On the impact of functional imaging accuracy on selective boosting IMRT

Abstract

In order to quantify the impact of loss of functional imaging sensitivity and specificity on tumor control and normal tissue toxicity for selective boosting IMRT four selective boosting scenarios were designed: SB91-81 (EUD=91Gy for the high risk tumor subvolume and EUD=81Gy for a remaining low risk PTV (rPTV)), SB80-74, SB90-70, and risk-adaptive optimization. For each sensitivity loss level the loss in tumor control probability (ΔTCP) was calculated. For each specificity loss level, the increase in rectal and the bladder toxicity was quantified using the radiobiological indices (equivalent uniform dose (EUD) and normal tissue complication probability (NTCP)) and %-volumes irradiated.The impact of loss in sensitivity on local tumor control was maximal when the prescription dose level for rPTV had the lowest value. The SB90-70 plan had a ΔTCP= 29.6%, the SB91-81 plan had a ΔTCP = 9.5%, while for risk-adaptive optimization a ΔTCP= 4.7% was found. Independent of planning technique loss in functional imaging specificity appears to have a minimal impact on the expected normal tissue toxicity, since an increase in rectal or bladder toxicity as a function of loss in specificity was not observed. Additionally, all plans fulfilled the rectum and the bladder sparing criteria found in the literature for late rectal bleeding and genitourinary complications.Our study shows that the choice of a low-risk classification for the rPTV in selective boosting IMRT may lead to a significant loss in TCP. Furthermore, for the example considered in which normal tissue complications can be limited through the use of a tissue expander it appears that the therapeutic ratio can be improved using a functional imaging technique with a high sensitivity and limited specificity. While for cases were this is not possible an optimal balance between sensitivity and specificity has to be found.

Biological optimization of simultaneous boost on intra-prostatic lesions (DILs): Sensitivity to TCP parameters

“…The combined use of 11 C-choline PET-CT and DWI MRI could be beneficial in selected patients but it should be explored [18]. On the other hand, lmage-Guided Intensity Modulated Radiotherapy (IG-IMRT) permits to properly manage geometric uncertainties and to improve physical conformation of the dose distribution, even at the tumor sub-volume level [19].…”

Choline PET based dose-painting in prostate cancer - Modelling of dose effects

“…In another paper Kim et al derive similar results, but mention the importance of the underlying imaging modality and consecutively their sensitivity in detecting occult tumor cells [69]. …”

“…Furthermore, risk-adaptive optimization increases the therapeutic ratio as compared to conventional selective boosting IMRT. In another paper Kim et al derive similar results, but mention the importance of the underlying imaging modality and consecutively their sensitivity in detecting occult tumor cells [ 69 ].…”

Risk-Adaptive Volumetric Modulated Arc Therapy Using Biological Objective Functions for Subvolume Boosting in Radiotherapy

“…Kim and Tomé have shown that static gantry angle IMRT can achieve the required modulation [1, 3–5]. In recent years, volumetric modulated arc therapy (VMAT) has become an attractive method to efficiently deliver modulated dose distributions.…”

“…SIB delivery requires increased modulation of the dose so as to achieve the desired boosting level while maintaining a sufficient dose gradient outside of the target to minimize the dose to surrounding healthy tissues. Kim and Tomé have shown that static gantry angle IMRT can achieve the required modulation [ 1 , 3 – 5 ]. In recent years, volumetric modulated arc therapy (VMAT) has become an attractive method to efficiently deliver modulated dose distributions.…”