Adaptive Proton Therapy for Pediatric Parameningeal Rhabdomyosarcoma: On-Treatment Anatomic Changes and Timing to Replanning. Issue 4 (April 2023)

• Record Type: Journal Article
• Authors: Uh, J.; Jordan, J.A.; Pappo, A.S.; Krasin, M.J.; Hua, C.
• Is Part Of: Clinical oncology. Volume 35:Issue 4(2023)
• Page Start: 245
• Page End: 254
• Publication Date: 2023-04
• Subjects: adaptive proton therapy -- on-treatment imaging -- parameningeal rhabdomyosarcoma -- upfront proton therapy -- weekly MRI; Oncology -- Periodicals; Tumors -- Periodicals; Cancer -- Treatment -- Periodicals; Radiotherapy -- Periodicals; Neoplasms -- Periodicals; Cancer -- Radiotherapy; Cancer -- Treatment; Oncology; Medical radiology; Radiotherapy; Tumors; Electronic journals; Periodicals; 616.994
• DOI: 10.1016/j.clon.2023.01.013
• Languages: English
• ISSNs: 0936-6555

Abstract

Abstract: Purpose: To characterize on-treatment changes in GTV morphology in children with parameningeal rhabdomyosarcoma receiving upfront proton therapy with concurrent chemotherapy and thereby provide guidance on the timing of on-treatment imaging and adaptive replanning. Methods and Materials: GTV was delineated on 86 simulation and weekly MR images of 15 prospectively enrolled patients (aged 1–21 years). Temporal changes from baseline in volume and surface (95% Hausdorff distance) were analyzed in relation to the need for plan verification and the resultant doses with hypothetical no treatment adaptation. Results: The median time was 6 days from the initiation of chemotherapy to CT+MR simulation and 15 days from the simulation to the start of radiotherapy. All but 1 patient showed a continuous decrease in GTV (0.16–1.52%/day) after simulation. At 3 weeks from simulation, 10 of 15 patients exhibited a significant reduction in volume (median, 20%; range, 6–29%). Without replanning, these changes could lead to a reduction in CTV V95 by 7–14% (n = 2) and/or an increase in D0.01 cc/Dmean of adjacent organs at risk by 6–21% of the prescribed target dose (n = 7). Significant dosimetric consequences occurred in cases with (1) a considerable weight gain, (2) shrinkage of the skin surface, or (3) tumor regression in the oral or nasal cavity and sinus that altered air-tissue components in the beam path. The subsequent GTV and dosimetry after 3 weeks from simulation (4 weeks from chemotherapy initiation) demonstrated a relatively stable trend. Conclusions: On-treatment imaging at 3 weeks after simulation is recommended, if the simulation is performed at 1 week after the initiation of chemotherapy, to detect significant anatomic changes that could result in >5% deviation from planned target coverage and/or organ doses in pediatric patients with parameningeal rhabdomyosarcoma receiving early proton therapy. Highlights: An early GTV change is common in paediatric PM RMS receiving upfront proton therapy. Target underdose and/or OAR overdosage may occur without adaptation to new anatomy. Care should be taken when proton beams intersect variable air–tissue interfaces. On-treatment imaging at 3 weeks from RT simulation was beneficial in our cohort.