Investigation of pulsed low dose rate radiotherapy using dynamic arc delivery techniques

Abstract

There has been no consensus standard of care to treat recurrent cancer patients who have previously been irradiated. Pulsed low dose rate (PLDR) external beam radiotherapy has the potential to reduce normal tissue toxicities while still providing significant tumor control for recurrent cancers. This work investigates the dosimetry feasibility of PLDR treatment using dynamic arc delivery techniques. Five treatment sites were investigated in this study including breast, pancreas, prostate, head and neck, and lung. Dynamic arc plans were generated using the Varian Eclipse system and the RapidArc delivery technique with 6 and 10 MV photon beams. Each RapidArc plan consisted of two full arcs and the plan was delivered five times to achieve a daily dose of 200 cGy. The dosimetry requirement was to deliver approximately 20 cGy/arc with a 3 min interval to achieve an effective dose rate of 6.7 cGy min⁻¹. Monte Carlo simulations were performed to calculate the actual dose delivered to the planning target volume (PTV) per arc taking into account beam attenuation/scattering and intensity modulation. The maximum, minimum and mean doses to the PTV were analyzed together with the dose volume histograms and isodose distributions. The dose delivery for the five plans was validated using solid water phantoms inserted with an ionization chamber and film, and a cylindrical detector array. Two intensity-modulated arcs were used to efficiently deliver the PLDR plans that provided conformal dose distributions for treating complex recurrent cancers. For the five treatment sites, the mean PTV dose ranged from 18.9 to 22.6 cGy/arc. For breast, the minimum and maximum PTV dose was 8.3 and 35.2 cGy/arc, respectively. The PTV dose varied between 12.9 and 27.5 cGy/arc for pancreas, 12.6 and 28.3 cGy/arc for prostate, 12.1 and 30.4 cGy/arc for H&N, and 16.2 and 27.6 cGy/arc for lung. Advanced radiation therapy can provide superior target coverage and normal tissue sparing for PLDR reirradiation of recurrent cancers, which can be delivered using dynamic arc delivery techniques with ten full arcs and an effective dose rate of 6.7 ± 4.0 cGy min⁻¹.

Volumetric-modulated arc therapy for oropharyngeal carcinoma: A dosimetric and delivery efficiency comparison with static-field IMRT

“…The dosimetric quality and treatment delivery characteristics have been evaluated by previous investigators [5–9,12–18] . Intrinsically, VMAT uses more beam angles and therefore spreads the incident/exit beams more evenly in surrounding normal tissues leading to more uniform surface doses.…”

Tissue TGF-β expression following conventional radiotherapy and pulsed low-dose-rate radiation

“…[1][2][3][4] This involves spreading out a conventional radiation therapy dose into short pulses of dose with breaks in between. By example, a PLDR regimen may involve delivering a dose of 2 Gy as 10 pulses of 0.2 Gy, each 3 minutes apart.…”

“…3,4 While cell survival data from cell lines and in vivo animal experiments have been published, no mechanistic data are available to explain the phenomenon of improved clinical toxicity with this treatment technique. Therefore, we performed in vivo experiments in mice to investigate the effect of PLDR and conventional radiotherapy (CRT) on normal tissues.…”

TrueBeam Low Dose Rate Investigation for Pulsed Reduced Dose Rate IMRT

“…Researchers are actively investigating ways to apply PRDR to more advanced techniques, such as static field Intensity Modulated Radiation Therapy (IMRT) [6], Volumetric Modulated Arc Therapy (VMAT) [7] [8], and tomotherapy [9] [10]. The primary challenge with IMRT-based PRDR, however, is that IMRT fields are difficult to separate into 0.2 Gy pulses.…”

“…Currently available treatment planning systems do not include optimization constraints that specifically limit dose rate. Instead, treatments must be split into multiple (often ten or more) beams or arcs each delivering less than 0.2 Gy, or the same beams/arcs must be delivered repeated times with each sub-fraction less than 0.2 Gy [7].…”