Dosimetric Evaluation of a Simple Planning Technique for Improving Intensity-Modulated Radiotherapy for Nasopharyngeal Cancer

Abstract

PurposeTo evaluate the dosimetric outcomes of a simple planning technique for improving intensity-modulated radiotherapy (IMRT) for nasopharyngeal cancer (NPC).MethodsFor 39 NPC cases, generally acceptable original plans were generated and were improved by the two planning techniques, respectively: (1) a basal-dose-compensation (BDC) technique, in which the treatment plans were re-optimized based on the original plans; (2) a local-dose-control (LDC) technique, in which the original plans were re-optimized with constraints for hot and cold spots. The BDC, original, and LDC plans were then compared regarding homogeneity index (HI) and conformity index (CI) of planning target volumes (PTVs), organ-at-risk (OAR) sparing and monitor units (MUs) per fraction. The whole planning times were also compared between the BDC and LDC plans.ResultsThe BDC plans had superior HIs / CIs, by 13-24% / 3-243%, respectively, over the original plans. Compared to the LDC plans, the BDC plans provided better HIs only for PTVnx (the PTV of nasopharyngeal primary tumor) by 11% and better CIs for all PTVs by 2-134%. The BDC technique spared most OARs, by 1-9%. The average MUs of the BDC, original, and LDC plans were 2149, 2068 and 2179, respectively. The average whole planning times were 48 and 69 minutes for the BDC and LDC plans, respectively.ConclusionsFor the IMRT of nasopharyngeal cancer, the BDC planning technique can improve target dose homogeneity, conformity and OAR sparing, with better planning efficiency.

Study of dosimetric indices and dose constraints to critical organs for head and neck tumours treated with inverse planned simultaneous integrated boost intensity-modulated radiotherapy

“…Both over-treatment and undertreatment are detrimental as the former may result in acute reactions in normal cells and later increases the likelihood of tumour recurrence. 25 Investigation of H&N cancer radiotherapy using SIB IMRT, proves that highly conformal and homogenous dose distribution as well as better sparing of OARs is achieved, thus verifying quality assurance results to be satisfactory. Treatment of H&N carcinoma using SIB IMRT is feasible, more efficient, and dose escalation is achieved in a single plan.…”

“…Any deviation of RCI values from ideality propose over-treatment or under-treatment of target volume. Both over-treatment and under-treatment are detrimental as the former may result in acute reactions in normal cells and later increases the likelihood of tumour recurrence 25 …”

“…Plans having values between 2 and 2·5 show minor deviation and values of HI>2·5 suggest major deviation ( 9 , 19 , 22 , 24 ) . Homogenous dose distribution is necessary to avoid radiation-induced toxicity 25 …”

Investigation of fusion dose distribution for locally advanced cervical cancer under different bladder statuses for intensity‐modulated radiotherapy combined with intracavitary brachytherapy

“…The radiation sources were 6‐MV X‐ray, prescription dose of Dt = 50 Gy/25 Fr, the targets of PTV were D95% ≥45Gy, the maximum dose ≤110%, and the minimum dose ≥93%. The conformity index and homogeneity index were determined according to the literature computation for conformity index ≥0.70 and homogeneity index ≤1.20. For the OAR requirements, D2% of the unilateral femoral head <50 Gy, D50% of bladder <30 Gy, D50% of small intestine <25 Gy, and D50% of rectum <50 Gy were used.…”