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Improved Lung and Gonadal Sparing During Total Body Irradiation Using a VMAT Technique: Preliminary Single-Institutional Experience

N Kovalchuk1*, L Skinner1, E Blomain1, R Hoppe1, S Hiniker1, (1) Stanford University Cancer Center, Palo Alto, CA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Pulmonary toxicity and infertility has a paramount influence on the quality of life of the patients undergoing Total Body Irradiation (TBI). Here we report on implementation of the Volumetric Arc Therapy (VMAT)-based TBI technique aimed at achieving improved lung and gonadal sparing.


Methods: From October 2019 to March 2020 seven patients were treated with a VMAT-based TBI technique on C-arm LINAC. VMAT plans were generated with 3 isocenters in head first supine (HFS) position with additional AP-PA plans with 1-2 isocenters in feet first supine (FFS) position. To switch from HFS to FFS positions without re-positioning the patient, an in-house-developed rotational couch-top was used enabling 180°-rotation. Patients were treated with a range of TBI doses (2Gy-12Gy) depending on protocol. For dosimetric comparison between conventional 2D and VMAT approaches, a simulated 2D plan replicating our current clinical setup with lung blocks, chest wall boosts and testes shield was created for one patient receiving 2Gy TBI.


Results: With VMAT TBI technique for all patients, the mean dose to lungs and kidneys was 63.3%±6.8% and 58.3%±10.9% of prescription, respectively. Three pediatric aplastic anemia patients undergoing 2Gy-TBI regimen received mean doses to testes <0.4Gy, ovaries <0.6Gy, brain <1.5Gy, thyroid <1.4Gy. Compared to 2D conventional TBI technique, VMAT TBI technique provided superior target coverage (D90% = 100% for VMAT vs 95.3% for 2D), lower lung dose (Dmean=55% for VMAT vs 89% for 2D), lower testes dose (Dmean=22.3% for VMAT vs 67.8% for 2D). The average treatment time was 43.3 min (range, 25.1 min to 57.5 min).


Conclusion: This preliminary report suggests that VMAT TBI exhibited improved lung and gonadal sparing compared to the conventional approach. This treatment was clinically tractable and well-tolerated. The present study can serve as a proof-of-concept for further prospective studies evaluating this technique for wider applications in populations receiving TBI.

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