Free‐breathing conformal irradiation of pancreatic cancer

Abstract

The purpose of this study was to assess treatment margins in free‐breathing irradiation of pancreatic cancer after bone alignment, and evaluate their impact on conformal radiotherapy. Fifteen patients with adenocarcinoma of the head of the pancreas underwent implantation of single fiducial marker. Intrafraction uncertainties were assessed on simulation four‐dimensional computed tomography (4D CT) by calculating maximal intrafraction fiducial excursion (MIFE). In the first ten patients, after bony alignment, the position of the fiducial was identified on weekly acquired megavolt cone‐beam CT (MV‐CBCT). The interfraction residual uncertainties were estimated by measuring the fiducial displacements with respect to the position in the first session. Patient mean (pM) and patient standard deviation (pSD) of fiducial displacement, mean (μnormalM) and standard deviation (μSD) of pM, and root‐mean‐square of pSD (σres) were calculated. In the other five patients, MIFE was added to the residual component to obtain personalized margin. In these patients, conformal kidney sparing (CONKISS) irradiation was planned prescribing 54/45 Gy to PTV1/PTV2. The organ‐at‐risk limits were set according to current NCCN recommendation. No morbidity related to the fiducial marker implantation was recorded. In the first ten patients, along right–left, anterior–posterior, and inferior–superior directions, MIFE was variable (mean±std=0.24±0.13.2emcm,0.31±0.14.2emcm,0.83±0.35.2emcm, respectively) and was at most 0.51, 0.53, and 1.56 cm, respectively. Along the same directions, μnormalM were 0.09,−0.05,−0.05.2emcm,μSD were 0.30, 0.17, 0.33 cm, and σres were 0.35, 0.26, and 0.30 cm, respectively. MIFE was not correlated with pM and pSD. In the five additional patients, it was possible to satisfy recommended dose limits, with the exception of slightly higher doses to small bowel. After bony alignment, the margins for target expansion can be obtained by adding personalized MIFE to the residual interfraction term. Using these margins, conformal free‐breathing irradiation is a reliable option for the treatment of pancreatic cancer.PACS number: 87.55.D‐

Interfraction positional variation in pancreatic tumors using daily breath‐hold cone‐beam computed tomography with visual feedback

“…Markers implanted either in the tumor itself or nearby are often used as the internal surrogate with which to localize the tumor position. (13,14) Although van der Horst et al (13) stated that small changes in the pair distance of implanted markers over the course of treatment may be attributed to tissue deformation rather than to marker migration, we have previously experienced large marker migration. (This case was not a participating patient in the present study.)…”

“…Several investigators have examined interfraction positional variation of the pancreas using a variety of methods; (12)(13)(14)19) however, most examinations were performed under free breathing. van der Horst et al (13) demonstrated large interfractional pancreatic position variation of > 10 mm using fiducial markers visible on daily CBCT scans.…”

“…(5,6) Several researchers have reported that pancreatic tumor motion due to breathing exceeded 10 mm using cine magnetic resonance images, four-dimensional computed tomography (CT), electromagnetic transponders, and cone-beam CT (CBCT). (7)(8)(9)(10)(11)(12)(13)(14) Without respiratory management, a large planning target volume (PTV) is needed to cover such internal motion, resulting in inclusion of a large volume of OARs.…”

“…CBCT imaging is suitable for online correction of tumor position errors. Whitfield et al, (11) van der Horst et al, (13) and Solla et al (14) reported the use of CBCT to assess interfractional position changes of pancreatic tumors under free breathing. However, there have been no reports of interfraction positional variations in pancreatic tumors using BH-CBCT at EE.…”

Determination of Acquisition Frequency for Intrafractional Motion of Pancreas in CyberKnife Radiotherapy

“…Solla et al present that the potential target underdosage may occur due to respiration and small PTV margin [27]. Several studies have shown a survival advantage for higher dose levels [28–33].…”