Dosimetric comparison between carbon, proton and photon radiation for renal retroperitoneal soft tissue sarcoma recurrence or metastasis after radical nephrectomy

Intensity-modulated proton and carbon-ion radiotherapy using a fixed-beam system for locally advanced lung cancer: dosimetric comparison with x-ray radiotherapy and normal tissue complication probability (NTCP) evaluation

Objective. To assess the dosimetric consequences and the normal tissue complication probability (NTCP) for the organs at risk (OARs) in intensity-modulated particle radiotherapy of proton (IMPT) and carbon-ion (IMCT) using a fixed-beam delivery system when compared with intensity-modulated photon radiotherapy (IMRT) for locally advanced small-cell lung cancer.Approach. The plans were all designed under the same total relative biological effectiveness (RBE)-weighted prescription dose, in which the planning target volume (PTV) of the internal gross target volume(IGTV) and the PTV of the clinical target volume was irradiated with 69.3 Gy (RBE) and 63 Gy (RBE), respectively, using a simultaneously integrated boosting (SIB) technique. NTCPs were estimated for heart, lung, esophagus and spinal cord by Lyman-Kutcher-Burman (LKB) and logistic models. Dose escalation was simulated under the desired NTCP values (0.05, 0.10 and 0.50) of the three radiation techniques.Main results. Under the similar target coverage, almost all OARs were significantly better spared (p< 0.05) when using the particle radiotherapy except for D1cc (the dose to 1 cm3of the volume) of the proximal bronchial tree (p> 0.05). At least 57.6% of mean heart dose, 28.8% of mean lung dose and 19.1% of mean esophageal dose were reduced compared with IMRT. The mean NTCP of radiation-induced pneumonitis (RP) in the ipsilateral lung was 0.39 ± 0.33 (0.39 ± 0.31) in IMPT plans and 0.36 ± 0.32 (0.35 ± 0.30) in IMCT plans compared with 0.66 ± 0.30 (0.64 ± 0.28) in IMRT plans by LKB (logistic) models. The target dose could be escalated to 78.3/76.9 Gy (RBE) in IMPT/IMCT plans compared with 61.7 Gy (RBE) in IMRT plans when 0.50 of NTCP in terms of RP in the ipsilateral lung was applied.Significance. This study presents the potential of better control of the side effects and improvement of local control originating from the dosimetric advantage with the application of IMPT and IMCT with the SIB technique for locally advanced lung cancer, even with limited beam directions.

Comparative In Silico Analysis of Ultra-Hypofractionated Intensity-Modulated Photon Radiotherapy (IMRT) Versus Intensity-Modulated Proton Therapy (IMPT) in the Pre-Operative Treatment of Retroperitoneal Sarcoma

BACKGROUND

While pre-operative radiation did not improve abdominal recurrence-free survival for retroperitoneal sarcoma (RPS) in the randomized STRASS trial, it did reduce rates of local recurrence. However, the risk of toxicity was substantial and the time to surgery was prolonged. A combination of hypofractionation and proton therapy may reduce delays from the initiation of radiation to surgery and limit the dose to surrounding organs at risk (OARs). We conducted a dosimetric comparison of the pre-operative ultra-hypofractionated intensity-modulated photon (IMRT) and proton radiotherapy (IMPT).

METHODS

Pre-operative IMRT and IMPT plans were generated on 10 RPS patients. The prescription was 25 Gy radiobiological equivalents (GyEs) (radiobiological effective dose of 1.1) to the clinical target volume and 30 GyEs to the margin at risk, all in five fractions. Comparisons were made using student T-tests.

RESULTS

The following endpoints were significantly lower with IMPT than with IMRT: mean doses to liver, bone, and all genitourinary and gastrointestinal OARs; bowel, kidney, and bone V5-V20; stomach V15; liver V5; maximum doses to stomach, spinal canal, and body; and whole-body integral dose.

CONCLUSIONS

IMPT maintained target coverage while significantly reducing the dose to adjacent OARs and integral dose compared to IMRT. A prospective trial treating RPS with pre-operative ultra-hypofractionated IMPT at our institution is currently being pursued.

Treatment for local control of retroperitoneal and pelvis sarcomas: A review of the literature

Retroperitoneal and pelvis sarcomas are uncommon tumors for which complete surgical resection is the mainstay of treatment. However, achieving complete gross resection with microscopically negative margins is challenging, and local recurrence rates can be high. Patients often succumb to uncontrolled local disease. Radiation therapy offers a potential means for sterilizing microscopic residual disease, although its use continues to be controversial. Chemotherapy alone or in combination with radiation continues to be investigated as an adjunct to surgery, along with immunotherapy and targeted therapies. In this review, we discuss the current management of retroperitoneal and pelvis sarcomas, focusing on studies of surgery and radiation therapy to maximize local control.

Dosimetry impact of gating latency in cine magnetic resonance image guided breath-hold pancreatic cancer radiotherapy

Objective.We investigated dosimetry effect of gating latency in cine magnetic resonance image (cine MRI) guided breath-hold pancreatic cancer radiotherapy.Approach.The gating latency was calculated based on cine MRI obtained from 17 patients who received MRI guided radiotherapy. Because of the cine MRI-related latency, beam overshoot occurs when beam remains on while the tracking target already moves out of the target boundary. The number of beam on/off events was calculated from the cine MRI data. We generated both IMRT and VMAT plans for all 17 patients using 33 Gy prescription, and created motion plans by applying isocenter shift that corresponds to motion-induced tumor displacement. The GTV and PTV coverage and dose to nearby critical structures were compared between the motion and original plan to evaluate the dosimetry change caused by cine MRI latency.Main results.The time ratio of cine MRI imaging latency over the treatment duration is 6.6 ± 3.1%, the mean and median percentage of beam-on events <4 s are 67.0 ± 14.3% and 66.6%. When a gating boundary of 4 mm and a target-out threshold of 5% is used, there is no significant difference for GTV V33Gy between the motion and original plan (p = 0.861 and 0.397 for IMRT and VMAT planning techniques, respectively). However, the PTV V33Gy and stomach Dmax for the motion plans are significantly lower; duodenum V12.5 Gy and V18Gy are significantly higher when compared with the original plans, for both IMRT and VMAT planning techniques.Significance.The cine MRI gating latency can significantly decrease the dose delivered to the PTV, and increase the dose to the nearby critical structures. However, no significant difference is observed for the GTV coverage. The dosimetry impact can be mitigated by implementing additional beam-on control techniques which reduces unnecessary beam on events and/or by using faster cine MRI sequences which reduces the latency period.