between the two groups (p = 0.216 and p = 0.156, respectively). Acute and late adverse events did not differ significantly between the two groups (p = 0.803 and p = 1.000, respectively). In an analysis limited to oldest old patients, ambulatory patients tended to have better OS than non-ambulatory patients (p = 0.065).
Conclusion: Definitive radiation therapy for oldest old patients was as effective and safe as that for patients =89 years. Completion rates were similar. These results suggest that definitive radiation therapy is beneficial, especially for ambulatory patients. Abstract 2149 – Table 1

		Oldest old (=90 years)	Non-oldest old (<90 years)	p value
Age	Median (range)	91 (90–96)	78 (56–89)	<0.001
Primary site				1.000
CNS/H&N/Eso/Lung/Liver/Gyn/Uro/Lym/Skin		1/6/1/8/1/4/1/2/8	1/6/1/8/1/4/1/2/8
Stage (except for glioma)	I/II/III/IV	11/6/8/6	10/7/5/9	0.715
BED (Gy)	Median (range)	84.0 (45.6–105.6)	81.6 (45.6–105.6)	0.817
PS	0/1/2/3	10/16/3/3	19/12/0/1	0.050
Ambulation	Possible/not possible	21/11	29/3	0.032
Sex	Male/female	11/21	14/18	0.609
Concurrent chemotherapy	Yes/no	5/27	5/27	1.000