Complementary Relation Between the Improvement of Dose Delivery Technique and PTV Margin Reduction in Dose-Escalated Radiation Therapy for Prostate Cancer.

PURPOSE: The purpose of this study is to demonstrate quantitatively the complementary relationship between the introduction of intensity modulated radiation therapy (IMRT) and planning target volume (PTV) margin reduction with an image guided technique in reducing the risk of rectal toxicity in dose-escalating prostate radiation therapy. METHODS AND MATERIALS: Three-dimensional conformal radiation therapy (CRT) and IMRT plans were generated for 10 patients with prostate cancer based on 2 PTV margin protocols (10/8 mm and 6/5 mm) and 2 dose prescriptions (70 Gy and 78 Gy). The normal tissue complication probability (NTCP) for each of the 8 scenarios was calculated using the Lyman-Kutcher-Burman model to estimate the risk of rectal and bladder late toxicity. The conformity and homogeneity indices of PTVs were calculated for each plan. RESULTS: The IMRT plans showed superiority in conformity and inferiority in homogeneity over 3-dimensional CRT plans. The rectal NTCPs were increased 3.5 to 4.1 times when the prescribed total dose was changed from 70 Gy to 78 Gy and the dose delivery and the image guided radiation therapy techniques remained unchanged. PTV margin reduction was shown to reduce the value of rectal NTCP significantly. Overall, implementing the IMRT technique alone could reduce the NTCP values only by 2.1% to 7.3% from those of 3-dimensional CRT. The introduction of both IMRT and PTV margin reduction was found to be necessary for rectal NTCP to remain <5% in the dose escalation from 70 to 78 Gy. CONCLUSIONS: The complementary relationship between the introduction of IMRT and PTV margin reduction was proven. We found that both approaches need to be implemented to safely deliver a curative dose in dose-escalating prostate radiation therapy.

Definitive chemoradiotherapy with low-dose continuous 5-fluorouracil reduces hematological toxicity without compromising survival in esophageal squamous cell carcinoma patients.

BACKGROUND AND PURPOSE: To compare chemoradiotherapy (CRT) with low-dose continuous 5-fluorouracil (5FU) to CRT with 5FU+cisplatin (CDDP) for esophageal squamous cell carcinoma (ESCC) in a retrospective cohort study. METHODS AND MATERIALS: We reviewed the cases of Stage I-IV ESCC patients who underwent definitive CRT in 2000-2014. Concomitant chemotherapy was one of the three regimens: (1) high-dose intermittent 5FU and CDDP (standard-dose FP: SDFP), (2) low-dose continuous 5FU and CDDP (LDFP), or (3) low-dose continuous 5FU (LD5FU). The general selection criteria for chemotherapy were: SDFP for patients aged <70 yrs; LDFP for those aged 70-74 yrs; LD5FU for those aged ≥75 yrs or with performance status (PS) ≥3. Propensity scores were derived with chemotherapy (LD5FU vs. 5FU+CDDP) as the dependent variable. RESULTS: In a multivariate analysis, chemotherapy (LD5FU vs. SDFP, p = .24; LDFP vs. SDFP, p = .52) did not affect the overall survival (OS). LD5FU caused significantly less grade 3-4 leukopenia (9%) compared to SDFP (47%) and LDFP (44%) (p < .001). In a propensity-matched analysis, LD5FU affected neither OS (HR 1.06; 95%CI 0.55-2.05; p = .87) nor progression-free survival (HR 0.95, 95%CI 0.50-1.81; p = .87). CONCLUSION: CRT with low-dose continuous 5FU may be a less toxic option for elderly ESCC patients.

Respiratory gating and multifield technique radiotherapy for esophageal cancer.

PURPOSE: To investigate the effects of a respiratory gating and multifield technique on the dose-volume histogram (DVH) in radiotherapy for esophageal cancer. METHODS AND MATERIALS: Twenty patients who underwent four-dimensional computed tomography for esophageal cancer were included. We retrospectively created the four treatment plans for each patient, with or without the respiratory gating and multifield technique: No gating-2-field, No gating-4-field, Gating-2-field, and Gating-4-field plans. We compared the DVH parameters of the lung and heart in the No gating-2-field plan with the other three plans. RESULT: In the comparison of the parameters in the No gating-2-field plan, there are significant differences in the Lung V5Gy, V20Gy, mean dose with all three plans and the Heart V25Gy-V40Gy with Gating-2-field plan, V35Gy, V40Gy, mean dose with No Gating-4-field plan and V30Gy-V40Gy, and mean dose with Gating-4-field plan. The lung parameters were smaller in the Gating-2-field plan and larger in the No gating-4-field and Gating-4-field plans. The heart parameters were all larger in the No gating-2-field plan. CONCLUSION: The lung parameters were reduced by the respiratory gating technique and increased by the multifield technique. The heart parameters were reduced by both techniques. It is important to select the optimal technique according to the risk of complications.

A study on a dental device for the prevention of mucosal dose enhancement caused by backscatter radiation from dental alloy during external beam radiotherapy.

The changes in dose distribution caused by backscatter radiation from a common commercial dental alloy (Au-Ag-Pd dental alloy; DA) were investigated to identify the optimal material and thicknesses of a dental device (DD) for effective prevention of mucositis. To this end, 1 cm3 of DA was irradiated with a 6-MV X-ray beam (100 MU) in a field size of 10 × 10 cm2 using a Novalis TX linear accelerator. Ethylene vinyl acetate copolymer, polyolefin elastomer, and polyethylene terephthalate (PET) were selected as DD materials. The depth dose along the central axis was determined with respect to the presence/absence of DA and DDs at thicknesses of 1-10 mm using a parallel-plate ionization chamber. The dose in the absence of DDs showed the lowest value at a distance of 5 mm from the DA surface and gradually increased with distance between the measurement point and the DA surface for distances of ≥5 mm. Except for PET, no significant difference between the DA dose curves for the presence and absence of DDs was observed. In the dose curve, PET showed a slightly higher dose for DA with DD than for DA without DD for thicknesses of ≥4 mm. The findings herein suggest that the optimal DD material for preventing local dose enhancement of the mucosa caused by DA backscatter radiation should have a relatively low atomic number and physical density and that optimal DD thickness should be chosen considering backscatter radiation and percentage depth dose.