Intensity-modulated radiotherapy in nasopharyngeal carcinoma: dosimetric advantage over conventional plans and feasibility of dose escalation

On correlations in IMRT planning aims

“…This is in agreement with the recommendations that strict ${\mathrm{normalD}}^{\text{max}}$ constraints are essential to maintain functionality of such critical organs 19 , 20 , 21 , 22 . However, Fig.…”

“…However, a tighter control is not necessary because the probability of myelopathy vanishes for $\mathrm{D}\hspace{0.17em}<\hspace{0.17em}40\hspace{0.17em}\text{Gy}$ to the cord (18) . These observations may be considered as an indirect effect of the predominant ${\mathrm{normalD}}^{\text{max}}$ constraints on brainstems and spines, as common in head‐and‐neck cases 19 , 20 , 21 , 22 . Note that ${\mathrm{normalD}}^{\text{max}}$ thresholds lead to $\mathrm{V}\hspace{0.17em}=\hspace{0.17em}0\%$ at $\mathrm{D}\hspace{0.17em}\ge \hspace{0.17em}{\mathrm{normalD}}^{\text{max}}$, resulting in narrower ${\text{IQR}}^{\text{vol}}$.…”

“…The first DVH falloff is attributed to an artifact of the patient geometry (for some cases, lower doses to significant portions of organs is common, but not for all). On the other hand, the turning point at $\mathrm{D}\hspace{0.17em}=\hspace{0.17em}40\hspace{0.17em}\text{Gy}$ is a direct result of maximum dose constraints for brainstem and spine, which are typically imposed in head‐and‐neck cancer cases 19 , 20 , 21 , 22 …”

“…For brainstem, ${\mathrm{normalD}}^{\text{con}}\hspace{0.17em}=\hspace{0.17em}50\hspace{0.17em}\text{Gy}$ and for spine, ${\mathrm{normalD}}^{\text{con}}\hspace{0.17em}=\hspace{0.17em}45\hspace{0.17em}\text{Gy}$. This corresponds to maximum dose constraints that are usually imposed on all structures, often being the only constraint for brainstem or spine 19 , 20 , 21 , 22 . When ${\mathrm{normalV}}_{110}$, ${\mathrm{normalV}}_{50}$, or ${\mathrm{normalV}}_{45}$ are negligible $\left(\le \hspace{0.17em}2\%\right)$, we hypothesize them to be a consequence of maximum dose constraints, and otherwise $\left(>\hspace{0.17em}2\%\right)$ independent.…”

Plan Dose Evaluation of Three Dimensional Conformal Radiotherapy Planning (3D-CRT) of Nasopharyngeal Carcinoma (NPC): Experience of a Tertiary Care University Hospital in Pakistan

“…It represents a major step forward in modern treatment planning. However the problem of dose inhomogenity and suboptimal coverage is still unresolved because of highly infiltrative growth pattern with a propensity to spread through skull base foramina to the intracranial structures particularly visual apparatus as well as parapharyngeal space and large neck lymph nodes, in addition, there is a variation of the anatomic structure of the nasopharynx between individuals (Kam et al, 2003). This has led the radiation oncologist to break the treatment plan into different phases that has also compromised tumor coverage.…”