Treatment planning with a 2.5 MV photon beam for radiation therapy

Abstract

Purpose The shallow depth of maximum dose and higher dose fall‐off gradient of a 2.5 MV beam along the central axis that is available for imaging on linear accelerators is investigated for treatment of shallow tumors and sparing the organs at risk (OARs) beyond it. In addition, the 2.5 MV beam has an energy bridging the gap between kilo‐voltage (kV) and mega‐voltage (MV) beams for applications of dose enhancement with high atomic number (Z) nanoparticles. Methods We have commissioned and utilized a MATLAB‐based, open‐source treatment planning software (TPS), matRad, for intensity‐modulated radiation therapy (IMRT) dose calculations. Treatment plans for prostate, liver, and head and neck (H&N), nasal cavity, two orbit cases, and glioblastoma multiforme (GBM) were performed and compared to a conventional 6 MV beam. Additional Monte Carlo calculations were also used for benchmarking the central axis dose. Results Both beams had similar planning target volume (PTV) dose coverage for all cases. However, the 2.5 MV beam deposited 6%–19% less integral doses to the nasal cavity, orbit, and GBM cases than 6 MV photons. The mean dose to the heart in the liver plan was 10.5% lower for 2.5 MV beam. The difference between the doses to OARs of H&N for two beams was under 3%. Brain mean dose, brainstem, and optic chiasm max doses were, respectively, 7.5%–14.9%, 2.2%–8.1%, and 2.5%–19.0% lower for the 2.5 MV beam in the nasal cavity, orbit, and GBM plans. Conclusions This study demonstrates that the 2.5 MV beam can produce clinically relevant treatment plans, motivating future efforts for design of single‐energy LINACs. Such a machine will be capable of producing beams at this energy beneficial for low‐ and middle‐income countries, and investigations on dose enhancement from high‐Z nanoparticles.

The effects of different photon beam energies in stereotactic radiosurgery with cones

“…The peaks are 0.128, 0.263, 0.508, 0.500, 0.358, and 0.507 MeV for 2.5 MV, 6 MV‐FFF, 6 MV‐SRS, 6 MV, 10 MV‐FFF, and 10 MV beams, respectively. Our results are consistent with previous studies 5,24,27 of 2.5 and 6 MV beams reported by Khaledi et al. The peak for 10 MV‐FFF beam is lower than that of 6 MV‐SRS or 6 MV beams although it has a much higher maximum energy.…”

“…It is also interesting to note that the benefits of using 2.5 MV in reducing the dose to OARs are less for the Larger field with the 10 mm cone as seen in Table 2‐3. This observation is consistent with the findings for IMRT plans using 2.5 MV beam 5 …”

“…consistent with the findings for IMRT plans using 2.5 MV beam. 5 Figure 5 presents dose-volume histograms (DVH) comparison for the tremor plan to show changes of doses to organs-at-risk including the brain stem, chiasm, optic nerves, and eyes among the six different energy beams. The comparison is based on achieving the same maximum dose to the target for each energy beam.…”

“…Additionally, the 10-MV FFF can deliver dose rates up to 2400 MU/min, thus further reducing the amount of time required for these high dose deliveries if its known increased dosimetric penumbra is acceptable. Khaledi et al 5 investigated the benefit of using a 2.5 MV beam for IMRT treatment planning for therapeutic purposes in addition to its benefit for imaging purposes reported by Ding and Munro. 6 This study focusses on the small fields used in the SRS to determine the dosimetric effects of different available photon beam energies including the low energy 2.5 MV beam or the higher dose rate 10 MV-FFF beam to determine if these deliveries can be used for SRS to meet the need of sharper dose fall off or shorter delivery time, respectively.…”

“…Additionally, the 10‐MV FFF can deliver dose rates up to 2400 MU/min, thus further reducing the amount of time required for these high dose deliveries if its known increased dosimetric penumbra is acceptable. Khaledi et al 5 . investigated the benefit of using a 2.5 MV beam for IMRT treatment planning for therapeutic purposes in addition to its benefit for imaging purposes reported by Ding and Munro 6 …”