A dosimetric evaluation of a novel technique using abutted radiation fields for myeloablative total body irradiation

Abstract

Background: The present study reports myeloablative total body irradiation (TBI) on an isocentrically mounted linac by laying the patient on the floor and management of abutting radiation fields and partial shielding of lungs. Dosimetrical efficacy of this novel technique was evaluated. Materials and methods: In this retrospective study, dosimetrical parameters from TBI plans on whole-body CT scans of 46 patients were analysed. The prescribed dose to TBI was 12 Gy in six fractions delivered over a period of 3 days for myeloablative conditioning. TrueBeam STx platform Linac (Varian Medical Systems Inc., Palo Alto, CA, USA) was used to deliver opposing fields. Radiation fields were abutted to form a single large field using an arithmetic formula at source-to-skin-distance of 210 cm. Results: Discrepancies in dose calculated by treatment planning system were within 1·6% accuracy, and dose profile at the junction of abutting radiation fields was reproduced within 3·0% accuracy. The real treatment time for each patient was ~30 minutes/fraction. Monitor unit was weighted for multiple sub-fields to achieve dose homogeneity within 5·0% throughout the whole body, and the mean dose to lung was ≤10 Gy. Conclusion: Our abutting radiation field technique for myeloablative TBI is feasible in any existing linac bunker. ‘Island-blocking’ is feasible in this technique using multi-leaf collimator. This technique is cost-effective as it does not require any costly equipment than the readily available equipment in any radiotherapy facility. In general, TBI requires laborious planning procedures and spacious linac bunkers; this novel technique has the potential to change previously held notions.

Improving total body irradiation with a dedicated couch and 3D-printed patient-specific lung blocks: A feasibility study

“…Also, the number of MUs per session was lower compared to the one reported in experiences based on MLCs, despite achieving the prescribed dose in midplane due to the use of large fields ( 45 ). In our study, the treatment required about 1500 MU delivered in around 12 minutes for both prone and supine sessions, after a short learning curve (of about 4 treatments).…”

“…In our study, the treatment required about 1500 MU delivered in around 12 minutes for both prone and supine sessions, after a short learning curve (of about 4 treatments). In particular, the mean ± standard deviation of MUs for the supine TBI treatment were 1472 ± 200 MUs in our cohort of patients while they were 3456 ± 264 in ( 45 ), considered as a representative paper of MLC-modulated TBI treatment.…”

“…The sweeping arc technique was feasible without using the spoiler because the use of contra-opposite and angulated beams (gantry angles higher than ±40°) increases the entrance dose to the patient skin, allowing a homogenous treatment, as reported in ( 31 , 45 ).…”

“…Other authors have chosen to decrease the dose rate for beams contributing to lung doses, to reduce radiation-induced lung toxicity, while they increased the dose rate of beams irradiating other sites with the aim to reduce the overall treatment time ( 45 ).This solution could be easily implemented as a further improvement of our approach. At the last follow-up, we did not observe any lung toxicity likely due the fulfilling of the mean dose constraint on the lung.…”