Radiobiologic comparison of helical tomotherapy, intensity modulated radiotherapy, and conformal radiotherapy in treating lung cancer accounting for secondary malignancy risks

NTCP Modeling and Dose-Volume Correlations of Significant Hematocrit Drop 3 Months After Prostate Radiation Therapy

Purpose

Our purpose was to determine and model the dose-response relations of different parts of the pelvis regarding the endpoint of hematocrit level drop after pelvic radiation therapy (RT).

Methods and Materials

Two hundred and twenty-one patients treated with RT for prostate adenocarcinoma between 2014 and 2016 were included. All patients had complete blood counts collected at baseline and 3 months post-RT. The net difference of hematocrit level post-RT versus baseline was calculated, and the level of the 15th percentiles defined the thresholds of response in each case. The doses to 8 different pelvic structures were derived and fitted to the hematocrit levels using the relative seriality normal tissue complication probability model and the biologically equivalent uniform dose (D = ).

Results

Pelvic structures that correlated with significant decreases in hematocrit were the os coxae bilaterally superior to the acetabulum (OCUB), the total os coxae bilaterally, and the bone volume of the whole pelvis. The structure showing the highest correlation was OCUB with a maximum area under the curve (AUC) of 0.74. For V20 Gy < 30% the odds ratio was 9.8 with 95% CI of 2.9 to 32.9. For mean dose (Dmean) to OCUB, an AUC of 0.73 was observed where the dose threshold was 23 Gy and the odds ratio was 2.7 and 95% CI 1.3 to 5.6. The values for the D50, γ, and s parameters of the relative seriality model were 26.9 Gy (25.9-27.9), 1.3 (1.2-2.2), and 0.12 (0.10-0.83), respectively. The AUC of D = was 0.73 and patients with D = to OCUB ≥ 27 Gy had 8.2 times higher rate of significant hematocrit drop versus <27 Gy.

Conclusions

These findings confirm the association of radiation-induced damage to pelvic bone marrow with a drop in hematocrit. A threshold of V20 Gy < 30%, Dmean < 23 Gy, or D = < 27 Gy to OCUB may significantly reduce the risk for this endpoint.

Radiobiological assessment of nasopharyngeal cancer IMRT using various collimator angles and non-coplanar fields

Aim:

The aim of this study was to evaluate clinical efficacy and radiobiological outcome of intensity-modulated radiation therapy (IMRT) modalities using various collimator angles and non-coplanar fields for nasopharyngeal cancer (NPC).

Materials and methods:

A 70-Gy planning target volume dose was administered for 30 NPC patients referred for IMRT. Standard IMRT plans were constructed based on the target and organs at risk (OARs) volume; and dose constraints recommended by Radiation Therapy Oncology Group (RTOG). Using various collimator angles and non-coplanar fields, 11 different additional IMRT protocols were investigated. Homogeneity indexes (HIs) and conformation numbers (CNs) were calculated. Poisson and relative seriality models were utilised for estimating tumour control probability (TCP) and normal tissue complication probabilities (NTCPs), respectively.

Results:

Various collimator angles and non-coplanar fields had no significant effect on HI, CN and TCP, while significant effects were noted for some OARs, with a maximum mean dose (Dmax). No significant differences were observed among the calculated NTCPs of all the IMRT protocols. However, the protocol with 10° collimator angle (for five fields out of seven) and 8° couch angle had the lowest NTCP. Furthermore, the standard and some of non-coplanar IMRT protocols led to the reduction in OARs Dmax.

Conclusions:

Using appropriate standard/non-coplanar IMRT protocols for NPC treatment could potentially reduce the dose to the OARs and the probability of inducing secondary cancer in patients.